An Anatomic Approach to Minimally Invasive Spine Surgery [2 ed.] 9781626236431, 1626236437, 9781626239333, 1626239339

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World-renowned spine neurosurgeons Mick Perez-Cruet, Richard Fessler, Michael Wang, and a cadre of highly regarded spine surgery experts provide masterful tutorials on an impressive array of cutting-edge technologies. Organized by seven sections and 51 chapters, the book presents a diverse spectrum of current safe and efficacious MIS procedures and future innovations. Nonsurgical approaches include injection-based spine procedures and stereotactic radiosurgery. Surgical technique chapters discuss MIS anterior, posterior, and lateral approaches to the cervical, thoracic, and lumbar spine, with procedures such as endoscopic microdiscectomy, vertebroplasty and kyphoplasty, percutaneous instrumentation, and robotic spine surgery. Key Features • Step-by-step illustrations, including more than 400 depictions by master surgical and anatomic illustrator Anthony Pazos, portray the surgeon’s-eye-view of anatomy, intraoperative images, and surgical instruments, thereby aiding in the understanding of anatomy and procedures • 20 online videos feature real-time operative fluoroscopy, pertinent anatomy, operative set-up, and common cervical, thoracic, and lumbar approaches • Discussion of novel MIS techniques reflected in 16 new or expanded chapters, including Robotic Assisted Thoracic Spine Surgery and Stem-Cell Based Intervertebral Disc Restoration

An Anatomic Approach to Minimally Invasive Spine Surgery

Significant advances have been made in minimally invasive spine (MIS) surgery approaches, techniques, and innovative technologies. By preserving normal anatomic integrity during spine surgery, MIS approaches enable spine surgeons to achieve improved patient outcomes, including faster return to normal active lifestyles and reduced revision rates. Exposing only the small portion of the spine responsible for symptoms via small ports or channels requires a deep understanding of spinal anatomy and spinal pathophysiology. Building on the widely acclaimed first edition, An Anatomic Approach to Minimally Invasive Spine Surgery, Second Edition, provides an expanded foundation of knowledge to master minimally invasive spine surgery.

Perez-Cruet Fessler/Wang

Learn state-of-the-art MIS techniques from master spine surgeons!

An Anatomic Approach to Minimally Invasive Spine Surgery Mick J. Perez-Cruet Richard G. Fessler Michael Y. Wang

There is truly no better clinical reward for spine surgeons than giving patients suffering from debilitating spinal disorders their life back. This quintessential MIS surgery resource will help surgeons and clinicians accomplish that goal. Miguelangelo (Mick) J. Perez-Cruet, MD, MSc, is Vice Chairman and Professor, Department of Neurosurgery, Oakland University William Beaumont School of Medicine, Royal Oak, Michigan; and Michigan Head and Spine Institute, Southfield, Michigan, USA. Richard G. Fessler, MD, PhD, is Professor, Department of Neurosurgery, Rush University Medical Center, Chicago, Illinois, USA.

An award-winning international medical and scientific publisher, Thieme has demonstrated its commitment to the highest standard of quality in the state-of-the-art content and presentation of all its products. Founded in 1886, the Thieme name has become synonymous with high quality and excellence in online and print publishing.

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Second Edition

Michael Y. Wang, MD, FACS, is Professor of Neurological Surgery and Rehab Medicine, Miller School of Medicine, University of Miami; and Chief of Neurosurgery and Director of the Neurosurgical Spine Fellowship, University of Miami Hospital, Miami, Florida, USA.

Second Edition

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Perez-Cruet et al, An Anatomic Approach to Minimally Invasive Spine Surgery, 2nd Ed. (ISBN 978-1-62623-643-1), copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.

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Perez-Cruet et al, An Anatomic Approach to Minimally Invasive Spine Surgery, 2nd Ed. (ISBN 978-1-62623-643-1), copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.

TPS 23 x 31 - 2 | 01.10.18 - 16:45

Perez-Cruet et al, An Anatomic Approach to Minimally Invasive Spine Surgery, 2nd Ed. (ISBN 978-1-62623-643-1), copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.

TPS 23 x 31 - 2 | 01.10.18 - 16:45

An Anatomic Approach to Minimally Invasive Spine Surgery Second Edition

Mick J. Perez-Cruet, MD, MSc Vice Chairman and Professor Department of Neurosurgery Oakland University William Beaumont School of Medicine Royal Oak, Michigan Michigan Head and Spine Institute Southfield, Michigan Richard G. Fessler, MD, PhD Professor Department of Neurosurgery Rush University Medical Center Chicago, Illinois Michael Y. Wang, MD, FACS Professor of Neurological Surgery and Rehab Medicine Miller School of Medicine University of Miami Chief of Neurosurgery Director, Neurosurgical Spine Fellowship University of Miami Hospital Miami, Florida

439 illustrations

Thieme New York • Stuttgart • Delhi • Rio de Janeiro Perez-Cruet et al, An Anatomic Approach to Minimally Invasive Spine Surgery, 2nd Ed. (ISBN 978-1-62623-643-1), copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.

Executive Editor: Timothy Y. Hiscock Developmental Editor: Kathleen Sartori Managing Editor: Nikole Y. Connors Director, Editorial Services: Mary Jo Casey Production Editor: Naamah Schwartz International Production Director: Andreas Schabert Editorial Director: Sue Hodgson International Marketing Director: Fiona Henderson International Sales Director: Louisa Turrell Director of Institutional Sales: Adam Bernacki Senior Vice President and Chief Operating Officer: Sarah Vanderbilt President: Brian D. Scanlan

Library of Congress Cataloging-in-Publication Data Names: Perez-Cruet, Mick J., 1961- editor. | Wang, Michael Y., 1971- editor. | Fessler, Richard G., editor. Title: An anatomic approach to minimally invasive spine surgery / [edited by] Mick J. Perez-Cruet, MD, MSc, Vice-Chairman and Professor, Director, Minimally Invasive Spine Surgery and Spine Program, Department of Neurosurgery, Oakland University William Beaumont School of Medicine, Michigan Head and Spine Institute, Royal Oak, Michigan USA, Michael Y. Wang, MD, Professor & Spine Director, Departments of Neurological Surgery & Rehabilitative Medicine, Chief of Neurosurgery, University of Miami Hospital, Miami, Florida USA, Richard G. Fessler, MD, PhD, Professor, Department of Neurosurgery, Rush University Medical Center, Chicago, Illinois USA. Description: Second edition. | New York : Thieme, 2019. | Includes bibliographical references and index. | Identifiers: LCCN 2018021924 (print) | LCCN 2018022448 (ebook) | ISBN 9781626239333 (e-) | ISBN 9781626236431 (print) Subjects: LCSH: Spine–Endoscopic surgery. | Spine–Anatomy. Classification: LCC RD533 (ebook) | LCC RD533 .A53 2018 (print) | DDC 617.4/71–dc23 LC record available at https://lccn.loc.gov/2018021924 © 2019 Thieme Medical Publishers, Inc.

Printed in The United States of America by King Printing Company, Inc.

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ISBN 978-1-62623-643-1 Also available as an e-book: eISBN 978-1-62623-933-3 Important note: Medicine is an ever-changing science undergoing continual development. Research and clinical experience are continually expanding our knowledge, in particular our knowledge of proper treatment and drug therapy. Insofar as this book mentions any dosage or application, readers may rest assured that the authors, editors, and publishers have made every effort to ensure that such references are in accordance with the state of knowledge at the time of production of the book. Nevertheless, this does not involve, imply, or express any guarantee or responsibility on the part of the publishers in respect to any dosage instructions and forms of applications stated in the book. Every user is requested to examine carefully the manufacturers’ leaflets accompanying each drug and to check, if necessary in consultation with a physician or specialist, whether the dosage schedules mentioned therein or the contraindications stated by the manufacturers differ from the statements made in the present book. Such examination is particularly important with drugs that are either rarely used or have been newly released on the market. Every dosage schedule or every form of application used is entirely at the user’s own risk and responsibility. The authors and publishers request every user to report to the publishers any discrepancies or inaccuracies noticed. If errors in this work are found after publication, errata will be posted at www.thieme.com on the product description page. Some of the product names, patents, and registered designs referred to in this book are in fact registered trademarks or proprietary names even though specific reference to this fact is not always made in the text. Therefore, the appearance of a name without designation as proprietary is not to be construed as a representation by the publisher that it is in the public domain.

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Perez-Cruet et al, An Anatomic Approach to Minimally Invasive Spine Surgery, 2nd Ed. (ISBN 978-1-62623-643-1), copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.

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We dedicate this book . . . In recognition of the giving work of Dr. Daniel Roy Pieper, who worked tirelessly until his untimely death at a relatively young age. Dan left behind a legacy of minimally invasive skull base endoscopic surgery. His mastery and teaching of endoscopic pituitary and skull base surgery significantly advanced neurosurgery. He founded the Michigan Head and Spine Institute, and was co-founder of the Minimally Invasive Neurosurgical Society (MINS). His patients adored him for his compassion, empathy, and willingness to tackle the toughest of cases. His humor, mentoring, and leadership has been truly missed. There was no better friend and colleague. Most of all, his wonderful family legacy lives on within his loving wife, Donna, and children: Stephanie, Lindsey, Brett, John Paul, and Michelle. They are a lasting reflection of his love, honesty, integrity, and kindness, and carry on his legacy of giving to others. We are grateful for those who, like Dan, look beyond themselves to help others be successful and lead full and productive lives.

Perez-Cruet et al, An Anatomic Approach to Minimally Invasive Spine Surgery, 2nd Ed. (ISBN 978-1-62623-643-1), copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.

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To my wife Donna and children Kristin, Joshua, Rachel, and David. Balancing practice, academics and family life is a tremendous challenge. I thank them for their unwavering love and support through this challenging life process. To my residents, fellows, teachers, and mentors for their contribution to my knowledge and inspiration to do this work. M.J.P-C. To my wife Amy and my children Patrick, Evan, and Sarah: Thank you for your love and support so that projects like this would be made possible M.Y.W. Academic medicine has a way of consuming nonclinical “free” time, which otherwise would be spent with family and friends. First, and most importantly, I would like to thank my wife Carol and my children Laura, David, and Linda, for their years of support, encouragement, and sacrifice, which enabled me to pursue my academic passions. I would also like to apologize to my many friends, for whom my commitments have made me a less “present” friend than they deserved. R.G.F.

Perez-Cruet et al, An Anatomic Approach to Minimally Invasive Spine Surgery, 2nd Ed. (ISBN 978-1-62623-643-1), copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.

Contents Video Contents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xii Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiv Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv Part I Fundamentals 1.

History of Minimally Invasive Spine Surgery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Michael A. Leonard, Dino Samartzis, and Mick J. Perez-Cruet

2.

Anatomy of the Spine: An Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Joshua E. Medow and Daniel K. Resnick

3.

Biomechanical Role of the Osseous, Ligamentous, and Muscular Structures of the Spine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 E. Emily Bennett, Jeffrey P. Mullin, Rick Placide, and Edward C. Benzel

4.

Pathophysiology and Operative Treatment of Discogenic Back Pain . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 Mick J. Perez-Cruet, Charles D. Ray, and Michael Y. Wang

5.

Pathophysiology of Back Pain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 Jorge Mendoza-Torres and Mick J. Perez-Cruet

6.

Rationale for Minimally Invasive Spine Surgery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 Manish K. Kasliwal, Mick J. Perez-Cruet, Lee A. Tan, Richard G. Fessler, Larry T. Khoo, and Moumita S.R. Choudhury

7.

Overcoming the Learning Curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 Efrem M. Cox, David J. Hart, and Mick J. Perez-Cruet

8.

Operating Room Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 Lee A. Tan, Mick J. Perez-Cruet, Manish K. Kasliwal, and Richard G. Fessler

Part II Patient Education and Business Basics 9.

Patient Education . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 Holly Weissman

10.

Establishing an Ambulatory Spine Surgery Center . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 Richard N.W. Wohns, Hiroshi W. Nakano, and Laura Miller Dyrda

11.

Establishing Ancillary Services and Health Care Regulatory Implications . . . . . . . . . . . . . . . . . . . . 113 Ann T. Hollenbeck and Richard A. Shapack

12.

Bringing Novel Spine Devices to the Marketplace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 John A. Redmond, Mick J. Perez-Cruet, and James M. Moran

Perez-Cruet et al, An Anatomic Approach to Minimally Invasive Spine Surgery, 2nd Ed. (ISBN 978-1-62623-643-1), copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.

vii

Contents

Part III Image Guidance, Monitoring, and Nonoperative Techniques 13.

Computer Navigational Guidance in Spine Surgery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 Fernando G. Diaz and Mick J. Perez-Cruet

14.

Intraoperative Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 Stephen W. Bartol

15.

Injection-Based Spine Procedures and Diagnostic Procedures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 Henry Tong and Mick J. Perez-Cruet

16.

Stereotactic Radiosurgery for Tumors of the Spine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170 Maha Saada Jawad and Daniel K. Fahim

Part IV Surgical Techniques Section I Cervical Spine 17.

Transoral and Transnasal Approaches to the Craniocervical Junction . . . . . . . . . . . . . . . . . . . . . . . . 181 Matthew L. Rontal, Daniel Roy Pieper, and Mick J. Perez-Cruet

18.

Posterior Cervical Microforaminotomy and Discectomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191 Carter S. Gerard, Lee A. Tan, and Richard G. Fessler

19.

Posterior Cervical Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197 Michael Y. Wang, Mick J. Perez-Cruet, Dino Samartzis, and Richard G. Fessler

20.

Anterior Cervical Discectomy, Fusion, and Instrumentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207 Mick J. Perez-Cruet and Moumita S.R. Choudhury

21.

Cervical Arthroplasty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213 K. Daniel Riew and Kevin R. O’Neill

22.

Cervical Case Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223 Mick J. Perez-Cruet, Richard G. Fessler, and Michael Y. Wang

Section II Thoracic Spine 23.

Posterior Thoracic Microdiscectomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231 Robert E. Isaacs, Mick J. Perez-Cruet, and Steven H. Cook

24.

Anterior Thoracoscopic Sympathectomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240 Curtis A. Dickman and Hasan A. Zaidi

25.

Thoracoscopic Discectomy and Thoracoscopy-Assisted Tubular Retractor Discectomy . . . . 249 Hyun-Chul Shin, Jonathan B. Lesser, Robert E. Isaacs, and Noel I. Perin

26.

Anterior Thoracoscopic Vertebral Reconstruction and Instrumentation. . . . . . . . . . . . . . . . . . . . . 256 Francisco Verdú-López and Rudolf W. Beisse

27.

Minimally Invasive Deformity Correction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266 Neel Anand, Zeeshan M. Sardar, Andrea Simmonds, and Eli M. Baron

viii

Perez-Cruet et al, An Anatomic Approach to Minimally Invasive Spine Surgery, 2nd Ed. (ISBN 978-1-62623-643-1), copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.

Contents

28.

Minimally Invasive Treatment of Thoracic and Thoracolumbar Idiopathic Scoliosis . . . . . . . . 275 Peter F. Picetti, Alexander R. Vaccaro, Zachary D. Patterson, David L. Downs, and George D. Picetti III

29.

Kyphoplasty and Vertebroplasty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286 Sina Rajamand and Daniel K. Fahim

30.

Minimally Invasive Robotic-Assisted Thoracic Spine Surgery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290 Mick J. Perez-Cruet and Jorge Mendoza-Torres

31.

Minimally Invasive Spine Surgery: Thoracic Case Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299 Mick J. Perez-Cruet, Richard G. Fessler, and Michael Y. Wang

Section III Lumbar Spine 32.

Endoscopic Spine Techniques: An Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311 Nima Salari, Christopher Yeung, and Anthony T. Yeung

33.

Muscle Preserving Lumbar Microdiscectomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323 Mick J. Perez-Cruet and Moumita S.R. Choudhury

34.

Far-Lateral Microdiscectomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333 Lee A. Tan, Carter S. Gerard, Mick J. Perez-Cruet, and Richard G. Fessler

35.

Minimally Invasive Laminectomy for Lumbar Stenosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 340 Mick J. Perez-Cruet, Ronnie I. Mimran, R. Patrick Jacob, and Richard G. Fessler

36.

Anterior Lumbar Interbody Fusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362 Manish K. Kasliwal, Carter S. Gerard, Lee A. Tan, and Richard G. Fessler

37.

Percutaneous Pedicle Screw Placement for Spinal Instrumentation . . . . . . . . . . . . . . . . . . . . . . . . . 370 Steven H. Cook, Robert E. Isaacs, Hyun-Chul Shin, Jonathan B. Lesser, Moumita S.R. Choudhury, and Mick J. Perez-Cruet

38.

Transforaminal Lumbar Interbody Fusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377 Mick J. Perez-Cruet, Moumita S.R. Choudhury, Esam A. Elkhatib, and Jorge Mendoza-Torres

39.

Transpsoas Anatomical Approach to the Spine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 388 Steven L. Gogela and William D. Tobler

40.

eXtreme Lateral Interbody Fusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398 Luiz Pimenta, Rodrigo Amaral, Luis Marchi, and Leonardo Oliveira

41.

Trans-sacral Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 406 William D. Tobler

42.

Stabilization of the Sacroiliac Joint with the Sacroiliac Bone Surgical Implant . . . . . . . . . . . . . . 416 Fred H. Geisler and Jake P. Heiney

43.

Lumbar Disc Replacement: The Artificial Disc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 440 Fred H. Geisler

44.

Minimally Invasive Spine Surgery: Lumbar Case Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 464 Mick J. Perez-Cruet, Richard G. Fessler, Roman Chornij, and Michael Y. Wang

Perez-Cruet et al, An Anatomic Approach to Minimally Invasive Spine Surgery, 2nd Ed. (ISBN 978-1-62623-643-1), copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.

ix

Part V Minimally Invasive Spine Surgery for Tumors 45.

Advances in Minimally Invasive Surgery for Spine Tumors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 478 A. Karim Ahmed, Alp Yurter, Patricia Zadnik Sullivan, Daniel M. Sciubba, and Rory Goodwin

46.

Benign Spinal Tumors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488 Manish K. Kasliwal, Lee A. Tan, Carter S. Gerard, John E. O’Toole, and Richard G. Fessler

47.

Radiofrequency Tumor Ablation with Vertebroplasty for the Treatment of Spine Metastases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 497 Anthony A. Turk and Daniel K. Fahim

48.

Minimally Invasive Resection of Intradural Spinal Tumors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 505 Trent L. Tredway and Mick J. Perez-Cruet

Part VI Complications and Outcome Analysis 49.

Clinical Outcome Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 516 Dino Samartzis, Devanand A. Dominique, Mick J. Perez-Cruet, Michael G. Fehlings, and David R. Nerenz

50.

Avoiding Complications in Minimally Invasive Spine Procedures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 528 Gabriel A. Smith and David J. Hart

Part VII Future Considerations 51.

Stem Cell–Based Intervertebral Disc Restoration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 538 Mengqiao Alan Xi and Mick J. Perez-Cruet

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 551

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Video Contents I. Fundamentals 01. Minimally Invasive Spinal Decompression, Fusion, Reduction and Instrumentation II. Patient Education and Business Basics 02. Forming a Minimally Invasive Spinal Surgery Practice & Improving Patient Outcomes III. Cervical 03. Microendoscopic Cervical Discectomy 04. C6–C7 Anterior Cervical Discectomy and Fusion 05. C5–C6 Posterior Cervical Foraminotomy IV. Thoracic 06. Microendoscopic Thoracic Discectomy 07. Thoracoscopic Treatment of a L-1 Burst Fracture 08. Minimally Invasive Thoracic Spine Surgery: State of the Art 09. Minimally Invasive Treatment of Elderly Patients with Levodextroscoliosis

V. Lumbar 10. Lumbar Spinal Stenosis: Clinical Case & Surgical Video 11. L4–L5 Microdiscectomy 12. Minimally Invasive Transforaminal Lumbar Interbody Fusion 13. L3–L4 and L4–L5 Decompressive Laminectomy 14. Microendoscopic Decompression for Lumbar Stenosis 15. Microendoscopic Transforaminal Lumbar Intervertebral Fusion & Percutaneous Pedicle Screw-Rod Instrumentation 16. Microendoscopic Lumbar Discectomy 17. The Bonebac Press 18. Minimally Invasive Transforaminal Lumbar Interbody Fusion (TLIF): Improving Spinal Fusion and Patient Outcomes 19. MI-TLIF Surgery 20. Lumbar Spinal Stenosis: Clinical Case and Surgical Video

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Preface Minimally invasive spine (MIS) surgery encompasses approaches, techniques, and innovative technology to reduce approach-related morbidity by attempting to preserve normal anatomic integrity during spine surgery. Perhaps we receive no greater gift than our healthy bodies. The body’s anatomical structures and integrated functions are truly amazing and cannot be reproduced by man. Clearly our body is our most precious commodity. Innovative MIS surgeons have been critical to developing approaches and technologies that attempt to limit harm to normal anatomical structures, improve patient outcomes and offer cost effective care. Working closely with industry to design products that facilitate these approaches, surgeons have developed methods by which patients are able to recover faster with less pain, while maintaining vital supporting structures of the spine. Additionally, smaller more focused surgery requires that the surgeon properly identify the etiology of the patient’s symptomatology. This requires an understanding and knowledge of not only spinal anatomy but of spinal pathophysiology. This text hopes to add knowledge to enable physicians to more accurately identify and treat a variety of spinal pathologies with more focused surgical care. This ultimately leads to improved long-term spine health, reduced re-operation rates, and faster return to normal active lifestyles. This objective is attractive to our patients, who are becoming increasingly knowledgeable through the doctors, the internet, friends, and family about the benefits of MIS surgery and actively seek out those physicians that can offer these procedures and treatments. MIS techniques can be offered to treat a variety of spine pathologies and are a compelling alternative to larger traditional open approaches. Many areas of surgery today incorporate minimally invasive technologies such as laparoscopy, endovascular techniques, and arthroscopic procedures. An Anatomic Approach to Minimally Invasive Spine Surgery, second edition, provides a compendium of current MIS procedures that can be performed safely and effectively. We have included some of the most cutting-edge technologies that exist today in chapters written by the world experts in the field. The text is designed to guide each surgeon’s mastery of these techniques rather than show what the experts alone can do. Although there is a learning curve in performing these procedures, this text facilitates the surgeon’s mastery of MIS approaches and techniques. The chapters are arranged to enhance patient care and comprehension of each technique. Step-by-step illustrations depicting the surgeon’s-eye-view of anatomy; intraoperative images and surgical instruments aid understanding of the surgery. Master surgical and anatomic illustrator Anthony Pazos has been critical to this

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process by providing beautifully detailed illustrations of critical steps in each surgical procedure so that the reader can understand the method in detail. This text is not only an atlas of MIS procedures of the spine for surgeons but is also a useful adjunct for educating patients, nonsurgical health care providers, residents, students, and fellows. Accompanying technical videos also show some of the more commonly performed MIS procedures, including intraoperative videos that incorporate real-time operative fluoroscopy, pertinent anatomy, and operative set-up. To perform MIS procedures, it is paramount that the surgeon thoroughly understand the pertinent surgical anatomy. However, understanding the gross anatomy is not enough; the surgeon needs to understand the anatomy when viewed via small ports or channels since only a portion of the spine anatomy is exposed to reduce tissue damage. This is quite different from what a surgeon visualizes when performing standard procedures that entail resection of significant muscles, bone, and ligamentous structures to expose relatively large portions of the spine. In MIS procedures, the goal is to preserve supporting spine architecture while exposing only a small portion of the spine (that is, the immediate site of the pathologic condition). This is akin to seeing only a piece of a puzzle, yet the surgeon must understand and be able to visualize the orientation in relation to the entire puzzle. In mastering these techniques, we can truly appreciate the fine anatomy and surgical orientation of the spine through the smallest exposure possible. This paradigm shift in how we perform spine surgery will ultimately result in improved patient outcomes and a better understanding of spine anatomy, as well as the pathophysiology of the patient’s underlying symptomatology. Additional benefits include reducing the overall cost of spine care delivery, since the ultimate goal of treating patients can be achieved with greater efficacy. Many of the techniques described and illustrated in this text are truly novel and, when applied properly, can be used to treat the most common spine pathologies even in an ambulatory setting. The book is divided into sections to facilitate exploration of the topics. Part I contains chapters on history, anatomy, biomechanics, pathophysiology, rationale for MIS, overcoming the learning curve, and operative set-up. An overview of the spinal anatomy, as well as the biomechanics of the supporting structures of the spine are presented. When reviewing the forces that are involved in simple bending of the spine, one can understand why preserving these structures is so vital to maintaining the long-term health of the spine and potentially preventing adjacent segment

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Preface pathology. An overview of degenerative disc disease leading to chronic pain conditions is reviewed, as well. Part II contains chapters on patient education, business pearls, establishing an ambulatory spine center, ancillary spine services, and bringing novel MIS devices to the market place. Once MIS techniques are mastered, incorporation into a minimally invasive spine center can lead to significant tangible goals. Part III contains chapters on image guidance and robotics, operative monitoring, nonsurgical techniques, and stereotactic radiosurgery. These chapters present the use of electrophysiologic techniques that improve safety and efficacy. The chapter on injection-based procedures discusses how these techniques can be used not only in treatment but also as diagnostic tools. Part IV "Surgical Techniques" is divided into cervical, thoracic, and lumbar sections. Each section discusses MIS anterior, posterior, and lateral approaches to the spine. Artificial disc technology is reviewed, since the goal of these procedures is similar to that of MIS surgery: to preserve function. Many of these operations can be performed in more complex cases, such as spine fusion and instrumentation, transoral, thoracoscopic, and robotic assisted surgery. In addition, many of the procedures can be done in the outpatient setting, ultimately improving patient outcomes

while reducing health care costs. In each section a chapter is dedicated to case studies. Part V is dedicated to MIS surgery for tumors and includes chapters on advances, treatment of benign and intradural tumors, and radiofrequency ablation therapy. It appears that even the most complex cases can be performed safely and effectively using MIS techniques. Part VI is dedicated to outcome analysis and avoiding complications. The chapter on avoiding complications gives particular insight. Lastly, Part VII features future considerations for spine therapy and contains a chapter reviewing stem cell–based intervertebral disc regeneration. As the ultimate goal to treating degenerative spinal conditions, biologic restoration of function using stem cell–based technology instead of tissue resection, fusion and instrumentation may be the treatment of the future. Our goal has been to create a text that can enhance a surgeon’s clinical practice while helping to improve the spine care of our patients. We would like to acknowledge the creative work and innovation of all the contributing authors. It is hoped that their contributions will be lasting and beneficial to our patient health care community. Mick J. Perez-Cruet, MD, MSc

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Acknowledgments We wish to thank all the contributing authors. Without their knowledge and effort this textbook would not have been possible. In addition to our patients, mentors, publisher, and contributors, we are indebted to our colleagues, fellows, residents, students, wives, and families for their support and encouragement during the development of this text. Their strength has been our guiding force. We wish to personally thank Kathleen Sartori and Thieme Publishers for their untiring work in getting the job done. Considerable time was spent reviewing saw bones, cadavers, videos and intraoperative cases with our tal-

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ented illustrator, Anthony Pazos. His ability to capture the essence of the surgical procedures is illustrated throughout this text. We are especially thankful for our institutional, neurosurgery departmental and practice support, including William Beaumont, Oakland University, Michigan Head and Spine Institute, Detroit, Michigan; Rush-PresbyterianSt. Luke’s Medical Center, Chicago, Illinois; and University of Miami, Florida. Finally, we wish to encourage all those who treat spinal disease to persevere in our mutual quest to improve the lives and care of our patients.

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Contributors A. Karim Ahmed, BS MD Candidate Department of Neurosurgery Johns Hopkins University School of Medicine Baltimore, Maryland Rodrigo Amaral, MD Surgeon Minimally Invasive Spinal Surgery Instituto de Patologia da Coluna São Paulo, São Paulo, Brazil Neel Anand, MD, MCh Orth Clinical Professor and Director of Spine Trauma Spine Center Cedars-Sinai Medical Center Los Angeles, California Eli M. Baron, MD Associate Professor Department of Neurosurgery Cedars-Sinai Medical Center Los Angeles, California Stephen W. Bartol, MD, MBA, FRCSC Assistant Professor Department of Orthopaedic Surgery Wayne State University School of Medicine Division Head Division of Orthopaedic Spine Surgery Henry Ford Health System Director, Michigan Spine Surgery Improvement Collaborative Detroit, Michigan Rudolf W. Beisse, MD Adjunct Professor Department of Neurosurgery University of Utah Salt Lake City, Utah Medical Director and Chief Surgeon Department of Spine Surgery Benedictus Hospital Tutzing Tutzing, Germany E. Emily Bennett, MD, MS Resident Department of Neurosurgery Neurological Institute Cleveland Clinic Cleveland, Ohio

Edward C. Benzel, MD Emeritus Chair of Neurosurgery Cleveland Clinic Cleveland, Ohio Roman Chornij Wayne State University West Bloomfield, Michigan Moumita S.R. Choudhury, MD, MS Lecturer Department of Biomedical Sciences Oakland University Rochester, Michigan Steven H. Cook, MD Department of Surgery Duke University Medical Center Durham, North Carolina Efrem M. Cox, MD Resident Department of Neurological Surgery University Hospitals Cleveland Medical Center Case Western Reserve University Cleveland, Ohio Fernando G. Diaz, MD, PhD Professor and Chair Neurological Surgery Department Oakland University William Beaumont School of Medicine Neuroscience Clinical Care Program System Chair Royal Oak, Michigan Curtis A. Dickman, MD Associate Chief, Spine Section Director, Spinal Research Department of Neurosurgery Barrow Neurological Institute Phoenix, Arizona Devanand A. Dominique, MB, BCh, BAO Neurosurgeon NeuroSpine Associates Harrisburg, Pennsylvania David L. Downs, MD, FAAOS Fullerton Orthopaedic Surgery Medical Group Fullerton, California

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Contributors Esam A. Elkhatib, MD, PhD Neurosurgery Research Fellow Department of Neurosurgery William Beaumont Hospital Oakland University Royal Oak, Michigan Daniel K. Fahim, MD, FAANS Director of Neurosurgical Oncology Associate Professor of Neurosurgery Department of Neurosurgery Oakland University William Beaumont School of Medicine Royal Oak, Michigan Michael G. Fehlings, MD, PhD, FRCSC, FACS Vice Chair of Research Department of Surgery Professor of Neurosurgery University of Toronto Halbert Chair in Neural Repair and Regeneration Toronto Western Hospital, University Health Network Toronto, Ontario, Canada Richard G. Fessler, MD, PhD Professor Department of Neurosurgery Rush University Medical Center Chicago, Illinois Fred H. Geisler, MD, PhD President Copernicus Dynamics Group, LP Chicago, Illinois Adjunct Professor Department of Medical Imaging College of Medicine University of Saskatchewan Saskatoon, Saskatchewan, Canada Carter S. Gerard, MD Resident Department of Neurological Surgery Rush University Medical Center Chicago, Illinois Steven L. Gogela, MD Neurosurgeon Neurological and Spinal Surgery, LLC Lincoln, Nebraska Rory Goodwin, MD, PhD Assistant Professor Department of Neurosurgery

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Duke University Durham, North Carolina David J. Hart, MD Assistant Professor Department of Neurological Surgery Case Western Reserve University School of Medicine Cleveland, Ohio Jake P. Heiney, MD, MS President and CEO Cutting Edge Orthopaedics, LLC Sylvania, Ohio Ann T. Hollenbeck, Esq. Partner Jones Day Detroit, Michigan Robert E. Isaacs, MD Associate Professor of Neurosurgery Director, Spine Surgery Department of Surgery Duke University Medical Center Durham, North Carolina R. Patrick Jacob, MD, FAANS Dunspaugh Dalton Professor Chief of Spine Surgery Department of Neurosurgery University of Florida Gainesville, Florida Maha Saada Jawad, MD Assistant Professor Department of Radiation Oncology Oakland University William Beaumont School of Medicine Royal Oak, Michigan Manish K. Kasliwal, MD, MCh Director, Minimally Invasive Spine Surgery University Hospitals Cleveland Medical Center Assistant Professor of Neurological Surgery Case Western Reserve University School of Medicine Cleveland, Ohio Larry T. Khoo, MD Co–Director University of Southern California Neuroscience Center Good Samaritan Hospital The Spine Clinic of Los Angeles Los Angeles, California

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Contributors Michael A. Leonard, MD Director Alamo Neurosurgical Institute San Antonio, Texas Jonathan B. Lesser, MD Professor Department of Anesthesiology Icahn School of Medicine at Mount Sinai New York, New York Luis Marchi, PhD Researcher Minimally Invasive Spinal Surgery Instituto de Patologia da Coluna (IPC) São Paulo, São Paulo, Brazil Joshua E. Medow, MD, MS, FAANS, FACS, FNCS, FAHA, FCCM Tenured Associate Professor of Neurosurgery, Pathology, and Biomedical Engineering Director of Neurocritical Care University of Wisconsin School of Medicine and Public Health Madison, Wisconsin Jorge Mendoza-Torres, MD Neurosurgeon Brain and Spine Section Minimally Invasive Spine Surgery Vallarta Medical Center Hospital Puerto Vallarta, Jalisco, México Laura Miller Dyrda Editor-in-Chief Becker’s ASC Review and Becker’s Spine Review Becker’s Healthcare Chicago, Illinois Ronnie I. Mimran, MD, MBA Neurosurgeon Pacific Brain and Spine Medical Group Danville, California James M. Moran, D. Eng. President Device Commercialization Consultants, LLC Sagamore Hills, Ohio Jeffrey P. Mullin, MD, MBA Resident Department of Neurosurgery Neurological Institute Cleveland Clinic Cleveland, Ohio

Hiroshi W. Nakano, MBA Director, Value Based Care University of Washington Medicine Valley Medical Center Renton, Washington David R. Nerenz, PhD Vice-Chair for Research Department of Neurosurgery Henry Ford Hospital Detroit, Michigan Leonardo Oliveira, BSc Researcher Minimally Invasive Spinal Surgery Instituto de Patologia da Coluna São Paulo, São Paulo, Brazil Kevin R. O’Neill, MD, MS Spine Surgeon OrthoIndy, Inc. Indianapolis, Indiana John E. O’Toole, MD, MS Professor Department of Neurosurgery Rush University Medical Center Chicago, Illinois Zachary D. Patterson, BS DO Candidate Touro University–California Vallejo, California Mick J. Perez-Cruet, MD, MSc Vice Chairman and Professor Department of Neurosurgery Oakland University William Beaumont School of Medicine Royal Oak, Michigan Michigan Head and Spine Institute Southfield, Michigan Noel I. Perin, MD, FRCS(ed), FAANS Director, Minimally Invasive Spine Department of Neurosurgery New York University Medical Center New York, New York George D. Picetti III, MD Director of Pediatric and Adult Spinal Deformities Sutter Neuroscience Medical Group Sacramento, California

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Contributors Peter F. Picetti, MFA, ABD Teaching Assistant University of Nevada–Reno Reno, Nevada Daniel Roy Pieper, MD Professor Department of Neurosurgery Oakland University William Beaumont School of Medicine Michigan Head and Spine Institute Royal Oak, Michigan Luiz Pimenta, MD, PhD Assistant Professor Department of Neurosurgery University of California San Diego San Diego, California Director Minimally Invasive Spinal Surgery Instituto de Patologia da Coluna São Paulo, São Paulo, Brazil Rick Placide, MD, PT Spine Surgeon and Orthopaedic Surgeon OrthoVirginia Chief of Orthopaedics Chippenham and Johnston-Willis Medical Centers Assistant Clinical Professor Department of Physical Medicine and Rehabilitation Virginia Commonwealth University Medical Center Richmond, Virginia Sina Rajamand, DO Neurosurgery Resident Michigan State University College of Human Medicine Providence-Providence Park Hospital Southfield, Michigan Charles D. Ray, MD, FACS, FRSHS Past President, American College of Spine Surgery; Past President, International Spine Arthroplasty Society; Past President, North American Spine Society, Yorktown, Virginia John A. Redmond CEO RSB Spine, LLC and RJR Surgical, Inc. Cleveland, Ohio

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Daniel K. Resnick, MD, MS Professor and Vice Chairman Department of Neurosurgery University of Wisconsin School of Medicine and Public Health Madison, Wisconsin K. Daniel Riew, MD Professor of Orthopaedic Surgery Chief of Cervical Spine Surgery Director of Spine Fellowship Department of Orthopaedic Surgery Columbia University College of Physicians and Surgeons The Daniel and Jane Och Spine Hospital New York, New York Matthew L. Rontal, MD Associate Professor Department of Surgery Oakland University William Beaumont School of Medicine Royal Oak, Michigan Partner Rontal-Akervall Clinic Farmington Hills, Michigan Nima Salari, MD Orthopedic Spine Surgery Desert Institute for Spine Care, PC Phoenix, Arizona Dino Samartzis, Dip EBHC, MSc, MA(C) Associate Professor Director, Clinical Spine Research Deputy Director, Laboratory and Clinical Research Institute for Pain Li Ka Shing Faculty of Medicine Hong Kong, China Zeeshan M. Sardar, MD, MSc, FRCSC Assistant Professor Spine and Scoliosis Surgery Department of Orthopaedic Surgery & Sports Medicine Temple University, Lewis Katz School of Medicine Philadelphia, Pennsylvania Daniel M. Sciubba, MD Professor of Neurosurgery, Oncology, and Orthopaedic Surgery Department of Neurosurgery Johns Hopkins University School of Medicine Baltimore, Maryland

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Contributors Richard A. Shapack, BS, MBA, JD Principal Shapack Law Group PLC Bloomfield Hills, Michigan

Anthony A. Turk, MD Department of Surgery University of California San Francisco, California

Hyun-Chul Shin, MD, PhD Fellow Chicago Institute of Neurosurgery and Neuroresearch Chicago, Illinois Department of Neurosurgery Seoul Kangbuk Samsung Hospital Sungkyunkwan University College of Medicine Seoul, Korea

Alexander R. Vaccaro, MD, PhD, MBA Richard H. Rothman Professor and Chairman Department of Orthopaedic Surgery Professor of Neurosurgery and Co-Director Delaware Valley Spinal Cord Injury Center Co-Chief of Spine Surgery Sidney Kimmel Medical Center at Thomas Jefferson University President Rothman Institute Philadelphia, Pennsylvania

Andrea Simmonds, FRCSC Clinical Fellow Department of Spine Surgery Cedars-Sinai Medical Center Los Angeles, California Gabriel A. Smith, MD Department of Neurological Surgery University Hospital Cleveland Medical Center Cleveland, Ohio Patricia Zadnik Sullivan, MD Resident Department of Neurosurgery University of Pennsylvania Philadelphia, Pennsylvania Lee A. Tan, MD Assistant Professor Department of Neurological Surgery University of California–San Francisco Medical Center San Francisco, California William D. Tobler, MD Professor of Neurosurgery Department of Neurosurgery University of Cincinnati College of Medicine Chairman, Mayfield Spine Surgery Center Director, Mayfield Surgical Innovation Center Cincinnati, Ohio Henry Tong, MD, MS Staff Physician Michigan Head and Spine Institute Southfield, Michigan Trent L. Tredway, MD Neurosurgeon NeoSpine Seattle, Washington

Francisco Verdú-López, MD Neurosurgeon Department of Neurosurgery and Spine Surgery Hospital General Universitario de Valencia Teacher Collaborator, University of Valencia Valencia, Spain Michael Y. Wang, MD, FACS Professor of Neurological Surgery and Rehab Medicine Miller School of Medicine University of Miami Chief of Neurosurgery Director, Neurosurgical Spine Fellowship University of Miami Hospital Miami, Florida Holly Weissman, MS, RN, NP-C, CNRN Nurse Practitioner Department of Neurosurgery Beaumont Health System Royal Oak, Michigan Richard N.W. Wohns, MD, JD, MBA Associate Clinical Professor Department of Neurosurgery University of Washington Seattle, Washington Founder and Managing Partner NeoSpine Puget Sound Region, Washington Mengqiao Alan Xi, BSc Medical Student Year III Oakland University William Beaumont School of Medicine Royal Oak, Michigan

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Contributors Anthony T. Yeung, MD Voluntary Professor Department of Neurosurgery University of New Mexico School of Medicine Albuquerque, New Mexico Affiliate Orthopedic Spine Surgery Desert Institute for Spine Care, PC Phoenix, Arizona

Alp Yurter, BS Yale School of Medicine New Haven, Connecticut Hasan A. Zaidi, MD Department of Neurosurgery Barrow Neurological Institute Phoenix, Arizona

Christopher Yeung, MD President Desert Institute for Spine Care, PC Phoenix, Arizona

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Part I Fundamentals

I

1 History of Minimally Invasive Spine Surgery

2

2 Anatomy of the Spine: An Overview

12

3 Biomechanical Role of the Osseous, Ligamentous, and Muscular Structures of the Spine

27

4 Pathophysiology and Operative Treatment of Discogenic Back Pain

39

5 Pathophysiology of Back Pain

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6 Rationale for Minimally Invasive Spine Surgery

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7 Overcoming the Learning Curve

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8 Operating Room Setup

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Fundamentals

1 History of Minimally Invasive Spine Surgery Michael A. Leonard, Dino Samartzis, and Mick J. Perez-Cruet Abstract Since the seventh century, a wide variety of approaches and techniques have been developed for operative treatment of the spine. William S. Halsted’s concept of minimally invasive surgery coupled with economic pressures, patient satisfaction, and the desire to enhance postoperative outcomes has contributed to the clear advantages of minimally invasive spine surgery. This chapter highlights the historical contributions of endoscopy, microsurgery, and image guidance in the field of minimally invasive spine surgery. Keywords: endoscopy, microsurgery, image guidance, minimally invasive spine surgery, magnetic resonance imaging, computed tomography, cervical spine, thoracic spine, lumbar spine

1.1 Introduction Since the earliest recorded history, a variety of pathologies have ravaged the spine. The first concrete delineation of operative treatment of the spinal column was proposed by Paulus of Aegina in the seventh century.1 He advocated and conducted direct removal of osseous tissue at the site of pathology. Since then, a wide variety of approaches and techniques for operative treatment of the spine have been developed. The concept of minimally invasive surgery can be traced back to William S. Halsted, who noted that outcome could be optimized when certain surgical principles were applied. Before this, it was believed that speed was the critical determinant in patient outcome. Halsted, although a quick surgeon himself, stressed the principles of minimizing tissue disruption, meticulous hemostasis, and proper closing of anatomic layers as essential to optimizing patient outcome. These principles were among the first that stressed techniques that made surgery less invasive and are still the basic fundamentals that underlie what is known today as minimally invasive surgery, or MIS. In more recent times, economic pressures from the competitive health care climate as well as a desire to optimize patient satisfaction have also helped in spurring developments throughout multiple surgical disciplines that reduce operative time and complications, minimize intraoperative tissue trauma, diminish the length of hospital stay, lessen postoperative use of narcotics, and enhance postoperative outcome. With initial experiences of successful early ambulation after surgery and the advantages of outpatient surgery to the patient, hospital, and physician, the trend toward minimally invasive surgical procedures has progressed rapidly.2,3,4,5,6

1.2 General Advancements Central to the evolution of the field of minimally invasive spine surgery has been the development of three essential techniques: (1) endoscopy, (2) microsurgery, and (3) image guidance. Although it may seem that the technical advancements that have facilitated the development of minimally invasive procedures are

2

new, in fact many of these innovations were conceived more than 100 years ago. The evolution of the endoscope has its roots in 1806 when Philipp Bozzini developed an endoscopic device to delineate the exploration of various body cavities.7 In 1853, Desormeaux implemented the use of a lens and an alcohol-based fluid on the endoscope for direct-light focus and increased intensity, respectively.8,9 The first endoscopic procedure was performed by Bevan in 1868 to address esophageal pathology.8 Later, Nitze10 developed a cystoscope that consisted of a working channel, illumination, and an optical lens for reflection. In 1902, the first laparoscopic surgery was performed,11 and in 1911, Lespinasse, a urologist working in Chicago, performed the first ever cranial neuroendoscopic procedure when he fulgurated the choroids plexus in two infants with hydrocephalus.12 In 1931, Burman13 first reported on the use of endoscopy for the spine, which he termed myeloscopy, and in 1938, Pool14 reported on his experience with myeloscopy to inspect the nerve roots and spinal cord in cases of disc herniation, hypertrophied ligamentum flavum, benign and malignant neoplasms, and arachnoiditis. As the years progressed, the endoscope was improved and used for various diagnostic and therapeutic purposes. Since then, there has been an explosion of endoscopic instruments that have made a large variety of endoscopic procedures possible. In 1997, Foley and Smith15 attached an endoscope to a tubular retractor system, and the concept of microendoscopic discectomy, or MED, was born. Although tubular retractors have been used for quite some time in cranial neurosurgery,16 their introduction to spine surgery would help usher in a new era in minimally invasive spine surgery. In 1998, the METRx System (Medtronic Sofamor Danek) was introduced, which used the same tubular retractors as MED but allowed the use of either the endoscope or a microscope. The development of the operating microscope has an equally interesting history and has been meticulously detailed elsewhere.17 Although the exact origin of the microscope is uncertain, it is believed to have been invented around 1600 in Holland.18,19 Anton van Leeuwenhoek, a Dutch scientist from the 1600s, advanced the field of microscopy by improving considerably on the microscopes of his time and making countless microscopic observations.19 In the 1800s, Carl Zeiss, a German machinist, began building microscopes and was able to standardize lens production, allowing mass production of microscopes, and he also introduced the first binocular microscope.17 In 1921, Carl Nylen,20 a Swedish otolaryngologist, was the first person to use a microscope in surgery, treating a case of chronic otitis media. Over the next several decades, many clinicians in the fields of ophthalmology and otolaryngology continued to advance the field of microsurgery and the development of the operating microscope. In 1957, Theodore Kurze performed the first microneurosurgery procedure,17 the removal of a seventh nerve schwannoma, and in 1962 he published the first series on microneurosurgery.21 In 1958, Raymond Donaghy established the first microsurgery research laboratory in Burlington, Vermont, and in 1960 Jacobson, a vascular surgeon who had worked earlier with Donaghy, teamed with the Zeiss corporation to develop the first two-person microscope to allow the assistant to actually assist.17 Pool and Colton22

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History of Minimally Invasive Spine Surgery published the first account of the use of a microscope for intracranial aneurysm surgery in 1966. Mahmut Gazi Yasargil spent a year in Donaghy’s laboratory in 1966, returning then to Zurich to establish his own microneurosurgery program.17 Over the next several decades, the work of Yasargil and many others demonstrated the invaluable assistance that use of the microscope provided to the performance of surgery of the central nervous system. Over time, the techniques that were developed for intracranial surgery would be adapted to surgery of the spine. More recently, image guidance has played a major role in advancing minimally invasive spine surgery. The development of the magnetic resonance imaging (MRI) scan has allowed the very precise location and characterization of spinal pathologies, allowing surgeons to attack the problem in the most direct manner. The only difficulty has been finding a way to more precisely guide the surgeon to the intraoperative pathology based on preoperative imaging. For the past several decades, intraoperative fluoroscopy has been utilized to confirm levels and help ensure proper localization for the surgeon. This provided for the ability of more frequent imaging than standard flat plate radiography, with images being obtained in real time, even in a continuous manner to closely monitor the placement of hardware. In more recent years, the O-arm (Medtronic Navigation) and Airo (Brainlab) have allowed more complete spinal imaging equivalent to a computed tomography (CT) scan to be done in real time by the surgeon in the operating room. Frequently, this imaging is paired with a surgical guidance system to assist in the placement of spinal hardware, such as the Brainlab Spinal Navigation system (Brainlab) or the StealthStation S7 (Medtronic Navigation). As helpful as these technologies have been, one major drawback has been the increase in radiation exposure as a result of their use, to both the patient and the operative team. In 2004, Mazor Robotics introduced its SpineAssist robotic spine surgery platform, with its second-generation platform, the Renaissance Guidance System, later launched in November 2011. This system continues to be the only robotic spine surgery platform Food and Drug Administration (FDA) approved for robotic guidance to the cervical, thoracic, and lumbar spine. This system uses two fluoroscopic images obtained with fiducial markers in place to register to the patient’s preoperative CT scan in a fashion similar to the technique used by the Cyberknife Robotic Radiosurgery System (Accuray). The Renaissance robot is then mounted to the patient’s spine and guides the placement of the spinal hardware without the need for repeated and excessive fluoroscopic images being taken. To date,

there have been an estimated 50,000 or more screws placed with this system with no reported incidents of permanent nerve injury.

1.3 Advancements in Cervical, Thoracic, and Lumbar Surgical Spine Techniques Although the development of endoscopic and microsurgical techniques is applicable to all regions of the spine, the history of the cervical, thoracic, and lumbar areas is sufficiently distinct to warrant discussing these topics separately. The focus will largely be on the treatment of disc herniations and spondylosis, because much of the progress in the field of minimally invasive spine surgery was made while treating these degenerative diseases due to the large number of patients with such diagnoses compared to other ailments. However, these advancements were quickly adapted to treat virtually all other conditions that involve the spine.

1.3.1 Cervical Surgical Spine Techniques The first report of anterior spinal cord compression from posterior protrusion of a herniated disc was by Key in 1838.23 Walton and Paul,24 in 1905, reported on a patient with an apparent herniated disc that they operated on for a presumed cervical spinal cord tumor. Mixter and Barr,25 in their landmark 1934 paper, included four patients with cervical disc herniations. Initial description of a lateral cervical disc herniation with nerve root compression (vs. a central herniation and compression of the cord) was made by Stookey, in 1928,26 and lateral cervical disc herniation with nerve root compression resulting in neck pain and radiating arm pain was further detailed by Semmes and Murphy in 1943.27 Initially, the posterior approach was used exclusively to approach cervical disc disease, with a transdural approach taken to the disc herniation, as first described by Elsberg.28 In 1928, Stookey26 introduced a less invasive hemilaminectomy to address cervical herniations, and Semmes and Murphy27 advanced the minimally invasive approach to these lesions by operating through a smaller laminotomy. Frykholm,29 Spurling and Segerberg,30 and Scoville31 further advanced this procedure to the keyhole foraminotomy that is still in use today29 (▶ Fig. 1.1).

Fig. 1.1 (a,b) Drawings showing the extent of bony removal for posterior laminoforaminotomy for lateral cervical disc herniation. (Reproduced with permission from Frykholm.29)

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Fundamentals Although the posterior approach had been used with success for several decades, patients all too frequently had new postoperative neurologic deficits, particularly when they had central herniations that caused spinal cord compression. To address these shortcomings, Robinson and Smith, in 1955,32 made their initial report of the anterior approach to the cervical spine to treat disc herniations. This allowed access to the primary pathology without the need to manipulate the intervening neural elements. Their report was followed by Cloward’s in 1958,33 detailing experience and describing specific equipment designed for the procedure. After a gradual period of acceptance, the anterior approach became the procedure of choice for most spine surgeons. In 1975, Hankinson and Wilson34 were the first to report on the use of the microscope for spine surgery when they reported on the series of 51 patients in whom microsurgical anterior cervical discectomies were performed. Although the anterior approach was a significant advancement in cervical spine surgery, clinicians continued to strive to make this procedure as minimally invasive as possible. Originally, it was common practice for patients to spend prolonged periods of time in rigid cervical collars. During the 1970s, the concept of internal fixation to aid in cervical fusion was introduced, and in the 1980s the Caspar anterior cervical plating system was introduced.35,36 This soon led to the development of numerous other types of anterior cervical plating systems. As plates have evolved over the years, clinicians have gradually stopped using collars routinely after single-level fusions and allowed patients’ more rapid return to normal activities. Use of allograft for cervical fusion was popularized throughout the 1990s, which allowed patients to avoid the morbidity of an iliac crest autograft.37 Even with the freedom that these new internal fixation devices and fusion options have provided, there have been some who have continued to worry about the loss of a cervical motion segment and the possibility of progression of adjacent-level spondylosis when a fusion is performed. Anterior cervical decompressions done without fusions were originally promoted as a solution to this potential problem; however, even these procedures have shown a high rate of spontaneous fusion and ultimate loss of a motion segment.34,38 In an effort to address this concern, Snyder and Bernhardt, in 1989,39 building on the work of Verbiest,40 developed the anterior cervical foraminotomy, which was further refined by Jho in 1996.41 This allowed decompression of the affected nerve root but maintained preservation of the motion segment. Jho42 went on to illustrate how this technique could be used to perform the central canal decompression required to treat patients with myelopathy. However, the inherent risks to the vertebral artery, nerve roots, and spinal cord when utilizing this approach elevate the technical demand of these procedures and have precluded this technique’s widespread adoption. In more recent times, the application of endoscopy and other new techniques to spine surgery has led to an explosion in minimally invasive procedures for the cervical spine. The MED system, or one of its variants, has been used for minimally invasive procedures to attack pathology from both the anterior and posterior cervical approaches with great promise, particularly with posterior approaches, for which these new techniques seem to offer a significant advantage over the traditional open procedure.43,44,45, 46,47,48,49,50 Although these procedures are essentially identical to

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their open-procedure predecessors, the use of the tubular retractor system, in particular, has made possible significant advances toward the ultimate goal of making cervical spine surgery as minimally invasive as possible. Over the past several years, there has been an increased emphasis on motion preservation when performing spine surgery, in the hope of avoiding the development of adjacent segment degeneration following a spinal fusion. In 2007, Mummaneni et al51 first published their results with the PRESTIGE ST Cervical Disc System (Metronic Sofamor Danek) that allowed artificial disc motion preservation at the operated level in the hope that this would eliminate the appearance of adjacent segment degeneration, and since then many additional variants of the artificial disc have been developed and marketed. Initial studies have shown equivalency of the artificial disc to a standard anterior discectomy and fusion.52,53,54 More recent studies appear to begin to show superiority of the artificial disc over fusion.55,56 In the cervical spine, the ease of the standard anterior approach, which surgeons are already very familiar with, has helped make the acceptance of the cervical artificial disc considerably easier than its lumbar counterpart.

1.3.2 Thoracic Surgical Spine Techniques One of the first proposals for surgical intervention for an ailment of the thoracic spine was made by Pott, in 1779,57 when he recommended drainage of the tuberculum abscess in his work on paraplegia. Since then, patients with an assortment of ailments afflicting the thoracic spine have undergone a wide variety of surgical approaches in an attempt to minimize the morbidity of this procedure. Surgery for the anterior column of the thoracic spine poses certain challenges not seen in either the cervical or lumbar region. Operating on either the thoracic or cervical region means that the surgeon will have anatomic structures that complicate their anterior exposure. It was for this reason that early surgical approaches to the thoracic spine, like approaches to the cervical spine, were posterior in nature and resulted in the same relatively poor outcomes, prompting surgeons to seek alternate approaches. However, unlike the cervical spine, which is easy to approach anteriorly, the contents of the chest make anterior approaches challenging for the thoracic spine. Thus, when surgeons first began to devise alternate approaches to treat lesions of the thoracic spine, they needed to contend with the presence of the spinal cord posteriorly and the thoracic cavity contents anteriorly. This led to the development of a number of approaches that varied in how they addressed these two limitations, all with the intention of making surgery of this nature as minimally invasive as possible. The history of the treatment of thoracic disc herniations provides an excellent example of how surgery of the thoracic spine has evolved over the past century. The first reported case of a herniated thoracic disc was made by Key in 1838.23 In 1911, Middleton and Teacher58 provided additional evidence that disc herniations occur in the thoracic spine. The first known case of operative treatment of a thoracic herniated disc was described in 1922 by Adsen, who performed disc removal after a laminectomy.59 For much of the next several decades, the procedure of choice was a posterior approach, but the results were dismal.59,60,61,62 The lateral extracavitary approach

Perez-Cruet et al, An Anatomic Approach to Minimally Invasive Spine Surgery, 2nd Ed. (ISBN 978-1-62623-643-1), copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.

History of Minimally Invasive Spine Surgery was first described by Menard, in 1894,63 to treat Pott’s disease and was later adapted to treat disc herniations.64 Cauchoix and Binet65 reported, in 1957, on their initial experience with a transsternal approach to the upper thoracic spine. In 1969, Perot and Munro,66 and separately Ransohoff et al,67 adapting the transthoracic technique of Hodgson and Stock,68 simultaneously reported on a transthoracic approach to treat thoracic disc herniations. In 1978, Patterson and Arbit69 described the transpedicular approach in an attempt to avoid entering the thoracic cavity, and in 1998 Stillerman et al70,71 introduced the slightly less invasive transfacet pedicle-sparing approach. In 1995, McCormick72 described the retropleural approach, which avoided entering the thoracic cavity and also avoided disruption of the facet joint. In 1997, Jho73 introduced the posterior microendoscopic approach to treat thoracic disc herniations. Although the evolution of these approaches details significant advances in making surgery for thoracic disc herniations much less invasive, such approaches were still somewhat invasive. In an attempt to minimize operative morbidity, thoracoscopic video-assisted spine surgery was developed and first performed in the early 1990s simultaneously by Mack et al74 in the United States and Rosenthal and Dickman8 in Europe. Initially, thoracoscopic spine procedures were implemented to treat disc herniations or for tumor biopsies. However, in the ensuing years, thoracoscopy was used to address scoliosis, anterior interbody fusion, drainage of disc space abscess, and vertebrectomy for tumor.75,76,77,78,79,80

ment of lumbar disc disease. In addition, Caspar’s 1977 paper88 described instruments and techniques that bear a striking resemblance to those used two decades later by Foley and Smith15 in their description of MED88 (▶ Fig. 1.2). Williams90 further supported and popularized microdiscectomy in the 1970s by advocating minimizing the skin incision and removing only the herniated disc fragment through an intralaminar window not unlike Love’s technique. During the 1990s, an explosion in the number of endoscopic procedures and techniques occurred in numerous fields, and spine surgery was no exception. The use of an endoscope for lumbar discectomy was introduced by Mayer and Brock in 1993.91 A transforaminal endoscopic microdiscectomy was reported in the mid-1990s and provided direct visualization of the epidural space via entry under the pars and superior articular facet.92 In 1997, Foley and Smith15 illustrated the development and application of the MED system. Shortly thereafter, the METRx-MD system (Medtronic Sofamor Danek) was introduced and allowed surgeons to take advantage of the tubular retractors that could be used with either the endoscope or the microscope. Based on the success of these systems in treating herniated discs,93 a minimally invasive technique for treatment

1.3.3 Lumbar Surgical Spine Techniques In 1857, Virchow81 described traumatic intervertebral disc rupture, and in 1911 Middleton and Teacher58 expanded on his first account when they reported on their autopsy findings of traumatic disc rupture. Also, in 1911, Goldthwaite82 speculated that lumbar disc herniations were responsible for sciatica. The first account of a lumbar laminectomy performed in the United States occurred in 1829 and was performed by Smith to treat progressive paresis stemming from a previous fracture.83 Using this laminectomy approach, in 1908 Oppenheim and Krause,84 and later Elsberg,28 performed resection of what were, in all likelihood, herniated lumbar discs. In 1929, Dandy85 reported the first definitive description of operative treatment of lumbar disc disease, recognizing its traumatic origin. In 1934, the influential description by Mixter and Barr25 of neurologic deficits associated with a herniated lumbar disc and subsequent treatment by a lumbar discectomy via a laminectomy stressed the practicality of operative intervention to address such lumbar pathology. In 1938, Love86 advanced the practice of lumbar disc surgery when he reported on his experience of removal of herniated discs through a minimally invasive interlaminar approach that typically required no bone removal. Adaptations of this technique form the basis for the lumbar microdiscectomy that is still in use today. In 1973, Scoville and Corkill87 reported on their experience with early mobilization of the postoperative discectomy patient. Before this, patients were usually left in bed for days and had their activity severely restricted for weeks or months after a discectomy. Striving to promote intraoperative visual acuity and reduce tissue trauma, Caspar88 and Yasargil89 simultaneously introduced the use of an operating microscope and microsurgical techniques in 1977 for the treat-

Fig. 1.2 Drawing of a retractor introduced by Caspar in 1977, with striking similarities to the technique of microendoscopic discectomy introduced by Foley and Smith in 1997. (Reproduced with permission from Caspar.88)

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Fundamentals of lumbar stenosis was developed, which avoids many of the consequences of the traditional laminectomy, including excessive scar tissue formation, disruption of the posterior bony elements, subsequent instability of the spine, and ensuing biomechanical alterations.94 In an attempt to further decrease tissue trauma and enhance postoperative outcome, various other minimally invasive surgical procedures have been developed to address lumbar disc herniation. In 1941, Jansen and Balls95 first isolated chymopapain, a proteolytic enzyme extracted from papaya latex. After indepth animal experimentation, chymopapain was injected into human subjects, and subsequent results were reported by Smith in 1964.96 This process, aptly called chemonucleolysis, alters the characteristics of the nucleus pulposus by liberation of chondroitin sulfate and keratin sulfate by hydrolysis of noncollagenous proteins of mucopolysaccharide involvement and leads to depolymerization of the nucleus pulposus. The efficacy of chemonucleolysis in randomized prospective clinical trials as compared to open techniques remains controversial.97,98,99,100 In 1975, Hijikata101 demonstrated a percutaneous nucleotomy by using arthroscopic techniques for disc removal via intradiscal access for the treatment of posterior or posterolateral lumbar disc herniations. Automated percutaneous discectomy (APD) was developed in 1985 by Onik et al,102 and this entailed the insertion of a 2-mm probe for rapid, safe removal of the disc material. In the late 1980s, percutaneous laser discectomy was introduced by Choy et al,103 and has since been used when performing endoscopic discectomy. As with APD, this technique uses a percutaneous approach to the disc, but then uses a laser with varying intensity to absorb the nucleus pulposus. Stereotactic lumbar microdiscectomy has also been suggested, as well as intraoperative MRI for discectomies.104,105 Whether these advancements were better than the traditional open procedure is a subject of debate, but each is representative of the continued striving by clinicians to make surgery for herniated lumbar discs as minimally invasive as possible. In addition to the progress made in the treatment of herniated lumbar discs, progress has also been made in the area of making lumbar spinal fusions less invasive. Posterior lumbar interbody fusion (PLIF) was proposed by Cloward in 1953106 to treat degenerative disc disease or spondylolisthesis. Since that time, the procedure has been modified and advocated by many others and has proved to be effective in treating select patients who require fusion, but has remained essentially as invasive as when Cloward first proposed it.107,108,109,110,111,112,113 In 2002, Foley and Gupta114 reported on their experience with the Sextant pedicle screw-rod instrumentation (Medtronic Sofamor Danek) to perform a percutaneous minimally invasive PLIF. Since then, multiple other MIS systems have been developed to allow for percutaneous placement of lumbar spine instrumentation, with a variety of techniques being employed for rod passage. Based on previous reports on the success of a unilateral PLIF,115,116 Isaacs et al117 reported their experience with a modification of Foley and Gupta’s technique by incorporating a unilateral, less invasive approach. In addition, as mentioned previously, continuous developments in fluoroscopic technology, image-guided computer systems, and even robotic spine surgery systems have greatly facilitated the safe and expeditious application of instrumentation. As an alternative to PLIF for those patients requiring fusion, an anterior lumbar interbody fusion (ALIF) has been described. Since

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ALIF was first reported, the preferred route to the anterior lumbar spine has been via a retroperitoneal approach.118,119,120 In recent years, several authors have modified the retroperitoneal approach to make it less invasive.121,122,123,124 In 1997, McAfee et al125 described a minimally invasive endoscopic retroperitoneal approach, which allowed a small skin incision and less tissue disruption. In the early 1990s, the use of laparoscopic procedures to address various pathologies of the spine began and has gained immense momentum. Laparoscopic spine surgery was first reported in 1991 by Obenchain126 in his description of a lumbar discectomy of L5–S1. Instrumented interbody fusion of the spine conducted laparoscopically was performed in 1993 by Zucherman et al.127 Since then, the experience with laparoscopic spinal procedures has grown significantly.128,129,130,131,132,133,134,135 However, a steep learning curve and reported higher complication rates compared to traditional open procedures, without appreciable increased benefits, have made laparoscopic anterior interbody fusion less attractive.136,137,138,139,140 In an effort to minimize risks and difficulties of the ALIF procedure, including the need for an access surgeon, in 2006, Ozgur et al141 developed and published their experience with a novel approach to the disc space via a minimally invasive transpsoas approach. Initially, this approach was termed XLIF, for eXtreme Lateral Interbody Fusion, and was performed using the instruments and spinal hardware developed in collaboration with Nuvasive. In addition, they developed a proprietary electrophysiologic monitoring tool for testing and localizing the lumbosacral plexus nerve roots near the psoas muscle in order to protect them from inadvertent injury.142 This method has allowed for large interbody cages to be placed to maximize restoration of disc height or to help restore sagittal and coronal balance in a minimally invasive way. More recently, others have developed similar extreme lateral approaches. Although the XLIF and its variations have made access to the anterior lumbar spine for interbody fusion much easier, these approaches are not feasible for access to the L5–S1 level in most patients due to interference from the iliac crest. To address this, the AxiaLIF (TranS1) was first described in 2008 by Aryan et al,143 which uses a percutaneous paracoccygeal approach to access the L5–S1 disc space through the corridor between the rectum and the sacrum. Although intuitively there was some concern for inadvertent bacterial seeding of the disc space and postoperative infection due to close proximity of the anus to the entry point, Gundanna et al,144 in 2011, reported on their extensive experience with over 9,000 cases with a low overall complication rate of 1.3% and a very low infection rate. In an effort to find a less invasive way to treat discogenic back pain, Saal and Saal145 developed intradiscal electrothermal therapy (IDET) in the late 1990s. The IDET approach places a navigable thermal heated coil catheter within the nucleus pulposus. However, clinical results were mixed,145,146,147 and this procedure has largely fallen out of favor. As with the cervical spine mentioned earlier, there has been an interest in motion preservation surgery in the lumbar spine as well. The first entry into this field in the United States was the Charite lumbar artificial disc, released in the United States in October 2004, with the early clinical results from this device being published in 2005 by Blumenthal.148 Since that time, numerous other devices have been promoted for lumbar spine motion preservation as an alternative to fusion. After an exciting initial

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History of Minimally Invasive Spine Surgery reception by the spine surgery community, the need for an anterior lumbar approach, typically necessitating use of an access surgeon, as well as not getting approved for Medicare patient use and the steep learning curve experienced by many surgeons in placing the prosthesis, regardless of which type of artificial disc was used, has dampened the enthusiasm for lumbar arthroplasty.

1.4 Additional Minimally Invasive Developments The spine is composed of a rich trabecular lattice of cancellous bone encased in a hard cortical shell. This combination of cancellous and cortical bone is exposed to a significant amount of compressive loads. Osteoporotic and neoplastic invasion of the vertebral bodies can result in erosion of the cancellous network and the cortical shell, leading to development of vertebral compression fractures, which can cause severe pain, neurologic deficit, gross spinal instability, and ensuing deformity. Initially, these problems were treated (when necessary) with open procedures that were technically challenging and associated with high morbidity. Additionally, many of the patients who were treated with only immobilization and narcotic analgesics (as well as radiation for neoplastic lesions) frequently endured severe chronic pain. In response to these shortcomings, percutaneous vertebroplasty was developed in 1984 by Galibert and Déramond,149,150 in France, as a minimally invasive outpatient procedure to offer immediate pain relief by the injection of polymethylmethacrylate (PMMA) bone cement into the vertebral body through a transpedicular percutaneous approach. Although a popular procedure in Europe, percutaneous vertebroplasty was not performed in the United States until 1994.151 Since then, it has gained popularity and is now frequently performed in patients who have persistent pain. However, in an effort to restore the height lost from a vertebral compression fracture, reduce the high incidence of cement extravasation seen with vertebroplasty, and optimize sagittal balance, kyphoplasty was developed.152 Kyphoplasty uses an inflatable bone tamp inserted by a bilateral transpedicular approach to create cavities in the collapsed vertebral bodies that are then injected with PMMA. Numerous reports have supported its efficacy in alleviating the pain associated with compression fractures.153,154,155,156,157 Additionally, because in kyphoplasty the cement is injected into the preformed cavities, it can be injected at a relatively low pressure, as opposed to the high pressure injection of vertebroplasty, which may reduce the incidence of extravertebral spread.158 In addition, the risk of subsequent vertebral fractures may be decreased due to the restoration of the sagittal balance.159,160 Although PMMA has been used for some time in a number of orthopaedic and spinerelated procedures, various bioactive substrates possessing osteoconductive and osteoinductive potential have been under investigation as alternatives to PMMA.161,162,163 One particularly interesting area of recent development has been the work with bone morphogenetic proteins (BMPs). These proteins, initially identified in 1965 by Urist,164 are multifunctional cytokines that function as osteoinductive agents by recruiting stem cells to differentiate into osteoblasts to aid in the formation of bone. Recombinant BMPs promote and enhance solid fusion, avoid the morbidity associated with bone graft harvesting, diminish the need for internal instrumentation, and can potentially avoid reoperation associated with nonunions or

implant failure. Early results, especially with BMP-2 and BMP-7, in animal models and in human subjects were promising,165,166, 167,168,169,170,171 and as a result when these products became commercially available, their use exploded. Although there is little doubt that these proteins have a role to play in select cases, the finding of apparent related complications, such as heterotopic ossification, prevertebral soft-tissue swelling, and swallowing issues when used in anterior cervical procedures, and an unclear relationship to the development of certain malignancies has dampened the enthusiasm for the use of BMP.172,173,174 In addition to the use of the BMP proteins, there has been investigation into the potential of gene therapy, and preliminary results have demonstrated the successful promotion of bone growth and intervertebral disc regeneration through the expression of various desired bioactive factors for prolonged periods of time.166,175,176,177,178 In addition, in recent years several authors have published on various forms of cell-mediated therapies that have been utilized to treat a variety of spinal conditons.179,180, 181,182 Concentrated bone marrow aspirate has recently been promoted as a way to enhance the stem cell population present in the vicinity of a fusion bed area.183,184,185 It is believed that providing a boost to the number of stem cells present will result in more cells being available to commit to developing into osteoblasts to help with bone formation. Stem cells derived from adipose tissue have also been utilized with similar results.182,186 Stem cells have been used for some time as a stand-alone treatment for severely degenerated joints in both animal and human subjects with promising results,187,188,189 and these uses are beginning to be expanded to include the spine with a focus on treating disc degeneration.190,191,192 There is even a report in the literature by Attar and colleagues180 of treating four patients with American Spinal Injury Association Level A (ASIA/A) spinal cord injuries with intralesional autologous bone marrow stem cell injections, with three of the four patients achieving postinjection neurological improvement. However, this form of treatment remains investigational.193

1.5 Conclusion The field of spine surgery has been witness to immeasurable growth in the past four decades. The evolution of surgical techniques and treatment methodologies is a testament to the optimal quality of care each physician seeks to offer the patient. As many of the articles referred to in this chapter have demonstrated, advances in minimally invasive spine surgery have led to significantly improved outcomes, while reducing complication rates, shortening hospital stays, and lowering costs. Undoubtedly, future developments will continue to improve the care that patients with spinal ailments receive. However, as always, appropriate patient selection and proper technical execution will remain essential to obtaining optimal clinical outcome and patient satisfaction.

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fusion: part I: evaluation of clinical outcomes. Spine. 2005; 30(14):1565–1575, discussion E387–E391 Galibert P, Deramond H, Rosat P, Le Gars D. Preliminary note on the treatment of vertebral angioma by percutaneous acrylic vertebroplasty [in French]. Neurochirurgie. 1987; 33(2):166–168 Galibert P, Déramond H. La vertébroplastie acrylique percutanée comme traitement des angiomes vertébraux et des affections dolorigènes et fragilisantes du rachis. Chirurgie. 1990; 116(3):326–334, discussion 335 Jensen ME, Evans AJ, Mathis JM, Kallmes DF, Cloft HJ, Dion JE. Percutaneous polymethylmethacrylate vertebroplasty in the treatment of osteoporotic vertebral body compression fractures: technical aspects. AJNR Am J Neuroradiol. 1997; 18(10):1897–1904 Belkoff SM, Mathis JM, Fenton DC, Scribner RM, Reiley ME, Talmadge K. An ex vivo biomechanical evaluation of an inflatable bone tamp used in the treatment of compression fracture. Spine. 2001; 26(2):151–156 Dudeney S, Lieberman IH, Reinhardt MK, Hussein M. Kyphoplasty in the treatment of osteolytic vertebral compression fractures as a result of multiple myeloma. J Clin Oncol. 2002; 20(9):2382–2387 Garfin SR, Yuan HA, Reiley MA. New technologies in spine: kyphoplasty and vertebroplasty for the treatment of painful osteoporotic compression fractures. Spine. 2001; 26(14):1511–1515 Lieberman IH, Dudeney S, Reinhardt MK, Bell G. Initial outcome and efficacy of “kyphoplasty” in the treatment of painful osteoporotic vertebral compression fractures. Spine. 2001; 26(14):1631–1638 Theodorou DJ, Theodorou SJ, Duncan TD, Garfin SR, Wong WH. Percutaneous balloon kyphoplasty for the correction of spinal deformity in painful vertebral body compression fractures. Clin Imaging. 2002; 26(1):1–5 Watts NB, Harris ST, Genant HK. Treatment of painful osteoporotic vertebral fractures with percutaneous vertebroplasty or kyphoplasty. Osteoporos Int. 2001; 12(6):429–437 Phillips FM, Todd Wetzel F, Lieberman I, Campbell-Hupp M. An in vivo comparison of the potential for extravertebral cement leak after vertebroplasty and kyphoplasty. Spine. 2002; 27(19):2173–2178, discussion 2178–2179 Heaney RP. The natural history of vertebral osteoporosis. Is low bone mass an epiphenomenon? Bone. 1992; 13 Suppl 2:S23–S26 Riggs BL, Melton LJ, III. The worldwide problem of osteoporosis: insights afforded by epidemiology. Bone. 1995; 17(5) Suppl:505S–511S Hitchon PW, Goel V, Drake J, et al. Comparison of the biomechanics of hydroxyapatite and polymethylmethacrylate vertebroplasty in a cadaveric spinal compression fracture model. J Neurosurg. 2001; 95(2) Suppl:215–220 Lim TH, Brebach GT, Renner SM, et al. Biomechanical evaluation of an injectable calcium phosphate cement for vertebroplasty. Spine. 2002; 27 (12):1297–1302 Heini PF, Berlemann U. Bone substitutes in vertebroplasty. Eur Spine J. 2001; 10 Suppl 2:S205–S213 Urist MR. Bone: formation by autoinduction. Science. 1965; 150 (3698):893–899 Boden SD. Clinical application of the BMPs. J Bone Joint Surg Am. 2001; 83-A (Pt 2) Suppl 1:S161 Boden SD, Hair GA, Viggeswarapu M, Liu Y, Titus L. Gene therapy for spine fusion. Clin Orthop Relat Res. 2000(379) Suppl:S225–S233 Boden SD, Martin GJ, Jr, Horton WC, Truss TL, Sandhu HS. Laparoscopic anterior spinal arthrodesis with rhBMP-2 in a titanium interbody threaded cage. J Spinal Disord. 1998; 11(2):95–101 Boden SD, Schimandle JH, Hutton WC. 1995 Volvo Award in basic sciences. The use of an osteoinductive growth factor for lumbar spinal fusion. Part II: Study of dose, carrier, and species. Spine. 1995; 20(24):2633–2644 Burkus JK, Gornet MF, Dickman CA, Zdeblick TA. Anterior lumbar interbody fusion using rhBMP-2 with tapered interbody cages. J Spinal Disord Tech. 2002; 15(5):337–349 Patel TC, Erulkar JS, Grauer JN, Troiano NW, Panjabi MM, Friedlaender GE. Osteogenic protein-1 overcomes the inhibitory effect of nicotine on posterolateral lumbar fusion. Spine. 2001; 26(15):1656–1661 Ripamonti U, Ramoshebi LN, Matsaba T, Tasker J, Crooks J, Teare J. Bone induction by BMPs/OPs and related family members in primates. J Bone Joint Surg Am. 2001; 83-A(Pt 2) Suppl 1:S116–S127 Carragee EJ, Hurwitz EL, Weiner BK. A critical review of recombinant human bone morphogenetic protein-2 trials in spinal surgery: emerging safety concerns and lessons learned. Spine J. 2011; 11(6):471–491 Carragee EJ, Chu G, Rohatgi R, et al. Cancer risk after use of recombinant bone morphogenetic protein-2 for spinal arthrodesis. J Bone Joint Surg Am. 2013; 95(17):1537–1545

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History of Minimally Invasive Spine Surgery [174] Devine JG, Dettori JR, France JC, Brodt E, McGuire RA. The use of rhBMP in spine surgery: is there a cancer risk? Evid Based Spine Care J. 2012; 3(2):35–41 [175] Boden SD. Bioactive factors for bone tissue engineering. Clin Orthop Relat Res. 1999(367) Suppl:S84–S94 [176] Kang JD, Boden SD. Orthopaedic gene therapy. Spine. Clin Orthop Relat Res. 2000; 379(379) Suppl:S256–S259 [177] Ripamonti U. Tissue morphogenesis and tissue engineering by bone morphogenetic proteins. SADJ. 1999; 54(6):257–262 [178] Scaduto AA, Lieberman JR. Gene therapy for osteoinduction. Orthop Clin North Am. 1999; 30(4):625–633 [179] Guyton GP, Miller SD. Stem cells in bone grafting: Trinity allograft with stem cells and collagen/beta-tricalcium phosphate with concentrated bone marrow aspirate. Foot Ankle Clin. 2010; 15(4):611–619 [180] Attar A, Ayten M, Ozdemir M, et al. An attempt to treat patients who have injured spinal cords with intralesional implantation of concentrated autologous bone marrow cells. Cytotherapy. 2011; 13(1):54–60 [181] Vadalà G, Di Martino A, Tirindelli MC, Denaro L, Denaro V. Use of autologous bone marrow cells concentrate enriched with platelet-rich fibrin on corticocancellous bone allograft for posterolateral multilevel cervical fusion. J Tissue Eng Regen Med. 2008; 2(8):515–520 [182] Schroeder J, Kueper J, Leon K, Liebergall M. Stem cells for spine surgery. World J Stem Cells. 2015; 7(1):186–194 [183] Smith B, Goldstein T, Ekstein C. Biologic adjuvants and bone: current use in orthopedic surgery. Curr Rev Musculoskelet Med. 2015; 8(2):193–199

[184] Lee DH, Ryu KJ, Kim JW, Kang KC, Choi YR. Bone marrow aspirate concentrate and platelet-rich plasma enhanced bone healing in distraction osteogenesis of the tibia. Clin Orthop Relat Res. 2014; 472(12):3789–3797 [185] Jäger M, Herten M, Fochtmann U, et al. Bridging the gap: bone marrow aspiration concentrate reduces autologous bone grafting in osseous defects. J Orthop Res. 2011; 29(2):173–180 [186] Helder MN, Knippenberg M, Klein-Nulend J, Wuisman PI. Stem cells from adipose tissue allow challenging new concepts for regenerative medicine. Tissue Eng. 2007; 13(8):1799–1808 [187] Fibel KH, Hillstrom HJ, Halpern BC. State-of-the-art management of knee osteoarthritis. World J Clin Cases. 2015; 3(2):89–101 [188] Counsel PD, Bates D, Boyd R, Connell DA. Cell therapy in joint disorders. Sports Health. 2015; 7(1):27–37 [189] Swart JF, Wulffraat NM. Mesenchymal stromal cells for treatment of arthritis. Best Pract Res Clin Rheumatol. 2014; 28(4):589–603 [190] Wang SZ, Rui YF, Lu J, Wang C. Cell and molecular biology of intervertebral disc degeneration: current understanding and implications for potential therapeutic strategies. Cell Prolif. 2014; 47(5):381–390 [191] Li Z, Peroglio M, Alini M, Grad S. Potential and limitations of intervertebral disc endogenous repair. Curr Stem Cell Res Ther. 2015; 10(4):329–338 [192] Richardson SM, Hoyland JA. Stem cell regeneration of degenerated intervertebral discs: current status. Curr Pain Headache Rep. 2008; 12(2):83–88 [193] Khan SN, Hidaka C, Sandhu HS, Girardi FP, Cammisa FP, Jr, Diwan AD. Gene therapy for spine fusion. Orthop Clin North Am. 2000; 31(3):473–484

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11

Fundamentals

2 Anatomy of the Spine: An Overview Joshua E. Medow and Daniel K. Resnick Abstract The spine is composed of bone, ligament, muscle, discs, smooth, lubricated articular surfaces, spinal cord and meninges, blood supply originating from the vertebral, radicular, and deep cervical arteries, and the thyrocervical trunk. Typically, the adult spine consists of 33 vertebrae: 7 cervical, 12 thoracic, 5 lumbar, 5 fused sacral, and 4 coccygeal. It allows humans to walk upright, and the pathology of the spine and associated component parts affects multiple organ systems, including the nervous system. Keywords: bone, ligament, muscle, discs, spinal cord, meninges, vertebrae, cervical vertebrae, thoracic vertebrae, lumbar vertebrae, sacral vertebrae, coccygeal vertebrae, kyphotic curvatures, lordotic curvatures, lamina, pedicle, foramina, cartilage, anterior triangle, submental triangle, submandibular triangle, carotid triangle, muscular triangle, posterior triangle, occipital and supraclavicular triangles, suboccipital triangle

2.1 Introduction The human spine and its associated structures are an amazing feat of engineering that permit considerable mobility and support of the body under substantial strain and pressure. This dynamic conglomerate is an exceptionally well-balanced scaffolding that is remarkably adaptable to both internal and external forces. Its elegant design separates humans from other vertebrates in that it allows us to persistently walk upright. As a result, pathology of the spine or associated muscles, ligaments, discs, or vascular supply can result in serious consequences to multiple organ systems, the most common of which is the nervous system. The spine is composed of the following: ● Bone. ● Ligament. ● Muscle. ● Discs. ● Smooth, lubricated articular surfaces. ● Spinal cord and meninges. ● Blood supply originating from the vertebral, radicular, and deep cervical arteries and the thyrocervical trunk. The normal adult spine typically has 33 vertebrae: 7 cervical, 12 thoracic, 5 lumbar, 5 fused sacral, and 4 coccygeal. Of these, the seven cervical vertebrae are always conserved in number, but variations in the number of thoracic, lumbar, and sacral vertebrae occur in approximately 5% of the population and are not considered pathologic.1 The 24 rostral vertebrae permit movement to varying degrees and are limited by their shape and by muscle, ligaments, and the 23 intervertebral discs. The absence of discs between the occiput and the atlas and between the atlas and the axis contributes to the increased movement potential at these two levels. The four coccygeal vertebrae are relatively fixed and in some cases completely fused. The length of the spine is variable from one person to another, but approximately 75% of its

12

length is due to the height of the vertebral bodies and 25% is due to the height of the discs.2 With age, as the discs lose water, this proportion changes. The human spine has four curvatures: two kyphotic and two lordotic. The kyphotic curvatures are located in the thoracic and sacral regions. They develop during embryogenesis and are known as the two primary curvatures. This physiologic kyphosis occurs because of the relatively greater height of the posterior vertebral wall compared to the anterior vertebral wall.3 The cervical and lumbar curvatures begin to develop before birth but are not accentuated until the spine bears weight axially. The cervical curvature develops when the infant begins to hold its head erect, and the lumbar curvature develops when the infant begins to stand and walk.2 Consequently, these two curvatures are known as lordotic or secondary curvatures. The cervical curvature is transiently lost during flexion, whereas the other curvatures are either increased or decreased during flexion and extension but are not lost in their entirety. Because the sacrum is fused, its curvature does not change with movement. In general, the cervical, thoracic, and lumbar vertebrae are composed of a body and a vertebral arch. The atlas is the exception; it is a ring structure without a body or pedicles. The vertebral bodies increase in size from T4 to the sacrum to accommodate the increasing load at each caudal level.4 Above T4, there is a general progression in size in rostral caudal fashion, but in some instances a rostral vertebra may be larger than a caudal vertebra2 (refer to the Cervical Vertebrae section for a more specific description). The vertebral arch is formed as the two pedicles protrude posteriorly from the superolateral aspect of the vertebral body. Where two adjacent vertebrae articulate, the pedicles form the rostral and caudal borders of the intervertebral foramina. The nerve roots exit through these foramina, and the dorsal root ganglia reside within them.2 The laminae extend from the pedicles and triangulate to form the spinous process in the posterior midline of the spine. The enclosed space is known as the vertebral foramen, and the sum total of these foramina forms the spinal canal. The spinous and transverse processes serve as origin and insertion sites for tendons and ligaments. The cervical vertebrae are unique in that they contain a foramen transversarium in each of the transverse processes. The facets arise where the lamina and pedicle join together and their angle varies between cervical, thoracic, and lumbar regions.2,4 Sensory innervation of the facets comes from the dorsal rami of spinal nerves exiting the intervertebral foramina.2

2.2 Development of the Spine The vertebrae and intervertebral discs arise from the somites during embryologic development. They are initially cartilaginous structures but the vertebrae begin to ossify around the seventh week.2 Ossification occurs in three primary centers within the vertebrae: one in the centrum (which will become the vertebral body) and one in each half of the vertebral arch.5 The sacrum and coccyx do not begin to ossify until infancy.5 At birth, each vertebra consists of three ossified components that

Perez-Cruet et al, An Anatomic Approach to Minimally Invasive Spine Surgery, 2nd Ed. (ISBN 978-1-62623-643-1), copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.

Anatomy of the Spine: An Overview are joined by hyaline cartilage. The right and left halves of the vertebral arch connect with the centrum at the neurocentral joint. This will become the pedicle.5 The spinous process has yet to completely form and remains the cartilaginous connection between each half of the vertebral arch posteriorly. Fusion across the arch takes place in the cervical region during the first year of life and progressively occurs throughout the rest of the spine until it is complete around age 6.5 The neurocentral joint fuses between 5 and 8 years of age.5 During puberty, five secondary ossification sites develop: one at the tip of the spinous process; one at the tip of each transverse process; and one at each of the two epiphyses (superior and inferior). By age 25, these ossification sites will disappear.5 Failure of ossification has been implicated in ossiculum terminale and os odontoideum. Early during embryonic development of the spine, the spinal cord extends through the entire length of the spinal canal. Hence, the vertebrae and associated spinal cord segments reside at the same level. As development proceeds throughout life, the vertebrae lengthen at a faster rate than the spinal cord.5 At birth, the spinal cord resides at the L2–L3 vertebrae. Subsequent growth causes the spinal cord to typically end at the L1 vertebra. Below the cervical spine, the nerve roots must descend before exiting through the appropriate intervertebral foramina. The distance they must travel before leaving increases with each caudal level and is most evident at the cauda equina.5

2.3 Vertebrae and Surrounding Structures 2.3.1 Cervical Vertebrae There are seven cervical vertebrae that differ considerably from each other. The atlas (C1) is a ring structure that has a posterior tubercle and two transverse processes that act as origin and insertion sites for muscle and ligamentous structures. The lateral masses of C1 include the transverse process, the tubercle for the transverse ligament, and the superior articular surface that articulates with the occipital condyle. The area within the anterior and posterior arches is divided into two foramina by the transverse ligament. The anterior foramen houses the dens. The posterior foramen is the vertebral foramen. Lateral to this foramen, in the posterior arch, are the grooves for the two vertebral arteries that ascend through the foramen magnum after passing through the foramen transversaria of the transverse processes (▶ Fig. 2.1). The atlas has five articulating synovial surfaces. Four are typically described as facets. The superior facets of C1 are articulating surfaces that allow flexion, extension, and limited rotation of the occipital condyles on C1. The inferior facets of C1 articulate with the superior facets of the axis (C2) and also allow for flexion and extension, but rotation is less than that of the occipital condyles and occurs by translation.4 The greatest amount of rotation at C1–C2 is permitted by the anterior articulating surface within the ring that comes in contact with the dens, the fifth articular surface at this level.4 Flexion, extension, and translation of C1 on the dens are limited because of the transverse and alar ligaments that hold the dens in place around a cushion of surrounding synovium.4 Because C1 does not have a true body, there are no intervertebral discs adjacent to it. The first cervical disc is at the C2–C3 interspace.

Fig. 2.1 C1–C2 anatomy. Craniocervical junction demonstrating the attachments of the transverse ligament to the lateral masses of C1. Anterior to the ligament, the dens is held in place against the anterior arch of C1. The vertebral arteries run through the vertebral foramen and then run medially along the rostral aspect of C1 until entering the foramen magnum dorsolaterally.

The morphology of the remainder of the cervical spine is on a continuum, with small changes in the dimensions and surfaces of the vertebrae as they are stacked caudally.2,4 The spinous process at C7 is the longest and consequently is known as the vertebra prominens. Conversely, cervical body height decreases from C3 to C6 before enlarging again.2,4 This is unlike the thoracic and lumbar regions where increased axial load progressively results in larger stronger vertebrae.2 In fact, C2 is the strongest of the cervical vertebrae.2,4 The spinal canal also progressively narrows to its minimum at C5 where the cervical enlargement is at its maximal circumference. The spinal cord at C5 is typically 8 mm anteroposterior by 13 mm wide, and the spinal canal at this location is typically 14 mm anteroposterior by 24 mm wide.6 Of these dimensions, the anteroposterior diameter is of the most clinical relevance in cervical stenosis. The canal width is usually more than adequate unless a mass is present.6 There are four facets on each of the cervical vertebrae below C2, two superior and two inferior. They are at approximately 45-degree angles with respect to the vertebral body end plates and are arranged so that the superior facets are anterior to the inferior facets of the next rostral vertebra. These zygapophyseal articulations allow variable flexion and extension but minimal rotation individually. Their angulation prevents translation. The lateral masses are the bony area between the superior and inferior facets of a single vertebra (▶ Fig. 2.2 and ▶ Fig. 2.3). The pedicles of the cervical spine join the lateral masses to the vertebral body. The distinction between the pars interarticularis and the pedicle of C2 is important because of the popularity of transpars and transpedicular screw techniques. The bone in between C1–C2 and C2–C3 is the pars interarticularis of C2. The bone joining this structure to the vertebral body is of

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13

Fundamentals

Fig. 2.2 Anatomy of the subaxial cervical vertebrae. Note the position and angle of the facet joints (shaded areas) as well as the relationship of the cervical pedicle to the spinal canal and vertebral foramen.

Fig. 2.3 Angulation of facet joints. Subaxial cervical vertebral bodies (left) have facets that are angled approximately 45 degrees in the sagittal plane. This helps prevent anteroposterior translation while allowing flexion and extension. The thoracic facets (middle) are nearly coronal in orientation, preventing any translation whatsoever. The rib cage (via the costovertebral joints) adds significant rigidity to this portion of the spine. The lumbar facets (right) are oriented in the sagittal plane, allowing for some rotation, flexion, and extension.

the pedicle of C2. At other levels, the distinction is easier to make. Pedicle width from C3 to C7 is approximately 6 mm, and height is between 5 and 10 mm at each level.7,8,9,10,11 Although screw placement within the cervical pedicles is possible, the small size of the pedicles and their proximity to the vertebral artery (above C6) make screw placement dangerous. Transverse processes project from the lateral masses and contain a foramen through which the paired vertebral arteries can pass12 (▶ Table 2.1). The exception to this is C7.12 It contains the foramina, but the vertebral arteries usually pass anterior to the transverse processes and then enter the foramina of C6 as they ascend toward the foramen magnum (▶ Fig. 2.4). C6 has a prominence known as the carotid tubercle that projects anteriorly from the transverse process.

2.3.2 Thoracic Vertebrae The thoracic vertebrae differ from the cervical and lumbar vertebrae in many ways; however, T1 to T4 have features on a continuum with the cervical vertebrae, and T9 to T12 are similarly on a continuum with the lumbar vertebrae2 (▶ Fig. 2.5). At the superolateral aspect of the pedicle, the posteroinferolateral aspect

14

Table 2.1 Percentage of vertebral arteries that enter the transverse foramina at each level Level

% vertebral arteries

C3

1%

C4

2%

C5

5%

C6

90%

C7 Source: Adapted from Sobotta et

2% al.12

of the vertebral body, and the inferolateral aspect of the transverse process are three additional articular surfaces not present in the other sections of the spine. The first two combine with the rib head, and the third with the rib tubercle to form the costal facets. The rib tubercles point dorsally and mark the joining of the rib neck and shaft. They provide attachment sites for the ribs bilaterally to the first 10 thoracic vertebrae (▶ Fig. 2.6). Ribs 11 and 12 articulate via facets on the bodies of their respective vertebrae only. They have a single facet on their heads and no

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Anatomy of the Spine: An Overview

Fig. 2.4 The course of the vertebral artery and deep cervical ligaments of the spine. (a) Anterior cervical spine anatomy. (b) Anterior cervical spine anatomy with vertebral body removed.

Fig. 2.5 Bony and deep ligamentous anatomy of the thoracic spine. (a) Lateral thoracic anatomy. (b) Anterior thoracic anatomy. (c) Posterior thoracic anatomy. 1, costotransverse ligaments; 2, superior costotransverse ligaments; 3, lateral costotransverse ligaments; 4, ligamentum flavum; 5, supraspinal ligaments; 6, intertransverse ligaments; 7, costotransverse facet; 8, rib.

neck or tubercle. T1 is somewhat divergent in its configuration in that it has a complete costal facet on the superolateral aspect of its body for the first rib and a demifacet on its inferolateral border for the second rib. The 12th rib is of particular importance anatomically because the pleura passes rostral to this rib beginning 3 to 4 cm lateral to its head and continuing along its shaft approximately 7 to 8 cm.2 Pedicle dimensions vary significantly over the entire thoracic spine. Initially, the transverse diameter is around

8.2 mm at T1 but decreases to 5.5 mm at T4. The pedicle diameter then progressively grows in size again to its maximum at T12 of approximately 8.8 mm.7,10,13 The width of the pedicle in the sagittal plane is on an increasing continuum from T1 to T11. The superior and inferior articular facets are angled primarily in the coronal plane to prevent anterior translation of a rostral vertebra on the caudal one.4 Orientation of the facets changes to a more lumbar orientation in the T9 to T12 region.4

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15

Fundamentals

a

b Rib

c

Transverse process rib articulation

Costotransverse ligaments

Costovertebral ligaments

T7 vertebral body Fig. 2.6 The thoracic vertebral body. The thoracic vertebral body is characterized by coronally oriented facets and the presence of articulations for the rib heads. Pedicle dimensions are highly variable dependent on level and individual variation. (a) This drawing was made from the T7 vertebral body. (b) Anterior view showing the anterior longitudinal ligament. (c) Posterior view after laminectomy showing the posterior longitudinal ligament.

Fig. 2.7 (a,b) The lumbar vertebral body is characterized by larger pedicles, a sagittal orientation of the articular facets (except at L5–S1), and large transverse processes for the attachment of the paraspinal muscles.

2.3.3 Lumbar Vertebrae The lumbar spine is distinguished anatomically by its large vertebral bodies, strong lamina, and gaps between its spinous processes. Its vertebral bodies are kidney shaped and increase in size at each caudal level. The lumbar pedicles are wide and thick and are widely spaced, with their height typically half that of their associated vertebral body. Typical pedicle width is 9 mm at L1 and 18 mm at L5, and pedicle height is about 15 mm throughout the lumbar spine.7,8,9,10,11 The transverse pedicle angle increases from 12 to 30 degrees from L1 to L5, and the transverse pedicle diameter increases as well from 9 to 18 mm.14 The sagittal pedicle angle decreases from about 3 degrees at L1 to 0 degrees at L5 (▶ Fig. 2.7).3,14 The rostral hemifacet is a concave structure that faces dorsomedially and articulates with the convex caudal hemifacet of the next rostral vertebra. The caudal hemifacet is an extension of the lamina and faces anteromedially, complementing its caudal counterpart. The junction of these two articulating surfaces forms the root of the intervertebral foramina. The near perpendicularity (90-degree angle) of the facets in the transverse plane and variable lateral angle from 15 to 70 degrees from L1–L2 to L5–S1 significantly limit rotation and translation of the lumbar spine at each level and as

16

a functional unit.14 In fact, rotation at any given level of the lumbar spine is limited to approximately 1 to 2 degrees.15 The first 60 degrees of flexion of the spine occurs in the lumbar region with an additional 25 degrees at the hip, and this is reversed with extension.16 Flexion/extension increases at each increasing level from between 5 and 16 degrees at L1 to between 10 and 24 degrees at S1.15 Lateral flexion varies between 3 and 12 degrees at each level except at S1, where it is between 2 and 6 degrees.

2.3.4 Sacral and Coccygeal Vertebrae The sacrum is the only part of the spine that is entirely fused. It tapers caudally at the lateral masses because this region (the inferior half of the sacrum) is not weight-bearing. The superior half of the sacrum transmits the axial load of the spinal column to the pelvis via the sacroiliac joints.2 The sacrum also acts to stabilize and strengthen the pelvic girdle.2 The base of the sacrum is actually its most rostral part. Its superior articulating processes articulate with the inferior articulating processes of L5 forming the lumbosacral angle. The L5–S1 facet acts to prevent anterolisthesis of the lumbar spine on the sacrum. The anterior edge of the first sacral vertebra forms the sacral promontory and it is typically larger in males than in females.2

Perez-Cruet et al, An Anatomic Approach to Minimally Invasive Spine Surgery, 2nd Ed. (ISBN 978-1-62623-643-1), copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.

Anatomy of the Spine: An Overview However, the width/length proportion of the sacrum as a whole is usually larger in women.2 In approximately 5% of the population, the L5 vertebra is incorporated into the sacrum.2 If it is completely fused, it is referred to as sacralization of the L5 vertebra; if it is partially fused, it is termed hemisacralization. The reverse is also true in that the S1 vertebra can sometimes be incorporated into the lumbar spine. This is known as lumbarization. If L5–S1 is fused as in a sacralized L5 vertebra, a greater strain is placed on the L4–L5 interspace with consequences to the intervertebral disc, ligaments, and facets. If the S1 vertebra is lumbarized, the strain will be placed on S1–S2.2 The pelvic surface of the sacrum is smooth and concave, and the posterior surface is rough and convex. On the anterior surface are four transverse lines that indicate where the sacral vertebrae have fused. Unlike the cervical, thoracic, and lumbar regions, which have one pair of intervertebral foramina that opens laterally, the sacrum has one pair of foramina that opens to the anterior surface and one pair that opens to the posterior surface at each level. There are four levels in total, and they are located between the adjacent fused vertebrae. This allows for the exit of the posterior and anterior sacral nerve roots. On the posterior surface are five longitudinal ridges. The two lateral ridges represent the fused sacral transverse processes, the two intermediate ridges represent the fused articular processes/ pedicles, and the central ridge represents the small spinous processes of S1–S4.2 Anterior to the S1–S4 laminae is the sacral canal. It contains the sacral nerve roots, connective tissue, and the caudal thecal sac.2 Because S5 does not have a spinous process or lamina, a dorsal opening develops, known as the sacral hiatus. The depth of the hiatus is often dependent on the amount of S4 lamina and spinous process that is missing, as the S4 vertebra may not form a complete posterior arch.2 The hiatus contains the filum terminale, the S5 and coccygeal nerves, and fatty connective tissue. Inferiorly are the sacral cornua (horns) that represent the inferior articular surfaces of S5.2 They extend from the apex of the sacrum and articulate with the coccygeal cornua that represent the superior articulating surfaces of the first coccygeal vertebra forming the sacrococcygeal joint.2 The coccyx is the remnant of the embryologic tail that persists until the beginning of the eighth week of development.5 It typically has four vertebrae but this can vary by one vertebrae in the normal population.2 The vertebrae are rudimentary and the first three consist of vertebral bodies only without arches or processes.2 The first coccygeal vertebra usually does not fuse with the sacrum except in the elderly.2 The remaining vertebrae fuse earlier in life, typically around age 40.2 The coccyx has a more anterior curvature in males than in females and is part of the pelvic inlet.2 The wider curvature in females assists in the birthing process. It also serves as an insertion site for the gluteus maximus and coccygeus muscles, and the anococcygeal ligament.

2.3.5 Intervertebral Discs The intervertebral discs are fibrocartilage structures that are important in weight-bearing and movement. They are typically 45% of the height of the surrounding vertebral bodies.2 The an-

nulus fibrosis is a ligamentous structure that forms the outer limit of the disc, and the nucleus pulposus is the gelatinous center that gives the disc its height and cushioning effect. The annulus fibrosis is composed of concentric lamellae of fibrocartilage that run between the smooth hyaline cartilage plates of the vertebral bodies. The lamellae are at right angles to each other.2 They are fewer, thinner, and less numerous posteriorly than they are anteriorly or laterally, which may help to explain why disc protrusions typically occur at the posterior surface of the disc.2,14 The annulus surrounds the nucleus pulposus, a structure that forms the core of the disc. It contains significantly more cartilage than fibrous tissue and is highly elastic.14 The nucleus is slightly posterior in its location within the disc complex.14 It retains a significant amount of water (88% in infancy) that is lost with age (65% in the elderly) and must get its nourishment via diffusion because it is an avascular structure.2

2.4 Ligaments The ligaments that connect the vertebrae together are tough fibrous bands that are strategically placed to limit movement. The anterior ligaments prevent excessive hyperextension, whereas the posterior ligaments are primarily responsible for limiting flexion.15 All ligaments are involved in stabilizing the spine against translational motion.15 The atlanto-occipital and atlantoaxial regions are inherently the most mobile portions of the cervical spine. More strategically placed ligaments are necessary to restrain unwanted motion of these vertebrae with respect to the occiput and each other.

2.4.1 Anterior Ligaments The anterior longitudinal ligament (ALL) binds the vertebral bodies beginning at the anterior surface of the sacrum and extending to the ring of C1. It continues rostrally to the basilar occipital bone as the anterior atlanto-occipital membrane. It is a strong ligament that is thickest opposite the intervertebral discs and is fixed to their anterior surface and also to the vertebral periosteum. The ALL primarily limits hyperextension and consequently is stronger in the thoracic region than in the cervical region15 (see ▶ Fig. 2.4).

2.4.2 Posterior Ligaments The posterior longitudinal ligament (PLL) is more narrow and weaker than the ALL15 (see ▶ Fig. 2.4). Its course is within the spinal canal and it spans the posterior aspect of the vertebral bodies beginning caudally at the sacrum. Like the ALL, the PLL is also fixed to the intervertebral discs. The PLL functionally limits hyperflexion and aids in preventing disc retropulsion.15 It continues rostrally from C2 as the accessory tectorial membrane, which is the widest portion of the ligament. The accessory tectorial membrane bridges the anterior portion of the foramen magnum to the posterior aspect of the arch of C1 and the body of C2 as it traverses over the dens and cruciform ligament. It limits extension between the occiput and C2 and flexion to a lesser extent.15 This ligament, however, does not limit axial rotation.15

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Fundamentals

2.4.3 Cruciform Ligament There is a small synovial capsule between the atlas and the dens that is surrounded posteriorly by the cruciform ligament. The cruciform ligament is composed of superior and inferior fibers, and the transverse ligament of the atlas. The superior fibers anchor the dens to the anterior portion of the foramen magnum, whereas the inferior fibers originate at the base of the dens and the body of C2. The transverse ligament is a 10-mm thick band that contains no elastic fibers and is the largest component of the cruciform ligament.17 It originates from the medial aspect of the lateral masses of C1 and wraps around the dens, thereby limiting atlantoaxial subluxation anteriorly. The anterior portion of the dens and posterior surface of the anterior arch of C1 are thus tightly bound together.

2.4.4 Odontoid Ligaments Deep to the cruciform ligament are the odontoid ligaments, which consist of the apical and paired alar ligaments. The apical ligament is a thin band that originates at the tip of the dens and inserts on the anterior margin of the foramen magnum. It confers little stability between the occiput and C2.15 The alar ligaments are subdivided into two portions. The posterior bands anchor the dens to each of the occipital condyles. If present, the anteroinferior bands usually anchor the atlas to each of the occipital condyles.15 The alar ligaments collectively limit axial rotation.15

2.4.5 Ligamentum Flavum The remaining cervical, thoracic, and lumbar vertebrae are linked together by their lamina externally to the next rostral vertebral lamina internally within the spinal canal by the ligamentum flavum. This extremely strong ligament is larger and thicker in the lumbar regions and progressively becomes smaller rostrally as the load-bearing of the spine decreases.2 Some of its lateral fibers contribute to the posterior aspect of the intervertebral foramina before inserting on the facet joints.2 The posterior atlanto-occipital membrane that anchors the occiput to the atlas is an extension of this ligament. The ligamentum flavum functions to maintain the normal curvature of the spine and helps assist the posterior musculature in straightening out the spine when returning from a flexed position2 (▶ Fig. 2.8).

Ligamentum Nuchae The cervical spinous processes are all anchored to each other and to the inferior nuchal line via the dense fibrous bands of the broad ligamentum nuchae. This ligament is a combination of the weaker interspinous ligaments and a strong cordlike supraspinous ligament that is present throughout the entire spine. In the thoracic and lumbar regions, the intraspinous ligaments become somewhat larger and stronger as the load increases caudally.2

Ligamentous Capsules There are also ligamentous capsules that bind the facets at all levels. They are longer and less taut in the cervical region to promote increased mobility, particularly flexion.2 They permit gliding of the articular surfaces of the facet joints between vertebrae. Small, weak intertransverse ligaments attach between

18

Fig. 2.8 (a) The lumbar ligamentum flavum comes into view immediately upon removal of the caudal lamina. It attaches rostrally to the ventral aspect of the rostral lamina and caudally at the rostral edge of the caudal lamina. (b,c) Anatomical illustrations showing the attachments of the ligamentum flavum to the lamina.

the transverse processes throughout the spine but are scattered and provide minimal support except in the lumbar region where they are membranous and more developed.2

2.4.6 Thoracic Ligaments In the thoracic spine, additional ligaments are necessary to articulate the ribs to the vertebral column (see ▶ Fig. 2.5). The costovertebral ligaments are divided into three groups: anterior, middle, and posterior. At each level, the anterior costovertebral ligament fixes the rib neck to the caudal portion of the transverse process rostral to it.2 The middle costovertebral ligament attaches the posterior neck of the rib to the anterior sur-

Perez-Cruet et al, An Anatomic Approach to Minimally Invasive Spine Surgery, 2nd Ed. (ISBN 978-1-62623-643-1), copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.

Anatomy of the Spine: An Overview face of the transverse process.2 The posterior costovertebral ligament connects the rostral portion of the rib neck to the caudal aspect of the transverse process.18 Costotransverse ligaments span between the transverse process of each vertebra and the rib.2 This ligament group is subdivided into superior, posterior, and inferior components.2 Finally, capsular ligaments secure the rib at its costal facets.

2.4.7 Lumbar Ligaments There are three ligaments that serve to attach the crura of the diaphragm to the lumbar spine. The medial arcuate ligament acts to unite the medial aspects of the right and left crura of the diaphragm at the level of the T12–L1 intervertebral disc.2 The crura blend with the ALL of the vertebral column.2 This ligament is not to be confused with the medial arcuate ligaments, which are also one of the three ligament groups involved in securing the diaphragm to the spine. The medial arcuate ligaments, also known as the medial lumbocostal arches, form as thickenings of the anterior layer of the thoracolumbar fascia over the superior aspects of the psoas major muscles.2 Each ligament serves to attach the diaphragmatic crus to the transverse process of L1 anterior to the surface of the psoas major muscle.2 The lateral arcuate ligaments or lateral lumbocostal arches (of Henle) form as thickenings of the anterior layer of the thoracolumbar fascia over the quadratus lumborum muscles.2 It connects the transverse processes of L1 to the inferior border of the 12th rib2 (▶ Fig. 2.9).

2.4.8 Sacral and Coccygeal Ligaments The ligaments of the sacral and coccygeal regions connect the spine to the pelvis. The iliolumbar ligament is a strong triangleshaped ligament that connects the tips of the L5 spinous processes (and occasionally the processes of L4) to the iliac crest. The inferior fibers of this ligament insert on the lateral aspect of the sacrum forming a band called the lateral lumbosacral ligament.2 The purpose of this ligament is to limit gliding and rotation of L5 on S1. The sacrotuberous ligament attaches the dorsal surface of the sacrum and coccyx to the ischial tuberosity. This ligament resists posterior rotation of the caudal aspect of the sacrum but permits some movement when there are sudden changes in force as in the transfer of weight from the legs to the spine during a jump.2 The sacrospinous ligament functions similarly to the sacrotuberous ligament but connects the sacrum and coccyx to the ischial spine. Together, the iliolumbar, sacrospinous, and sacrotuberous ligaments form the accessory ligaments of the sacroiliac joint and are sometimes referred to as the vertebropelvic ligaments.2 The sacroiliac and interosseous ligaments are situated within the sacroiliac joint (between the surfaces of the sacrum and the ilium). This joint has irregular articular surfaces that help impede motion and also act as insertion points for the three types of ligaments that reside here.2 The sacroiliac ligament is subdivided into two ligaments: anterior (ventral) and posterior (dorsal) components. The interosseous and posterior sacroiliac ligaments are the primary contributors to stability of the pelvis in this region.2 The interosseous ligaments are massive, short, and exceptionally strong ligaments that span the iliac and sacral tuberosities.2 They merge with the posterior sacroiliac ligament.2 The posterior sacroiliac ligament has two components.2 The short transverse fibers connect to the ilium and the first and second tubercles of the lateral crest of the sacrum. The relatively longer vertical fibers connect the third and fourth transverse tubercles of the sacrum to the posterior iliac spines. These fibers join the sacrotuberous ligaments along their course.2 The anterior sacroiliac ligaments are thinner and quite wide, covering the abdominopelvic surface of the sacroiliac joint. They begin to ossify after age 50.2 The sacrum and coccyx are interconnected at the sacrococcygeal joint. Although many ligaments connect these two structures to other structures of the spine and pelvis, two ligaments are specifically responsible for the articulation of these two regions. The sacrococcygeal ligaments correspond to the ALL and PLL and function similarly to them.2 There are also intercornual ligaments that span across the articular cornua of the sacrum and coccyx to assist in the approximation of these two bony structures. The filum terminale (an extension of the pia of the spinal cord) exits the sacrum and blends with the anococcygeal ligament to form the caudal attachment of the spinal cord.2

2.5 Muscles of the Spine Fig. 2.9 The diaphragm attaches to the lumbar spine at the transverse process. The lumbocostal arches then traverse the quadratus lumborum and psoas muscles and attach to the ventral spine. Mobilization of the diaphragmatic crus is frequently required in thoracolumbar approaches.

2.5.1 Muscles of the Cervical Spine The cervical musculature not only produces movement of the head and the neck, but also reinforces and stabilizes the cervical spine. A study by Groh et al19 in 1967 demonstrated that the

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Fundamentals pressure on the lower cervical discs was 550 kPa with normal posture and muscle tone. Without intact musculature, the pressure increased to 3,900 kPa. Perhaps, elevated stress secondary to muscle imbalances can result in significant degeneration of the cervical spine and may be a component in the pathophysiology of cervical disc disease.

Platysma, Sternocleidomastoid, and Trapezius Muscles There are three superficial muscles of the neck: 1. Platysma. 2. Sternocleidomastoid anteriorly. 3. Trapezius posteriorly. The platysma has no direct insertion on the cervical spine and has only minimal involvement in its stabilization. The sternocleidomastoid has two origins, the sternal head and the clavicular head. The two bellies of the muscle come together to form a common insertion onto the lateral portion of the mastoid process and the lateral half of the superior nuchal line. It is innervated by the spinal root of the accessory nerve (CN XI) and branches of the second and third cervical nerves.2 The sternocleidomastoid functions to laterally flex the head and rotate the face superiorly and to the contralateral side.2,15 When these muscles contract bilaterally, the head is flexed forward.2,15 The trapezius muscle, also innervated by the spinal root of the XI and additionally by branches of C3 and C4, has little involvement in the movement of the head but is instead focused on squaring/raising the shoulders. It attaches medially to the superior nuchal line, external occipital protuberance, ligamentum nuchae, and the spinous processes of C7 to T12 and sometimes to those of the lumbar and sacral regions.2 It inserts laterally on the lateral third of the clavicle, acromion, and scapula. As a result of all of its medial attachments, the trapezius does assist in stabilizing the cervical spine.2,15

Prevertebral Muscles The deep anterior cervical musculature is known collectively as the prevertebral muscles.2 They act to flex the neck and are supplied by the anterior rami of the cervical nerves.2 The longus colli is the longest and the most medial of the prevertebral muscles.2 It extends from the anterior tubercle of C1, the bodies of C2 to C4, and the transverse processes of C3 to C6; it inserts on the bodies of C5 to T3. The longus capitis muscle arises from the anterior tubercles of the transverse processes of C3 to C6 and attaches superiorly to the anterior skull base (▶ Fig. 2.10). The rectus capitis anterior is a short wide muscle that originates from the lateral mass of C1 and inserts superiorly on the skull base anterior to the occipital condyle. The rectus capitis lateralis, also a short wide muscle, originates from the transverse process of the atlas and inserts on the jugular process of the occipital bone. In addition to flexing the neck, the two anterior rectus muscles are important in stabilizing the skull on the superior cervical vertebrae.2,15

Posterior Cervical or Intrinsic Muscles The deep posterior cervical muscles that form the floor of the posterior triangle of the neck include the splenius capitis, levator

20

scapulae, scalenus posterior, and scalenus medius. The splenius capitis, which derives its innervation from the dorsal rami of the middle cervical nerves, laterally flexes and rotates the head to the ipsilateral side.2,15 If acting bilaterally, these muscles extend the neck.2,15 In essence, the splenius capitis muscles act to oppose the sternocleidomastoid muscles.2,15 Its origin is the ligamentum nuchae and the first six thoracic vertebrae. It inserts on the lateral aspect of the mastoid process and the lateral third of the superior nuchal line. The levator scapula, innervated by the dorsal scapular nerve (C5) and branches of C3 and C4, elevates and tilts the scapula forward and as such provides minimal stabilization of the cervical spine.2 Its origin is the posterior tubercles of the transverse processes of C1 to C4, and it inserts on the superior aspect of the medial border of the scapula. The scalenus posterior is innervated by the anterior rami of C7 and C8.2 It acts to flex the neck laterally and to elevate the second rib during forced inspiration.2 The scalenus posterior originates from the posterior tubercle of the transverse processes of C4 to C6 and inserts on the external border of the second rib. The scalenus medius, the largest of the scalene muscles, is innervated by the anterior rami of C3 to C8 and is perforated by the dorsal scapular nerve and the two superior roots of the long thoracic nerve.2 It originates from the four posterior tubercles of the transverse processes of C2 to C7 and inserts on the posterior surface of the first rib. Like the posterior scalene, it flexes the neck laterally but because of its insertion on the first rib, the first rib is elevated during forced inspiration.2

Superficial Intrinsic Muscles The deep posterior muscles or intrinsic muscles of the cervical spine are separated into three layers: superficial, intermediate, and deep. The superficial layer includes the splenius muscles or “bandage” muscles from the word splenion (bandage). They are divided into a cranial (capitis) portion and a cervical (cervicis) portion. The muscle originates from the inferior half of the ligamentum nuchae and the spinous processes of T1 to T6. The capitis portion inserts on the lateral aspect of the mastoid and lateral third of the superior nuchal line. The cervicis portion inserts on the posterior tubercles of the transverse processes of C1–C4. The splenius muscle as a whole is innervated by the dorsal rami of the inferior cervical nerves.2 Its function is to laterally flex and rotate the head ipsilaterally.2,15 However, when acting in conjunction with its bilateral counterparts, the splenius muscles cause the head and neck to extend.2,15

Intermediate Intrinsic Muscles The intermediate layer of the intrinsic back muscles is comprised of the longissimus muscle (see ▶ Fig. 2.10). The upper two sections of the muscle, the longissimus capitis and longissimus cervicis, have origins in the upper thoracic and cervical transverse processes. The longissimus cervicis inserts onto the cervical transverse processes and the capitis inserts onto the mastoid process. It acts to laterally flex the head and neck.2,15

Deep Intrinsic Muscles The deep layer of the intrinsic back muscles is composed of the semispinalis cervicis and capitis, the interspinales and intertransversarii, and the rotatores cervicis, which collectively form

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Anatomy of the Spine: An Overview

Fig. 2.10 (a,b) Superficial spinal musculature of the cervical, thoracic, and lumbar spine. (c,d) Intermediate spinal musculature of the cervical, thoracic, and lumbar spine. (e,f) Posterior deep spinal musculature of the cervical, thoracic, and lumbar spine.

the transversospinal muscle of the cervical spine.2 The semispinalis cervicis originates at the transverse processes of the thoracic and cervical spine and inserts on the spinous processes superiorly. The semispinalis capitis arises from the transverse processes of T1–T6 and inserts onto the medial portion of the occipital bone between the superior and inferior nuchal lines. It is the largest muscle of the posterior neck, and acts to laterally flex and rotate the head when activated unilaterally.2,15 When bilaterally activated, the semispinalis muscles will cause the

neck to extend.2,15 The interspinalis muscles are small muscles that attach between the spinous processes of consecutive vertebrae. They are particularly well developed in the cervical spine but are located throughout all regions.2,15 They are innervated by the dorsal rami of the cervical nerves and act to extend the neck. The intertransversarius muscles connect between the transverse processes and are also well developed in the cervical region. They are innervated primarily by the anterior rami of the cervical nerves and receive contributions from the dorsal

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Fundamentals rami as well.2 Individually they act to laterally flex the neck, but when activated bilaterally, these small muscles cause neck extension.2,15 The rotator muscles are composed of longus and brevis components that span the entire vertebral column.2,15 These muscles originate from the transverse processes of a caudal vertebra and insert onto the next consecutive rostral vertebra. They are innervated by the dorsal rami of the cervical nerves and act to contralaterally rotate and stabilize the next superior vertebra.2,15

Suboccipital Muscles The rectus capitis posterior major, rectus capitis posterior minor, superior obliquus capitis muscle, and inferior obliquus capitis muscles together comprise the suboccipital muscles. They are mainly postural muscles but can manipulate head position.2,15 All muscles of this group are innervated by the dorsal ramus of C1.2 The rectus capitis posterior major originates from the spinous process of C2 and inserts on the occiput, inferior to the inferior nuchal line. The rectus capitis minor originates from the posterior tubercle of C1 and inserts on the occiput medial to the rectus capitis posterior major muscle. In addition to stabilizing the head, they have the ability to rotate the head ipsilaterally.2,15 When acting together, they cause the head to extend.2,15 The obliquus capitis superior arises from the transverse processes of C1 and inserts onto the occiput between the superior and inferior nuchal lines. It acts to stabilize the head and can laterally flex and extend it.2,15 The obliquus capitis inferior originates on the spinous process of C2 and inserts

on the transverse process of C1. Although this muscle does not actually insert onto the cranium, the term capitis is used because of its action in rotating the head to the ipsilateral side by pulling on C1.2

2.5.2 Muscular Triangles of the Neck Surgical approaches to the cervical spine and other structures of the neck are more easily referenced when anatomic borders can define the area of interest. In general, the neck is divided into an anterior (ventral) surface and a posterior (dorsal) surface, with the sternocleidomastoid as the common boundary between them (▶ Fig. 2.11).

Anterior Triangle The anterior neck is defined by a large triangle consisting of the anterior border of the sternocleidomastoid muscle, the inferior border of the mandible, and the midline of the neck. The floor of the triangle is the pharynx, larynx, and thyroid gland. The roof is formed by the investing cervical fascia.2 This triangle is subdivided into four smaller triangles: the submental, submandibular, carotid, and muscular triangles.

Submental Triangle The submental triangle incorporates both sides of the neck. Its borders are the anterior bellies of the right and left digastric muscles laterally with the apex at the symphysis menti, and the

Fig. 2.11 Anatomical view of the cervical anatomy demonstrating the commonly used muscular landmarks for defining the anterior and posterior triangles of the spine.

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Anatomy of the Spine: An Overview body of the hyoid bone at its base inferiorly. The floor of the triangle is formed by the mylohyoid muscle, which is joined with its contralateral partner in the midline by a median raphe. Its contents include the veins that form the anterior jugular vein and the submental lymph nodes that are responsible for draining the inferior parts of the mouth and face.2

Submandibular Triangle There is a submandibular (digastric) triangle on each side of the neck. It is defined by the inferior border of the mandible and the anterior and posterior bellies of the digastric muscles. Its floor consists of the mylohyoid, hyoglossus, and middle constrictor of the pharynx in anteroposterior fashion. Its contents include the hypoglossal nerve, the nerve of the mylohyoid muscle (a branch of the inferior alveolar nerve), parts of the facial vein and artery, the submandibular lymph nodes, the submandibular duct, and the submandibular gland, which by itself fills most of the triangle.2

Carotid Triangle The carotid triangle is defined by the anterior border of the sternocleidomastoid, the superior belly of the omohyoid, and the posterior belly of the digastric muscles. Its contents include the carotid sheath, the sympathetic trunk posteriorly, the recurrent laryngeal nerve (a branch of the vagus nerve) medially, the glossopharyngeal nerve (CN IX) posteriorly, the accessory nerve (CN XI) laterally, and the hypoglossal nerve (CN XII) anteriorly.2 Within the carotid sheath are a number of structures including the ansa cervicalis anteriorly (a division of CN XII), the vagus nerve (CN X) posteriorly, the internal jugular vein laterally, and the common, internal, and external carotid arteries medially.2 The carotid bifurcation typically occurs at the level of the superior border of the thyroid cartilage.2

Muscular Triangle The muscular triangle is separated from the carotid triangle by the superior belly of the omohyoid muscle and is also defined by the anterior border of the sternocleidomastoid muscle, and the midline of the neck. The visceral structures of the neck and the infrahyoid muscles are located within this triangle.2

Posterior Triangle The posterior cervical triangle is defined by the posterior border of the sternocleidomastoid muscle anteriorly, the trapezius muscle posteriorly, and the middle third of the clavicle inferiorly at its base. The apex of the triangle is located at the superior nuchal line where the sternocleidomastoid and trapezius muscles meet. The roof of the posterior triangle is formed by the investing layer of the deep cervical fascia.2 The floor is formed by the splenius capitis, levator scapulae, scalenus medius, and scalenus posterior muscles, in rostral-caudal fashion. They are covered by the prevertebral layer of the deep cervical fascia. It is divided into two triangles, the occipital triangle (the majority of the posterior triangle named for the cervical artery exiting at its apex) and the supraclavicular triangle (named for the subclavian artery deep to it), by the inferior belly of the omohyoid muscle.2

Occipital and Supraclavicular Triangles The occipital triangle contains most of the structures mentioned in the posterior triangle. Superior to CN XI is the occipital artery, which leaves the posterior triangle at its apex to supply the dorsal scalp and the lesser occipital nerve that divides to innervate the scalp posterior to the ear.2 Inferior to this is the external jugular vein, which is formed by the confluence of the posterior auricular and posterior division of the retromandibular veins.2 It courses superficial to the sternocleidomastoid muscle to anastomose with the subclavian vein.2 The suprascapular and transverse cervical arteries (branches of the thyrocervical trunk) supply blood to the periscapular muscles and appear in this triangle as well.2 The lymphatic system of the posterior triangle consists of superficial cervical lymph nodes that accompany the external jugular vein. They descend into the subclavian triangle and join with the lymphatic system from the anterior cervical triangle to drain into the supraclavicular lymph nodes in the supraclavicular triangle.2 CN XI divides into a spinal and a cranial root. The spinal root innervates the sternocleidomastoid muscle and then leaves the anterior triangle and enters the posterior triangle to innervate the trapezius muscle.2 The branches of the cervical plexus (C2–C4) enter the occipital triangle deep to the posterior border of the sternocleidomastoid muscle.2 The anterior rami will form the nerves discussed in this triangle.2 The lesser occipital (C2, and occasionally C3) nerve innervates the scalp, the superior aspect of the auricle (ear), and the skin of the neck, and lies rostral to CN XI.2 The greater auricular nerve (C2, C3) innervates the skin of the neck and the inferior part of the auricle.2 The transverse cervical nerve (C2, C3) arises behind the posterior border of the sternocleidomastoid muscle and crosses it to supply the skin superficial to the anterior cervical triangle.2 The supraclavicular nerves (C3, C4) arise as a single trunk that divides into three branches: medial, intermediate, and lateral. All three branches supply the skin of the neck, chest, and shoulders.2 The medial branch innervates the sternoclavicular joint, whereas the lateral branch innervates the acromioclavicular joint.2 The phrenic nerve (C3–C5) curves around the lateral border of the scalenus anterior muscle and descends toward the thorax. The three trunks of the brachial plexus (superior, middle, and inferior) exit rostral to the clavicle deep to the posterior cervical triangle between the scalenus anterior and scalenus medius muscles. The brachial plexus is derived from the anterior rami of C5–C8 and T1, and is responsible for innervating the upper limb.2

Suboccipital Triangle Deep to the posterior triangle is the suboccipital triangle, which is bounded by the rectus capitis posterior major, the obliquus capitis superior, and the obliquus capitis inferior (▶ Fig. 2.12). Its floor is formed by the posterior atlanto-occipital membrane and the posterior arch of C1, and its roof is formed by the semispinalis capitis muscle. This triangle is important because it contains the vertebral artery and the suboccipital nerve that stems from the dorsal ramus of C1.2 These two structures can be found in a groove on the surface of the posterior arch of C1.2

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23

Fundamentals

Fig. 2.12 Dissection of the suboccipital triangle with important landmarks identified.

The sympathetic chain is deep to the prevertebral fascia. There are usually three ganglia present on each side of the cervical spine.2 The rostral-most ganglion is known as the superior cervical ganglion. It is typically juxtaposed to the atlantoaxial region and innervates the pupil.2 The other two ganglia are usually located at C6 and at the level of the first rib.2

2.5.3 Muscles of the Thoracic Spine The muscles of the thoracic spine can be divided into three general layers: superficial, intermediate, and deep (see ▶ Fig. 2.10). The superficial and intermediate muscles are primarily concerned with movement of the upper limbs and respiration, and use the thoracic spine as a scaffolding for their sites of origin.2

Superficial Layer The superficial muscles include the latissimus dorsi and the trapezius muscles. The intermediate muscles include the serratus posterior and superficial respiratory muscles. Consequently, they are known as the extrinsic back muscles.2 The deep layer will be the primary group that is discussed.

Intermediate Layer The intermediate layer of the intrinsic thoracic spinal muscles is composed of the erector spinae muscle, which is a massive group of muscles that forms the muscular bulge on either side of the spinous processes.2 It resides between the anterior and posterior layers of the thoracolumbar fascia.2 It is divided into three columns of muscles: the iliocostalis, longissimus thoracis, and spinalis muscles. These columns share a common origin

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from the spinous processes of the sacrum and inferior lumbar region, the sacroiliac ligaments, the posterior aspect of the sacrum, and the iliac crest.2 This muscle group when activated unilaterally causes lateral flexion of the head and vertebral column to the ipsilateral side.2,15 When the muscles act bilaterally, they extend the head and vertebral column.2,15 The iliocostalis muscle is divided into three segments: cervicis, thoracis, and lumborum. The iliocostalis thoracis inserts on all of the ribs.2 It forms the lateralmost column of the erector spinae group. The longissimus muscle is also divided into three parts: (1) capitis, (2) cervicis, and (3) thoracis. The longissimus thoracis inserts on the transverse processes of all of the thoracic vertebrae and into the tubercles of the 2nd to 12th ribs.2 It forms the intermediate column of the erector spinae. The spinalis muscle forms the medial column of the erector spinae and is a narrow band of muscle fibers that is also subdivided into three parts: capitis, cervicis, and thoracis. The spinalis thoracis inserts on the spinous processes of the upper thoracic spine.

Deep Layer The deep muscles of the thoracic spine are obliquely oriented and located between the spinous and transverse processes of the vertebral column.2 They are collectively referred to as the transversospinal muscle group.2 This group includes the semispinalis muscle and the multifidus muscle that is subdivided into the rotatores, interspinalis, intertransversarii, and levator costarum muscles. The semispinalis muscle has three divisions: capitis, cervicis, and thoracis. The semispinalis thoracis originates from the transverse processes and inserts on the spinous processes of the thoracic and lumbar spine. When activated unilaterally, this muscle causes rotation of the spine to the contralateral side.2,15 When acting bilaterally, it causes the

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Anatomy of the Spine: An Overview vertebral column to extend.2,15 The multifidus connects the spinous processes to the lamina of the next one to three vertebrae.2 If acting unilaterally, it causes the spine to flex and rotate to the contralateral side.2,15 Acting bilaterally, these little muscles extend and stabilize the spine.2,15 The rotatores are most easily observed in the thoracic spine but are present at every level of the spine.2 They are composed of longus and brevis components. These muscles originate from the transverse processes of a caudal vertebra and insert onto the next consecutive rostral vertebra.2 They are innervated by the dorsal rami of the spinal nerves and act to contralaterally rotate and stabilize the next superior vertebra.2,15 The interspinalis muscles are small muscles that attach between the spinous processes of consecutive vertebrae. They are particularly well developed in the cervical spine but are located throughout all regions.2 They are innervated by the dorsal rami of the spinal nerves and cause extension.2,15 The levator costarum muscles are only in the thoracic region as they interconnect between the tip of the transverse process and the rib one level inferior to their origin.2 Insertion is between the rib tubercle and angle. These muscles are the equivalent of the intertransversarius muscles of the cervical spine.2 They act to raise the ribs during inspiration and are innervated by the lateral division of the dorsal rami of the spinal nerves.2,15

2.5.4 Muscles of the Posterior Abdominal Wall The muscles of the posterior abdominal wall act to stabilize the spine and hip; depending on the muscle activated, they will cause

flexion or extension (▶ Fig. 2.13). There are four muscles of the posterior abdominal wall. The posterior diaphragm is one of them, but it does not cause significant movement of the spine.2 The psoas group, iliacus, and quadratus lumborum are the muscles primarily responsible for movement in this region.

Psoas Group The psoas group is composed of two separate muscles. The psoas major is a thick, powerful muscle that originates on the anterolateral aspect of the vertebral bodies and intervertebral discs of T12 to L5.2 It also has origins on the transverse processes of the lumbar vertebrae. The distal tendon of this muscle passes inferior to the inguinal ligament and inserts on the lesser trochanter of the femur. The psoas major gets its innervation from the anterior rami of L2–L4 of the lumbar plexus that is embedded in it.2 This muscle acts on its own to flex the vertebral column laterally and is used to balance the trunk when sitting.2,15 When acting in conjunction with the iliacus muscle (hence the term iliopsoas), it will either flex the thigh superiorly or flex the trunk inferiorly.2,15 The psoas minor muscle is a short, weak muscle with a long tendon that is absent in 40 to 50% of the population and, when present, may only exist on one side.2 It originates from the anterolateral aspect of the vertebral bodies and intervertebral discs of T12–L1.2 It is located anterior to the psoas major muscle and contributes to its function. It is innervated by the anterior ramus of L1.2

Iliacus The iliacus muscle is a large, triangular muscle that originates from the superior two-thirds of the iliac fossa.2 It extends across

Fig. 2.13 Musculature of the thoracic and abdominal cavity.

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Fundamentals the sacroiliac joint, inserting on the lesser trochanter of the femur and a portion of the shaft inferior to it. Its action is to flex the thigh and stabilize the hip in conjunction with the psoas major muscle.2,15 It receives its innervation from the femoral nerve segments L2–L4.2

Quadratus Lumborum The quadratus lumborum counters the efforts of the other two muscles.2,15 It is a thick, square muscle that extends the spine when acting bilaterally and laterally flexes the spine when acting unilaterally.2,15 It also fixes the 12th rib during inspiration.2 The quadratus lumborum attaches to the medial half of the 12th rib and the distal aspect of the transverse processes of the lumbar spine (see ▶ Fig. 2.13).

2.6 Considerations for Minimally Invasive Spine Surgery In addition to a detailed knowledge of spinal anatomy, ideal application of minimally incisional techniques requires an appreciation for anatomical corridors to the spine. For example, in posterolateral approaches to the lumbar spine, tissue planes between the erector spinae muscles allow for access to the facet joint and medial transverse process without the need for splitting or sacrifice of any muscles with the exception of the traversing local multifidus. Similarly, the traditional exposure for an anterior cervical discectomy may be considered minimally incisional as it requires no muscle dissection, save splitting of the superficial platysma and elevation of the longus colli. Appreciation for these anatomic planes and avoidance of extensive muscle dissection maximizes the advantages of minimally incisional approaches.

2.7 Conclusion Knowledge of anatomy is an inherent requirement of any surgical procedure, and considering the complexity of the human spine it is a subject not to be taken lightly. A basic tenet of minimally invasive surgery is the avoidance of tissue damage when possible. This can be accomplished with smaller strategic incisions, with less muscle retraction, and with less bone and ligament removal.

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The purpose of this chapter was to review the anatomic structures and their function with appropriate technical data to help promote successful surgical interventions.

References [1] Bergman R, Thompson S, Afifi A, et al. Compendium of Human Anatomic Variation: Text, Atlas, and World Literature. Baltimore, MD: Urban & Schwarzenberg; 1988 [2] Moore KL. Clinically Oriented Anatomy. 2nd ed. Baltimore, MD: Williams & Wilkins; 1985 [3] Benzel EC. Spine Surgery Techniques, Complication Avoidance, and Management. 1st ed. Philadelphia, PA: Churchill Livingstone; 1999 [4] White AA, Panjabi MM. Clinical Biomechanics of the Spine. 2nd ed. Philadelphia, PA: Lippincott; 1990 [5] Moore KL. The Developing Human: Clinically Oriented Embryology. 4th ed. Philadelphia, PA: Saunders; 1988 [6] McRae D. The significance of abnormalities of the cervical spine. AJR Am J Roentgenol. 1960; 84:3–25 [7] Berry JL, Moran JM, Berg WS, Steffee AD. A morphometric study of human lumbar and selected thoracic vertebrae. Spine. 1987; 12(4):362–367 [8] Krag MH, Weaver DL, Beynnon BD, Haugh LD. Morphometry of the thoracic and lumbar spine related to transpedicular screw placement for surgical spinal fixation. Spine. 1988; 13(1):27–32 [9] Panjabi M, Dvorak J, Duranceau J, et al. Three-dimensional movements of the upper cervical spine. Spine. 1988; 13(7):726–730 [10] Panjabi MM, Takata K, Goel V, et al. Thoracic human vertebrae. Quantitative three-dimensional anatomy. Spine. 1991; 16(8):888–901 [11] Zindrick MR, Wiltse LL, Doornik A, et al. Analysis of the morphometric characteristics of the thoracic and lumbar pedicles. Spine. 1987; 12(2):160–166 [12] Sobotta J, Putz R, Pabst R, et al. Sobotta Atlas of Human Anatomy. 12th ed. Baltimore, MD: Williams & Wilkins; 1997 [13] Cotterill PC, Kostuik JP, D’Angelo G, Fernie GR, Maki BE. An anatomical comparison of the human and bovine thoracolumbar spine. J Orthop Res. 1986; 4 (3):298–303 [14] White AA III, Panjabi M. Physical properties and functional biomechanics of the spine. In: Clinical Biomechanics of the Spine. 2nd ed. Philadelphia, PA: JB Lippincott; 1990:85–125 [15] White AA III, Panjabi M. Kinematics of the spine. In: Clinical Biomechanics of the Spine. 2nd ed. Philadelphia, PA: JB Lippincott; 1990:277–378 [16] Farfan HF, Cossette JW, Robertson GH, Wells RV, Kraus H. The effects of torsion on the lumbar intervertebral joints: the role of torsion in the production of disc degeneration. J Bone Joint Surg Am. 1970; 52(3):468–497 [17] Spence KF, Jr, Decker S, Sell KW. Bursting atlantal fracture associated with rupture of the transverse ligament. J Bone Joint Surg Am. 1970; 52 (3):543–549 [18] Rothman RH, Simeone FA. The Spine. 2nd ed. Philadelphia, PA: WB Saunders; 1982 [19] Groh H, Thös FR, Baumann W. The static load of the spinal column through the sagittal curvature [in German]. Int Z Angew Physiol. 1967; 24(2):129–149

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Biomechanical Role of the Osseous, Ligamentous, and Muscular Structures of the Spine

3 Biomechanical Role of the Osseous, Ligamentous, and Muscular Structures of the Spine E. Emily Bennett, Jeffrey P. Mullin, Rick Placide, and Edward C. Benzel Abstract The study of biomechanics of the spine is especially complex. The cervical, thoracic, lumbar, and sacral portions of the spine greatly affect the function of the muscular, ligamentous, and bony structures that support the spine. All elements play a role in stability and mobility of the body. Keywords: stability, mobility, biomechanics, sagittal balance, coronal balance, kinematics, rotational motions, flexion, extension, rotation, lateral flexion, transitional motions, distraction, compression, ventral subluxation, dorsal subluxation, medial subluxation, lateral subluxation, osseous, vertebra, thoracic cage, vertebral arch, ligamentous, anterior longitudinal ligament, posterior longitudinal ligament, ligamentum flavum, interspinous ligament, supraspinous ligament, intertransverse ligament, concentric muscle contractions, eccentric muscle contractions, isometric muscle contractions

3.1 Introduction The study of biomechanics involving any portion of the human body is complex. This is particularly true with regard to the spine. The nonuniform anatomy throughout the cervical, thoracic, lumbar, and sacral spine is partly responsible for the changes in the biomechanical function of the muscular, ligamentous, and bony structures supporting the spine and their overall role in providing stability and mobility. An appropriate balance between stability and mobility is required for functional efficiency of the spine. Unlike most joints in the body that provide predominantly mobility or stability with a relative sacrifice of the other, the spine and its components make important contributions to stability as well as mobility. The coordinated efforts of these spinal ligamentous, muscular, and bony structures allow the body to move in and out of sagittal and coronal balance as required for normal functional activities.

3.2 Essential Biomechanical Principles To understand spine biomechanics, several physical and kinematic properties must also be addressed. Spinal kinematics is the study of spinal motion in normal physiological movements. A coordinate system involving three orthogonal planes and three axes has been designed to describe human movement. The axes are termed x, y, and z and are based on the Cartesian coordinate system1 (▶ Fig. 3.1). The three planes are the sagittal, coronal (frontal), and axial (transverse). The sagittal plane divides the body into left and right portions, the coronal plane divides the body into ventral and dorsal portions, and the axial plane divides the body into rostral and caudal portions (▶ Fig. 3.2).

Two specific types of motion exist between the two surfaces of a joint: rotation and translation. Rotation occurs about an axis and translation occurs along a plane. These motions can occur in positive and negative directions. This yields a total of six rotational and six translational motions (▶ Fig. 3.3). The six rotational motions are flexion, extension, left and right rotation, and left and right lateral flexion. The six translational motions are distraction, compression, ventral and dorsal subluxation, and medial and lateral subluxation. The concept of motion segment, or functional spine unit (FSU), as it is sometimes called, facilitates the study of the mechanical properties of the spine and has properties with respect to spine biomechanics and motion addressed earlier. The FSU consists of two adjacent vertebrae with their intervening disc, muscles, ligaments, and facet joints.2 Spinal motion occurs within these FSUs or across a multilevel spinal unit. Another key point when discussing spine mechanics is the concept of the instantaneous axis of rotation (IAR). By definition, the IAR is an axis that is perpendicular to a plane of movement that passes through the center of rotation at a particular instant.1 The spine rotates in this axis after a moment arm is applied. Knowledge of normal spine anatomy as it relates to coronal and sagittal balance is essential in understanding spine mechanics in healthy and pathologic states. In the coronal plane, the same vertical line should bisect all the vertebrae.3 Some have described a slight right thoracic curve as normal because of either the thoracic aorta or a predominance of right-handedness. Specifically, the central sacral line assesses coronal balance, which is a perpendicular line to the iliac crests drawn up from the center of the sacrum. If the line passes through C7, coronal balance is

Rostral

Dorsal

Right

Ventral

Left

Caudal

Fig. 3.1 Cartesian coordinate system demonstrating the x-, y-, and z-axes. (From Benzel EC. Biomechanics of Spine Stabilization. Rolling Meadows, IL: American Association of Neurological Surgeons, 2001.)

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Fundamentals

Fig. 3.3 Demonstration of the 12 cardinal plane motions possible in the spine. There are six rotational and six translational motions available. Fig. 3.2 The three cardinal planes used to describe movement about the axes of the Cartesian system. (a) Sagittal plane; (b) coronal plane; (c) axial plane.

present. When the line is lateral to C7, coronal imbalance may occur. Although earlier evidence suggested coronal balance was important in patient function, more recent studies have shown restoring sagittal balance is more significant in improving patient outcomes.4 In the sagittal plane, several normal curves are encountered. Primary curves are present from the time of development as a fetus and are termed kyphosis (dorsal convexity). These are throughout the whole spine initially but are retained past infancy only in the thoracic and sacral spine. In the thoracic region, this is at least in part due to the intravertebral height differences with the ventral height being less than dorsal vertebral body height, thus contributing to kyphosis. Normal thoracic kyphosis is approximately 20 to 40 degrees. In the sacrum, sacral inclination is approximately 40 to 45 degrees and varies with anterior and posterior pelvic tilting and patient habitus. Moreover, when infants begin to hold their heads up, cervical lordosis (dorsal concavity) develops. Further, as the child begins to stand and ambulate, the lumbar lordotic curve forms. The original kyphosis in the cervical and lumbar spine thus reverses during infancy and are termed secondary curves. In the cervical

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spine, vertebral body height is greater ventrally and the intervertebral disc is wedge shaped, resulting in an overall cervical lordosis of approximately 15 to 20 degrees. Similar vertebral body and intervertebral disc characteristics are found in the lumbar spine, resulting in an overall lumbar lordosis that ranges from 40 to 60 degrees and is approximately 30 degrees greater than the thoracic kyphosis. The amount of lumbar lordosis is influenced not only by the anatomy of the vertebral bodies and intervertebral discs but also by the angle of sacral inclination (▶ Fig. 3.4). Muscular forces and hip flexibility largely control pelvic tilting. In the sagittal plane, muscular force couples exist to help control pelvic tilt and, therefore, sacral inclination and lumbar lordosis. This muscular force includes the rectus abdominis and iliopsoas ventrally and the erector spinae and gluteal/hamstring group dorsally (see ▶ Fig. 3.4). For example, simultaneous contraction of the abdominals and the gluteal/hamstring group results in posterior pelvic tilting with axis of rotation being the hip joint. Therefore, these muscles are important in sagittal spine balance and overall posture, and are important clinically in conditions such as flat-back syndrome. Similar muscular force couples exist in the coronal plane with the quadratus lumborum and contralateral gluteus medius. Maintaining and restoring sagittal balance has been associated with improved patient outcomes.

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Biomechanical Role of the Osseous, Ligamentous, and Muscular Structures of the Spine

Fig. 3.4 Lumbosacral angle. Angle created by a line paralleling the rostral aspect of S1 and a horizontal line. Note how the muscles attached to the pelvis can influence the lumbosacral angle and hence the suprajacent spinal curves.

As stated, lumbar lordosis develops as bipedalism occurs in infancy and is critical to maintain upright posture.5 The sagittal curves in the cervical and lumbar spine help to counterbalance the thoracic curve in the sagittal plane so the head can be positioned centrally over the pelvis. In the sagittal plane, the center of gravity in humans is just ventral to S2. This, of course, depends on how the individual is proportioned. The lumbar spine bears the greatest mechanical loads of the spine and is a common site for degenerative changes resulting in back pain. With aging, decreased lumbar lordosis and increased thoracic kyphosis may also occur resulting in loss of sagittal alignment and lumbar flattening. With sagittal malalignment, knee flexion, pelvic retroversion, and thoracic hypokyphosis may occur to compensate.5 To assess sagittal balance, the sagittal vertical axis is used and a sagittal plumb line is drawn from the center of the C7 vertebrae toward the S1 vertebrae on a standing radiograph. The line should cross through C7–T1 and T12–L1, and through the dorsal aspect of the L5–S1 disc1 (▶ Fig. 3.5). If the plumb line falls

Fig. 3.5 Example of normal sagittal balance and approximately where a plumb line should fall.

behind the S1 vertebral body, the patient is in negative sagittal imbalance; and, if the line is in front of the S1 vertebral body, the patient is in positive sagittal imbalance. Further, when changes occur in one region of the spine, another region of the spine must undergo a compensatory change in curvature to

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Fundamentals maintain sagittal balance. As stated earlier, other measures, such as knee flexion, may also occur. The sagittal curves assist with shock absorption, the distribution of applied loads, mobility and stability, and the maintenance of normal soft tissue length–tension relationships for strength and endurance, not only of the trunk but of the extremities as well. Lastly, the pelvis, including the pelvic incidence (PI), pelvic tilt (PT), and sacral slope (SS), is also significantly important in addition to spinal curvature in maintaining sagittal balance.5 PI is a sacral orientation fixed clinical measure which is equal to PT and SS. SS is the angle that is created between the sacral plate and a horizontal line,5 whereas PI is the angle between a line connecting the midpoint of the sacral point to the femoral head axis and a vertical line. Lumbar spine deformity is related to the difference between the PI and lumbar lordosis measured by the Cobb angle.5 Corrective surgical intervention aims at resolving differences in PI and lumbar lordosis and decreasing sagittal malalignment.5

3.3 Anatomy and Mechanical Properties: Osseous, Ligamentous, and Muscular Structures Tissues containing relatively high amounts of collagen such as bone and ligaments have certain unique mechanical properties. They demonstrate anisotropic and viscoelastic properties. Anisotropy means that a tissue has mechanical characteristics that differ with different loading directions. This is largely due to nonuniform microanatomy. Viscoelasticity is a property that allows a tissue to behave differently under varying loading rates. For example, increasing the rate of loading of a particular tissue increases its mechanical strength.6

3.3.1 Osseous Structures The bony elements of the spine include the vertebra and thoracic cage (see discussion later in this chapter in the Spinal Stability Schemes section). The bony structures provide the scaffolding on which ligaments and muscles act to provide stability. When injury or disease affects the bony structures of the spine, the soft tissues can maintain stability provided the bony damage is not extensive. Clinically, isolated bony pathology occurs in the setting of metastatic disease to the spine or conditions of bone such as

osteoporosis. In the setting of trauma, it is difficult to injure the bony elements in isolation without injury (to some extent) of the supporting ligaments and muscles. This has led to the development of several models to describe spine stability as well as potential mechanisms of injury and treatment recommendations, which will be discussed in detail in the section on spine stability. Vertebral anatomy is largely the same throughout the spine, especially from C3 to L5. These vertebrae have a ventrally positioned body that is roughly cylindrical (vertebral body). There is a dorsal bony arch (vertebral arch or neural arch), consisting of the pedicles, transverse processes, superior and inferior articular processes (facets), lamina, and spinous process, which serves to protect the spinal cord/cauda equina and act as attachment sites for ligaments and muscles. The rostral and caudal termini of the spine have atypical vertebrae in the form of the atlas and axis rostrally and the sacrum and coccyx caudally. The vertebral body is essentially a block of cancellous (trabecular) bone covered by a layer of cortical bone. The cortical layer is reinforced by vertical and horizontal trabecular “struts” that help prevent vertebral body collapse. The cortical layer extends to cover the rostral and caudal surfaces of the vertebral bodies. The periphery of this covering is thickened in the region of the epiphyseal plates, and the center is composed of a hyaline cartilage covering, termed the cartilaginous end plate. The internal architecture of the cancellous bone of the vertebral body has various trabeculae that correspond to the compressive, tensile, and torsional stresses placed on the bone1,3,6 (▶ Fig. 3.6). When examining this trabecular pattern, it is apparent that a weakness exists in the ventral aspect of the body. This manifests itself clinically as a compression fracture. During axial compressive loading, the cancellous bone contributes 25 to 55% of the strength of the vertebral body in those under the age of 40 years. As one ages, declining bone density causes a decrease in weight-bearing through the cancellous bone as the cortical bone carries a greater proportion of the load. A loss of approximately 25% of vertebral body bony tissue results in a loss of over 50% of the vertebral body strength.7 A recent study suggests that biomechanical age changes decrease the ventral loading causing increased bone loss in the already relatively weak ventral vertebral body.8 The vertebral arch is a bit more complex anatomically. In the area where the transverse process, articular process, and pedicle meet, the bone demonstrates a reinforcing, crossing trabecular pattern that develops secondary to the stresses applied to the area.

Fig. 3.6 Diagrammatic representation of the trabeculae within the vertebra. Note the relative decrease in reinforcement in the ventral vertebral body. (From Benzel EC. Biomechanics of Spine Stabilization. Rolling Meadows, IL: American Association of Neurological Surgeons, 2001.)

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Biomechanical Role of the Osseous, Ligamentous, and Muscular Structures of the Spine In addition to providing ligamentous attachment sites, the transverse and spinous processes are attachment sites for the erector spinae musculature. These are relatively long levers, and the muscular forces acting on these levers are transmitted to the lamina. Because these muscles are an important component of spinal stability, any compromise in the lamina (injury or surgery) can, in turn, compromise stability. This is particularly obvious regarding postlaminectomy kyphotic deformity in the cervical spine.9 The thoracic spine, however, has been shown in cadaver studies to maintain stability following laminectomy.10 As part of the dorsal vertebral arch, the articular processes, and hence the facet (zygapophyseal) joints, play a significant role in the mechanics of the spine. The facet joints serve two particularly important roles: first, guiding and limiting the direction and range of motion (ROM) and, second, sharing in the role of weight-bearing.11 Although the majority of spinal axial loads are borne through the vertebral bodies and intervertebral discs, the facet joints share in the distribution of axial loads. The literature provides a wide range of overall load bearing by the facet joints, depending on the region of the spine studied and whether the spine was in a flexed, extended, or neutral posture.2 Furthermore, the amount of loading varies based on prior surgeries; for example, facet loading has been shown to double following nucleotomy.12 The facet joints tend to be loaded in extension and unloaded in flexion. The orientation of the facet joints is different in the cervical, thoracic, and lumbar regions, and can vary from side to side at the same level (▶ Fig. 3.7). This orientation is largely responsible for determining what planes of motion are available at a particular motion segment. Accordingly, the facets guide the motion of one vertebra on the next, but they also are involved in limiting ROM (see Zygapophyseal [Facet] Joints section (p. 37)). Additionally, there are zones of transition of facet orientation from cervical to thoracic, thoracic to lumbar, and lumbar to sacral regions where the facet orientation gradually changes over several segments.

3.3.2 Ligamentous Structures The six major ligaments of the spine are the following: 1. Anterior longitudinal ligament (ALL). 2. Posterior longitudinal ligament (PLL).

3. 4. 5. 6.

Ligamentum flavum. Interspinous ligament. Supraspinous ligament. Intertransverse ligament.

This is, of course, excluding spinal cord and nerve root–related ligaments. The ALL, PLL, and supraspinous ligament are intersegmental, and the others are intrasegmental. These ligaments protect the spinal cord and its nerve roots by restricting motion and absorbing energy of the FSU. The majority of spinal ligaments are made of collagen with the exception of the ligamentum flavum, which is composed primarily of elastin. Ligament strength varies between spinal regions and between types of ligaments.1,2 To understand the role a particular ligament has in providing spinal stability, the material properties or strength of the ligament and the length of the moment arm through which it functions must be considered. The moment arm is defined as the perpendicular distance from the IAR to the applied force1 (▶ Fig. 3.8). Ligaments with longer moment arms may have a mechanical advantage over stronger ligaments with shorter moment arms. Additionally, structures ventral to the IAR are taut in extension and shortened with flexion, and structures dorsal to the IAR are shortened in extension and taut with flexion.

Anterior Longitudinal Ligament The ALL runs along the ventral and ventrolateral surface of the vertebral column from C2 (the axis) to the sacrum. It continues rostrally as the atlanto-occipital ligament. The ALL has attachments to the vertebral bodies and discs. There are superficial fibers that span several vertebral segments and deep fibers that run between adjacent vertebrae. The deep fibers blend with the ventral annulus of the disc and serve to reinforce the intervertebral discs. The ALL demonstrates its greatest strength in the upper cervical, lower thoracic, and lumbar regions, with its greatest tensile strength in the lumbar region. In general, the ALL is approximately twice as strong as the PLL.3 The ALL is usually ventral to the IAR and therefore provides resistance to extension.

Fig. 3.7 Facet joint orientation in the cervical, thoracic, and lumbar spine.

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Fundamentals

Fig. 3.8 Relative moment arm lengths of the various intrasegmental and intersegmental spinal ligaments and their relationship to the instantaneous axis of rotation.

Posterior Longitudinal Ligament

Ligamentum Flavum

The PLL runs along the dorsal surfaces of the vertebral bodies, in the spinal canal. It extends from C2 to the coccyx and continues rostrally from C2 as the tectorial membrane. The ligament attaches to the vertebral bodies and the dorsal annulus, which provides additional support to the disc. However, in the lumbar spine the ligament narrows, providing less dorsal reinforcement. At this level, the tensile strength of the PLL is only about one-sixth of the tensile strength of the ALL.3 The PLL in this region has therefore less resistance to flexion, given its lack of strength and relatively small moment arm. In fact, in certain pathologic states, the IAR migrates dorsally, rendering the PLL even less effective at controlling motion.

The ligamentum flavum has a discontinuous course along the dorsal aspect of the spinal canal from C2 to the sacrum, connecting the lamina of adjacent vertebrae. Some of the fibers extend laterally to attach to the facet joint capsules and are incomplete in the midline. The ligamentum flavum is strongest in the lumbar region and weakest in the cervical region. It provides resistance to flexion. As stated earlier, this ligament contains a significant amount of elastic fibers and is under constant tension, even in the neutral posture. The elastin allows the ligament to shorten back to neutral position without buckling into the spinal canal. This property may be referred as “pretension” and may serve to provide some compression to the intervertebral disc, increasing the intradiscal pressure, making the disc stiffer and more capable of providing stability to the spine when in neutral posture.3,7 However, as degenerative changes cause loss of disc height and axial settling, the pretension is lost and the ligament can buckle into the spinal canal with extension and contribute to the symptoms of stenosis. These changes in the ligamentum flavum are multifactorial and include increased fibrosis, increased rates of calcification, increased collagen fibers, and a loss of elastic fibers.

Supraspinous Ligament The supraspinous ligament runs along the tips of the spinous processes in the thoracic and lumbar spine and on to the sacrum. In the cervical spine, it continues rostrally as the ligamentum nuchae. It has the greatest moment arm for resisting flexion because of its position dorsal to the IAR. Lastly, in the lumbar spine, the supraspinous ligament is weaker than it is in the thoracic region.

Interspinous Ligament The interspinous ligament, like the supraspinous ligament, has a relatively long moment arm, which resists flexion of the spine. It is best developed in the lumbar region but is often absent at the L5–S1 interspace. The failure strength of the interspinous ligament is the weakest when compared to the remainder of the spinal ligaments. However, the relatively long moment arm affords the interspinous ligament the ability to provide resistance to flexion.

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Intertransverse Ligaments The intertransverse ligaments are paired ligaments that travel between adjacent transverse processes and are well developed only in the lumbar region. They are positioned to provide resistance to contralateral lateral bending, but their significance is still unclear. In addition to the ligaments traversing the spine as a whole as mentioned earlier, certain regions of the spine have additional ligaments that are important to their local function. The upper cervical spine and the lumbosacral spine are two regions of particular interest.

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Biomechanical Role of the Osseous, Ligamentous, and Muscular Structures of the Spine

Cruciform Ligament The upper cervical spine has several important unique ligaments. The cruciate (cruciform) and alar ligaments play a significant role in mobility and stability between the occiput, C1 (atlas), and C2. The cruciate ligament, as its name implies, is cross shaped, with the transverse portion (transverse atlantal ligament) being the stronger and more important part. It spans from one condyle of the atlas to the other and divides the ring of the atlas into a large dorsal space for the spinal cord and a smaller ventral space for the odontoid process of the axis. The transverse portion of this ligament has a thin layer of cartilage where it articulates with the dorsal aspect of the odontoid, and it secures the odontoid in close approximation to the dorsal aspect of the ventral arch of the atlas. This ligament is important in preventing ventral displacement of C1 on C2, and insufficiency or disruption of this structure can lead to instability and neurologic injury. One mechanism of injury to this ligament can occur with a Jefferson-type fracture of C1. When an axial load is applied from the occiput through C1, the lateral masses of C1 are driven apart by being pinched between the occipital condyles and the lateral masses of C2, and the transverse ligament may fail in tension. Failure of this ligament can be inferred on a good-quality anteroposterior radiograph by measuring the overhang of the lateral mass of C1 on C2, and adding the left and right sides. Based on a cadaveric study, a measure of greater than 6.9 mm indicates failure of the transverse ligament or bony avulsion from one of the attachment sites on the condyle.13 This is referred to as the “rule of Spence” and generally greater than 7 mm of overhang indicates failure. Lastly, this ligament also has a superior band attaching to the anterior edge of the foramen magnum and an inferior band attaching to the body of C2.

Alar Ligaments The paired alar ligaments attach to the tip of the odontoid process and run rostrally and obliquely to attach to the medial surface of the occipital condyles. The right alar ligament limits rotation of the head to the left, while the left alar ligament limits head rotation to the right; they also are involved in resisting lateral flexion.2 Both alar ligaments become taut during flexion and lax in extension. They are also positioned to resist distraction between the occiput and C2. Compromise of one or both alar ligaments can lead to rotational instability at the occiput/ C1–C2 complex.

Iliolumbar Ligaments The paired iliolumbar ligaments are important for stability at the lumbopelvic junction. The iliolumbar ligaments attach the tips of the transverse processes of L5 (and L4 according to some investigators) to the ipsilateral iliac crest. These ligaments are described as having multiple distinct parts, primarily ventral and dorsal bands as well as a sacral portion, providing evidence for an involvement in restraining sacroiliac motion.14 They help anchor the axial skeleton to the pelvis in addition to the strong intervertebral disc between L5 and S1. Thus, these ligaments are important in resisting motion at the lumbosacral junction, and there is some evidence that the morphology of these ligaments may be correlated to L4–L5 and L5–S1 disc degeneration.15 A biomechanical cadaver study demonstrated increased

lumbosacral motion by sectioning of the iliolumbar ligaments. In particular, flexion, extension, rotation, and lateral flexion were all increased after ligament sectioning, with lateral flexion being the most affected.16

3.3.3 Muscular Structures The biomechanical roles of the muscular system with regard to the spine include providing dynamic stability and mobility. The muscular system is intimately involved with the nervous system. However, a discussion of neuromotor control is outside the scope of this chapter. Suffice it to say the muscular system has a significant proprioceptive role in providing spinal stability and mobility. The skeleton acts as a system of levers through which muscles exert their force to produce movement. Fundamentally, there are three types of muscle contractions: (1) concentric, (2) eccentric, and (3) isometric. Concentric means the muscle is shortening while contracting, eccentric means the muscle is lengthening as it is contracting, and isometric means the muscle length does not change during contraction. For example, as one bends forward from a standing position (trunk flexion), the trunk flexors may initiate the motion, but as one continues to flex, the spine extensors (erector spinae) control the lowering of the trunk. In this situation, the erector spinae are contracting, but they are lengthening as their rostral and caudal attachments get further apart. Returning to an upright posture from a flexed position, the erector spinae contract concentrically as they are shortening to return the trunk to an upright position. For optimal functional efficiency of the spine, the muscular system must possess the qualities of strength, endurance, and coordination. Muscular coordination is related to neuromotor control and nervous system function, and will not be reviewed here. Keep in mind, however, that neuromotor diseases have the potential to significantly hinder muscle function. Strength is the ability to produce force; this force-generating ability is influenced by many factors. A muscle’s cross-sectional area is related to its strength as is the amount of thick and thin filament cross-bridging and the moment arm around which a muscle is acting. An optimal amount of overlap between actin and myosin exists for maximal force generation for a particular muscle fiber. This can be thought of as a length–tension relationship. Although the length–tension relationship may be related to force-producing capability, it cannot be applied directly to the body. In the body, muscles act to produce motion by causing movement around an axis and may (and often do) have a moment arm that varies throughout the ROM.17 For example, if two muscles generate the same force but act through moment arms of different lengths, they will produce different torque. Torque is equal to force times perpendicular distance (moment arm). Therefore, torque is a more appropriate term to use when discussing muscle function in the body. This can be measured clinically using an isokinetic dynamometer to generate a torque versus angle curve that can be compared to normative values (▶ Fig. 3.9). Muscle endurance is the ability to resist fatigue and is an extremely important component of normal spinal muscle function. Many occupations and activities of daily living require maintenance of various postures for extended periods of time. It has been demonstrated that patients with low back pain have decreased trunk extensor muscle endurance compared to those

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33

Fundamentals

Fig. 3.9 Example of an arbitrary torque curve with relative torque on the y-axis and angle or range of motion on the x-axis. Note how the torque changes as the angle of trunk flexion changes. This is, in part, related to changing length–tension relationships and the muscle moment arm.

100

Relative torque (%)

80

60

40

20

0 0

30

60

90

Angle of trunk flexion

without low back pain.4,18 Additionally, it has been shown that fatiguing trunk musculature causes the subjects to lose the ability to control the plane of movement and there was overall decreased speed of movement and decreased ROM.4,19,20 When the body moves out of sagittal or coronal balance, the muscles help to balance the eccentric loading that takes place. If muscular endurance is poor, then the passive restraints are subjected to increased stress with the potential for tissue damage, dysfunction, and pain. Strength and endurance come into play on a daily basis. Bone tends to be weaker in tension than in compression, and the posterior spinal muscles can help decrease tensile forces on the posterior bony elements. For example, as the cervical spine flexes, the passive restraints (ligaments and facet capsules) apply tension at their bony attachments. The posterior cervical musculature can limit the tensile stresses and apply compressive stresses by contracting.5 Even in the face of ligamentous instability, mechanically simulated cervical spine musculature has been demonstrated to strongly stabilize the spine in cadaveric specimens.21 In addition to muscular strength and endurance, flexibility is also important. This includes not only the axial skeletal muscles but also those connecting the pectoral and pelvic girdles to the spine. Decreased flexibility in a particular muscle group or limited motion in a certain direction imposes additional stress on adjacent structures and joints, much as in the case of fusion surgery. For example, limited hamstring flexibility or decreased hip ROM due to arthritis may limit forward bending. In general, the first 50 to 60 degrees of trunk flexion occurs through the lumbar spine followed by pelvic tilting around the hips for the remainder of the motion. If a patient’s occupation or recreation requires forward bending and the patient is limited by hip arthritis, he or she will complete the task by increasing the demand on an adjacent structure such as increasing lumbar spine flexion.

3.4 Spinal Stability Schemes Stability of the spine is achieved through the concerted efforts of three different but interconnected systems: (1) bony,

34

(2) ligamentous, and (3) muscular systems. Nervous system input is equally important. Any of the aforementioned systems has the ability to compensate when injury compromises the stabilizing effects of the other systems. However, this ability to compensate is limited; once it is surpassed, clinical instability results. Several models have been proposed to help the clinician describe, characterize, and differentiate between spinal stability and instability. The three most commonly referenced schemes are: (1) Denis’ three-column spine concept,22 (2) White and Panjabi’s checklists for clinical instability,2 and (3) Benzel’s instability categorization scheme.1 This section will also review the rib cage with respect to its stabilizing effect on the spine.

3.4.1 Denis’ Three-Column Spine Concept The concept of the three-column spine was proposed by Denis22 in an attempt to better understand, categorize, and treat acute thoracolumbar injuries. Some have applied the three-column concept from the subaxial cervical spine through the lumbar spine. This idea stemmed from the observation that the classification based on the two-column spine was not adequate to explain the injuries being seen based on the advent of computed tomography (CT), which allowed better visualization of spinal injuries. The three columns are the anterior, middle, and posterior columns.22 The anterior column includes the ALL, the anterior annulus, and the anterior two-thirds of the vertebral body. The middle column consists of the PLL, the posterior annulus, and the posterior one-third of the vertebral body. The posterior column is formed by the dorsal bony arch (pedicle, lamina, transverse processes, spinous processes), facet joints, ligamentum flavum, and interspinous and supraspinous ligaments. Clinically as well as experimentally, Denis and others contended that complete rupture of the posterior ligamentous complex alone was insufficient to create spinal instability.22 However, with additional disruption of the PLL and posterior annulus

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Biomechanical Role of the Osseous, Ligamentous, and Muscular Structures of the Spine (middle-column structures), instability could then result. Denis22 published an involved classification scheme for acute thoracolumbar injuries, with the four major injury types being compression fracture, burst fracture, seatbelt-type fracture, and fracture–dislocation. He also correlated his classification with instability. The term stable injury should be reserved for mild or moderate compression fractures where the posterior column remains intact. Instability in the first degree, or mechanical instability, describes injuries where the spine may angulate or buckle. An example of mechanical instability would be a severe compression fracture, causing disruption of the posterior ligaments and allowing the spine to angulate around the middle column as if it were a hinge. Instability of the second degree, or neurologic instability, can be represented by a burst fracture. By definition, the middle column is disrupted as a result of an axial load. According to Denis,22 the majority of neurologic injury occurs with the initial trauma. However, later neurologic injury comes from continued or progressive neural element compression from a bony fragment retropulsed from the middle column. This is allowed to happen if axial loading is permitted across the injury site. Instability of the third degree is also termed mechanical and neurologic instability. This injury pattern is seen with severe burst fractures and fracture–dislocations. Progressive deformity and neurologic decline may occur with these injuries.22

3.4.2 White and Panjabi’s Checklist for Clinical Instability White and Panjabi2 defined clinical instability as “the loss of the ability of the spine under physiologic loads to maintain its pattern of displacement so that there is no initial or additional neurologic deficit, no major deformity, and no incapacitating pain.” Their scheme of spinal instability divides the spine into the following: 1. Occipital atlantoaxial complex. 2. Middle and lower cervical spine. 3. Thoracic and thoracolumbar spine. 4. Lumbar and lumbosacral spine. 5. Sacroiliac joint and the pubis. Each section has its own unique checklist of clinical and radiographic criteria to help determine instability. These criteria are based largely on clinical and cadaveric studies and are not intended to be used as strict standards; they are intended as guidelines to be used in the context of the overall clinical picture. Interested readers should refer to White and Panjabi’s textbook on spinal biomechanics.2 More recently, the thoracolumbar injury classification severity score (TLICS) and the subaxial injury classification (SLIC) scale were proposed as new paradigms for further guiding decision-making processes in the cervical and thoracolumbar spines following injury.23,24 The TLICS was developed based on a survey of leading experts in the field of spine trauma to better characterize an algorithm for identifying and treating common thoracolumbar injuries and to incorporate the more detailed findings seen on magnetic resonance imaging (MRI).23 The TLICS classifies injuries based on three major categories: morphology of injury, the posterior ligamentous complex, and patient neurological status. Points are awarded for increased severity in each category; a sum of the points is used to guide

management of patients, with scores of 4 or greater possibly benefitting from surgical intervention but obviously other factors such as patients’ comorbidities must be taken into account in the decision-making processes. Similarly to the TLICS, the SLIC scale was developed by leading experts in spine trauma and classifies injury based on injury morphology, status of discoligamentous complex, and neurological examination.24 A sum is also made based on the severity and grade of each individual category, and an overall score of 4 or more is generally a threshold for surgical intervention. Lastly, spinal level, description of bony injury, and confounding features are subcategories that must be taken into consideration as well.

3.4.3 Benzel’s Instability Categorization Scheme Benzel’s categorization of instability1 was, in part, derived from the inability to assign strict criteria to differentiate between spinal stability and instability in a clinically useful manner. Instead, instability is divided into two categories: acute and chronic. The acute category is subdivided into overt instability and limited instability. Overt instability is defined as the inability of the spine to support the torso during normal activity. Limited instability is the loss of either ventral or dorsal spinal integrity, with preservation of the other. This situation is sufficient to support some normal activity. The chronic category is divided into glacial instability and dysfunctional segmental motion. Glacial instability is spinal instability that is not overt and does not pose a significant risk of rapid deformity progression. However, as with a glacier, deformity does progress gradually. Dysfunctional segmental motion is a type of instability related to disc interspace or vertebral body degenerative or destructive changes, resulting in the potential for pain of spinal origin. In this scheme, instability is unique to a specific clinical situation and it is not intended to be applied globally.1 If none of the above categories, including limited or overt instability, glacial instability, or dysfunctional segmental motion, are present, the spine is stable.1 However, if instability exists in one or more the subcategories, the extent and category of the instability must be determined and symptoms and neurological compromise as well as the patients’ concerns in the decisionmaking processes for treatment must be considered.1

3.4.4 Rib Cage The thoracic spine is intimately associated with the rib cage and hence with the diaphragm and abdominal cavity. The osseous components of the thorax include the thoracic vertebrae, ribs, sternum, manubrium, and xiphoid process, all of which help make the thoracic region of the spine the most stable and least mobile segment of the spine. At the cervicothoracic and thoracolumbar junctions, the transition from a relatively rigid thoracic spine to the more mobile and less stable cervical and lumbar spines causes a significant increase in stresses across these regions. In addition, these junctional regions are where transition from the thoracic kyphosis to cervical and lumbar lordosis occurs. Ribs 1 through 10 attach dorsally to the vertebrae and intervertebral discs as well as ventrally to the sternum, thus creating a closed kinematic chain with respect to function of the thorax. This has implications for coupled movements between the thoracic vertebrae and ribs.

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Fundamentals Articulations in the thoracic cage include the manubriosternal and xiphisternal joints, which are synchondroses, and the costovertebral and costotransverse joints, which are synovial joints. These joints have been shown to be important in thoracic spine stability.25,26,27 Others include the costochondral, chondrosternal, and interchondral articulations. The axes of motion about which the costovertebral and costotransverse joints move are not entirely agreed on; however, several aspects of thoracic spine–rib interaction are more accepted. For example, during normal respiration with normal spine mechanics, inhalation results in a subtle straightening of the normal sagittal cervical, thoracic, and lumbar curves, whereas exhalation exaggerates the normal sagittal curves. Additionally, the orientation of the axis of motion for ribs 2 to 10 at the costovertebral and costotransverse joints changes from the upper to the lower thoracic spine.3 These motions have been described as pump-handle and bucket-handle motions and allow for the rib cage to expand in ventral, rostral, and lateral directions during inspiration, thus maximizing lung volume. As mentioned, the stability and limited motion of the thoracic spine are enhanced by the bony confines of the rib cage.11 Recent data suggest the rib cage contributes more to thoracic stability than previously thought; greater than 75% of thoracic stability was estimated to be attributed to intact rib cage.28 In addition to the rib cage, there are several ligaments unique to the thoracic spine that are involved in stability. The ligaments associated with stabilizing the ribs to the thoracic vertebrae are the radiate ligament of the head of the rib and the superior and lateral costotransverse ligaments. The rib cage also contributes to the stability of the lumbar spine in an indirect manner. Because the rib cage serves as an attachment for the abdominal muscles, a stable rib cage is needed for optimal abdominal muscle function. It has been demonstrated that intra-abdominal pressure is an important stabilizing factor in the lumbar spine.29,30

3.5 Spinal Mobility Normal spinal motion occurs at the intervertebral and zygapophyseal (facet) joints. The intervertebral joints are composed of the superior and inferior end plates of adjacent vertebral bodies and the interposed intervertebral disc. It is a fibrocartilage joint, classified as a symphysis, and the intervertebral disc that act as the main motion segment of the spine.31 The facet joints are formed from the superior and inferior articular processes of adjacent vertebrae and are classified as diarthrodial joints. The ROM available at any particular spinal motion segment is in part determined by the height of the intervertebral disc, whereas the direction of motion available is partly governed by the facet joint orientation.

motion, particularly when comparing the thickness of the disc to the height of the vertebral body—that is, the greater this ratio (disc thickness to vertebral body height), the greater the motion available. This ratio is greater in the cervical and lumbar spine when compared to the thoracic spine, which is one factor contributing to differences in motion among the different regions of the spine. The normal intervertebral disc can be divided into three main sections: (1) annulus fibrosus radially, (2) nucleus pulposus centrally, and (3) annular epiphysis cranially and caudally. The annulus can be further divided into outer and inner portions. The outermost layer of the annulus fibrosus is a ring of densely packed type 1 collagen. The inner annulus consists of less densely packed type 2 collagen. The annular collagen fibers are arranged in layered sheets termed lamellae. The concentric rings of the annulus have their fibers oriented 120 degrees in opposite directions from one layer to the next, contributing to torsional resistance.2 Further, it has been demonstrated that a disc with a disrupted annulus is less able to resist rotational or torsional loading. The annulus also has fibers that attach to the rostral and caudal vertebral bodies, thereby connecting adjacent vertebrae. Therefore, the outer annulus is suited to resist high tensile stresses and to minimize disc bulging. The innermost part of the intervertebral disc is the nucleus pulposus. Unlike the annular layers that contain a relatively higher proportion of collagen, the nucleus contains a relatively greater proportion of proteoglycans. These proteoglycans are negatively charged; thus, the repulsion between the proteoglycan molecules and their hydrophilic nature causes disc pressurization and hydration by pulling water into the nucleus, which provides resistance to axial loading or compression. The end plates are firmly attached to the vertebral body by calcified cartilage and have the ability to undergo compressive deformation. This contributes to the force distribution between the intervertebral disc and the vertebral body during axial loading. During rotational loading, such as flexion and extension, the intervertebral disc undergoes eccentric deformation. The disc is subjected to tensile stresses on the convexity and compression and disc bulging on the concavity of the curve1 (▶ Fig. 3.10). Several studies have evaluated the intradiscal pressure in the lumbar spine during various positions.32,33 In general,

3.5.1 Intervertebral Discs There are typically 23 intervertebral discs (6 cervical, 12 thoracic, and 5 lumbar) in the human spine; generally, no discs are observed between C1 and C2 or in the sacrum or coccyx. Normally, they increase in height and diameter as one descends through the cervical, thoracic, and lumbar levels. For instance, in the cervical spine, the intervertebral disc is on average 3 mm thick, whereas the intervertebral disc in the lumbar spine averages 9 mm in thickness.3 The size of the intervertebral disc influences

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Fig. 3.10 Intervertebral disc undergoing axial loading and eccentric loading. Note that the nucleus moves away from the compression side. (From Benzel EC. Biomechanics of Spine Stabilization. Rolling Meadows, IL: American Association of Neurological Surgeons, 2001.)

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Biomechanical Role of the Osseous, Ligamentous, and Muscular Structures of the Spine gives rise to what is termed coupled motions. Coupled motions refer to the fact that motion along or around one cardinal axis coexists with an obligatory motion along or around another axis and are normal phenomena. In the subaxial cervical spine, for example, axial rotation (rotation around the y-axis) is coupled with lateral flexion (rotation around the z-axis). For example, in the cervical spine (C3–C7) and usually the upper thoracic spine, rotation is accompanied by ipsilateral lateral flexion, whereas in the lumbar spine and lumbosacral articulation rotation is accompanied by contralateral lateral flexion1,4 (▶ Fig. 3.11). Moreover, the occipitoatlantal articulation is similar to that of the lumbar spine, and the atlantoaxial joint involves primarily axial rotation coupled with rostrally and caudally directed translation.7 Lastly, the thoracic spine demonstrates axial rotation and lateral flexion that can be coupled to the same or opposite sides. The reasons for this variation include individual differences, the level of the thoracic spine tested, the proximity to the apex of the kyphosis, and whether rotation or lateral flexion is introduced first.

3.6 Conclusion The spine has the unique quality of providing both mobility and stability in a way not appreciated elsewhere in the body. This is dependent on the coordinated interactions between the osseous, ligamentous, and muscular systems. However, optimal efficiency is possible only when all of the components are functioning in a healthy state. Injury or impairment of one or more of the three components will limit efficiency, be it minor or catastrophic. Our role as spine care professionals is to understand how the various spinal systems interact and how to intervene when these interactions are not optimal. A sound knowledge of basic spine biomechanics is essential for providing quality care to those with spinal disease.

Fig. 3.11 Example of cervical spine and lumbar spine coupled motions. Note how rotation and lateral flexion occur to the same side in the cervical spine and to opposite sides in the lumbar spine.

the lying-down position had the least intradiscal pressure. As one rises to a standing position, the disc takes on increasing axial loads of the body, which raises the disc pressure but less than the seated position, especially if the seated position included leaning forward.

3.5.2 Zygapophyseal (Facet) Joints The facet joints are planar diarthrodial joints. The articular surfaces are covered with hyaline cartilage, and the joint is encased in a synovial-lined joint capsule. As such, they are prone to any of the afflictions of synovial joints, such as degenerative arthritis, rheumatoid arthritis, gout, and so forth. The combination of articular surface spatial orientation and capsular restraints allows the facet joints to play a significant role in restraining and guiding motion in the spine. They are particularly important in resisting translational and torsional forces. Because these joints are planar in nature, the motion afforded is translation. A combination of facet orientation and ligament and muscle influences

References [1] Benzel EC. Biomechanics of Spine Stabilization. Rolling Meadows, IL: American Association of Neurological Surgeons; 2001 [2] White AA, Panjabi MM. Clinical Biomechanics of the Spine. 2nd ed. Philadelphia, PA: Lippincott; 1990 [3] Norkin CC, Levangie PK, eds. Joint Structure and Function. 2nd ed. Philadelphia, PA: FA Davis; 1992 [4] Daubs MD, Lenke LG, Bridwell KH, et al. Does correction of preoperative coronal imbalance make a difference in outcomes of adult patients with deformity? Spine. 2013; 38(6):476–483 [5] Sparrey CJ, Bailey JF, Safaee M, et al. Etiology of lumbar lordosis and its pathophysiology: a review of the evolution of lumbar lordosis, and the mechanics and biology of lumbar degeneration. Neurosurg Focus. 2014; 36(5):E1 [6] Buckwalter JA, Einhorn TA, Simon SR. Orthopaedic Basic Science, Biology and Biomechanics of the Musculoskeletal System. 2nd ed. Rosemont, IL: American Academy of Orthopaedic Surgeons; 2000 [7] Moskovich R. Biomechanics of the cervical spine. In: Nordin M, Frankel VH, eds. Basic Biomechanics of the Musculoskeletal System. 3rd ed. Baltimore, MD: Lippincott Williams & Wilkins; 2001 [8] Giambini H, Salman Roghani R, Thoreson AR, Melton LJ, III, An KN, Gay RE. Lumbar trabecular bone mineral density distribution in patients with and without vertebral fractures: a case-control study. Eur Spine J. 2014; 23(6):1346–1353 [9] Subramaniam V, Chamberlain RH, Theodore N, et al. Biomechanical effects of laminoplasty versus laminectomy: stenosis and stability. Spine. 2009; 34 (16):E573–E578 [10] Healy AT, Lubelski D, Mageswaran P, et al. Biomechanical analysis of the upper thoracic spine after decompressive procedures. Spine J. 2014; 14(6):1010–1016 [11] Sham ML, Zander T, Rohlmann A, Bergmann G. Effects of the rib cage on thoracic spine flexibility. Biomed Tech (Berl). 2005; 50(11):361–365

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[24] Whang PG, Patel AA, Vaccaro AR. The development and evaluation of the subaxial injury classification scoring system for cervical spine trauma. Clin Orthop Relat Res. 2011; 469(3):723–731 [25] Oda I, Abumi K, Lü D, Shono Y, Kaneda K. Biomechanical role of the posterior elements, costovertebral joints, and rib cage in the stability of the thoracic spine. Spine. 1996; 21(12):1423–1429 [26] Takeuchi T, Abumi K, Shono Y, Oda I, Kaneda K. Biomechanical role of the intervertebral disc and costovertebral joint in stability of the thoracic spine. A canine model study. Spine. 1999; 24(14):1414–1420 [27] Oda I, Abumi K, Cunningham BW, Kaneda K, McAfee PC. An in vitro human cadaveric study investigating the biomechanical properties of the thoracic spine. Spine. 2002; 27(3):E64–E70 [28] Brasiliense LB, Lazaro BC, Reyes PM, Dogan S, Theodore N, Crawford NR. Biomechanical contribution of the rib cage to thoracic stability. Spine. 2011; 36 (26):E1686–E1693 [29] Hodges PW, Cresswell AG, Daggfeldt K, Thorstensson A. In vivo measurement of the effect of intra-abdominal pressure on the human spine. J Biomech. 2001; 34(3):347–353 [30] Essendrop M, Andersen TB, Schibye B. Increase in spinal stability obtained at levels of intra-abdominal pressure and back muscle activity realistic to work situations. Appl Ergon. 2002; 33(5):471–476 [31] Kramer J. Intervertebral Disc Disease: Causes, Diagnosis, Treatment, and Prophylaxis. 3rd ed. New York, NY: Georg Thieme Verlag; 2008:15–32, 43–54 [32] Nachemson A. Towards a better understanding of low-back pain: a review of the mechanics of the lumbar disc. Rheumatol Rehabil. 1975; 14 (3):129–143 [33] Wilke HJ, Neef P, Caimi M, Hoogland T, Claes LE. New in vivo measurements of pressures in the intervertebral disc in daily life. Spine. 1999; 24(8):755–762

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Pathophysiology and Operative Treatment of Discogenic Back Pain

4 Pathophysiology and Operative Treatment of Discogenic Back Pain Mick J. Perez-Cruet, Charles D. Ray, and Michael Y. Wang Abstract In order to adequately treat patients with chronic lower back pain, an understanding of the pathophysiology of back pain is paramount. Although further basic science and clinical research into this subject is necessary, inflammatory nerve-irritating substances released from the degenerate disc have recently been identified as playing a critical role. This chapter will discuss the anatomic architecture of the disc as well as the pathophysiology of disc degeneration leading to chronic back and/or leg pain. Keywords: degenerated disc, back pain, discogenic back pain, inflammatory mediators

4.1 Introduction The intervertebral disc is an active organ in which the normal and pathologic anatomy are well known but the normal and pathologic physiology have been less clear. The flexible disc, interposed between each movable segment, permits cyclical motions required of all vertebrate animals in their various forms of locomotion. The disc is a high-pressure system composed primarily of absorbed water, an outer multilayered circumferential belt of strong, flexible but essentially inelastic collagen fibers, and an inner core of a hydrogel called the nucleus pulposus. The swelling of the contained hydrogel creates the high pressure that tightens the annular fibers and maintains disc height

and resilience, very much as the air in a belted tire tightens its laminations. Degeneration of discs is a slow, complex process involving several mechanical and physiologic components. Discogenic pain arises from either component but is primarily due to altered chemistry. When this pain is severely disabling and unyielding, the preferred contemporary treatments are primarily surgical—namely, fusion or total disc replacement.

4.1.1 Disc Physiology The embryology, developmental anatomy, and physiology of the disc are complex.1,2,3,4,5,6,7,8 The annulus fibrosus of the disc has a mesenchymal embryologic origin as does muscle, bone, and connective tissue. The nucleus pulposus, however, develops from the notochord. The intervertebral discs allow for dynamic motion of the axial skeletal structure at each vertebral segment. The disc is composed primarily of absorbed water, a multilayered annular ring of flexible inelastic type 1 long collagen fibers (similar to those found in ligaments), and a gelatinous core.2,8,9 The annulus provides the means by which the disc attaches to vertebral bone. Annular collagen fibers are arranged in circumferential belts or laminations inserting strongly and tangentially in right- and left-handed angulated patches into each adjacent vertebral body2 (▶ Fig. 4.1). Inside the annular ring is contained an aggrecan, glycosaminoglycan, a protein-sugar complex gel having great hygroscopic (i.e., water holding) ability.9 The swelling pressure of this gel of the nucleus maintains the pressure within the annulus, forcing the vertebrae apart and tightening

Fig. 4.1 (a) Diagram of a multibelted radial tire showing circumferential, radial, and tangential fibers. This configuration provides maximum stability, but the fibers must be kept tight as a result of the high internal air pressure. With loss of internal pressure, the tire laminations bulge, debond, delaminate, and disintegrate. Between fiber layers is interposed a thin layer of flexible rubber. (The image is provided courtesy of Semperit Tire & Rubber Co.) (b) Diagram of an intervertebral disc showing the multilaminated annulus. Type 1 long collagen fibers firmly attach to adjacent vertebral bodies. The overlapping laminations, randomly constructed in right-hand and left-hand patches in a given layer, provide maximum stability of the segment in all degrees of freedom so long as the fibers are tightened by the internal swelling of the nucleus gel. This swelling of the gel is analogous to the air inside the tire.

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39

Fundamentals the annular fibers. This tightening provides the primary mechanical stability and flexibility of each discal segment of the spinal column.3,10,11 Further, the angulated arrangement of the fibers also controls the segmental stability and flexibility of the motion segment in multiple planes as motion can occur with six degrees of freedom. The same gel is also found in thin layers separating the annular laminar construction, providing some apparent elasticity and separating the laminations, reducing interlaminar torsional abrasion. With aging or degeneration, nucleus gel declines, while collagen content, including fibrosis, relatively increases.1,5,12,13,14 The internal nucleus pressure varies from approximately 2 to 10 atmospheres depending on the load, and is clearly far above normal arterial pressure, so there cannot be an intrinsic vascular supply within the normal annulus or nucleus.6,15,16 The lumbar discs are the largest avascular structures of the body. This semi-sealed disc chamber is anaerobic, with the oxygen saturation approximately 5%.6,15 Only the outer six annular layers have a direct arteriolar supply, along with a thin arteriolar supply lying outside of the end plate.17 Normally, small arterioles are always accompanied by small free nerve endings, or C-fibers, mediators of pain perception. These tiny nerves, 2 to 6 μm in diameter, are polymodal, responding to chemical, thermal, or mechanical stimuli17 (▶ Fig. 4.2). C-fiber pain is sharp and highly localized, and serves as an early warning system, triggering protective reflexes such as local muscle contractions. The normal intact disc functions painlessly, even though the nucleus accumulates anaerobic metabolites that could stimulate the free

nerve endings in the outer annulus and sensitive structures just outside the annulus.6,18,19,20 A potential source of chronic low back pain could be disruption of the annulus fibrosus and irritation of these nerve endings by extruded irritants originating in the nucleus pulposus. Additionally, the relatively close proximity of the dorsal root ganglion, a major origin of pain sensation, to the disrupted annulus fibrosus may also contribute to low back pain symptoms. The disc normally expands and contracts during the daily cycle by applied force, contraction of trunk muscles, and gravity, causing a change in height of 1 to 1.5 mm or approximately a 15% change in volume.11,12 This slow cycling flushes out the free water loosely bound in the nucleus gel plus the nutrients and by-products.4,9,14,21,22 Firmly bound water within the hygroscopic gel does not fluctuate. Exchange of water and small molecular species occurs, but nutrients and waste products do not pass through the intact annulus; instead, the flow of these elements is through the end plates, across the thin, intact cartilage, and also through tiny (0.5 mm) perforations of the end plates.8,14,20,23 The flow is regulated by both applied and osmotic pressure gradients across the end plate. Through the tubular channels of these perforations, only small molecules are allowed to pass into the nucleus and inner annulus, while the potentially toxic anaerobic by-products pass out from them.8,20 At the outer end of these channels are located clumps of arteriolar tissue, which have been shown to behave like primitive glomeruli8,20 (▶ Fig. 4.3). Therefore, the passage of substances to and from the nucleus is controlled, allowing molecules smaller

Fig. 4.2 (a,b) Diagram of the innervation and parallel vascularity of the outer annulus—both pass together in the belt around the annulus. ALL, anterior longitudinal ligament; PLL, posterior longitudinal ligament. The gray ramus and the accompanying somatosensory nerve pass together from the sensory ganglion to the autonomic ganglion. The small free nerve endings and arterioles penetrate the outer layers of the annulus at right angles and then arborize within the six outer annular layers.

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Perez-Cruet et al, An Anatomic Approach to Minimally Invasive Spine Surgery, 2nd Ed. (ISBN 978-1-62623-643-1), copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.

Pathophysiology and Operative Treatment of Discogenic Back Pain

Fig. 4.3 Cross-section micrograph of the end plate of a rabbit disc showing the large venous passages of the vertebral spongiosa and a thin arteriolar layer just outside the end plate. The small clump of arteriolar tissue from which the descending passage originates is the equivalent microglomerulus. The descending tubular passage crosses the bony and cartilaginous end plate, through which nutrients and waste pass bidirectionally. (Reproduced with permission from Oki et al.8)

than about 200,000 Da (molecular diameters) to pass.4,14,20 Because body enzymes could destroy the hygroscopic behavior of the gel, this membrane acts as a protective barrier to enzyme passage. Changes in the end plate that alter the permeability of these microglomeruli will cause changes in the structure and behavior of the contained gel, then secondarily its mechanical behavior, and thirdly that of the annular fiber tightness, altering the stability of the entire segment. Potentially protecting and replenishing the gel could potentially preserve spinal stability and prevent discogenic back pain.4,5,11,12,24,25 With age there is a progressive loss of water within the nucleus pulposus leading to disc degeneration and disc space collapse. This process has been characterized using Thompson’s grading (▶ Fig. 4.4). The process of disc degeneration can be reproduced in an animal model of disc degeneration by needle puncture of the annulus in rabbits, thus mimicking what occurs in humans with annular tears26 (▶ Fig. 4.5). The accumulated anaerobic by-products of the nucleus and inner annulus are potentially neurotoxic. Lactic acid particularly accumulates in this anaerobic environment.4,15,16 When the internal pH is below 6.2, regeneration of the gel and inner annular fibers ceases. This is a major contributor to the degenerative cascade. Other by-products, such as metalloproteinases, stromelysin, and phospholipase A2, accumulate and are also neurotoxins.18,19 Thus, when the disc, like a belted automobile tire, loses its internal swelling pressure and its sidewalls or circumferential annular belts bulge, tears may occur.21,24,25 This result is much like a tire losing internal air pressure and flattening. In the disc, if the radial

Fig. 4.4 Progressive loss of nucleus pulposus integrity seen with aging of the disc and classified using the Thompson grading system. Illustration from top to bottom shows grade 1 to 5 as the disc progressively degenerates.

tears pass full thickness through the annulus, the neurotoxins may escape, and may reach and irritate the free nerve endings in the outer annular belt resulting in back and often radicular leg pain (see ▶ Fig. 4.4). Both plant and animal cell walls have phospholipids that help regulate water loss. When cells die, fracture, or wear out, the remaining cell wall lipid debris must be solubilized so it can be removed by the circulation. In response to cell wall disruptions, a rate-limiting enzyme, phospholipase A2, is released to convert the insoluble cell wall lipids into soluble arachidonic acid, but in so doing also releases prostaglandins and leukotrienes, both drivers of inflammation and pain.19 The level of phospholipase A2 is related to the degree of tissue injury. Because the disc nucleus is essentially sealed, the accumulation of phospholipase A2 is higher than in any other tissue. In an experiment at the University of California, San Diego,19 discograms using injections of saline solution were performed on normal and degenerated discs of

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Perez-Cruet, An Anatomical Approach to Minimally Invasive Spine Surgery | 01.10.18 - 10:53

Fundamentals

Fig. 4.5 (a–f) Fluoroscopic-guided needle puncture of the annulus fibrosus in the rabbit to (g,h) induce disc degeneration. (Reproduced with permission from Sheikh H, Zakharian K, Perez De La Torre R, Facek C, Vasquez A, Chaudhry R, Svinarich D, Perez-Cruet MJ. In vivo intervertebral disc regeneration using stem cell-derived chondroprogenitors. J of Neurosurgery (Spine) 2009;10:265-272.)

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Perez-Cruet et al, An Anatomic Approach to Minimally Invasive Spine Surgery, 2nd Ed. (ISBN 978-1-62623-643-1), copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.

Pathophysiology and Operative Treatment of Discogenic Back Pain patients. Samples from the disc spaces in the same patients were injected into bilateral sciatic nerves of rats. The sciatic nerves injected with samples collected from individuals with normal disc morphology produced only a mild inflammation, whereas the fluid from patients with degenerative discs destroyed the sciatic nerve, partly paralyzing the animal.19 Therefore, the toxic material in degenerated discs, even in submicroscopic quantities, can be pumped out through annular tears by the motion of the disc and cause severe disabling back pain. Furthermore, if the nearby ganglion is also reached, there may be permanent damage with altered sensation and weakness of a limb. This is highlighted with the reproduction of concordant disabling back or leg pain after the injection of less than 0.5 mL of normal saline or X-ray-visible contrast dye in some patients with tiny annular radial tears.27

4.2 Structure and Physiology of Disc Components Urban and McMullin9 at Oxford University have studied the physiology of disc degeneration. The following analysis and description of the constituents of the disc are in part drawn from their work. In keeping with the preceding discussion, they emphasize that “The ability of the discs to support compressive loads and allow flexion, bending, and torsion, depends on the organization and composition of the major macromolecules that make up this tissue.” The collagen fibers are common in the body, but the proteoglycans that compose the gel of the nucleus as well as the thin flexible layers between annular fiber layers are unique.13 The molecular configuration of the aggrecan resembles that of a feather, where the central shaft or spine is hyaluronic acid, a powerful hygroscopic material. The extending fronds of glycosaminoglycan are attached to the hyaluronic acid core by an amino group. The rather loose, feathery layout permits significant free water to become loosely trapped. This is the only nucleus in which water can move in and out under changes in applied force. However, water bound by the hyaluronic acid is not free to move. Numerous collagen subtypes are present within the intervertebral disc. The main composition of the disc collagen is type I and II collagen. More recently, collagen type IX mutations have been found to be associated with accelerated early degeneration and spondylolisthesis. Collagen IX is critical in the cross linking of collagen types II, IX, and XI and also participates in the adhesion between the disc and vertebral end plate. Specifically, the tryptophan mutations in the genes encoding COL9A2 and COL9A3 have been implicated in both epidemiological and twin studies to synergize with mechanical stressors such as a person’s occupation as genetic risk factors. In patients with Stickler’s syndrome who harbor an abnormality in collagen IX, numerous skeletal abnormalities, including early disc degeneration, are found. There are also shorter collagen fibrils within the nucleus.2 These are much finer and loosely scattered, providing minimal structural integrity to the otherwise freely mobile gel. Daily changes in loading of the spine alter the intradiscal water and its height; indeed, in the absence of applied load, such as in antigravity space, the disc heights of astronauts increase dramatically.5,7 The movements of solutes, nutrients, and waste into and out of the aggrecan are also related to its ionic charges. Viable cells of the inner disc, comprising only about 1% of its volume, are involved in the synthesis and replication of damaged cells,

proteoglycans, collagen fibrils, various enzymes, and balancing inhibitors.6 The degenerative cascade of the disc is related to not only end plate and permeability changes but also failure of these viable cells within the disc to produce, maintain, and repair disc tissues and the complex disc matrix.

4.3 Altered Metabolism, Degeneration of the Disc, and Discogenic Pain The metabolism of disc cells is affected by a number of factors. The limited access to a vascular bed is aggravated by atherosclerosis of segmental arteries and more so by cigarette smoking since nicotine is a strong vasoconstrictor. Sclerosis of the disc end plate also contributes to limited vascular access. Mechanically, the intervertebral discs are always subjected to forces. Within a tolerable range of forces, cells of the disc as well as the vertebral bone respond to increased loads by proliferation and strengthening. However, under excessive and prolonged forces, there may be vertebral, end plate, discal, and intradiscal cellular degeneration.4,5,11,12 A major change in disc loading, even for as little as 20 seconds or more, may alter intradiscal metabolic activity for several hours. The outer annulus, with its intrinsic vascular supply, is not so easily affected. Static loading, in addition to changing the disc height, also alters fluid and nutritional balance, which in turn may affect proteoglycan production and osmotic balance. As such, the intervertebral disc is better adapted to quadrupedal rather than bipedal postures.7 In accordance with Wolf ’s law, the normal lens-shaped intradiscal cavity of bipeds is primarily due to a hydrated nucleus. As the disc nucleus degenerates by losing its water-binding ability and shrinking, a process called desiccation, the end plates become narrowed, more planar, and even parallel. Further, the cells of the disc respond by producing metabolic growth factors and cytokines that stimulate disc growth and regeneration, although the capacity of these cells is not yet fully known.6,7 In summary, disc degeneration, which involves matrix, collagen, and aggrecan, usually begins with annular tears or alterations in the end plate nutritional pathways by mechanical or pathophysiologic means. However, the disc ultimately fails for cellular reasons. Progressive injury and aging of the disc occur normally in later life and abnormally after trauma or metabolic changes. In addition to the chemical effects on the free nerve endings as a source of discogenic pain, other factors may lead to chronic back pain disorders. Free nerve endings in the annular fibers may be stimulated by stretching as the disc degenerates and bulges and circumferential delamination of annular fibers occurs.28 Nonetheless, the vast majority of degenerated discs are essentially painless, likely related to variations in the location, concentration, and distribution of free nerve endings in the outer annuli. Certainly, back pain has many potential sources other than discal. Structures such as the facet joints, sacroiliac joints, and dorsal musculature can also be pain generators. When discogenic pain becomes severely disabling, satisfactory contemporary treatment is primarily through obliteration/removal of the degenerated nucleus and stabilization either by interbody fusion or total disc replacement with an artificial disc.1,27,28,29

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Fundamentals

4.4 Surgical Treatment of Discogenic Back Pain There has been a significant body of literature to support the surgical treatment of discogenic low back pain.29,30,31,32,33,34,35,36, 37,38,39,40,41,42,43,44,45,46,47,48,49,50,51 However, there has been a relative lack of evidence that clearly identifies those patients that may benefit from surgical intervention who suffer from discogenic low back pain. A study was conducted using provocative discography and CT to identify patients with refractory discogenic low back pain that might benefit from interbody lumbar fusion surgery. The interbody fusion replaces the degenerated nucleus pulposis with bone graft material and thus might be beneficial to these patients since the nucleus pulposus appears to represent the source of pain generators. Forty-three consecutive patients presenting with refractory chronic lower back pain and nonresponsive to conventional treatments underwent lumbar discography with subsequent CT studies of the injected disc segments. Concordant pain was defined as low back pain of similar character and location with an intensity of greater than 8 out of 10. Potential interbody fusion candidates were those who demonstrated a positive level discography and concordant annular tears on CT at no more than two contiguous levels and at least one negative control disc with intact annulus fibrosus. A total of 129 intervertebral disc levels were examined with 126 discs at risk and the remaining 3 previously fused52 (▶ Table 4.1). The results revealed that the volume of injected dye was significantly higher in patients with concordant pain (1.91 ± 1.19 mL) than those without (1.58 ± 1.05 mL, p < 0.05). Additionally, the volume of injected dye was significantly higher in patients with annular tears (2.01 ± 1.28 mL) than those without (1.25 ± 0.54 mL, p < 0.001) (▶ Fig. 4.6). Lumbar discography and postdiscography CT was performed with the aim to identify the source of the patient’s discogenic pain and identify the level at which to perform interbody fusion52 (▶ Fig. 4.7). Interbody fusion and instrumentation via a minimally invasive TLIF, extreme lateral, or ALIF approach was performed on patients that had one or two level disruption of the annulus fibrosus and corresponding concordant pain provided they had a negative control level52 (▶ Fig. 4.8). Those

patients that had disruption of the annulus fibrosus at all levels of injection and had either concordant or nonconcordant pain on discography were not deemed to be ideal surgical candidates and were treated with a variety of pain management modalities including epidural steroid injections, facet block, physical therapy, rhizotomy, etc.52 (▶ Fig. 4.9). Patients evaluated and treated in this manner had excellent clinical outcomes by showing statistically significant improvements in visual analog scale (VAS), Oswestry Disability Index (ODI), and both physical and mental SF-36 scores. ▶ Table 4.2 shows statistically significant improvement in patients’ outcomes (VAS, SF-36 mental and physical components, and ODI) after undergoing surgical interbody fusion for discogenic pain evaluated via lumbar discography at most postoperative time points. This study revealed that there was a significant association between concordant discogenic pain and annular tears, as determined by discography and CT, respectively. Discography in combination with CT can be a reliable diagnostic tool in identifying the location of pathologic discogenic back pain. Thus, surgery based on both positive discography and positive annular tears with a negative control disc leads to statistically significant symptomatic and functional outcome improvements. Table 4.1 Study results Lumbar level L3–L4

L4–L5

L5–S1

Pain score

4.84 ± 4.10

7.36 ± 4.97

9.30 ± 3.98

Concordant pain

9 (20.9%)

21 (50.0%)

33 (80.5%)

Annular tears

20 (43.9%)

33 (78.6%)

34 (79.1%)

Fusion recommended

6

18

30

Note: A total of 129 intervertebral disc levels were examined, with 126 discs at risk and the remaining 3 previously fused. (From Xi MA, Tong HC, Fahim DK, Perez-Cruet M. Using Provocative Discography and Computed Tomography to Select Patients with Refractory Discogenic Low Back Pain for Lumbar Fusion Surgery. Cureus. 2016 Feb 27;8(2):e514.)

Fig. 4.6 Showing the volume of injected dye was significantly higher in patients with concordant pain (1.91 ± 1.19 mL) than those without (1.58 ± 1.05 mL, p < 0.05). Additionally, the volume of injected dye was significantly higher in patients with annular tears (2.01 ± 1.28 mL) than those without (1.25 ± 0.54 mL, p < 0.001). (From Xi MA, Tong HC, Fahim DK, Perez-Cruet M. Using Provocative Discography and Computed Tomography to Select Patients with Refractory Discogenic Low Back Pain for Lumbar Fusion Surgery. Cureus. 2016 Feb 27;8(2):e514.)

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Pathophysiology and Operative Treatment of Discogenic Back Pain

Fig. 4.7 Lumbar discography showing (a–c) sagittal CT, corresponding (d–f) axial CT, and plain (g) AP, (h) lateral radiographs showing intact annulus fibrosus (AF) at the L3–L4 and L4–L5 levels and disruption of the AF at the L5–S1 level. Patient had concordant pain with injection at the L5–S1 level and nonconcordant or minimal pain with injection at the L3–L4 and L4–L5 levels. (i) Postoperative lateral radiography where L5–S1 minimally invasive TLIF was. Patient had an excellent clinical outcome. (From Xi MA, Tong HC, Fahim DK, Perez-Cruet M. Using Provocative Discography and Computed Tomography to Select Patients with Refractory Discogenic Low Back Pain for Lumbar Fusion Surgery. Cureus. 2016 Feb 27;8(2):e514.)

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45

Fundamentals

Fig. 4.8 Lumbar discography showing (a–c) sagittal CT, corresponding (d–f) axial CT, showing intact annulus fibrosus (AF) at the L3–L4 level and disruption of the AF at the L4–L5 and L5–S1 levels. Patient had concordant pain with injection at the L4–L5 and L5–S1 levels and nonconcordant or minimal pain with injection at the L3–L4 level. Postoperative (g) AP and (h) lateral radiography where L4–L5 and L5–S1 minimally invasive TLIF was performed. Patient had an excellent clinical outcome with resolution of back pain and returned to work full-time. (From Xi MA, Tong HC, Fahim DK, Perez-Cruet M. Using Provocative Discography and Computed Tomography to Select Patients with Refractory Discogenic Low Back Pain for Lumbar Fusion Surgery. Cureus. 2016 Feb 27;8(2):e514.)

4.5 Conclusion Proposals for replacement of the damaged nucleus through tissue grafting, injection of cytokines and growth factors, or genetic alteration of the disc tissue must take into account the hostile milieu of the degenerated disc. Methods will likely be needed to first modify this milieu before implanting new cells or tissue; otherwise, the new grafts will succumb to the same fate as the native tissues. As detailed earlier, the degenerative disc disease

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involves not only the contained tissues but also the end plates and their microvascular supply, which cannot at present be replaced or repaired.7,23 Therefore, future investigation into disc replacement therapy will require a multimodality approach. Currently, studies are being conducted to test the feasibility of stem cells to regenerate the disc.53 Future biological disc restoration offers exciting clinical options for clinicians and patients, but investigation into this evolving area of spinal surgery needs to include careful objective and prospective multicenter clinical trials.

Perez-Cruet et al, An Anatomic Approach to Minimally Invasive Spine Surgery, 2nd Ed. (ISBN 978-1-62623-643-1), copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.

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Pathophysiology and Operative Treatment of Discogenic Back Pain

Fig. 4.9 Lumbar discography showing (a–c) sagittal CT, corresponding (e–g) axial CT, showing disruption of the annulus fibrosus (AF) at all the levels injected and corresponding (d) AP, and (h) lateral plain radiographs. The patient experiences concordant or nonconcordant pain at all levels injected. This patient was not offered surgical intervention and was treated with nonoperative pain management. (From Xi MA, Tong HC, Fahim DK, Perez-Cruet M. Using Provocative Discography and Computed Tomography to Select Patients with Refractory Discogenic Low Back Pain for Lumbar Fusion Surgery. Cureus. 2016 Feb 27;8(2):e514.)

Table 4.2 Postoperative outcomes

VAS

Pre-op

2 wk

6 mo

≥ 12 mo

7.9 ± 2.8

4.8 ± 2.4

4.5 ± 3.1

4.0 ± 2.7

0.018

0.025

0.013

43.6±8.4

53.6±9.7

52.0±8.5

0.239

0.009

0.018

36.6 ± 11.5

32.2 ± 18.3

28.3 ± 16.9

0.010

0.020

0.009

p-Value SF-36 Mental

39.8±9.3

p-Value ODI p-Value

52.5 ± 9.3

Note: VAS, SF-36, and ODI postoperative outcome scores in patients suffering from discogenic low back pain and evaluated preoperatively with discography. (From Xi MA, Tong HC, Fahim DK, Perez-Cruet M. Using Provocative Discography and Computed Tomography to Select Patients with Refractory Discogenic Low Back Pain for Lumbar Fusion Surgery. Cureus. 2016 Feb 27;8(2):e514.)

References [1] Adams MA, Hutton WC. Gradual disc prolapse. Spine. 1985; 10(6):524–531 [2] Butler WF. Comparative anatomy and development of the mammalian disc. In: Ghosh P, ed. The Biology of the Intervertebral Disc. Boca Raton, FL: CRC Press; 1989:84–108 [3] Cassidy JD, Yong-Hing K, Kirkaldy-Willis WH, Wilkinson AA. A study of the effects of bipedism and upright posture on the lumbosacral spine and paravertebral muscles of the Wistar rat. Spine. 1988; 13(3):301–308 [4] Holm S, Maroudas A, Urban JP, Selstam G, Nachemson A. Nutrition of the intervertebral disc: solute transport and metabolism. Connect Tissue Res. 1981; 8(2):101–119 [5] Keller TS, Hansson TH, Holm SH, Pope MM, Spengler DM. In vivo creep behavior of the normal and degenerated porcine intervertebral disk: a preliminary report. J Spinal Disord. 1988; 1(4):267–278 [6] Oegema TR, Jr. Biochemistry of the intervertebral disc. Clin Sports Med. 1993; 12(3):419–439 [7] Thompson JP, Oegema TR, Jr, Bradford DS. Stimulation of mature canine intervertebral disc by growth factors. Spine. 1991; 16(3):253–260

[8] Oki S, Matsuda Y, Itoh T, Shibata T, Okumura H, Desaki J. Scanning electron microscopic observations of the vascular structure of vertebral end-plates in rabbits. J Orthop Res. 1994; 12(3):447–449 [9] Urban JPG, McMullin JF. Swelling pressure of the inervertebral disc: influence of proteoglycan and collagen contents. Biorheology. 1985; 22(2):145–157 [10] Boos N, Wallin A, Gbedegbegnon T, Aebi M, Boesch C. Quantitative MR imaging of lumbar intervertebral disks and vertebral bodies: influence of diurnal water content variations. Radiology. 1993; 188(2):351–354 [11] Paajanen H, Lehto I, Alanen A, Erkintalo M, Komu M. Diurnal fluid changes of lumbar discs measured indirectly by magnetic resonance imaging. J Orthop Res. 1994; 12(4):509–514 [12] Matsumoto T, Kawakami M, Kuribayashi K, Takenaka T, Tamaki T. Cyclic mechanical stretch stress increases the growth rate and collagen synthesis of nucleus pulposus cells in vitro. Spine. 1999; 24(4):315–319 [13] Sztrolovics R, Alini M, Roughley PJ, Mort JS. Aggrecan degradation in human intervertebral disc and articular cartilage. Biochem J. 1997; 326(Pt 1):235–241 [14] Whalen JL, Parke WW, Mazur JM, Stauffer ES. The intrinsic vasculature of developing vertebral end plates and its nutritive significance to the intervertebral discs. J Pediatr Orthop. 1985; 5(4):403–410

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Fundamentals [15] Bartels EM, Fairbank JC, Winlove CP, Urban JP. Oxygen and lactate concentrations measured in vivo in the intervertebral discs of patients with scoliosis and back pain. Spine. 1998; 23(1):1–7, discussion 8 [16] Ohshima H, Urban JP. The effect of lactate and pH on proteoglycan and protein synthesis rates in the intervertebral disc. Spine. 1992; 17(9):1079–1082 [17] Bogduk N, Tynan W, Wilson AS. The nerve supply to the human lumbar intervertebral discs. J Anat. 1981; 132(Pt 1):39–56 [18] Goupille P, Jayson MI, Valat JP, Freemont AJ. Matrix metalloproteinases: the clue to intervertebral disc degeneration? Spine. 1998; 23(14):1612–1626 [19] Saal JS, Franson RC, Dobrow R, Saal JA, White AH, Goldthwaite N. High levels of inflammatory phospholipase A2 activity in lumbar disc herniations. Spine. 1990; 15(7):674–678 [20] Oki S, Matsuda Y, Itoh T, Shibata T, Okumura H, Desaki J. Scanning electron microscopic observations of the vascular structure of vertebral end-plates in rabbits. J Orthop Res. 1994; 12(3):447–449 [21] Brown JW. Crew height measurement. The Apollo-Soyuz test project: Medical report. NASA SP411, 1977 [22] Hutton WC, Elmer WA, Boden SD, et al. The effect of hydrostatic pressure on intervertebral disc metabolism. Spine. 1999; 24(15):1507–1515 [23] Roberts S, Menage J, Urban JP. Biochemical and structural properties of the cartilage end-plate and its relation to the intervertebral disc. Spine. 1989; 14 (2):166–174 [24] Ishihara H, McNally DS, Urban JP, Hall AC. Effects of hydrostatic pressure on matrix synthesis in different regions of the intervertebral disk. J Appl Physiol (1985). 1996; 80(3):839–846 [25] Wilke HJ, Neef P, Caimi M, Hoogland T, Claes LE. New in vivo measurements of pressures in the intervertebral disc in daily life. Spine. 1999; 24(8):755–762 [26] Sheikh H, Zakharian K, De La Torre RP, et al. In vivo intervertebral disc regeneration using stem cell-derived chondroprogenitors. J Neurosurg Spine. 2009; 10(3):265–272 [27] Ray CD. The artificial disc: introduction, history, and socioeconomics. In: Weinstein JN, ed. Clinical Efficacy and Outcome in the Diagnosis and Treatment of Low Back Pain. New York, NY: Raven Press; 1992:205–225 [28] Anderson MW. Lumbar discography: an update. Semin Roentgenol. 2004; 39 (1):52–67 [29] Bachmeier B, Nerlich A, Weiler C, Paesold G, Jochum M, Boos N. Analysis of tissue distribution of TNF-alpha, TNF-alpha-receptors, and the activating TNF-alpha-converting enzyme suggests activation of the TNF-alpha system in the aging intervertebral disc. Ann N Y Acad Sci. 2007; 1096:44–54 [30] Block AR, Vanharanta H, Ohnmeiss DD, Guyer RD. Discographic pain report. Influence of psychological factors. Spine. 1996; 21(3):334–338 [31] Boden SD, Davis DO, Dina TS, Patronas NJ, Wiesel SW. Abnormal magneticresonance scans of the lumbar spine in asymptomatic subjects. A prospective investigation. J Bone Joint Surg Am. 1990; 72(3):403–408 [32] Borthakur A, Maurer PM, Fenty M, et al. T1ρ magnetic resonance imaging and discography pressure as novel biomarkers for disc degeneration and low back pain. Spine. 2011; 36(25):2190–2196 [33] Chen JY, Ding Y, Lv RY, et al. Correlation between MR imaging and discography with provocative concordant pain in patients with low back pain. Clin J Pain. 2011; 27(2):125–130 [34] Derby R, Kim BJ, Lee SH, Chen Y, Seo KS, Aprill C. Comparison of discographic findings in asymptomatic subject discs and the negative discs of chronic LBP patients: can discography distinguish asymptomatic discs among morphologically abnormal discs? Spine J. 2005; 5(4):389–394

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[35] Deyo RA, Weinstein JN. Low back pain. N Engl J Med. 2001; 344(5):363–370 [36] Eck JC, Sharan A, Resnick DK, et al. Guideline update for the performance of fusion procedures for degenerative disease of the lumbar spine. Part 6: discography for patient selection. J Neurosurg Spine. 2014; 21(1):37–41 [37] Gill K, Blumenthal SL. Functional results after anterior lumbar fusion at L5S1 in patients with normal and abnormal MRI scans. Spine. 1992; 17 (8):940–942 [38] Lim CH, Jee WH, Son BC, Kim DH, Ha KY, Park CK. Discogenic lumbar pain: association with MR imaging and CT discography. Eur J Radiol. 2005; 54 (3):431–437 [39] Margetic P, Pavic R, Stancic MF. Provocative discography screening improves surgical outcome. Wien Klin Wochenschr. 2013; 125(19–20):600–610 [40] McCarron RF, Wimpee MW, Hudkins PG, Laros GS. The inflammatory effect of nucleus pulposus. A possible element in the pathogenesis of low-back pain. Spine. 1987; 12(8):760–764 [41] Mummaneni PV, Dhall SS, Eck JC, et al. Guideline update for the performance of fusion procedures for degenerative disease of the lumbar spine. Part 11: interbody techniques for lumbar fusion. J Neurosurg Spine. 2014; 21(1):67–74 [42] Nachemson A, Elfström G. Intravital dynamic pressure measurements in lumbar discs. A study of common movements, maneuvers and exercises. Scand J Rehabil Med Suppl. 1970; 1:1–40 [43] Nesson S, Yu M, Zhang X, Hsieh AH. Miniature fiber optic pressure sensor with composite polymer-metal diaphragm for intradiscal pressure measurements. J Biomed Opt. 2008; 13(4):044040 [44] Ohtori S, Inoue G, Miyagi M, Takahashi K. Pathomechanisms of discogenic low back pain in humans and animal models. Spine J. 2015; 15(6):1347–1355 [45] Perez-Cruet M, Beisse R, Pimenta L, Kim D. Minimally Invasive Spine Fusion: Techniques and Operative Nuances. London: CRC Press; 2011 [46] Simmons JW, Emery SF, McMillin JN, Landa D, Kimmich SJ. Awake discography. A comparison study with magnetic resonance imaging. Spine. 1991; 16 (6) Suppl:S216–S221 [47] Sivan SS, Merkher Y, Wachtel E, Urban JP, Lazary A, Maroudas A. A needle micro-osmometer for determination of glycosaminoglycan concentration in excised nucleus pulposus tissue. Eur Spine J. 2013; 22(8):1765–1773 [48] Tong H, Carson J, Haig A, Quint D, Choksi V, Yamakawa K. Magnetic resonance imaging of the lumbar spine in asymptomatic older adults. J Back Musculoskelet Rehabil. 2006; 19:1–6 [49] Weishaupt D, Zanetti M, Hodler J, Boos N. MR imaging of the lumbar spine: prevalence of intervertebral disk extrusion and sequestration, nerve root compression, end plate abnormalities, and osteoarthritis of the facet joints in asymptomatic volunteers. Radiology. 1998; 209(3):661–666 [50] Wiesel SW, Tsourmas N, Feffer HL, Citrin CM, Patronas N. A study of computer-assisted tomography. I. The incidence of positive CAT scans in an asymptomatic group of patients. Spine. 1984; 9(6):549–551 [51] Zuo J, Joseph GB, Li X, et al. In vivo intervertebral disc characterization using magnetic resonance spectroscopy and T1ρ imaging: association with discography and Oswestry Disability Index and Short Form-36 Health Survey. Spine. 2012; 37(3):214–221 [52] Xi MA, Tong HC, Fahim DK, Perez-Cruet M. Using provocative discography and computed tomography to select patients with refractory discogenic low back pain for lumbar fusion surgery. Cureus. 2016; 8(2):e514 [53] Beeravolu N, Brougham J, Khan I, McKee C, Perez-Cruet M, Chaudhry GR. Human umbilical cord derivatives regenerate intervertebral disc. J Tissue Eng Regen Med. 2016

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Pathophysiology of Back Pain

5 Pathophysiology of Back Pain Jorge Mendoza-Torres and Mick J. Perez-Cruet Abstract This chapter reviews the definition of back pain and some of the pathophysiological factors leading to back pain. Back pain can be generated from a number of sources, including compression of nerve roots, the disc, ligaments, facets, sacroiliac joint, bone, and musculature. The goal of the minimally invasive spine surgeon is to identify the source of pain so that the least invasive procedure can be performed to achieve lasting pain resolution. Treating those levels or area of the spine not responsible for the patient’s symptoms can lead to iatrogenic tissue damage and less than optimal patient outcomes. Thus, understanding the pathophysiology of back pain disorders is critical to successful patient care. Keywords: back pain, pathophysiology, etiology, focused treatment, nociceptors, anatomy

5.1 Introduction Low back pain continues to be a major global health problem and a leading cause of disability.1 To better understand the complex nature of low back pain and to identify potential targets for treatment, previous studies have investigated patient characteristics associated with the course and severity of low back pain and associated disability. Factors identified to date include high baseline levels of pain and disability, older age, obesity, smoking, unemployment, poor general health, depression, anxiety, and widespread pain.2

5.2 Definition of Low Back Pain The International Association for the Study of Pain3 defines lumbar spinal pain as pain perceived anywhere within a region bounded by the last thoracic spinous process, the first sacral spinous process, and the lateral borders of the erectors spinae muscles (▶ Fig. 5.1a, b). They define sacral spinal pain as pain perceived anywhere in a region bounded by the first sacral spinous process, the posterior sacrococcygeal joints, and the posterior superior iliac spines. In the light of these definitions, back pain can be defined as lumbar spinal pain or sacral spinal pain or any combination of the two. The significance of this definition is not so much to establish what low back pain is, but to establish what it is not. Pain over the posterior thorax is not low back pain, but thoracic spinal pain (▶ Fig. 5.1c). For thoracic spinal pain, the differential diagnosis is different from that for low back pain, and a different evidence base applies.4 Pain over the gluteal region, not encompassing the lumbar spine or sacrum, does not constitute low back pain (▶ Fig. 5.1c). This type of pain could originate from the hip joint and surrounding structures (e.g., the sacral iliac joint). Pain over the loin is not back pain, and could have an etiology originating from the urinary tract or other viscera (▶ Fig. 5.1d).

5.3 Peripheral Pain Mechanisms Pain has been categorized by duration (acute vs. chronic), location (superficial, deep, bone, muscle, or visceral), and cause or type (inflammatory, neuropathic, cancer). Generally, activation of activity in nociceptors underlies the experience of pain regardless of how it is categorized.

5.3.1 Anatomy of Nociceptors The nociceptors are key players in understanding mechanisms of and managing pain. Nociceptors are sensory neurons with a cell body located in dorsal root, trigeminal, or nodose ganglia. All sensory neurons arising from these ganglia are pseudounipolar neurons with a central process terminating in the central nervous system (CNS; spinal dorsal horn) and a peripheral process terminating in a peripheral target such as the skin, muscle, or viscera5 (▶ Table 5.1). Nociceptors are said to have “free” (unencapsulated) nerve endings because peripheral terminals of these afferents do not appear to be associated with any specific cell type. Four distinct events are necessary for a nociceptor to convey information to the CNS about noxious stimuli impinging on peripheral tissues: 1. “Energy” from the stimulus (mechanical, thermal, or chemical) must be converted into an electrical signal. This process, referred to as signal transduction, results in a generator potential or depolarization of the peripheral terminal. 2. The generator potential must initiate an action potential, the rapid “all or nothing” change in membrane potential that constitutes the basic unit of electrical activity in the nervous system. 3. The action potential must be successfully propagated from the peripheral terminal to the central terminal. 4. The propagated action potential invading the central terminal must drive a sufficient increase in intracellular calcium ions to enable release of enough transmitters to initiate the whole process once again in the secondorder neuron. Distinct sets of proteins underlie each of these processes, and are therefore the targets of a wide variety of therapeutic interventions. The primary afferent’s presynaptic nerve terminal in the dorsal horn of the spinal cord represents a site for a therapeutic intervention. Primary afferent fibers transmit the pain signal to the spinal cord and possess numerous receptor systems that can reduce this transmission by reducing transmitter release such as the alpha2-adrenergic, glycinergic, serotoninergic, opioidergic, and GABAergic receptors as well as ion channels sensitive to local anesthetics and anticonvulsants including voltage-gated calcium, sodium, and potassium channels.

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Fundamentals

Fig. 5.1 (a,b) Topographic location of what is low back pain; (c,d) what is not low back pain.

5.4 Spinal Cord and Supraspinal Structures Aδ and C fiber neurons synapse primarily within laminae I, II, and V of the dorsal horn of the spinal cord. These primary afferents release neurotransmitters and neuropeptides that activate the second-order projection neurons of the spinal cord. Pain transmission through the spinal cord may be modulated by an endogenous descending pain inhibitory system and may be influenced by exogenously administered medications. The primary components of this descending pain inhibition system are the “triad” of the: 1. Periaqueductal gray (PAG). 2. Rostral ventromedial medulla (RVM). 3. Dorsal lateral pontine tegmentum (DLPT), which includes the locus coeruleus (LC) and the A7 nuclei.

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The PAG is an important site for the production of analgesia following systemic administration of opioids. The endogenous opioid [Met5]-enkephalin is present within this nucleus and opioid receptors of each subtype are present in this region. The PAG provides dense projections to the RVM and brainstem noradrenergic nuclei LC and A7. Although each of these regions has direct projections to the spinal cord, it has been proposed that their projections to the RVM are important components in the modulation of pain by these regions. The RVM can function as a relay nucleus in the production of antinociception by more rostral midbrain structures (PAG), but it also has a primary role in the suppression of nociceptive transmission at the level of the spinal cord. The suppression of nociceptive reflex behavior is thought to be mediated by the axons of RVM neurons that descend within the dorsolateral funiculus and terminate bilaterally in laminae I, II, V, VI, and VII of the spinal cord. Anatomical studies have shown these axons terminate coincident with

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Pathophysiology of Back Pain Table 5.1 Low back pain generators5 Disc

Bone

Nerve roots

Spinal muscle

The outer one-third of the annulus fibrosus is innervated by different pain nerve fibers

Pain can result from a traumatic fracture in the setting of normal bone

●

Compression secondary to: Herniated disc ● Lateral recess stenosis

Pain can be induced by mechanical pressure or stretch and can be relieved by rest

Chondrocytes within the nucleus pulposus produce phospholipase A2, which regulates the arachidonic acid cascade and liberates arachidonic acid from cell membranes at the site of inflammation

A pathologic fracture can be caused by the following: ● Osteoporosis ● Multiple myeloma ● Paget’s disease ● Primary spine tumor ● Metastatic spine tumor ● Osteomyelitis

Radiculitis may manifest as peripheral nerve root motor and sensory abnormalities

Anaerobic exercise leads to the accumulation of potential toxic metabolites

Phospholipase A2 generates membranedestabilizing products (unsaturated fatty acids), causing membrane injury and edema

Ischemia results in intermittent claudication

Spinal ligaments

Facet joint

Sacroiliac joint

Visceral sources

Chronic lifting may stress the spinal ligamentous complex (supraspinatus, interspinous, posterior longitudinal ligament, anterior longitudinal ligament, and ligamentum flavum)

Responsible for 15 to 40% of chronic low back pain symptoms

Cause of 5 to 10% of low back pain

Retroperitoneal inflammation

Ligamentum flavum contains nerve endings

The anatomy consists of paired synovial joint lined with a synovial membrane, an articular surface covered with hyaline cartilage, fibrous capsule, and mechanosensitive nociceptive fibers

Pain can be elicited with palpation Gallbladder, pancreas, kidney, and of the posterior inferior iliac spine, stomach dysfunction buttock, thigh, or groin region

The posterior longitudinal ligament has large numbers of free nerve endings and is innervated by the sinuvertebral nerves (a branch of the somatic ventral rami and autonomic gray ramus communicans)

Facet joints connect the inferior articular process of the vertebra above and the superior articular process of the vertebra below

Sacroiliac joint dysfunction may result in axial and referred to lower limb pain

Intrapelvic pathology

The anterior longitudinal ligament receives innervation from the gray ramus communicans and ventral rami

spinothalamic tract cells and interneurons of the dorsal horn that are related to pain transmission. Consistent with the anatomical terminations of the RVM axons, physiological studies have shown that stimulation of the RVM results in the inhibition of a population of pain-specific neurons within the dorsal horn. Spinally projecting neurons of the RVM possess numerous neurotransmitters including serotonin, enkephalin, GABA, glutamate, and substance P. The DLPT contains all of the noradrenergic neurons that project to the RVM and the spinal cord. In animal models, electrical stimulation of the DLPT sites produces analgesia and the analgesia produced by the activation of these nuclei is mediated by the alpha-2 adrenergic receptor. The physician can pharmacologically manipulate each of these neurotransmitter systems to modulate pain transmission throughout the CNS.

5.5 Descending Pathways of the Central Nervous System There are descending pathways from the cortex that modulate sensory impulses. For example, somatotopically organized fibers

from the S1 terminate in the thalamus, brainstem, and spinal cord, which selectively modulate both facilitating and inhibiting sensory signals from specific receptors and/or areas of the body. The inhibitory effects are most common and are usually transmitted through inhibitor interneurons. The sensory system is designed to react to the dynamic nature of the environment. As a result, sensory signals are highly monitored at multiple levels of the nervous system.4 Collateral fibers from the PAG modulate both descending and ascending pain pathways. The PAG has been experimentally demonstrated to produce analgesia when stimulated and is felt to play a major role in modulating nociception at the level of the dorsal horn as well as at higher levels of the CNS.6 The PAG receives signals from limbic and cortical centers involved in the affective component of pain. The descending signal from the PAG travels through the nucleus raphe magnus (NRM) in the medulla as well as the medullary reticular formation. The serotonergic NRM fibers descend to inhibit peripheral nociceptors in the dorsal horn in laminae I and II. Clinically, this descending system blocks the spinal withdrawal reflex at the level of the dorsal horn. The PAG has

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Fundamentals ascending connections, which may modulate sensory signals at the level of the thalamus. The PAG also supplies the reticular activating system responsible for arousal to painful stimuli. Of note, there are a number of other pathways in the CNS, which modulate the sensation of pain and the response to nociceptive input.

5.6 Physiology of Back Pain The physiological cause of back pain cannot be established definitively in up to 85% of patients.7 However, pain has a wide variety of qualities and arises through a number of different types of sensory innervation.8 Deep somatic pain has its source in the vertebral column, the muscles, tendons, ligaments and fascia supplied by the sinuvertebral nerves, and the unmyelinated pain fibers of the posterior primary rami of spinal nerves. Examples include: neurogenic pain, for example, femoral neuropathy, resulting from the involvement of the sensory portion of the peripheral nerve; and referred pain, which can arise from viscera sharing segmental innervation with the lumbosacral spine. A potential source of back pain is compression of the exiting nerve root and dorsal root ganglion. This severe debilitating pain is often experienced by those patients suffering from spondylolisthesis with subluxation of one vertebral body with respect to another. This anatomy results in compression of the exiting nerve root and dorsal root ganglion as it passes through the neural foramina. This process can also result in engorgement of the perineural vascular sheath and further lead to relative hyperemia of the nerve root. The symptoms tend to be worsened by axial loading as seen in standing, walking, and increased activity. Thus, an effective treatment of this condition is restoration of foraminal height and disc height achieved with interbody fusion and reduction using pedicle screws to restore sagittal alignment and foraminal diameter9 (▶ Fig. 5.2 and ▶ Fig. 5.3). Radicular pain is characteristic of a herniated disc or spinal stenosis and occurs as a result of inflammation of the nerve or any process that reduces blood flow to the proximal spinal nerves. The distinguishing clinical features are described in ▶ Table 5.2, and the signs are described in ▶ Table 5.3. The pathophysiology mechanisms are illustrated in ▶ Fig. 5.4. Ninety-eight percent of clinically important disc herniations occur at L4–L5 and L5–S1.10,11 Finally, central pain is perceived at the level of the cerebral cortex. Patients displaying this type of pain typically describe pain that fails to follow anatomical patterns and may have yellow flags (e.g., markers of chronicity) (see ▶ Table 5.2).

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5.7 Conclusion Low back pain is a common condition that affects the majority of individuals in their lifetime. Understanding the etiology of low back pain can lead to focused treatments that can provide improved outcomes. Surgical treatments such as minimally invasive decompression and transforaminal lumbar interbody fusion (TLIF) can result in lifelong cure of chronic debilitating back pain conditions such as lumbar spondylolisthesis. Additional studies to further understand the pathophysiology of low back pain conditions can lead to more cost-effective care for patients suffering from debilitating back pain disorders.

Clinical Caveats ●

●

●

●

●

●

●

●

●

●

Eighty-four percent of the population experience at least one episode of low back pain in their lifetime. In total, 26.4% experienced at least one full day of back pain in the past 3 months. Low back pain is a common, frequently recurring condition that often has a nonspecific cause. History and physical examination should focus on evaluation for evidence of systemic or pathologic causes. Imaging is only indicated when there is evidence of neurologic deficits or red flags to suggest fracture, malignancy, infection, or other systemic disease, or when symptoms do not improve after 4 to 6 weeks. Most nonspecific low back pain will improve within several weeks with or without treatment. Back pain that radiates to the lower extremities, occurs episodically with walking or standing erect, and is relieved by sitting or forward spine flexion is typical of neurological claudication and suggests central spinal stenosis. All patients with acute or chronic low back pain should be advised to remain active. Treatment of chronic nonspecific low back pain involves a multidisciplinary approach targeted at preserving function and preventing disability. Surgery is indicated in the presence of severe or progressive neurologic deficits or signs and symptoms of cauda equina syndrome.

5.8 Acknowledgment We acknowledge Reynoso-Tapia Dania, MD, for her illustrations for this chapter.

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Pathophysiology of Back Pain

Fig. 5.2 Etiology of back pain can include: (a) spondylolisthesis resulting in (b) compression of exiting nerve root and dorsal root ganglion as it exits the neural foramen.

Fig. 5.3 (a) Sagittal and axial T2-weighted MRI showing grade 1 spondylolisthesis with associated stenosis. (b) Postoperative sagittal and axial CT showing restoration of sagittal alignment with adequate neural decompression.

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Fundamentals Table 5.2 Clinical features of radicular pain Simple back pain

Radicular pain

Inflammatory pain

Serious causes of back pain (red flags)

90% of acute low back pain

5% of acute low back pain

1% of acute low back pain

< 1% of acute low back pain

Age: 20–55 years old

Unilateral leg pain worse than low History of morning stiffness for back pain more than 30 min for 6 or more weeks

< 20 or > 55 years old

Pain location: low back, buttocks, thighs

Radiates to foot or toes

Pain improves with exercise but not rest

No mechanical pain

Mechanical pain

Numbness or paresthesia in same distribution

Alternating buttocks pain

Thoracic pain

Markers of chronicity (yellow flags)

Straight leg raising reproduces pain

History of psoriasis, inflammatory bowel disease, uveitis, spondyloarthropathy

Red flags for spine fracture

Fear-avoidance behavior and reduced activity levels

Localized neurological signs

Major accident or minor trauma in patient with osteoporosis

Tendency to low mood and withdraw from social interaction

Red flags for cancer, infection

A belief that back pain is harmful or potentially severely disabling

History of carcinoma, steroids, HIV, immunosuppression, IV drug abuse, recent infection

Expectation of passive treatment rather than a belief that active participation will help

Weight loss, unwell

Dissatisfaction at work

Red flags for cauda equina compression

Problems with claims, compensation, or time off work

Saddle anesthesia, bladder dysfunction, fecal incontinence

Table 5.3 Signs of radicular pain

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Nerve root

L4

L5

S1

Pain radiation

Lateral, anterior thigh

Lateral leg

Posterior leg

Numbness

Anterior

Lateral calf

Posterior calf and sole, lateral border of foot

Motor weakness

Knee extension

Dorsiflexion of the great toe and foot

Plantar flexion: toe, foot

Reflexes

Decreased knee jerk

None reliable

Decreased ankle jerk

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Pathophysiology of Back Pain

Fig. 5.4 Low back pain mechanisms: inflammatory agents induce sensitization, stimulation, and degeneration of the nerve provoking mechanical, nociceptive, neuropathic, and central pain.

References [1] Vos T, Flaxman AD, Naghavi M, et al. Years lived with disability (YLDs) for 1160 sequelae of 289 diseases and injuries 1990–2010: a systematic analysis for the Global Burden of Disease Study 2010. Lancet. 2012; 380(9859):2163–2196 [2] Grotle M, Foster NE, Dunn KM, Croft P. Are prognostic indicators for poor outcome different for acute and chronic low back pain consulters in primary care? Pain. 2010; 151(3):790–797 [3] Australian Acute Musculoskeletal Pain Guidelines Group. Evidence-Based Management of Acute Musculoskeletal Pain. Brisbane: Australian Academic Press; 2003 [4] Vanegas H, Schaible HG. Descending control of persistent pain: inhibitory or facilitatory? Brain Res Brain Res Rev. 2004; 46(3):295–309 [5] Tasker R. Central pain states. In: Loeser JD, ed. Bonica’s Management of Pain. 3rd ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2001:433–457

[6] Deyo RA, Rainville J, Kent DL. What can the history and physical examination tell us about low back pain? JAMA. 1992; 268(6):760–765 [7] Borenstein DG. Low back pain. In: Klippel JH, Dieppe PA, eds. Preface to Rheumatology. 2nd ed. London: Mosby; 1998 [8] Perez-Cruet MJ, Hussain NS, White GZ, et al. Quality-of-life outcomes with minimally invasive transforaminal lumbar interbody fusion based on longterm analysis of 304 consecutive patients. Spine. 2014; 39(3):E191–E198 [9] Bigos S, Bowyer O, Braen G, Brown K, Deyo R, Haldeman S, et al. Acute Low Back Problems in Adults. Clinical Practice Guideline 14. Rockville, MD: AHCPR Publication No. 95-0642. Agency for Health Care Policy and Research, Public Health Service, US Department of Health and Human Services; December 1994 [10] Golob AL, Wipf JE. Low back pain. Med Clin North Am. 2014; 98(3):405–428 [11] Merskey H, Bogduk N, eds. Classification of Chronic Pain: Descriptions of Chronic Pain Syndromes and Definitions of Pain Terms. 2nd ed. Seattle, WA: IASP Press; 1994

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Fundamentals

6 Rationale for Minimally Invasive Spine Surgery Manish K. Kasliwal, Mick J. Perez-Cruet, Lee A. Tan, Richard G. Fessler, Larry T. Khoo, and Moumita S.R. Choudhury Abstract This chapter discusses the rationale for minimally invasive surgery in treating spinal disorder. Effectively addressing spinal pathology of the cervical, thoracic, and lumbar spine in a minimally invasive fashion leads to better patient outcomes and significantly reduces the cost of care by leading to faster patient recoveries and return to activities of daily living and high-quality lifestyles. These goals represent an evolution in spine surgery for the treatment of a variety of spinal disorders. Patients will continue to seek out those surgeons that have mastered minimally invasive spinal surgery. Keywords: rationale, preservation, spinal anatomy, cervical, thoracic, lumbar

6.1 Introduction Minimally invasive spinal surgery (MISS) has experienced an exponential growth over the last decade. A growing number of spine surgeons now routinely utilize MISS techniques to treat a wide range of spinal pathologies that traditionally required large incisions with wide tissue dissections. With the continuing innovation and improvements in minimally invasive instrumentations and techniques, MISS is altering treatment paradigms across the whole realm of spine surgery.1 There has been revolution in the treatment of spinal pathologies from the time before the advent of metallic fixation as compared to the present era of spinal surgery as can be seen in ▶ Fig. 6.1.

6.2 Goals and Benefits of MISS The primary goals of MISS are to reduce approach-related tissue injury and complications in order to reduce postoperative pain, blood loss, and recovery time while achieving the same clinical objectives.2,3 Preclinical, histological, serological, radiological, and clinical outcome data have demonstrated clear evidence of extensive iatrogenic tissue injuries associated with typical open posterior spinal approaches.4 Further evidence has emerged to reveal significant reductions in muscle injury, pain, and disability with

MISS techniques compared with open techniques for lumbar fusion.5 With traditional open posterior approaches for lumbar decompression, extensive injury to the paraspinous soft tissue is common and midline ligaments are completely removed during the exposure. The result of these disruptions to the patient’s native anatomy can lead to substantial pain and muscular atrophy.6,7 Several studies have documented negative effects of paraspinal muscle injury including weakness, disabilities, and pain. The MISS techniques are less destructive to the paraspinal muscles and have the potential to facilitate better clinical outcomes (▶ Fig. 6.2). While initial applications of MISS were limited to conditions such as discectomy and decompression,2,8 its applications have been expanded to include a wide variety of more complex pathologies including: traumatic spinal fractures, spinal column and spine cord tumors, and spinal deformity.9,10,11,12,13 Given the emphasis on “evidence-based medicine” and “cost-effectiveness” in the current health care environment, it is important to understand the rationale and available evidence that demonstrates advantages of MISS for various pathologies. This chapter will summarize the rationale for application of various MISS techniques for commonly treated pathologies of the cervical, thoracic, and lumbar spine. The purported benefits of MISS are summarized below.1,2,3,14,15,16

Advantages of Minimally Invasive Spinal Surgery ● ● ●

●

● ● ● ●

Decreased soft-tissue and muscle injuries. Decreased intraoperative blood loss. Reduced postoperative pain and decreased pain medications requirement. Faster recovery, shorter hospital stay, and less rehabilitation required. Better cosmetic results from smaller skin incisions. Reduced risk of postoperative infection. Decrease in overall medical cost and earlier return to work. Less likely to cause adjacent-level disease by minimizing disruption of ligaments and musculature.

Fig. 6.1 (a) Ancient historical treatment of deformity by traction-based apparatus inset treatment of deformity with multi-segmental instrumentation. (b) Current minimally invasive correction of spondylolisthesis using (c) minimally invasive techniques.

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Rationale for Minimally Invasive Spine Surgery

Fig. 6.2 (a) Postoperative magnetic resonance imaging (MRI) sagittal (left inset axial image) showing extensive posterior scar tissue and (right inset axial image) adjacent-level stenosis created by extensive removal of lamina and spinous processes following traditional laminectomy for stenosis. Compare (b) preoperative sagittal and axial T2-weighted MRI showing lumbar stenosis treated with minimal invasive laminectomy with (c) postoperative sagittal and axial MRI demonstrating adequate decompression with preservation of the spinous processes and minimal scar formation and tissue damage.

6.3 Minimally Invasive Approaches in the Cervical Spine 6.3.1 Anterior Approaches The anterior cervical microforaminotomy and the endoscopicassisted anterior cervical discectomy and fusion are the two most commonly used MISS procedures in the anterior cervical spine. The anterior cervical microforaminotomy was first described in 1968 by Verbiest17 for the treatment of vertebral ar-

tery insufficiency. In essence, Verbiest’s approach is a slightly lateralized modification of the standard anterior approaches as described by Cloward, Robinson, and Smith.18 However, popularity of this approach for the treatment of spondylotic cervical radiculopathy has been limited due to the concerns for injuries to the vertebral artery and the intervertebral disc complex. Most recently, this approach has been popularized in the literature by Jho,19,20 who applied modern microsurgical techniques and instruments to the operation with great success. However, the excellent clinical results and the already “minimally

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Fundamentals invasive” nature of the traditional anterior cervical approach,18 along with the lack of reproducibility of the results of anterior endoscopic approaches as reported by Jho,19,20 have impeded the widespread application and adoption of minimally invasive anterior approaches of the cervical spine.

6.3.2 Posterior Approaches A number of cervical spine pathologies can be effectively treated with posterior decompression. The posterior cervical approach avoids many complications associated with the anterior cervical approach, including esophageal injury, recurrent laryngeal nerve paralysis, dysphagia, and adjacent-level disease.21 While the standard open posterior cervical approach can achieve excellent decompression of the lateral recess and neural foramen, the exposure often requires extensive stripping of paraspinal musculature that can lead to significant postoperative pain, muscle spasm, and dysfunction.22 In addition, disruption of ligaments and the posterior tension band can contribute to development of kyphotic deformity postoperatively; the fear of this complication prompted many spine surgeons to fuse the spine along with decompression or to perform laminoplasty instead (▶ Fig. 6.3). Minimally invasive approaches have been developed to avoid these pitfalls of open surgery. Developments in percutaneous surgical access, optical technology with high-magnification endoscopes, neuroanesthetic techniques, and noninvasive imaging modalities have brought posterior foraminotomy into a new millennium of spine surgery. In 2002, the senior author23 reported the initial experience of posterior cervical microendoscopic foraminotomy (CMEF) in a case–control cohort study where 25 patients with cervical root compression from either foraminal stenosis or disc herniation were compared to another 26 patients treated via open cervical laminoforaminotomy. CMEF cases had less blood loss (138 vs. 246 mL per level), recovered more rapidly, had a shorter postoperative stay (20 vs. 68 hours), and needed fewer narcotics (11 vs. 40 equivalents). There were two durotomies after CMEF. Overall, the CMEF procedure yielded symptomatic improvement for approximately 87 to 92% of patients, depending on which symptom was analyzed. After CMEF, the patients with radiculopathy experienced

resolution of their symptoms in 54%, improvement in 38%, and no change in 8% of cases. For open surgery, radiculopathy resolved in 48%, improved in 40%, and remained unchanged in 12%. For neck pain, the CMEF results were 40% resolved, 47% improved, and 13% unchanged. Open results for neck pain were 33% resolved, 56% improved, and 11% unchanged. Overall, the posterior CMEF technique yielded clinical results equivalent to those of the open surgical group; however, CMEF patients had less blood loss, shorter hospitalizations, and a much lower postoperative pain medication requirement. Several other studies have reported excellent clinical results and have endorsed the clinical efficacy and advantages of minimally invasive cervical foraminotomy.24,25,26 While a number of studies have utilized tubular retractors and microscopes instead of endoscopes as described initially, the overall technique remains the same. In addition to foraminotomy, posterior cervical endoscopic and percutaneous techniques have also been used for more extensive procedures including laminectomy.27

6.4 Minimally Invasive Approaches in the Thoracic Spine 6.4.1 Thoracic Disc Herniation The management of symptomatic thoracic disc herniation (TDH) has significantly evolved along with the technological advancement in the field of spine surgery. Better understanding of the pathology and evolution of minimal access techniques have provided newer treatment options with decreased morbidity as compared to open posterior and transthoracic approaches. Several minimally invasive posterolateral and anterior approaches have been developed in the last decade to treat various TDH pathologies with the selection of best approach dependent on mediolateral localization of the disc herniation, presence or absence of calcification, health of the patient, and experience of the surgeon.28 There is absence of randomized controlled studies comparing minimally invasive approaches to open approaches for TDH, with most of the evidence being restricted to level III studies. Posterior approaches can be employed at any

Fig. 6.3 (a,b) Postoperative plain X-ray images and incision with atrophy of paraspinous muscles seen after multilevel cervical laminectomy, fusion, and instrumentation. However, it appears this condition is better tolerated in the cervical spine compared to the lumbar spine, most likely due to less loading forces.

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Rationale for Minimally Invasive Spine Surgery level, and its utility depends largely on the location of the disc herniation. The laterally located disc herniation is much more accessible via the posterior approach. The posterior approaches are much better tolerated by patients with medical comorbidities, especially in patients with existing pulmonary disease.28 Chi et al29 compared the minimally invasive transpedicular approach using tubular retractors with open posterolateral approach. The authors concluded that a mini-open transpedicular discectomy for TDHs results in better modified Prolo scores at early postoperative intervals and less blood loss during surgery than open posterolateral discectomy. However, a centrally located, giant calcified TDH is best treated via an anterior approach to maximize visualization and to minimize spinal cord manipulation.30 Bartels and Peul31 compared mini-thoracotomy (mini-TTA) versus thoracoscopy for the treatment of calcified thoracic herniated disc. Seven patients underwent a thoracoscopy, and 21 patients underwent mini-TTA. There was no statistically significant difference in duration of surgery, duration of the necessity of a chest drain, intraoperative blood loss, or duration of the postoperative stay on the intensive care unit (ICU) between the two groups. The authors concluded that though both the techniques had similar clinical outcomes, the mini-TTA had some theoretical advantages over a thoracoscopy allowing classic microsurgical bimanual techniques (▶ Fig. 6.4). The key driver for minimally invasive anterior or lateral approaches for TDH has been the fact that morbidities associated with thoracotomy are significant, which may include postthoracotomy pain in as many as 50% of patients and continuing 4 to

5 years postoperatively in 30% of patients.32 Thoracoscopic approaches were the initial minimally invasive alternative to open thoracotomy for large calcified thoracic disc and were largely successful in providing results similar to those of open procedures but with less blood loss, less approach-related morbidity, and faster recovery time ultimately translating into reduced exposure-related morbidity. However, practical implementation of thoracoscopic techniques is challenging because of the 2D visualization of 3D pathology, the high costs of instrumentation, and the need for highly trained staff, the relative difficulty in managing intraoperative complications, and an extended learning curve.33,34 The mini-open lateral approach represents a middle-ground alternative between endoscopic and open-approach procedures for the treatment of large anterior symptomatic TDH providing direct visualization and an adequate working field for TDH and does not require single-lung intubation.34,35 In fact, the retropleural minimally invasive approach is our preferred approach for centrally located TDH (▶ Fig. 6.5). We published our clinical experience with this approach in seven patients (ages: 30–70 years) with central TDH.35 All patients presented with thoracic myelopathy on physical examination. The average length of stay in the hospital was 2.6 days (range: 1–4 days). Three of the seven patients improved by one point on the Nurick scale. There were no complications related to the approach. Another study by Uribe et al34 included 60 patients from five institutions who were treated using a mini-open lateral approach for 75 symptomatic thoracic herniated discs with or without calcification. The median operating time, estimated blood loss (EBL), and length Fig. 6.4 (a,b) Intraoperative images showing mini-thoracotomy technique and (c) bone harvested from surgical site for expandable cage reconstructions for treating a large calcified thoracic disc herniation with spinal cord compression. (d) Local autograft was collected during vertebral corpectomy using the BoneBac Press (Thompson MIS, Salem, NH) and used for fusion material.

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Fundamentals

Fig. 6.5 (a) Preoperative axial and (b) sagittal CT/myelogram showing large central calcified thoracic disc herniation. (c) Postoperative coronal (d) axial and (e) sagittal CT after removal of thoracic disc herniation and reconstruction. (f) Photo showing minimally invasive thoracotomy incision.

of stay were 182 minutes, 290 mL, and 5.0 days, respectively. Four major complications occurred (6.7%): pneumonia in 1 patient (1.7%); extrapleural free air in 1 patient (1.7%), treated with chest tube placement; new lower-extremity weakness in 1 patient (1.7%); and wound infection in posterior instrumentation in 1 patient (1.7%). Excellent or good overall outcomes were achieved in 80% of the patients, a fair or unchanged outcome resulted in 15%, and a poor outcome occurred in 5%. Both studies endorse the efficacy of this technique as a less invasive option than conventional surgical techniques providing the rationale for minimally invasive approach for this condition.

6.4.2 MISS for Thoracolumbar Spine Fracture Stabilization Thoracolumbar fractures are relatively common problems encountered by spine surgeons, with an estimated incidence of more than 160,000 cases per year in the United States.36 Various authors have reported the utilization of endoscopic techniques in

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the management of thoracolumbar trauma with excellent clinical outcomes and minimal approach-related complications. In 2002, Khoo et al37 published a large series consisting of 371 patients with thoracoscopic-assisted treatment of thoracolumbar fractures. There were five cases (1.3%) of serious complication consisting of aortic injury, splenic contusion, neurological deterioration, cerebrospinal fluid leak, and severe wound infection. Compared to a control group of 30 patients with open thoracotomy, the thoracoscopic group required 42% less narcotics for postoperative pain. Several other clinical series have demonstrated the feasibility of various endoscopic approaches for management of these fractures with very low rate of complications.38,39,40,41 A recent review article by Koreckij et al42 demonstrated that the overall complication rate for standard open approaches to the spine was 11.5%, including 0.33% mortality, 0.16% paraplegia, and 9.17% postthoracotomy pain syndrome. Therefore, the minimally invasive endoscopic-assisted approach compares favorably in terms of approach-associated complications. Nevertheless, the current level of evidence for utilization of minimally invasive

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Rationale for Minimally Invasive Spine Surgery approaches to manage traumatic thoracolumbar burst fractures is low with lack of high-quality prospective controlled trials.43

6.5 Minimally Invasive Approaches in the Lumbar Spine 6.5.1 Lumbar Microdiscectomy Lumbar disc herniation is one of the most common conditions encountered by spine surgeons. This can be envisaged from the fact that an estimated 300,000 discectomies are performed annually in the United States alone.44 Although open discectomy (OD) performed with or without an operating microscope remains the standard and highly effective treatment for lumbar disc herniations,45,46 minimally invasive discectomy (MID) via tubular retractor system using either a microscope or an endoscope has been increasingly utilized given its potential benefits of less muscle damage, decreased pain, and faster recovery period after surgery.47,48,49,50,51 In addition, in morbidly obese patients, the minimally invasive approach using tubular dilators makes access to the disc space much quicker, the incision much smaller, and the risk for wound complications much less. Advances in muscle-sparing technology to approach the spine have eliminated the need for K-wire and serial muscle dilators (▶ Fig. 6.6). A number of recent prospective randomized controlled studies have compared clinical outcomes following OD versus minimally invasive microdiscectomy. Righesso et al52 performed a prospective controlled randomized study consisting of 40 patients with sciatica secondary to lumbar disc herniation who failed conservative treatment and subsequently underwent OD or microendoscopic discectomy (MED) with 24-month followup. They found that the final clinical and neurological results were satisfactory in both the OD and the MED groups, but the MED group had smaller incisions and shorter length of hospital stay. This result should not be surprising given the goal of discectomy is to remove the disc fragment compressing the neural element, regardless of the approach. The advantage of MISS is

smaller incision and less tissue trauma, therefore quicker recovery and shorter length of stay, which were all confirmed by the results of the study. Many other published studies echoed these results.53,54 Huang et al conducted a randomized trial and demonstrated that there was less systemic cytokine response in patients following microendoscopic versus open lumbar discectomy.55 The difference in the systemic cytokine response supports the notion that MED is less traumatic and causes less inflammatory response. Teli et al56 studied 240 patients aged 18 to 65 years affected by posterior lumbar disc herniation who failed 6 weeks of conservative management. These patients were randomized to microendoscopic, microdiscectomy, or OD groups. They reported higher risk of dural tears and recurrent herniation with lumbar MED.56 A recent meta-analysis by Dasenbrock et al51 analyzed the results of six randomized trials comprising 837 patients (of whom 388 were randomized to MID and 449 were randomized to OD). They failed to demonstrate any advantage of MID as compared to OD and reported that intraoperative complications (incidental durotomies and nerve root injuries) were significantly more common in patients undergoing MID (relative risk [RR], 2.01; 95% confidence interval [CI], 1.07–3.77). There was no significant difference in relief of leg pain between the two approaches with either short- or long-term follow-up. While most studies concluded that both the MISS and open microdiscectomies lead to equivalent improvements in leg pain postoperatively, these studies were relatively small (n = 22–200 patients), and they were underpowered to detect some potentially clinically relevant differences between the two surgeries. Ultimately, the true benefits of MISS techniques are unlikely to be realized in a procedure that already has low complication rates and morbidity with rapid recovery rates, leading to heterogeneous outcomes from underpowered studies with variable applications of the techniques in variably skilled surgeons’ hands. Discovering the true benefits for MID requires an understanding of the roles played by surgeon experience, patientspecific factors (e.g., obesity or comorbidities), and the type and magnitude of the procedure performed. Only then can appropriate studies be designed to address the most compelling

Fig. 6.6 (a–c) Surgical approach to the spine via a muscle-splitting fashion using the One-Step-Dilator (Thompson MIS) eliminates K-wire and serial muscle dilators.

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Fundamentals clinical concerns. Another point to keep in mind is that MISS is a relatively new technique with significant learning curve; therefore, the complication rates may be slightly higher during the early part of the learning curve. McLoughlin and Fourney57 demonstrated that the operative time and complication rate associated with MID both decreased over time with increased experience.

6.5.2 Minimally Invasive Decompression/Laminectomy Lumbar stenosis commonly occurs with aging and spinal degeneration. Fortunately, surgical treatment of symptomatic lumbar stenosis is highly effective in symptomatic relief.58,59 Even though minimally invasive lumbar decompression was first independently described by the senior author and Palmer et al2,60 more than a decade ago, there is yet to be a large prospective, randomized study that compares the clinical outcomes of open approaches versus MISS for lumbar decompression. Most of the data comparing outcome for open versus minimally invasive lumbar decompression are level II or III. Nevertheless, the unilateral laminotomy/internal laminectomy for bilateral decompression had become the minimally invasive surgery (MIS) procedure of choice for many spine surgeons in treatment of lumbar stenosis. A number of prospective and retrospective studies with midto long-term outcomes suggest that this approach has a superior overall clinical success rate compared with open laminectomy. In 2002, Khoo et al2 published a series consisting of 25 consecutive patients treated with MEDS and retrospectively compared to a historical control group of 25 consecutive patients treated with open laminectomies. There was a statistically significant decrease in intraoperative blood loss (68 vs. 193 mL), postoperative narcotic requirement (31.8 vs. 73.7 eq), and length of hospital stay (42 vs. 94 hours). At 1-year followup visit, 90% of the patients in the MEDS group reported improved or complete resolution of their pain symptoms.2 In a recent prospective randomized clinical study by Mobbs et al,61 the authors compared minimally invasive unilateral laminectomy for bilateral decompression (ULBD) with open laminectomy. They found that microscopic ULBD was as effective as open decompression in improving function (the Oswestry Disability Index [ODI] score), while ULBD had better pain relief (visual analog scale [VAS] score), shorter postoperative recovery time, less time to mobilization, and less opioid use. These findings were also demonstrated in the study by Komp et al.62 In another study, Asgarzadie and Khoo63 compared 48 patients with MED to 32 patients with open laminectomies with a follow-up of 4 years. The average EBL for the MEDS group was 25 versus 193 mL for the open laminectomy group. The preoperative ODI score in the MEDS group was 46, and improved to 26 at 3 years. The average length of hospitalization for the MEDS group was 36 hours compared to 94 hours in the open laminectomy group. The rate of durotomies was 4% for the MEDS group. Since open lumbar laminectomy is a procedure with an excellent surgical outcome, and it has been the standard of care for decades, it should not be surprising that the long-term outcome of various studies comparing open versus minimally invasive laminectomies may not be dramatically different. The immediate

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advantages of MISS which translate into better satisfaction in the early postoperative period cannot be ignored.64 Postoperative spinal instability is also a concern in patients undergoing laminectomy for lumbar stenosis, especially in patients with some degree of spondylolisthesis preoperatively. The MISS approach maintains the posterior tension band and preserves the facet joints, which may minimize the risk of postoperative spinal instability. This has been demonstrated in a biomechanical study with cadaveric lumbar spine, in which the radiographic evidence of spondylolisthesis progression was present if greater than 50% of the facet joint was resected at any one level.65 Various other studies also demonstrated that significant loading forces were absorbed by the supraspinous and inTherefore, terspinous ligaments during flexion.66,67 preservation of these ligaments during MEDS is biomechanically appealing in order to reduce the risk of slip progression in patients with stenosis secondary to degenerative spondylolisthesis (DS). This was also clearly demonstrated in a biomechanical study, where a unilateral MISS approach for bilateral decompression with intact facets maintained up to 80% of the native anatomic “stiffness” compared to large bilateral decompressions with facetectomies.68 Yagi et al69 were able to demonstrate the efficacy and safety of MEDS compared to open laminectomy in a prospective, randomized trial consisting of 41 patients. Single-level decompressions were performed in patients with grade I spondylolisthesis without preoperative instability on dynamic X-rays. Outcomes were measured by pre- and postoperative imaging, VAS, Japanese Orthopedic Association (JOA), cross-sectional areas of paraspinal muscles, and postoperative CPK-MM levels as a measurement of muscle destruction. Comparing the MEDS group to the open laminectomy group, the mean operative time was 71.1 versus 63.6 minutes, and the EBL was 37 versus 71 mL, respectively. In addition, the MEDS group required decreased amounts of post-op analgesics, and had decreased levels of CPK-MM, decreased atrophy of paraspinal muscles, and improved functional outcome scores at the 1-year follow-up. None of the patients in the MEDS group had spinal instability postop, while two patients in the open laminectomy group developed progression of spondylolisthesis. Pao et al70 prospectively operated on 60 patients over 2 years with MEDS for multilevel lumbar stenosis. They showed that the MED approach in patients with spondylolisthesis or scoliosis can be performed without introducing additional spinal instability or the necessity for fusion after decompression. Müslüman et al71 reported their midterm outcome after a microsurgical unilateral approach for bilateral decompression of lumbar DS. Postoperative clinical improvement and radiological findings clearly demonstrated that the unilateral approach for treating single-level and multilevel lumbar spinal stenosis with DS is a safe, effective, and minimally invasive method in terms of reducing the need for stabilization. Similar results were echoed in the study by Sasai et al.72 Park et al73 retrospectively compared the outcomes of patients undergoing either decompression alone or decompression with fusion for the treatment of DS. This study provided level III therapeutic evidence that in patients with stable degenerative lumbar spondylolisthesis, functional outcomes and lower extremity pain scores in the minimally invasive, unilateral laminectomy and bilateral decompression group were similar

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Rationale for Minimally Invasive Spine Surgery to decompression with instrumented fusion group. In fact, the latest guidelines from the North American Spine Society had a level B recommendation for patients with a symptomatic single-level low-grade DS (< 20%) without lateral foraminal stenosis, decompression alone with preservation of midline structures provide equivalent outcomes when compared to surgical decompression with fusion. Another subpopulation of patients where a minimally invasive approach may be beneficial is the elderly or the medically frail, or the obese patients. Jansson et al reported that the perioperative mortality was four times greater in patients older than 80 years undergoing open laminectomy for lumbar stenosis.74 In contrast, Rosen et al75 reported their success in treating elderly patients with MEDS for lumbar stenosis with minimal complications. They evaluated 57 patients with an average age of 80.8 years with multiple medical comorbidities. The elderly population demonstrated improved and sustained VAS, ODI, and SF-36 scores that reached statistical significance. Rosen et al75 also showed no operative complications and the overall minor complication rate was 2%. Similarly, obese patients tend to have longer operative times, increased blood loss, larger incisions and soft-tissue dissection for exposure, and increased perioperative complications. Some authors have quoted obesity-related complications to range from 36 to 67% higher than a normal body mass index (BMI) patient.76 Kalanithi et al77 reported an absolute increase in length of hospitalization (2 extra days) and perioperative complications (6.7%) in obese patients undergoing spinal surgery. The majority of their complications were from wound infections and pulmonary disease. In contrast, MISS approaches would employ a smaller incision with minimal wound exposure and decreased soft-tissue trauma. Theoretically, there would be a decreased “potential space” for infection with overall decreased surgical trauma. With tubular microsurgery, obese patients experienced the same or equally beneficial outcome, compared to nonobese patients, while incision lengths, blood loss, operative times, and length of stay were less when compared to open procedures. Other comorbidities and age had no significant impact on perioperative complications and clinical outcome.78

Transforaminal Lumbar Interbody Fusion For over three decades, transforaminal lumbar interbody fusion (TLIF) has been used to treat a variety of degenerative lumbar disorders. Although the efficacy of conventional open TLIF has been proven in literature, several drawbacks such as lengthy hospital stays, excessive blood loss, and postoperative complications were observed with open TLIF. A number of studies have demonstrated that MI-TLIF (minimally invasive transforaminal lumbar interbody fusion) had similar long-term pain reduction, functional improvement, fusion rates, and operative complications with less postoperative pain, blood loss, and hospital length of stay.79,80,81,82 Dhall et al80 compared mini-open TLIF with open TLIF in 42 patients with long-term follow-up. There was statistically significant difference between mean EBL (194 vs. 505 mL, p < 0.01) and mean length of stay (3 vs. 5.5 days, p < 0.01) in favor of MI-TLIF. Archavlis and Carvi y Nievas79 compared MI-TLIF with open TLIF for severe stenotic DS. In their study, 49 patients were

treated using either MI-TLIF or open TLIF. They found that the MI-TLIF group had lesser blood loss, less need for blood transfusion (p = 0.02), more rapid improvement of postoperative back pain in the first 6 weeks of follow-up, and a shorter length of stay. The comparison between MI-TLIF and open TLIF also has been a subject matter of a number of meta-analysis and systematic reviews. Goldstein et al82 performed a systematic review comparing outcomes of minimally invasive and open posterior lumbar fusion. Twenty-six studies of low or very low quality (GRADE protocol) met the author’s inclusion criteria. They found that patient-reported outcomes, including VAS pain scores and ODI values, were clinically equivalent between the MIS and open cohorts at 12 to 36 months postoperatively. However, MIS fusion tended to have less blood loss and shorter hospital stay along with trends toward lower rates of surgical/medical adverse events. Another review of the literature by Habib et al83 comparing MI-TLIF and open TLIF demonstrated important differences between the two approaches. EBL and length of stay were consistently lower in the minimally invasive cohorts (282 vs. 693 mL, and 5.6 vs. 8.1 days, respectively); however, the operative times were similar between the two groups. Complication rates were also different, with a greater incidence of surgical site infections (SSIs), urinary tract infections, and other unclassified complications in the open cohorts, while there were a higher number of new transient neurological deficits, unintended durotomies, and hardware complications in the minimally invasive cohorts. The latter finding highlights the initial learning curve associated with minimally invasive approach that tapers off over time with greater surgeon experience. Despite this early learning curve, comparative effectiveness studies have convincingly shown that MI-TLIF is associated with reduced costs over a 2-year period while generating equivalent improvements in quality-adjusted life-years compared with open TLIF.16 Parker et al84 studied effect of minimally invasive technique on return to work and narcotic use following transforaminal lumbar interbody fusion. While very few directly described time to return to work or duration of narcotic use postoperatively or both, the reviewed literature suggested that MI-TLIF may be associated with an accelerated time to narcotic independence and return to work versus open TLIF. MISS has been significantly associated with reduced rate of SSI irrespective of the type of procedure. Parker et al85 performed a literature review to identify the rates of postoperative infection for both MI-TLIF and open TLIF. They found an average infection rate of 0.6% in MI-TLIF compared with 4.0% in the open TLIF series. The rate of SSI after open TLIF was similar to their cohort of 120 patients, which showed a 5% incidence after open TLIF, amounting to $29,110 in costs for post-TLIF SSI care. Spine surgery in obese patients is challenging. It has been reported that the incidence of postoperative complications in lumbar decompression and fusion in obese patients may be as high as 44%.86 Rosen et al87 studied obesity and self-reported outcome after minimally invasive lumbar spinal fusion surgery. The mean BMI was 28.7 kg/m2; 31% of patients were overweight (BMI, 25–29.9), and 32% of patients were obese (BMI, > 30). Linear regression analysis did not identify a correlation between weight or BMI and pre- and postsurgery changes in any of the outcome measures.

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Fundamentals Despite the mounting evidence that demonstrates specific techniques and clinical situations in which MISS may be preferable to open surgery, the overall evidence base has relied heavily on retrospective studies with a relatively small number of patients and surgeons involved with absence of class I evidence. Even though there is need of further higher-quality studies to provide higher level of evidence, it should be understood that study design in spinal surgery is highly complex, and the application of the traditional research “gold standard” randomized controlled trial (RCT) has significant limitations. The inherent heterogeneity of the populations studied, the pathologies encountered, and the procedures used in spinal surgery make the strict confines of a typical RCT unrealistic and ultimately lacking in external validity. Nevertheless, numerous studies, mostly retrospective in nature, have consistently demonstrated statistical similarity of long-term improvement in VAS scores, ODI scores, and bony fusion rates between groups, with durability of clinical improvement over several years. Also, the perioperative outcomes of MI-TLIF appear to be better than those for open TLIF with a number of studies showing a decrease in length of hospital stay, intraoperative blood loss, and perioperative narcotic use. Elderly and obese patient group seems to benefit from the favorable low complication profile associated with MI-TLIF as compared to traditional open approaches.87,88,89

6.6 Minimally Invasive Spine Surgery for Adult Spinal Deformity The principal goal of adult scoliosis surgery is to achieve a balanced spine in both sagittal and coronal planes.90 Surgical correction of symptomatic spinal deformity in appropriately selected patients can lead to substantial clinical improvement and improved quality of life. However, factors such as advanced age, medical comorbidities, osteoporosis, and the rigidity of the spine can contribute to high surgical complication rates, especially in patients older than 75 years.91 MIS is being applied to this patient population in an effort to reduce complication rates associated with adult deformity surgery.92,93,94 Nevertheless, clinical and radiographic outcomes of MISS scoliosis correction need to be comparable with open surgery to justify its application in adult scoliosis. Following the initial experience demonstrating the technique and feasibility of minimally invasive techniques for correction of adult spinal deformity by Anand et al,92 several other studies have been published demonstrating the efficacy of MISS in patients with adult spinal deformity. Acosta and colleagues95 reviewed radiographic records of 36 patients undergoing transpsoas discectomy and interbody fusion for lumbar degenerative disease. They found that the transpsoas interbody fusion significantly improved segmental, regional, and global coronal plane alignment in these patients. However, the regional lumbar lordosis and global sagittal alignment were not improved in these patients. Isaacs et al93 evaluated extreme lateral interbody fusion (XLIF) for the treatment of adult degenerative scoliosis in a prospective multicenter nonrandomized study. A total of 107 patients who underwent the XLIF procedure with or without supplemental posterior fusion for the treatment of degenerative scoliosis were prospectively studied. The rate of major

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complications in this study was 12.1%, which is much lower compared to conventional open deformity surgeries. Dakwar et al96 reported early outcomes and safety of the minimally invasive, lateral retroperitoneal transpsoas approach for adult degenerative scoliosis. Perioperative complications include one patient with rhabdomyolysis requiring temporary hemodialysis, one patient with subsidence, and one patient with hardware failure. Three patients (12%) experienced transient postoperative anterior thigh numbness, ipsilateral to the side of approach. Caputo et al97 evaluated the clinical outcomes of adults with degenerative lumbar scoliosis treated with XLIF. The study group demonstrated improvement in multiple clinical outcome scores. A total of six minor complications (20%) were recorded, and two patients (6.7%) required additional surgery. In another retrospective study, Wang and Mummaneni98 studied clinical and radiographic results in 23 patients who underwent MIS for adult thoracolumbar deformity surgery. This study again documented the advantages of MISS in terms of reduced infection rates and blood loss, with satisfactory radiographic and clinical outcomes again showing the promising role of reducing surgical morbidity. Tormenti et al99 used a combined approach of minimally invasive transpsoas XLIF and open posterior segmental pedicle screw instrumentation with TLIF for the correction of coronal deformity. The complications in this study were significant, with one patient suffering an intraoperative bowel injury necessitating laparotomy and segmental bowel resection secondary to XLIF, two patients in the XLIF group sustaining motor radiculopathies, and six of eight patients (75%) experiencing postoperative thigh paresthesia or dysesthesia. Haque et al100 recently reported a multicenter study comparing radiographic results after minimally invasive, hybrid, and open surgery for adult spinal deformity from a prospective open surgery database and a retrospective MIS and hybrid surgery database. A total of 184 patients had pre- and postoperative radiographs and were thus included in the study (MIS, n = 42; hybrid, n = 33; open, n = 109). There were no significant differences between groups in terms of pre- and postoperative mean ODI and VAS scores at the 1-year follow-up. However, patients in the MIS group had much lower EBL and transfusion rates compared with patients in the hybrid or open groups (p < 0.001). Major complications occurred in 14% of patients in the MIS group, 14% in the hybrid group, and 45% in the open group (p = 0.032). This study demonstrated that minimally invasive surgical techniques can result in clinical outcomes at 1 year comparable to those obtained from hybrid and open surgical techniques. Uribe et al,94 in a recent study from the International Spine Study Group, compared the complications in adult spinal deformity between various approaches. In all, 60 matched patients were available for analysis (MIS = 20, hybrid = 20, open = 20). Blood loss was less in the MIS group than in the hybrid and open groups, but a significant difference was only found between the MIS and the open group (669 vs. 2,322 mL, p = 0.001). In patients with complete data, the overall complication rate was 45.5% (25 of 55). There was no significant difference in the total complication rate among the MIS, hybrid, and open groups (30, 47, and 63%, respectively; p = 0.147). Intraoperative complications were reported for 5.3% for the hybrid group and 25% for the open group (p < 0.03); no intraoperative complications

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Rationale for Minimally Invasive Spine Surgery were reported for the MIS group. At least one postoperative complication occurred in 30, 47, and 50% (p = 0.40) of the MIS, hybrid, and open groups, respectively. All patients had significant improvement in both the ODI and VAS scores after surgery (p < 0.001), although the MIS group did not have significant improvement in leg pain. Results in this study suggest that the surgical approach may impact complications. The MIS group had significantly fewer intraoperative complications than did either the hybrid or open groups. Though various studies have shown the feasibility and efficacy of various combinations of minimally invasive approaches in the correction of adult spinal deformity, there are various limitations. Recent data suggest that there are ceiling effects to both the amount of Cobb correction and the sagittal vertical axis (SVA), which can be corrected using circumferential MISS techniques (incorporating the lateral transpsoas approach) in spinal deformity with a ceiling of Cobb angle correction of up to 40 degrees and SVA correction of 10 cm.101 Because sagittal plane alignment is a critical parameter for outcomes in the setting of Adult Spinal Deformity (ASD)90 patients with considerable SVA imbalance or pelvic incidence/lumbar lordosis mismatch may be better considered for appropriate osteotomy or other open techniques rather than relying solely on MISS techniques for sagittal plane deformity correction. With the continued innovations in minimally invasive technology, MISS for scoliosis will continue to evolve. Compelling advantages of MISS include reduced blood loss, potentially reduced complication rates, and reduced tissue trauma. While there is certain ceiling to what extent the deformity can be corrected using the currently available techniques, newer techniques such as anterior longitudinal ligament release, minimally invasive osteotomies, and hybrid techniques may obviate some of the limitations. More importantly, long-term follow-up studies demonstrating maintenance of clinical success with low rate of complication rates such as proximal junctional kyphosis will provide further data to support the benefits of minimally invasive scoliosis surgery as compared to open surgery.

6.7 Minimally Invasive Spine Surgery for Spinal Malignancies/ Extradural Tumors Spinal metastases are the most common spinal neoplasms being present in as many as 70% of patients with cancer.102 Spinal malignancies are often associated with substantial pain, structural deformity, and symptomatic neural compression, which can require surgery. While surgery can have a critical role in the preservation of quality of life in patients with metastatic epidural spinal cord compression (MESCC),103 because of the presence of immunocompromised status from ongoing chemotherapy, poor nutrition, and comorbid medical conditions, these patients cannot tolerate the conventional surgical methods. The importance of minimizing the complications of surgery in these patients is paramount. MISS techniques have the potential to considerably limit the morbidity associated with the large exposures required for open corpectomy and cage placement, therefore making surgery an option for the sicker patients who cannot tolerate the standard

open surgery. Following the success of some cadaveric studies in demonstrating the feasibility of minimally invasive corpectomy,104,105 various small clinical series have documented results of MIS in patients with spinal metastasis.13,106,107,108,109,110 In an initial technical note of eight mini-open transpedicular corpectomy cases from 2008 to 2009, Lau and Chou111 found a mean EBL of 1,250 mL and a low complication rate. The posterior mini-open transpedicular corpectomy offers circumferential decompression and complete metastatic tumor removal from a single midline incision. Although prospective and large case series are lacking, initial data suggest rates of neurologic improvement comparable to those of open cases, with low complication rates. Mühlbauer et al109 published the first description of MISS for managing metastatic spine disease in 2000. At follow-up, all patients had experienced neurological improvement characterized by either progressing from ambulating with a cane to ambulating unassisted or progressing from nonambulatory to ambulating with a cane. Huang et al108 published a retrospective analysis of 46 patients to compare outcomes in minimal access spinal surgery (MASS) (n = 29) and standard thoracotomy (ST, n = 17) in the setting of metastatic spine disease. There was no significant difference in mean operative time, blood loss, neurological improvement, or complications rate. Mean operative time for MASS was 179 minutes versus 180 minutes for ST (p = 0.54). Mean blood loss for MASS was 1,100 mL versus 1,162 mL for ST (p = 0.63). However, the authors found that the percentage of patients requiring at least a 2-day postoperative admission to the ICU was significantly different when comparing MASS to ST, with MASS resulting in significantly less admissions (MASS 6.9% vs. ST 88%, p ≤ 0.001). Kan and Schmidt112 published a retrospective case series of five patients with metastatic disease of the thoracic spine who underwent ventral decompression via MASS. All patients who presented with neurological deficits were neurologically intact at 6-month follow-up, with all patients experiencing some degree of pain relief. Deutsch et al107 reported a retrospective case series of eight patients undergoing MASS posterolateral vertebrectomy and decompression to treat symptomatic thoracic MESCC. The patient population was composed of patients not deemed candidates for conventional open thoracotomy due to age (mean, 74 years), limited life expectancy, and/or systemic metastatic burden. All patients presented with substantial neurologic deficit (mean Nurick grade: 4.35 [range, 3–5]) and pain (mean numerical pain score [NPS], 5.5 [range, 3–8]). Postoperatively, five patients experienced neurologic improvement, and the mean Nurick grade of all patients decreased to 3.13. Five patients experienced pain alleviation, with the group mean NPS decreasing to 3.10. The use of expandable retractors for direct lateral access to the anterior column has also been described.13 The minimally invasive lateral approach allows for a much smaller incision and a smaller amount of rib resection. Blood loss, postoperative pain, time to mobilization, and hospital stay are all reduced with minimally invasive approaches. Uribe and colleagues13 presented a series of 21 consecutive patients treated for thoracic spine tumors via an MIS lateral approach, 13 of whom required corpectomy. There was one perioperative pneumonia,

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Fundamentals representing the lone complication in the series during a mean follow-up period of 21 months. Percutaneous vertebral augmentation (PVA) is another minimally invasive palliative procedure for the treatment of patients who have spinal metastasis and are not ideal candidates for conventional open surgery because of a limited life span (less than 3 months) or high risk for morbidity. Painful vertebral fractures and severe osteolysis with impending fracture related to benign (e.g., hemangioma, eosinophilic granuloma) or malignant (e.g., myeloma, metastasis) tumors constitute primary indications. PVA provides immediate stabilization and pain relief and dramatically improves the quality of life in these patients. Various retrospective and prospective studies have shown that both vertebroplasty (VP) and kyphoplasty (KP) result in marked reduction of spinal pain in approximately 90% of the patients.113 Fourney and colleagues114 retrospectively reviewed 97 (65 VP and 32 KP) procedures in a group of patients who had cancer (21 who had myeloma and 35 who had other malignancies). Patients noted marked or complete pain relief after 49 procedures (84%) and no change in the rest. Reductions in VAS pain scores remained significant for up to 1 year. The Cancer Patient Fracture Evaluation (CAFE) study was a multicenter RCT comparing balloon KP versus nonsurgical fracture management for treatment of painful vertebral body compression fractures in patients with cancer. The primary end point was back-specific functional status measured by the Roland-Morris Disability Questionnaire (RDQ) score at 1 month. A total of 134 patients were enrolled and randomly assigned to KP (n = 70) or nonsurgical management (n = 64). In total, 65 patients in the KP group and 52 in the control group had data available at 1 month. The mean RDQ score in the KP group changed from 17.6 at baseline to 9.1 at 1 month (mean change, -8.3 points; 95% CI, -6.4 to 10.2; p < 0.0001). The mean score in the control group changed from 18.2 to 18.0 (mean change, 0.1 points; 95% CI, -0.8 to 1.0; p = 0.83). This study clearly shows that for painful vertebral compression fractures (VCFs) in patients with cancer, KP is an effective and safe treatment that rapidly reduces pain and improves function.

6.8 Minimally Invasive Resection of Intradural Lesions Resection of spinal tumors traditionally requires bilateral subperiosteal muscle stripping, extensive laminectomy, and, in cases of foraminal extension, partial or radical facetectomy. Fusion is often warranted in cases of facetectomy to prevent deformity, pain, and neurological deterioration. Advancement in surgical techniques allowing primary dural repair during MISS techniques has allowed removal of intradural spinal cord tumors, including extramedullary tumors (such as schwannomas and meningiomas), intramedullary tumors, and various other lesions.11,12,115,116 MISS for the removal of spinal tumors is associated with reduced blood loss and postoperative pain, as well as improvements in functional recovery during the weeks and months following surgery, when compared with open surgery approaches. As MISS for intradural lesions is fairly recent, comparative studies between open and minimally invasive resection of intradural tumors are lacking.

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Nzokou et al117 reported their clinical experience with minimally invasive removal of thoracic and lumbar spinal tumors using a nonexpandable tubular retractor. Gross total resection was achieved in 12 patients with no major procedure-related complications. The average length of hospitalization was 66 hours (range, 24–144 hours). At last follow-up, 92% of patients had improvement or resolution of pain with a VAS score that improved from 7.8 to 1.2. This approach may be associated with even less tissue destruction than mini-open techniques, translating into a quicker functional recovery.117 Haji et al118 demonstrate use of MISS for resection of a variety of extradural, intradural, and intramedullary spinal tumors, further supporting the safety and efficacy of minimally invasive techniques in management of intradural neoplasms. Tredway et al12 described a retrospective series of minimally invasive resection of intradural-extramedullary spinal neoplasms in six patients. All patients underwent successful, complete resection of their intradural-extramedullary tumors. There were no complications associated with this surgical technique. Potential reduction in blood loss, hospitalization, and disruption to local tissues suggest that, in the hands of an experienced surgeon, this technique may present an alternative to traditional open tumor resection.12 Minimally invasive resection of intramedullary tumors is relatively new to the neurosurgeon’s armamentarium, and thus clinical outcome measures are sparse in the literature to date. Ogden and Fessler reported on the resection of an intramedullary ependymoma with a good clinical outcome,11 with recent description of minimally invasive treatment of spinal dural arteriovenous fistula.116 As experience in minimally invasive techniques grows further, it is fairly certain that more reports and outcomes studies regarding the application of minimally invasive techniques will be forthcoming. Currently, investigations are underway using surgical robots to help resect difficult-to-reach tumors in the thoracic spine.119

6.9 Conclusion The development of MISS techniques has made a tremendous impact in the field of spine surgery. While the initial enthusiasm led to tremendous technological innovations, the rate of change is likely to slow and the focus will be turned to addressing the shortcomings of the currently existing MISS instrumentations and techniques. The results across various studies and spectrum of pathologies are remarkably consistent in demonstrating that MISS is associated with decreased rate of infection, less blood loss, and shorter hospital stay. While RCTs are highly desirable, surgical RCTs are highly complex and are not without limitations. Short of level I evidence, various prospective national data registries such as the National Neurosurgery Quality and Outcomes Database may provide large database allowing more robust and generalizable research conclusions. Further research and development is still needed to establish, maintain, and evolve minimally invasive spine surgery.

References [1] Smith ZA, Fessler RG. Paradigm changes in spine surgery: evolution of minimally invasive techniques. Nat Rev Neurol. 2012; 8(8):443–450 [2] Khoo LT, Fessler RG. Microendoscopic decompressive laminotomy for the treatment of lumbar stenosis. Neurosurgery. 2002; 51(5) Suppl:S146–S154

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Fundamentals [54] Ryang YM, Oertel MF, Mayfrank L, Gilsbach JM, Rohde V. Standard open microdiscectomy versus minimal access trocar microdiscectomy: results of a prospective randomized study. Neurosurgery. 2008; 62(1):174–181, discussion 181–182 [55] Huang TJ, Hsu RW, Li YY, Cheng CC. Less systemic cytokine response in patients following microendoscopic versus open lumbar discectomy. J Orthop Res. 2005; 23(2):406–411 [56] Teli M, Lovi A, Brayda-Bruno M, et al. Higher risk of dural tears and recurrent herniation with lumbar micro-endoscopic discectomy. Eur Spine J. 2010; 19 (3):443–450 [57] McLoughlin GS, Fourney DR. The learning curve of minimally-invasive lumbar microdiscectomy. Can J Neurol Sci. 2008; 35(1):75–78 [58] Atlas SJ, Deyo RA, Keller RB, et al. The Maine Lumbar Spine Study, Part III. 1year outcomes of surgical and nonsurgical management of lumbar spinal stenosis. Spine. 1996; 21(15):1787–1794, discussion 1794–1795 [59] Weinstein JN, Tosteson TD, Lurie JD, et al. Surgical versus nonoperative treatment for lumbar spinal stenosis four-year results of the Spine Patient Outcomes Research Trial. Spine. 2010; 35(14):1329–1338 [60] Palmer S, Turner R, Palmer R. Bilateral decompression of lumbar spinal stenosis involving a unilateral approach with microscope and tubular retractor system. J Neurosurg. 2002; 97(2) Suppl:213–217 [61] Mobbs RJ, Li J, Sivabalan P, Raley D, Rao PJ. Outcomes after decompressive laminectomy for lumbar spinal stenosis: comparison between minimally invasive unilateral laminectomy for bilateral decompression and open laminectomy: clinical article. J Neurosurg Spine. 2014; 21(2):179–186 [62] Komp M, Hahn P, Merk H, Godolias G, Ruetten S. Bilateral operation of lumbar degenerative central spinal stenosis in full-endoscopic interlaminar technique with unilateral approach: prospective 2-year results of 74 patients. J Spinal Disord Tech. 2011; 24(5):281–287 [63] Asgarzadie F, Khoo LT. Minimally invasive operative management for lumbar spinal stenosis: overview of early and long-term outcomes. Orthop Clin North Am. 2007; 38(3):387–399, abstract vi–vii [64] Ang CL, Phak-Boon Tow B, Fook S, et al. Minimally invasive compared with open lumbar laminotomy: no functional benefits at 6 or 24 months after surgery. Spine J. 2015; 15(8):1705–1712 [65] Abumi K, Panjabi MM, Kramer KM, Duranceau J, Oxland T, Crisco JJ. Biomechanical evaluation of lumbar spinal stability after graded facetectomies. Spine. 1990; 15(11):1142–1147 [66] Goel VK, Fromknecht SJ, Nishiyama K, Weinstein J, Liu YK. The role of lumbar spinal elements in flexion. Spine. 1985; 10(6):516–523 [67] Hindle RJ, Pearcy MJ, Cross A. Mechanical function of the human lumbar interspinous and supraspinous ligaments. J Biomed Eng. 1990; 12(4):340–344 [68] Hamasaki T, Tanaka N, Kim J, Okada M, Ochi M, Hutton WC. Biomechanical assessment of minimally invasive decompression for lumbar spinal canal stenosis: a cadaver study. J Spinal Disord Tech. 2009; 22(7):486–491 [69] Yagi M, Okada E, Ninomiya K, Kihara M. Postoperative outcome after modified unilateral-approach microendoscopic midline decompression for degenerative spinal stenosis. J Neurosurg Spine. 2009; 10(4):293–299 [70] Pao JL, Chen WC, Chen PQ. Clinical outcomes of microendoscopic decompressive laminotomy for degenerative lumbar spinal stenosis. Eur Spine J. 2009; 18(5):672–678 [71] Müslüman AM, Cansever T, Yılmaz A, Çavuşoğlu H, Yüce İ, Aydın Y. Midterm outcome after a microsurgical unilateral approach for bilateral decompression of lumbar degenerative spondylolisthesis. J Neurosurg Spine. 2012; 16 (1):68–76 [72] Sasai K, Umeda M, Maruyama T, Wakabayashi E, Iida H. Microsurgical bilateral decompression via a unilateral approach for lumbar spinal canal stenosis including degenerative spondylolisthesis. J Neurosurg Spine. 2008; 9 (6):554–559 [73] Park JH, Hyun SJ, Roh SW, Rhim SC. A comparison of unilateral laminectomy with bilateral decompression and fusion surgery in the treatment of grade I lumbar degenerative spondylolisthesis. Acta Neurochir (Wien). 2012; 154 (7):1205–1212 [74] Jansson KA, Blomqvist P, Granath F, Németh G. Spinal stenosis surgery in Sweden 1987–1999. Eur Spine J. 2003; 12(5):535–541 [75] Rosen DS, O’Toole JE, Eichholz KM, et al. Minimally invasive lumbar spinal decompression in the elderly: outcomes of 50 patients aged 75 years and older. Neurosurgery. 2007; 60(3):503–509, discussion 509–510 [76] Yadla S, Malone J, Campbell PG, et al. Obesity and spine surgery: reassessment based on a prospective evaluation of perioperative complications in elective degenerative thoracolumbar procedures. Spine J. 2010; 10(7):581–587 [77] Kalanithi PS, Patil CG, Boakye M. National complication rates and disposition after posterior lumbar fusion for acquired spondylolisthesis. Spine (Phila Pa 1976). 2009; 34(18):1963–1969

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[78] Tomasino A, Parikh K, Steinberger J, Knopman J, Boockvar J, Härtl R. Tubular microsurgery for lumbar discectomies and laminectomies in obese patients: operative results and outcome. Spine. 2009; 34(18):E664–E672 [79] Archavlis E, Carvi y Nievas M. Comparison of minimally invasive fusion and instrumentation versus open surgery for severe stenotic spondylolisthesis with high-grade facet joint osteoarthritis. Eur Spine J. 2013; 22 (8):1731–1740 [80] Dhall SS, Wang MY, Mummaneni PV. Clinical and radiographic comparison of mini-open transforaminal lumbar interbody fusion with open transforaminal lumbar interbody fusion in 42 patients with long-term follow-up. J Neurosurg Spine. 2008; 9(6):560–565 [81] Foley KT, Holly LT, Schwender JD. Minimally invasive lumbar fusion. Spine. 2003; 28(15) Suppl:S26–S35 [82] Goldstein CL, Macwan K, Sundararajan K, Rampersaud YR. Comparative outcomes of minimally invasive surgery for posterior lumbar fusion: a systematic review. Clin Orthop Relat Res. 2014; 472(6):1727–1737 [83] Habib A, Smith ZA, Lawton CD, Fessler RG. Minimally invasive transforaminal lumbar interbody fusion: a perspective on current evidence and clinical knowledge. Minim Invasive Surg. 2012; 2012:657342 [84] Parker SL, Lerner J, McGirt MJ. Effect of minimally invasive technique on return to work and narcotic use following transforaminal lumbar inter-body fusion: a review. Prof Case Manag. 2012; 17(5):229–235 [85] Parker SL, Adogwa O, Witham TF, Aaronson OS, Cheng J, McGirt MJ. Post-operative infection after minimally invasive versus open transforaminal lumbar interbody fusion (TLIF): literature review and cost analysis. Minim Invasive Neurosurg. 2011; 54(1):33–37 [86] Carreon LY, Puno RM, Dimar JR, II, Glassman SD, Johnson JR. Perioperative complications of posterior lumbar decompression and arthrodesis in older adults. J Bone Joint Surg Am. 2003; 85-A(11):2089–2092 [87] Rosen DS, Ferguson SD, Ogden AT, Huo D, Fessler RG. Obesity and self-reported outcome after minimally invasive lumbar spinal fusion surgery. Neurosurgery. 2008; 63(5):956–960, discussion 960 [88] Lee DY, Jung TG, Lee SH. Single-level instrumented mini-open transforaminal lumbar interbody fusion in elderly patients. J Neurosurg Spine. 2008; 9 (2):137–144 [89] Terman SW, Yee TJ, Lau D, Khan AA, La Marca F, Park P. Minimally invasive versus open transforaminal lumbar interbody fusion: comparison of clinical outcomes among obese patients. J Neurosurg Spine. 2014; 20(6):644–652 [90] Schwab F, Lafage V, Patel A, Farcy JP. Sagittal plane considerations and the pelvis in the adult patient. Spine. 2009; 34(17):1828–1833 [91] Acosta FL, Jr, McClendon J, Jr, O’Shaughnessy BA, et al. Morbidity and mortality after spinal deformity surgery in patients 75 years and older: complications and predictive factors. J Neurosurg Spine. 2011; 15(6):667–674 [92] Anand N, Baron EM, Thaiyananthan G, Khalsa K, Goldstein TB. Minimally invasive multilevel percutaneous correction and fusion for adult lumbar degenerative scoliosis: a technique and feasibility study. J Spinal Disord Tech. 2008; 21(7):459–467 [93] Isaacs RE, Hyde J, Goodrich JA, Rodgers WB, Phillips FM. A prospective, nonrandomized, multicenter evaluation of extreme lateral interbody fusion for the treatment of adult degenerative scoliosis: perioperative outcomes and complications. Spine. 2010; 35(26) Suppl:S322–S330 [94] Uribe JS, Deukmedjian AR, Mummaneni PV, et al. International Spine Study Group. Complications in adult spinal deformity surgery: an analysis of minimally invasive, hybrid, and open surgical techniques. Neurosurg Focus. 2014; 36(5):E15 [95] Acosta FL, Liu J, Slimack N, Moller D, Fessler R, Koski T. Changes in coronal and sagittal plane alignment following minimally invasive direct lateral interbody fusion for the treatment of degenerative lumbar disease in adults: a radiographic study. J Neurosurg Spine. 2011; 15(1):92–96 [96] Dakwar E, Cardona RF, Smith DA, Uribe JS. Early outcomes and safety of the minimally invasive, lateral retroperitoneal transpsoas approach for adult degenerative scoliosis. Neurosurg Focus. 2010; 28(3):E8 [97] Caputo AM, Michael KW, Chapman TM, Jr, et al. Clinical outcomes of extreme lateral interbody fusion in the treatment of adult degenerative scoliosis. Sci World J. 2012; 2012:680643 [98] Wang MY, Mummaneni PV. Minimally invasive surgery for thoracolumbar spinal deformity: initial clinical experience with clinical and radiographic outcomes. Neurosurg Focus. 2010; 28(3):E9 [99] Tormenti MJ, Maserati MB, Bonfield CM, Okonkwo DO, Kanter AS. Complications and radiographic correction in adult scoliosis following combined transpsoas extreme lateral interbody fusion and posterior pedicle screw instrumentation. Neurosurg Focus. 2010; 28(3):E7 [100] Haque RM, Mundis GM, Jr, Ahmed Y, et al. International Spine Study Group. Comparison of radiographic results after minimally invasive, hybrid, and

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Rationale for Minimally Invasive Spine Surgery

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open surgery for adult spinal deformity: a multicenter study of 184 patients. Neurosurg Focus. 2014; 36(5):E13 Wang MY, Mummaneni PV, Fu KM, et al. Minimally Invasive Surgery Section of the International Spine Study Group. Less invasive surgery for treating adult spinal deformities: ceiling effects for deformity correction with 3 different techniques. Neurosurg Focus. 2014; 36(5):E12 Cole JS, Patchell RA. Metastatic epidural spinal cord compression. Lancet Neurol. 2008; 7(5):459–466 Patchell RA, Tibbs PA, Regine WF, et al. Direct decompressive surgical resection in the treatment of spinal cord compression caused by metastatic cancer: a randomised trial. Lancet. 2005; 366(9486):643–648 Kim DH, O’Toole JE, Ogden AT, et al. Minimally invasive posterolateral thoracic corpectomy: cadaveric feasibility study and report of four clinical cases. Neurosurgery. 2009; 64(4):746–752, discussion 752–753 Smith ZA, Li Z, Chen NF, Raphael D, Khoo LT. Minimally invasive lateral extracavitary corpectomy: cadaveric evaluation model and report of 3 clinical cases. J Neurosurg Spine. 2012; 16(5):463–470 Arts MP, Brand R, van den Akker ME, et al. Tubular diskectomy vs conventional microdiskectomy for the treatment of lumbar disk herniation: 2-year results of a double-blind randomized controlled trial. Neurosurgery. 2011; 69(1):135–144, discussion 144 Deutsch H, Boco T, Lobel J. Minimally invasive transpedicular vertebrectomy for metastatic disease to the thoracic spine. J Spinal Disord Tech. 2008; 21 (2):101–105 Huang TJ, Hsu RW, Li YY, Cheng CC. Minimal access spinal surgery (MASS) in treating thoracic spine metastasis. Spine. 2006; 31(16):1860–1863 Mühlbauer M, Pfisterer W, Eyb R, Knosp E. Minimally invasive retroperitoneal approach for lumbar corpectomy and anterior reconstruction. Technical note. J Neurosurg. 2000; 93(1) Suppl:161–167

[110] Payer M, Sottas C. Mini-open anterior approach for corpectomy in the thoracolumbar spine. Surg Neurol. 2008; 69(1):25–31, discussion 31–32 [111] Lau D, Chou D. Posterior thoracic corpectomy with cage reconstruction for metastatic spinal tumors: comparing the mini-open approach to the open approach. J Neurosurg Spine. 2015; 23(2):217–227 [112] Kan P, Schmidt MH. Minimally invasive thoracoscopic approach for anterior decompression and stabilization of metastatic spine disease. Neurosurg Focus. 2008; 25(2):E8 [113] Ofluoglu O. Minimally invasive management of spinal metastases. Orthop Clin North Am. 2009; 40(1):155–168, viii [114] Fourney DR, Schomer DF, Nader R, et al. Percutaneous vertebroplasty and kyphoplasty for painful vertebral body fractures in cancer patients. J Neurosurg. 2003; 98(1) Suppl:21–30 [115] Ferroli P, Franzini A, Messina G, Tringali G, Broggi G. Use of self-closing Uclips for dural repair in mini-invasive surgery for herniated disc. Acta Neurochir (Wien). 2008; 150(10):1103–1105 [116] Fontes RB, Tan LA, O’Toole JE. Minimally invasive treatment of spinal dural arteriovenous fistula with the use of intraoperative indocyanine green angiography. Neurosurg Focus. 2013; 35(2) Suppl:5 [117] Nzokou A, Weil AG, Shedid D. Minimally invasive removal of thoracic and lumbar spinal tumors using a nonexpandable tubular retractor. J Neurosurg Spine. 2013; 19(6):708–715 [118] Haji FA, Cenic A, Crevier L, Murty N, Reddy K. Minimally invasive approach for the resection of spinal neoplasm. Spine. 2011; 36(15): E1018–E1026 [119] Perez-Cruet MJ, Welsh RJ, Hussain NS, Begun EM, Lin J, Park P. Use of the da Vinci minimally invasive robotic system for resection of a complicated paraspinal schwannoma with thoracic extension: case report. Neurosurgery. 2012; 71(1) Suppl Operative:209–214

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Fundamentals

7 Overcoming the Learning Curve Efrem M. Cox, David J. Hart, and Mick J. Perez-Cruet Abstract There is a learning curve to mastering minimally invasive spinal surgery approaches, techniques, and technology safely and effectively. This can be achieved through class study, cadaveric labs, fellowships, and experience in the operative arena with an accomplished minimally invasive spine surgeon. However, careful patient work-up and selection is also critical to providing effective minimally invasive spine surgery care. This chapter will discuss not only the evolution of minimally invasive spine surgery but also the various modalities used to teach surgeons how to perform these procedures safely and effectively. In learning these techniques, we recommend starting with straightforward cases such as lumbar microdiscectomy and advancing to more complex cases as each stepped approach and technique is mastered. Keywords: minimally invasive, approaches, technique, technology, safety, complication avoidance, cadaver training, operative experience

7.1 Introduction Minimally invasive spinal surgery (MISS) encompasses modifications of techniques and procedures to allow for decreased morbidity from exposure and dissection, as well as new techniques for treatment of spinal disease. The recent past has seen a significant increase in the volume and breadth of MISS procedures. Some believe that the increasing use of MISS represents a natural and logical progression of the field of spine surgery. As patients continue to learn more about MISS procedures through advertisements and patient testimonials, there will be further demand for practicing physicians to garner the skills to perform these newer techniques. MISS represents a shift away from the traditional surgical paradigm of maximal exposure, with the expected benefits of improved outcomes and decreased morbidity, operative time, length of hospitalization, and, ultimately, cost. The techniques of MISS aim to achieve the goals of proven open surgical techniques with less associated short-term morbidity and decreased hospital stays. MISS in combination with newer intraoperative navigational tools also offers potentially reduced radiation exposure and more accurate placement of instrumentation.1 MISS generally requires the use of unique or modified tools and the acquisition of new skills. Minimally invasive surgery further represents a departure from traditional surgery with regard to operative view and approach to the anatomy. As a result, operative times may increase initially compared with traditional surgeries. Those with experience in minimally invasive techniques caution that significant investment by the surgeon is required before the benefits of MISS may be realized, as the learning curve is steep.2 A proper understanding of the fundamental differences and similarities between MISS and traditional surgery serves as the basis to overcome the learning curve. With focused attention to the novel aspects of MISS, similar or improved surgical outcomes can be achieved with less

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operative time, decreased hospital stay, and decreased postoperative analgesia requirements.

7.2 Evolution of Minimally Invasive Spine Surgery While MISS is considered by many to be fairly new, attempts to develop less invasive spinal procedures can be found as far back as the mid-20th century with Dr. Smith’s percutaneous injection of chymopapain for the treatment of sciatica.3 In the 1960s, Gazi Yasargil4,5,6 worked with R. Peardon Donaghy, developing microsurgical instrumentation and techniques best known for the their impact on cerebral microsurgery. These same principles were later applied to spinal surgery. The use of the microscope for microsurgical techniques, pioneered by Drs. Yasargil, Williams, and Caspar7,8 in the late 1970s, served as the foundation for MISS. The first publication of a microsurgical discectomy was in 1978.9 Dr. Williams9 popularized the procedure with his results described on 532 patients. His impression of its benefits with regard to decreased incision size and cosmesis, reduced blood loss, and decreased morbidity was confirmed in numerous subsequent studies. Percutaneous procedures were then developed. Percutaneous discectomy and laser discectomy were attempted in the 1980s prior to the 1993 Mayer and Brock10 paper detailing the use of the endoscope for spine surgery. Shortly thereafter, Drs. Smith, Foley, Fessler, and PerezCruet11 designed modified operative spinal instruments for endoscopic tubular-access microdiscectomy and expanded the “tubology” applications. Incorporation of endoscopic techniques refined in other surgical disciplines served to further broaden the scope of MISS. Over the past decade, there have been further advancements in MISS treatment options ranging from instrumentation (e.g., tubular and expandable retractors) to intraoperative imaging to neuronavigation. Many of these advancements in MISS have centered on the goal of improvement in exposure for surgical approaches, yet minimizing soft-tissue destruction and compromise of the posterior paraspinous musculoligamentous complex. Tubular retractor systems have undergone various modifications that have expanded the role of MISS approaches in accomplishing lumbar fusion techniques (e.g., transforaminal lumbar interbody fusion [TLIF]) for treatment of spondylolisthesis, degenerative disc disease, spinal deformity, and trauma. In comparison to open procedures, MISS has demonstrated comparable outcomes to open techniques, but with decreased complications, blood loss, narcotic pain medication usage, return to work time, and hospital length of stay.12,13,14,15,16,17,18,19, 20,21,22 Intraoperative imaging has commonly been used in spinal instrumentation; however, complications of malpositioned screws are variably reported throughout the literature.23,24,25 Some surgeons using open approaches have utilized free-hand methods to limit radiation exposure. On the contrary, MISS is dependent on intraoperative imaging for proper localization of the operative site and placement of instrumentation. This does, however, provide a certain degree of radiation exposure to the

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Overcoming the Learning Curve surgeon, patient, and operating room personnel. Recently, there has been an evolution of intraoperative imaging/navigation and robotic modalities (e.g., plain fluoroscopy, 2D, 3D, and intraoperative computed tomography (CT)-guided robotics) with the aim to increase the accuracy of spinal instrumentation placement and decrease radiation exposure26,27 (▶ Fig. 7.1). Nevertheless, general acceptance and incorporation of minimally invasive techniques have been a slow process. Chymopapain nucleolysis and the automated percutaneous lumbar discectomy were part of the growing pains of MISS. The chymopapain studies, while serving as a platform for the development of further minimally invasive therapies, also brought attention to the learning curve associated with these new procedures. Proponents of chymopapain indicated that lack of familiarity and training, and application with poor indications were significant factors contributing to the high rate of complications. Indeed, the severe complication of hemiparesis and paraplegia resulting from intrathecal injection as well as anaphylaxis resulting in death from intrathecal injection may have been avoidable. Further developments in MISS have been coupled with improved clinical studies, many published since the turn of the 21st century, and a focused attention on the differences in surgical technique with the resultant need for appropriate training to overcome the learning curve. MISS represents a departure from traditional spine surgery with regard to use of intraoperative image guidance, hand–eye dissociation with endoscopy and microscopy, increased work-

ing distance, different surgical view, and a narrow working channel with modified instrumentation. Attention to these unique aspects of MISS and their advantages as well as limitations is paramount to overcoming the learning curve. For practicing physicians, the novelty of the different instrumentation and operating through a narrow corridor may cause some to be less comfortable initially, when transitioning from open procedures. In a systematic review, Sclafani and Kim28 report that the learning curve of performing MISS procedures could be overcome within performing 30 consecutive cases. There is considerable variation in the level of difficulty of different MISS procedures (e.g., laminectomy, microdiscectomy, percutaneous instrumentation, TLIF, posterior cervical decompression). Proficiency with MISS techniques will progress with one’s increasing comfort with the instrumentation and familiarity with operative corridors.

7.2.1 Cadaveric Training Cadaveric training under the tutelage of expert minimally invasive spine surgeons remains the standard to learning minimally invasive spinal procedures. These cadaveric labs can be developed to mimic the operative environment and improve mastery of various minimally invasive spinal techniques (▶ Fig. 7.2). These labs are being conducted by various industry leaders, national and state surgical organizations, and smaller focused organizations such as the Minimally Invasive Neurosurgical Society (MINS) (▶ Fig. 7.3). These labs provide an excellent venue for small group or one-on-one training with the experts and include focused didactic sessions.

7.2.2 Operative Training Training surgeons in the operative suite is an invaluable method to learn minimally invasive spine surgery. Training in the operative suite effectively shows surgeons how to set up the operative arena, position the patient, and perform the procedure. This exposure is critical and can be conducted as a visiting surgeon, medical student, resident, or fellow. Residency and fellowship training of minimally invasive spinal techniques remains a critical learning venue to improving patient care and outcomes. Additionally, participation in the preoperative clinic evaluation and work-up of these patients as well as postoperative follow-up can lead to mastery of these techniques. As these techniques continue to evolve, robotic simulation training will take on an increasing role (▶ Fig. 7.4). These techniques can result in improved patient outcomes in those patients suffering from complex spinal pathologies such as difficult-to-approach thoracic apex tumors (▶ Fig. 7.5).

7.3 Indications and Contraindications Fig. 7.1 Surgeon learning robotic Mazor X (Mazor Robotics Inc., Orlando, FL) system for placement of percutaneous pedicle screws.

The necessity of a thorough understanding of the indications and contraindications cannot be overstated. While the indications and contraindications for the individual minimally invasive techniques are described in detail in other chapters, we would like to speak to some general principles in this chapter.

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Fundamentals

Fig. 7.2 (a–c) Operative suites mimic the operative environment of the surgeon and facilitate learning and mastery of minimally invasive spinal techniques.

Fig. 7.3 Cadaveric minimally invasive laboratory held at the Beaumont Simulation Learning Center, Royal Oak, MI, and sponsored by the Minimally Invasive Neurosurgical Society (MINS, Royal Oak, MI). (a,b) Course registrants learn through cadaveric training held in state-of-the-art operative suites. (c) Didactic sessions taught by MIS experts in the field. (d) Image guidance laboratory for learning percutaneous pedicle screw placement. (e) MINS organizers Mick Perez-Cruet, MD, MS (President and Founder, center), and administrators Jennifer Harris (left) and Joe Edwards (right).

7.3.1 Patient Selection Each patient should receive a thorough history and physical examination. Available nonsurgical options should always be considered and discussed with the patient. Relevant imaging should be obtained. The surgeon should consider both tradi-

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tional surgical options and minimally invasive ones that are indicated to treat the patient’s pathology. Patients who are not good surgical candidates in general are usually also not good candidates for MISS. Patients who have severe osteoporosis may not be appropriate for instrumented fusion surgery, whether open or MISS. The advantages of MISS approaches

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Overcoming the Learning Curve

Fig. 7.4 (a) Mimic training station. (b,c) Teaching minimally invasive assisted robotic spine surgery (MARSS).

Fig. 7.5 Once mastered, these techniques can be used to remove complex tumor pathology using the da Vinci robot. (a,b) Surgeon at the da Vinci robotic console used to robotically remove an apically located thoracic tumor (c) seen on the right-side coronal CT (d).

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Fundamentals become truly evident in patients with morbid obesity or severe degenerative changes (particularly in the lumbar spine, and/or when anatomic variation such as hypertrophied facets affect exposure) that can lead to a significant amount of retraction and muscle disruption to achieve adequate exposure. In contrast, MISS techniques decrease the amount of exposure one needs, thus lessening the length of incision and subsequently decreasing the “dead space” within the wound. This is particularly beneficial in patients with risk factors for poor wound healing, such as those with diabetes, obesity, and poor nutritional status. The surgeon must weigh the risks and benefits of all options and should factor in his or her own level of comfort and experience with the surgical techniques under consideration. For example, an elderly, medically frail patient with multiple (> 2) levels of lumbar canal stenosis would typically be treated in our practice with a traditional open approach. The benefits of MISS in this patient, such as smaller incision and decreased soft-tissue injury, might be outweighed by the increased surgical time needed to treat three or more levels with MISS, thus increasing time under general anesthetic and increasing perioperative morbidity risk. In this case, we would elect to treat the patient in an open manner. Hence, patient selection is of utmost importance in surgical decision making, whether open or MISS. While there may be significant controversies regarding the use of MISS in degenerative spinal conditions, treatment of spinal deformity with MISS is even more problematic. Some studies, and many experts in surgical correction of spinal deformity, suggest that MISS approaches for deformity may undercorrect sagittal spinal parameters resulting in suboptimal outcomes.29, 30,31,32 There have been several algorithms developed. Most recently, the minimally invasive spinal deformity (MISDEF) algorithm, developed by the International Spine Study Group,33 provides three classifications. The algorithm categorizes patients based on radiographic parameters such as sagittal vertebral axis, pelvic tilt, lumbar lordosis to pelvic incidence mismatch, degree of listhesis, thoracic kyphosis, and coronal Cobb angle. Based on the criteria, classes I and II are amenable for MISS. Class III patients who have a sagittal vertebral axis greater than 6 mm, pelvic tilt greater than 25 mm, a lumbar lordosis to pelvic incidence mismatch greater than 30 degrees, and thoracic hyperkyphosis greater than 60 degrees are more appropriate candidates for an open approach, due to potential need for osteotomies to achieve adequate correction of the deformity.33 However, many authors are currently developing and testing MISS strategies to accomplish osteotomies and major curve corrections, with data on these techniques expected soon after this writing.

7.4 Preoperative Planning Preoperative work-up should include routine laboratory studies and further imaging as indicated. Evaluation and appropriate work-up of any and all comorbidities should be performed. If possible, the surgical plan should be reviewed in advance with anesthesia with attention to special considerations as necessitated by various MISS procedures. For example, thoracoscopic procedures requiring mainstem bronchus intubation and single-lung ventilation may necessitate preoperative pulmonary function testing and cardiac work-up.

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7.4.1 Instrumentation Acquisition of necessary tools and equipment should be arranged with the operating suite staff in advance. In particular, necessary imaging tools, such as X-ray, fluoroscopy equipment, or CT scanner, should be reserved. In addition, an endoscope with video tower and lighting source or microscope should be pretested and reserved. If electrophysiologic monitoring is indicated, arrangements with the appropriate technician should be made in advance. Additionally, appropriate minimally invasive instrumentation should be selected along with appropriate hemostatic agents.

7.4.2 Patient Positioning Patient positioning is of paramount importance in MISS. Careful attention should be paid to placing the patient in the ideal position for the planned surgical procedure and any special bed or positioning equipment required should be reserved in advance. Once a patient is positioned properly, it is imperative to assure that anatomic alignment is correct before proceeding. One should check alignment of the spinous processes in relationship to the pedicles as well as the orientation of the end plates with fluoroscopy (C-arm). If navigational tools are to be employed, care should be taken to ensure that the patient or the reference instruments are not moved once 3D imaging has been acquired. Specific details of different instrumentation types, neuronavigation, and intraoperative imaging will be covered in detail elsewhere in this book.

7.5 Surgical Approach We will defer specific discussion of individual MISS techniques, as those are covered in detail elsewhere in this book, but in general, fascial incision is key for almost every procedure. In thin patients, one may dissect with a Kelly clamp and monopolar cautery, strip fat with a sponge, and directly visualize the fascial incision. In obese patients, we generally rely on tactile feel of scalpel against the fascia. Avoid cutting deeply—muscle bleeding will be problematic. Palpate with a finger before proceeding to ensure adequate incision length (should be at least as long as skin incision, no shorter).

7.5.1 Surgical Technique The operative techniques for the individual procedures are discussed in other chapters of this work. In this section, we will elucidate the unique aspects of MISS that form the basis of operative differences between MISS and traditional surgery. Minimally invasive surgery presents several unique and novel challenges to the surgeon. A unique operative field view with decreased overall exposure is the first major difference noted by most surgeons upon their first experience with MISS. A smaller incision, generally off midline, or several small incisions, represents a departure from the traditional midline incision associated with posterior cervical or lumbar procedures. Hand–eye dissociation, lack of depth perception, increased distance from the operative field, modified instrumentation, increased use of intraoperative imagine guidance, and a narrow working channel constitute the other major challenges. Each of these aspects, however, can be mastered with due diligence.

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Overcoming the Learning Curve

The Incision The most obvious difference for both the surgeon and the patient is a smaller incision or a set of small incisions (▶ Fig. 7.6). Attention to incision placement is of utmost importance for nearly all MISS procedures. For both percutaneous procedures and those utilizing narrow tubular working channels, the trajectory to the desired location is paramount. As such, increased use of intraoperative image guidance is a must. For most minimally invasive posterior procedures, we position the C-arm fluoroscopy machine (or two machines for procedures requiring biplanar fluoroscopy, such as percutaneous pedicle screws or kyphoplasty) and mark the appropriate level with a Kelly clamp or K-wires prior to surgical field preparation and sterile draping (▶ Fig. 7.7). CT guidance for screw placement has also been described. Depending on the procedure to be undertaken, the incision is drawn at various distances lateral to the spinous

process at the appropriate level. For example, endoscopic laminectomy with a 16-mm working channel would necessitate a 1.8-cm incision roughly 2 cm lateral to the spinous process. The exact location of the incision would be slightly adjusted depending on whether a hemilaminectomy or complete laminectomy was going to be performed and depending on the patient’s body habitus. Kyphoplasty would require a stab incision from a more lateral position. Percutaneous pedicle screw instrumentation would require a slightly longer incision at roughly the same position as for kyphoplasty. Selecting the appropriate location for the incision is important and extra time should be taken by the less experienced to double- and triple-check location and relevant landmarks. As the working channel will be very narrow, small deviations from the ideal position can lead to significant time spent adjusting and angling the working channel in an effort to obtain an adequate view. For thoracoscopic or laparoscopic approaches, a thorough understanding of the relevant anatomy is a must to prevent unintended injury to the thoracic or abdominal viscera. In these procedures, patient positioning (particularly with the thoracoscopic procedures) and port placement is essential to obtaining a satisfactory operative view with sufficient room for the necessary instrumentation. Of particular importance in laparoscopic procedures is obtaining familiarity with the initial trocar. The first trocar insertion is performed without direct visualization, and excessive force and/or poor site choice could lead to visceral injury.

The Working Channel

Fig. 7.6 Example of smaller incisions for minimally invasive transforaminal lumbar interbody fusion (TLIF).

Developing the working channel also represents a departure from previous surgical technique and is believed to be a major underlying reason for the benefits of MISS (▶ Fig. 7.8). This is the procedure that “splits the muscle.” When performing this for a minimally invasive decompression, one must be sure to dock the K-wire on the surface of a lamina and confirm with imaging. Subsequently, the initial dilator is inserted over the

Fig. 7.7 Example of preoperative marking of lumbar spine, using K-wire and C-arm fluoroscopy.

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Fig. 7.8 Sequence showing developing the working channel. (a) Initial incision; (b) K-wire placement; (c–f) subsequent dilator placement; (g) final retractor positioning for posterior cervical foraminotomy at C7–T1.

K-wire. Again, repeated confirmation with imaging is recommended. The K-wire is then removed, and sequential dilators are inserted. Care must be taken in this step to keep the K-wire and dilators firmly docked on the lamina to prevent muscle encroachment. If the dilators should migrate, replacement of the first dilator and reinsertion of the other dilator tubes in stepwise fashion is recommended. Subsequently, the working channel is placed over the dilators. Choosing the correct length of the channel should be emphasized. Too short of a channel will allow muscle and soft tissue to encroach from below, making visualization difficult. An unnecessarily long channel increases the likelihood of movement and angulation when attached to the retractor arm and exponentially increases the difficulty of instrument manipulation through the tube.

The View The limited operative view is generally the most concerning variation from standard surgical techniques for those with reservations about MISS. The narrow view provided by the working channel, however, does provide sufficient access to the

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pathology as well as visualization of bony landmarks for orientation, albeit less visualization than with open procedures (▶ Fig. 7.9). A thorough review of the local anatomy can help the surgeon avoid losing his/her orientation. Lack of depth perception is also a distinction for endoscopic and thoracoscopic/laparoscopic procedures. However, careful technique and a thorough understanding of local anatomy will help to prevent untoward complications. Currently, depth perception can be achieved within the working channel with microscopy or use of surgical loupes, although the latter often is problematic due an inability to obtain adequate illumination of the field. The narrow working channel can be uncomfortable to a surgeon unfamiliar with such an approach. The limited working space requires an alteration in how the instruments are held and the way the field is approached. Use of the limited space has been made more efficient with the development of modified instruments for minimally invasive surgery. Longer, bayoneted instruments and longer curved drills allow the surgeon to see around the instruments, but the use of these instruments in a safe manner requires practice. Particularly concerning to

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Overcoming the Learning Curve models and simulations can be very useful in developing comfort and control with these modalities. Generally, the variations described above can be well tolerated individually, but MISS procedures often involve simultaneous exposure to several variations in any given procedure, which can frustrate the surgeon. Adequate preparation will allow the surgeon to safely perform MISS, and practice and experience will inevitably lead to decreased operative time and increased operator comfort, as it has in our experience.

7.5.2 Postoperative Care

Fig. 7.9 View of left C6–C7 facet joint after placement of tubular retractor. Note easy visualization of both articular processes, as well as the lamina medially (to the right).

many surgeons is the use of a high-speed pneumatic or electric drill in a narrow working channel with limited depth perception. However, with appropriate positioning, attention to landmarks, and frequent irrigation, the bony removal can be performed safely and quickly. Aside from modifying the grip on the drill, other advancements such as ultrasonic bone scalpels have also made MISS bone removal more comfortable for some surgeons. Increased need for image guidance necessitates proper positioning of the patient and equipment prior to prepping and draping to allow the C-arm fluoroscopy machines to be placed in useful positions. For minimally invasive procedures utilizing a working channel, the image guidance is typically needed only until the working channel is inserted and anatomic landmarks are visually confirmed. For percutaneous procedures, imaging is essential throughout the procedure. Familiarity with the anteroposterior and lateral anatomy is a must to allow for safe placement of percutaneous pedicle screws, interbody cages, and other techniques. Careful attention should be paid to the initial point of entry as well as to the access needle, tap, or screw throughout its course, and positioning should be repeatedly confirmed with biplanar imaging if intraoperative navigation is not being utilized. Thoracoscopic and laparoscopic procedures require familiarity with trocar placement and appropriate site selection. Additionally, complete hand–eye dissociation may take some time and practice before the surgeon becomes comfortable with the “video game–like” aspect of endoscopy, unless the spine surgeon has had previous training and experience with endoscopy. The instruments used, although similar in design to those used by laparoscopic general surgeons, are generally new to the spine surgeon unfamiliar with MISS. Practice with cadaveric

Postoperative care for MISS may differ in comparison to open procedures in regard to required length of stay, usually related to postoperative pain. For ambulatory procedures (e.g., MIS lumbar discectomy, cervical foraminotomy), patients rarely experience significant pain and are usually able to be discharged from the perioperative anesthesia care unit after demonstrating the ability to tolerate fluids, ambulate, and void. For other procedures, the general care provided to patients does not differ greatly, but we have noticed less frequent need for the use of muscle relaxants and patient-controlled analgesic pumps. Patients are able to achieve early mobilization, expediting their discharge to home. This is supported in much of the recent literature, including many articles and a recent systematic review of open compared to MISS TLIF.12,13,14,15,16,17,18,19,20,21,22 In the early postoperative period, patients are typically advised to follow the usual postoperative precautions including avoidance of heavy lifting, bending, and strenuous activities. Early ambulation is always encouraged. In regard to fusions, some surgeons may prefer the use of orthoses; however, we do not routinely use them unless the patient has very poor bone quality or other issues concerning for possible loss of fixation, or if one chooses to perform an uninstrumented fusion.

7.5.3 Management of Complications The complications of minimally invasive spine surgery are similar in nature to, but often less frequent than, those of traditional spine surgery. In our experience as well as in the literature, there may be a slightly higher risk of some complications early in the learning curve, but overall there actually appears to be a similar or even lower complication rate with many MISS procedures compared to open. Much of this is thought to be related to decreased medical morbidity, lower infection rate, fewer wound dehiscences, etc.12,13,14,15,16,17,18,19,20,21,22 The management of complications, however, may be slightly different due to unique constraints of MISS.

Dural Tears Dural tears are possible and are largely encountered through the same manner as traditional surgery. Of note, improper Kwire placement may also lead to a durotomy. Durotomies are difficult to repair primarily in a narrow channel as the limited diameter and significant depth preclude primary repair unless the surgeon is quite experienced and/or manually dexterous. Specially adapted needle holders can help as well. Small, dorsal

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Fundamentals or dorsolateral durotomies can often be managed with primary repair with or without chemical sealant. Axillary, lateral, or ventral durotomies can be managed with fat or muscle overlay with subsequent placement of chemical adhesive. Patients are generally kept flat for 24 hours and then allowed to slowly advance activity. We generally do not use lumbar catheter drainage, but this could be considered in cases of very large, irregular, and irreparable durotomies. Many authorities have reported treating spinal fluid leaks after MISS with little or no activity restriction, no particular intraoperative repair, and no extended hospital stay, and they report no delayed pseudomeningoceles or spinal fluid leaks in follow-up, attributing this different clinical behavior to the lack of dead space over the epidural space. This “laissez-faire” approach has not been universally adopted, however.

Table 7.1 Challenges and benefits of MISS Challenges

Benefits

Smaller, paramedian incision(s) Alternate operative view Decreased exposure Increased use of image guidance Hand/eye dissociation Loss of depth perception Modified instruments/new instruments Narrow working corridor(s) Limited tactile feedback

Muscle splitting vs. dissection Preservation of ligamentous bands Decreased scarring, decreased denervation injury Decreased hospitalization Earlier mobility Decreased postoperative pain and resultant decreased analgesia requirements Cosmesis

Clinical Caveats ●

Hemorrhage Hemorrhage can be of particular concern. With the limited working room and magnification, visualization can be significantly impaired by brisk bone bleeding or by epidural bleeding. Bleeding that cannot be visualized for bipolar cautery can generally be controlled with local packing, topical hemostatic agents such as mixtures of powdered gelatin and thrombin, or even fibrin glue. Arterial injury resulting in brisk hemorrhaging that cannot be directly visualized may require conversion to an open procedure. In our experience, one postoperative epidural hematoma required reoperation after a bilateral laminectomy for lumbar canal stenosis. Complications of destabilization while working within a restricted channel may occur and may require fusion and instrumentation (which may also be performed using minimally invasive techniques). In our experience, surgical outcomes with regard to patient improvement and symptom resolution are comparable to standard surgical procedures. Rarely has reoperation been necessary. On the other hand, several reoperations of open procedures have been performed at our institution using minimally invasive techniques.

7.6 Conclusion Minimally invasive spine surgery is an evolving field. It represents a departure from traditional spine surgeries in several ways and is associated with a steep learning curve. The loss of tactile feedback, hand–eye dissociation, different operative angle, and decreased operative view coupled with the narrow working channel(s) and new instrumentation represent the major departures from traditional spine surgery, and it is the incorporation of this large number of changes simultaneously that makes the learning curve steep. However, with proper attention to each of these variables, due diligence, and patience, the learning curve can be mastered and the benefits of minimally invasive surgery realized (▶ Table 7.1). Minimally invasive surgery will represent an increasing portion of overall spine surgery as surgeons continue to master these techniques and the potential for minimally invasive techniques is further realized.

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●

●

●

The initial transition from performing open procedures to MISS can be challenging. The novelty of operating through a narrow corridor, limited tactile feedback, and significant reliance on fluoroscopic image guidance can make the learning curve steep. Devoting time to performing consecutive MISS operations and familiarizing oneself with the new instrumentation may lessen the operative time, decrease complications, and improve one’s comfort level with performing more complex procedures. There are numerous systems available to the surgeon, any of which, if comfortable to the surgeon, may aid in the transition to performing MISS approaches. Patient selection, preoperative work-up, and intraoperative positioning are imperative to the use of MISS approaches. Understanding who the ideal candidate is for a given approach will likely provide the surgeon and patient with the best outcomes and decrease complications.

References [1] Kim TT, Drazin D, Shweikeh F, Pashman R, Johnson JP. Clinical and radiographic outcomes of minimally invasive percutaneous pedicle screw placement with intraoperative CT (O-arm) image guidance navigation. Neurosurg Focus. 2014; 36(3):E1 [2] Perez-Cruet MJ, Fessler RG, Perin NI. Review: complications of minimally invasive spinal surgery. Neurosurgery. 2002; 51(5) Suppl:S26–S36 [3] Smith L, Garvin PJ, Gesler RM, Jennings RB. Enzyme dissolution of the nucleus pulposus. Nature. 1963; 198:1311–1312 [4] Yaşargil MG. Intracranial microsurgery. Proc R Soc Med. 1972; 65(1):15–16 [5] Yasargil MG. Significance of microsurgery in brain surgery [in German]. Dtsch Med Wochenschr. 1969; 94(29):1496–1497 [6] Yasargil MG, Vise WM, Bader DC. Technical adjuncts in neurosurgery. Surg Neurol. 1977; 8(5):331–336 [7] Caspar W. A new surgical procedure for lumbar disc herniation causing less tissue damage through a microsurgical approach. In: Wüllenweber R, Brock M, Hamer J, Klinger M, Spoerri O, eds. Lumbar Disc Adult Hydrocephalus. Advances in Neurosurgery, vol 4. Berlin: Springer; 1977:74–80 [8] Yasargil MG. Microsurgical operation of herniated lumbar disc. In: Wüllenweber R, Brock M, Hamer J, Klinger M, Spoerri O, eds. Lumbar Disc Adult Hydrocephalus. Advances in Neurosurgery, vol 4. Berlin: Springer; 1977:81 [9] Williams RW. Microlumbar discectomy: a conservative surgical approach to the virgin herniated lumbar disc. Spine. 1978; 3(2):175–182 [10] Mayer HM, Brock M. Percutaneous endoscopic discectomy: surgical technique and preliminary results compared to microsurgical discectomy. J Neurosurg. 1993; 78(2):216–225

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Overcoming the Learning Curve [11] Perez-Cruet MJ, Foley KT, Isaacs RE, et al. Microendoscopic lumbar discectomy: technical note. Neurosurgery. 2002; 51(5) Suppl:S129–S136 [12] Al-Khouja LT, Baron EM, Johnson JP, Kim TT, Drazin D. Cost-effectiveness analysis in minimally invasive spine surgery. Neurosurg Focus. 2014; 36(6):E4 [13] Brodano GB, Martikos K, Lolli F, et al. Transforaminal lumbar interbody fusion in degenerative disk disease and spondylolisthesis grade I: minimally invasive versus open surgery. J Spinal Disord Tech. 2015; 28(10):E559–E564 [14] Goldstein CL, Macwan K, Sundararajan K, Rampersaud YR. Comparative outcomes of minimally invasive surgery for posterior lumbar fusion: a systematic review. Clin Orthop Relat Res. 2014; 472(6):1727–1737 [15] Karikari IO, Isaacs RE. Minimally invasive transforaminal lumbar interbody fusion: a review of techniques and outcomes. Spine. 2010; 35(26) Suppl:S294–S301 [16] Lau D, Khan A, Terman SW, Yee T, La Marca F, Park P. Comparison of perioperative outcomes following open versus minimally invasive transforaminal lumbar interbody fusion in obese patients. Neurosurg Focus. 2013; 35(2):E10 [17] Parker SL, Adogwa O, Witham TF, Aaronson OS, Cheng J, McGirt MJ. Post-operative infection after minimally invasive versus open transforaminal lumbar interbody fusion (TLIF): literature review and cost analysis. Minim Invasive Neurosurg. 2011; 54(1):33–37 [18] Parker SL, Mendenhall SK, Shau DN, et al. Minimally invasive versus open transforaminal lumbar interbody fusion for degenerative spondylolisthesis: comparative effectiveness and cost-utility analysis. World Neurosurg. 2014; 82(1–2):230–238 [19] Seng C, Siddiqui MA, Wong KP, et al. Five-year outcomes of minimally invasive versus open transforaminal lumbar interbody fusion: a matched-pair comparison study. Spine. 2013; 38(23):2049–2055 [20] Singh K, Nandyala SV, Marquez-Lara A, et al. A perioperative cost analysis comparing single-level minimally invasive and open transforaminal lumbar interbody fusion. Spine J. 2014; 14(8):1694–1701 [21] Terman SW, Yee TJ, Lau D, Khan AA, La Marca F, Park P. Minimally invasive versus open transforaminal lumbar interbody fusion: comparison of clinical outcomes among obese patients. J Neurosurg Spine. 2014; 20(6):644–652 [22] Wong AP, Shih P, Smith TR, et al. Comparison of symptomatic cerebral spinal fluid leak between patients undergoing minimally invasive versus open lumbar foraminotomy, discectomy, or laminectomy. World Neurosurg. 2014; 81 (3–4):634–640

[23] Castro WH, Halm H, Jerosch J, Malms J, Steinbeck J, Blasius S. Accuracy of pedicle screw placement in lumbar vertebrae. Spine. 1996; 21(11):1320–1324 [24] Farber GL, Place HM, Mazur RA, Jones DE, Damiano TR. Accuracy of pedicle screw placement in lumbar fusions by plain radiographs and computed tomography. Spine. 1995; 20(13):1494–1499 [25] Vaccaro AR, Rizzolo SJ, Balderston RA, et al. Placement of pedicle screws in the thoracic spine. Part II: An anatomical and radiographic assessment. J Bone Joint Surg Am. 1995; 77(8):1200–1206 [26] Holly LT, Foley KT. Intraoperative spinal navigation. Spine. 2003; 28(15) Suppl:S54–S61 [27] Ughwanogho E, Patel NM, Baldwin KD, Sampson NR, Flynn JM. Computed tomography-guided navigation of thoracic pedicle screws for adolescent idiopathic scoliosis results in more accurate placement and less screw removal. Spine. 2012; 37(8):E473–E478 [28] Sclafani JA, Kim CW. Complications associated with the initial learning curve of minimally invasive spine surgery: a systematic review. Clin Orthop Relat Res. 2014; 472(6):1711–1717 [29] Anand N, Rosemann R, Khalsa B, Baron EM. Mid-term to long-term clinical and functional outcomes of minimally invasive correction and fusion for adults with scoliosis. Neurosurg Focus. 2010; 28(3):E6 [30] Dakwar E, Cardona RF, Smith DA, Uribe JS. Early outcomes and safety of the minimally invasive, lateral retroperitoneal transpsoas approach for adult degenerative scoliosis. Neurosurg Focus. 2010; 28(3):E8 [31] Tormenti MJ, Maserati MB, Bonfield CM, Okonkwo DO, Kanter AS. Complications and radiographic correction in adult scoliosis following combined transpsoas extreme lateral interbody fusion and posterior pedicle screw instrumentation. Neurosurg Focus. 2010; 28(3):E7 [32] Wang MY, Mummaneni PV. Minimally invasive surgery for thoracolumbar spinal deformity: initial clinical experience with clinical and radiographic outcomes. Neurosurg Focus. 2010; 28(3):E9 [33] Mummaneni PV, Shaffrey CI, Lenke LG, et al. Minimally Invasive Surgery Section of the International Spine Study Group. The minimally invasive spinal deformity surgery algorithm: a reproducible rational framework for decision making in minimally invasive spinal deformity surgery. Neurosurg Focus. 2014; 36(5):E6

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8 Operating Room Setup Lee A. Tan, Mick J. Perez-Cruet, Manish K. Kasliwal, and Richard G. Fessler Abstract This chapter reviews the general concept of operating room layout, equipment, equipment setup, radiation safety, monitoring, and patient positioning pertinent to MISS in order to ensure smooth workflow and increase operational efficiency. Keywords: operating room, endoscopy, minimally invasive, spine, surgery, setup

8.1 Introduction Minimally invasive spine surgery (MISS) has experienced an incredible advancement over the last decade and is being adopted by an increasing number of spine surgeons.1,2 One important aspect of learning and mastering the minimally invasive techniques is to gain a solid understanding of the basic concept of the operating room (OR) setup, as well as to be familiar with various imaging tools and navigation systems available for MISS. Although the OR setup for MISS is similar to traditional open approaches in many ways, additional equipment such as microscope, endoscope, video monitor towers, C-arm, and O-arm require additional space and must be positioned in such a way that the workflow of the operation is optimized. Hence, the importance of standardization of the setup and of the OR conditions cannot be overemphasized to optimize the ergonomics of the workflow during MISS. This chapter reviews the general concept of OR layout, equipment setup, and patient positioning pertinent to MISS in order to ensure smooth workflow and increase operational efficiency.

8.2 Equipment 8.2.1 Placement First and foremost, the OR used for minimally invasive spinal procedures should be of sufficient size to accommodate the fluoroscopy machine (and/or O-arm), microscope or endoscope, and various video monitors, in addition to the usual OR equipment such as the operating table, Mayo stand, anesthesia setup, and neuromonitoring personnel. It is important to have enough space to maneuver the C-arm or O-arm intraoperatively. The setup of the entire equipment within the OR should be standardized to facilitate maximum performance by the surgeon and the entire team. In general, the anesthesia setup is at the head of the patient, the surgeon is at the side of the spinal pathology, the endoscope monitor or operating microscope base positioned at the opposite side of the surgeon, the C-arm is either cranial or caudal to the area of operation, and the fluoroscopy monitor is either at the feet of the patient or on the opposite side of the surgeon for easy visualization (▶ Fig. 8.1). Position of the surgical microscope is critically important too. If the arms are long enough, positioning the microscope behind the surgeon enables easy handling. The joints of the lever arms of the microscope should be bent in such a way that the optical

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unit is midline squared toward the patient, so that the surgeon and the assistant have a comfortable working position, especially regarding their head and neck posture. Essentially, all the equipment has to be placed in such a way that the surgeon has maximum flexibility and is as comfortable during the procedure as possible. It is useful to place the video monitor in such a way that the scrub nurse also has full view of the screen to follow the procedure. An example of OR setup for minimally invasive microdiscectomy is demonstrated in ▶ Fig. 8.2.

8.2.2 Essential Equipment In addition to the usual OR setup, various additional equipment may be required for MISS depending on the specific procedure in question. In general, a radiolucent bed is required for localization with fluoroscopy or O-arm navigation. We prefer a Jackson table that allows for the free movement of image guidance or fluoroscopic unit into and away from the surgical field. This is especially crucial when performing percutaneous instrumentation placement as it allows for unencumbered view of the spinal anatomy (▶ Fig. 8.3). Various tubular retractors are available ranging from 14-mm tubes to X-tube (25 mm expandable to 40 mm) for larger exposures. Minimally invasive instruments are also available from various vendors. For intraoperative visualization, endoscope, microscope, or loupes can be used depending on the pathology and intended procedure. The endoscope should be properly set up and white-balanced to optimize intraoperative visualization (▶ Fig. 8.4). A list of typical equipment needed for various MISS procedures is: ● Radiolucent bed (Wilson frame, Jackson bed). ● Tubular dilator system or spine access system (▶ Fig. 8.5). ● Minimally invasive instruments. ● Fluoroscopy (C-arm) or O-arm (▶ Fig. 8.6). ● Microscope. ● Endoscope and video tower.

8.3 Patient Positioning Correct patient positioning for MISS is critical and is often similar to open approaches. For decompressive procedures such as discectomy or laminectomy, using the Wilson frame may help to widen the interlaminar space to allow easier decompression (▶ Fig. 8.7). For fusion procedures, a Jackson table allows the abdomen to hang free with gravity and allows the spine to fall into its natural contour and is preferable. For lateral transpsoas procedures, the patient should be positioned in such a way that the iliac crest is at the break of the table. The adjustable surgical table is flexed so as to increase the iliac crest–rib cage distance. The disc in question is localized with lateral fluoroscopy, and marked directly lateral to the disc space. The importance of doing X-rays and ensuring the visualization anticipated during the surgery cannot be overemphasized. The patient should be properly secured with belts and cloth tape (▶ Fig. 8.8).

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Operating Room Setup

Fig. 8.1 Diagram demonstrating a typical OR layout for minimally invasive spine surgery. (a) The fluoroscopic unit is brought into the operative field to identify the level while the surgeon and personnel stand behind radiation shields. (b) The fluoroscopic unit is brought toward the feet and the microscope positioned to view the surgical field.

All pressure points must be carefully padded, with special attention paid to the eyes. The arms should be positioned 90 degrees at the elbow to minimize risk of brachial plexus injury. The tubular retractor holder can be secured to the side of the table and should be positioned so as not to get in the way of intraoperative fluoroscopy.

8.4 Radiation Safety Radiation safety is an important aspect of spine surgery, especially in MISS when fluoroscopy is used for percutaneous procedures. The fluoroscopy machine and O-arm emit ionizing

radiation in the form of X-ray (electromagnetic waves with frequency between 3 × 1016 and 3 × 1019 Hz). According to the ICRP (International Commission on Radiological Protection), the annual radiation dose limit is 20 mSv per year averaged over 5 years, with a maximal dose of 50 mSv in any single year.3 Proper radiation protection should be worn at all times to minimize radiation exposure. Thyroid shield, lead glasses, and lead gown are essential for reduction of radiation exposure (▶ Fig. 8.9). Typically, lead gowns with 0.25-inch thickness have 90% reduction in radiation, whereas 0.50-inch thickness gowns have 99% reduction. Protective lenses and gloves can also be worn to reduce radiation exposure to eyes and hands. All

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Fig. 8.2 An intraoperative photo showing OR setup during an endoscopic discectomy.

Fig. 8.3 Intraoperative images showing: (a) position of patient on a Jackson table with fluoroscopic unit, (b) pneumatic arm to hold tubular retractor, and (c) tubular retractor in place.

Fig. 8.4 (a) Demonstrating the white balancing of the endoscope prior to surgery to ensure good video quality. (b) Alternatively, an operative microscope can be used which provides for excellent 3D visualization of the anatomy and is readily available in most ORs.

nonessential personnel should leave the room or be stationed behind a lead shield as far away from the fluoroscope as the room allows. Additionally, instruments have been developed to hold the instruments when performing percutaneous procedures so that the surgeon can step away from the OR table while performing fluoroscopy. In addition, the surgeon and the OR personnel should stand as far from the radiation source as possible and turn head 90 degrees away from patient when taking images to reduce

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scatter to the eyes. Since the radiation follows the inverse squared law and drops significantly with increased distance,4 a person standing 3 feet away from the radiation source will experience four times greater radiation compared to someone standing at 6 feet away, and nine times greater radiation than someone standing at 9 feet away (see ▶ Fig. 8.9). Continuous fluoroscopy has significantly higher radiation dose compared to pulsed fluoroscopy; therefore, continuous fluoroscopy should be avoided if possible. During O-arm spin, the OR staff should

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Operating Room Setup go outside the room to minimize radiation exposure. It is preferred to stand opposite to the X-ray source (near the image intensifier) during lateral fluoroscopic imaging, and position the X-ray source below the patient to limit scatter. Also, image intensifier should be positioned as close to the patient as possible to reduce scatter to the rest of the room.

8.5 Operative Instruments and Retractors Operative instruments for minimally invasive procedures are specifically designed to facilitate visualization through the small surgical corridor. Tubular retractors and bayoneted instruments as well as a long tapered drill allow for easier maneuverability within the confines of a tubular retractor (▶ Fig. 8.10).

8.6 Electrophysiologic Monitoring Developments in implants have allowed for tissue-sparing percutaneous applications, which do not require bony spine anatomy exposure. Though one of the primary benefits of these techniques is to reduce tissue dissection and trauma, their application can potentially be made safer with intraoperative stimulation. Kwires can be stimulated before percutaneous pedicle screws are placed to make placement safer for the patient. Additionally, instrumentation can be stimulated using electromyographic (EMG) monitoring to help assure safe placement (▶ Fig. 8.11).

8.7 Conclusion Fig. 8.5 Intraoperative photograph demonstrating serial tubular dilators used for providing minimal access exposure during various minimally invasive procedures.

Understanding the basic OR layout and equipment setup is essential for ensuring a smooth workflow during minimally invasive procedures. Spine surgeons should also pay particular attention to radiation safety given the long-term health effect of excessive radiation.5

Fig. 8.6 An intraoperative photo demonstrating the room setup for MIS endoscopic discectomy including positions of the patient, surgeon, assistant, endoscope, video tower, C-arm, and the fluoroscopy monitors.

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Fundamentals

Fig. 8.7 (a) An intraoperative photo demonstrating a patient placed in the prone position on a Wilson frame for minimally invasive lumbar microdiscectomy. All pressure points are carefully padded with special attention paid to the eyes. (b) The Jackson table allows for easy anteroposterior visualization of the spine during percutaneous instrumentation placement.

Fig. 8.8 Intraoperative photo demonstrating a patient in the lateral position for an extreme lateral approach. The iliac crest is positioned at the break of the operating table with the patient properly secured with leather belts and cloth tape.

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Operating Room Setup

Fig. 8.9 Protective gear for radiation, including the thyroid shield and lead apron.

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Fundamentals

Fig. 8.10 (a) Bayoneted instruments and (b) long tapered drill designed for easy surgical maneuverability inside the (c) tubular retractors.

Fig. 8.11 Intraoperative stimulation of (a) Kwires and (b) percutaneous pedicle screws can help to assure safe placement and limit revisions.

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Operating Room Setup

References [1] Snyder LA, O’Toole J, Eichholz KM, Perez-Cruet MJ, Fessler R. The technological development of minimally invasive spine surgery. BioMed Res Int. 2014; 2014:293582 [2] Smith ZA, Fessler RG. Paradigm changes in spine surgery: evolution of minimally invasive techniques. Nat Rev Neurol. 2012; 8(8):443–450

[3] Wrixon AD. New ICRP recommendations. J Radiol Prot. 2008; 28(2):161–168 [4] Yu E, Khan SN. Does less invasive spine surgery result in increased radiation exposure? A systematic review. Clin Orthop Relat Res. 2014; 472 (6):1738–1748 [5] Singer G. Occupational radiation exposure to the surgeon. J Am Acad Orthop Surg. 2005; 13(1):69–76

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Part II Patient Education and Business Basics

II

9 Patient Education

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10 Establishing an Ambulatory Spine Surgery Center

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11 Establishing Ancillary Services and Health Care Regulatory Implications

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12 Bringing Novel Spine Devices to the Marketplace

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Patient Education and Business Basics

9 Patient Education Holly Weissman Abstract Evidence has shown that appropriate preoperative patient education prior to minimally invasive spine surgery can be very beneficial in terms of patient satisfaction and clinical outcomes. In the past, patient education prior to surgery consisted of a short, quick speech given by the surgeon or his or her assistant in the office, usually during the same visit as the initial preoperative office consultation. Patients usually have not found this very helpful, mostly because of the hurried nature of the speech and fear of asking questions. This chapter demonstrates the advantages of preoperative education programs compared to the more traditional “surgeon’s office” education. Specifically, we examine a computer-assisted education program, where patients can review slides on a computer at their own pace, and a preoperative education class offered at the hospital where the surgery will be performed. Advantages of each approach are discussed along with a review of why such programs are beneficial to the patient, the patient’s family, the hospital staff, and the surgeon. In our program, because of our preoperative patient education program, we have found a significant improvement in terms of length of stay as well as patient satisfaction surveys. Keywords: preoperative spine surgery, patient education

9.1 Introduction Historically, spine surgery for patients meant several weeks of a long recovery and restricted activity. Minimally invasive spine surgery has led to a paradigm shift for patients to have a shorter recovery period with a faster return to normal activity. Furthermore, since most patients have preconceived notions about spine surgery and the associated risks, benefits, recovery times, and long-term implications, it is imperative that surgeons and their support staff properly educate patients to help make patient expectations congruent with the new reality. In 2008, Keulers et al1 demonstrated that surgeons often underestimate their patients’ desire to receive extensive information prior to surgery. The study also found that surgeons and patients had differing opinions regarding the educational priorities. As one might predict, surgeons tended to focus on details of the surgery, while patients were more interested in receiving details on anesthesia, the postoperative course, and self-care. Patients considered these issues approximately 25% more important than their surgeons did. In other words, each party was most interested in what they perceived to be most important. Additionally, Keulers et al1 found that women demonstrated a significantly greater need for information than men. Women visit doctors more often, require more emotional support, often ask more questions, and are engaged in more conversation with health care providers than men. For many years, the medical literature has supported the fact that improved patient education results in improved clinical outcomes.2,3,4 The orthopaedic field has been able to demonstrate a decrease in length of stay for joint replacement patients

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who attend a preoperative class on joint replacements. The patient’s level of knowledge can quickly decline from the initial consultation despite supportive measures. This illustrates the need for a comprehensive spine education program prior to surgery.

9.2 Method of Patient Education The first priority is the method by which patient education will be delivered. Traditionally, the surgeon, together with office staff, has provided the majority of preoperative education in the office at the time of consultation. Unfortunately, patients seem to remember only a few basic points by the time they have their surgery. The brief nature of this “traditional” patient education, coupled with the high level of patient anxiety at that particular time, would clearly lead to decreased retention of the facts.

9.2.1 Traditional Patient Education Traditionally, surgeons provide basic education to their patients in the form of a brief discussion of what to expect pre-, peri-, and postoperatively, possible complications and risks, pain management, and how long it will take to heal and resume normal activities. Some surgeons do this in the form of a 5- to 10-minute didactic speech in their office; some utilize a nurse, midlevel provider, or another office employee; some rely on printed literature and brochures; and many use some combination of the above. The problem is that all forms of traditional patient education require passive learning on the part of the patient. Either someone is lecturing him or her, or the patient is asked to read or watch something with no way of determining the patient’s comprehension of the material. Additionally, anecdotally, patients have expressed that they are often too intimidated to interrupt the physician to ask “a stupid question” or afraid that the doctor is short on time and do not want to bother him or her to spend more of their time explaining. In contrast, a computer program controlled by the patient would help to standardize the educational material and ensure that all topics are covered, and the patient would ultimately control the pace of the learning.

9.2.2 Computer-Assisted Education A trial by Keulers et al5 compared patient education by a doctor versus a patient engaging computer program and concluded the computer program can be at least equally effective, and possibly more effective, than the physician. Interestingly, patients actually learned more by using the computer program but were also equally satisfied with either education they received. For many patients, an interactive computer program would be less intimidating and would allow patients to control the pace at which they learned. Preconceived notions of a physician-led education might lead patients to believe the physician would be less patient if they had questions or needed to slow down the flow of information.

Perez-Cruet et al, An Anatomic Approach to Minimally Invasive Spine Surgery, 2nd Ed. (ISBN 978-1-62623-643-1), copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.

Perez-Cruet, An Anatomical Approach to Minimally Invasive Spine Surgery | 01.10.18 - 10:54

Patient Education A well-designed computer program with appropriate audiovisual instruction, as well as patient interaction, can be much more effective and certainly more efficient with respect to time and cost. Such a program would allow patients to learn at their own pace, to take notes and copy and/or record segments to review again later, and to provide some degree of interaction (such as a quiz) which could evaluate the patient’s comprehension of the information received prior to surgery. The advantage of a computer education program is that it would save the spine surgeon and office staff a great deal of time by referring the patient to the computer program for the education. The surgeon and staff could answer any remaining questions patients may have after completing the computer program.

9.2.3 Preoperative Education Class Another option is to offer a preoperative spine class taught by a midlevel provider or office nurse. We currently offer such a class weekly at Beaumont Hospital in Royal Oak, MI, for all patients and their family members who are scheduled for both neurosurgery and orthopaedic spine surgery. The class has been very well received by the patients since it is taught by an experienced midlevel provider who describes each step of spine surgery starting with where to park on the day of the surgery and ending with what to expect following hospital discharge. The class has unexpectedly become a “peer support group” for some patients, as there are often patients and/or family members attending the class who have had spine surgery in the past. These people often give reassurance to first-time spine surgery patients, as it is always comforting for people to meet others who have undergone the same procedure. In fact, sometimes patients with spine surgery experience can be more helpful than the health care professionals. This preoperative spine class was developed using a multidisciplinary approach with input from spine surgeons, anesthetists, bedside nurses, midlevel providers, physical therapists, and discharge planning nurses. Based on prior patient satisfaction surveys, the group was able to identify the most common spine patient complaints and concerns, which were pain control, fear of anesthesia, fear of Foley catheter, fear of mobilization after surgery, and fear of going home too soon. The foundation for the class was built upon these complaints and concerns. The class lasts approximately 1 hour and 30 minutes to accommodate all patients’ questions and concerns.

9.2.4 Introductory Education Spine anatomy is reviewed at the beginning of the class using slides along with models of the normal and pathologic spine. It is notable that the patients really enjoy and appreciate the spine models, as they allow a hands-on, interactive experience. The class also has other interactive props including an incentive spirometer, sequential compression device, Jackson Pratt (JP) and hemovac drains, cervical collars, and back braces. Pictures of the hospital areas as well as a hospital scrub color guide are included in the class. Patients have stated the photos and hands-on props from the class decrease their level of anxiety prior to their spine surgery since they have a better idea of what to expect.

Pain Management The majority of the class is dedicated to pain control and a review of the pharmacologic and nonpharmacologic methods. Intravenous pain medication is compared to oral pain medication with respect to duration of each drug and the importance of transitioning to oral medication as soon as possible. Patients are taught that they will not be “pain free” after surgery, as they will have incisional pain. Most likely their preoperative, neuropathic pain will be resolving if not gone immediately after surgery. Additionally, patients are given reassurance that incisional pain is normal, and nurses will work closely with them to help control their pain. They are instructed to notify the nurse when pain is moderate and not to wait for it to be intolerable. Patients are also reminded they will have less postoperative pain with the minimally invasive spine technique compared to the traditional open spine technique.

Postoperative Education Early mobility is also highly emphasized in the class since minimally invasive spine surgery allows patients to return to activity faster than the traditional open spine technique. Patients are instructed that they will be out of bed on the same day of surgery, which in turn decreases muscle spasms and pain along with a shorter length of hospital stay. Patients are often surprised but happy to hear they will be out of bed on the same day of surgery. Spine precautions are explained in detail several times throughout the class to remind the patient to avoid bending, twisting, driving, and lifting until cleared by their spine surgeon. Patients are also reminded to consider alternative measures for caring for their pets after surgery since pets often weigh more than 10 pounds. Constipation and proper nutrition are also discussed in the class. Patients are instructed to maintain a healthy diet with protein for proper wound healing, and high fiber and adequate water intake is recommended to prevent constipation. Patients are also instructed to begin a bowel regimen, stool softener, and/or polyethylene glycol 3350 prior to surgery since constipation following spine surgery can cause a great deal of pain and potential surgical problems. Patients are also instructed to continue some kind of bowel regimen after surgery and to pay attention to their bowel movements as constipation could occur once they are at home. Specifically, patients are informed how opiate pain medications, anesthesia, decreased mobility, and decreased fluid and/or fiber intake can all lead to constipation. The question and answer session at the end of the session has been one of the patients’ favorite sections of the class. Many patients stated that they benefited greatly from listening to questions of other patients and the subsequent answers. A few frequently asked questions include: ● “When will I be put to sleep and will I hear anything in the OR?” ● “How far will I have to be pushed down the hall to go into the OR?” ● “Will I be asleep when the Foley catheter is placed?” ● “What will I be wearing into the OR?” These are just a few examples of information the spine surgeon would most likely not address as part of the traditional education given during a preoperative office consultation. The

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Patient Education and Business Basics

Fig. 9.1 Comparison of the average length of hospital stay among pre- and postclass patients.

class welcomes any and all questions, many of which patients might feel uncomfortable asking their surgeon.

9.3 Conclusion Each patient who attends the class completes an evaluation on a scale of 1 to 5, where 1 is “not useful” and 5 is “very useful” information. The majority of the class attendees ranked the class at a 5, and none of the attendees ranked it as a 1 or 2. A retrospective review of elective minimally invasive spine patients who attended the class was performed. It demonstrated a decrease in the average length of stay for patients who attended the class as compared to patients who did not attend. A target length of stay is 2.3 days. For patients who attended the class, the average length of stay was just 1.8 days. Additionally, the overall length of stay for all patients decreased from 2.4 to 2.3 days following initiation of the class. This demonstrates the impact of the class, even though a large majority of patients did not even attend (▶ Fig. 9.1). Moving forward, Beaumont Hospital in Royal Oak, MI, is developing a DVD version of the class that can be distributed to all

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patients prior to spine surgery. This will allow us to provide the same patient education to everyone, not just the small minority of patients who are able to attend classes at the times offered. It is anticipated that by providing more thorough patient-focused preoperative education, we will be able to effectively improve patient satisfaction, decrease average length of stay, and ultimately improve clinical outcomes.

References [1] Keulers BJ, Scheltinga MRM, Houterman S, Van Der Wilt GJ, Spauwen PH. Surgeons underestimate their patients’ desire for preoperative information. World J Surg. 2008; 32(6):964–970 [2] Pederson LL. Compliance with physician advice to quit smoking: a review of the literature. Prev Med. 1982; 11(1):71–84 [3] Mullen PD, Mains DA, Velez R. A meta-analysis of controlled trials of cardiac patient education. Patient Educ Couns. 1992; 19(2):143–162 [4] Krishna S, Balas EA, Spencer DC, Griffin JZ, Boren SA. Clinical trials of interactive computerized patient education: implications for family practice. J Fam Pract. 1997; 45(1):25–33 [5] Keulers BJ, Welters CFM, Spauwen PHM, Houpt P. Can face-to-face patient education be replaced by computer-based patient education? A randomised trial. Patient Educ Couns. 2007; 67(1–2):176–182

Perez-Cruet et al, An Anatomic Approach to Minimally Invasive Spine Surgery, 2nd Ed. (ISBN 978-1-62623-643-1), copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.

Establishing an Ambulatory Spine Surgery Center

10 Establishing an Ambulatory Spine Surgery Center Richard N.W. Wohns, Hiroshi W. Nakano, and Laura Miller Dyrda Abstract Outpatient spine surgery allows the spine surgeon to maintain tight control of cost and quality, responding to the needs of not only the surgeon and the patient, but also insurance companies. The cost for outpatient spine surgery is 50 to 70% lower than for the same procedure performed in a hospital. MIS spine procedures are 30 to 60% less costly than traditional surgery. Besides the lower cost, MIS also offers the significant advantages of shorter recovery times and decreased rates of recurrence. In this era of cost containment, particularly given the increased demands by baby boomers for healthy spines, outpatient and MIS spine surgery will continue to increase in frequency. My prediction is that we will see an increasing percentage of spine surgeries transition to outpatient surgery centers. It is therefore critical for spine surgeons to understand how to establish an outpatient spine surgery center. Keywords: outpatient spine surgery, outpatient spine surgery center, minimally invasive spine surgery, MIS spine surgery, ambulatory spine surgery

10.1 Introduction Over the past 20 years, an increasing number of spinal surgeries have transitioned from inpatient to outpatient. This is due to multiple factors including the evolution of minimally invasive spine surgery (MIS), improved anesthetic regimens, lower infections and higher patient satisfaction in outpatient facilities than in hospitals, and market forces. The new era of health care reform allows opportunities for small, market-responsive outpatient spine surgery centers to capture segments of the market by providing high-quality care in a narrowly defined, specific area. Outpatient spine centers are essentially boutiques that deliver world-class care in a highly focused niche, i.e., Regina Herzlinger’s “focused factories.”1 The Shouldice Hospital model for hernia surgery in Canada was the original focused factory. The Shouldice model proved that when a limited number of procedures are done in high volume by the same providers and staff, the outcomes are better, the costs are lower, and the patients are more satisfied. Outpatient spine surgery allows the spine surgeon to maintain tight control of cost and quality, responding to the needs of not only the surgeon and the patient, but also insurance companies. The cost for outpatient spine surgery is 50 to 70% lower than for the same procedure performed in a hospital. MIS spine procedures are 30 to 60% less costly than traditional surgery. Besides the lower cost, MIS also offers the significant advantages of shorter recovery times and decreased rates of recurrence. In this era of cost containment, particularly given the increased demands by baby boomers for healthy spines, outpatient and MIS spine surgery will continue to increase in frequency.

Presently, the range of spinal procedures that are frequently performed in an outpatient setting includes the following procedures: ● Anterior cervical discectomies with fusions (one, two, and three level). ● Cervical disc arthroplasties (one and two level). ● Cervical foraminotomies and posterior discectomies. ● Lumbar microdiscectomies. ● Lumbar laminoforaminotomies. ● Lumbar laminectomies. ● MIS lumbar fusions including XLIFs, TLIFs, and interspinous process fusions. Cervical arthroplasties, or total disc replacements (TDRs), are an excellent example of a fairly new and very successful addition to the world of outpatient spine surgery. Based on the proven safety, cost effectiveness, clinical outcomes, and patient satisfaction with anterior cervical discectomy and fusion (ACDF), it was a natural next step to perform outpatient arthroplasties. Arthroplasties offer quicker recovery than ACDF, preserved motion of the neck, and less chance of developing adjacent disc degeneration which might require further surgery. The 5-year disc replacement data compared with fusion have demonstrated that patients who underwent TDR had 97.1% probability of no secondary procedures, compared with 85.5% for ACDF patients.2 No reoperations were due to implant breakage or device failure. In total, 2.9% of TDR patients had reoperations within 5 years of the initial surgery, compared with 14.5% of ACDF patients. I have recently reported a consecutive series of 132 outpatient cervical arthroplasties from 2009 through April 2013 with 92% improved symptoms, an average operative time of 60 minutes for one level and 80 minutes for two levels, and an average time to discharge of 3 hours. There was no significant morbidity and no mortality. There were no transfers to a hospital, no postoperative ER visits, and no late hospitalizations. The cost for outpatient cervical arthroplasty is lower than the cost for ACDF, and is less than 50% of the cost of the same procedure in a hospital. My prediction is that we will see an increasing percentage of spine surgeries transition to outpatient surgery centers. It is therefore critical for spine surgeons to understand how to establish an outpatient spine surgery center.

10.2 Ambulatory Spine Centers The new era of health care and managed care introduced in the mid-1990s created an opportunity for market-responsive organizations and outpatient surgery centers to capture new market segments by providing high-quality specialty care. Outpatient surgery centers have now become the standard practice in many communities across the United States. These boutique health care providers are designed as “Centers of Excellence” to deliver world-class care in highly focused medical or surgical niches. Herzlinger,1 of the Harvard Business School,

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Patient Education and Business Basics called them “focused factories” in her book titled Market Driven Health Care. Procedures performed in an outpatient spine surgery center cost approximately 30 to 60% of the cost of the same procedures performed in a traditional acute care hospital; this will be a key driver of outpatient spine surgery growth in the future. Freestanding or independent ambulatory surgery centers (ASCs) designed specifically for outpatient spine surgery allow experienced neurosurgeons and orthopaedic spine surgeons to perform high-quality spine surgery in an environment that maintains tight control of costs and is responsive to the needs of these surgeons and their patients. ASCs provide an outstanding venue for spine surgery from the patient, surgeon, and insurance company (payor) perspective. The benchmarks of success for this concept are as follows: ● Payor recognition of the cost-savings opportunities in outpatient spine surgery centers. ● High availability of operating room utilization at each location. ● Patient and surgeon satisfaction with the surgical experience and outcomes. ● Adequate return on investment. As payors and the government evaluate clinical outcomes and patient satisfaction, as well as price to determine the proper site of service for spine surgery, ASCs will be well positioned to contribute to the solution. Eventually, patients throughout the world with disc herniations, stenosis, and spondylolisthesis—which contribute to the majority of spinal disorders—will become aware of the opportunities and advantages outpatient surgery centers afford, and they will demand such treatment. A real-world precedent for this concept is the Shouldice Hospital in Toronto, Canada, which is worldrenowned for its specialization in hernia surgery. The Shouldice reputation is such that patients with hernias worldwide desire surgery at this institution, and these hernia patients even return to Shouldice Hospital for reunions to compare their scars! However, not all back pain patients are good candidates for surgery. Incorporating an interventional pain program into an outpatient spine surgery center will promote greater facility utilization and a broader set of agreements with payors, and extend the reputation of the outpatient spine surgery facility by capitalizing on word-of-mouth endorsements in both the medical and patient communities.

10.2.1 Inpatient versus Outpatient Surgical Services: Effect of Managed Care on Facilities and Surgeons The health care market is progressing along a path that leads to various degrees of managed care. For surgical procedures, payors may have an approved list of surgeons to whom they direct their members. Typically, payors negotiate contracts for fees with these preapproved surgeons, who provide significant discounts—in the range of 30 to 50% of standard fees—to patients who are covered by these payors.

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Insurance companies use tracking data to obtain the cost of a given surgical procedure—which includes the surgeon’s fees plus hospital costs—for all qualifying physicians in a geographic area to develop physician-specific profiles and steer their members toward low-cost providers. Surgeons view this cost profiling with concern because it could have a significant impact on an individual surgeon’s patient flow. Although insurance companies have not yet made significant use of profiles to select surgeons, the surgical community is deeply concerned this will eventually occur. Consequently, surgeons have become acutely aware of surgical costs. Outpatient spine surgery centers leverage lower costs to positively impact surgeon profiles. Surgery performed in these specialized facilities will be less costly and have demonstrably better outcomes than similar procedures performed in hospitals. As a result, surgeons who choose to operate at an outpatient spine surgery facility will have better insurance cost profiles and insurance companies, referring physicians, and patients will see them as a preferred caregiver. Clearly, the trend toward same-day, or ambulatory, surgery is not just a fad. Rather, it is a major change in the practice of surgery and here to stay. According to the U.S. National Health Statistics,3 48.3 million surgical procedures and nonsurgical procedures were performed during 28.6 million ambulatory surgery visits in 2010. Around 22.5 million of those visits occurred in ASCs. The number of ambulatory procedures performed in the United States based on the National Health Statistics Report revision is based on 2010 numbers published in February 2017 (▶ Table 10.1).3 Minimally invasive surgery is less costly than traditional surgery. A 2012 study published in Risk Management and Healthcare Policy journal4 found minimally invasive posterior lumbar interbody fusion cost $2,825 less on average than the traditional open technique at the hospital. When the procedure is performed in an outpatient surgery center, the cost savings is estimated at 30 to 60% of the cost of comparable inpatient hospital procedures. Table 10.1 The number of ambulatory procedures performed in the United States based on the National Health Statistics Report3 Procedure category

Procedures

Endoscopy of large intestine

4 million

Endoscopy of small intestine

2.2 million

Extraction of lens

2.9 million

Insertion of prosthetic lens

2.6 million

Injection of agent into spinal canal 2.9 million Digestive system

10 million

Integumentary system

4.3 million

Nervous system

4.2 million

Musculoskeletal procedures

7.9 million

Eye procedures

7.9 million

Perez-Cruet et al, An Anatomic Approach to Minimally Invasive Spine Surgery, 2nd Ed. (ISBN 978-1-62623-643-1), copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.

Establishing an Ambulatory Spine Surgery Center Even if raw costs are not compared, minimally invasive surgery holds huge advantages in areas such as quicker return to work, decreased recidivism rate, higher facility utilization, and increased physician productivity. An example of the benefits of minimally invasive or outpatient spine surgery is presented in ▶ Table 10.2.5 Many patients fear traditional invasive surgery and they “suffer in silence.” Such patients are more likely to accept minimally invasive surgery, which will improve their productivity and quality of life. Nationally recognized surgeons have begun to perform these procedures on an ambulatory basis with excellent outcomes, high patient satisfaction, and diminished costs for patients and insurers.

10.2.2 Furnishing a Minimally Invasive Spine Surgery Suite The minimally invasive spine surgery suite has different equipment needs than the traditional operative arena, so the optimal operative suite is somewhat larger. Because the goal of these approaches is to minimize tissue dissection, surgeons frequently use fluoroscopy. At times, two fluoroscopy units are required, such as when surgeons perform vertebroplasty or kyphoplasty. Table 10.2 Cost examples for minimally invasive or outpatient surgery Inpatient

Outpatient

Single-level minimally invasive instrumented posterior lumbar fusion Total bill charges

$75,663

$42,500

Average insurance payment

$26,711

$23,208

Single-level minimally invasive transforaminal lumbar interbody fusion Total bill charges

$160,606

$45,499

Average insurance payment

$59,251

$25,000

Source: Data from Dyrda.5

Video imaging equipment is also required. Outpatient spine surgeons have found high-definition video monitors provide the best image quality and are oftentimes readily available. Endoscopes, cameras, and light sources play a critical role in video image quality. Outpatient spine surgeons have also found a three-chip camera provides the best image. The video image’s contrast and color can be adjusted to allow for adequate operative field visualization. Alternately, many of these procedures can be performed under loupe or microscope magnification, which provides the added benefit of three-dimensional visualization. However, the angulation of the endoscope allows one to “look beyond the confines of the tube,” and is particularly useful when performing contralateral decompression such as in endoscopic lumbar laminectomy. Additionally, laparoscopic and thoracoscopic equipment can use similar light sources, cameras, and monitors. The standard tubular dilator system comes with tubes of varying sizes. When performing these procedures, larger tube diameters (i.e., 22 and 24 mm) facilitate the process. More recently, expandable tubular systems allow even greater exposure at the depth of the tube. Patients should be positioned on a radiolucent frame, particularly when anteroposterior fluoroscopic imaging is necessary, such as during percutaneous pedicle screw placement or vertebroplasty. The operating table’s base should allow for both anteroposterior and lateral fluoroscopic images. Therefore, an operating table with a large fixed center base is often not suitable, particularly when anteroposterior fluoroscopic images are required. The operating room setup should provide the surgeon with a clear field of view of both the video monitor and the fluoroscopic monitor (▶ Fig. 10.1). Two monitors are frequently used on either side of the patient: one opposite the surgeon and the other opposite the assistant. Properly position and secure cables to reduce clutter. Instruments specifically made for minimally invasive procedures are required. These instruments are usually long, tapered, and bayoneted to reduce field-of-view obstruction and facilitate dissection (▶ Fig. 10.2). Precision instruments such as No. 1 and 2 Kerrison punches, micropituitary rongeurs, and fine 1- and 2-mm curettes help facilitate these procedures. In this regard,

Fig. 10.1 Operating room setup with video monitor and C-arm in place.

Perez-Cruet et al, An Anatomic Approach to Minimally Invasive Spine Surgery, 2nd Ed. (ISBN 978-1-62623-643-1), copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.

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Patient Education and Business Basics

Fig. 10.2 Frequently used operative equipment in operating theater for minimally invasive spine surgery. (a) Long tapered electric drill. (b) Bayoneted and microsurgical instruments. (c) Expandable tubular retractor.

a long tapered smooth-running electric drill is used with a 1- or 2-mm bit. Foot pedal control frees hand movement, and the lack of a “kick” experience when using an electric drill improves safety when working near the neural elements. Suction retractors are also useful and permit one instrument to perform two functions, thus reducing the number of instruments in the operative field. Electrophysiologic monitoring is also critical. We frequently employ somatosensory evoked potentials and electromyography, and these monitoring techniques require a dedicated team of electrophysiologists to properly interpret readings. Some systems allow the surgeon to easily interpret readings in situations such as during pedicle screw stimulation to access screw placement. The operating room staff should be familiar with the equipment needs as well as the setup to facilitate the procedures. This can be achieved by reviewing the equipment needs and, if necessary, performing a “dry run” to make sure that the cables, cameras, and other equipment are in proper working order. The staff can also identify potential problems that add time to the operative procedure during this rehearsal. At the outset, outpatient spine surgery centers should be developed in major urban areas in the United States. The number of spine surgeries performed in the United States in 2012 reached 600,000.6 Initially, each outpatient spine surgery facility should have two fully equipped operating theaters. Operating rooms should be designed for rapid and efficient patient turnover and to allow physicians to concentrate on the parts of the procedure that require their skills. Space for an additional two theaters should be available to accommodate future expansion as demand increases. An outpatient spine surgery facility with two to four operating rooms provides the scale to cover fixed costs, yet remains sufficiently small and responsive to patients. Additionally, this size will ensure a high facility utilization rate.

10.2.3 The Market for Outpatient Spine Surgery Services Market Sizing The national occurrence of a range of primary diagnosis that resulted in spinal discectomy procedures in 2011 gives a reported

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occurrence of more than 370,000 spinal discectomies. These data were reported by “The Burden of Musculoskeletal Diseases in the United States,”7 which is a joint project of the American Academy of Orthopaedic Surgeons, American Academy of Physical Medicine and Rehabilitation, American College of Rheumatology, American Society for Bone and Mineral Research, Arthritis Foundation, National University of Health Sciences, Orthopaedic Research Society, Scoliosis Research Society, and the United States Bone and Joint Initiative. Using an estimate to equate to an outpatient spine surgery center capturing a market share of 20% of the spine surgeries currently being treated with minimally invasive techniques, this results in 38,400 lumbar discectomies in an ASC and approximately 27,850 cervical discectomies nationwide (data obtained using SG2 Analytics). Using the national occurrence numbers above, the estimated number of patients in King County, WA, in 2007, who had similar set of diagnosis that resulted in a lumbar discectomy was 1,187. Similarly, the estimated number of patients with a cervical disc diagnosis who underwent a cervical microdiscectomy was 860.8 The 2007 population of King County was approximately 1,861,300, according to the King County Annual Growth Report.8

A Trend toward Outpatient Surgery Hospitals are concluding it is more profitable to have all types of outpatient procedures moved into ASCs. Existing ASCs are looking to add new and profitable services. Single-practice specialty groups reeling from lower reimbursements and higher overhead costs associated with new regulations have found ASC ownership is one of the last bastions of profitability in private practice medicine. ASCs depend on physicians bringing their cases for survival, and the key to increasing case volume is pleasing surgeons with an efficient facility. Neurosurgeons will be able to directly influence patient flow into an outpatient spine surgery center using their ties in the medical community. The target patient customer is someone who requires “high-tech” minimally invasive procedures such as microscopic or microendoscopic discectomy. Among payors, the outpatient centers should target health care

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Establishing an Ambulatory Spine Surgery Center plans that will provide sufficient payment to ensure an adequate return; they should further target health plans that show a preference for an ASC and would be willing to develop an ongoing relationship. These health plans may even share in promotion, outcome studies, and Health Plan Employer Data and Information Set reporting. Surgeons consider a variety of factors when choosing a surgical facility. Most important is the quality of service, including anesthesia and nursing care. One important aspect of quality for surgeons is the ability to create an environment in which they can work best. This includes employing staff who are familiar with their style and preferences (i.e., a smoothly functioning team), and providing high-tech equipment. Another unspoken but important criterion is the way the staff interacts with the surgeon. A surgeon is unlikely to prefer working in a facility where the staff is cold, impersonal, hostile, or unpracticed. The “facility mix” for surgeons includes associations with: ● One or more hospitals. ● Zero, one, or two outpatient surgery centers with a high likelihood that these are affiliated with a hospital rather than freestanding. ● One’s practice office. ● One or more satellite offices. Orthopaedic surgery physician practice groups may own their own surgical center, and increasing numbers of neurosurgery practice groups own their own surgical center. Outpatient spine surgery center owners and operators must educate ASC administrators, surgeons, insurance companies, and patients that spine surgery and other related pain management and surgical procedures can be performed more cost-effectively and to the same level of quality as they could in an inpatient hospital setting in order to attract new business. At present, most neurosurgeons conduct 5% of their practices in an outpatient setting, yet this percentage could conceivably increase to 50% in an outpatient spine surgery center.9 The centers should select and hire anesthesiologists, nurses, and technicians with established reputations for the highest quality, most efficient outpatient surgical care. For surgeons, bringing cases to the ASC is attractive because of its geographic proximity to the office, speed of transportation to the facility, and short procedure time from start to finish. Being able to schedule operations at a convenient time is also important to surgeons and patients. When surgeons use a facility frequently, block time is reserved for their sole use. The facility’s ability to respond to unusual requests, such as an additional case in the late afternoon, will also influence a surgeon’s perception of a surgical facility. The outpatient spine surgery center should be able to meet and exceed these needs.

10.2.4 Physician Benefits Most surgeons have dedicated insurance staff to process claims and negotiate each claim individually with the payor. This approach is expensive and frustrating for the surgeon. In fact, interacting with insurance companies is often cited as one of the factors responsible for diminishing job satisfaction among surgeons. To address this issue, the outpatient spine surgery center should offer “bundled” fees to the insurance companies, which

would include the surgery center fee, the surgical fee, and the anesthesia fee. Such bundled fees are attractive to insurance companies, especially if the bundled total is significantly less than the sum of the component fees. Such an arrangement can be a “win-win” situation because the insurance company has a lower payment, the ASC is motivated to control costs even more tightly, and the patient may have a lower deductible fee. A bundled fee will further allow the outpatient spine surgery center more room to negotiate reimbursement schedules with payors if necessary. To support cost containment, the outpatient centers should maintain a database for outcomes analysis, which is becoming a requirement for managed care contracting. Increased emphasis on accountability is anticipated in addition to cost containment going forward. An additional need among surgeons is part-time office space. Some surgeons have two or three offices, each with its own overhead. A surgeon may want a presence in a certain geographic market but will not be able to use the office on a full-time basis. The outpatient spine surgery center should have available office space surgeons can rent on an hourly basis. The surgeon would be able to operate part of the day and see patients the rest of the day without traveling to a different office. The surgeon could thus maintain an additional office with less expense. This office space may be considered a virtual office and will be paperless, and staffed by a receptionist and nurse, with commensurate low overhead per surgeon as a result of time-sharing. Generate standardized preoperative (▶ Fig. 10.3) and postoperative (▶ Fig. 10.4) order forms for patients undergoing outpatient spinal procedures to further improve efficiency. The outpatient spine surgery centers should simplify and streamline record keeping with a major focus on easing the surgeons’ paperwork burden. At the completion of an operation, the surgeon usually dictates a detailed record of what was done and sends a letter to the referring physician. Dictation can simplify this process. Where possible, a dictation template should be used for a particular operation as performed by a particular surgeon. The surgeon would then fill in the necessary blanks to complete the dictation, and a letter would be generated to the referring physician. Surgeons will find this approach attractive as it will free them up to spend more time performing surgery, and satisfied surgeons generate positive word-of-mouth recommendations in the local surgical community. Another benefit of the outpatient spine surgery center is a reduction in paperwork for the staff. In most hospitals, the circulating nurse in the operating room spends much of his or her time filling out paperwork. At the outpatient spine surgery center, this paperwork will be completed electronically with considerable time savings for the nurse.

10.2.5 Patient Benefits The patient’s most important need is to have a successful outcome of surgery with the least possible disruption of daily living and normal routine. The nature of the facility is not usually an expressed need of the patient, beyond certain minimal expectations. If all goes well, however, the facility and its function become important. Patients will favorably receive a pleasant, punctual, comfortable facility that provides amenities for both patients and their families. Patient education including clear preoperative

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Patient Education and Business Basics Fundamentals

Fig. 10.3 Standard preoperative order form.

OUTPATIENT SPINE SURGERY PREOPERATIVE ORDERS (optional) DIAGNOSIS

Outpatient admission PREOPERATIVE and INTRAOPERATIVE NPO after midnight prior to surgery

CONSENT FOR

SURGEON

PREOP MEDICATIONS PRIMARY CARE PHYSICIAN(S)

CBC BUN/CREAT PT LYTES PTT GLUC EKG CXR HCG Start IV—LR @ TKO rate (0.9 NaCl if diabetic) SCD and TED hose Muscle Relaxants Diazepam, 10 mg PO, with sip of water on call to OR Cyclobenzaprine, 10 mg PO, with sip of water on call to OR Antibiotics Cefazolin, 2 gm IVPB Clindamycin, 600 mg IV (PCN allergy) Vancomycin, 1 gm IV slowly Steroids Decadron, 8 mg IV

(▶ Fig. 10.5) and discharge (▶ Fig. 10.6) instructions helps to eliminate confusion and improves patient care.

10.3 Keys to Establishing a Successful Minimally Invasive Spine Center 10.3.1 Philosophy of Care Key elements of a successful practice include a well-articulated philosophy of care that drives all decisions made within the practice; a knowledgeable staff whose personalities and personal objectives support those of the practice; and an effective communication system for patients, physicians, staff, and referring health care providers. Although most practitioners have personally defined a broad philosophy for patient care, few actually articulate their patient care philosophies to their staff and those around them in a formal manner. According to the Institute of Medicine,10 the following principles apply: ● Safe: avoiding injuries to patients from the care that is intended to help them. ● Effective: providing services based on scientific knowledge to all who could benefit, and refraining from providing services to those not likely to benefit.

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●

●

●

●

Patient-centered: providing care that is respectful of and responsive to individual patient preferences, needs, and values and ensuring that patient values guide all clinical decisions. Timely: reducing waits and sometimes harmful delays for both those who receive and those who give care. Efficient: avoiding waste, including waste of equipment, supplies, ideas, and energy. Equitable: providing care that does not vary in quality because of personal characteristics such as gender, ethnicity, geographic location, and socioeconomic status.

The role of leaders is to define and communicate the purpose of the organization clearly and establish the work of practice teams as being of highest strategic importance. Leaders must be responsible for creating and articulating the organization’s vision and goals; listening to the needs and aspirations of those working on the front lines; providing direction; creating incentives for change; aligning and integrating improvement efforts; and creating a supportive environment and a culture of continuous improvement that encourages and enables success.10 Leadership is imperative to create and maintain effective health care teams. Physicians play a key role (whether formal or informal) in determining the direction of their organizations. The health care team’s philosophy of care, mission, objectives,

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Establishing an Ambulatory Spine Surgery Center

OUTPATIENT SPINE SURGERY POSTOPERATIVE STANDING ORDERS (optional) ACTIVITY Up as tolerated

MEDICATIONS Analgesics Vicodin, 1-2 tablets PO every 4-6 hours PRN pain Roxicet 5/500, 1-2 tablets PO every 6 hours PRN pain Darvocet N-100, 1-2 tablets PO every 4-6 hours PRN pain Acetaminophen with codeine #3, 1-2 tablets PO every 4-6 hours PRN pain

CONSULTS Physical therapist/occupational therapist to see patient for evaluation and treatment prior to discharge TREATMENTS/NURSING Vital signs every 30 minutes for the first 2 hours; then every hour until discharge Incentive spirometry every hour with 10 inhalations Maintain surgical dressing; change only if soiled

Muscle Relaxants Valium, 5 mg PO TID PRN muscle spasm Baclofen, 10 mg PO every 8 hours PRN muscle spasm Flexeril, 10 mg PO TID PRN muscle spasm

NUTRITION NPO until fully awake; then clear liquids and advance to general as tolerated

Antibiotics

DISCHARGE PLANNING On discharge, give patient prescriptions (front of chart) Provide patient/family with discharge instruction sheet Discharge patient if able to ambulate independently, void, and tolerate taking food or liquid by mouth and meets outpatient discharge criteria

Cefazolin, 2 gm IVPB, to be given 8 hours after preop dose Clindamycin, 600 mg IVPB, to be given 8 hours after preop dose Vancomycin, 1 gm IVPB, to be given 12 hours after preop dose

APPOINTMENT DATE AND TIME with Dr. Fig. 10.4 Standard postoperative order form.

OUTPATIENT SPINE SURGERY PREOPERATIVE INSTRUCTIONS (optional) You are scheduled for surgery on

with Dr.

.

Surgery Details 1. Please contact your primary care physician for a medical evaluation prior to your surgery. 2. Please make sure you contact your insurance company with your surgery date. Surgical Procedure Preoperative Preparation 1. Stop smoking. 2. Stop taking nonsteroidal anti-inflammatory agents (Advil, Aleve, Anaprox, aspirin, baby aspirin, Celebrex, Daypro, ibuprofen, Indocin, Lodine, Lovenox, Motrin, Naprosyn, Nuprin, Relafen, Toradol, Vioxx, Voltaren) at least 10 days before your surgery. 3. Shower and wash your hair the night before or the morning of surgery. 4. Take only required medications (blood pressure meds, etc.) with a sip of water the morning of surgery. 5. Do not eat or drink after midnight the night before surgery. 6. Please inform us if you have a cold, fever, infection, or new onset of conditions that may increase your surgical risk before the day of surgery. 7. The hospital will contact you several days before your surgery to set up a day and time for testing and to meet with an anesthesiologist. 8. If your x-rays were taken at a different facility from where you will be having surgery, please remember to bring them with you on the day of surgery. DO NOT HESITATE TO CALL OUR OFFICE WITH ANY FURTHER QUESTIONS. Fig. 10.5 Preoperative instructions.

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OUTPATIENT SPINE SURGERY DISCHARGE INSTRUCTIONS (optional) Your follow-up appointment is on

with Dr.

.

After Surgery 1. Use your prescribed pain medication, muscle relaxants, and laxatives as directed. 2. You have NO stitches to remove. Do not soak in a bathtub for one week after surgery. An adhesive was used to seal the incision. You can shower the next morning, and pat your incision dry. Steri-Strips were used to close your incision. You can shower after surgery, but keep the incision dry until after the fourth postoperative day. The light wound dressing can be removed after 2 days. After 7 days, if the Steri-Strips begin to peel off, they can be removed. 3. Do not bend, twist, or lift any excessive weight and keep weight lifted to less than 8 pounds (gallon of milk), for 2 weeks after surgery. Walking is encouraged. 4. Progressively increase your activity level as you become more comfortable. You can resume work activities 1 to 3 weeks after surgery depending on the type of work you perform. Please consult with your physician. 5. Do not drive until you are comfortable doing so or after your follow-up appointment and you have full range of motion. 6. If you experience ANY signs of a wound infection (see below), do not hesitate to call our office. 7. You can have sex when comfortable to do so.

NOTIFY your physician if you experience any of the following: 1. Fever 2. Chills 3. Warmth or redness at surgical site 4. Drainage from incision 5. Persistent headache 6. Swelling or tenderness of calf or thigh DO NOT HESITATE TO CALL OUR OFFICE WITH ANY FURTHER QUESTIONS. Fig. 10.6 Discharge instructions.

and goals should be thoughtfully defined and articulated to all team members. Although it is a common occurrence for these types of documents to be enthusiastically developed and then filed away, never to be seen again, highly effective teams will incorporate these blueprints into their everyday decisions for personnel selection, performance evaluations, quality improvement processes, outcomes evaluation, and program development. Whether the team is a solo physician practice or a large physician organization, the philosophy of care should drive all decisions for the team (▶ Fig. 10.7). Whereas the philosophy of care and mission statements are considered relatively stable elements of the organization, objectives and goals should be fluid, with adjustments made in response to market changes, new technology, and other outside forces. Well-articulated philosophies, mission statements, objectives, and goals are only as good as the people who carry them out. Individual team members’ philosophies and objectives need to align with those of the organization.

10.3.2 Advisory Board and Strategic Partners The outpatient spine surgery center should establish strategic relationships with a number of companies. Establishing partnerships with both a major manufacturer of instruments for spine surgery and a manufacturer of surgical microscopes is

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Philosophy of Care

Mission Statement (Overall description of why the organization/group exists)

Objectives (Broad statements of overall goals)

Goals (Specific statements that support the overall objectives that are time-oriented and measurable)

Fig. 10.7 Philosophy of care algorithm.

considered key to an outpatient spine surgery center’s success because these relationships will ensure the center’s ready access to high-quality surgical equipment.

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Establishing an Ambulatory Spine Surgery Center

10.3.3 Ambulatory Surgical Center Staff Key responsibilities at the corporate level include management and oversight of clinic operations; payor, hospital, patient, and physician relationship management; and management of the information generated by operational activities at the clinic level. The outpatient spine surgery center should have a core team of dedicated surgical and administrative staff as well as a select group of participating neurosurgeons from the surrounding geographic area. As the patient volume grows at a given location, additional surgical theaters should be brought online and additional nursing staff added. ▶ Table 10.3 shows the typical staffing of both associated professionals and full-time employees at a representative outpatient spine surgery center. The health care team may be comprised of any number of caregiver types depending on the size of the organization, types of patients cared for, acuity level of the patients, and number of physicians. The clinical team may consist of a variety of caregivers.

Physician Assistants The typical physician assistant (PA) program is 24 to 25 months long and requires at least 2 years of college and some health care experience before admittance. More than half of the programs award a master’s degree.11 Physician assistants are trained within the medical model and are seen as an extension of the physician rather than a different type of practitioner. Physician assistants are certified (PA-C) through the National Commission on Certification of Physician Assistants. To maintain certification, physician assistants must log 100 hours of continuing medical education every 2 years and take the recertification examination every 6 years. Physician assistants may obtain medical histories, perform physical examinations, assist in surgery, and perform certain procedures. They may prescribe medication in all 50 states.12 Physician assistants must be supervised by a physician in order to practice. In 2015, the average annual salary for physician assistants was $99,270 per year, or $47.73 per hour; however, this salary varies depending on the specialty, years of experience, and geographic location.11

Nurse Practitioners A nurse practitioner is a registered nurse who has advanced education (usually a master’s degree in nursing) and clinical

training in a health care specialty area. Most nurse practitioners have practiced as registered nurses for several years before obtaining a master’s degree in advanced nursing practice. The Masters/Nurse Practitioner degree usually takes 2 to 3 years to complete and most nurse practitioners are certified within their specialty. In the neurosciences, persons achieve Certified Neuroscience Registered Nurse status after passing a written examination, and continuing education units are required to maintain the certification. Nurse practitioners practice under the state’s Nurse Practice Act. Nurse practitioners may obtain medical histories, perform physical examinations, diagnose and treat health problems, order and interpret diagnostic tests, assist in surgery, perform some procedures, and prescribe medications using their own DEA (Drug Enforcement Administration) number. They focus on prevention, wellness, and patient education as well as patients’ medical conditions. Most nurse practitioners practice within a collaborative relationship with a physician or group of physicians. However, in more than half of the states they are allowed to practice independently without a physician’s supervision. This is especially common in rural areas where physicians may not be available. The median annual salary for nurse practitioners in 2015 was $101,260, or $48.68 per hour; however, there is wide variability related to years of experience and practice setting.13

Registered Nurses There are three paths to becoming a registered nurse: (1) a 2-year associate’s, degree; (2) a 3-year diploma; or (3) a 4-year bachelor’s degree. Graduates of all three programs take the same licensing examination, the NCLEX-RN. Some have advocated that the bachelor’s degree program be the minimum requirement for entrance into the nursing profession. However, with a critical nursing shortage, it may be impractical to mandate that all registered nurses hold a bachelor’s degree. The registered nurse coordinates patient care, assesses patients, assists with procedures, provides patient education, and “triages” telephone calls. Registered nurses may not prescribe medication or medical treatment. Registered nurses may obtain certification in their specialty, for example, Certified Neuroscience Registered Nurse. The median annual salary for registered nurses working in physician offices in the year 2015 was $65,350 per year, $31.42 per hour.11

Table 10.3 Typical staffing for an outpatient spine surgery center Staffing relationship

Title

Number

Affiliated employees

Orthopaedist/neurosurgeon

10

Anesthesiologist

2

Receptionist

1

Surgical nursing personnel

2

Technician

2

Administration

1

Permanent/full-time employees

Equipment manager Recovery room aRecovery

nursea

1 3

room is 24 hours per day/three shifts to allow for overnight stays.

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Licensed Practical Nurses Licensed practical nurses complete a 1-year training program and pass a state licensing examination. Licensed practical nurses provide basic patient care such as taking vital signs or assisting with procedures. Some states allow them to administer prescribed medications and intravenous fluids. The median annual income for licensed practical nurses in the year 2015 was $43,170 per year, or $20.76 per hour.11

Medical and Nursing Assistants Although formal training is not required for medical or nursing assistants, most complete a 1-year certificate program offered in vocational-technical high schools or postsecondary vocational schools. Courses include anatomy and physiology, medical terminology, and record keeping, as well as laboratory techniques and some clinical and diagnostic procedures, such as performing electrocardiograms. Clinical duties vary by state law but may include taking medical histories and vital signs, telephoning prescriptions to a pharmacy, removing sutures, and changing dressings. Median annual earnings for medical assistants in 2015 were $30,590 per year, or $14.71 per hour.13 The outpatient spine surgery center should provide a “surgeon-friendly” environment. Although a core staff of 10 fulltime nursing and administrative personnel, 10 affiliated neurosurgeons, and 2 anesthesiologists is optimal, small practices may employ only a nurse or medical assistant to assist with escorting patients to and from the examining room, telephoning prescriptions to a pharmacy, and assisting with minor procedures. Larger practices often include at least one nurse practitioner and/or physician assistant, registered nurses in the clinic, and medical or nursing assistants. Although nurse practitioners and physician assistants may be more expensive than registered nurses and medical/nursing assistants, they have a wider variety of skills and are often reimbursed by insurance companies for assisting in surgery as well as performing physical examinations. In addition, some studies have reported increases ranging from 20 to 90% in productivity for practices after adding a nurse practitioner.14

Performance Management Office staff attrition not only is expensive but also often results in low morale and decreased productivity. It is estimated that one full-time registered nurse replacement (which includes recruitment and orientation) can cost up to $15,000. This figure does not take into account productivity loss and decreased staff morale. Although it cannot be avoided entirely, careful applicant screening and a thorough orientation process are imperative for reducing staff turnover. Personnel should be selected and trained for competence, ability to function as a member of a team, reliability, responsiveness, and ability to communicate with others. It is recommended that physicians take an active role in the interview and screening process for key positions within their practice. The philosophy of care, mission, and objectives of the practice should determine what questions are asked during the interview. Follow-up questions should further probe the applicant’s responses. For example, the interview might proceed as shown in the following:

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Interviewer: “What is it that you like about being a nurse?” Applicant: “I really enjoy working with people.” At this point, interviewers often accept the response and go on to the next question. However, interviewer can gain much more information if he or she probes the applicant’s response in the following manner: Interviewer: “What types of people do you enjoy working with most?” or “What types of people do you prefer not to work with?” or “Give me an example of a situation in your nursing career that you found particularly satisfying.” The interviewer should continue to probe responses in order to gain as much information as possible about the individual’s personality, motives, and potential “fit” within the practice. This technique is particularly useful in avoiding “canned,” practiced responses that are essentially useless in making hiring decisions.

References should be carefully screened. Although administrative or human resources personnel often complete reference checks, it is worth a physician’s time to personally check the references of staff that will be working closely with him or her. Physicians often spend more time with their staff than they do with their spouses and families. Therefore, investing the time necessary to choose the right candidate may avoid problems in the future. In addition, asking references for other references may provide information that would not have been found otherwise. No matter how busy or short staffed the practice may be, adherence to a thorough orientation plan is crucial. It may be helpful for staff to spend time in patient care areas they will not directly work in. For instance, a clinic nurse should spend some time observing in the operating room or intensive care unit in order to gain a full perspective of the patients’ experience.

10.3.4 100 Surgery Center Benchmarks and Statistics to Know In Becker’s ASC Review,15 there are 100 benchmarks and statistics for ASCs based on reports from Accreditation Association for Ambulatory Health Care, Ambulatory Surgical Centers of America, Ambulatory Surgery Center Association, HealthCare Appraisers, Provista, RemitData, MedPAC, Objective Health, and VMG Health. All benchmarks and statistics on this list are averages gathered by compiling data from multiple ASCs.

100 Surgery Center Benchmarks and Statistics to Know16 Operational benchmarks: 1. Administrator salary is $109,184. 2. Administrators in the west receive the highest salary, at $114,109, while administrators in the Midwest receive the lowest salary at $104,317. 3. Staff hours per case at ASCs are 14.5 hours. 4. Administrative hours per case are 4.5 hours. 5. Nurse hours per case are 7 hours.

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Establishing an Ambulatory Spine Surgery Center

6. Administrative hours at one- to two-OR centers are 3.8 hours. 7. Nurse hours at ASCs with three- to four-ORs are 6.3 hours. 8. Administrative hours at ASCs with three- to four-ORs are 4.1 hours. 9. Ambulatory Surgery Center of America (ASCOA) surgery centers have a per room goal of 10 cases per day to encourage compressed schedules. 10. Gastrointestinal (GI) and pain-driven centers with less than 5 clinical hours would have a total of around 8 staff hours per case. 11. Centers with more complicated cases such as orthopaedics and spine would have clinical hours around 7 to 8 hours per case and total staff hours around 10 to 12 hours per case. 12. Average room turnover time goal is 7 to 10 minutes at ASCOA surgery centers, depending on the case mix. 13. Fifty-three percent of ASCs maintain paper records and 23% track their supply chain on spreadsheets. 14. Typical surgery centers have 19 cases per day. 15. Seventy-four percent of the cases are performed by the top five physicians at the ASC. 16. ASCs have of three surgical cases per operating room per day. 17. Total operating expenses per OR is $1.2 million. 18. Employee salary and wages per operating room is $421,820. 19. Medical and surgical expenses per OR are $375.37. 20. General and administrative expenses per OR are $259.38. 21. Total cases per center are 4,714 per year. 22. Average number of nonsurgical cases per year is 1,146. 23. A total of 765 cases are performed per operating room annually, with 4.6 cases per day. 24. ASC procedure rooms see around 1,144 nonsurgical cases per room annually, with 4.6 procedures per day. 25. The top five physicians performed 54% of the ASC’s case volume. 26. Surgery centers with more than four operating rooms performed 24 cases per day, while those with one to two operating rooms performed 12 cases per day. 27. Surgery centers with one to two operating rooms had the highest annual surgical case rate per operating room, at 782, while those with more than four operating rooms hosted 744 cases annually per operating room. 28. Nonsurgical case volume per year at facilities with one to two operating rooms is 1,017 cases per procedure room. 29. Surgery centers with three to four ORs reported 769 nonsurgical cases per procedure room annually, which dropped to 705 cases in centers with more than four ORs. 30. In surgery centers with more than four ORs, only 22% of the cases were performed by the top two physicians, while 62% were performed by the top 10 physicians. 31. Median operating room time per patient encounter: 50.2 minutes. 32. Procedure room time per patient encounter: 34.2 minutes. 33. Median rate of unscheduled direct transfers: .6 transfers per 1,000 patient encounters. 34. Thirty-four percent of ASC leaders plan to standardize products used in their center.

35. Twenty-four percent plan to evaluate their Group Purchasing Organization GPO). 36. Nineteen percent plan to implement an order management system. 37. Six percent plan to change or join a GPO. 38. Six percent plan to change distributors.

Revenue cycle benchmarks: 39. A total of 79.9% of ASCs collect between 0 and 30 days from the date of service to the check date. 40. In total, 13.3% of ASCs receive cash collection between 31 and 60 days from the service date to the check date. 41. Twenty percent of ASC claims are not collected for more than 30 days. 42. The top reason for ASC procedures to receive an unexpected denial is “claims or service lacks information which is needed for adjudication.” The second most common reason is “duplicate claim or service” followed by “procedure or treatment is deemed experimental or investigational by the payor.” 43. Commercial insurance companies have a 12% unexpected denial rate for the top 10 Current Procedural Terminology (CPT)TM. codes that have unexpected denials at ASCs. 44. Medicare’s unexpected denial rate is 6% for the top 10 CPT codes that have unexpected denials at ASCs. 45. Medicaid has a 26% denial rate for the top 10 CPT codes that have unexpected denials at ASCs. 46. Around 47% of ASCs with fewer than 3,000 cases have 0 to 30 A/R days, while 18.7% have 31 to 60 A/R days. 47. Most ASCs with at least 6,000 cases annually have 0 to 30 A/R days. 48. Of all ASCs, about 15.9% have more than 120 A/R days. 49. For ASCs with three to four ORs, average ENT revenue is $1,734 per case. 50. Average GI/endoscopy revenue per case for medium-sized ASCs is $776. 51. Orthopaedics revenue per case for three- to four-OR ASCs is $2,617. 52. Average general surgery revenue per case for medium sized ASCs is $1,721. 53. For ASCs with three to four ORs, average ophthalmology revenue is $1,249 per case. 54. Average plastic surgery revenue per case for medium-sized ASCs is $1,516. 55. Podiatry revenue per case for three- to four-OR ASCs is $2,021. 56. For medium-sized ASCs, average obstetrics/gynecology revenue per case is $1,958. 57. Average pain management revenue per case for three- to four-OR ASCs is $890. 58. Revenue per case for urology procedures in medium-sized ASCs is $1,476. 59. ASCOA centers have a goal of low-to-mid 30 s for A/R days out.

Clinical benchmarks: 60. Seventy-seven percent of patients wait at least a month after scheduling cataract surgery before undergoing the procedure.

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61. Ninety-six percent of patients are able to schedule their cataract surgery at their desired time in the ASC. 62. Ninety-five percent of patients resume daily living within a week of undergoing cataract surgery. 63. Ninety-four percent of patients reported improved vision after cataract surgery in an ASC. 64. Ninety-nine percent of patients say they are comfortable while undergoing cataract surgery in the ASC and 99% are comfortable after discharge. 65. Ninety-nine percent of patients report they would recommend cataract surgery after undergoing the procedure in an ASC. 66. Preprocedure time is 81 minutes for cataract surgeries. 67. Procedure time for cataract surgeries in ASCs is 13 minutes. 68. Discharge time for cataract surgeries is 20 minutes. 69. Seventy-one percent of colonoscopy patients report little or no discomfort during bowel preparation. 70. Seventy-six percent of colonoscopy patients wait less than a month between scheduling their colonoscopy and having the procedure. 71. Ninety-eight percent of colonoscopy patients report being comfortable after discharge. 72. Ninety-nine percent of colonoscopy patients report little or no discomfort during the procedure and would recommend it to others. 73. One hundred percent of colonoscopy patients report understanding the procedure. 74. Colonoscopy procedure time is 9–10 minutes to 27 minutes. 75. Preprocedure time for colonoscopy is 11 to 98 minutes, covering patient check-in to scope insertion. 76. Colonoscopy discharge time is 6 to 80 minutes for ASCs. 77. Preprocedure time for knee arthroscopy is 81 minutes, and organizations with shortest times attribute results to calling patients the day before to remind them of the appointment and preprocedure requirements. 78. Knee arthroscopy procedure time is 20 minutes in the ASC. 79. Discharge time for knee arthroscopy is 67 minutes in the ASC, and organizations with short discharge times attribute results to having patients leave the operating room as they are waking up to assess their comfort level as soon as possible. 80. Eighty-three percent of knee arthroscopy patients wait less than a month for their procedure after scheduling. 81. Eighty-nine percent of knee arthroscopy patients are able to schedule the procedure as soon as they wanted in the ASC. 82. Ninety-nine percent of knee arthroscopy patients say they are comfortable postdischarge in the ASC. 83. Preprocedure time for low back injections is 42 minutes, and organizations with the shortest discharge times attribute results to not using or using low levels of sedation or controlling the type and amount of medication administered. 84. Procedure time is 7 minutes for low back injections in the surgery center. 85. Discharge time after low back injections in the ASC is 22 minutes, with a range of 1 to 42 minutes.

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86. Ninety-two percent of patients wait less than a month from scheduling their low back injection to undergoing the procedure in the ASC. 87. Ninety-three percent of patients say they are able to schedule their low back injections in an ASC within a “reasonable” period to time. 88. Eighty-five percent of patients report returning to daily activities after undergoing low back injections in ASCs. 89. Seventy-seven percent of patients say they experienced less pain after the low back injections, and 51% reduced pain medications after the procedure.

Growth benchmarks: 90. One hundred percent of surgery center management companies in the HealthCare Appraisers 2013 ASC Valuation Survey found orthopaedics/sports medicine a desirable specialty. 91. Ninety-four percent of ASC management companies find orthopaedic spine a desirable specialty in 2013. 92. Ninety-four percent of ASC management companies find ENT desirable in 2013. 93. Eighty-eight percent of ASC management companies find general surgery desirable in 2013. 94. Eighty-eight percent of ASC management companies find pain management desirable in 2013. 95. Eighty-two percent of ASC management companies find gastroenterology a desirable specialty in 2013. 96. The number of Medicare-certified ASCs increased 81% from 2000 to 2015. In 2015, there were more than 16,000 ORs in ASCs, an average of three ORs per center.16 97. Medicare made $4.1 billion in payments to ASCs for 3.4 million fee-for-service Medicare beneficiaries in 2015.16 98. There were 5,500 Medicare-certified ASCs in 2015.16 99. In 2011, 60% of hospitals had an ASC within 5 minutes of their facility. 100. ASCs can save commercial insurance providers and their beneficiaries $38 billion per year as an alternative to hospital outpatient departments for outpatient surgical care. ASCs save Medicare $2.3 billion annually per year and can save Medicare beneficiaries $1.5 billion personally due to lower copayments.17 (From Dyrda.15)

10.3.5 Communication Systems: The Electronic Medical Record Communication systems are also essential for an effective and efficient practice. Communication structures can include any type of interaction from basic day-to-day communications to staff meetings, e-mail or voicemail systems, and highly technological electronic medical record (EMR) systems. The common thread running through these systems supports the mission and objectives of the organization. For example, staff meetings can be an opportunity to review and collect a status update on the group’s goals and objectives.

Perez-Cruet et al, An Anatomic Approach to Minimally Invasive Spine Surgery, 2nd Ed. (ISBN 978-1-62623-643-1), copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.

Establishing an Ambulatory Spine Surgery Center Medical records are notoriously difficult to computerize, and systems that offer complete, integrated solutions are currently under development. Fortunately, surgical records are more easily reduced to electronic form. Electronic data linkage should be established with the office of each surgeon who makes more than a minimum use of the facility. Scheduling of operations and transmitting patient information can be done by computer, and the risk of losing records is minimized. When the operation is scheduled, the surgeon’s desired equipment and instruments should also be scheduled so they are available the day of surgery. Each surgeon should be able to customize his or her preferences and make changes from the office. If the patient has other medical problems, these can be noted to address. The EMR represents a complex communication and information structure for supporting information flow between clinicians, patients, and administrative staff. Such groups as the National Academy of Medicine and the Leapfrog Group (a consortium of Fortune 500 companies) have affirmed the need for health care organizations to increase their use of EMRs to improve patient care and decrease medical error.18,19 Although many health care providers’ goal is the realization of an EMR, EMR implementation can be challenging, and it can take months —if not years—to realize its full benefits. In a systematic review of the literature for best practices in EMR implementation, researchers identified the most important aspects of successful implementation include: involving and gaining the support of multiple stakeholders (physicians, nurses, administrative staff); training the staff; and being prepared for and proactively solving problems that inevitably arise during EMR implementation.20 Despite the obstacles involved in implementation, an EMR can offer substantial benefits to a physician’s practice, including: ● Decreasing costs related to labor and time associated with paper medical records. ● Documenting services provided and verifying appropriate billing codes. ● Providing the ability for multiple providers to asynchronously update medical records and exchange notes. ● Facilitating work flow via a system of reminders, alerts, and e-mail messages. ● Preventing error by alerting clinicians to drug interactions, allergies, and established recommended clinical protocols. ● Providing clinicians the ability to access medical records remotely 24 hours a day, 7 days a week. ● Allowing patients access to their medical records and the ability to e-mail their clinician. ● Developing a database of discrete data elements for quality improvement processes and outcomes analyses. Although having a completely paperless chart may be the “holy grail” of EMRs, it may be more manageable and appropriate to implement an EMR in stages. For instance, medications and allergies, physician orders, and electronic fee tickets may be implemented before the more complex electronic history of presenting illness documentation and physical examination. Some practices have addressed this issue by scanning or creating interfaces for reports, examination information, and dictation. Implementing an EMR supports a streamlined workflow and efficient clinical environment. Integrated software components allow for realtime exchange of patient information. Demographic and work status information automatically transfers into the clinical record.

One example of a successful neurosurgical practice EMR implementation is presented in the following Box. This system allows customization for each screen to meet specific provider needs. Any previous information is maintained within each new encounter.

Elements for a Successful EMR ● ● ● ● ● ● ● ● ● ●

Patient history. Physical examination. Medications. Allergies. Orders. Diagnosis. Procedures. Plan of care. Educational materials. Health status.

The work flow process integrates a provider’s schedule, e-mail address, and tasks collectively in one view on the desktop. By clicking on a patient’s name from the appointment view, providers are able to directly access the patient’s EMR. Tasks may be sent to other physicians and staff within the organization to complete prescription refills, orders, or clinical trial protocols. Telephone calls from patients inquiring about test results, medication refills, instructions, and other information are documented and forwarded to the appropriate resource. As a result, the office staff are able to view a record of the patient’s inquiries and can respond efficiently and intelligently to their queries. Templates provide office staff with telephone triage protocols. The ability to electronically route particular sections of the chart to the provider allows for a prompt response with accurate and complete information. Data are concisely summarized or can be discretely displayed in greater detail (▶ Fig. 10.8). The summary template can be customized to summarize any type of data element, including specific examination information or standardized assessment tools such as the Oswestry scale, visual analog pain scale, or SF-36.21 A variety of clinicians can summarize and access work injury information. Customized payor-specific forms document work status and restriction levels to the case manager, employer, and referral source. Current information is immediately faxed on completion of the visit. Medication order entry and the refill process are done electronically as well. Drug and allergy interactions as well as information regarding dosing are automatically generated. The patient’s preferred pharmacy information can be stored online and prescriptions faxed directly to the pharmacy appended with an electronic signature. Orders are entered directly into the system and alerts notify or remind providers of potential conflicts, such as ordering a myelogram for a patient taking a blood thinner. Order entry templates can be customized to reflect specific provider protocols. Diagnoses and ICD-10 codes are automatically included on each physician order. A document is generated to the facility performing the service and contains accurate, legible instructions, diagnoses, ICD-10 codes, and an electronic signature. Information is easily exchanged with hospitals and other providers via fax or printed copy to enable efficient order processing.

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Fig. 10.8 Patient summary display on the electronic medical record.

EMR integration also promotes sharing information crucial to an efficient work flow. Detailed procedure and diagnosis information is captured at the end of the visit and immediately posted to the patient’s bill. Providers may manually enter diagnoses codes and level of service or the system can calculate suggested Evaluation and Management (E and M) codes. When the patient checks out at the end of the visit, charges are clearly indicated and posted immediately to the patient’s electronic account. The electronic record maintains a summary of all current and historical procedures and associated diagnoses for reference at any time. All information entered into the system can be included in a customized document replacing traditionally dictated notes. Letters can be faxed to referring physicians before the patient even leaves the office. In addition, patients can receive a summary of their visits that includes a current list of their medications, orders, instructions, and care plan. Clinicians can also customize patient education materials within the EMR and print pamphlets specific to each patient and provider, medication information sheets, and videos of specific surgical procedures. Patients log into a secured website with a password and view educational materials specific to their diagnoses. All information presented to the patient can be easily documented, providing supporting documentation of informed consent. The ability to easily collect and manage data supports a continual quality improvement process, evidence-based practice, and outcome analysis. Clinicians can standardize tools and scales electronically to collect and measure various outcomes. The patient can enter data directly in a kiosk fashion and continue in the examination room itself, or patients may choose to log into a secure website from their personal computers and complete data collection. Automatic prompts can be sent to researchers reminding them to collect patient data according to specified data collection protocols, or patients may be sent e-mails via a secured site reminding them to complete tools online. With creative minds and the drive to provide the best possible patient care, the opportunities and potential for an EMR are limitless.

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10.4 Ambulatory Surgery Center Features and Services 10.4.1 Features Focus on Ambulatory Surgery The facility should be designed expressly for ambulatory spine surgery. Waiting areas should be comfortable and tasteful, and not clinic- or hospital-like. The most important design concepts include the following.

Unidirectional Patient Flow The facility should be designed so the patient flow is unidirectional—patients come in the door, go to the waiting area, go to surgery, go to recovery, and leave without crossing paths with other patients. This design keeps patients who are waiting from seeing unconscious or postoperative patients.

Operating Rooms To allow maximum flexibility, an outpatient spine surgery facility should have two to four operating rooms, which provides the scale to cover fixed costs, yet remains intimate and responsive for patients. Additionally, this size will ensure a high utilization factor for the facility. Initially, each facility will have two operating rooms opened. Additional operating rooms—to a maximum of four—can be brought online as demand dictates.

Multiple Office Suites Several offices should be available for rent to surgeons to see office patients, so surgeons can operate part of the day and see patients the rest of the day. The surgeon could thus maintain an additional office with less expense and see patients without traveling to another office.

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Establishing an Ambulatory Spine Surgery Center

10.4.2 Services Each facility should have enough surgical and nursing staff to allow for overnight stays, which will increase the complexity of minimally invasive spine procedures the ASC can offer. Entrepreneurial surgeons who desire to establish an outpatient spine surgery program should target existing ambulatory surgical facilities. Then, the following services will be necessary: ● Assistance with complete facility setup for outpatient spine surgery. ● Recruitment, selection, and training of spine surgery professionals and staff. ● Assistance with payor and company relationships and negotiations. ● Assistance in establishing an effective patient satisfaction and outcomes database. An affiliated physician is estimated to need a minimum of 25 surgeries per year to remain proficient. Participating physician should readily be able to complete 100 to 125 outpatient spine surgeries per year without incurring an adverse impact on his or her other medical practice activities. The outpatient spine surgery center should provide additional specific services as shown:

Facility Development ●

● ●

Design and construction company collaboration for operating room(s) buildout. Capital equipment purchase selection and coordination. Program supervision and management during the launch phase.

Operations ● ●

● ●

Manage the outpatient spine surgery facility. Establish an interventional pain program in conjunction with outpatient spine services. Establish spine rehabilitation and physical therapy services. Ensure delivery of cost-effective, quality care through internal audits and external surveys with interested parties including physicians and former patients.

Training and Licensing ● ●

● ●

Hiring and cross-training operating room and clerical personnel. Critical pathways and clinical guidelines development, establishment, and supervision. Credentialing neurosurgeons and orthopaedic surgeons. Comprehensive (community, staff, and physician) education programs related to spine disorders.

Information Technology ● ● ●

Computer database for clinical outcomes. Computer database for patient satisfaction. Integration with corporate website, intranet, and extranet.

Marketing and Promotion ●

●

Marketing plan development for outpatient spine surgery programs. Media presentations and professional presentations development for insurance companies and other payors.

Business Development ●

● ●

Negotiating and contracting with payors including insurance companies and managed care companies. Strategic planning for outpatient spine surgery programs. Budget and pro forma financial development.

10.4.3 Medical Procedures Outpatient spine surgery centers should initially focus only on ambulatory spine surgery procedures including the following: ● Anterior cervical microdiscectomy with fusion. ● Posterior cervical microdiscectomy. ● Lumbar microdiscectomy. ● Single-level lumbar laminectomy. ● Lumbar microendoscopic discectomy. ● Additional procedures as appropriate (cervical arthroplasty, minimally invasive lumbar fusions, etc.). Depending on both the patient base and the surgical skill base in a given community, one or more of the following procedures could be added to an outpatient spine surgery center: ● Pain management. ● Pain management consultation and treatment. ● Fluoroscopic-guided epidural steroid injections (cervical, thoracic, lumbar, or caudal) for radicular pain. ● Sympathetic blocks (sphenopalatine, stellate, celiac, and lumbar). ● Fluoroscopic-guided facet joint (zygapophyseal), selective nerve root injections. ● Diagnostic dorsal root ganglion and median branch blocks. ● Discography (cervical, lumbar). ● Radiofrequency lesioning (ablation diagnosis of dorsal root ganglion (DRG) and median branch blocks). ● Cancer pain management. ● Neuromodulation techniques (spinal cord stimulation, implantation, and management). ● Surgical implantation of intrathecal and epidural programmable fusion pumps (opioids or Baclofen). ● Special interest in the interventional management of head and neck pain.

10.4.4 Streamlined Payment Relationships with Insurance Companies The outpatient spine surgery center should help surgeons streamline their interaction and payment relationships with insurance companies. Reduced cost surgical options will be viewed favorably by insurance companies. Given that the center will likely provide the lowest cost surgical option for specific spinal procedures, insurance companies will be interested in formalizing their relationship with the outpatient spine surgery center to secure access to these low-cost procedures. An additional driving factor will be that patients generally prefer the outpatient spine surgery experience over the inpatient hospital alternative for reasons of convenience, quicker and more complete recovery, less time lost from work, lower recidivism, and fewer out-of-pocket expenses. In combination,

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Patient Education and Business Basics the lower cost and higher patient satisfaction of this approach will be of significant interest to insurance companies, which could translate into several actionable alternatives.

Preapproval of Surgical Procedures It may be possible to develop relationships with insurance companies that facilitate approval of a significant proportion of surgical cases at the time they are scheduled.

Bundled Fees Normally, the insurance company will pay the surgeon, anesthesiologist, and facility separately, meaning three separate transactions must take place for each operation. If an outpatient spine surgery center can offer a single fee or a global case rate for a given operation and then apportion the fee among the surgeon, anesthesiologist, and facility, the process could be simplified with advantages to all parties including the insurance companies. As a result, medical practitioners are relieved of a great source of irritation, and insurance companies have predictable fees with less negotiation and office work. In addition, depending on their insurance coverage, patients also experience a cost savings. The net result is both surgeons and insurers prefer to work at and with an outpatient spine surgery facility. Outpatient spine surgery centers will provide expertise in evaluation, management, and CPT coding.

Competitive Pricing One critical aspect of outpatient spine surgery is the ability to compete on price. The outpatient spine surgery center should offer low prices to the insurance companies for surgical procedures on par with those performed in hospital inpatient settings. A unique aspect of an outpatient spine surgery center is its ability to offer a reduced price without sacrificing the highquality care. When developing a small ambulatory spine surgery facility, one can employ the following measures to avoid the high-cost structure of hospitals: ● Reducing overhead costs because of simplified administration and a less complex facility. ● Decreasing labor costs by selecting flexible staff and through staff cross-training to perform a larger array of tasks. ● Limiting the number of procedures to eliminate specialist staff, reduce inventory, and cut specialized equipment. ● Increasing scheduling, physician utilization, and facility utilization by partnering with surgeons. ● Concentrating on established surgeons and procedures to keep research and training expenditures to a minimum. ● Selecting only highly qualified surgeons to reduce time for an individual operation and keep reimbursement for facility use (based on per case use) high. One can measure surgeon and patient effectiveness by how frequently they use the facility. Number of cases per month, minutes of operating time, and facility utilization are major metrics that centers should track. Measure economic effectiveness by revenues, profit, and return on investment. Effectiveness with payors should be measured by the number, duration, and quality of contracts the center is able to negotiate.

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Payment Methodologies from Payers With low cost and high quality as the major focus, it is crucial to review past and present insurance company payment methodologies. Until recently, payers reimbursed services at an ASC based on a discount off retail charges, from a low of 65% to a high of 95%.17 However, the Health Care Financing Administration (now the Centers for Medicare and Medicaid Services), HCFA, as with DRG codes, developed a predictable payment rate per outpatient surgical case called ambulatory service categories. Some commercial payors have followed with the ambulatory service categories method and more will follow. HCFA and commercial payors have made several efforts in package pricing all hospital and physicians’ services for some higher cost DRGs such as organ transplant and cardiac surgery. Providers agreed to further discounts in exchange for being selected as a center of excellence with geographic exclusivity. Payors are now unwilling to reimburse providers for investing in technology, and little is paid for medical education. Patients have become more knowledgeable about health care and will not allow their cost-share to continue to skyrocket. Payors have had some success shifting the financial and medical management to providers for employees and dependents, not just patients, through shared-risk management methodologies such as capitation, a fixed payment rate per enrollee per month, and a percentage of a billed premium. With the continued emphasis on lower costs and high quality, payment rates for any health care service will drop. In addition, drug companies have capital and continue to invest in research and development to discover nonoperative treatment modalities. History does repeat itself when it comes to payment methodologies. Within the next 5 years, all outpatient surgery will be reimbursed through a case rate similar to the ambulatory service categories. Some national chains of outpatient surgery centers and hospital-based centers will enter into some capitation or percentage of premium arrangements. With new ways to treat a condition that traditionally required surgery, there will be an excess of outpatient surgery centers, and pricing will become very competitive. Payors will, as always, use this leverage to obtain the lowest reimbursement rates possible.

10.5 Regulatory Considerations The health care industry is subject to federal, state, and local government regulation. The various levels of regulatory activity affect outpatient spine surgery center business activities by controlling its growth, requiring facility licensure or certification, regulating properties use, and controlling the reimbursement.

10.5.1 Licensure, Certification, and Certificate of Need Requirements State regulators may review any addition of beds or the acquisition of existing facilities under a statutory scheme sometimes referred to as a Certificate of Need program. States with Certificate of Need programs place limits on health care facility construction and acquisition, and the expansion of existing facilities and services. In such states, approvals are required for

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Establishing an Ambulatory Spine Surgery Center capital expenditures exceeding certain amounts that involve inpatient rehabilitation facilities or services or outpatient surgery centers. Outpatient rehabilitation, occupational health and diagnostic facilities, and services do not require such approvals in most states. State Certificate of Need statutes generally provide that, prior to the addition of new beds, the construction of new facilities, or the introduction of new services, a state health planning designated agency, State Health Planning Development Agency (SHPDA), must determine a need exists for those beds, facilities, or services. The Certificate of Need process is intended to promote comprehensive health care planning, assist in providing high-quality health care at the lowest possible cost, and avoid unnecessary duplication. Typically, the service provider submits an application to the appropriate SHPDA with information concerning the area and population to be served, anticipated facility or service demand, amount of capital expenditure, estimated annual operating costs, relationship of the proposed facility or service to the overall state health plan, and cost per patient day for the type of care contemplated. Whether the Certificate of Need is granted is based on SHPDA’s finding of need in accordance with criteria set forth in Certificate of Need statutes and state and regional health facilities plans. If SHPDA finds the proposed facility or service is necessary and the applicant is the appropriate provider, it will issue a Certificate of Need containing a maximum expenditure amount and a specific time period for the Certificate of Need holder to implement the approved project. Licensure and certification are separate but related regulatory activities. The former is usually a state or local requirement, and the latter is a federal requirement. In almost all instances, licensure and certification will follow specific standards and requirements that are set forth in readily available public documents. Compliance with the requirements is monitored by annual on-site inspections by representatives of various government agencies. Substantially, licensure will be required for all outpatient spine surgery centers.

10.5.2 Other Regulatory and Licensing Considerations Various state and federal laws regulate relationships among health care service providers, including employment or service contracts and investment relationships. These restrictions include a federal criminal law prohibiting (1) the offer, payment, solicitation, or receipt of remuneration by individuals or entities to induce referrals of patients for services reimbursed under the Medicare or Medicaid programs, or (2) the leasing, purchasing, ordering, arranging for or recommending the leasing, purchasing, or ordering of any item, good, facility, or service covered by such programs (the Fraud and Abuse Law). In addition to federal criminal sanctions, violators of the Fraud and Abuse Law may be subject to significant civil sanctions including fines and/or exclusion from the Medicare and/or Medicaid programs. In 1991, the Office of the Inspector General (OIG) of the United States Department of Health and Human Services22 promulgated

regulations describing compensation arrangements that are not viewed as illegal remuneration under the Fraud and Abuse Law (the Safe Harbor Rules). The Safe Harbor Rules create certain standards (Safe Harbors) for identified types of compensation arrangements which, if fully complied with, assure the OIG will not treat such participation as a criminal offense under the Fraud and Abuse Law or as the basis for an exclusion from the Medicare and Medicaid programs or an imposition of civil sanctions. The OIG closely scrutinizes health care joint ventures involving physicians and other referral sources. In 1989, the OIG published a Fraud Alert that outlined questionable features of “suspect” joint ventures (see Chapter 11).23 In 1992, regulations were published in the Federal Register implementing the OIG sanctions and civil monetary penalty provisions established in the Fraud and Abuse Law.24 The regulations (the Exclusion Regulations) provide that the OIG may exclude a Medicare provider from participation in the Medicare Program for a 5-year period on a finding that the Fraud and Abuse Law has been violated. The regulations expressly incorporate a test adopted by three federal circuit courts providing that if one purpose of remuneration offered, paid, solicited, or received is to induce referrals, then the statute is violated. The regulations also provide that after the OIG establishes a factual basis for excluding a provider from the program, the burden of proof shifts to the provider to prove the Fraud and Abuse Law has not been violated. Outpatient spine surgery facilities can be established as limited partnerships or limited liability companies (collectively, “partnerships”) with third party investors. The investor group as a whole will likely include physicians associated with a specific location, hospitals, and institutional or corporate operators of existing outpatient centers. Some of the physician limited partners may eventually refer patients to their respective facilities. Those partnerships that are providers of services under the Medicare program, and their limited partners, are subject to the Fraud and Abuse Law. A number of the relationships that the outpatient spine surgery center establishes with physicians and other health care providers may not fit within any of the Safe Harbors. The Safe Harbor Rules do not expand the scope of activities that the Fraud and Abuse Law prohibits, nor do they provide that failure to fall within a Safe Harbor constitutes a violation of the Fraud and Abuse Law; however, the OIG has informally indicated that failure to fall within a Safe Harbor may subject an arrangement to increased scrutiny. Most of the outpatient spine surgery centers will be owned by partnerships, which include physicians who perform surgical procedures at such centers as partners. Subsequent to the promulgation of the Safe Harbor Rules in 1991, the Department of Health and Human Services issued for public comment additional proposed Safe Harbors, one of which specifically addresses surgeon ownership interests in ASCs (the “Proposed Ambulatory Surgery Centers Safe Harbor”).25 As proposed, the Proposed Ambulatory Surgery Centers Safe Harbor would protect payments made to surgeons as a return on investment interest in a surgery center if, among other conditions, all the investors are surgeons who are in a position to refer patients directly to the center and perform surgery on such referred patients.

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Patient Education and Business Basics The so-called Stark II provisions of the Omnibus Budget Reconciliation Act of 199325 amend the federal Medicare statute to prohibit the making by a physician of referrals for “designated health services” (including physical therapy, occupational therapy, radiology services, or radiation therapy) to an entity in which the physician has an investment interest or other financial relationship, subject to certain exceptions. Such prohibitions took effect on January 1, 1995, and will apply to all outpatient spine surgery center partnerships with physician partners. On January 9, 1998, the Department of Health and Human Services26 published proposed regulations (the Proposed Stark Regulations) under the Stark II statute and solicited comments thereon. The Proposed Stark Regulations would implement, amplify, and clarify the Stark II statute. In addition, a number of states have passed or are considering statutes that prohibit or limit physician referrals to facilities in which they have an investment interest (see Chapter 11). Ambulatory surgery is not identified as a “designated health service” under Stark II, and the statute is not intended to cover ambulatory surgery services. The Proposed Stark Regulations would expressly clarify that the provision of designated health services in an ASC would be exempt from the referral prohibition of Stark II if payment for such designated health services is included in the ASC payment rate.

10.6 Marketing, Advertising, and Promotion Strategy 10.6.1 Marketing Budget A $100,000 first-year marketing budget should be established for an outpatient spine surgery center to create awareness of the facility and to promote use by physicians and patients in the communities. These funds should be used to purchase advertisements in local and regional publications and sponsorrelated spine care seminars/events. In addition to these activities, the outpatient facility should engage in significant additional marketing and promotion such as: ● A book on back care, with a specific focus on injury prevention and treatment. ● A corporate website. ● Seminars on back care. ● Retention of an aggressive and effective public relations firm to create high visibility for the outpatient spine surgery center in the press and media. ● Retention of an experienced advertising firm to assist in developing a multipart message that will convey the effectiveness of the outpatient spine surgery approach to all interested parties—patients, potential participating physicians, hospitals, existing ASCs, and insurers. This marketing could take the form of advertising placement in mass media, whereas targeted advertising in medical and insurance trade publications makes physicians and insurers aware of the outpatient alternative. A pleasant outpatient surgical experience is also a valuable marketing tool to promote the center’s reputation among current and future patients.

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Core Concepts for a Positive Patient Experience ● ●

● ● ● ●

A calm, quite atmosphere. Informing patient in advance and in detail about surgical expectations. Efficiency. Patient and family access to surgeons. Prompt information about surgical outcomes. Anesthesia and surgery techniques that minimize debilitating postoperative effects.

The staff will be concerned about patient needs and will strive to minimize unpleasantness, such as pain, nausea, and vomiting. In general, it is expected that patients who undergo surgery at an outpatient spine surgery facility will provide strong, positive word-of-mouth recommendations to other potential patients and that these de facto testimonials will help to strengthen the brand. In addition to indirect marketing, the outpatient center’s business development staff will contact payors directly to promote the center given that it will be necessary to negotiate contracts with each of the major payors for outpatient spine procedures. The center should take the approach that the contract negotiation is the beginning of a long-term relationship. The payors should be informed of the goals and historical outcomes of providing cost-effective, high-quality care using the outpatient approach.

10.6.2 Advertising to Target Audiences The long-term goal of outpatient spine surgery centers should be to develop a high-quality, pleasant ambulatory surgery facility that allows cost-effective outpatient neurosurgery and orthopaedic spine surgery in a nonhospital environment. In the start-up period, the outpatient approach can be marketed to any one or more of the five primary groups: 1. Hospitals: The outpatient spine group could market to hospitals who desire to have an outpatient spine surgery program to become a profit center and further free up time in the main operating rooms for higher acuity cases such as open heart surgery. Hospitals running their operating rooms at or near capacity will be a select target market for this reason. 2. Existing ambulatory surgery centers: The outpatient spine group could market to ASCs that would like to see an increase in their caseloads and/or have their case mix reflect higher reimbursements. 3. Single-practice physician specialty groups: The outpatient spine group could market to single-practice specialty groups who desire to move part of their practice to wholly owned ambulatory facilities. A surgeon’s primary concern is a highquality surgical experience and outcome. In addition, surgeons want to be able to do their work without delays and in their own preferred manner. To this end, surgeons do not want to work with a surgical staff unfamiliar with how they work or which instruments they prefer, the pace of their operations, and so forth. They want their patients to have a

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Establishing an Ambulatory Spine Surgery Center good experience, as the patient often holds the surgeon responsible for all aspects of the experience. Finally, surgeons’ fees have been markedly cut, and many desire to tap into the revenue stream of facility fees wherever possible. 4. Patients: Patients want to have the necessary operation carried out with no complications. They want to have their health restored. They want minimal waiting, as little discomfort as possible, and as pleasant surroundings as possible. They want their out-of-pocket costs to be as low as possible. 5. Payors: Insurers want to have only necessary operations performed in the most cost-effective manner, with high-quality outcomes and acceptable patient satisfaction. The outpatient spine surgery center should be a leader in cost and service. The outpatient center should not offer research and teaching, and because emphasis will be on efficiency, innovative surgical procedure development should not be a focus. Once new procedures have been developed and surgeons are trained in them, such new procedures can be offered at the outpatient surgery center. In other words, the center should not develop new procedures but should rapidly adopt them as they become accepted as standard practice. Cost leadership will be possible because of the efficiencies obtained from a small facility with a limited spectrum of offerings. Service will be possible because of the small size and the ability to provide a more intimate and personal atmosphere. Because surgeons and staff do the same procedures over and over again, process improvement opportunities are readily identified and implemented, which raises quality and lowers costs.

10.7 Financial Projections Five-year financial projections for an outpatient spine surgery center should be created. A center should expect to see positive net income as early as the second fiscal year and a positive ending cash balance by the third fiscal year. Forecasted revenue for current products is comprised of spine surgery procedures performed at outpatient spine surgery centers and renting office space to surgeons.

10.7.1 The Competition Outpatient spine surgery centers will compete primarily with hospitals in attracting physicians and patients, and developing relationships with payors and large companies. The primary competitive factors in the outpatient surgery business are convenience, cost, quality of service, physician loyalty, and reputation. Hospitals have many competitive advantages in attracting physicians and patients, including established standing in a community, historical physician loyalty, and convenience for physicians making rounds or performing inpatient surgery in the hospital. An outpatient spine surgery center will potentially face competition any time it initiates a Certificate of Need project or seeks to acquire an existing facility or Certificate of Need. This competition may arise either from competing national or regional companies or from local hospitals or other providers that file competing applications or oppose the proposed Certificate of Need project. The necessity for these approvals serves as a barrier to entry and has the potential to limit competition by creating a franchise to provide services to a given area.

10.7.2 Risks Interest in ambulatory surgery alternatives is widespread and of interest to several key stakeholders: physicians, patients, insurers, and hospitals. As such, competitive risk exists from new entrants, existing firms in the ambulatory surgical care business, and existing players such as hospitals who may decide to extend their service offerings to include ambulatory spine surgery. Outpatient spine surgery centers should plan to create significant value for their patients, affiliated physicians, and contracted insurance companies. However, no guarantee exists that clients will perceive such value on a consistent basis. Outpatient spine surgery facilities will be dependent on reimbursement by third-party payors. There can be no guarantees that reimbursement for ambulatory surgical procedures will remain at current levels or that centers will be able to collect all reimbursements due to them. The operation of outpatient spine surgery centers is subject to extensive regulation at the federal, state, and local level, including certification and licensure laws, physician self-referral, Medicare fraud and abuse, Certificate of Need laws, and laws relating to financial relationships among health care services providers. The operation of outpatient spine surgery facilities and provision of health care services are subject to federal, state, and local certification and licensure laws. As part of this regulation, these facilities are subject to periodic inspections to ensure compliance with the relevant regulations. Additionally, some states will require Certificates of Need for expansion of services. No warranty can be provided that the center will be able to comply with all applicable regulations during the course of normal business operations. A large array of Medicaid/Medicare fraud and abuse provisions will apply to the operation of outpatient centers, and the centers will also be subject to a number of federal and state regulations with respect to financial relationships among health care providers, physician self-referral, and other fraud and abuse issues. Penalties for federal and state law violations include exclusion from Medicaid/Medicare program participation, civil and criminal penalties, and asset forfeiture. Health care reform legislation may adversely affect the business of outpatient spine surgery centers.

10.8 Conclusion: A Prototype Facility Microneurosurgery for spinal disc herniations is a very profitable specialty niche for ASCs. As stated previously, the estimated number of patients in King County, WA, in 2007, who had a diagnosis of lumbar disc herniation and who underwent a lumbar microdiscectomy was 1,187.8 Similarly, the estimated number of patients with a diagnosis of cervical disc herniation who underwent an anterior cervical microdiscectomy was 860. The facility charges for the lumbar procedure are approximately $5,000 per case and for the cervical procedure approximately $5,500 per case. A conservative estimate of the average contractual allowance was 50% in 2007. A neurosurgeon or an orthopaedic spine surgeon with a core competency in microdiscectomy surgery might perform an average of 125 lumbar procedures and 75 cervical procedures per year. The ASC would collect $518,750

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Patient Education and Business Basics in facility fees for these microdiscectomies. Using a conservative estimate, if three neurosurgeons and/or orthopaedic spine surgeons referred all of their microdiscectomy patients to an outpatient spine surgery center, the center would be servicing about 30% of the potential King County market yet receiving $1,256,250 in fees for outpatient spine surgery. Therefore, establishing a minimally invasive spine center can contribute significantly to the fiscal health of a practice.

References [1] Herzlinger RE. Market-Driven Health Care: Who Wins, Who Loses in the Transformation of America’s Largest Service Industry. Reading, MA: Addison Wesley; 1997 [2] Zigler JE, Delamarter RB. Does 360° lumbar spinal fusion improve long-term clinical outcomes after failure of conservative treatment in patients with functionally disabling single-level degenerative lumbar disc disease? Results of 5year follow-up in 75 postoperative patients. Int J Spine Surg. 2013; 7:e1–e7 [3] Hall MJ, Schwartzman A, Zhang J, Liu X. Ambulatory Surgery Data From Hospitals and Ambulatory Surgery Centers: United States, 2010. Natl Health Stat Report. 2017;(102):1–15 [4] Lucio JC, Vanconia RB, Deluzio KJ, Lehmen JA, Rodgers JA, Rodgers W. Economics of less invasive spinal surgery: an analysis of hospital cost differences between open and minimally invasive instrumented spinal fusion procedures during the perioperative period. Risk Manag Healthc Policy. 2012; 5:65–74 [5] Dyrda L. ASCs vs. hospital: how spine surgery reimbursement compares. Becker’s ASC Review, 2012 [6] Costello T. “The Today Show.” The Today Show (ep. 9–11–2012) NBC. New York, n.d. Television. Available at: http://www.today.com/video/today/ 48985429#48985429 [7] Andersson G, Watkins-Castillo SI. United States Bone and Joint Initiative: The Burden of Musculoskeletal Diseases in the United States. 3rd ed. Rosemont, IL: United States Bone and Joint Initiative; 2014. Available at: http://www. boneandjointburden.org. Accessed January 28, 2015 [8] King County Office of Management and Budget: The 2007 Annual Growth Report, January 2008, King County, WA [9] Becker S, Wood M. The growth of outpatient spine–9 key points. Becker’s Spine Review. Available at: http://www.beckersspine.com/spine/item/29474-thegrowth-of-outpatient-spine-9-key-points.html. Accessed September 2017 [10] Institute of Medicine. Crossing the quality chasm: a new health system for the 21st century. Copyright ©2000 by the National Academy of Sciences. Available at: http://www.iom.edu/~/media/Files/Report%20Files/2001/Crossing-the-Quality-Chasm/Quality%20Chasm%202001%20%20report%20brief. pdf. Accessed September 2017

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[11] American Academy of Physician Assistants. Facts at a Glance. February 10, 2003. Retrieved March 16, 2003 from: http://www.aapa.org/glance.html [12] United States Department of Labor. Bureau of Labor Statistics. (n.d.). 2002–03 Occupational Outlook Handbook. Retrieved March 17, 2003 from: http:// www.bls.gov/oco/ [13] Central NP. NP Salary Summary. April 9, 2002. Retrieved March 17, 2003 from: http://www.nurse.net/cgi-bin/start.cgi/salary/index.html [14] LeRoy L, Solkowitz S. The Costs and Effectiveness of Nurse Practitioners: Health Technology Case Study #16 (prepared for the Office of Technology Assessment, U.S. Congress, OTA-HCS-16). Washington, DC: U.S. Government Printing Office; 1980 [15] Dyrda L. 100 Surgery Center Benchmarks and Statistics to Know, 2016 Becker’s ASC Review, October 2013, ASC Communications, 2017. Available at: http://www.beckersasc.com/asc-turnarounds-ideas-to-improve-performance/110-asc-benchmarks-statistics-to-know-2016.html. Accessed September 2015 [16] Medicare Payment Advisory Commission. Report to the Congress: Medicare Payment Policy. Medpac. Washington, DC. March 2017. Available at: http:// medpac.gov/docs/default-source/reports/mar17_entirereport.pdf?sfvrsn=0. Accessed September 2017 [17] Ambulatory Surgery Center Association and Ambulatory Surgery Foundation. Study: Commercial Insurance Cost Savings in Ambulatory Surgery Centers. ASCA. Available at: http://www.ascassociation.org/advancingsurgicalcare/reducinghealthcarecosts/costsavings/healthcarebluebookstudy. Accessed September 2017 [18] Shane R. Computerized physician order entry: challenges and opportunities. Am J Health Syst Pharm. 2002; 59(3):286–288 [19] Berkowitz L. Clinical informatics tools in physician practice. Healthcare Informatics Online. April 2002. Available at: http://www.healthcare-informatics. com/issues/2002/04_02/berkowitz.htm. Accessed March 19, 2003 [20] Keshavjee K, Troyan S, Holbrook A, et al. Successful computerization in small care practices: a report on 3 years of implementation experiences. May 27, 2001. Available at: http://www.competestudy.com/PDF/Successful_Computerization_in_Small_Primary_Care_Pracises.pdf. Accessed March 19, 2003 [21] Ware JE, Jr, Davies-Avery A, Stewart AL. The measurement and meaning of patient satisfaction. Health Med Care Serv Rev. 1978; 1(1):1, 3–15 [22] Kusserow, RP: Inspector General, Department of Health and Human Services. Medicare and State Health Care Programs: Fraud and Abuse; OIG Anti-Kickback Approved: July 22, 1991. Department of Health and Human Services [23] Brown, JG: Medicare and State Health Care Programs: Fraud and Abuse; OIG Anti-Kickback, Dec. 1994, Department of Health and Human Services [24] Federal Register Volume 59, Number 119 (Wednesday, June 22, 1994, Office of Inspector General, Department of Health and Human Services) [25] Bills C. 103rd Congress, H.R. 2264 Public Print, 6/29/1993, From the U.S. Government Printing Office [26] Min DeParle, NA Administrator, Health Care Financing Administration. Federal Register / Vol. 63, No. 6 / Friday, January 9, 1998 / Proposed Rules

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Establishing Ancillary Services and Health Care Regulatory Implications

11 Establishing Ancillary Services and Health Care Regulatory Implications Ann T. Hollenbeck and Richard A. Shapack Abstract Many physicians have expanded their traditional provision of physician services via the office and the hospital setting. Before the decision to include ancillary services, factors such as providing services that complement your practice, evaluating existing competition, and accounting for the costs involved in terms of investment, staff time, training, space, and billing have to be carefully considered. A comprehensive business plan with realistic projected volume data, contingency plans, and an exit strategy is highly suggested. This chapter covers those aspects along with presenting the dangers involved that could harm not only the ancillary services venture, but the initial practice, as well. Keywords: ancillary services, the Stark Law, Anti-Kickback Statute, ambulatory surgery centers (ASCs), Safe Harbor regulations, designated health services, physician-owned device company (POD)

and regulations. The focus of this chapter is limited to the federal Anti-Kickback Statute and the federal Stark Laws, each of which is described in general terms in the following. It is essential for any physician seeking to expand his/her practice offerings or pursue ownership in any health care venture to consult with counsel experienced in these health care regulatory matters. The ever-changing applicable laws and regulations and evolving state and federal enforcement activities require careful planning and ongoing compliance efforts on the part of physician, his/her group, and related accountants and legal advisors.

Ancillary Services ● ● ● ● ●

11.1 Introduction

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During the past several decades, many physicians have expanded their traditional provision of physician services via the office and the hospital setting. In fact, 21 to 33% of neurology and orthopaedic practices offer ancillary services to their patients that benefit their patients and boost practice revenue and profitability.1 However, there are a number of vital aspects; the delivery of ancillary services must be legal, within qualityof-care standards, and appropriate for the needs of the patients. Similar to any business or investment decision, factors such as providing services that complement your practice, evaluating existing competition, and accounting for the costs involved in terms of investment, staff time, training, space, and billing have to be carefully considered. And, similar to any investment, a comprehensive business plan with realistic projected volume data, contingency plans, and an exit strategy is a prerequisite. As will be covered in detail later, understanding the potential grave dangers involved, an absolute essential will be to obtain expert advice and to take all actions necessary at inception and thereafter to insure that the practice, including the ancillary services, is and remains fully compliant with the Stark regulations and the Anti-Kickback statutes. And the very sage advice from the non–health care law co-author is that the ongoing involvement of a very knowledgeable health care attorney is an absolute necessity. Physicians today are routinely involved as owners of ambulatory surgery centers (ASCs), provide surgery services in that setting, and have expanded the scope of care provided in their offices to include a variety of services (e.g., advanced imaging) that were traditionally performed in hospital-based settings (see "Ancillary Services" Box). A more recent trend is physician ownership in equipment distributorships. At issue with each of these activities is the often-debated controversy surrounding physician self-referral and its associated financial incentives. These matters are governed by federal and state laws

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X-ray. MRI. CT. Physical therapy. Ambulatory surgical centers. Diagnostic testing. Sale of medical devices. Point of care dispensing prescription drugs. Laboratories.

11.2 Ambulatory Surgery Centers: Anti-Kickback Statute The principal federal anti-kickback and abuse statute potentially applicable to the parties hereunder is the Medicare and Medicaid Anti-Kickback Statute.2 In pertinent part, the AntiKickback Statute prohibits the offer, solicitation, payment, or receipt of any remuneration, directly or indirectly, to induce a person to refer patients or to order, arrange for, or recommend ordering any goods, facility, service, or item for which payment may be made in whole or in part by the Medicare or Medicaid programs (or other federal health care programs, though for ease of reference this content refers to Medicare and Medicaid). The language of the Anti-Kickback Statute is very broad and is potentially applicable to any arrangement under which remuneration passes between providers who are in a position to make referrals to each other. In the context of an ASC, the principal concern is whether a return on an investment in an ASC is actually a disguised payment for referrals. In this regard, to the extent that physicians who invest in an ASC acquire their investment interests for less than fair market value (FMV), an enforcement agency likely would view the “discount” as remuneration offered with the intent of inducing referrals to the ASCs by the physician investors. Thus, in order to support the validity of an ASC arrangement, the participants must document the FMV of the transaction, such as by engaging an experienced, independent valuation consultant, to establish the value of the ownership units.

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Patient Education and Business Basics Civil and criminal penalties under the Anti-kickback Statute are applicable to both parties to a transaction that is found to violate the Anti-kickback Statute.2 Each violation of the Anti-Kickback Statute is a felony punishable by a fine of not more than $25,000, imprisonment of not more than 5 years, or both.2 Conduct that violates the Anti-Kickback Statute could also lead to exclusion from the Medicare and Medicaid programs under Section 1128(a) of the Social Security Act and substantial civil monetary penalties under Section 1128A of the Social Security Act, and has the potential for providing the basis for civil suits by competitors and/or patients who believe they have been harmed by improper conduct.3 Such conduct may also expose the parties to civil and criminal sanctions under other federal statutes, including, without limitation, the Racketeer Influenced and Corrupt Organizations Act and the Mail Fraud Statute.4 Violations of the Anti-Kickback Statute also may serve as the basis for private or governmental suits and substantial penalties under state or federal False Claims Acts.

11.3 Safe Harbor Regulations Because of the great uncertainty that existed concerning what was actually prohibited by the Anti-Kickback Statute, Congress directed the Office of Inspector General (OIG) to specify in regulations those practices that, although capable of being construed as falling within the prohibition of the Anti-Kickback Statute, will not serve as a basis for civil exclusion from the Medicare and Medicaid programs and will not give rise to criminal prosecution. In response to this mandate, the OIG5 published a number of final safe harbor regulations in the Federal Register on July 29, 1991, and again on November 19, 1999 (collectively the “Final Safe Harbor Regulations”). The safe harbors set forth specific conditions that, if met, assure that the parties to the transaction will not be prosecuted for an arrangement that qualifies for safe harbor protection. An arrangement will qualify for safe harbor protection, however, only if the arrangement precisely meets all of the conditions set forth in the safe harbor. Failure to fall inside of a particular safe harbor does not mean that the arrangement is per se violative of the statute, however. Where a particular arrangement does not qualify for safe harbor protection (e.g., because a hospital participant may be deemed to be in a position to refer to the ASCs through its employed or affiliated physicians), this, by itself, does not mean that the arrangement necessarily violates the Anti-Kickback Statute. Rather, in such case, the analysis of the arrangement’s risk under the statute is a facts and circumstances inquiry, especially as to factors from which an enforcement agency potentially could infer that the parties to the transaction had the requisite intent to violate the statute. Further, while an arrangement failing to satisfy, to any degree, any condition of a safe harbor will not be afforded protection, in defending the arrangement, it nonetheless is constructive to establish that its structure substantially conforms with the safe harbor’s requirements.

11.3.1 Ambulatory Surgery Center Safe Harbor Requirements The ASC Safe Harbor provides that “remuneration” under the Anti-Kickback Statute does not include any payment that is a return on an investment interest (such as a dividend) as long as6:

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The investment entity is a certified ASC (i.e., under the Medicare program) whose operating and recovery room space is dedicated exclusively to the ASC (e.g., the space cannot be used by the hospital for the treatment of the hospital’s inpatients or outpatients). Patients referred to the investment entity by an investor are fully informed of the investor’s investment interest. All of the following standards are met for hospital- and physician-owned ASCs: ○ The physician investor class must comprise solely investors (1) who are not in a position to provide items or services to the entity or any of its investors, and are not in a position to refer patients directly or indirectly to the entity or any of its investors or (2) who satisfy the “1/3rd test,” meaning that at least one-third of each surgeon investor’s medical practice income from all sources for the previous fiscal year or previous 12-month period must be derived from the surgeon’s performance of procedures (i.e., any procedure or procedures on the list of Medicare-covered procedures for ASCs, which includes services that require an ASC or hospital surgical setting). In practice, therefore, to enable an ASC to fit within the safe harbor’s requirement, surgeons should be eligible to invest in the entity, provided they meet the 1/3rd test. ○ The terms on which an investment interest is offered to an investor must not be related to the previous or expected volume of referrals; neither the hospital nor the entity may loan funds to obtain the investment interest; and the amount of payment to an investor in return for the investment must be directly proportional to the amount of the capital investment. ○ The ASC and all investors (i.e., hospital and physician investors) must treat federal health care program beneficiaries (e.g., Medicare and Medicaid patients) in a nondiscriminatory manner. ○ All ancillary services for Medicare/Medicaid patients performed at the ASC must directly and integrally relate to primary procedures performed at the facility, and none may be separately billed to Medicare or other Federal health care programs. ○ The hospital may not include on its cost report or any claim for payment from a Federal health care program any costs associated with the ASC (unless such costs are required to be included by a Federal health care program). ○ The hospital may not be in a position to make or influence referrals directly or indirectly to any investor or the entity. As noted in the Commentary, “a hospital may be in a position to influence referrals when it employs physicians who make referrals.” As a practical matter, this requirement is likely to preclude many hospital/physician ASC joint ventures from qualifying for safe harbor protections, absent additional guidance.

In two advisory opinions (OIG Adv. Op. 01–17 and 01–21)7 in which the OIG determined that an ASC to be owned and jointly operated by a hospital and physicians (i.e., that did not qualify for the safe harbor on account of the “hospital nonreferral requirement”) did not violate the Anti-Kickback Statute, the determination was based, in significant part, on certain safeguards which the hospital investor agreed to implement in

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Establishing Ancillary Services and Health Care Regulatory Implications order to limit its ability to control referrals to the ASC and the physician-investors: ● The hospital-employed physicians would not make referrals directly to the ASC, although they could refer patients to the physician investors. ● The hospital would not take any actions to require or encourage hospital-affiliated physicians to refer patients to the ASC or any of the physician investors. ● The hospital would not track referrals made by hospital-affiliated physicians to the ASC or any of the physician investors. ● Compensation paid to hospital-affiliated physicians by hospital would not be related directly or indirectly to the volume or value of (1) referrals by such physicians to the ASC or any of the physician investors, or (2) business otherwise generated by such physicians. Arguably, therefore, where a hospital adopts safeguards, such as the foregoing, it is likely that they would serve to substantially mitigate the risks of a proposed joint venture ASC as violating the Anti-Kickback Statute.

11.4 Imaging Centers: Stark Law Implemented in the 1990s, these laws were designed to remove the financial conflicts of interest from physician decision-making for clinical laboratory tests (Stark I) and a variety of other ancillary services, including imaging (Stark II).8 To preserve the potential efficiency advantages of legitimate business arrangements, however, numerous exceptions were established. The most commonly cited of these is the “in-office ancillary services exception,” which permits self-referral to a physician-owned entity for certain services performed in the office. Although office-based care was initially designed for simple services, such as laboratory tests and chest radiography, this care setting has evolved to include expensive, high-end services, such as MRI, CT, and cardiac stress imaging.

11.4.1 The Stark Law The Stark Law and its corresponding regulations prohibit, with certain exceptions, physicians from making referrals (see Text Box, 1) to an entity (see Text Box, 2) for designated health services (DHS) (see Text Box, 3) that would otherwise be paid under the Medicare or Medicaid programs, if the physician (or a member of the physician’s immediate family) (see Text Box, 4) has a “financial relationship” (as defined in the Stark Law) with that entity. A financial relationship includes both direct and indirect ownership and compensation relationships. The Stark Law also prohibits the entity providing the DHS from billing for any DHS that are furnished pursuant to a prohibited referral arrangement. An entity that collects payment for a DHS performed pursuant to a prohibited referral must refund amounts collected on a timely basis. Unlike the federal antifraud and abuse laws, the Stark Law does not focus on a party’s intent to induce referrals and, thus, a referral may be prohibited regardless of the parties’ intent.9 There are a number of exceptions to the Stark Law referral prohibition set forth in the Stark Law and in the Regulations. If an arrangement falls within one of these exceptions, it will not violate the Stark Law. On the other hand, if an arrangement fails

to meet all of the requirements of at least one Stark Law exception, the referrals made pursuant to that arrangement will be prohibited referrals under the Stark Law. The penalties for violating the Stark Law are potentially severe. All improperly collected monies must be returned and each instance of service arising from a prohibited referral is subject to civil monetary penalties of up to $15,000.9 Additionally, penalties of up to $100,000 may be imposed for certain referral arrangements and schemes. Finally, both the physician and the entity providing the DHS are subject to possible exclusion from the Medicare and Medicaid programs.9

1. A referral means the request by a physician for, or ordering of, or the certifying or recertifying of the need for, any DHS for which payment may be made under Medicare Part B, including a request for a consultation with another physician and any test or procedure ordered by or to be performed by (or under the supervision of) that other physician, but not including any DHS personally performed or provided by the referring physician. Note that a referral can be in any form, including, but not limited to, written, oral, or electronic. 2. An entity means a physician’s sole practice or a practice of multiple physicians or any other person, sole proprietorship, public or private agency or trust, corporation, partnership, limited liability company, foundation, non-for-profit corporation, or unincorporated association that furnishes DHS. An entity does not include the referring physician himself or herself, but does include his or her medical practice. 3. The Stark Law and Regulations define the term “designated health services” as the following items or services: clinical laboratory services; physical therapy, occupational therapy and speech-language pathology services; radiology and certain other imaging services; radiation therapy services and supplies; durable medical equipment and supplies; parenteral and enteral nutrients, equipment, and supplies; prosthetics, orthotics, and prosthetic devices and supplies; home health services; outpatient prescription drugs; and inpatient and outpatient hospital services. The Phase II Final Regulations include a list of CPT Codes used to describe these DHS. This list of CPT Codes is updated and published annually in the CMS physician fee schedule. 4. The term “immediate family member” is defined broadly to mean a husband or wife; birth or adoptive parent, child or sibling; stepparent, stepchild, stepbrother, or stepsister; father-in-law, mother-in-law, son-in-law, daughter-in-law, brother-in-law, or sister-in-law; grandparent or grandchild; and spouse of a grandparent or grandchild.

11.4.2 The Stark Law Exception Applicable to In-Office Ancillary Services In-office ancillary exception. Under the in-office ancillary services exception to the Stark Law, referrals for certain DHS ancillary to physicians’ services are not prohibited referrals under the Stark Law if the following requirements are met10:

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Patient Education and Business Basics Identity of the individual providing services. The DHS must be furnished personally by one of the following individuals: ● The referring physician. ● A physician who is a member of the same group practice as the referring physician. ● An individual who is supervised by the referring physician or by another physician in the group practice, provided applicable Medicare supervision and coverage requirements are met. Location where services are provided. The DHS must be provided in the “same building” as defined in the Stark Law. Further, one of three practice requirements must be met by the physician group while practicing in that “same building.” Billing for services. The services must be billed by one of the following: (1) the physician performing or supervising the service; (2) the group practice of which the performing or supervising physician is a member under a billing number assigned to the group practice; (3) the group practice if the supervising physician is a “physician in the group” under a billing number assigned to the group practice; (4) an entity that is wholly owned by the performing or supervising physician or by that physician’s group practice under the entity’s own billing number or under a billing number assigned to the physician or group practice; or (5) an independent third party billing company acting as an agent of the physician, group practice, or entity under a billing number assigned to the physician, group practice, or entity, provided the billing arrangement meets the applicable Medicare requirements.11 Group practice requirements. In cases where multiple physicians are practicing together, “group practice” definition must also be satisfied.12 Single legal entity. Each group practice must consist of a single legal entity operating primarily for the purpose of being a physician group practice in any organizational form recognized by the state in which it is formed. Physicians. Each group practice must have at least two physicians who are members of the group. Members of the group are defined to include a direct or indirect physician owner of a group practice, a physician employee of the group practice, a locum tenens physician, or an on-call physician while providing on-call services for members of the group.12 An independent contractor or a leased employee is not considered a member of the group (unless the leased employee meets the definition of an employee under the Stark Law). Members of the group are also deemed “physicians in the group” which also include independent contractor physicians while providing services for the group practice under a contract with the group. Range of care. Each physician who is a “member of the group” must provide substantially the full range of patient care services which the physician routinely provides, including medical care, consultation, diagnosis, or treatment, through the joint use of shared office space, facilities, equipment, and personnel. Services furnished by members of the group. Substantially, all of the services of the physicians who are members of the group must be provided through the group and billed under a billing number assigned to the group, and amounts received must be treated as receipts of the group. For these purposes, the Regulations clarify that “substantially all” means at least 75% of the total patient care services provided by group practice members and “patient care services” means any tasks

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performed by a group practice member that address the medical needs of specific patients, regardless of whether they involve direct patient encounters.13 Patient care services can include, for example, the services of physicians who do not treat patients, time spent by a physician consulting with other physicians, time spent reviewing laboratory tests, or time spent training staff members or performing administrative or management tasks. Groups must maintain data and supporting documentation to demonstrate compliance with this “substantially all” requirement. “Patient care services” generally are measured by the total patient care time each member spends on these services. For example, if a physician practices 40 hours a week and spends 32 of those hours on patient care services for the group practice, the physician has spent 80% of his or her time providing patient care services for purposes of the Stark Law. Physician–patient encounters. Members in the group practice must personally conduct at least 75% of the group practice’s physician–patient encounters. Distribution of expenses and income. Overhead expenses and income of the group practice must be distributed according to methods determined before the receipt of payment giving rise to the expenses or income, subject to the provisions described in paragraph 1 below. Unified business. The Regulations apply a “unified business test” for group practices. In the view of CMS, the unified business requirements are necessary to guard against the development of sham groups formed primarily for the purpose of profiting from self-referrals. Accordingly, the Regulations state that in order to qualify as a group practice, the group must be a unified business having at least the following features: 1. Centralized decision-making by a body representative of the group practice that maintains effective control over the group’s assets and liabilities (including, without limitation, budgets, compensation, and salaries). 2. Consolidated billing, accounting, and financial reporting. The unified business requirements permit location- and specialty-based compensation practices with respect to revenues derived from services that are not DHS and may permit such practices derived from DHS that comply with Stark Law requirements regarding productivity bonuses and profit sharing for physicians in a group practice. Volume or value of referrals. No physician who is a member of the group practice may receive compensation based, directly or indirectly, on the volume or value of referrals of DHS by the physician, except as provided below. Distribution of profits and productivity bonuses. Under the Regulations, a physician in a group practice may be paid a share of the overall profits of the group or a productivity bonus based on services personally performed by the physician,14 provided that the share of profits or bonus is not determined in any manner that is directly related to the volume or value of referrals of DHS by the physician. In other words, no physician who is a member of the group practice directly or indirectly may receive compensation based on the volume or value of a member’s referrals for “designated health services.” Because a group practice by necessity must distribute its DHS profits to the group in some way and because each physician’s referrals for DHS will at least indirectly affect his/her distribution of the DHS profit, the

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Establishing Ancillary Services and Health Care Regulatory Implications following are acceptable methods for distributing or otherwise crediting or allocating DHS profits to group practice members: ● A physician in the group practice may be paid a share of overall profits of the group, provided that the share is not determined in any manner that is directly related to the volume or value of referrals of DHS by the physician. A physician in the group practice may be paid a productivity bonus based on services that he or she has personally performed. ● The group can pool its DHS income and divide it among the physicians in any reasonable and verifiable manner that does not directly take into account the volume or value of a physician’s DHS referrals. Two methods that are deemed not to directly take into account the volume or value of DHS referrals are: (1) an equal distribution; and (2) a distribution based on each physician’s relative clinical productivity (excluding the physician’s DHS or ancillary production, government or commercial-pay). For example, if a physician in the group is twice as productive as another physician in the group based on their relative clinical nonancillary services, one physician can receive twice the share of the DHS as the other physician. Be advised that careful analysis of physician compensation, particularly bonuses and incentives, is essential.15 The “same building” is defined as: “a structure with, or combination of structures that share a single street address as assigned by the U.S. Postal Services, excluding all exterior space (for example, lawns, court yards, driveways, parking lots) and interior loading docks or parking garages. For purposes of this section, the ‘same building’ does not include a mobile vehicle, van or trailer.”16 More liberal rules apply if the group practice is located in a “health professional shortage area,” as defined by CMS.

11.5 Physician-Owned Distributorships On March 26, 2013, the OIG issued a Special Fraud Alert declaring that physician-owned device companies (PODs) are inherently suspect under the federal Anti-Kickback Statute.17 The OIG defines a POD as an entity that sells or arranges for the sale of medical devices ordered by their physician-owners, and refers to its longstanding position that an opportunity for a referring physician to earn a profit from his/her referral could constitute illegal remuneration under the Anti-Kickback Statute. The OIG acknowledges that whether or not a particular POD violates the Anti-Kickback Statute will depend on the intent of the parties, evidence of which is shown in varying ways, such as: the POD’s legal structure, its operational safeguards and the actual operations, and conduct of the physician owners. However, the Alert specifically states that disclosing a physician’s financial interest in a POD to a patient is not sufficient to protect against the POD’s violation of the Anti-Kickback Statute. The OIG provides a list of suspect characteristics that it views as particularly concerning. Several of those characteristics include:

●

●

●

The size of the investment offered to each physician varies with the expected or actual volume or value of devices that will be used by the physician. Physicians pay different prices for their ownership interests and distributions are not made in proportion to a physician’s ownership interest because of the expected or actual volume or value of devices used by the physician. The POD is a “shell” entity that does not perform any routine services expected of a distributorship, such as product evaluation, maintenance of inventory, employment of personnel.

A physician considering an ownership investment in a POD should understand that the federal government views PODs with a jaundiced eye. The physician investing in a POD would be subject to significant risk under the Anti-Kickback Statute and, as such, it is imperative that he or she seek knowledgeable, experienced health care counsel to advise him/her as to these risks and suspect characteristics.

Suggestions for Physicians Considering Ancillary Services 1. With the significant concerns regarding Stark and Anti-Kickback statutes, the involvement of a very knowledgeable health care attorney is essential. 2. This is a business and has to be operated accordingly with thorough assessment on an ongoing basis of revenue and costs, including physician and staff time, equipment, training, space, billing, etc.

11.6 Conclusion The addition of ancillary services to a physician’s medical practice will almost always increase revenue and profitability. However, because of the legal dangers and the potentially grave related results, there is a strong cautionary aspect; one must pay very strict attention to the Stark Laws and Regulations as well as the AntiKickback Statutes (and any other future laws or changes to the present restrictions). While not intending to frighten one into not considering the addition of ancillary services, this potential minefield is such that failure to pay strict attention and to have knowledgeable advice can and may have disastrous results. Beyond that, the operation of ancillary services should be approached in the same manner as any other investment—namely, a comprehensive business plan with realistic projected volume data, contingency plans, and an exit strategy as a prerequisite coupled with careful analysis and the consideration of factors such as providing services that complement the practice, evaluating existing competition, and accounting for the costs involved in terms of investment, physician and staff time, training, space, and billing. The ongoing attention to detail, both in terms of the business analysis of the ancillary services operations and ensuring that those operations are 100% compliant with all federal and state laws, is the necessary prescription for the success of this venture.

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References [1] Kane L, Peckham C. Medscape Physician Compensation Report, 2014. WebMD LLC; 2014 [2] The Public Health and Welfare, Criminal Penalties for Acts Involving Federal Health Care Programs, 42 U.S.C. § 1320a-7b(b) [3] Social Security Act 42 U.S.C. Ch 7. §§ 301–1397 [4] Racketeer Influenced and Corrupt Organizations. 18 U.S.C. Ch 96. §§ 1961– 1968; Mail Fraud and Other Fraud Offenses 18 U.S.C Ch 6. §§ 1341–1351 [5] Office of Inspector General, Medicare and State Health Care Programs: Fraud and Abuse; OIG Anti-Kickback, Provisions in Federal Register, Monday, July 29, 1991/Rules and Regulations (56 FR 35952); Office of Inspector General, Federal Health Care Programs: Fraud and Abuse; Statutory Exception to the Anti-Kickback Statute for Shared Risk Arrangements; Final Rule in Federal Register, Friday, November 19, 1999/Rules and Regulations (64 FR 63518) [6] 42 C.F.R. §1001.952(a)(2) [7] Office of Inspector General, Dept. of Health and Human Services), OIG Advisory Opinion No. 01–17. Issued October 10, 2001; Office of Inspector General, Dept. of Health and Human Services, OIG Advisory Opinion No. 01–21. Issued November 16, 2001

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[8] Centers for Medicare & Medicaid Services. Physician self-referral overview. Available at: http://www.cms.gov/physicianselfreferral. Accessed January 25, 2017. Updated January 5, 2015 [9] Exclusions from Medicare and Medicare Limitations on Medicare Payment 42 C.F.R, §411.353 and Conditions for Medicare Payment 42 CFR Part 424 [10] 42 U.S.C. §1395nn(b)(2); 42 C.F.R. §411.355(b) [11] Prohibition of Reassignment of Claims by Suppliers 42 U.S.C. § 424.80(b)(6) [12] 42 C.F.R. § 411.352 for definition of a “Group Practice” under the Stark Law [13] 42 C.F.R. §411.352(d) [14] 42 C.F.R. §411.352(i) [15] United States ex rel. Drakeford v. Tuomey Healthcare Sys., Inc., 675 F.3d 394 (4th Cir. 2012); United States ex rel. Baklid-Kunz v. Halifax Hosp. Med. Ctr., No. 6:09-cv-1002-Orl-31TBS, 2012 WL 5415108 (M.D. Fla. Nov. 6, 2012) [16] 42 C.F.R. §411.351 [17] Department of Health and Human Services. Office of Inspector General: Special Fraud Alert: Physician-Owned Entities, March 26, 2013. (https://oig.hhs.gov/ fraud/docs/alertsandbulletins/2013/pod_special_fraud_alert.pdf). Accessed 9/17

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Perez-Cruet, An Anatomical Approach to Minimally Invasive Spine Surgery | 01.10.18 - 10:54

Bringing Novel Spine Devices to the Marketplace

12 Bringing Novel Spine Devices to the Marketplace John A. Redmond, Mick J. Perez-Cruet, and James M. Moran Abstract Unsatisfactory surgical outcomes and frustration with available techniques and instrumentation often lead surgeons to develop novel improvements and solutions. The surgeon then faces a difficult decision regarding what to do with that solution. In addition to the typical intellectual property, production, and distribution concerns associated with any new product, there are unique regulatory, marketing, and reimbursement issues that must be considered when developing novel medical technology. This chapter discusses points to consider throughout the entire product realization process. Crucial first steps require introspection on the part of the surgeon, who must gauge his level of interest in becoming an entrepreneur. An entrepreneur must be willing to make a significant investment in time and money for the project to be successful. An alternative is to partner with an existing commercial concern to develop the product. The surgeon must also have some basis for believing the technology can be shown to provide value. This includes an evaluation of cost/benefit from the market’s perspective, without bias due to the developer’s personal beliefs and preferences. Additional topics covered in this chapter include determining ownership of the technology, creating and protecting intellectual property, sources of capital, design and development including quality management, regulatory considerations, manufacturing options, and distribution. While the topics are treated discretely, it must be remembered these factors are interrelated. A single change in the user requirements can have a ripple effect that spreads through all facets of the development program. Keywords: entrepreneur, commercialization, medical device, product development, medical technology, product realization

12.1 Introduction The invention and development of novel medical devices has been a critical component in the improvement of surgical techniques and patient outcomes for as long as surgery has been performed on humans. The role of the surgeon/inventor in that advancement cannot be understated. It was true in the early days of spine surgery and even more so today, especially given the complexity of minimally invasive spine (MIS) procedures, devices, and implants. Some surgeons have been content to scratch out an initial concept on a napkin and rely on a company to do the development. Others have taken on the complete project, from designing the initial concept to patents, prototyping, U.S. Food and Drug Administration (FDA) approval, starting companies, sales and marketing, and everything in between. If you have developed products and commercialized products, this brief chapter is probably not going to be of significant value. It is geared more toward novice inventors. No matter how you decide to approach getting your concept to market, there are critical steps you will need to take to protect your idea, maximize its patient benefit, and ensure your financial rewards are commensurate with the amount of time

and money you spend. Bringing a novel device or implant to market can be a complex, expensive, and daunting task even for the most business savvy surgeon. Depending on the device and how it is approached, the process can be fairly straightforward or very complicated and expensive. Making the right decisions early can insure the process goes smoothly. For our purposes, we are going to focus generally on products that can be brought to market via the FDA 510(k) process, which allows for clearance of devices equivalent to previously marketed devices. Any other processes, such as a PMA (PreMarket Approval) and IDE (Investigational Device Exemption), require time-consuming and expensive clinical studies, and in many instances can be difficult for an individual surgeon to manage. Our goal in this chapter is to give you a broad overview, advice, and tools you can use to avoid making costly mistakes. It is not meant to be an exhaustive step-by-step manual. We plan to discuss some of the critical topics that should help you decide the best approach to navigate the complexities of product development.

12.2 First Steps Probably the best advice for any surgeon thinking about turning their device concept into a commercial product is to “know thy self.” Bringing a device to market requires hundreds of hours, multiple layers of experienced people, and usually lots of money. Honestly addressing some basic questions will help determine if you want to go it alone, hire someone and start a company, or work with an established corporation. Are you risk averse? How much time and money do you really have to devote to the project? Do you have practical experience and expertise on the business/engineering side? What is your motivation? A good analogy is your overall approach to the practice of spine surgery. Are you most interested in being a medical center employee so you can concentrate more on patient care and surgery, or do you feel the need to strike out on your own and open a surgery center? The decision on the best way to bring your product to market really comes down to who you are.

12.2.1 Value Proposition One of the first things to think about is exactly how your product idea improves a procedure and ultimately patient outcomes. Determining how a device or implant will improve patient outcomes has always been the most important factor in bringing a new product to market. It is always the best place to start and should be primary in your thinking. If, for example, you come up with a surgical instrument that makes a particular procedure easier and faster for you and your colleagues, then you have indirectly improved patient outcomes even though you may not be able to immediately quantify it. The same holds true for novel implants. Once you have determined that your idea has the potential to improve patient outcomes, the next step is to investigate

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Patient Education and Business Basics whether or not there is a market for your device. This process is sometimes called determining your value proposition and it is the collection of reasons why a customer would buy your device. Does it fill an unmet need? Are there enough potential procedures or usage to make it financially worthwhile to spend the time and money bringing the device to market? Is there a reimbursement code for the procedure and device? Who is going to pay for it? Can the product be manufactured and delivered to the end user at a competitive price? How do you protect your position? Surgical instruments, such as a new MIS retractor, are usually capital expenditures paid by hospitals or brought in by implant companies if they are proprietary and part of their implant system. Most hospitals do not buy implant sets currently, so this needs to be taken into consideration during the planning and budgeting phase of the project.

12.2.2 Legalities There are also legal considerations depending on if you are working alone in private practice or in a group, hospital employed, or work for a university. Make sure you fully understand your employment contracts since a partner or institution may have claims to your invention. One other important question to consider is the financial outcome you want to achieve. Do you want to build a company around your invention or sell it off at the appropriate time? If it is a new implant, a brief investigation into reimbursement codes is fairly easy. The best source for both Current Procedural Terminology (CPT) and Healthcare Common Procedure Coding System (HCPCS), which codes for products, is www.cms. gov. Most companies also offer coding advice or services for their products. The days of having the next generation of implant and expecting to be paid a premium are over. Even truly novel devices and implants need to show a proven cost/benefit to avoid commodity pricing, so this is an important consideration. Finally, investigate the patent landscape to see if your device is truly unique and what barriers there may be to actually designing it and getting it made.

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yourself. Ultimately, you will need a good patent attorney who will help you protect your business and insure the freedom to practice. However, be aware that a patent is only as good as your willingness and resources available to defend it. Choosing the right patent attorney is critical, and you should ask for recommendations from medical professionals in the business. Your patent attorney should be very familiar with devices such as yours, which will reduce the learning curve and save you time and money. There are different types of patents and you can find the details on the USPTO website. However, in most cases, for first-time inventors, you will be considering either a provisional patent or a nonprovisional patent, usually a utility patent. The benefit of filing a provisional patent is to establish the first inventor to file. Provisional patents are only good for 1 year and then a nonprovisional patent needs to be filed or it expires without being published. The other benefits are that the provisional patent will not be examined by the USPTO, and you do not need to disclose any prior art or make claims. Provisional patents are especially beneficial when you do not have all the details of your invention worked out but are far enough along that you want some protection and an early filing date. They are also much less expensive to file and you can even do it yourself. You will also need to decide if you want to file only in the United States or in other countries, which can get expensive. If there is going to be a large market for your invention, you should consider at the very least filing in the major European Union countries and critical countries in Asia and South America. If you already have a design, it is important to have a Freedom to Practice Opinion. This is a legal opinion prepared by your patent attorney that provides a well-reasoned determination as to whether your device infringes any other patents. It is no guarantee that you will not be sued, but offers some protection if you are (▶ Fig. 12.1).

12.3 Partnering, Going It Alone, and Funding Your Device

12.2.3 Patents

12.3.1 Partnering

It is critical that you take all the necessary steps to protect your novel idea, and the best place to start is to document everything. When you start thinking about a new device and write down anything, date and sign it, even though it will probably evolve as you start to think about it in more detail. The obvious reason is to file your patent application at the earliest date possible and document when you first thought of the idea. The best source for patent and trademark information is actually our government, and it is available online at no charge. The U.S. Patent and Trademark Office (USPTO) website (www.uspto.gov) is easy to use and provides all the basics and the ability to search other patents. Searching patents for products in the same category as your invention will probably turn up a lot of devices that seem similar, but do not get discouraged too quickly. The devil is in the details and patents need to be interpreted very carefully. Even though your idea may be truly novel and unique, you will certainly find devices that have similar characteristics. You will learn a lot and it is less expensive to do the initial searches

Before revealing your proprietary information to anyone, whether you have an issued or pending patent, always have them sign a nondisclosure agreement (NDA). They are fairly standard and most have basically the same language. However, we have seen some that are one-sided and leave too much wiggle room on important issues. Make sure you have an attorney review before signing or disclosing anything. If possible, have the recipient of your information sign your NDA or obtain an attorney review before signing theirs. It is important to manage your expectations. Commercial concerns are in business to make money and no one is going to highly compensate you for a “concept on a napkin,” no matter how good it is. They will, however, generously compensate for a well thought out, novel, and patented or pending product idea that they can sell, or better yet is already generating revenue. If you have decided that you just do not have the time, money, or inclination to take the product from concept to the market, partnering with an established company is a good option. Your choices range from multibillion dollar international firms to local start-ups.

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Bringing Novel Spine Devices to the Marketplace

Fig. 12.1 (a–c) Patented BoneBac Press device invented and designed by MI4Spine LLC (Bloomfield, MI) to collect drilled autograft bone from the surgical site and use it to achieve spinal fusion as in (d,e). Multiple other uses are currently being investigated.

Large companies have the funds, personnel, and know-how to bring products to market. They also offer a very critical component of financial success, national and international distribution. The downside is that your idea may not get the attention it deserves and you may get frustrated with the slow pace. You are also probably going to get input from engineers and other medical advisory surgeons, which you may not welcome or who do not share your vision. Large companies will offer a licensing and royalty agreement or may just buy your product outright. Your device concept could get acquired and shelved simply to prevent competition and any disagreements are a true David and Goliath situation. Small to medium companies can offer a good alternative, but you need to perform due diligence. Do they have a track record? How do they propose to distribute your final product? Who are the owners and do they have a good reputation? Are you convinced they have staying power and have enough capital to complete your project? In any contract negotiation with any company, large or small, make sure there is a clause returning all rights and ownership in your product if there is a breach, including any manufacturing tooling, drawings, etc. A breach can take many forms, such as failure to complete the project, missed sales targets, or anything else you and your attorney decide protects your interests (▶ Fig. 12.2). Assuming your idea is truly novel, it will increase in value the farther along the development process you are, so deciding when to partner is important. Large companies are risk averse, so the more risk you remove, the more value your device has. In fact, we feel the best approach is to take your product as far as you financially can, but at the very least have a patent application.

12.3.2 Going It Alone Going it alone and developing your product can be both financially rewarding and personally fulfilling. If this is your decision, there are consultants who can help you. You will need advice

on the regulatory side, both in preparing regulatory submissions and in setting up a quality system if you are going to start your own company. The quality management system controls all aspects of your company, including design and development processes, so make sure you get the best possible professional help. Your company will have to be registered with the FDA, which is not difficult and can be done online. The FDA website is www.fda.gov. More than likely you will not be manufacturing your product in-house, so you will probably fall under the category of “Specification Developer,” which is nonetheless considered the manufacturer in the eyes of the FDA. The annual fee in 2017 for registering a company is $3,382. You can do much of the development work without registering with the FDA, which will delay having to pay the registration fee. When you have determined that you have a viable device with commercial value and want to proceed with the development, you will then be operating under what is referred to as design controls. In simple terms, this documents all the activity surrounding the product development process, testing, and manufacturing of your device. This will ultimately lead to what is called a Design History File, which essentially has everything in it from beginning to end. It is one of the first things the FDA looks at when conducting an audit, in addition to product complaint files. The detail of setting up an FDA-registered company and quality management system would constitute a complete textbook. It is very important to do it right and not take shortcuts. The intent of FDA regulation is to insure devices are safe and effective, and you do not want to get on the wrong side of the FDA.

12.3.3 Funding Funding your project can take many forms, from self-financing to raising money from outside investors. There are angel investor groups in many cities that can sometimes be a good source for initial capital and critical review of your business plan. You

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Patient Education and Business Basics

Fig. 12.2 Company MI4Spine LLC, under which product ideas, patents, engineering, and prototypes are developed, partners with midsize medical company Thompson Surgical Instruments to create Thompson MIS. This new corporation provides regulatory support, manufacturing, and distribution of products to bring technology to the marketplace.

can also look into government grants or partnering with a small device company. However you choose to do it, you will almost certainly need more capital than you anticipate.

12.3.4 Design and Development Despite the fact that this chapter is organized into sections, keep in mind that all components of the commercialization process are interrelated. Take an interbody device with integral fixation as an example. FDA tracks devices using a three-letter product code that helps organize devices into technology and indication groups. The interbody device could have one or more of several different product codes. The product code for which you attempt to have your device cleared should be tied to your business objectives, the target indications, and how the device can be coded for reimbursement. If you attempt to market your device for indications not associated with that product code, you will be guilty of off-label promotion. The indications also control the American Society for Testing and Materials (ASTM) test standards that are applicable. The indications can also lead you down a path necessitating clinical trials, which are usually responsible for a significant increase in cost and time to market. The developer needs to be conscious of these interrelationships and carefully monitor technology, regulatory, and business changes to prevent unintended consequences. It is relatively easy to have a part or implant assembly made, particularly with the advent of 3D printing technologies that are capable of producing devices from materials that are much like medical grade titanium alloy. Holding a looks-like, workslike implant prototype sometimes seduces inventors into believing they are close to commercialization, but nothing could be farther from the truth. The challenge is making thousands of parts that all meet specifications, fit properly with other components in the implant assembly, and interface with the surgi-

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cal instruments used for implantation. Every implant pulled from inventory must work properly with any mating instrument pulled from inventory, first time, every time, so tolerances are tight and proper inspection critical. There is often a failure to appreciate the full impact of such quality assurance issues and regulatory affairs (QA/RA) on operations, which, if not done correctly, can lead to product complaints or worse. It is not “just paperwork.” Consultants may assist with preparing the framework, but unless company management is deeply involved, there is likely to be a mismatch between systems and business operations and objectives. Innovators may be among the medical or academic elite, but without commercial experience they are typically novices when it comes to QA/RA and developing and managing in-house or outsourced production. The most critical step in the development process is completely and correctly identifying what is typically called user requirements, user specifications, or marketing specifications. These requirements are usually broken into three major categories: technical, regulatory, and business. Every characteristic of the product must be identified. Sometimes, the inventor assumes they represent the opinions of all surgeons when in fact market research leads to a diversity of opinions that must be resolved before the user requirements can be set. It is not necessary or desirable to provide design solutions when listing user requirements. The focus should be on what requirement the device needs to meet, not how to meet the requirement. The who, what, when, where, and why approach is a good starting point. Who is the typical user of the product? What is the device supposed to do? Why use this device? Where is the device going to be used? When will it be used? Some specific issues are: sizing, known risks based on complaints and FDA Total Product Lifecycle reports, economic and political outlook affecting reimbursement, instrument set

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Bringing Novel Spine Devices to the Marketplace contents, indications desired, domestic and international distribution plans, production cost, selling price, competitive devices, market trends, competitor patents, user surveys, and clinical trends from medical society meetings. The overall development process is often described as a waterfall. User requirements lead to quantifiable product specifications; the product is designed to the specifications, tested to insure the specifications are met, and then tested to insure the user requirements have indeed been met. Showing the specifications have been met is called verification. It answers the question “Are we building the device right?” Showing the user requirements have been met is called validation and answers the question “Are we building the right device?” One common way of tracking this process is called a traceability matrix. The first column of the matrix might list the user requirements, the second column would be a conversion of the requirements into a complete, testable, and ideally quantifiable specification, the third column an indication if the requirement is mandatory or optional, the fourth column the acceptable outcome, and finally the results of the verification and validation processes. Moving across a row left to right demonstrates that the user requirement has been met, and moving right to left reveals why the finished device possesses a certain characteristic, in case a change to that characteristic is proposed. The traceability matrix also facilitates FDA audits of design control, which are a certainty. Quality documentation should always be assembled in a manner that is readily auditable. Keep in mind the design must be frozen before undertaking verification and validation. Any change to the device is very likely to invalidate the results and some or all of the testing, verification, and validation will have to be repeated. Regarding the initial cost of getting a device approved via the 510(k) process, it has been our experience that a typical implant (plate, spacer, pedicle screw) should cost between $200,000 and $300,000, depending on the complexity of the system. This, of course, assumes having the internal personnel to do much of the work as described earlier. It would go up from there if you had to hire an outside firm to do much of it or clinical trials were required. This does not include any inventory for a product launch or company expenses related to forming a company and hiring the appropriate personnel. Murphy’s law for product development is important to keep in mind. You should complete a budget estimate and then double it. Pick a date you think it will be completed and add 6 months. Set a first year sales target and cut it in half. If you do that, you will probably be close.

12.3.5 Manufacturing There are many excellent device and implant manufacturers in the United States and internationally, both large and small. Choosing the right partner can save thousands of dollars and many headaches, but it is not always easy. Whoever you choose should already be manufacturing tight tolerance medical devices and implants in the same material as your invention. There are trade organizations such as Medical Device Manufacturers Association (MDMA) and others, and they are a good place to start looking. However, getting recommendations from industry experts is always the best approach. During your initial commercialization phase, you will probably not be ordering

Fig. 12.3 Medical device (a) prototype machinery and (b) polyether ether ketone (PEEK) manufacturing facility at Royal Oak Industries MD (ROIMD).

large quantities, and getting the lowest cost at low volumes is never easy. Some manufacturers will let a company issue a blanket purchase order for a larger volume, but take delivery according to a schedule. This can be a good compromise if you have accurate sales projections for the first 6 months or so. If your invention is an implant, it will almost certainly come with associated instruments and a sterilization tray, and these are the most expensive parts of any system. This is why user requirements, specifications, and marketing specifications are so critical in the design and development phase. Having to order new trays because a needed instrument was left out can be very costly (▶ Fig. 12.3).

12.3.6 Sales and Marketing Assuming you have developed a device yourself and want to bring it to market, you will need to decide on distribution. You have three primary choices: independent distributors, a direct sales force, or signing an agreement with an established company. Unless your device is truly unique and there is nothing like it on the market, finding good distributors to focus on selling your device can be difficult. Single product companies are at a major disadvantage because of this. However, if your device is truly unique, it may make financial sense to raise money and market it yourself. The marketing of your device is going to mean website development and at the very least medical convention attendance to introduce your product to prospective

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Fig. 12.4 (a) Medtronic marketing personnel with product inventor. (b) BoneBac Press product taken up for global distribution by Medtronic and debut at the American Association of Neurological Surgeons meeting Washington, DC, 2015.

users and dealers (▶ Fig. 12.4). Strategic acquirers typically value a company based on a multiple of sales versus a multiple of EBITDA, so the more sales the higher the valuation, even if you are not profitable at first.

12.4 Conclusion As we have discussed in this chapter, many considerations must be taken into account when deciding how to bring your novel idea to market. It can be a rewarding experience that benefits your patients and other surgeons. If you are able to develop a novel product and run a lean profitable company, you will be successful regardless of whether or not it is acquired or licensed. The spine market would not be what it is today without innovative, entrepreneurial surgeon inventors, and thankfully many have decided it was worth taking the risk to develop a novel device (▶ Fig. 12.5 and ▶ Fig. 12.6).

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Bringing a novel device or implant to market can be a complex, expensive, and daunting task even for the most business-savvy surgeon. Probably the best advice for any surgeon thinking about turning their device concept into a commercial product is to “know thy self.” Know the time you want to commit, the expertise you have, and the financial resources you need to get the project to market. Questions to ask yourself: Are you a risk-taker? How much time and money are you willing commit? Do you have business savvy? Do you have the necessary engineering skills? What are your motivating factors?

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Determining how a device or implant will improve patient outcomes has always been the most important factor in bringing a new product to market. Make sure you fully understand your employment contracts since a partner or institution may have claims to your invention. Investigate the patent landscape to see if your device is truly unique and what barriers there may be to actually designing it and getting it made. Choose the right patent attorney. Have your patient attorney prepare a Freedom to Practice Opinion. Before revealing your proprietary information to anyone, always have them sign an NDA. Large companies have the funds, personnel, and know-how to bring products to market. Small to medium companies require due diligence on your part in trying to get your device to market. Seek a consultant if you are “going it alone” to design and develop your product for the marketplace. When registering your company with the FDA or setting up quality management controls, do it right and do not take shortcuts. Funding your project can take many forms, from self-financing to raising money from outside investors. Appreciate the full impact of quality assurance issues and regulatory affairs (QA/RA) on all operations. Completely and correctly identify what is typically called user requirements, user specifications, or marketing specifications. To be realistic with expenses and due dates, estimate a budget and then double it; set a date for completion and then add 6 months.

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Bringing Novel Spine Devices to the Marketplace

Protect your idea Determine Value Proposition

Maximize patient benefit

Ensure financial rewards

Address legalities

Research patent

Consider partnering or “Going it alone”

Find funding

Design and develop

Create and act upon a marketing plan

Fig. 12.5 Steps to brings a novel idea to the marketplace.

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Patient Education and Business Basics

USER REQUIREMENTS REVIEW

DESIGN INPUTS REVIEW

DESIGN & DEVELOPMENT REVIEW

VERIFICATION

DESIGN OUTPUT REVIEW

VALIDATION

FINISHED DEVICE

Fig. 12.6 The product development process.

Suggested Readings [1] CMS.gov. HCPCS - General information. Available at: https://www.cms.gov/ Medicare/Coding/MedHCPCSGenInfo/index.html?redirect=/medhcpcsgeninfo. Accessed April 23, 2017

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[2] United States Patent and Trademark Office. Available at: https://www.uspto. gov/. Accessed April 23, 2017 [3] Device Registration and Listing. Available at: https://www.fda.gov/MedicalDevices/DeviceRegulationandGuidance/HowtoMarketYourDevice/RegistrationandListing/. Accessed April 23, 2017

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Part III Image Guidance, Monitoring, and Nonoperative Techniques

13 Computer Navigational Guidance in Spine Surgery

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14 Intraoperative Monitoring

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15 Injection-Based Spine Procedures and Diagnostic Procedures

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16 Stereotactic Radiosurgery for Tumors of the Spine

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III

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Image Guidance, Monitoring, and Nonoperative Techniques

13 Computer Navigational Guidance in Spine Surgery Fernando G. Diaz and Mick J. Perez-Cruet Abstract Computer navigation allows the surgeon to use minimally invasive techniques by pinpointing the position of the pathology and the surgeon-guided instrumentation. This chapter reviews the various applications of computer navigational guidance in spinal surgery including preoperative and intraoperative image acquisition, computer-aided navigation, and various operative procedures. Keywords: three-dimensional imaging, computer navigation, navigational space, radiographic imaging, fluoroscopic imaging, CT imaging, dynamic reference array, implantable device

13.1 Introduction Computer navigational guidance has been used for multiple surgical procedures in neurological surgery, predominantly for cranial surgery. Computer navigation allows the surgeon to use minimally invasive surgical techniques by clearly pinpointing the position of the surgical pathology to be addressed and by guiding the surgeon to the precise location where the surgical procedure is to take place. In cranial procedures, the technique is limited by the relative instability of the cerebral structures that may render the precision less than desired. In spine surgery, the rigidity of the bony structures and the greater stability of the spine allow the surgeon to have greater predictability in the position of the vertebra in a three-dimensional environment. This chapter will review the technique and applications of computer navigational guidance in spine surgery: the benefits and limitations of the technique as well as the potential application to multiple spine procedures.

13.2 Navigational Concepts The success of any surgical procedure rests on the ability of the surgeon to know and understand surgical anatomy, and apply it to the purpose intended by the intervention. Surgical technique requires the execution of the operative procedure in a safe and expedient manner with adequate exposure and visualization of the area, minimal damage to the surrounding structures, and limited or minimal blood loss. Open surgical procedures allow the surgeon to expose and visualize the tissues and structures to be operated on, but require large exposures, damage to collateral structures, and occasionally significant blood loss. Computer navigation in surgical procedures is premised on the anatomical understanding of the structures operated on, translated into the computer software, and used to guide the various instruments into safe positions where they will allow the surgeon to complete the procedure intended. Computer navigation allows the surgeon to access the various structures through small or limited approaches, limiting visualization of the surrounding tissues, and compromising the transmission of light into the area. Specialized instrumentation is required to have sensors that allow the computer system to capture the position of the instruments in a three-dimensional space, and integrate that position with the computerized anatomical rendering of

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the area being operated on. Various magnification and lighting systems are also required to allow the surgeon to visualize the surgical field adequately. Computer navigation was introduced in cranial surgery to allow access to difficult areas of the brain or the base of the skull, through limited access exposures. The surgeon prepares the operative approach using the computerized trajectory determined by the system, and follows the path through small and frequently narrow spaces to reach the target where the pathology is located. The trajectory developed on the computerized map facilitates the planning and execution of a surgical corridor with limited exposure and minimal damage to surrounding structures. Deep-seated brain tumors, arteriovenous malformations, intraventricular lesions, or placement of ablative lesions or stimulating electrodes can all be detected using three-dimensional cranial navigational techniques. The success of cranial navigation is based on the small space contained within the cranial cavity, the relative proximity of all the intracranial structures, the rigidity of the skull, and the ability to affix the skull to a rigid supporting frame. Reference points of localization for navigational purposes require a fixed reference frame or fixed anatomical structures that can be targeted and remembered by the computer software. Limitations of the cranial navigational techniques are that the intracranial structures are soft, not fixed, and frequently change position when the intracranial dynamic balance is altered by the craniotomy procedure itself. Removal of cerebral tissue or cerebrospinal fluid will result in shifts of the intracranial structures, and will create errors in the fine identification of intracranial lesions. Spinal navigation requires reference points as well which are frequently fixed to the spinous process of one of the vertebrae in the area being operated on, the skull, or the pelvis, and which can be correlated to fixed anatomical bony structures for confirmation or realignment. The mobility of the individual spinal segments and the changes that take place following distraction of the intravertebral spaces, the placement of instrumentation, or the resection of vertebral elements result in distortions of the original navigational images, and will require skill and understanding to correct for them during the operative procedure.

13.2.1 Navigational Space Spine surgery for degenerative disease, spine reconstruction, and spine trauma require intensive radiographic monitoring and imaging. Initial approaches to surgical reconstruction were all done with multiple simple radiographs in the anteroposterior or lateral position, requiring considerable delays and radiation to the patient and the surgical team. Progress in radiographic imaging allowed for the introduction of fluoroscopic imaging that allowed the surgeon to see in real time the manipulation of the operative field and the placement of instrumentation. Spine fluoroscopy allows for the immediate visualization of the area in question on a fluoroscopic screen, but requires the surgeon and the team to wear protective gear, including aprons, thyroid shields, gloves, and goggles, making the procedures considerably uncomfortable. The radiation dose required in complex spinal reconstruction can increase rapidly to significant levels.

Perez-Cruet et al, An Anatomic Approach to Minimally Invasive Spine Surgery, 2nd Ed. (ISBN 978-1-62623-643-1), copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.

Computer Navigational Guidance in Spine Surgery Surgeons and assistants alike can be subject to significant radiation doses in cumulative bases, resulting from repeated use over time. Computer navigational guidance provides the opportunity for the surgeon and the team to acquire all the images needed at the beginning of the surgical procedure, and to navigate the instruments in a virtual computer environment with the same precision obtained with real-time fluoroscopy. The navigational space can be defined as the surgical area that will be recognized by the computer based on image acquisition and image reconstruction in a three-dimensional environment. Image acquisition then becomes the essential element to allow the surgeon to establish the areas where the surgical procedure will occur. Images can be obtained with fluoroscopic systems that incorporate a reference array directly on fluoroscopic unit and correlate the position of the reference frame located on the spine with the radiographic images reconstructed by the computer in a threedimensional space.1 Similar images can be obtained directly with a surgical CT scanner that allows the recognition of fixed anatomical bony landmarks in relation to a rigid frame affixed to the spine during the acquisition time of the CT scan. Images acquired through either system are reconstructed by the computer software to create a three-dimensional environment in axial, coronal, and sagittal planes, as well as a true three-dimensional model, through which the surgeon will be able to navigate the different instruments during the execution of the surgical procedure.

13.2.2 Navigational Reference Points A rigid frame is currently required as the primary source of reference for the computer to merge the anatomical images acquired by the radiographic technique with the actual instrumentation that will be used to complete the surgical procedure.2 The reference frame is equipped with reflective spheres located in four or five different positions (passive arrays) within the reference frame (▶ Fig. 13.1a). The passive arrays will reflect the laser light emitted by the light-emitting diodes (LEDs; active arrays) located in the electro-optical camera tracker, and will allow the computer to establish the position of the fixation point of the reference frame, or dynamic reference array, in the specific anatomical location in the spine. The anatomical registration of the spine structures is completed in that process when the input from the imaging system is then correlated with the dynamic frame reference input registered by the optical camera tracker and integrated by the computer software merging program (▶ Fig. 13.1b,c). This process will then allow the system to recognize the position of the surgical instruments in the surgical navigational space. Each surgical instrument is equipped with a passive array frame that reflects the light from the LED camera, allowing the system tracker to register each instrument with its specific physical characteristics, which have been preprogrammed in the computer software, and then permitting the precise recognition of each instrument in the surgical space. The ability of the software to then reconstruct the anatomical structures being highlighted by the tip of the instrument in the surgeon’s hands allows the surgeon to view the instrument in a virtual three-dimensional space on the computer screen.3 Newer software computer programs and devices allow the surgeon to obtain three-dimensional reconstruction of rigid structures using surface overlays that adapt to the surgical field, and are fixed in place by attaching them directly to the patient’s

Fig. 13.1 Minimally Invasive Neurosurgical Society (MINS) (Royal Oak, MI) cadaveric training lab images showing surgeons training on (a,b) O-arm image guidance navigation system for placement of (c) percutaneous pedicle screws.

skin. Other systems use normal anatomical bony landmarks as the reference points for the computer, since they are permanently fixed to the patient, are not going to move in location unless the surgeon removes them, and can be reused if the system loses its tracking arrangements. Small implantable electronic radiofrequency-emitting devices have been used in pediatric surgery to serve as reference points, since the bony anatomy in children may be too weak to sustain a large dynamic reference array that may damage the normal pediatric bone.

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Image Guidance, Monitoring, and Nonoperative Techniques These radiofrequency-emitting devices provide an orthogonal electromagnetic field in the surgical navigational space, allowing the surgeon to track the instruments as they move through the field. Their size and dimensions limit their use at the moment to small operative fields such as the pediatric skull. Computerized navigation allows the surgeon to visualize the surgical space in a real-time environment without the need to use additional radiation. The images give a three-dimensional representation of the surgical space in which the various surgical instruments move. At any point during the surgery when an instrument equipped with a passive reflective array is used, the surgeon can view the precise localization of the instrument in the axial, coronal, and sagittal direction, and anticipate the trajectory the instrument will follow. The navigational instrument equipped with a passive reflective array can be used to identify anatomical points on the patient, precisely place points of access for penetrating instruments, plot the trajectory of implantable devices such as pedicle screws and cages, and determine the ultimate resting position of any device the surgeon wants to leave in place. The safety and convenience derived from the knowledge of the precise location of the instrument at any time during the surgery when navigational guidance is used give the surgeon predictability in the position of the surgical procedure, the extent of resections, and the placement of implantable devices, all through limited access, minimally invasive approaches.4

13.3 Image Acquisition Radiographic images for spine surgery consist of the review of plain film radiographs, scoliosis full-length radiographs, and MRI and CT scans of the areas in question. Not all imaging modalities are used for every patient, and the surgeon will select some or all of the modalities in the evaluation. Occasionally, radioisotope studies of bones will be required to document the presence of neoplastic or infectious lesions. The correlation of the preoperative studies with intraoperative imaging allows the accurate localization of the pathology and the correction of the deformities in question. Unlike computer navigation in cranial surgery, spine surgery is predominantly done with CT images acquired either preoperatively or most commonly intraoperatively. Image acquisition for spine surgery with computer-guided navigation requires the placement of a dynamic reference array on a fixed point in the spine, skull, or pelvis. Most commonly, the spinous process of one of the immediately adjacent vertebrae is selected because of its proximity to the operative field and the ease of exposure. When the spinous process is selected, it is necessary to insure that the direction and position of the dynamic array is out of the field of view of the electro-optical camera to prevent interference in the recognition of the passive reflective arrays located in the navigational instruments. The spinous process fixation device is a simple clamp that must sit fully on its entire length on the long axis of the spinous process, and must be rigidly fixed to prevent its movement during the surgical procedure that may disrupt the accuracy of the navigational system. The second most common site is to place a rigid bar in the posterior superior iliac spine or high on the iliac crest, making sure that when the bar is placed in the iliac crest region the placement is bicortical to prevent displacement during surgery. The dynamic array is mounted on either device with a ratcheted device that allows for orientation of the dynamic array in relation to the position of the

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patient, the imaging, and navigational system used. For cervical procedures, the dynamic reference frame may be placed on the C7 spinous process or on the skull. The selection of the site is surgeon dependent. Having placed the dynamic array in a fixed and stable manner, the images are then acquired for the region being operated on. Fluoroscopic devices that replicate the three-dimensional reconstruction abilities of a true CT scan, such as the O-Arm or the Brainlab systems, provide imaging of an area of the spine generally limited to four or five immediately adjacent spinal levels. If surgery is required at more than four levels, a second run is required to complete the imaging acquisition before surgery. An intraoperative motorized three-dimensional C-arm acquires 190 two-dimensional projection images during a single rotation. A multiplanar reconstruction algorithm creates autoregistered high-resolution three-dimensional reconstructions from the set of projection images. The resultant volume can be reformatted, using multiplanar reformatting (MPR) computer programs to display CT-like intraoperative images. True intraoperative CT scanners are equipped with the ability to travel along the length of the entire spine and can get an entire spine reconstruction on a single run, decreasing the radiation dose to the patient and the time required to complete the study. The spine three-dimensional reconstruction obtained by either methodology provides an immediate real-time view of the position of the instruments in the operative field in the coronal, axial, and sagittal planes, allowing the surgeon to have great precision on the localization of the operative site and guiding the placement of the instruments. Furthermore, the navigational plans provide measuring tools that allow for the exact dimensions required for the specific anatomical location in all three dimensions, providing the width, height, and length specific to the anatomical location and the instrument to be used (▶ Fig. 13.2).

13.4 Computer-Navigated Surgical Procedure Preoperative preparation in spine surgery is fundamental to the successful completion of any surgical procedure. A thorough understanding of the patient’s clinical presentation and physical findings, coupled with a complete assessment of appropriate imaging and diagnostic studies, provides the surgeon with the ideal environment to perform a navigated surgical procedure. Computer navigation in spine surgery provides the surgeon with greater accuracy and safety when performing any spine reconstruction procedure. The surgeon is still required to be totally proficient in the understanding of the following: ● Surgical anatomy of the operative area. ● Pathology to encounter. ● Surgical technique to be used. ● Equipment needed. ● Potential complications to face and how to solve those complications when they present themselves. Computer navigation facilitates the surgeon’s ability to visualize with greater precision and accuracy areas of the spine that are not readily visualized in the operative field, but is not a substitute for an appropriate selection of the patient or a complete understanding of the anatomy and the techniques to be used, or

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Computer Navigational Guidance in Spine Surgery

Fig. 13.2 (a) Intraoperative photo showing sterile draping of O-arm and (b) registration of surgical instruments for image guidance surgery.

how to solve potential complications that arise during the operative procedure. Depending on the system available to the surgeon in the different operating rooms, some generalities can be described on the application of computer navigation in spine surgery. The technique is useful for open as well as for minimally invasive procedures. Since the majority of the procedures conducted using computer navigational guidance are performed in the lumbar spine, the description of a surgical procedure in the lumbar spine with pedicle screw insertion at L4–L5–S1 will serve to illustrate the steps followed in the implementation of computer navigation in spine surgery. In our institution, the navigational system available is the Medtronic O-Arm and StealthSystem (▶ Fig. 13.3). All patients are operated on on an electric Misuho OSI Jackson spine four-poster table, and the patient’s head is supported by a Misuho OSI Prone View cradle to provide free access to the patient’s face, eyes, and airway without compression.

13.4.1 System Placement The electro-optical camera tracker for the navigational system is placed at the head of the bed, and should be located in such a manner that the anesthesia intravenous poles, overhead lights, and monitoring equipment do not block the LED light trajectory (see ▶ Fig. 13.1 and ▶ Fig. 13.2). The computer navigational unit and monitor are placed on the patient’s right side, and a slave monitor is placed directly opposite to the computer to allow the surgeon and the assistants to have clear view of the navigational procedure as it occurs. The scrub nurse is generally on the left side of the patient, and the surgeon may be on either side of the patient depending on the nature of the surgical procedure.

Fig. 13.3 StealthStation S8 navigational system. (Source: Medtronic Neurosurgery, Louisville, CO.)

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13.4.2 Patient Position Once the patient is under general anesthesia and positioned prone on the Jackson table, the operative field is prepped and draped in the usual manner. The O-Arm is placed around the patient as part of the sterile field, at the foot of the bed where it will remain until the conclusion of the operation. When the images are acquired, the O-Arm is moved into the operative field, and once the images are satisfactory, the O-Arm returns to its resting position minimizing the time spent moving the instrument in or out of the surgical field. Once the team is comfortable having the O-Arm in the operative field, the total time required for its movement in and out of the operative area, and image acquisition is 13 minutes.

13.4.3 Imaging Procedure A stab wound incision is made in the midline over a spinous process one or two segments above the level to be operated on. The dorsal fascia is incised on either side of the spinous process, and the paraspinous muscles are gently dissected off the spinous process. The fixation clamp for the reference frame is then applied on the spinous process, making sure that the entire length of the blades rests on the spinous process, and the clamp is tightly applied to prevent its dislodgement during surgery. Since the electro-optical camera tracker is placed at the head of the table, the reference frame must face inclined toward the head in an ergonomic manner to limit collision or obstruction with the surgical instruments (see ▶ Fig. 13.1 and ▶ Fig. 13.2). When the dynamic reference frame is placed on the iliac crest, the room setup has to be reversed with the electro-optical camera located at the foot of the bed, the dynamic array facing toward the foot of the bed, and the O-Arm resting above the thorax. Once the dynamic array is positioned securely, initial anteroposterior and lateral images are obtained to center the field within the margins of image acquisition for the O-Arm. The surgical team is escorted out of the operative room into an adjacent clean area and the navigational images are obtained. The team reenters the room and verifies the quality and correctness of the images acquired. The surgical instruments to be used during the surgical procedures are then individually registered by the computer using the dynamic reference frame as the common registration site. For most spine procedures requiring navigation, the various systems provide a directional probe—a Jamshidi needle, pedicle probes, pedicle taps, pedicle screw drivers, and intervertebral cage insertion instruments, all equipped with passive reference arrays to guide their position.

13.4.4 Operative Procedure—Pedicle Screw Placement Once the image acquisition and image and instrument registration are completed, the surgeon identifies on the patient’s skin surface the area where the surgical procedure will take place. The targeting probe can identify on the computer screen the exact position of the probe in relation to the spine area being targeted. The surgeon marks the exact position for the surgical incision, and proceeds with opening the area. The Jamshidi needle is then positioned on the dorsal lumbar fascia and advanced under navigational guidance through the pedicle into the vertebral body (▶ Fig. 13.4). The rigid portion of the needle with the passive ar-

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Fig. 13.4 Navigated Jamshidi needle.

ray is removed, and a guidewire is placed in the needle and the wire tip is driven through the front wall of the vertebral body to secure its position once the needle cannula is removed. A cannulated pedicle tap with its passive array is then navigated through the pedicle to the back portion of the vertebral body, generally using a diameter 1 or 2 mm smaller than the size of the pedicle screw diameter to be used. The diameter can be determined on the computer screen visualizing the axial and coronal sections to estimate the smallest available space. The pedicle screw should preferably be 1 mm smaller than the smallest diameter of the pedicle. The cannulated pedicle tap can be used to calculate the length of the pedicle screw by adding a color extension on the computer screen to simulate the entire length of the pedicle screw from the dorsal surface of the facet to the anterior wall of the vertebral body. The pedicle tap is then removed, and replaced with the cannulated pedicle screw with its passive array. The pedicle screw is then navigated to its final resting position flush with the posterior wall of the vertebral body, or the tip through the anterior wall of the vertebra to obtain bicortical purchase. Once the pedicle screws are all in place, the facet and lamina are exposed through a minimally invasive retractor and removed to achieve decompression. The ligamentum flavum is resected allowing visualization of the exiting and traversing nerve roots over the disc space. The disc is identified visually or with a guiding navigational probe, and resected. The cartilaginous end plates are removed, the bony end plates scored, and the space dilated with the aid of the pedicle screw heads. The dimensions of the disc space are measured on the computer

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Computer Navigational Guidance in Spine Surgery

a

Fig. 13.5 (a,b) Image-guided spinal navigation used during complex redo operation in which interbody cage devices had been previously placed. The image guidance was useful for defining pertinent spinal anatomy, determining pedicle screw placement, and identifying case location through previous scar tissue.

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screen with the preoperative or intraoperative scan images, and the appropriate cage is selected. The cage is mounted on a navigational inserter equipped with a passive array, and navigated in the intervertebral space (▶ Fig. 13.5). A final scan with the OArm verifies the accuracy of placement of the pedicle screws and cage before the wound is closed (▶ Fig. 13.5). If the surgeon identifies an inadequate position of the instruments, that can be corrected immediately before the wound is closed and the patient leaves the operating room.

13.5 Navigational Applications in Spine Surgery Navigational techniques are applicable to any level of spine surgery, so long as a satisfactory dynamic reference source can be established. Most navigational procedures have been used for posterior approaches, but the recent expansion of the anterior access surgery for the spine has promoted the development of equipment that will allow for registration of a stable anterior dynamic reference source and navigated instruments for anterior spine surgery.

13.5.1 Cervical Spine Pedicle screw insertion for the cervical spine requires extreme precision because of the size of the pedicles, and the intimate relationship the pedicles have with the cervical spinal nerve roots, and their proximity to the vertebral arteries. A similar relationship exists for the lateral mass of C1 with the vertebral artery as it passes through the arterial foramen and comes to rest on the superior portion of the dorsal arch of C1. Furthermore, the anterior surface of the lateral mass of C1 is in direct contact with the distal internal carotid artery as it enters the carotid canal in the temporal bone. Spinal navigation in cervical spine surgery becomes the ideal method to place screws in the cervical vertebra and lateral mass of C1, since real-time visualization of the critical anatomy of the cervical spine allows the surgeon to avoid the potential pitfalls of perforation of the bony landmarks.5 Significant limitations exist in the cervical spine for the accurate placement of pedicle screws. Since the pedicles in the cervical vertebra may be small in either the vertical or the horizontal diameter, and sometimes the diameter of the pedicle may vary from side to side, navigational guidance of pedicle screws becomes a necessity for accuracy and safety.6

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Image Guidance, Monitoring, and Nonoperative Techniques An important potential application for computer navigation in the cervical spine is the anterior insertion of an odontoid screw for undisplaced type 2 odontoid fractures. The conventional landmarks used with fluoroscopy to place an odontoid screw are fraught with significant potential technical difficulties including the penetration of the posterior wall of the fractured odontoid process encroaching on the anterior aspect of the cervical spinal cord, inadequate passage of the screw through the entire aspect of the fractured odontoid process, or the incomplete reduction of the fracture.7 However, computer navigational insertion of odontoid screws is limited by the difficulty of placing a dynamic reference frame in an area adjacent to the odontoid process. It is possible that the electromagnetic reference array may have a potential use in these procedures since it could be inserted in the body of C2 or C3 prior to the insertion of the screws. Alternatively, surface points of reference for CT scanning can be used with frameless systems through the posterior approach.6 An excellent application of image guidance is the posterior approach for placement of C1–C2 transarticular screws for the treatment of type 2 odontoid fractures, particularly in the elderly (▶ Fig. 13.6). Anterior vertebrectomies for degenerative processes in the upper cervical spine such as basilar invagination, or rheumatoid arthritis, as well as for the resection of vertebral tumors anywhere

in the cervical spine can be accomplished safely using navigational techniques. The surgical ability to determine the completeness of the bony or tumor resection intraoperatively using navigation allows the surgeon the certainty that the surgical plan has been truly completed before leaving the operating room.8

13.5.2 Thoracic Spine Pedicle screw insertion in the thoracic spine can be performed under computer navigational guidance using the same principles described for the lumbar spine. The extent of the procedure may require the surgical team to acquire more than one O-Arm run to include all the segments to be operated on, but a true CT-based study may obtain the entire field of interest with a single pass of the automated CT surgical unit. The dynamic reference frame may be placed on the spinous process of one of the vertebrae to be operated on, preferably in the center of the field, to maintain equidistance between the ends of the surgical navigated area. When operating in a long construct, surface correlation at multiple levels may reduce the surgical error that distance from the dynamic reference frame may produce. Pedicle screw placement in the thoracic spine is difficult without navigational guidance because of the narrow vertical diameter of the thoracic pedicles.9 Medial breaches of the pedicles

Fig. 13.6 (a) Coronal and (b) sagittal CT images showing type 2 odontoid fracture. (c) Preoperative planning to determine C1–C2 transarticular screw length and assure vertebral artery location for safe approach. (d) O-arm generated CT-guided navigation of bilateral C1–C2 transarticular screw placement and (e) final lateral fluoroscopic view showing adequate screw placement.

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Computer Navigational Guidance in Spine Surgery

Fig. 13.7 Navigated pedicle screw placement in the thoracic spine.

by the screws in the thoracic spine are dangerous because of the proximity of the spinal cord to the medial walls of the spinal canal (▶ Fig. 13.7). Lateral breaches are tolerated better, and the stability of the construct is not compromised to a significant degree by the extrapedicular placement of the screw.10 Various reports have noted an incidence of thoracic screw misplacements when not using navigational techniques to be as high as 41%; when navigation is used to place thoracic spine pedicles, the incidence of extrapedicular placements is reduced to as low as 1.8%.9 Anterior thoracic spinal surgery requires precise localization of the level to be operated on, especially when the pathology is not clearly seen on fluoroscopic images. Precise localization of herniated discs, areas of spinal stenosis, or tumor pathology requiring an anterior procedure becomes difficult for the surgical team intraoperatively.11 Placement of instrumentation in the anterior spinal column in the thoracic spine can be fraught with serious potential morbidity because of the proximity of the great vessels to the surgical field, and the position of the heart and the lungs. Computer navigational guidance facilitates intraoperative localization, and allows for the safe placement of instrumentation with less potential risk to the patient.12 Potentially, the placement of anterior interbody cages for the correction of degenerative or congenital scoliosis may be facilitated by the use of spinal navigational techniques.

13.5.3 Lumbar Spine Computer navigational procedures for the lumbar spine have been used widely for multiple problems including posterior

instrumented fusions from L1 to S1 for degenerative scoliosis, spondylolisthesis, acquired kyphosis, degenerative disc disease with retrolisthesis, intraspinal tumor resections with combined anterior and posterior reconstruction, and combined anterior and posterior spinal reconstruction for traumatic injuries. Computer navigational guidance in lumbar spine surgery is particularly useful in minimally invasive procedures such as transverse lumbar interbody fusions for degenerative disc disease, primary or recurrent disc herniations, decompressions for spinal stenosis, removal of intraspinal synovial cysts, and small intraspinal tumors that may destabilize the spine and will require instrumented fusions for stabilization. Pedicle screw placement in the lumbar spine is associated with misplaced screws in up to 30% of the patients when standard insertion techniques without navigation are used. The accuracy of pedicle screw placement utilizing computer navigational guidance limits the number of misplaced screws to less than 1%.2

13.6 Conclusion Computerized image guidance in spine surgery provides the patient and the surgeon with a greater level of safety, precision, and accuracy. The operative procedures can be done with a significant reduction of the radiation dose to the patient and the surgical team. The procedures can be done through conventional open or minimally invasive approaches without compromising the quality of the results. Once the technique is learned and the surgical team has gone successfully through the learning

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Image Guidance, Monitoring, and Nonoperative Techniques curve, the operative time is significantly reduced because of the ease of placement of the instrumentation and the accuracy of delivery of the material utilizing smart instruments. The potential misplacement of the instrumentation may be corrected in real time, as soon as confirmation of the position of the instrument is obtained on the table, therefore limiting the need for postoperative imaging studies or return to the surgical suite for a revision of the procedure. By reducing the operative time, there is a consequent reduction of the infection rate, tissue damage, and blood loss. The outcomes from the shorter and more precise procedures are improved by early mobilization, reduced hospital stays, and reduced cost by not doing additional postoperative studies, or returning to surgery. However, computer navigational guidance is not a substitute for acquiring a thorough and complete understanding of the surgical anatomy and conventional surgical techniques. The surgeon must first be totally familiar with the anatomy of the spine, be fully trained in conventional spine surgical techniques, know and understand how to deal with the complications associated with conventional surgical techniques, and be able to resolve any intraoperative problems that may occur during a conventional spine procedure. Computer navigational guidance is not replacement for excellent basic surgical principles in spine surgery, but an additional tool that may make the procedures more precise and reliable with a greater degree of safety for the patient and the surgical team.

Clinical Caveats ●

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Computer navigational guidance use during spine surgery can limit radiation to the surgeon and operating room personnel. Make sure the fixation clamp for the reference frame is applied securely to the entire length of the spinous process to prevent its dislodgement during surgery. A thorough understanding of spinal anatomy can facilitate the accuracy and safety of instrumentation placement using image guidance navigation. A final CT scan after instrumentation placement can assure proper placement before the patient leaves the operating room.

References [1] Glaser DA, Doan J, Newton PO. Comparison of 3-dimensional spinal reconstruction accuracy: biplanar radiographs with EOS versus computed tomography. Spine. 2012; 37(16):1391–1397 [2] Foley KT, Simon DA, Rampersaud YR. Virtual fluoroscopy: computer-assisted fluoroscopic navigation. Spine. 2001; 26(4):347–351 [3] Fernandez PM, Zamorano L, Nolte L, Jiang Z, Kadi AM, Diaz F. Interactive image guidance in skull base surgery using an opto-electronic device. Skull Base Surg. 1997; 7(1):15–21 [4] Vinas FC, Holdener H, Zamorano L, et al. Use of interactive-intraoperative guidance during vertebrectomy and anterior spinal fusion with instrumental fixation: technical note. Minim Invasive Neurosurg. 1998; 41 (3):166–171 [5] Guppy KH, Chakrabarti I, Banerjee A. The use of intraoperative navigation for complex upper cervical spine surgery. Neurosurg Focus. 2014; 36(3):E5 [6] Acosta FL, Jr, Quinones-Hinojosa A, Gadkary CA, et al. Frameless stereotactic image-guided C1-C2 transarticular screw fixation for atlantoaxial instability: review of 20 patients. J Spinal Disord Tech. 2005; 18(5):385–391 [7] Konstantinou DLA. Barrow Quarterly. March 1997. Available at: www.thebarrow.org/education_And_Resources/Barrow_Quarterly/: www.thebarrow.org/education_And_Resources/Barrow_Quarterly/204832. Accessed February 21, 2015 [8] Ugur HC, Kahilogullari G, Attar A, Caglar S, Savas A, Egemen N. Neuronavigation-assisted transoral-transpharyngeal approach for basilar invagination– two case reports. Neurol Med Chir (Tokyo). 2006; 46(6):306–308 [9] Tjardes T, Shafizadeh S, Rixen D, et al. Image-guided spine surgery: state of the art and future directions. Eur Spine J. 2010; 19(1):25–45 [10] Kothe R, Matthias Strauss J, Deuretzbacher G, et al. Computer navigation of parapedicular screw fixation in the thoracic spine: a cadaver study. Spine (Phila Pa 1976). 2001; 26(21):E496–E501 [11] Rajasekaran S, Kamath V, Shetty AP. Intraoperative Iso-C three-dimensional navigation in excision of spinal osteoid osteomas. Spine. 2008; 33:25–29 [12] Vaccaro AR, Yuan PS, Smith HE, Hott J, Sasso R, Papadopoulos S. An evaluation of image-guided technologies in the placement of anterior thoracic vertebral body screws in spinal trauma: a cadaver study. J Spinal Cord Med. 2005; 28 (4):308–313

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Intraoperative Monitoring

14 Intraoperative Monitoring Stephen W. Bartol Abstract Minimally invasive spinal surgery carries with it an increased inherent risk of nerve injury. These risks must be mitigated and this can be accomplished through the use of nerve mapping and monitoring technologies. In this chapter, we review the state-of-the-art techniques for locating, mapping, and monitoring neurological structures during spine procedures. The history of intraoperative neuromonitoring is reviewed and the rationale for each modality is discussed. Step-by-step techniques are outlined for somatosensory evoked potentials, motor evoked potentials, electromyography, and mechanomyography monitoring. Intraoperative anesthesia concerns and complications associated with each technique are reviewed. The advantages and disadvantages of each technology are discussed in a way that is designed to assist the minimally invasive spine surgeon in selecting the most appropriate monitoring options for each individual procedure. The author also provides his own preferences and procedure-specific recommendations. Keywords: intraoperative neuromonitoring, somatosensory evoked potentials, motor evoked potentials, electromyography, mechanomyography

14.1 Introduction The application of intraoperative neurophysiological monitoring (IONM) to spinal surgery has expanded rapidly in the last two decades, and the introduction of minimally invasive techniques to the field of spine surgery has led to greater interest in the use of nerve monitoring and mapping. Injury to neurological structures is an inherent risk of minimally invasive spine surgery and can occur through a variety of mechanisms including: ● Direct trauma, usually to nerves that cannot be directly visualized during tissue dissection or during instrumentation. ● Stretch injury, such as during correction of a spinal deformity or through traction (e.g., spondylolisthesis reduction or overretraction of the femoral plexus). ● Ischemia. The overall risk of neurological injury during spine surgery is small, but with growing public awareness and increasing emphasis on safety, even a relatively low risk of injury carries a lot of focus and demands attention.1,2,3 Public expectations are that risks will be managed wherever possible, resulting in increasing use of technology to reduce risks whenever such technology is available.4,5 The reported incidence of major neurologic complications (such as paraplegia) after scoliosis surgery ranges from 0.55 to 1.6%.6,7,8 The placement of pedicle screws has been associated with varying rates of breeched cortex, and while most breeches are not associated with neurological symptoms, nerve symptoms that result in permanent injury or a need for revision surgery are reported in about 1% of patients.9,10,11,12,13,14,15 The growth in popularity of the lateral, transpsoas approach has heightened attention on nerve complications. Up to 30%

incidence of transient nerve symptoms has been reported with this approach.14,16,17,18,19 Complex anatomy emphasizes the need for nerve identification and mapping techniques that reduce the risk of nerve complications.20,21 Numerous studies have shown that various forms of intraoperative monitoring may be useful in reducing neurological complications. Modern intraoperative approaches use a combination of techniques tailored to the risks associated with the particular surgery being planned. In this chapter, we will review historical and recent developments within the field of intraoperative monitoring and discuss the clinical applications. We hope that in understanding these various monitoring techniques, surgeons can choose from the menu of options available to them, and make appropriate choices that minimize the risk of nerve injury during surgery.

14.2 Historical Review The original form of intraoperative monitoring in spine surgery involved the wake-up test during scoliosis surgery: waking patients on the operating room (OR) table, during the procedure, to assess neurologic function. This was generally done immediately following correction of the spinal deformity (usually scoliosis), at which time patients were told to move their feet and toes. Successful movement indicated preservation of spinal cord motor function, and the patient was then reanesthetized for continuation of the surgical procedure. Now known as the Stagnara wake-up test,22 this test is still in use, despite its obvious limitations, which include the risk of uncontrolled patient movement and postoperative anxiety in patients who have recall of the intraoperative experience.7,23,24 While comforting when it works, a survey of orthopaedic surgeons reported poor agreement between the results of the wake-up test and the postoperative outcome, reflecting the inherent difficulties associated with administration of this test.7 An alternative (or supplement) to the wake-up test came with the development of the somatosensory evoked potential (SSEP). This electrophysiologic test allows examination of the neuraxis from a peripheral nerve to the central cortex. In normal subjects, electrical stimulation of a peripheral nerve causes a change in the EEG of the patient’s contralateral sensory cortex, which can be studied by averaging many signals over time. This change in EEG can be monitored using EEG electrodes on the cranium. SSEPs were first used in surgery to monitor spinal cord function during scoliosis surgery. Good success was reported early on, and SSEPs were gradually recognized as a viable alternative or adjunct to the use of the wake-up test during spine surgery.25,26,27,28,29,30,31,32,33 It was soon recognized, however, that the SSEP test has significant limitations. Nerve fibers conducting motor command signals from the brain to the spinal cord do not contribute to the SSEP, nor do spinal motor neurons. SSEP is also neither sensitive nor specific for spinal nerve root (lower motor neuron) and peripheral nerve injuries, which are the primary concern with most common lumbar spine procedures. In recognition of these limitations of SSEPs, the field of IONM has been expanded considerably

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Image Guidance, Monitoring, and Nonoperative Techniques

Fig. 14.1 Surgeon-driven systems provide a userfriendly feedback system that delivers real-time information directly to the surgeon.

in the last two decades. Motor evoked potentials (MEP) and electromyography (EMG) were introduced to better monitor the motor neuraxis. These offered considerable advances and changed the landscape of neuromonitoring in spine surgery.5 Increasingly, however, the demands of surgery are pushing the limits of these technologies. Surgeons need more rapid real-time feedback in order to perform minimally invasive surgery safely and that has led to the push for surgeon-driven, immediate-feedback systems (NuVasive, DePuy Synthes) (▶ Fig. 14.1). A high degree of variability in the interpretation of IONM signals remains a serious issue.34 At the heart of this problem is the tremendous role that electrical noise plays in the signals detected using EEG-type electrodes. Electrical noise picked up by these electrodes causes tremendous variability and complexity of signals.35,36,37 Given the need for greater nerve mapping accuracy in minimally invasive surgical procedures, this has led to the push for newer, smart sensor technologies, which offer greater consistency than is possible when using simple electrodes in a complex electrical environment such as the OR. The evolution of mechanomyography (MMG) smart sensor systems (SentioMMG, DePuy Synthes) has occurred largely in response to these needs. As a result of these various developments, the field of IONM today offers a varied menu of options to the surgeon. Each item in the menu offers advantages and disadvantages, depending on the operative scenario. Choosing the right option(s) for a given procedure is critical if surgeons are to avoid injuring neurological structures, especially during challenging minimally invasive procedures where direct visualization of neurological structures is not possible.

14.3 Somatosensory Evoked Potentials SSEPs are used to assess dorsal column function within the spinal cord. Specifically, they monitor the integrity of the large fiber

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sensory system, which is responsible for accurate perception of vibration and joint position sense. SSEPs are obtained by stimulating peripheral nerves (typically tibialis anterior in the lower extremities and ulnar or median in the upper extremities). Recording may be done at various points along the neuraxis (brachial or lumbar plexus, cervical spine, parietal somatosensory cortex) to assess the integrity of the pathway. The inherent difficulty with SSEP monitoring lies in the low amplitude (0.1–20 μV) of the signals generated and the intense levels of background noise that are created by numerous biologic signals and the ubiquitous electrical equipment found in the OR. Isolation of SSEP signals therefore requires the use of signal-averaging techniques. Signal averaging involves taking the signal of interest, amplifying it, time-locking it to the stimulus, and averaging out random background noise by performing hundreds of successive trials. On average, it takes several hundred stimuli (up to 1,000) to extract a baseline SSEP signal from background noise.

14.3.1 Technique Typically, baseline signals are recorded at the start of the surgical case. During the procedure, any events that interfere with this sensory nerve conduction will be reflected by diminished amplitude or increased latency of the response at recording electrode(s) proximal to the site of interference. For operations involving neurologic segments at or above C6, it is common to use the median or ulnar nerves for stimulation; under normal circumstances, median nerve stimulation will give rise to a larger cortical potential compared to the ulnar-mediated SSEP. For operations caudal to the C6 segment, it is common to use the SSEP from stimulation of the posterior tibial nerve at the ankle. If this nerve is not available (e.g., because of fracture, amputation, or severe peripheral neuropathy), it is possible to obtain satisfactory recordings from stimulation of the common peroneal nerve at the knee. The cathode (-ve lead) is placed over the most

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Intraoperative Monitoring accessible portion of the nerve, and the anode (+ ve lead) is placed distal to it. The stimulus used is a square wave signal with a pulse duration of 100 to 200 μs, at a frequency that does not divide evenly into 60 (60 Hz being the frequency found most commonly in background electrical noise). Normal nerve recovery time dictates that signal strength diminishes above 5 Hz.38 As a result, we generally use a non–whole number below 5 such as 3.17 Hz. It takes an average of 500 to 1,000 stimulated responses to obtain a strong waveform. It is not uncommon, therefore, for signal averaging to require 2 to 4 minutes in order to develop a satisfactory waveform, meaning that there is almost always a delay associated with starting an SSEP test and obtaining the results. Because of this delay, SSEPs cannot be considered a “real-time” test modality. Provided that the patient has no neuromuscular block, stimulation should result in a clearly visible twitch in adjacent muscles near the stimulating electrode. In the hand, a thumb twitch is observed, and in the foot the toes will twitch. The appearance of a good motor twitch is a good indication that adequate current levels have been reached. In the upper extremity, this is usually reached at 15 to 20 mA and in the lower extremity at 30 to 60 mA. We rarely increase current up to 75 mA. Best results are obtained by stimulating left- and right-sided nerves independently. Modern evoked potential machines allow the user to automatically alternate stimulus to the left and right sides and display the two SSEP signals simultaneously. If monitoring of both the upper and lower limbs is being used, then stimulus intervals can be adjusted to allow simultaneous display of all four signals. If the equipment allows, both upper and lower extremity SSEP monitoring may be used not only for cervical spine surgery but also for thoracic and lumbar spine surgery. Upper extremity SSEP data may help prevent palsy of the brachial plexus and/or other upper extremity palsies resulting from poor positioning or during prolonged procedures.39 Upper extremity SSEP monitoring can also be useful as a comparison check when stimulus malfunction or anesthesia effects are suspected in situations where there is decreased amplitude or loss of responses from the lower extremities. While SSEP recordings can be done at multiple sites, most commercial systems can accommodate a total of only 16 or 32 channels. Since most of these channels are needed for simultaneous EMG/MEP monitoring, practically speaking, it becomes reasonable to limit the number of channels monitoring SSEPs. When selecting to use SSEPs, such as during spinal manipulation surgery, we therefore routinely use only four sites for SSEP

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We generally employ the following alarm criteria for SSEP changes: a decrease of greater than 50% in the amplitude of the response or an increase of greater than 10% in the latency of the response, or a sudden loss of evoked potentials. When any of these situations occur, the surgeon is immediately informed of the changes and surgical countermeasures are instituted when appropriate. If the loss is distal to the level of surgery, the surgeon will generally reverse any mechanical event that immediately preceded the change in SSEP. Alternatively, if the loss is unexpected and does not correlate with the level of surgery, alternate explanations are considered. For example, isolated loss in a single upper extremity during thoracic spine surgery may indicate a positioning problem (resulting in circulatory changes). Loss of signals in all four limbs may occur as a result of anesthesia effects. High levels of inhalational anesthetic agents can

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monitoring, leaving plenty of channels for other modalities. We use Cz (for posterior tibial stimulation), C3 and C4 (for upper limb right-sided and left-sided stimulation, respectively), and the cervical spine (except for posterior cervical approaches, in which case we eliminate this lead) (▶ Fig. 14.2). What we give up with this approach is information about the “traveling wave.” For example, in the lower limb, we lose confirmation of stimulation delivery that would normally be provided by a recording site in the popliteal fossa, and in the upper limb we lose the traveling wave signal in the brachial plexus. However, as long as there is no neuromuscular blockade, stimulation can always be confirmed with either MMG sensors or by feeling under the drapes for muscle twitches at the stimulus site. An intraoperative baseline should be established after the patient is anesthetized, when the patient has adjusted physiologically to anesthesia. The key parameters of interest during intraoperative SSEP recordings are the latency and amplitude of the responses. Latency prolongation and amplitude attenuation should be considered signs of impairment of spinal cord function. Unfortunately, there are no universally accepted warning criteria as to when the monitoring team should inform the surgeon that a change in the electrophysiologic status of the patient has occurred. Different centers may use any of the following to indicate a significant change in the patient’s condition8,40,41,42: ● Thirty to fifty percent decrease in the amplitude of the potentials. ● An increase of 2.5 ms in the response latency. ● Five to ten percent increase in the response latency. ● Any combination of the above.

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Image Guidance, Monitoring, and Nonoperative Techniques depress cortical function and subsequently depress the amplitude and prolong the latency of SSEP waveforms. These changes can mimic the effects of spinal cord compromise. Subcortical responses are, of course, much more resistant to anesthetic changes than cortical responses, and peripheral responses are highly resistant to the effects of anesthesia. Total intravenous anesthesia, with avoidance of inhalational agents altogether, has the least effect on SSEP but requires an experienced anesthesiologist and adds cost. It is critical for the surgical team to make known to the anesthesia team its intention to use SSEP monitoring prior to surgery. SSEPs are also affected by physiologic variables such as temperature and blood pressure. A decrease in limb or body temperature can result in increased latency and decreased amplitude of SSEP responses. Hypotension with global cerebral hypoperfusion and/or spinal cord ischemia can also result in amplitude attenuation or latency prolongation. Positioning can influence SSEP readings if there is prolonged pressure on vessels supplying the limb. Resulting vascular compromise will cause a reduction of SSEP signals.39 Brau et al43 demonstrated that retractor-induced iliac vessel compression in anterior lumbar surgery may similarly lead to SSEP alterations. These changes are reversible if vascular occlusion is removed. Failure of SSEP signals to recover may indicate ongoing vascular compromise.

14.3.2 Indications Surgical procedures that place the spinal cord at risk, such as correction of deformity, resection of a spinal cord mass, thoracic discectomy, and scoliosis correction procedures, are logically good candidates for SSEP monitoring. In any of these cases, a baseline SSEP would be obtained at the beginning of the procedure and then repeated on a regular basis throughout the surgical procedure. If SSEP waveforms change in response to an action by the surgical team (e.g., placement of a graft or hardware; rod distraction), the surgical team could be advised of this change, allowing these steps to be “undone” in the hope that signals recover to baseline levels. In the absence of changes in SSEP signals, one might hope that whatever surgical interventions had just transpired did not damage the spinal cord. Unfortunately, this is not always borne out.44 There are numerous reports of cases in which SSEPs were unchanged between baseline and final measures, yet the patient woke up with paralysis.45,46,47,48 Evidence tells us that the command signals for voluntary motor function are carried in corticospinal tract (CST) axons.49,50,51,52 These axons not only are physically separate from those of the dorsal columns, but also have a much greater dependence on the anterior spinal artery for perfusion than dorsal column axons (which are perfused via the posterior spinal arteries).53,54 Based on results of postmortem studies after traumatic spinal cord injury, the large myelinated axons of the CST are also more susceptible to physical trauma than are axons within the dorsal columns.55 Therefore, it should come as no surprise to learn that SSEP monitoring is not always a good indicator of spinal cord damage and specifically motor function. CST (motor) function is best monitored using MEPs (see Motor Evoked Potentials (p. 140) section). There are also fundamental difficulties associated with SSEP testing within the OR setting. First, the recorded SSEP signal

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amplitude is very small (often less than 1 μV), resulting in a need for signal averaging. Such averaging introduces delays, measured in minutes. The SSEP is therefore not a “real-time” test. Second, the SSEP is prone to electrical interference from the many sources of electrical noise found in the typical OR environment, including the lights, the OR bed, radios, the anesthesia machine, the microscope, blood warmer, suction, electrocautery, navigation tools, and fluoroscope. This electrical noise makes interpretation of small signals very difficult. Third, SSEP recordings are difficult to obtain in many patients with preexisting sensory conduction abnormalities in peripheral nerves (e.g., diabetes).32,41,56,57,58 Such patients are common in the population of adult patients undergoing most spinal procedures. An additional limitation of SSEPs is that it is a general test of sensory pathway status and not a specific test. Sensory signals enter the spinal cord via multiple spinal roots. This means that SSEPs are neither specific nor adequately sensitive to detect injury in a single nerve root or an isolated peripheral nerve, which are at risk with most lumbar spine procedures.59 For these cases, more appropriate intraoperative monitoring techniques include EMG and MMG. Gundanna et al13 assessed the use of SSEPs for placement of 888 pedicle screws in 186 consecutive patients. No patients demonstrated changes in SSEP during surgery, although five patients suffered new post-op radicular changes. Malposition was confirmed on CT imaging and all screws were subsequently removed or revised. The authors concluded that the use of SSEP in evaluating lumbar pedicle screw placement is of limited value. Finally, it is relatively common for SSEP traces to demonstrate significant worsening from baseline values in amplitude and/or latency, only to have the patient awaken with no obvious change (i.e., deterioration) in sensory status. Such false-positive findings have continued to limit reliance on SSEP monitoring in the OR setting.7,58,60,61,62,63,64,65 All of these limitations of SSEP testing have led to repeated calls for the development of monitors that are specific to both central and peripheral motor conduction.61,66,67 That has led to the rise in the use of MEPs, EMG, and MMG in spinal procedures.

14.4 Motor Evoked Potentials The integrity of descending motor pathways can be monitored by depolarizing the corticospinal system through transcranial (Tc) stimulation and then measuring the resulting MEP distal to the level of surgery. The main descending tract responsible for voluntary movement is the CST.48,68,69 This tract lies in the lateral portion of the spinal cord and innervates lower motor neuron cells located in the ventral horn (anterior horn cells). The blood supply to both the CST and anterior horn cells comes primarily from the anterior spinal artery. When the cranium is stimulated, all signals reaching muscles distally must travel the length of the motor pathway in the spinal cord. Therefore, transcranially triggered MEPs (TcMEPs) are useful in assessing the integrity of the CST and, indirectly, the integrity of spinal cord oxygenation and blood supply (through the anterior spinal artery). Calancie et al45 have pointed out that the large myelinated axons of the CST are very sensitive to mechanical trauma and the anterior horn cells are very sensitive to ischemic changes.70 MEP monitoring is especially sensitive to ischemia involving anterior horn cells.71

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Intraoperative Monitoring

14.4.1 Technique To achieve Tc stimulation of the cortex, very high stimulus amplitudes are needed to overcome skull impedance. For most cases, a single corkscrew electrode is used, offering reliable attachment to the scalp. Initial attempts to utilize TcMEPs focused on single, high-intensity pulses (up to 1,000 V).72,73,74,75,76,77,78, 79,80 Later, it was realized that activating upper motor neurons using a short, very high-frequency pulse train is more likely to be successful than a single pulse.81,82,83 Stimulation is applied to cortical sites roughly comparable to those used for EEG recording electrodes. Stimulation between the anode (positive lead) and cathode (negative lead) at sites just anterior to C3 and C4 (▶ Fig. 14.2) is a common configuration for activating the hand area on one side; reversal of the stimulating polarity activates the hand area on the contralateral side. This same configuration is also adequate for stimulating the leg area, although stronger stimuli are needed.45 MEP monitoring is accomplished by recording EMG tracings associated with muscle contractions. Clearly, this requires avoidance of neuromuscular blockade. Muscles whose innervation lies caudal to the area of surgery serve as target muscles. For example, the tibialis anterior would serve as a target muscle for correction of a thoracic scoliosis deformity. However, in most cases where we use MEPs, we attempt to monitor MEPs from at least one muscle receiving innervation above the surgical level. This muscle serves as a control, telling us that instrumentation is working correctly and that anesthesia is appropriate. Pairs of electrodes are placed over the muscles of interest. Regardless of the spine level, we routinely use hand and foot muscles, abductor pollicis brevus–abductor digiti minimi (APBADM) in the hand and abductor hallucis (AH) in the foot. This is because the motor regions of the hand and foot are well represented in the cortex and thus easier to stimulate. Even though the muscles are small, the triggered responses have high amplitude and are very reliable. We use pairs of 0.5 inch, needle electrodes placed just under the skin over the muscle of interest. The interelectrode distance is typically 2 to 4 cm. Filtering in the range of 50 Hz to 2.5 kHz is used for all EMG recording channels and an initial screen sensitivity of 100 μV per division. Most technicians who use TcMEPs rely on a very strong (i.e., supramaximal) stimulus to elicit a maximal motor response and then watch for reduction in response amplitude.81,84,85,86,87, 88,89,90,91 This technique uses a train of stimuli (typically 4–6 and less than 20) starting at 300 to 600 V. Voltage is increased up to 1,000 V if needed to obtain a strong response. Baseline readings are obtained following induction and positioning and then repeated periodically throughout the case, with emphasis on retesting following risky events such as spinal cord manipulation. Performing MEP tests is time-consuming and disruptive to the flow of surgery and, as a result, most surgeons do not want testing performed more than is necessary. As with SSEPs, alarm criteria vary widely. Most reports have used a criterion of a 50 to 80% decrease in amplitude, but some reports used complete loss of response or morphological change.93,94,95,96,97,98 With the exception of the complete loss criteria, each of the other criteria is associated with higher numbers of alerts and a lower percentage of true neurological changes. Recently, Kobayashi et al99 attempted to resolve this

conflict by examining 48 cases of true positive MEP signal changes. They concluded that a 70% decrease in signal amplitude was the ideal alarm point. This criterion resulted in 95% sensitivity and 91% specificity. Calancie et al24 have described an alternative “threshold-level method” of testing MEPs which avoids maximal stimuli. To achieve maximal motor responses to TcMEP, a stimulus of such magnitude is required that peripheral nerves become stimulated, increasing the risk of100: ● A shift in patient position. ● Bite-induced injury to the tongue, lips, teeth, or jaw. ● Tissue damage caused by a surgical instrument. For these reasons, Calancie et al45 have recommended the use of a threshold-level approach to TcMEP. Beginning with a three- or four-pulse train at 100 V stimulus intensity, the applied voltage is increased in increments of 25 or 50 V until a target muscle responds to the stimulation. This threshold reflects the minimal voltage needed to cause a minimal MEP response. If an event during surgery causes a partial conduction block in the spinal cord, some of the axons that were mediating the initial threshold-level response may no longer be capable of conducting action potentials across the region of the block. In order to induce a response, it then becomes necessary to recruit an additional population of upper motor neurons whose axons are not blocked. This additional recruitment occurs with a higher stimulus level. This increase in threshold value serves as the primary outcome measure of this approach. Calancie et al45 have shown that changes of 50 V in threshold during the operation are common and do not reflect underlying compromise of neural conduction. Changes of 100 V or more, in the absence of a decline in systemic blood pressure or an increased delivery of anesthetic, are associated with compromised neural conduction. Therefore, the surgical team should be warned in the event that the threshold of a given muscle increases by 100 V or more.101

14.4.2 Indications Any surgical procedure in which the spinal cord and/or its blood supply are at risk of injury could benefit from MEP monitoring. Put another way, any surgical procedure in which the SSEP is being used is also a candidate for MEP monitoring. Both SSEP and MEP have value. Each is designed to provide feedback about conduction within separate regions of the spinal cord and brain. Each test is good at predicting changes in either postoperative sensory (via the SSEP) or motor (via the MEP) function. The MEP is more likely to remain viable in cases when SSEP recording is not possible (e.g., polyneuropathy) and MEP is likely more sensitive to ischemic changes. Nevertheless, the two forms of monitoring should be considered complementary rather than competing. The use of TcMEP is not without its drawbacks, including a sensitivity and specificity that are less than perfect. Some surgeons use a wake-up test to confirm test accuracy if observed MEP changes do not reverse. Others simply abandon corrective procedures and rely on the postoperative examination to determine if further attempts should be made to go back and continue with more corrective procedures. TcMEP also carries inherent risk of injury, including bite-related injuries. There also remains the remote risk of seizures

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Image Guidance, Monitoring, and Nonoperative Techniques and twitch-related bumping against a surgical instrument. These risks are minimized through the use of an appropriate bite block, through a rigorous adherence to the use of minimal stimulus energy, and by alerting the surgical team to testing so that hazardous instruments are absent from the field during stimulation. We routinely have the surgical team remove all hands from the surgical field while Tc stimulus is applied. Finally, TcMEPs are nonspecific. They have no value in testing the function of individual nerve roots or peripheral nerves. When these structures are at risk (such as in most lumbar procedures and many cervical procedures), alternative monitoring techniques such as EMG and MMG become necessary.

14.5 Electromyography Spontaneous EMG occurs through the mechanical activation of axons distal to their cell body or as a result of ongoing central or peripheral nerve pathology. EMG activity is routinely seen with nerve root retraction, is especially prominent when the nerve roots are inflamed due to chronic compression or irritation, and can aid (indirectly) in the anatomic identification of specific nerve roots. EMG activity is measure by placing electrodes in or directly over the muscle(s) of interest (▶ Fig. 14.3). The use of spontaneous EMG to guide surgical procedures around delicate nerve roots was first reported for posterior fossa decompression surgery, in an attempt to preserve facial nerve function.102 This approach was later adopted for spinal nerves.103,104,105,106,107 When EMG signals are linked to a surgeon-directed user interface, immediacy of feedback represents a distinct advantage over the delay typically associated with SSEP monitoring, establishing a real-time test modality. The frequency and amplitude of spontaneous EMG discharge generally increases with greater degrees of nerve root manipulation. Despite this observation, investigators have been unable

Fig. 14.3 EMG is recorded by placing pairs of electrodes in muscle or in subdermal tissue directly over the muscle belly of interest.

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to demonstrate a quantitative relationship between the amount of spontaneous EMG and postoperative motor deficit for spinal nerves. This is in sharp contrast to facial muscle EMG, wherein excessive activity during the surgery almost always predicts significant facial nerve dysfunction postoperatively.102 The presence of spontaneous EMG signals is commonly used to provide an indication of nerve root proximity. This may be useful when anatomy is distorted or when placing instruments such as retractors. Spontaneous EMG may also be observed with ongoing nerve root irritation such as with acute compression.23 In general, surgeons attempt to minimize spontaneous EMG activity, with the reasonable expectation that these actions will help lower the incidence of new postoperative neurological symptoms.

14.6 Stimulus-Evoked EMG Absence of spontaneous EMG signals, however, is of no value in determining nerve integrity. The fundamental flaw in relying on spontaneous EMG activity is, in fact, that the absence of spontaneous EMG is not necessarily a good sign. Sharp transection of a spinal nerve can take place in the complete absence of EMG discharge. A better approach is to rely on controlled stimulation (stimulated EMG) to locate nerves that may be at risk during dissection. By using a weak electrical stimulus intensity that will only activate nerve fibers when the stimulating probe is in close proximity, it is possible to quickly differentiate between functional motor nerves and nonneural tissue such as tumor, scar tissue, or connective tissue such as the filum terminale. Again, this approach of stimulated EMG for spine surgery was adopted from a technique first used in the brainstem.102 Stimulated EMG is also used to assist with the placement of pedicle screws. To place a pedicle screw, a hole is first created in the pedicle using tactile feedback from a drill or pedicle probe, with or without image guidance. In one technique, a ball-tipped feeler is then placed in the pedicle screw hole, in an attempt to palpate the cortical wall. Studies have shown that this technique of relying on palpation alone is unreliable, especially in less experienced hands.108,109,110,111 A procedure to test screw placement was initially developed in the early 1990s using a stimulus source applied directly to the screw.107,112,113 Despite early reported successes, numerous studies have since shown problems associated with directly stimulating pedicle screws. First, stimulating screws has the undesirable effect of detecting potential nerve damage after it has already occurred (following screw insertion). Second, the technique of stimulating screws directly is fundamentally flawed because of potential problems associated with variable electrical conductivity in modern fixation devices. Anderson et al114 showed that electrical resistance in polyaxial pedicle screws is highly variable. A study by Donohue et al115 showed that commonly used titanium alloy screws have poor electrical conduction properties. Most titanium screws used today are anodized, rendering conduction even worse than it is in uncoated screws. Hydroxyapatite coating further affects conductivity and additional studies have shown that size, length, and cannulation can all change electrical resistance in screws.116 An improvement on the pedicle screw testing technique involves using a ball-tipped feeler probe as the stimulus source with the intent of detecting breeches prior to screw insertion.

Perez-Cruet et al, An Anatomic Approach to Minimally Invasive Spine Surgery, 2nd Ed. (ISBN 978-1-62623-643-1), copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.

Intraoperative Monitoring A low-intensity pulse is used so that if the cortical wall is intact, the nerve roots are not electrically stimulated. Conversely, a breach in the pedicle wall would create a low-impedance pathway between probe and nerve root so that the stimulus pulse causes activity in muscles innervated by the nerve root being stimulated. Thus, the presence of EMG when probing a potential site for pedicle screw placement may serve as a warning to the surgeon to pay particular attention to the possibility of defects in the bone, which could cause nerve root compression. If the probe test is negative, a screw is placed at that site. If the test is positive, the surgeon has the option of redirecting the pedicle screw. In general, it has been assumed that an EMG action potential that is seen at a threshold below 6 to 8 mA warrants evaluation of screw placement and possible repositioning. Numerous authors have claimed improved accuracy of pedicle screw placement using this stimulated EMG technique.117,118,119,120,121,122 When a positive response is elicited at low currents (< 6 to 8 mA), there is little doubt that repositioning of the screw is advisable. Raynor et al123 showed that specificity of a positive response increases significantly at low current levels, reaching 100% at thresholds < 3 mA. Specificity decreases dramatically, however, at higher thresholds. The difficulty arises from the low sensitivity of the test. The lower the threshold, the lower the sensitivity and there is no defined threshold at which sensitivity reaches 100%.122 Raynor et al123 recommended a threshold of 8 mA based on their observation that a stimulus lower than 8 mA has too low a sensitivity to be useful. Samdani et al124 confirmed a very low positive predictive value for the test, and Wang et al14 showed that results were unreliable for assessing percutaneously placed screws. They noted poor predictive values with current levels typically utilized (< 12 mA) (▶ Fig. 14.4). This high degree of variability in the magnitude of EMG responses occurs because EMG signal amplitude is random by nature and inherently unstable.125,126 EMG signals are by nature small, requiring amplification, and subject to many sources of electrical noise. Filters are essential to remove noise as well as

stimulus artifact.125,126,127,128,129,130,131,132,133,134,135,136,137,138,139 All of these factors result in lower sensitivity, especially at the low levels of current needed with the pedicle screw test. Attempting to determine whether a nerve is a millimeter or so away from the screw channel using EMG detection is often impractical in clinical applications. In recent years, the use of EMG for nerve mapping has been popularized with the development of the direct lateral approach.17,18,19,20,21,140,141,142 In this approach, the psoas muscle is dissected or retracted, placing the nerves of the femoral plexus at risk. The surgical technique is discussed in detail in a later chapter. A surgeon-directed neuromonitoring protocol has been developed to facilitate this approach, providing instantaneous, real-time feedback to surgeons while they traverse the psoas. Two surgeon-directed nerve-mapping systems are currently available. Both systems have the advantage of providing a simple to read, user-friendly computer interface that allows surgeons to make their own decisions in real time rather than relying on interpretation by a neurophysiologist. One system uses MMG monitoring (SentioMMG, DePuy Synthes) and is discussed in the section below. The other (NVM5, NuVasive) uses a seeking algorithm to determine the lowest threshold at which a stimulated EMG response is elicited. Both systems provide a more rapid method of determining stimulation thresholds than is possible using traditional EMG equipment. With both systems (MMG and EMG) the surgical technique is similar. A probe is inserted through the psoas muscle, while stimulating. A safe working space is identified by a lack of response below a threshold. Each system finds the lowest current that gives a response and, conversely, the highest current that does not give a response. The EMG system uses > 10 mA as a cutoff and defines a caution zone between 5 and 10 mA, while the MMG system, which is more sensitive, uses > 6 mA as a safe cutoff.143 Once a safe corridor is identified, the retractor is positioned. The surgical field is swept with a stimulated ball tip probe to ensure that the field is free of nerves. Once that is established, the surgeon can safely proceed with discectomy and

Fig. 14.4 Intraoperative EMG tracing.

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Image Guidance, Monitoring, and Nonoperative Techniques fusion. Most surgeons report that this technique of real-time feedback facilitates more rapid access to the spine than is possible with more traditional IONM approaches. Difficulties with the surgeon-directed EMG system include problems with setup. Surface electrodes have been used but success rates with these are lower than with EMG needle electrodes. If there is no neurophysiology technician in the room this becomes problematic, since most OR personnel are reluctant to learn the process of inserting needles into EMG recording sites. Surgeons have also reported false-positive and false-negative feedback using the EMG system. Electrical noise appears to be the culprit, and all attempts should be made to insure that other equipment in the room is properly shielded (and, when possible, turned off) in order to minimize this problem. All procedures that utilize stimulated EMG rely on the principle that the closer the nerve is to the stimulus source, the lower the threshold at which a response will be elicited. This allows nerve mapping by determining the threshold at which a motor action potential is generated. While this seems intuitive, there are few data to support this conclusion in clinical surgical practice.126 We know that some motor fibers are easier to stimulate than others: axon conduction velocity is directly proportional to the size of the axon.144 We also know that stimulus current falls off as the distance from the source increases. It follows that more axons will achieve threshold levels for depolarization if the stimulus source is closer to the nerve or if the stimulus current is higher. Problems with EMG occur, however, when electrical noise interferes with recording of the motor responses, masking low threshold responses and making interpretation difficult.125,145,146,147 That results in a need to stimulate at higher than true threshold levels to elicit a response that is greater than the background noise level. It is this problem that led to the development of newer, surgeon-driven, MMG monitoring techniques.

14.7 Mechanomyography MMG was first described in 1938.148 It involves measurement of the mechanical response of muscle fibers to a motor action potential. MMG, therefore, monitors the same physiologic event as EMG, but does so in a different way. Rather than detecting electrical changes in membrane potential, it detects the orthogonal expansion of muscle fibers as actin and myosin fibers slide during contraction. These mechanical and electrical events occur concurrently and can be accurately measured at the skin surface using accelerometers.149,150,151 MMG recordings are less susceptible to interference and, as a result, MMG has been shown to be superior to EMG in quantifying neuromuscular blockade.152,153,154,155,156,157 As a result, MMG is the basis for the twitch test, the simplest clinical form of MMG that all spine surgeons should be familiar with.146 Although used in research applications for decades, the clinical application of MMG in spine surgery required the development of a commercially viable system. This required technological advances in the production of low-cost, easy-to-use sensors capable of recording MMG responses. An FDA approved system (Sentio MMG, DePuy Synthes) first became available for general use in 2012. This system employs microelectromechanical sensors (MEMS) that are accelerometer based. This technology has been shown in independent studies to be less susceptible to the electrical noise found in environments such as the OR.147 This MEMS

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system is a “smart sensor” system, able to distinguish between muscle contraction and other types of motion. It does so by measuring the changes in muscle acceleration that are characteristic of muscle contraction. Because the technology is relatively new, few studies have been published on its clinical use. At the time of manuscript preparation, MMG has been used in approximately 4,000 cases with success (personal communication, 2014). The primary applications are those situations in which nerve mapping is needed, such as with the lateral transpsoas approach, or when close nerve proximity places nerves at risk, such as with pedicle screw placement or during scar tissue dissection. Because electrical interference plays a minimal role in MMG signals, a measurement of true stimulation threshold is possible and the current–distance relationship that is only theoretical with EMG becomes real and clinically practical with MMG.158 Larger, myelinated motor fibers are easier to stimulate than smaller fibers and motor nerves are composed of motor fibers of varying size.144 Since stimulus current levels decrease as the distance from the source increases, it follows that more axons will achieve threshold levels for depolarization if the stimulus source is closer to the nerve or if the stimulus current is higher.159 Our studies showed that as the amplitude of the stimulus increases, so does the MMG response signal. As the stimulus probe moves closer to the nerve, the amplitude of the MMG response increases.158 These two factors allow the use of MMG for accurate nerve mapping in situations where nerves are felt to be present but cannot be visualized (such as in transpsoas approaches or with revision surgery where scar tissue interferes with visualization). Precise nerve mapping becomes possible with MMG when it is not possible with EMG because the MMG signals are measuring mechanical rather than electrical events in muscle tissue. Mechanical signals are not affected by electrical noise, eliminating the need for complex filters and eliminating the need to stimulate at higher than threshold levels. Since responses are measured at the lowest threshold, where only large axons in proximity are depolarized, very low levels of stimulus current are possible. This creates the increased sensitivity to detection of nerves in close proximity that is observed clinically with MMG.143

14.7.1 Technique Adhesive MMG sensor patches are applied to the skin over muscles supplied by nerves being monitored (▶ Fig. 14.5). The dampening effects of tissue are less with MMG than with EMG since mechanical waves are propagated well through muscle and adipose tissue. The sensors are connected to a computer interface, which gives instantaneous feedback to the surgeon. A dilator probe or a ball-tipped probe is used to provide stimulus to the surgical field just as with stimulated EMG. The current levels used with MMG are typically lower than with EMG since filtering of electrical noise is not necessary. For lateral transpsoas approaches, the dilator probe is typically introduced with a stimulating current of 6 mA. If a nerve is in proximity at that level, the probe can be moved anterior to locate a nerve free zone. The feedback system will give a green signal to the surgeon when no nerve is in proximity. Once a satisfactory entry point free of nerves is located, the dilators and retractor are inserted. Alternatively, the probe can be inserted

Perez-Cruet et al, An Anatomic Approach to Minimally Invasive Spine Surgery, 2nd Ed. (ISBN 978-1-62623-643-1), copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.

Intraoperative Monitoring with a starting current of 15 mA and a downward ramping signal used to quickly find the lowest current at which there is a green signal (indicating no MMG response). A green response at 6 mA or greater indicates a safe zone for dilator insertion. Once the retractor is in position, the ball-tipped probe is used to sweep the field within the retractor, again stimulating at 6 mA. If no nerve is in the field, the surgeon may proceed. My recommended practice is to further verify nerve location by turning up the current (6-8 mA) and sticking the probe behind the posterior blade. A red light will verify that the nerve is safely behind the retractor.

For pedicle screw placement, the pedicle hole is made using standard techniques. A ball-tipped stimulus probe is used to palpate the pedicle walls (▶ Fig. 14.6). We start with current at 8 mA. If an MMG response is elicited, we recommend keeping the probe at the point on the pedicle wall where the strongest signal is elicited and lowering the current to find the threshold. A threshold ≥ 6 mA indicates that the nerve is far enough away to allow placement of the screw. If the threshold is < 6 mA, we recommend redirecting the screw hole and retesting (▶ Fig. 14.7). Although it is too early in the development of this technique to report published findings, we have placed > 1,000 screws using this technique without incident (unpublished results). When this pedicle screw technique is used in MIS procedures, it is essential to shield the stimulus probe from surrounding soft tissues by using an insulated sheath. Alternatively, an insulated Jamshidi needle can be used to create the pedicle screw hole, stimulating the needle during insertion. I prefer this latter technique. It is important to use an insulated Jamshidi needle to insure that current does not leak into surrounding soft tissues. MMG is also used during dissection to locate nerves where they are less visible. Since the lowest threshold of normal peripheral nerves is around 0.5 mA using a needle electrode,160 a 1-mA stimulus acts as a reasonable surrogate for the lowest threshold when using a slightly larger tipped, ball probe. If an MMG response is elicited at 1 mA, it can be assumed that the probe is in direct contact with the nerve (▶ Fig. 14.1). The higher the level of current required to stimulate the nerve, the greater the distance to the nerve. This technique of nerve localization is very useful in the presence of scar tissue where the nerve is buried (revision procedures) and I use it routinely when performing MIS decompressions in very obese patients where lighting and visualization are challenging.

14.7.2 Indications Fig. 14.5 MMG is recorded by placing a sensor on the skin over the muscle of interest.

MMG monitoring and mapping is applicable to all situations in which nerve roots or peripheral nerves are in jeopardy. This applies to most lumbar and many cervical procedures, as well as procedures that must navigate complex neuroanatomy (brachial

Fig. 14.6 Schematic showing technique of probing the pedicle to determine if a nerve is in proximity.

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145

Image Guidance, Monitoring, and Nonoperative Techniques

Fig. 14.7 If pedicle stimulation shows that a nerve is in proximity to the hole, then the hole is redirected away from the nerve.

plexus, lumbar plexus). Early reports also demonstrate effectiveness in dissection of spinal tumors, sacroiliac (SI) screw placement, pelvic floor procedures, and cranial nerve procedures (facial nerve, spinal accessory nerve). Anesthetic requirements are similar to those of EMG testing. Motor blockade must be avoided, and whenever short-acting paralytic agents are used during induction, we recommend that surgeons ask the anesthesiologist to demonstrate reversal of blockade before relying on either EMG or MMG responses. All stimulated nerve mapping techniques, whether employing EMG or MMG, rely on the creation of a motor unit action potential (MUAP) to detect nerves. If nerves are clinically compromised preoperatively, then higher current levels may be needed to elicit an MUAP. In the presence of a pre-op clinically significant motor deficit, surgeons must recognize this fact and realize that EMG and MMG responses may be reduced. Stimulating with higher currents will be necessary and a higher safe threshold adopted.

14.8 Anesthesia for Intraoperative Monitoring Modern intraoperative monitoring cannot be accomplished without the support of and cooperation with the anesthesia team. While it is beyond the scope of this chapter to describe neuroanesthesia practices, there are published reviews in the literature that offer good advice in this area.161,162 The importance of communication cannot be overemphasized since the anesthetic requirements of IONM vary with the type of monitoring used. On the simplest end of the spectrum are the requirements for EMG and MMG. Both require normal muscle contraction in response to nerve stimulus. For this to occur, neuromuscular blockade must be avoided. This must be communicated to the anesthesia team prior to induction since most anesthesiologists will routinely paralyze the patient during induction. Short-acting agents such as succinylcholine are usually not a problem but newer depolarizing agents such as rocuronium have largely

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replaced these nondepolarizing drugs. With rocuronium, the duration of blockade is dosage dependent, and it is important to communicate with the anesthesiologist the timeframe in which muscle activity monitoring will be needed. During most MIS procedures, monitoring needs are imminent and therefore it is essential that the period of muscle blockade be as short as possible. The train-of-four twitch test is a good indicator of neuromuscular blockade reversal. This test can be performed by the anesthesiologist or it can be done using EMG or MMG sensors to measure the amplitude of responses. The train-of-four pulses are delivered as four 0.2-m pulses, at 2 Hz. Motor response is noted. In its simplest form, the anesthesiologist observes the response, looking for four “strong” twitches. Objective measurement of responses can also be done using either EMG or MMG monitoring. A fourth twitch that is > 90% of the amplitude of the first twitch indicates reversal of motor blockade. Anesthetic agents affect both SSEPs and TcMEPs in profound ways, and it is important to convey intent to use these modalities to the anesthesia team prior to the procedure so that the anesthesiologist can plan accordingly.163 It is also critical to include both anesthetic effects and physiologic effects in considering the source of signal changes when monitoring SSEPs and TcMEPs. For SSEP monitoring, volatile anesthetics should generally be avoided since they do increase SSEP latency and decrease SSEP amplitude. Some anesthesiologists will use a brief period of isoflurane delivery at induction. This must be discontinued once the patient has been positioned for surgery if SSEPs are to be used. Nitrous oxide also decreases SSEP amplitude but does not affect latency.164 Barbiturates, benzodiazepines, and opiates may interfere with SSEPs but to a much lesser extent than volatile anesthetics. All of these agents may be used to achieve balanced anesthesia, but when used, it is important that they be used consistently so that effects are relatively constant throughout the critical portions of the procedure. TcMEP monitoring is even more susceptible to the effects of general anesthetic agents. Inhalational agents such as isoflurane, enflurane, and sevoflurane cause a marked attenuation or

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Intraoperative Monitoring complete loss of TcMEP responses.75,76,165,166,167,168,169,170 Total intravenous anesthesia is therefore recommended when relying on TcMEPs to monitor spinal cord status. Induction is usually accomplished with an induction agent, such as sodium pentothal or propofol, and a short-acting, nondepolarizing neuromuscular blocking agent may be used for intubation. Some surgeons are comfortable allowing a brief period of isoflurane delivery during induction, particularly if prolonged positioning and prepping is expected. Isoflurane must be discontinued before baseline readings are established since even low levels of isoflurane at this stage will likely interfere with the establishment of TcMEP thresholds. Once induction is achieved, steadystate anesthesia can rely on a continuous propofol infusion combined with narcotic infusion. Isolated TcMEP monitoring in the absence of EMG or MMG monitoring will tolerate a partial neuromuscular block (one to two twitches), since absolute amplitude of evoked motor responses is not of primary importance. However, when doing TcMEPs we still ask that no blocking agent be used because it is difficult to maintain consistent levels of partial block. Avoiding neuromuscular blockade altogether results in greater consistency. The keys to successful anesthetic management during the spinal surgery are listed in the following.

Keys to Successful Anesthetic Management ● ●

●

●

Communicate IONM plans to surgical and anesthesia teams. When using SSEPs and TcMEPs avoid halogenated agents unless their use is appropriate for induction and positioning. Minimize large fluctuations in the delivery of anesthetic whenever SSEPs and TcMEPs are used. Avoid neuromuscular blockade altogether or use transient, reversible blockade only for intubation if the plans for IONM include TcMEP, EMG, or MMG monitoring.

Physiologic monitoring by the anesthesia team is critical during the procedure. Temperature, blood pressure, PaO2, and PaCO2 affect both SSEPs and MEPs and must be controlled during surgery.164 Maintaining a steady state is most critical.

14.9 Recommended Use of Intraoperative Monitoring for Minimally Invasive Spine Surgery The basic menu of IONM options available for surgeons performing minimally invasive spine surgery includes SSEP, TcMEP, EMG, and MMG. Mindlessly choosing all options for a given procedure makes little sense, adds time, complexity, and cost to procedures, and is inappropriate in today’s world of accountable care. Surgeons are advised to develop an understanding of how these monitoring options work and where they are best applied. In this section, I will outline my personal preferences, which are summarized in ▶ Table 14.1.

Table 14.1 Author’s preferences for IONM in minimally invasive spine surgery SSEP

TcMEP

EMG

MMG

ACDF/ arthroplasty

ˣDo not ˣDo not recommend recommend

ˣDo not ˣDo not recommend recommend

Cervical foraminotomya

ˣDo not ˣDo not ˣDo not ✓Recomrecommenda recommenda recommend mend

Postcervical fusion

✓Recommend

✓Recommend

ˣ Do not ✓Recomrecommend mend

Thoracic procedures

✓Recommend

✓Recommend

✓Recommend

Lumbar decompression

ˣ Do not ˣ Do not recommend recommend

ˣ Do not ✓Recomrecommend mendc

Lumbar instrumentation

ˣ Do not ˣ Do not recommend recommend

ˣ Do not ✓Recomrecommend mend

Sacroiliac fusions

ˣ Do not ˣ Do not recommend recommend

ˣ Do not ✓Recomrecommend mend

✓Recommendb

aFor

open decompression with myelopathy, I add SSEP and TcMEP to monitor cord function. bEMG and/or MMG are optional but may add value for screw placement. cMMG is useful whenever visualization is compromised such as with revision scar tissue dissection, in the morbidly obese, for inside-out foraminotomy, or Kambin’s triangle surgery.

For procedures that involve manipulation of the spinal cord, or whenever spinal cord blood supply may be jeopardized by the surgical technique (such as with thoracic deformity procedures), I recommend the use of spinal cord monitoring techniques. I use both SSEPs and MEPs together, since each technique monitors a separate portion of the spinal cord and they complement each other well. There is an essential delay in any surgery that utilizes both SSEP and MEP. It takes time for setup and recording results adds delay. It takes additional time to analyze results for interpretation. These delays can be a major concern for surgeons who perform a high volume of MIS procedures that are otherwise very quick. There are professional fees associated with the use of these techniques, adding significant costs to surgical care. The specific anesthetic requirements of SSEP and MEP monitoring also ads additional time and expense. For all of these reasons, I carefully select both SSEP and MEP monitoring only when the spinal cord is at significant risk. For lumbar procedures and SI fusions, minimal access and safe hardware placement is the challenge, and for these to be accomplished, accurate localization of nerve roots and peripheral nerves is required. I use stimulated techniques for nerve mapping and the choices for this are EMG or MMG. I prefer MMG because of the ease and speed of setup and the increased reliability (fewer false-positives and false-negatives) that results from an improved signal/noise ratio. The use of an MMG surgeon-driven system makes the approach to lateral, transpsoas surgery much quicker and offers the added benefit of lowered costs through the elimination of a technician and neurophysiologist.

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Image Guidance, Monitoring, and Nonoperative Techniques For pedicle screw testing, I routinely use preinsertion MMG testing. For open screw placement, a stimulated ball-tip feeler is used to palpate the walls of the pedicle hole prior to screw insertion. Six milliampere is used as the MMG threshold. I prefer this to stimulated EMG because the lack of electrical noise makes MMG more sensitive at lower thresholds.143 I use MMG testing and a shielded, stimulated Jamshidi needle for minimally invasive, percutaneous screw insertion. Again, a 6-mA threshold is used. For SI fusions, I use MMG to monitor the L5 and S1 nerve roots. Stimulation is applied to the drill and/or guidewire through an insulated sleeve. Once implants are in place, I also use a stimulated ball-tip probe to test the implant itself, stimulating as the ball tip is passed through the implant. For 4-mm implants, I use 5 mA as a threshold and for 7-mm implants I use 8 mA as a stimulus threshold. Because lumbar spine surgery and SI fusions do not place the spinal cord or upper motor neurons in danger, I do not routinely add SSEP or TcMEP monitoring for these cases. The addition of cord monitoring techniques adds little benefit with significant increases in cost, time, and risk. Similarly, I do not use any monitoring for anterior cervical procedures. The cord is not at risk in routine anterior cervical procedures and cervical hardware placement anteriorly does not add significant risk of injury to neurological structures. The addition of monitoring to these procedures adds cost and time with no real benefit. I use MMG mapping for all revision cases. Using a stimulated probe as a dissection tool allows rapid location of nerves, eliminating the need for prolonged dissection through scar. I usually explore scar tissue with a stimulus of 4 mA. If a nerve is localized, I will further map it by dropping the current and finding it with the lowest threshold that elicits a response. If the nerve is clinically compromised but intact preoperatively, I will boost the current up to 15 mA in order to localize it. A new study has shown potential for the use of MMG to measure and monitor nerve health during surgery. In this study, immediate changes in MMG response were associated with changes in the degree of nerve compression. Further studies on the effectiveness and application of this technique are ongoing. While it is too early to assume that diagnostic capabilities will become important in the OR, this technology does open the door to the future development of tools that measure the effects of compression and retraction of nerves during surgery.

14.10 Conclusion IONM during spinal surgery offers various options for managing the risks of neurologic injury using techniques that are tailored to the specific risks associated with the planned procedure. Indiscriminate use of multiple modalities adds little value and great cost. I therefore recommend a careful consideration of the procedural risks and selection from the menu of best IONM options available. Appropriate choices will minimize the risk of nerve injury during surgery in a cost-effective way.

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Clinical Caveats ●

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Both SSEPs and MEPs are useful together to monitor cases where the spinal cord is in jeopardy. This includes some cervical and many thoracic decompression and deformity cases. Monitoring lower motor neurons with EMG or MMG is appropriate whenever spinal nerve roots or peripheral nerves are in jeopardy. This includes lateral access surgery, lateral mass screws, pedicle screws, and any surgery involving nerves of the cervical-brachial or lumbar-sacral plexus. Communicating IONM needs and intentions to the anesthesia team is essential. Minimizing electrical noise in the OR is critical for all IONM modalities except MMG. Surgeon-driven platforms improve standardization, eliminate delays, and reduce costs. MMG offers easy, rapid setup and eliminates the need for technicians.

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Intraoperative Monitoring [119] Djurasovic M, Dimar JR, II, Glassman SD, Edmonds HL, Carreon LY. A prospective analysis of intraoperative electromyographic monitoring of posterior cervical screw fixation. J Spinal Disord Tech. 2005; 18(6):515–518 [120] Ozgur BM, Berta S, Khiatani V, Taylor WR. Automated intraoperative EMG testing during percutaneous pedicle screw placement. Spine J. 2006; 6(6):708–713 [121] Duffy MF, Phillips JH, Knapp DR, Herrera-Soto JA. Usefulness of electromyography compared to computed tomography scans in pedicle screw placement. Spine. 2010; 35(2):E43–E48 [122] Raynor BL, Lenke LG, Bridwell KH, Taylor BA, Padberg AM. Correlation between low triggered electromyographic thresholds and lumbar pedicle screw malposition: analysis of 4857 screws. Spine. 2007; 32(24):2673–2678 [123] Samdani AF, Tantorski M, Cahill PJ, et al. Triggered electromyography for placement of thoracic pedicle screws: is it reliable? Eur Spine J. 2011; 20 (6):869–874 [124] Merletti R, Farina D. Analysis of intramuscular electromyogram signals. Philos Trans A Math Phys Eng Sci. 2009; 367(1887):357–368 [125] Kreifeldt JG. Signal versus noise characteristics of filtered EMG used as a control source. IEEE Trans Biomed Eng. 1971; 18(1):16–22 [126] Hogan N. A review of the methods of processing EMG for use as a proportional control signal. Biomed Eng. 1976; 11(3):81–86 [127] Clancy EA, Morin EL, Merletti R. Sampling, noise-reduction and amplitude estimation issues in surface electromyography. J Electromyogr Kinesiol. 2002; 12(1):1–16 [128] Winter DA, Fuglevand AJ, Archer SE. Crosstalk in surface electromyography: theoretical and practical estimates. J Electromyogr Kinesiol. 1994; 4(1):15–26 [129] Farina D, Merletti R, Indino B, Graven-Nielsen T. Surface EMG crosstalk evaluated from experimental recordings and simulated signals. Reflections on crosstalk interpretation, quantification and reduction. Methods Inf Med. 2004; 43(1):30–35 [130] Chowdhury RH, Reaz MBI, Ali MA, Bakar AAA, Chellappan K, Chang TG. Surface electromyography signal processing and classification techniques. Sensors (Basel). 2013; 13(9):12431–12466 [131] Day S. 2002. Important Factors in Surface EMG Measurement. Calgary: Bortech Biomedical Ltd [132] Türker KS. Electromyography: some methodological problems and issues. Phys Ther. 1993; 73(10):698–710 [133] Basmajian JV, De Luca CJ. Muscles Alive. Their Function Revealed by Electromyography. Baltimore, MD: Williams & Wilkens; 1985 [134] Lindström LH, Magnusson RI. Interpretation of myoelectric power spectra: a model and its applications. Proc IEEE. 1977; 65:653–662 [135] Mathiassen SE, Winkel J, Hägg GM. Normalization of surface EMG amplitude from the upper trapezius muscle in ergonomic studies - A review. J Electromyogr Kinesiol. 1995; 5(4):197–226 [136] Merletti R, Gulisashvili A, Lo Conte LR. Estimation of shape characteristics of surface muscle signal spectra from time domain data. IEEE Trans Biomed Eng. 1995; 42(8):769–776 [137] Merletti R, Migliorini M. Surface EMG electrode noise and contact impedance. In: Hermens HJ, Rau G, Disselhorst-Klug C, Freriks B, eds. Surface electromyography application areas and parameters: proceedings of the third general SENIAM workshop Aachen, Germany, May 1998. Roessingh Research and Development; 1998:S40–44. [138] Bergey DL, Villavicencio AT, Goldstein T, Regan JJ. Endoscopic lateral transpsoas approach to the lumbar spine. Spine. 2004; 29(15):1681–1688 [139] Pimenta LLH, Da Silva MM, Bellera AF, Parra ML, Schaffa DT. Abordaje endoscópico retroperitoneal transpsoas de la columna lumbar. Acta Ortop Mex. 2004; 18(3):91–95 [140] Ozgur BM, Aryan HE, Pimenta L, Taylor WR. Extreme Lateral Interbody Fusion (XLIF): a novel surgical technique for anterior lumbar interbody fusion. Spine J. 2006; 6(4):435–443 [141] Anderson E, Wybo C, Bartol S. An analysis of agreement between MMG vs. EMG systems for identification of nerve location during spinal procedures. Spine J. 2010; 10:93S–94S [142] Hursh JB. Conduction velocity and diameter of nerve fibers. Am J Physiol. 1939; 127:131–139 [143] Moritani T, Kimura T, Hamada T, Nagai N. Electrophysiology and kinesiology for health and disease. J Electromyogr Kinesiol. 2005; 15(3):240–255 [144] Hemmerling TM, Le N. Brief review: neuromuscular monitoring: an update for the clinician. Can J Anaesth. 2007; 54(1):58–72 [145] Murphy C, Campbell N, Caulfield B, Ward T, Deegan C. Micro electro mechanical systems based sensor for mechanomyography. In: 19th international conference BIOSIGNAL; 2008; Brno, Czech Republic

[146] Kaiser L. A small contribution to the knowledge of muscle sound in man. Arch Neerl Physiol Homme Anim. 1938; 23:27 [147] Gordon G, Holbourn AHS. The mechanical activity of single motor units in reflex contractions of skeletal muscle. J Physiol. 1949; 110(1–2):26–35 [148] Barry DT. Vibrations and sounds from evoked muscle twitches. Electromyogr Clin Neurophysiol. 1992; 32(1–2):35–40 [149] Watakabe M, Itoh Y, Mita K, Akataki K. Technical aspects of mechnomyography recording with piezoelectric contact sensor. Med Biol Eng Comput. 1998; 36(5):557–561 [150] Pugh ND, Kay B, Healy TE. Electromyography in anaesthesia. A comparison between two methods. Anaesthesia. 1984; 39(6):574–577 [151] Tammisto T, Wirtavuori K, Linko K. Assessment of neuromuscular block: comparison of three clinical methods and evoked electromyography. Eur J Anaesthesiol. 1988; 5(1):1–8 [152] Mellinghoff H, Diefenbach C, Arhelger S, Buzello W. Mechanomyography and electromyography–2 competing methods of relaxometry using vecuronium [in German]. Anasth Intensivther Notfallmed. 1989; 24(1):57–59 [153] Donati F, Meistelman C, Plaud B. Vecuronium neuromuscular blockade at the diaphragm, the orbicularis oculi, and adductor pollicis muscles. Anesthesiology. 1990; 73(5):870–875 [154] Nakata Y, Goto T, Saito H, et al. Comparison of acceleromyography and electromyography in vecuronium-induced neuromuscular blockade with xenon or sevoflurane anesthesia. J Clin Anesth. 1998; 10(3):200–203 [155] Hofmockel VR, Benad G, Pohl B, Brahmstedt R. Measuring muscle relaxation with mivacurium in comparison with mechano- and electromyography [in German]. Anaesthesiol Reanim. 1998; 23(3):72–80 [156] Bartol S, Wybo C. Relating current to distance in the detection of motor nerves. Paper presented at: the American Academy of Orthopaedic Surgeons Annual Meeting; San Diego, CA; 2011 [157] Rattay F. Ways to approximate current-distance relations for electrically stimulated fibers. J Theor Biol. 1987; 125(3):339–349 [158] Tsui B, Chan V, Finucane B, Grau Th, Walji A, eds. Atlas of Ultrasound- and Nerve Stimulation-Guided Regional Anesthesia. New York, NY: Springer; 2008 [159] Guérit JM. Neuromonitoring in the operating room: why, when, and how to monitor? Electroencephalogr Clin Neurophysiol. 1998; 106(1):1–21 [160] Sloan TB, Heyer EJ. Anesthesia for intraoperative neurophysiologic monitoring of the spinal cord. J Clin Neurophysiol. 2002; 19(5):430–443 [161] Banoub M, Tetzlaff JE, Schubert A. Pharmacologic and physiologic influences affecting sensory evoked potentials: implications for perioperative monitoring. Anesthesiology 2003;99(3):716–737 [162] Burke D, Hicks R, Stephen J, Woodforth I, Crawford M. Assessment of corticospinal and somatosensory conduction simultaneously during scoliosis surgery. Electroencephalogr Clin Neurophysiol. 1992; 85(6):388–396 [163] Antognini JF, Carstens E, Buzin V. Isoflurane depresses motoneuron excitability by a direct spinal action: an F-wave study. Anesth Analg. 1999; 88(3):681–685 [164] Haghighi SS, Madsen R, Green KD, Oro JJ, Kracke GR. Suppression of motor evoked potentials by inhalation anesthetics. J Neurosurg Anesthesiol. 1990; 2(2):73–78 [165] Pechstein U, Nadstawek J, Zentner J, Schramm J. Isoflurane plus nitrous oxide versus propofol for recording of motor evoked potentials after high frequency repetitive electrical stimulation. Electroencephalogr Clin Neurophysiol. 1998; 108(2):175–181 [166] Pelosi L, Stevenson M, Hobbs GJ, Jardine A, Webb JK. Intraoperative motor evoked potentials to transcranial electrical stimulation during two anaesthetic regimens. Clin Neurophysiol. 2001; 112(6):1076–1087 [167] Ubags LH, Kalkman CJ, Been HD. Influence of isoflurane on myogenic motor evoked potentials to single and multiple transcranial stimuli during nitrous oxide/opioid anesthesia. Neurosurgery. 1998; 43(1):90–94, discussion 94–95 [168] Sihle-Wissel M, Scholz M, Cunitz G. Transcranial magnetic-evoked potentials under total intravenous anaesthesia and nitrous oxide. Br J Anaesth. 2000; 85(3):465–467 [169] Godil S, Zuckerman S, Parker S, Aaronson O, Devin C, McGirt M. Comparative Effectiveness, Cost Utility and Cost Benefit Analysis of Intra-Operative Neuromonitoring in Cervical Spine Surgery: Where is the Value? Presented at the American Association of Neurological Surgeons (AANS) 81st Annual Scientific Meeting. Abstract 616. Presented April 29, 2013 [170] Khalil J, Anderson E, Bartol S. Assessment of nerve root decompression by mechanomyography (MMG). Paper presented at: the American Orthopaedic Association Annual Meeting; Montreal; 2014

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Image Guidance, Monitoring, and Nonoperative Techniques

15 Injection-Based Spine Procedures and Diagnostic Procedures Henry Tong and Mick J. Perez-Cruet Abstract This chapter deals with the basic information every clinician doing spinal injections needs to know. We start with reviewing the common medications injected. Then we review basic information on fluoroscopy, skin preparation, and complications. The next section reviews needle control techniques including advantages of a bent needle tip with spinal injections. Techniques for doing caudal epidurals, interlaminar epidurals, transforaminal epidurals, facet joint injections, medial branch blocks, medial branch radiofrequency neurotomy, and lumbar discogram are then reviewed. Keywords: spinal injections, caudal epidurals, interlaminar epidurals, transforaminal epidurals, facet joint injections, medial branch blocks, medial branch radiofrequency neurotomy, lumbar discogram

15.1 Fundamentals of Spine Injections 15.1.1 Pharmacology for the Spine Injectionist It is important the clinician understands the medications that are used in spinal injections. This section will give a brief overview of some medications in each category, but is by no means a comprehensive list. The clinician should refer to the official prescribing information for each drug. These can be found in the published manufacturer product information as well as the Physicians’ Desk Reference.1

Local Anesthetic A local anesthetic reversibly blocks neural sodium channels to interrupt nerve impulse conduction. The two most commonly used local anesthetics, lidocaine and bupivacaine, are amides. Lidocaine has a faster onset and shorter duration of action2 (▶ Table 15.1). Bupivacaine is more lipid soluble, so it is more potent and has a longer duration of action than lidocaine. Both are metabolized by the hepatic cytochrome P450 system as well as conjugation. Because of this, caution should be used in patients

with liver dysfunction. Because of potential adverse reaction with intravascular injection of a vasoconstrictor (i.e., epinephrine) or perineural injection of preservative (e.g., methylparaben), it is generally recommended to do spinal injections with preservative-free and vasoconstrictor-free medications. Because the local anesthetics are slightly acidic to enhance stability, which can cause a burning sensation when first injected into the skin and subcutaneous tissue, a small amount of sodium bicarbonate 8.4% can be added to the local anesthetic (1:20 volume ratio) to decrease the initial burning.3,4 This must be done carefully since adding too much sodium bicarbonate can cause drug precipitation.

Corticosteroids Glucocorticoids are anti-inflammatory by decreasing the local production of inflammatory medications such as prostaglandins, leukotrienes, interleukin 1, interleukin 6, and tumor necrosis factor α.5,6 Glucocorticoids are metabolized by the liver and excreted in the urine. They also transiently elevate blood glucose level, so they must be used with caution in patients with diabetes mellitus.7 The selection of the steroid to be used depends on the injection to be done. Commonly used corticosteroids include methylprednisolone acetate (Depo-Medrol), triamcinolone acetonide (Kenalog), and dexamethasone sodium. In general, nonparticulate steroids have been demonstrated to dissipate rapidly and therefore may have a limited duration of effect.8 Because of this, even though there is no randomized controlled trial verifying this, it is felt particulate steroids are longer acting.9 Thus, if there is no major risk of cerebral or spinal cord infarcts, it is reasonable to consider using particulate steroids. However, with cervical and thoracic epidurals, injection of particulate corticosteroids into a vertebral or foraminal artery can cause brain and spinal cord infarcts. It is felt the smaller particle size could decrease the risk of a clinically significant infarct. Dexamethasone sodium phosphate particle size is smaller than red blood cells and the particles did not aggregate. Triamcinolone acetonide and betamethasone sodium phosphate showed variable sizes. They aggregated and some particles were larger than red blood cells. Methylprednisolone acetate did not aggregate, and the majority were smaller than red blood cells.10 This was verified that same year in an animal study injecting

Table 15.1 Comparison of common local anesthetics Agent

Available concentrations (%)

Lidocaine Bupivacaine

0.25, 0.5, 0.75

Source: Data from Fenton and

152

Onset

Duration (h)

pKa (25 °C)

pH of plain solutions

Recommended maximal single dose (mg) without epinephrine

Fast

1–2

7.7

6.5

300

Slow

2–4

8.1

4.5–6

175

Czervionke.2

Perez-Cruet et al, An Anatomic Approach to Minimally Invasive Spine Surgery, 2nd Ed. (ISBN 978-1-62623-643-1), copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.

Injection-Based Spine Procedures and Diagnostic Procedures corticosteroids in the vertebral arteries of pigs. Methylprednisolone was injected into four pigs causing severe stroke and failure to ventilate, dexamethasone was injected into four pigs causing no symptoms or transient symptoms that resolved in 2 hours, and prednisolone caused no symptoms.11 In this situation, it may be prudent to use nonparticulate steroids with cervical and thoracic epidurals. Because local injection of corticosteroids into the skin can cause skin depigmentation, anytime corticosteroids are injected, the needle should be flushed with a small amount of local anesthetic or contrast before the needle is pulled to the skin.12 Alternatively, if infection is not a major issue, and good sterile technique is practiced, the stylet can be reinserted into the needle before the needle is withdrawn.

Contrast Contrast agents are used with fluoroscopic images to help verify the location of the needle tip. With joint injections, it helps determine if the tip is intra-articular. With epidurals and medial branch blocks, it also helps verify whether the tip is not intravascular. Nonionic water soluble iodine-based contrast agents are less irritating and allergenic than ionic iodine-based contrast. Two commonly used agents are iohexol (Omnipaque) and iopamidol (Isovue). These agents are excreted by the kidney. Potential side effects include headaches, nausea, vomiting, and central nervous system disturbances.13 For patients with anaphylactic allergic reactions to iodinated contrast, gadolinium contrast could be considered. This contrast is not as radiopaque as iodine-based contrast agents, so the contrast is harder to visualize than iodinated contrast. Also, gadolinium should not be injected intrathecally since this is irritating to nervous tissue and high doses can cause seizures.14 However, injection of low volume (0.5 mL) of gadolinium was reportedly done with low risk of complications.15

15.1.2 Fluoroscopic Guidance Fluoroscopic guidance is important to confirm accurate needle position in the correct anatomic location. It has been shown that with blinded interlaminar epidurals, 20 to 30% were not properly placed when done without fluoroscopic guidance.16,17 With blinded caudal epidurals, new clinicians had a 48% rate of improper needle placement, but experienced clinicians still had a 38% rate of improper needle placement.18 With sacroiliac joint injections, there was only a 78% rate of nonarticular injection with a blinded technique.19 Fluoroscopic guidance not only helps with improving needle placement accuracy, but also helps with decreasing the risk of intrathecal injection and intravascular injection.20 Fluoroscopic guidance can also help make sure the needle tip is not in a blood vessel. Even when the needle was correctly placed in the spinal canal with caudal epidurals, the presence of blood on the needle stylus was not a reliable indicator of venous placement, so venous injection was done 9.2% of the time with blinded caudal epidurals.18 More recently, it was shown that for lumbar transforaminal epidural injections, live fluoroscopic imaging was better at detecting intravascular needle placement, and even doing intermittent fluoroscopic images 1 second after contrast injection missed 57% of the vascular injections of contrast.21 To

help minimize radiation exposure to the hand, it is recommended to use a 6- to 12-inch extension tubing so the injecting hand can be kept out of the fluoroscopic image. It is not recommended to keep the hand in the fluoroscopic image with radiation gloves because the machine may then increase the fluoroscopic radiation output exposing the patient and clinician to more radiation. Also, radiation exposure should be kept “as low as reasonably achievable” (ALARA). Only 2 to 3 seconds of live fluoroscopic imaging with contrast injection is necessary to determine if there is intravascular uptake. Similarly, a minimal amount of contrast is needed to determine proper needle tip location with joint injections to allow more room for the medications to be injected. If the contrast shows the needle tip is in the wrong location, less contrast injection will obscure less of the image area, making it easier to redirect the needle to the correct target.

15.1.3 Skin Preparation The goal of skin preparation is to remove transient and pathogenic flora.22 The ideal agent should be safe and effective, quick acting, and inexpensive.22,23 The most commonly used agents are alcohol, povidone-iodine, and chlorhexidine gluconate. Seventy percent isopropyl alcohol after 2 minutes kills 90% of the bacteria on the skin.22 Some reviews felt that chlorhexidine was more effective than iodine.24,25 However, other reviews using more stringent criteria felt no conclusions could be drawn regarding using povidone-iodine versus chlorhexidine for reducing surgical site infections.26,27 Good skin antisepsis, sterile drapes, and sterile technique should be used with all spinal procedures.

15.2 Pre- and Postprocedure Care 15.2.1 Basic Needle Control Techniques Effect of Bevel Tip on Needle Direction Most spinal injections are done using a bevel-tip needle. If the needle is of larger caliber (22 gauge or smaller), the needle is less likely to bend during the procedure and the clinician can directly redirect the needle in the tissue with direct pressure. This is fine with procedures such as medial branch blocks, interlaminar epidurals, or hip joint injections where the path to the target location is fairly straight and it does not matter the direction the needle tip reaches the target. With smaller caliber (23 gauge or larger) bevel-tip needles, when the needle is advanced, it will generally move directly away from the beveled side (also generally away from the notch of the hub/stylet). This effect is less pronounced in tissue with less resistance such as adipose tissue and is more pronounced in tissue with more density such as muscle tissue and connective tissue.

Techniques for Advancing a Needle Tip in One Direction With advancing a needle, the tip will tend to move away from the bevel (hub notch) at an angle based on the tissue density. If the needle is desired to be directed more in that direction, the exposed part of the needle could be bent in an arc and translated away from the desired direction of motion.28 If the needle

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Image Guidance, Monitoring, and Nonoperative Techniques is desired to be directed even more laterally in that direction, the skin at the needle insertion site can be tractioned in the opposite direction of the desired direction of motion.

Joint Injections and Needle Considerations With intra-articular facet and sacroiliac joint injections, it is useful to use a smaller caliber needle to better enter the joint capsule because of their small joint widths. For many joints, especially with arthritic joints, bending the tip can further help facilitate directing the needle tip to an intra-articular position. This is because, even when the joint appears to be well visualized on fluoroscopic images, when the needle tip hits the joint, it may be 1 to 2 mm away from the joint space or, because of arthritic changes, not be facing the correct direction to successfully enter the joint space. Bending the distal needle about 3 to 5 mm from the tip about 10 to 15 degrees will laterally displace the needle tip about 1 to 2 mm from its original location. This is useful with intra-articular joint injections when the needle tip encounters the joint at what appears to be a radiolucent location, and the tip feels to be hitting only bony tissue instead of the softer joint capsule; the needle can be pulled 2 to 3 mm, rotated about 30 degrees, and then gently advanced again to try to enter the joint capsule. This can be repeated until an entire 360 degrees has been tried before redirecting the needle to another joint location.

Bent Tip and Other Spinal Injections For procedures such as transforaminal epidurals and discograms especially at the L5–S1 level, it is also commonly useful to be able to direct the needle around bony tissue and still successfully direct the needle tip to the target. In these cases, it is useful to use smaller caliber needle (e.g., 23- or 25-gauge needles) with a bent tip (▶ Fig. 15.1). From the author’s experience, using a 25-gauge, 3.5-inch Quincke tip needle is the best choice for most procedures. Some use 27-gauge needles, but these needles have much less stiffness so that even with a bent tip, the needle may tend to advance only along the patient’s tissue planes making it harder to steer to the desired target. If a longer needle needs to be used, using a 25-gauge 5- to 6-inch Quincke tip needle or 23-gauge 6-inch Quincke tip needle is the best choice. When trying to do a transforaminal epidural injection after posterior fusion, if the postoperative scar tissue in the paraspinal muscles is very dense and directs the needle tip in the wrong direction, a 22-gauge Quincke tip needle may be the best choice. With epidurals, medial branch blocks, and medial branch radiofrequency neurotomy, the bent tip is useful once the tip is at the target location, since, if the injection of contrast shows intravascular flow, the needle can be easily readjusted 1 to 2 mm by pulling a few millimeters, then rotating the needle and readvancing to the target depth to try to get out of the blood vessel.

Bending the Needle Tip In general, since the bevel is on the same side of the notch in the hub, to augment the direction the needle prefers to normally move when advanced, the needle tip is bent away from the bevel (away from the notch in the hub). There are several

154

Fig. 15.1 The effect of bent tip on needle trajectory. Using a flank of corned beef as the medium, with all three 25-gauge needles starting in the same angle and then advancing 1 inch, the straight needle (a) curves a little, the needle with a bend 10 mm from the tip (b) curves a little more, and the needle with a bend 4 mm from the tip (c) curves the most. In denser tissues, the needles would curve even more. In loose tissue such as adipose tissue, all three needles may not curve much at all.

ways to bend the needle tip. One way is to hold the tip of the needle between the thumb and second digit of one hand and then hold the hub of the needle with the other hand and then bend the needle (▶ Fig. 15.2a). A second way, using one hand, is to hold distal end of the needle with the thumb on one side and the second and third digits on the other side. The thumb then applies pressure on the needle, bending the needle tip (▶ Fig. 15.2b). With these two techniques, the bend usually occurs about 10 mm from the tip. If more precise needle control is needed, it is better to bend the needle tip about 4 to 5 mm from the tip. This can be accomplished by using a needle driver to gently grasp and bend the needle tip. Some use the needle driver or another hard sterile metal instrument to push the tip flat on the procedure tray and then bend the needle up with the other hand. However, this author does not do this since pushing the needle down against the procedure tray may puncture the sterile drape and contaminate the needle tip. Another technique is to insert the tip of the needle about 3 to 4 mm into the tip of a larger caliber needle such as an 18-gauge needle and then bend the tip (▶ Fig. 15.2c). When bending the needle tip using the last three techniques, the needle should only be bent about 10 to 15 degrees at one location because bending further can cause the needle to catch the stylet. If a larger angle is desired, a second bend can be done about 1 to 2 mm closer to the tip than the first bend. ▶ Fig. 15.3 shows some commonly used needles for spinal injections. A 22-gauge needle is harder to bend by hand and may need to be bent using the latter methods described above.

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Injection-Based Spine Procedures and Diagnostic Procedures

Fig. 15.2 (a) Bending the needle tip with two hands. One hand holds the needle tip between the thumb and second finger. The other hand holding the hub is pulled so the needle tip is bent away from the bevel. (b) Bending the needle tip with one hand. One hand holds the needle tip with the second and third finger on the bevel side and the thumb on the other side. The thumb applies pressure so the needle tip is bent away from the bevel. (c) The needle tip is inserted into the tip of a larger caliber needle of about 3 to 5 mL. The needle is then bent so the tip is bent away from the bevel. The tip should only be bent about 10 to 15 degrees at one location. Bending the needle more than 15 degrees at one location can catch the stylet, making it hard to remove and reinsert.

used to verify the needle tip is being advanced to the target. Mastery of all the needle control techniques above is necessary to ensure the spinal injection procedure is done correctly and efficiently with as little trauma as possible to the patient

15.3 Epidural Injections The goal of epidural injections is to deliver medications to decrease inflammation and pain around the spinal nerves and sometimes posterior aspect of the intervertebral discs. There are three different approaches: caudal, interlaminar, and transforaminal.

15.3.1 Caudal Epidurals

Fig. 15.3 Different needle configurations for spinal injections. (a) 22-gauge, 3.5-inch Quincke tip needle with a straight tip; (b) 25gauge, 3.5-inch Quincke tip needle with a straight tip; (c) 25-gauge, 3.5-inch Quincke tip needle with a bend 10 mL from the tip; (d) 25-gauge, 3.5-inch Quicke tip needle with a bend 4 mL from the tip; (e) 18-gauge, 3.5-inch Tuohy needle; (f) 20-gauge 5-inch Quincke tip needle; (g) 25-gauge, 8-inch Quincke tip needle with a bend 3 mL from the tip; (h) 25-gauge, 8-inch Quincke tip needle with a gradual bend about 1 inch from the tip.

Advancing the Needle with Bent Tip For most procedures, the clinician initially wants to direct the needle straight along a fluoroscopic tunnel view to the target. Because the bent tip will augment the needle tip to move in a direction away from the bevel (away from the hub notch), if the clinician wants to advance the needle straight, one technique is to rotate the needle as the needle is being advanced. Another technique is to advance the needle 5 to 10 millimeters and then rotate the needle 180 degrees and advance again. With both techniques, either live fluoroscopic images or multiple single shots should be

The caudal epidural was first reported in 1901.29 Corticosteroids were not added to the local anesthetic until 1952.20 The volume of injectate reported ranged from 5 to 25 mL.20 However, more recent data allow the clinician to better determine how much volume to inject. Freeman et al30 showed using live fluoroscopic images of caudal contrast injection that at most 3.8 mL of contrast injection was needed to reach the L5–S1 disc space and 5 mL was needed to reach the L4–L5 disc space. Manchikanti et al31 assessed filling patterns of the lumbosacral epidural space by injections of different volumes of nonionic contrast. They showed increased filling of up to 10 mL of contrast injection at the S1 level. However, good filling was seen in 82% at the S1 level and only in 12% at the L5 level in nonsurgical patients.31 Because of this, caudal epidurals are more appropriate for pathology in the sacral region or lower lumbar region. With the patient in the prone position (or lateral decubitus position if the patient cannot lie prone), the area just inferior to the sacral hiatus is palpated and highlighted on anteroposterior (AP) and lateral fluoroscopic view, and the skin over the area is prepared with 1 mL of 1% lidocaine using a 25- or 27-gauge 1.5inch needle. A 25-gauge, 3.5-inch spinal needle is then directed about 30 to 45 degrees taken down through the sacral hiatus using multiple fluoroscopic images. The needle is then directed to enter the sacral spinal canal. The needle should be kept below the S2 level to decrease risk of intrathecal injection. If the patient’s symptoms are more to one side, the needle tip should be directed slightly to that direction since some patients have a

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Image Guidance, Monitoring, and Nonoperative Techniques

Fig. 15.4 Caudal epidural. (a) Lateral view showing the needle passing thought the sacral hiatus. The tip should not extend above S2. (b) Anteroposterior (AP) view showing good contrast flow. The needle is kept to the right of midline since the patient’s symptoms were on the right side.

dorsal median epidural septum that confines the spread of medication injected to the side ipsilateral to the injection.32,33 Proper needle position is verified with two views. A 10-mL syringe should be used to ensure there is no blood flashback. Contrast should then be injected with live sequential fluoroscope imaging. This should highlight the nerve roots and epidural space without intravascular uptake (▶ Fig. 15.4). Injection is completed with 5 mL of a mixture of 1 mL of corticosteroid and 4 mL of local anesthetic. The needle is then flushed with a small amount of local anesthetic or contrast or the stylet is reinserted before the needle is completely removed.

15.3.2 Interlaminar Epidurals Interlaminar epidurals deliver medications into the posterior epidural space. Even though the injectate can flow anteriorly as it flows cranially, this does not always happen due to impedance from epidural fat, and the injectate may not reach the anterior space at the level of injection.34 In the lumbar spine, any level can be chosen based on the clinical situation. In the cervical spine, injections should not be done at a level with central stenosis less than 8 mL due to risk of causing an epidural hematoma.35

Loss of Resistance Technique With the patient in a prone position, the interlaminar space is identified on AP view. The skin and soft tissue along the planned injection route is prepared with 1 mL of 1% lidocaine. A 18-gauge, 3.5-inch blunt tip needle (usually either a Tuohy needle or pencil tip needle) is then taken down to the interlaminar space using multiple fluoroscopic images on AP view to verify the needle is directed to the upper portion of the lower laminar. Once the needle is close to the epidural space, a lateral view should be used to determine proper depth since the ligamentum flavum is located at the anterior aspect of the spinous processes. The needle is then redirected a little cranially to walk off the lamina into the interlaminar space. Loss of resistance with either air or saline ensures the tip passes the ligamentum flavum and is in the epidural space. Proper needle position should be verified with two views. There should be no bloody flashback and injection of nonionic contrast with live sequential fluoroscope imaging verifies epidural flow without intravascular uptake (▶ Fig. 15.5). The injectate should be a corticosteroid with or without local anesthetic. The needle is then flushed with a small amount of local anesthetic or contrast or the stylet is reinserted before the needle is completely removed.

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Fluoroscopy with Cervical Interlaminar Epidurals Because the epidural space is larger in the lower cervical spine, cervical interlaminar epidurals are usually done at the C7–T1 level. However, because there is more dense tissue at the T1–T3 levels with the shoulders, it is commonly harder to visualize the needle tip in the C7–T1 epidural space on lateral view. Two ways to help with visualizing the needle tip include depressing the patient’s shoulders to the foot so they overlie the target area less as well as moving the fluoroscope toward the foot so more shoulder is visualized, which will cause the machine to increase the power used.36 Another help is a spinal positioning platform (Oakworks Medical) which is placed under the patient’s chest when lying prone, and allows the shoulders to fall forward so they are not overlying the target C7–T1 epidural space.

Hanging Drop Technique The hanging drop technique was described by Gutierrez.37 This technique relies on the presence of negative pressure in the epidural space when the patient is sitting in the cervical and upper thoracic spine.38 Because of this, this technique should not be considered in the lumbar region. With the patient sitting up, a needle is directed to the C7–T1 interspace. Once the needle is in the interspinous ligament, the stylet is removed and a drip of saline or local anesthetic is placed on the hub. The needle is slowly advanced. When the needle passes the ligamentous flavum, the negative pressure in the epidural space draws the drop of fluid into the needle. If available, a Weiss needle should be used for this technique since the two side flaps at the hub allow the clinician to better control the advance of the needle.39 If fluoroscopy is available, it should be used to improve safety and efficacy. The ligamentum flavum cannot be seen, but lies at the anterior aspect of the spinous processes.

15.3.3 Transforaminal Epidurals Lumbar Transforaminal Epidural Steroid Injection With the patient in the prone position, the location of the neuroforamen just inferolateral to the corresponding pedicle is identified at about 15 degree lateromedial oblique view (▶ Fig. 15.6a). The skin and soft tissue along the planned injection route are prepared with 1 mL of 1% lidocaine. A 25-gauge,

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Injection-Based Spine Procedures and Diagnostic Procedures

Fig. 15.5 Interlaminar epidural. (a) Lumbar lateral view. (b) Lumbar AP view. (c) Thoracic lateral view. (d) Thoracic AP view. (e) Cervical lateral view. (f) Cervical AP view. If using a Tuohy needle, the needle is advanced from a caudal to cranial direction with the curved (blunt) side of the tip facing the spinal canal to decrease the risk of puncturing the dura mater. The needle tip should stop around the anterior aspect of the spinous processes. The cervical later view can still be hard to visualize even with moving the view to the thoracic level and using a spinal positioning platform.

3.5-inch spinal needle is then taken down to the neural foramen’s most superior aspect just inferior to the pedicle using multiple fluoroscopic images (▶ Fig. 15.6b). When the needle tip is about 1 inch from the target, AP views should be used to make sure the needle tip is always kept lateral to the 6 o’clock position of the pedicle on AP view (▶ Fig. 15.6c). Proper needle position is verified with two views (▶ Fig. 15.6c, d). Derby et al reported the safe triangle in the superior neuroforamen region as a good anatomic target for lumbar transforaminal epidurals that minimizes the risk of hitting the exiting nerve root or puncturing the thecal sac.40 The medial point of the triangle is the bottom of the pedicle with a base running inferolaterally where the nerve root runs and the lateral side is the outer margin of the intervertebral foramen. Later, Jasper and then Choi et al41,42 reported a second anatomic target, the retrodiscal space in the inferior neuroforamen previously described as Kambin’s triangle (▶ Fig. 15.7), that is useful especially at the L5–S1 level where the patient’s anatomy can make the safe triangle difficult to reach as well as the upper lumbar region to avoid the artery of Adamkiewicz, which unfortunately tends to be present in the upper part of the neuroforamen.41,42,43,44,45 There should be no bloody flashback, and injection of nonionic contrast with live sequential fluoroscope imaging verifies epidural flow without intravascular uptake

(▶ Fig. 15.6e and ▶ Fig. 15.7c). The injectate should be a corticosteroid with or without local anesthetic. If the level injected is the L2–L3 neuroforamen or more cranial, because of the risk of the artery of Adamkiewicz being present, a small particulate steroid such as dexamethasone should be considered.10,11,43,46 Before the needle is completely removed, the needle should be flushed with a small amount of local anesthetic or contrast or the stylet is reinserted.

Cervical Transforaminal Epidural Steroid Injection With the patient lying supine, the correct level is identified on lateral view and then the neuroforamen is identified and highlighted on oblique fluoroscopic images. The skin only over the injection site is prepared with 1 mL of 1% lidocaine. A 25-gauge, 3.5-inch spinal needle with a bent tip is then directed to the superior articulating process just posterior to the neuroforamen using a tunnel view technique. Once bone is contacted, the needle is redirected slightly anterior and medial to the posteroinferior part of the neuroforamen. Proper needle position is verified with two views. A catheter technique with a 6-inch extension tubing is used to prevent any needle tip motion. Injection of 0.5 mL of contrast with live fluoroscopic images verifies epidural

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Image Guidance, Monitoring, and Nonoperative Techniques

Fig. 15.6 Lumbar transforaminal epidural. (a) 15-degree oblique view with a needle on the skin localizing the needle entry site. (b) 15-degree oblique view with the needle directed to the safe triangle using a tunnel view technique. (c) AP view verifying the needle is lateral to the 6 o’clock position of the bottom of the pedicle. (d) Lateral view showing proper needle depth. The needle could be advanced more anterior if needed, but avoid the anterior canal if possible since the nerve root runs anterior as it exits the neuroforamen. (e) AP view showing the needle tip rotated a little to achieve good medial epidural flow of contrast since the initial cranial needle tip position showed only local soft tissue flow of contrast.

Fig. 15.7 Lumbar transforaminal epidural with retrodiscal approach. (a) Lumbar lateral view. The needle being directed to the safe triangle was not able to reach the safe triangle due to bony obstruction, presumed to be the facet joint. (b) Lumbar lateral view. The needle was withdrawn about 3 inches and redirected to the retrodiscal space. (c) Lumbar AP view showing good medial epidural flow of contrast.

flow without intravascular flow (▶ Fig. 15.8). A test injection of 0.5 mL of 1% preservative-free lidocaine is then injected. If the patient has a transient seizure, then the needle tip is partially intra-arterial despite not being seen on live fluoroscopic images and the procedure is aborted. If there is no complication,

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injection is completed with a small particulate corticosteroid such as 1 mL of single dose of dexamethasone 10 mg/mL to decrease the stroke risk.10,11 The needle is then flushed with 0.3 mL of Omnipaque and then removed. Some recommend starting with a lateral view and then slowly rotating the

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Injection-Based Spine Procedures and Diagnostic Procedures

Fig. 15.8 Cervical transforaminal epidural. (a) Oblique view. The needle is directed to the superior articulating facet joint posterior to the inferior neuroforamen. Once bone is contacted, the needle is gently walked off the bone. (b) AP view. Live fluoroscopic image shows good epidural flow of contrast without intravascular uptake.

Fig. 15.9 Thoracic transforaminal epidural. (a) Lateral view. The fluoroscope is slightly rotated to identify the neuroforamen on the same side as the needle tip. The needle is kept in the posterior part of the neuroforamen after just walking off the transverse process. (b) AP view shows good medial epidural flow of contrast.

fluoroscope toward AP view until the neuroforamen is visible, usually around 20 degrees. The logic is that the vertebral artery is anteromedial to the neuroforamen, so the more lateral the view, the less likely the needle will puncture the vertebral artery. However, a CT study of cervical spine reported the optimal angle of entry for cervical transforaminal epidurals was about 48 degrees.47 Others have also suggested keeping the needle extraforaminal to decrease the risk of intravascular uptake and stroke. The tradeoff is that keeping the needle tip lateral on AP view decreased the chance of the injectate from reaching the central epidural space and anomalous extraforaminal blood vessels can still expose the patient to risks of intravascular injection of steroid even with an extraforaminal placement.48,49

placed too lateral or it may puncture the lung. Because of risks with placing the needle tip to medial or lateral as well as too anterior, multiple images in both the AP and lateral views need to be obtained (▶ Fig. 15.9). One technique to help the clinician know the needle depth without needing a lateral fluoroscopic image is to touch the medial aspect of the transverse process cranial to the target level. The needle is then walked just off the transverse process anteriorly to reach the epidural space. Because of the risk of injection into the artery of Adamkiewicz risking a spinal cord infarct, a small particulate steroid such as dexamethasone should be considered.10,11,46 This artery is most commonly found at the T10 level, but can be present anywhere from T2 down to L3, and is usually found in the superior onehalf of the neuroforamen.46

Thoracic Transforaminal Epidural Steroid Injection

15.4 Facet Joint Injections

With the patient in the prone position, the location of the neuroforamen just inferior to the corresponding pedicle is identified at AP to15 degree lateral oblique view. The skin and soft tissue along the planned injection route are prepared with 1 mL of 1% lidocaine. A 25-gauge, 3.5-inch spinal needle is then taken down to the neural foramen’s most superior aspect using multiple fluoroscopic images just inferior to the pedicle. Proper needle position is verified with two views. The needle tip is always kept lateral to the 6 o’clock position of the pedicle on AP view. However, with the thoracic spine, the needle should not be

The facet joints, also called zygapophysial joints or Z-joints, are a pair of joints at the posterior aspect of each level of the spine. The facet joints have been shown to usually cause pain at certain areas of the body, as shown in the facet joint pain referral maps50,51,52,53 (▶ Fig. 15.10). Unfortunately, no physical examination findings have been proven to determine if pain is caused by the facet joints, so pain drawings and response to injection have been proposed to diagnose patients with facet joint–mediated pain.54,55 The goal of facet joint injections, similar to peripheral joint injections, is to decrease inflammation in the joint to help decrease pain from that

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Image Guidance, Monitoring, and Nonoperative Techniques

C2-3 C4-5 C6-7

C3-4 C7 C5-6

C7 T1

T3-4 T5-6 T7-8 T12 T9-10 T12 L5

a

b

Abnormal

d

joint. Local anesthetic is usually added to the injectate to help with more immediate relief. Frequently, even when the joint appears to be seen en face at the optimal joint angle of entry, the needle tip will only reach a bony end point that is not the joint space. Having a small bend at the needle tip is then very useful to quickly, easily, and less traumatically redirect the needle to enter the joint.

15.4.1 Lumbar Facet Joint Injections According to White and Panjabi,56 the lumbar facet joint is typically oriented obliquely 45 degrees anteromedial and posterolateral. However, the lumbar facet joint orientation can vary greatly from AP orientation, up to 80 degrees oblique. Also with degeneration, sometimes the posterior aspect of the joint may be oriented medially. Sometimes the fluoroscope machine alone will tell the clinician the best angle to enter the joint. However, in the author’s experience, sometimes, especially if the joint is curved, the fluoroscope images do not accurately show the optimal angle to enter the joint (▶ Fig. 15.11). Because of this, the author recommends, whenever possible, reviewing

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T6-7 T8-9 T10-11 L5

Normal

c

T4-5

Fig. 15.10 (a) Map showing pain referral patterns from cervical zygapophysial joints when stimulated in normal volunteers. (b) Map showing pain referral patterns from thoracic zygapophysial joints (T3–T4 to T10–T11) when stimulated in normal volunteers. (c,d) Map showing pain referral patterns from lumbar zygapophysial joints when stimulated in both asymptomatic (normal) and symptomatic (abnormal) patients. (Image b reproduced with permission from Lord et al.51 Image a reproduced with permission from Dreyfuss et al52 and image c reproduced with permission from Mooney and Robertson.50)

the joint anatomy on magnetic resonance imaging (MRI) or CT images prior to doing the injection. The joint should be viewed at multiple levels on AP images since the joint may have different orientations in the superior aspect compared to the middle or inferior aspect of the joint. With the patient in a prone position, the facet joint is identified and highlighted. The skin and soft tissue along the planned injection route are prepared with 1 mL of 1% lidocaine. A 25gauge, 3.5-inch spinal needle with a bent tip is then taken down to the facet joint using a tunnel view technique. Once bone is contacted, the needle is directed to enter the joint. Sometimes, if the joint cannot be directly entered due to arthritic changes, the needle can be directed to the inferior or superior joint capsule. Injection of a small amount of contrast with live fluoroscopic images verifies intra-articular location of the needle tip (▶ Fig. 15.11). The injectate at each joint should be 1 mL of a corticosteroid with local anesthetic. The lumbar facet joints should generally not be injected with more than 1.5 mL of volume.56 Before the needle is completely removed, the needle should be flushed with a small amount of local anesthetic or contrast or the stylet is reinserted.

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Injection-Based Spine Procedures and Diagnostic Procedures

Fig. 15.11 Lumbar facet joint injection. (a) On MRI scan, the right L4–L5 facet joint is fairly straight oriented about 30 degrees oblique. (b) With fluoroscopic imaging, the right L4–L5 facet joint is visible at 10-degree oblique images. (c) The right L4–L5 facet joint was entered at 30 degrees oblique with contrast verification.

15.4.2 Cervical Facet Joint Injections Posterior Approach The patient lies prone with a pillow under the chest, so the neck is flexed and rotated away from the side of injection. This helps move the jaw out of the fluoroscopic image and helps open up the facet joints. If the patient cannot comfortably turn in that direction due to physical restrictions, the cervical spine can be rotated to the side of injection. If the patient cannot turn their neck at all due to severe arthritis or contractures, the fluoroscope image intensifier can be rotated about 15 degrees away from the side to be injected so the jaw is not overlying the joints to be injected. The cervical facet joints from C2 to T1 generally lie in a plane tilted cranial anteriorly and caudal posteriorly. The cervical facet joints with this view are usually oriented 45 degrees anterior cranial and posterior caudal. Because of this, the fluoroscope image intensifier is tilted to the patient’s feet until the joints are seen en face.57 If the patient’s neck is flexed, tilt can be less than 45 degrees. The skin and soft tissue along the planned injection route are prepared with 1 mL of 1% lidocaine. A 25-gauge, 3.5-inch spinal needle with a bent tip is then taken directed to each facet joint using a tunnel view technique. Once bone is contacted, the needle is directed to enter the joint. Injection of contrast with live fluoroscopic images showing an arthrogram will verify intra-articular placement (▶ Fig. 15.12). Only a small amount of contrast should be used since the joints may only encase 1 mL or less of fluid. The injectate should be a corticosteroid with local anesthetic. Only 1 mL should be injected at each joint to avoid extravasation out of the joint and decrease specificity of the joint injection.28 Before the needle is completely removed, the needle should be flushed with a small amount of local anesthetic or contrast or the stylet is reinserted.

Lateral Approach With the patient in the side-lying position with the injectionside up or lying supine, the facet joint is identified and highlighted on lateral view. The skin and soft tissue along the planned injection route is prepared with 1 mL of 1% lidocaine.

Fig. 15.12 Cervical facet joint injection with the patient’s neck flexed over a pillow under the chest and rotated to the right. The image intensifier was tilted to the feet until the view was parallel to the facet joints.

Care must be taken to properly identify the correct joint space since both the left and right joints will be seen on lateral view. If the left and right cervical facet joints are hard to distinguish from each other, the fluoroscope can be slightly rotated or tilted to the foot so the left and right joints do not overlap.28 A 25gauge, 3.5-inch spinal needle with a bent tip is then directed to each facet joint using a tunnel view technique. Once bone is contacted, the needle is directed to enter the joint. Injection of a small amount of contrast with live fluoroscopic images verifies intra-articular joint placement. Only a small amount of contrast should be used since the joints may only encase one mL or less of fluid. The injectate at each joint should be 1 mL of a corticosteroid with local anesthetic. Before the needle is completely removed,

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161

Image Guidance, Monitoring, and Nonoperative Techniques the needle should be flushed with a small amount of local anesthetic or contrast or the stylet is reinserted.

15.4.3 Thoracic Facet Joint Injections The thoracic facet joint injection was first reported in 1987.58 The thoracic facet joints from T1 to T12 generally lie in a nearcoronal plane rotated about 70 to 80 degrees anterolaterally and posteromedially.56 Because of this, some authors feel the joints cannot be seen with fluoroscopic imaging, so the joints are entered by feel or with the aid of CT guidance.59,60 Knowing the anatomy and the limitations of the fluoroscope machine (can rotate all the way from 0 degrees AP view to 90 degrees lateral view on the side of the machine and to about 45 or 57 degrees oblique away from the side of the machine depending on the machine), with the patient lying prone, the fluoroscope machine can rotate to highlight the facet joints on the side away from the machine en face. To visualize the facet joints on the same side as the machine, either use a tilting table or place pillows under the patient on the side of the machine so the patient is tilted laterally about 20 to 30 degrees so the thoracic facet joints on the same side of the fluoroscope machine can be visualized when the fluoroscope machine is close to lateral view. The staff needs to make sure the patient is safely secured to the procedure table when doing this. Another option is to move the fluoroscope machine around to the other side or turn the patient on the procedure table so the machine is on the side opposite the joint to be injected so the image intensifier can be rotated about 70 to 80 degrees away from the side to be injected to visualize the facet joints. With the patient in a prone position, using an AP view, count up from the 12th rib or down from the 1st rib to identify the correct level to be injected. The approximate location of the facet joint posterior entry site is identified. The T5–T6 facet joint posterior entry site is at the inferior aspect of the joint just cranial to the T6 pedicle angled about 60 degrees anterior cranial and posterior caudal.56 Because of this, the skin about 1.5 inch caudal to that site (adjust depending on the patient’s body habitus) and soft tissue along the planned injection route are prepared with 1 mL of 1% lidocaine. A 25-gauge, 3.5-inch spinal needle with a bent tip is then taken down to approximate location of the inferior aspect of the facet joint along the pedicle line to ensure the lung and spinal cord are not punctured. Once bone is encountered, the fluoroscope is rotated based on the information above to highlight the facet joints and the needle is directed cranially or caudally as needed to enter the joint at the inferior capsule. When doing this, the clinician should be careful to not deviate the needle medially or laterally past the pedicles so the spinal cord or lungs are not punctured.28 Usually, the lamina over the inferior pedicle is reached first and then the needle is redirected cranially until the joint space is entered. Injection of contrast with live fluoroscopic images will highlight the joint (▶ Fig. 15.13). The injectate at each joint should be up to 1 mL of a mixture of corticosteroid with local anesthetic. One study showed the thoracic facet joint to hold about 0.6 mL.52 Before the needle is completely removed, the needle should be flushed with a small amount of local anesthetic or contrast or the stylet is reinserted. If bilateral thoracic facet joint injections are planned, the author will first have the patient lie prone with a pillow under the

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Fig. 15.13 Thoracic facet joint injection. At about 70 to 80 degrees medial oblique, the thoracic facet joint is visible with contrast verification of successful joint entry. Contrast is injected in the bottom joint.

side closer to the fluoroscope machine to rotate the patient about 30 degrees and inject the thoracic facet joints on the same side as the fluoroscope machine. After injection of the facet joints on the same side as the fluoroscope is completed, the pillow can be left in place to inject the facet joints on the other side since the fluoroscope can be rotated to the patient’s AP view as well as highlight the thoracic facet joints. However, if the clinician desires, the pillow can be removed to inject the thoracic facet joints on the other side of the fluoroscopy machine.

15.5 Medial Branch Blocks and Medial Branch Radiofrequency Neurotomy The medial branch nerves innervate the facet joint forming the neuroforamen of the exiting nerve, the facet joint caudal to that joint, and the adjacent deep paraspinal muscles.61,62 Because of this dual innervation, two medial branch blocks are needed to anesthetize one facet joint. Medial branch blocks are used to determine if a patient may benefit from a medial branch rhizotomy. Medial branch rhizotomy has been recommended if a patient has not responded to noninvasive treatment and responds temporarily to medial branch blocks.63,64,65 Patients who respond may have relief up to a year.63,64 For medial branch blocks, when injecting contrast, it is recommended to use live fluoroscopic imaging since intravascular uptake of the local anesthetic will prevent the medication from anesthetizing the medial branch nerves and gives a false-negative response.66 Some recommend doing comparative local blocks (once with a shorter acting local anesthetic and once with a longer acting local anesthetic) to determine if radiofrequency ablation should

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Injection-Based Spine Procedures and Diagnostic Procedures be tried.67,68 However, some recommend that blinded placebocontrolled blocks are the only valid means of establishing a diagnosis of lumbar facet joint pain.69

15.5.1 Lumbar Medial Branch Blocks With the patient in a prone position, the medial branch nerve is not seen, but has been shown in the lumbar spine to be consistently located along the junction of the superior articular process and transverse process where it passes under the mamilloaccessory ligament and runs about 5 mm before it divides into smaller branches.70,71 This location is best visualized at about 15 degrees oblique view. The L5 medial branch lies at the junction of the superior articular process and the sacral ala. The skin and soft tissue along the planned injection routes are prepared with 1 mL of 1% lidocaine. A 25-gauge, 3.5-inch spinal needle with a bent tip is then directed to each medial branch using a tunnel view technique. Needle position is perfected using multiple fluoroscopic views. Injection of contrast with live fluoroscopic images verifies soft tissue flow placement without intravascular uptake (▶ Fig. 15.14). Once needle position is ascertained, injection is completed at each location with 0.5 mL of local anesthetic.57

15.5.2 Thoracic Medial Branch Blocks With the patient in a prone position, the medial branch nerve is not seen, but has been shown in the thoracic spine to assume a reasonably constant course crossig the superolateral corners of the transverse processes and then passing medially and inferiorly across the posterior surfaces of the transverse processes before splitting into smaller branches.72 Because of this, the superolateral corners of the transverse processes are more

Fig. 15.14 Lumbar medial branch block. Using a 15-degree oblique view, the needles are advanced to the junction of the superior articulating process and transverse process. Live fluoroscopic images with contrast verify there is no intravascular flow.

accurate target points.72 However, the T5–T8 medial branch nerves curve in the soft tissue superior to the superolateral corners of the transverse process.72 The skin and soft tissue along the planned injection routes are prepared with 1 mL of 1% lidocaine. A 25-gauge, 3.5-inch spinal needle with a bent tip is then directed to each medial branch using a tunnel view technique. Needle position is perfected using multiple fluoroscopic images. Injection of contrast with live fluoroscopic images verifies soft tissue flow placement without intravascular uptake. Once needle position is ascertained, injection is completed at each location with 0.5 mL of local anesthetic.

15.5.3 Cervical Medial Branch Blocks With the patient in a prone position, the medial branch nerve is not seen, but has been shown in the cervical spine to consistently cross the center of the articular pillars on lateral view. The skin and soft tissue along the planned injection routes are prepared with 1 mL of 1% lidocaine. A 25-gauge, 3.5-inch spinal needle with a bent tip is then directed along the lateral aspect of the articular pillar using AP view until bone is contacted. The needle is then walked laterally with lateral view to the center of the articular pillar using multiple fluoroscopic images. Injection of contrast with live fluoroscopic images verifies soft tissue flow placement without intravascular uptake (▶ Fig. 15.15). Injection is completed at each location with 0.5 mL of local anesthetic.61

15.5.4 Medial Branch Radiofrequency Neurotomy (Rhizotomy) Medial branch radiofrequency neurotomy, also known as facet rhizotomy, was first described by Shealy in 1975.73 It is recommended that the electrodes be directed parallel to the target

Fig. 15.15 Cervical medial branch block. Lateral view shows the needle tips are in the center of the articular pillars.

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Image Guidance, Monitoring, and Nonoperative Techniques nerves to maximize the length of the nerves lesioned and increase the chance of successful lesions.74,75,76 In the lumbar spine, the medial branch nerve is consistently located along the junction of the superior articular process and transverse process where it passes under the mamilloaccessory ligament70,71 (▶ Fig. 15.16). The electrodes should be inserted inferolaterally to the target lesion and then directed obliquely to the superior articular facet overlying the target nerve as parallel as possible.74,75 In the thoracic spine, the medial branch nerves cross the superolateral corners of the transverse processes and then pass medially and inferiorly across the posterior surfaces of the transverse processes.72 Because of this, the electrodes should be inserted obliquely from an inferomedial position to target nerve. In the cervical spine, the approach for medial branch radiofrequency neurotomy is similar to doing a medial branch block with a posterior approach (▶ Fig. 15.17). Once the electrodes are in the correct anatomic location based on fluoroscopic images, electrical stimulation at 50 Hz for sensory stimulation at 0 to 1 V is used with slowly increasing voltage to see when the patient first feels the stimulation and where the stimulation is felt. Ideally, at a low voltage, the patient should feel the stimulation focally in the paraspinal region and not in the limbs. Then, electrical motor stimulation at 2 Hz at 1 to 1.5 V should stimulate the medial branch nerve to cause paraspinal muscle contraction. However, especially in the lower lumbar paraspinal region, paraspinal muscle atrophy and replacement with connective tissue may make the contractions hard to see, so the clinician can try palpating for muscle contractions. The stimulation voltage should then be increased to at least 2 to 3 V to ensure

the electrode tip is not near the main nerve root. Once proper electrode placement is verified with electrical stimulation, 0.5 to 1 mL of local anesthetic is injected and the nerve is lesioned at 75 to 80 °C for 90 seconds in the lumbar spine and 60 seconds in the cervical spine.77,78

15.6 Sacroiliac Joint Injection The sacroiliac joint is a true arthrodial joint but is unique in that the cartilage on the sacral side is hyaline cartilage and on the ilial side is fibrocartilage.79 With fluoroscopic guidance, the joint is best visualized at the inferior aspect. With the patient in a prone position, the sacroiliac joint is identified and highlighted. The skin and soft tissue along the planned injection route are prepared with 1 mL of 1% lidocaine. A 25-gauge, 3.5inch spinal needle is then taken down to the sacroiliac joint. Once bone is contacted, the needle is directed to enter the sacroiliac joint from the sacral ala. Injection of contrast with live fluoroscopic images should highlight the joint (▶ Fig. 15.18). The injectate should be 2 mL of a mixture of corticosteroid and local anesthetic. Before the needle is completely removed, the needle should be flushed with a small amount of local anesthetic or contrast or the stylet is reinserted. Sometimes the joint is best visualized with a straight AP view but sometimes the image intensifier may need to be rotated up to 15 degrees medial oblique. Sometimes the joint will be able to be seen as a fully radiolucent line. Sometimes the joint will be so convoluted the joint will not be easily seen. If the joint is not fully seen at any angle but the anterior and posterior as-

Fig. 15.16 Lumbar medial branch radiofrequency neurotomy. (a) Lateral view. (b) AP view with live fluoroscopic images verifies soft tissue flow of contrast without intravascular flow.

Fig. 15.17 Cervical medial branch radiofrequency neurotomy. (a) Lateral views show the needle tips are advanced to the center of the articular pillars. (b) AP view with live fluoroscopic images shows soft tissue flow without intravascular uptake of contrast.

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Injection-Based Spine Procedures and Diagnostic Procedures

Fig. 15.18 Sacroiliac joint injection. Contrast is flowing into the inferior joint capsule.

pects of the joint form a “K,” “X,” or “V” sometimes the intersection of the lines form radiolucent area which can be targeted. If the joint is never radiolucent at any angle, the inferior joint capsule can be targeted.

15.7 Lumbar Discogram It has been shown that advanced radiologic imaging tests such as MRI and CT scans of adults have false-positive rates of about 20 to 36% and 20%, respectively.80,81,82,83 This study has also been reported to be able to find problems even with a normal MRI scan.84 Early study suggested discography was positive in 36% of 30 prison inmates without history of low back pain.85 Others have felt this study was flawed due to selection bias since 23% of the injected discs were judged invalid and excluded from analysis due to technical difficulties.86,87 Later studies have shown using more rigorous techniques can have specificities of 90 to 100%.88,89 The goal of provocative discography is to help differentiate symptomatic from asymptomatic intervertebral discs. Because of this, the clinician needs to evaluate the patient to determine the patient’s usual pain location and severity. Also, usually at least three levels should be tested, to help verify that at least one level does not recreate the patient’s pain. Sedation can be used, but the patient must be awake and alert at the time of contrast administration. Narcotic medications which can block the pain response should be avoided until after the procedure is completed. Discitis is felt to be one of the worst complications of a discogram.90 To decrease the risk of infections, some have suggested intradiscal antibiotics or a double-needle technique.90,91,92 More recently, discograms have also been shown to have other risks such as accelerated disc degeneration, disc herniation, loss of disc height and signal, and the development of reactive end plate changes compared to matched controls.93 Discograms in subjects with significant emotional and chronic pain problems

have a lower specificity of 80% and may cause increased pain for at least 1 year after injection.94,95,96 Given the risks, careful consideration of risk and benefit should be used in recommending disc injection procedures93 Because of this, a discogram should not be performed unless a surgeon feels the results will help determine if surgery should be considered. With the patient in the prone position, fluoroscopy is used to identify the targeted vertebral interspace parallel to the superior end plate of the inferior vertebral body, which is then rotated about 30 degrees oblique so the superior articulating process is overlying the middle of the intervertebral disc (▶ Fig. 15.19a). The skin, subcutaneous tissue, and muscle in line with the planned approach are anesthetized with 1% lidocaine. Under fluoroscopy, a 25-gauge 5- to 8-inch or 23-gauge 6-inch spinal needle with a bent tip is inserted and directed to the intervertebral disc just anterior to the superior articulating process and then into the central nucleus of the intervertebral disc. It is important to direct the needle to the middle third of disc since injection into the annulus fibrosis can cause pain.97 This is repeated for each needle to be tested. Next, the testing phase begins with injection of 9 mL contrast (nonionic contrast) mixed with 1 mL of clindamycin 150 mg/mL (for a total concentration of 15 mg/mL) separately into each of the tested intervertebral discs in a random manner (▶ Fig. 15.19b,c). The clinician should maintain constant communication with the patient during the test. It has been shown that pressure-controlled discography showing highly sensitive discs (< 15 psi above the opening pressure) had better longterm outcomes with interbody/combined fusion rather than with intertransverse fusion.98 Once completed, the needles are withdrawn, the skin is cleaned, and sterile bandages are placed over the needle puncture sites. After the procedure, the patient should have a postdiscogram CT scan to better visualize the spread of contrast.99,100 At the L5–S1 level, because the sacral and iliac crest may extend cranially, forcing the needle trajectory to reach the L5–S1 intervertebral disc too steeply, direct the needle to the center of the L5–S1 intervertebral disc. If needed, a double-needle technique can be used. A larger 18- to 20-gauge, 3.5-to 5-inch needle (see ▶ Fig. 15.3f) is directed just above the junction of the superior articulating process and sacral ala. Then, a thinner longer 25- to 22-gauge, 5.5- to 8-inch spinal needle with a bent tip is inserted inside the large needle directed to the center of the L5–S1 intervertebral disc. A technique previously described uses a gradual bend of the thinner needle about 1 inch from the tip (see ▶ Fig. 15.3h).101 However, a second double-needle technique can be tried if a greater angulation of the needle is required. First, an 18-gauge Tuohy needle (or similar needle such as Hustead or Weiss) can be used as the introducer needle. The Tuohy needle, actually invented by Huber, with a curved bevel needle tip, was popularized by Tuohy to facilitate the introduction of subarachnoid catheters in the cephalad direction.39,102 The larger needle caliber and curved bevel needle tip will also help guide the inside needle to have a sharper curve when it first extends beyond the bevel of the introducer needle (▶ Fig. 15.20a). After extending about 1 inch beyond the introducer needle, the needle exiting the Tuohy needle still has a sharper curve. Second, an inside 25-gauge needle can be bent about 3 mm from the tip about 15 degrees where it can still fit inside the 18-gauge Tuohy needle. In ▶ Fig. 15.17c, after extending about 1 inch, the needles have about the same end point,

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Fig. 15.19 Lumbar discogram. (a) About 30 degrees oblique, needle tip localized the insertion site over the intervertebral disc just lateral to the superior articulating process; (b) lumbar lateral view showing contrast flowing into the intervertebral discs. There is leakage of contrast from the L5–S1 disc into the anterior epidural space; (c) lumbar AP view with contrast highlighting disc herniations at all three levels; (d) lumbar AP view showing the double-needle technique at L5–S1 level with a bend about 3 mm from the tip.

Fig. 15.20 Double-needle techniques using a 25-gauge needle with the same gradual bends with a 20-gauge Quincke tip needle and an 18-gauge Tuohy needle as introducers. (a) As the needles first exit the introducer needles, the needle exiting the Tuohy needle has a sharper curve. (b) When the needles are extended 1 inch into the tissue, the needle exiting the Tuohy needle continues to have a sharper curve. (c) When comparing the gradual bend about 1 inch from the tip and a focal bend about 3 mm from the tip, after extending about 1 inch, the needles have about the same end point, but with the author’s experience, the denser annulus fibrosis will usually direct the needle tip to the center of the disc.

but with the author’s experience, when the Tuohy is advanced to the L5–S1 intervertebral disc, the sharper initial curve when exiting the Tuohy needle into the denser annulus fibrosis will usually direct the needle tip to the center of the disc (see ▶ Fig. 15.19d). If needed, combining a bent tip at 3 mm from the tip and a gradual bend about 1 inch from the tip with an 18gauge Tuohy introducer needle will have the greatest curve. However, this should not be done automatically with every patient since too much of a curve will cause the needle to be directed too posteriorly in the posterior annulus fibrosis instead

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of the center of the disc. The amount of bend and type of bend and introducer needle should always be tailored to the patient’s anatomy.

15.8 Complications of Spinal Injections Common side effects after injection procedures include local soreness, local bleeding, and local swelling at the needle insertion

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Injection-Based Spine Procedures and Diagnostic Procedures site. These are managed with analgesics and local ice. Some patients may also experience vasovagal response. However, depending on the procedure being done, there may also be rare risks of serious complications such as nerve damage, stroke, and spinal cord injury. Because of this, the clinician should be trained and certified in airway management as well as advanced cardiac life support (ACLS) protocols. Bleeding complications may be minimized by stopping aspirin and nonsteroidal anti-inflammatory drugs for 5 to 7 days prior to epidurals and more invasive procedure. Other stronger blood thinners such as warfarin and newer blood thinners such as dabigatran and rivaroxaban should also be held prior to the procedures based on their duration of action.

[9]

[10] [11]

[12] [13] [14]

15.9 Conclusion

[15]

Injection-based spinal procedures are an important part of the treatment options for spinal pain. However, the clinician needs to know their strengths and weaknesses compared with the other treatment options such as medications, physical therapy, alternative medicine, and surgery. Only then can a comprehensive plan be tailored to each patient to optimally treat the patient’s problem.

[16]

Clinical Caveats ●

●

●

It is critical the clinician understand the three-dimensional anatomy where the injection is performed as well as master guiding the needle to ensure procedural success and minimize patient risk. When the needle is close to the target, the fluoroscope needs to be rotated to image the body where the needle will not be advanced too far and cause complications (e.g., lateral view with the interlaminar epidurals to minimize risk of puncturing the thecal sac or spinal cord). The patient must also be fully educated to the procedure being done, the risks, benefits, and alternative treatments so that a proper informed consent is obtained before the procedure is done.

[17] [18]

[19] [20] [21]

[22] [23] [24]

[25]

[26]

[27] [28]

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[100] Sachs BL, Vanharanta H, Spivey MA, et al. Dallas discogram description. A new classification of CT/discography in low-back disorders. Spine. 1987; 12 (3):287–294 [101] Fortin JD. Lumbar and thoracic discography with CT and MRI correlations. In: Lennard TA, ed. Physiatric Procedures in Clinical Practice. Philadelphia, PA: Hanley & Belfus; 1994:163–184 [102] Huber RL, inventor. Huber RL, assignee. Hypodermic needle. US patent 2,409,979. October 22, 1946

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16 Stereotactic Radiosurgery for Tumors of the Spine Maha Saada Jawad and Daniel K. Fahim Abstract Stereotactic radiosurgery for tumors of the spine has emerged as a safe and effective method for the primary treatment of localized spinal tumors or as salvage treatment in patients who have undergone prior irradiation to the spine. Treatment can be delivered using linear accelerator–based radiation treatment, incorporating the use of image-guided radiotherapy. Treatment planning using intensity-modulated radiation therapy or volumetric modulated arc therapy allows for delivery of highly conformal ablative tumor doses, while minimizing dose to surrounding organs at risk. Delayed treatment–related toxicity can include vertebral compression fractures or radiation-induced myelopathy. Appropriate patient and tumor selection, as well as careful attention to dose-volume data, is essential in minimizing the risks of these toxicities. Several studies have yielded favorable results with respect to tumor control and pain relief following stereotactic spinal radiosurgery, making it a favorable option for well-selected spinal tumors. Keywords: radiosurgery, stereotactic radiosurgery, spine tumors, radiation, treatment planning

16.1 Introduction Stereotactic radiosurgery (SRS) of the spine has emerged as a safe and effective method of primary treatment for localized spinal tumors, as well as a salvage option in patients who have received prior irradiation. The spinal SRS technique was developed by merging concepts and technology from intracranial SRS, frameless stereotaxis, and modern radiotherapy techniques. Intracranial SRS was first used by a neurosurgeon, Lars Leksell, in 1951,1 who introduced the concept of delivering a single high dose of radiation to a stereotactically defined target. Improvements in machine accuracy, multiplanar imaging, and computer speed have led to exponential growth in the use and effectiveness of intracranial SRS since that time, most commonly Gamma Knife radiosurgery (although other systems are also available).2,3,4,5 Many years of careful study of intracranial SRS were required to obtain even a rudimentary understanding of dose tolerance of critical organs such as the optic apparatus, trigeminal and facial nerves, brainstem, and motor cortex.6,7 Clear understanding of dose-volume toxicity also required the study of large numbers of treated patients.8,9 The dose–response relationships of benign and malignant tumors, as well as other benign conditions such as arteriovenous malformations and trigeminal neuralgia, also required extensive study, with the optimal total dose and dose fractionation still subjects for debate. However, certain basic information is now widely accepted, such as the tumor response and complication rates for single-dose treatment of acoustic neuromas and the high sensitivity to dose of sensory cranial nerves.10,11,12,13 Taking the lessons learned from intracranial SRS, the application of extracranial SRS first required the advancement of other methodologies. Frameless stereotaxis was originally developed for real-time intraoperative guidance.14,15 More recently, this

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technique has been introduced into the radiation suite to allow real-time tracking for extracranial stereotactic targets.16 Simultaneously, advancements in the delivery of radiation therapy including three-dimensional treatment planning, mini-multileaf collimators, intensity-modulated radiation therapy (IMRT), and volumetric modulated arc therapy (VMAT) enabled dose escalation with precise targeting and conformality.2,3,4,5 Additionally, the increasing use of image-guided radiotherapy (IGRT) has allowed further improvements in treatment delivery and accuracy. Taken together, these techniques have ushered in the modern age of spinal SRS.

16.2 Potential for Spine Stereotactic Radiosurgery Tumors involving the spinal column are common, the majority of which represent spinal metastases. Approximately 40% of patients with malignancy will develop spinal metastases, with over 18,000 new cases diagnosed in North America each year.17, 18 Patients may present with pain, neurological compromise, or vertebral fractures. While some tumors are amenable to surgical resection, many patients with cancer are poor surgical candidates, requiring some other less invasive form of therapy. For palliation, steroids, medical management of pain, and conventional external beam radiation therapy (EBRT) are frequently used. Although conventional EBRT does offer effective pain relief and maintenance of neurological function, options are limited in patients who fail treatment. Many patients experience recurrent symptoms within 6 to 9 months following EBRT. Initial studies of extracranial SRS demonstrated the accuracy and reproducibility of the various systems.16,19,20,21,22,23,24,25,26,27 More recently, larger case series and retrospective studies have emerged, demonstrating effective pain and tumor control following SRS.28,29,30,31,32,33,34,35,36

16.3 Challenges of Spine Stereotactic Radiosurgery The advancement of SRS as a treatment for tumors of the spine requires a thorough understanding of possible dose-related toxicity. Radiobiologic models have limitations for deciding what the maximal fraction dose and total dose should be, except at the extremes.37,38,39,40,41 Extending our knowledge about the safety and efficacy of intracranial SRS to the spine is difficult. It is not yet known whether the dose tolerance of the spinal cord is similar to those of the brainstem, cortex, or optic apparatus, which exhibit a wide range of sensitivity to single and cumulative doses. The spinal cord is smaller and more compact than even the brainstem, and peripheral nerves have no real counterpart in the cranial nerves. In addition, the effects of chemotherapy, surgery, medical conditions such as diabetes, and previous radiation treatments also have to be considered to fully understand dose-related toxicity of spine SRS.8,39 In addition, toxic effects of spine SRS on solid organs including the

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Stereotactic Radiosurgery for Tumors of the Spine heart, lung, kidneys, esophagus, bowel, and liver need to be considered. Optimal dosage regimens, margins, and early and late toxicity associated with this new technology continue to be studied. Finally, although theoretical accuracy has been demonstrated in all of the commercially available systems, the accuracy and reproducibility of treatment delivery in patients has yet to be determined.

16.4 Stereotactic Radiosurgery Technique Spine SRS is typically delivered using linear accelerator–based IMRT or VMAT in a radiosurgical treatment suite equipped with image-guidance, mini-multileaf collimation, and integrated treatment planning software with automated image fusion.

16.4.1 Patient Immobilization and Imaging During treatment simulation, the patient is positioned with their arms above their head or high on the chest, depending on the treatment location. Extracranial immobilization is performed using an Elekta BodyFIX (Elekta; Crawley, UK). The BodyFIX system is composed of a BlueBAG with a total body cover sheet, using a vacuum pump to create accurate and precise patient positioning and immobilization(▶ Fig. 16.1). The system is designed to reduce both voluntary and involuntary motion during treatment. Once the patient is immobilized, CT simulation is performed in the planned treatment position utilizing a CT scanner (Phillips Brilliance Big Bore, Phillips Medical Systems; Andover, MA). The area of interest and at least two vertebral bodies above and below the tumor level are scanned with 2- to 3-mm-thick contiguous slices. The field of view is set wide enough to encompass the area of interest as well. CT images are then transferred using the local area network and standard DICOM software to the SRS treatment planning system (Pinnacle, Phillips; Fitchburg, WI). In some patients, spinal MRI planning is also done with the

patient immobilized in the BodyFIX apparatus. Imaging sequences include gadolinium-enhanced, T1-weighted, contiguous 3mm images covering the same area covered with the CT images and also 2-mm images focused on the involved vertebral bodies. Additional sequences required for specific cases are also used. MRI images are transferred directly to the planning station in the same manner as the CT images. These images are then fused with the CT images to aid in target delineation. In patients who do not undergo MRI with immobilization but have a pretreatment diagnostic spinal MRI performed close to the CT simulation date, the diagnostic images are fused with the treatment planning CT images to aid in target delineation.

16.4.2 Treatment Planning Once the CT images are imported and fused with either diagnostic or planning MRI images, the radiation oncologist and neurosurgeon work together to delineate volumes for the target and organs at risk, and a treatment plan can be developed using the treatment planning system.

Target Volumes The target lesion is outlined on both the CT and MRI images by the radiation oncologist and neurosurgeon, with the assistance of a neuroradiologist as needed(▶ Fig. 16.2). The lesion can be defined by enhancing tumor mass or by bony changes directly attributable to tumor invasion. This is defined as the gross tumor volume, or GTV (extent of gross tumor). The clinical target volume (CTV) is then defined as the GTV plus a margin to account for subclinical disease. This volume represents an anatomical-clinical concept; it must be treated adequately in order to achieve the aim of the radiation therapy. The CTV is typically equal to the GTV in cases of spine SRS. The third volume to be defined is the planning target volume (PTV), which is a geometrical concept. The PTV accounts for uncertainties in planning or treatment delivery, which could include organ motion or setup errors. The PTV is defined as a 2-mm expansion of the GTV in three dimensions, excluding the volume represented by a 2-mm expansion of the spinal cord.

Fig. 16.1 Extracranial immobilization is performed using an Elekta BodyFIX (Elekta; Crawley, UK). The BodyFIX system is composed of a BlueBAG with a total body cover sheet, using a vacuum pump to create accurate and precise patient positioning and immobilization. (Reproduced with permission from Elekta: http://ecatalog.elekta.com/oncology/bodyfix(r)/products/ 0/22325/22341/20231/bodyfix(R).aspx.)

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Fig. 16.2 The target lesion is outlined on CT and MRI images by a radiation oncologist and neurosurgeon, with the assistance of a neuroradiologist as needed.

Critical Organ Definition Critical organs considered to be at risk for toxicity during treatment are defined as the organs at risk (OARs). These represent normal tissues whose radiation sensitivity may significantly influence treatment planning and/or prescribed dose. OARs are delineated anatomically using both CT and MRI images. The organs defined will depend on the level of the spine receiving treatment. These may typically include esophagus, lung, liver, heart, kidneys, bowel, and aorta. Some institutions also define the endplates as a critical structure due to the potential risk of increased fracture with high-dose radiation; however, this is currently being studied and not considered standard practice at this point. In all cases, a spinal cord volume must be defined. The spinal cord is considered the most critical structure. The cord is defined anatomically at least two vertebral bodies above and below the area of tumor involvement, and is defined by the thecal sac, usually visualized best on MRI. In addition to the spinal cord volume, the spinal cord + 2 mm is also defined, which is used in determining the PTV as previously described.

Dosimetric Planning The dose of radiation is prescribed to achieve coverage of a given isodose line. The concept of the isodose line reflects the volumetric and planar variation in absorbed radiation dose in tissue. These distributions are depicted by the isodose lines, which are expressed as a percentage of the dose at a reference point. For spinal SRS, the prescription isodose is chosen such that ≥ 80% of the PTV receives the prescription dose, ensuring coverage of the GTV. Careful attention is given to the dose constraints of the OARs. When tolerance to the OARs is exceeded,

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coverage to the target may have to be compromised. The most important dose constraint is that of the spinal cord, which is typically limited to a maximum dose of 10 Gy to 0.1 mL of the spinal cord volume, and 13 Gy to 0.1 mL of spinal cord + 2 mm. In patients who have had prior irradiation to the SRS site, adjustments in the dose constraints may be required to account for prior dose received by the OARs. Treatment optimization using IMRT or VMAT is completed. Four choices of treatment are presented by the software for review. One option, PTV-only, disregards all OAR to deliver the optimal dose to the lesion. Another option, OAR-high, gives maximal protection to OAR even at the cost of dose delivery to the lesion. The remaining treatment options, OAR-normal and OARlow, give variable weights to OAR and lesion dose. Once the optimal treatment optimization has been selected, the final plan is approved by both the radiation oncologist and the neurosurgeon.

Dose Selection A wide variety of total dose and fractionation schemes have been reported.27,28,30,31 At our institution, a dose of 16 to 18 Gy in a single fraction is typically chosen, if it can be achieved while respecting OAR constraints. The total dose prescribed and dose per fraction (in the case of multiple fractions) are selected on the basis of tumor location, tumor size and volume, proximity to critical structures, and previous radiation treatment within the given treatment field. In most cases, single-fraction treatment is the method of choice. However, in larger volume targets and previously irradiated areas, multifraction regimens are selected to offer further sparing of the critical structures. Patients may receive anywhere from one to five total treatments.

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Stereotactic Radiosurgery for Tumors of the Spine

16.4.3 Treatment Delivery At the time of treatment delivery, patients are positioned and immobilized in the BodyFIX apparatus on the treatment table. Once the patient is immobilized, image guidance is used to evaluate patient positioning and organ motion prior to treatment. This is performed with cone-beam CT (CBCT)—an X-ray volumetric imaging system which is mounted on the linear accelerator used at the time of treatment delivery with the patient in the treatment position. A three-dimensional CBCT (3D-CBCT) is taken to assess alignment and position in the x-, y-, and z-axes to a tolerance of 2 mm. If the position is found to be ≥ 2 mm off, adjustments are made. A 3D-CBCT is then repeated to ensure that the proper position has been achieved. If necessary, a third 3D-CBCT is performed. The treatment position is then verified with an orthogonal pair of X-ray images. Both the 3D-CBCT and orthogonal pair images must be reviewed and approved by the treating radiation oncologist prior to treatment delivery. The setup time including positioning, alignment, and quality checks for each treatment varies, ranging from 30 to 60 minutes. Radiation treatment is then delivered via a linear accelerator, most commonly using an energy of 6 MV, but as high as 15 MV if needed. The total beam-on treatment time varies depending on the complexity of the treatment plan and number of beams used, but can range from 10 to 20 minutes. Quality checks are performed daily, monthly, and annually on the linear accelerator as indicated. Complete IMRT or VMAT dose quality assurance is completed for each treatment plan prior to delivery of treatment. This can take several hours and is usually performed in the day prior to the first planned treatment.

16.5 Complications 16.5.1 Treatment-Related Toxicity Treatment-related toxicity is assessed immediately following treatment to monitor acute SRS complications. Following treatment, patients are then seen in follow-up with radiation oncologist, neurosurgeon, or both, at 8 and 12 weeks posttreatment, and then at approximately 3-month intervals (with additional follow-up as needed). At each follow-up, an assessment of pain control, neurological status, radiation-related toxicity, and local control is performed. Local control is typically evaluated with the use of MRI and/or CT images. Specific radiation-related toxicities will highly depend on the anatomic location of the treatment being delivered. In the acute setting, some of the possible side effects include pain, dysphagia, mucositis, esophagitis, nausea, diarrhea, or fatigue. In our experience, however, these side effects are rare and the majority of patients tolerate spinal SRS without incident. In the subacute setting, pneumonitis and myositis are possible. The most significant and feared complications of spinal SRS in the delayed setting are those of radiation-induced myelopathy (RIM) and vertebral compression fractures (VCF).

16.5.2 Radiation-Induced Myelopathy RIM is rare, but represents one of the most serious late radiation toxicities following spinal cord irradiation and can lead to paralysis or death. RIM is likely a multifactorial process, involving both

damage to the white matter and damage to the local vasculature. Acute RIM can lead to sensory or motor deficits, which are usually reversible. In delayed RIM, damage can potentially be permanent, leading to profound weakness, paresthesia, spasticity, pain, or bowel/bladder incontinence. Given the devastating consequences, understanding the need to respect spinal cord radiation tolerance is of paramount value in spinal SRS. Delayed RIM was examined by Gibbs et al,42 in a series of 1,075 patients with spinal cord tumors treated with CyberKnife radiosurgery at Stanford and the University of Pittsburgh. Of the 1,075 patients, 6 developed RIM in a mean time of 6.3 months and their data were retrospectively reviewed. Radiation doses ranged from 12.5 to 25 Gy in one to five fractions with 90% PTV coverage and a spinal cord dose constraint of 8 to 10 Gy maximum. Clinical symptoms were correlated with MRI findings, and specific biologic radiation dose equivalents were calculated. Logistic regression failed to demonstrate any predictors of spinal cord injury.42 Other series have demonstrated similarly low rates of RIM following stereotactic body radiation therapy. A multi-institutional collaboration between the University of Toronto, the University of California, San Francisco, and the MD Anderson Cancer Center43 evaluated the probability of RIM specific to spinal SRS. The relationship between dose at a given volume and the occurrence of RIM was determined using a logistic regression model, utilizing specific dose-volume data from treatment plans of 9 patients with RIM compared to 66 patients without. The greatest significance for basing dose thresholds was found for the maximum point value, or Pmax. Based on logistic estimates, the probability of RIM was < 5% when limiting thecal sac Pmax to 12.4 Gy in one fraction, 17 Gy in twofractions, 20.3 Gy in three fractions, 23 Gy in four fractions, and 25.3 Gy in five fractions.43 As the majority of centers follow more conservative dose constraints in comparison, the likelihood of RIM is low with current treatment planning methods.

16.5.3 Vertebral Compression Fractures A more frequent late effect of spinal SRS is compression fracture of the vertebral body. Crude rates of VCF following spinal SRS range from 11 to 39% in previously reported series. These rates are much higher in comparison to conventional radiation, where VCF is seen in < 5% of cases. The management and prevention of VCF is a major challenge because the tumor itself typically lies within the bone needing irradiation. Several series have explored predictors of VCF following SRS. The first major report of the risk of VCF following SRS is from Memorial Sloan-Kettering Cancer Center in 2009.44 This series included 62 patients with 71 sites treated using spinal SRS. Tumors received a median of 24 Gy in a single fraction. At a median follow-up of 19 months, the VCF rate following SRS was 39%, with a median time to fracture of 25 months. Predictors for VCF included larger volume of vertebral body involvement (> 40%), lytic tumors, and lesions in T10–sacrum. Interestingly, the rate of VCF was not associated with the radiation dose.44 Other centers have since reported their experience. In 2012, the MD Anderson Cancer Center45 reported the VCF outcomes of 93 patients who underwent spinal SRS to 123 vertebral bodies to doses of 18 to 30 Gy in one to three fractions. At 16 months of follow-up, new or progressive VCF was seen in 20%. Age over 55, preexisting fracture, baseline pain, and lytic lesions were

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Image Guidance, Monitoring, and Nonoperative Techniques predictors for VCF.45 Multi-institutional data were reported in 2013 by Sahgal et al46 for 252 patients with 410 spinal segments treated with spinal SRS. The rate of VCF in this series was lower, reporting a 14% rate at a median follow-up of 12 months. The 1- and 2-year cumulative incidence of VCF was 12.4 and 13.5%, respectively. Baseline fractures, lytic lesions, and spinal deformity were predictive of VCF. Unlike the prior studies, this series also found that radiation dose per fraction was a significant predictor, with the greatest risk seen at a dose of ≥ 24 Gy per fraction (vs. 20–23 Gy and ≤ 19 Gy).46 Unpublished data from our institution as part of a multi-institutional collaboration with seven total institutions evaluated 704 spinal tumors treated with spinal SRS to a median dose of 21 Gy (6–65 Gy). At a median follow-up of 10 months (1–33 months), the incidence of a new or progressive VCF was approximately 8%. Patients with a solitary metastasis at the time of SRS were more likely to develop a VCF, as well as those tumors with larger treatment volumes, higher prescription doses, and preexisting VCF at the site of treatment. With all of these factors in mind, more consideration could be made for percutaneous cement augmentation procedures in appropriately selected patients prior to spinal SRS, to help minimize the risk of VCF development.

16.6 Outcomes Multiple studies have evaluated the effectiveness of radiation therapy in the management of pain relief from bony metastases using either multifraction or single-fraction radiotherapy.47,48,49 Several of these studies demonstrated no significant difference in overall or complete pain relief between the multifractionated or singlefractioned regimens, providing the rationale for further study of single-fraction treatment for bony metastases. In these series, however, single-fraction treatments were delivered using conventional radiotherapy methods using a dose of 8 Gy. Current practice today utilizes much higher single-fraction doses, owing to the fact that treatment planning is much more conformal, allowing dose escalation in a safe manner. With more centers performing spinal SRS, increasing data are becoming available regarding the safety and efficacy with regard to pain relief and local control. To date, the largest single-institution series of spinal SRS in the literature comes from the University of Pittsburgh Medical Center.32 In this prospective, nonrandomized, longitudinal cohort study, 500 patients with spinal metastases were treated with single-fraction SRS using the CyberKnife Image-Guided Radiosurgery system. The study allowed patients with prior radiation therapy (n=344, 30 Gy in 10 fractions or 35 Gy in 14 fractions), in which further conventional radiotherapy was not possible. Patients with overt spinal instability or neurological deficit from bony compression of neural structures were excluded. A mean dose of 20 Gy (12.5–20 Gy) was delivered, prescribed to the 80% isodose line. At a median follow-up of 21 months, long-term radiographic tumor control was demonstrated in 90% of patients who had received SRS as primary treatment, and in 88% of patients who had received prior irradiation. Long-term pain control was demonstrated in 86% of patients overall following SRS. None of the patients developed radiation-induced spinal cord damage. Other smaller series have demonstrated similar outcomes. Yamada et al36 evaluated 93 patients with 103 spinal metastases without high-grade epidural compression treated with

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IMRT-based SRS at Memorial Sloan-Kettering Cancer Center. Patients were excluded for mechanical instability, epidural spinal cord compression, or previous radiotherapy to the SRS site. Patients received single-fraction SRS to a median dose of 24 Gy (18–24 Gy) prescribed to the 100% isodose line. The overall actuarial local control rate was 90% at a median follow-up of 15 months, noting a 9-month median time to local failure. Radiation dose was a predictor for local control, with 95 versus 80% local control in 24 Gy versus 18 to 23 Gy, respectively. Durable symptom palliation was achieved in all locally controlled patients, with no radiculopathy or myelopathy noted. Ahmed et al35 reported the experience of the Mayo Clinic, which prospectively assessed 85 malignant spinal lesions in 66 patients, 25% of which received prior radiotherapy to the site. With similar exclusion criteria as prior studies, eligible patients received a median of 24 Gy in one to three total fractions, with the most common dose regimen being 24 Gy in three fractions. Actuarial local control at 1 year was 89% overall, and 83 and 91% in patients with and without prior radiotherapy. Limited toxicity was noted, even in patients who had reirradiation. Besides local control, pain relief is regarded as one of the most important outcomes following spinal SRS. The Radiation Therapy Oncology Group (RTOG)50 reported favorable results from the phase II portion of RTOG 0631, a study designed to assess the feasibility and safety of spine SRS for localized spine metastases. The study is currently accruing to the phase III component, which is planned to compare pain relief and quality of life between single-fraction SRS to 16 to 18 Gy versus singlefraction conventional external beam radiation to 8 Gy. As the utilization of spinal SRS continues, results of this important trial will be critical in understanding the durability of pain relief for patients undergoing this type of treatment.

16.6.1 Clinical Cases Case 1 A 59-year-old woman presented with an abnormal screening mammogram, demonstrating a mass in the right breast, which was biopsy-proven invasive lobular carcinoma. Further workup was completed including staging with a CT of the chest, abdomen, and pelvis. CT revealed bony abnormalities within the left scapula and T11 vertebral body suggesting metastases, confirmed with MRI and bone scan. She underwent a biopsy of the T11 vertebra demonstrating metastatic disease. She was asymptomatic, specifically without back pain or neurological deficits. Given her excellent performance status in the setting of oligometastatic disease, she was treated with SRS to both the left scapular lesion and T11, to a dose of 15 Gy delivered in a single fraction. Images from her IMRT treatment plan can be seen in ▶ Fig. 16.3. SRS treatment was followed by systemic chemotherapy, right breast partial mastectomy, and adjuvant radiation therapy to the right breast and axillary lymph nodes. She had no treatment-related complications. Now 3 years out from treatment completion, she remains free of disease, with local control at the sites of SRS.

Case 2 A 39-year-old man presented to the emergency center with progressive lower back pain, with new-onset right lower extremity

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Stereotactic Radiosurgery for Tumors of the Spine

Fig. 16.3 IMRT treatment plan images for T11 SRS, 15 Gy in a single fraction.

Fig. 16.4 IMRT treatment plan axial image for T2 SRS, 18 Gy in a single fraction.

pain and weakness. MRI of the spine demonstrated diffuse bony abnormalities throughout the thoracic and lumbar spine concerning for metastatic disease with a pathological fracture of the T2 vertebral body and compression of the cauda equina with paraspinal involvement at L3–L4. He underwent immediate lumbar laminectomy of L1–L5, with pathology demonstrating metastatic prostate adenocarcinoma. Postoperatively, he underwent palliative external beam radiotherapy from the T6 vertebral level through the SI joints bilaterally. He received a dose of 45 Gy in 25 fractions of 1.8 Gy per fraction. He was initiated on androgen deprivation therapy. His disease at the T2 level progressed in the months following treatment, and he was treated with a course of spinal SRS to the T2 level to a dose of 18 Gy in a single fraction. Images from his IMRT treatment plan can be seen in ▶ Fig. 16.4. Following radiotherapy, his spinal disease remained controlled, specifically at the T2 level. He died of complications from cranial and pachymeningeal metastases 5 years later.

16.7 Conclusion Spinal SRS is a safe and effective treatment modality for patients with spinal tumors in the setting of primary treatment or salvage treatment after failing conventional radiation. This treatment may serve as a boost to traditional radiation and surgical treatments; as upfront, stand-alone, or adjuvant treatment; or possibly as an alternative to both radiation and surgery for some patients. The decision to use SRS instead of surgery or conventional EBRT is best reached in a multidisciplinary setting involving an oncologist, neurosurgeon, and radiation oncologist. Minimal risks of spinal cord or solid organ complications are seen, and significant benefits with respect to pain relief and improved local control have been observed. The high precision and conformity now established when spine SRS is delivered with modern radiation treatment methods and IGRT have the potential to move this treatment modality beyond short-term palliation while simultaneously improving quality of life.

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Clinical Caveats ●

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The majority of tumors involving the spinal column are spinal metastases. Patients with spinal cord tumors may present with pain, neurological compromise, or vertebral fractures. In patients who are poor surgical candidates, radiation therapy can be considered as an alternative treatment modality, which offers effective pain relief and maintenance of neurological function. Stereotactic radiosurgery (SRS) allows for the delivery of high doses of radiation to conformal target volumes, and can be achieved using intensity-modulated radiation therapy or volumetric modulated arc therapy, with the use of image guidance. SRS radiation dose prescription is typically selected on the basis of tumor location, tumor size, proximity to critical structures, and prior radiation treatment within the treatment field for patients presenting for retreatment. The most significant and feared late complications following spinal SRS are radiation-induced myelopathy and vertebral compression fractures, both of which must be considered carefully when creating treatment plans. Local control and pain relief outcomes following spinal SRS are promising in the available literature, with limited longterm toxicity reported.

References [1] Leksell L. The stereotaxic method and radiosurgery of the brain. Acta Chir Scand. 1951; 102(4):316–319 [2] Boyer AL, Ochran TG, Nyerick CE, Waldron TJ, Huntzinger CJ. Clinical dosimetry for implementation of a multileaf collimator. Med Phys. 1992; 19 (5):1255–1261 [3] Hogstrom KR, Boyd RA, Antolak JA, Svatos MM, Faddegon BA, Rosenman JG. Dosimetry of a prototype retractable eMLC for fixed-beam electron therapy. Med Phys. 2004; 31(3):443–462 [4] Tobler M, Leavitt DD, Watson G. Optimization of the primary collimator settings for fractionated IMRT stereotactic radiotherapy. Med Dosim. 2004; 29(2):72–79 [5] Wu VW, Kwong DL, Sham JS. Target dose conformity in 3-dimensional conformal radiotherapy and intensity modulated radiotherapy. Radiother Oncol. 2004; 71(2):201–206 [6] Mehta VK, Lee QT, Chang SD, Cherney S, Adler JR, Jr. Image guided stereotactic radiosurgery for lesions in proximity to the anterior visual pathways: a preliminary report. Technol Cancer Res Treat. 2002; 1(3):173–180 [7] Pollock BE, Kondziolka D, Flickinger JC, Maitz A, Lunsford LD. Preservation of cranial nerve function after radiosurgery for nonacoustic schwannomas. Neurosurgery. 1993; 33(4):597–601 [8] Flickinger JC, Kondziolka D, Lunsford LD. Dose selection in stereotactic radiosurgery. Neurosurg Clin N Am. 1999; 10(2):271–280 [9] Flickinger JC, Lunsford LD, Kondziolka D. Dose prescription and dose-volume effects in radiosurgery. Neurosurg Clin N Am. 1992; 3(1):51–59 [10] Kondziolka D, Lunsford LD, Flickinger JC. Acoustic tumors: operation versus radiation–making sense of opposing viewpoints. Part II. Acoustic neuromas: sorting out management options. Clin Neurosurg. 2003; 50:313–328 [11] Kondziolka D, Lunsford LD, McLaughlin MR, Flickinger JC. Long-term outcomes after radiosurgery for acoustic neuromas. N Engl J Med. 1998; 339 (20):1426–1433 [12] Stafford SL, Pollock BE, Leavitt JA, et al. A study on the radiation tolerance of the optic nerves and chiasm after stereotactic radiosurgery. Int J Radiat Oncol Biol Phys. 2003; 55(5):1177–1181 [13] Tishler RB, Loeffler JS, Lunsford LD, et al. Tolerance of cranial nerves of the cavernous sinus to radiosurgery. Int J Radiat Oncol Biol Phys. 1993; 27 (2):215–221

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[14] Barnett GH, Kormos DW, Steiner CP, Weisenberger J. Intraoperative localization using an armless, frameless stereotactic wand. Technical note. J Neurosurg. 1993; 78(3):510–514 [15] Guthrie BL, Adler JR, Jr. Computer-assisted preoperative planning, interactive surgery, and frameless stereotaxy. Clin Neurosurg. 1992; 38:112–131 [16] Yin FF, Ryu S, Ajlouni M, et al. A technique of intensity-modulated radiosurgery (IMRS) for spinal tumors. Med Phys. 2002; 29(12):2815–2822 [17] Chow E, Zeng L, Salvo N, Dennis K, Tsao M, Lutz S. Update on the systematic review of palliative radiotherapy trials for bone metastases. Clin Oncol (R Coll Radiol). 2012; 24(2):112–124 [18] Joaquim AF, Ghizoni E, Tedeschi H, Pereira EB, Giacomini LA. Stereotactic radiosurgery for spinal metastases: a literature review. Einstein (Sao Paulo). 2013; 11(2):247–255 [19] Hamilton AJ, Lulu BA, Fosmire H, Gossett L. LINAC-based spinal stereotactic radiosurgery. Stereotact Funct Neurosurg. 1996; 66(1)(–)(3):1–9 [20] Hamilton AJ, Lulu BA, Fosmire H, Stea B, Cassady JR. Preliminary clinical experience with linear accelerator-based spinal stereotactic radiosurgery. Neurosurgery. 1995; 36(2):311–319 [21] Adler JR, Jr, Chang SD, Murphy MJ, Doty J, Geis P, Hancock SL. The Cyberknife: a frameless robotic system for radiosurgery. Stereotact Funct Neurosurg. 1997; 69(1-4 Pt 2):124–128 [22] Adler JR, Jr, Murphy MJ, Chang SD, Hancock SL. Image-guided robotic radiosurgery. Neurosurgery. 1999; 44(6):1299–1306, discussion 1306–1307 [23] Chang SD, Main W, Martin DP, Gibbs IC, Heilbrun MP. An analysis of the accuracy of the CyberKnife: a robotic frameless stereotactic radiosurgical system. Neurosurgery. 2003; 52(1):140–146, discussion 146–147 [24] Lohr F, Debus J, Frank C, et al. Noninvasive patient fixation for extracranial stereotactic radiotherapy. Int J Radiat Oncol Biol Phys. 1999; 45(2):521–527 [25] Murphy MJ, Adler JR, Jr, Bodduluri M, et al. Image-guided radiosurgery for the spine and pancreas. Comput Aided Surg. 2000; 5(4):278–288 [26] Murphy MJ, Chang SD, Gibbs IC, et al. Patterns of patient movement during frameless image-guided radiosurgery. Int J Radiat Oncol Biol Phys. 2003; 55 (5):1400–1408 [27] Takacs I, Hamilton AJ. Extracranial stereotactic radiosurgery: applications for the spine and beyond. Neurosurg Clin N Am. 1999; 10(2):257–270 [28] Gerszten PC, Ozhasoglu C, Burton SA, et al. Evaluation of CyberKnife frameless real-time image-guided stereotactic radiosurgery for spinal lesions. Stereotact Funct Neurosurg. 2003; 81(1)(–)(4):84–89 [29] Medin PM, Solberg TD, De Salles AA, et al. Investigations of a minimally invasive method for treatment of spinal malignancies with LINAC stereotactic radiation therapy: accuracy and animal studies. Int J Radiat Oncol Biol Phys. 2002; 52(4):1111–1122 [30] Ryu S, Fang Yin F, Rock J, et al. Image-guided and intensity-modulated radiosurgery for patients with spinal metastasis. Cancer. 2003; 97(8):2013–2018 [31] Ryu SI, Chang SD, Kim DH, et al. Image-guided hypo-fractionated stereotactic radiosurgery to spinal lesions. Neurosurgery. 2001; 49(4):838–846 [32] Gerszten PC, Burton SA, Ozhasoglu C, Welch WC. Radiosurgery for spinal metastases: clinical experience in 500 cases from a single institution. Spine. 2007; 32(2):193–199 [33] Garg AK, Shiu AS, Yang J, et al. Phase 1/2 trial of single-session stereotactic body radiotherapy for previously unirradiated spinal metastases. Cancer. 2012; 118(20):5069–5077 [34] Heron DE, Rajagopalan MS, Stone B, et al. Single-session and multisession CyberKnife radiosurgery for spine metastases-University of Pittsburgh and Georgetown University experience. J Neurosurg Spine. 2012; 17(1):11–18 [35] Ahmed KA, Stauder MC, Miller RC, et al. Stereotactic body radiation therapy in spinal metastases. Int J Radiat Oncol Biol Phys. 2012; 82(5):e803–e809 [36] Yamada Y, Bilsky MH, Lovelock DM, et al. High-dose, single-fraction imageguided intensity-modulated radiotherapy for metastatic spinal lesions. Int J Radiat Oncol Biol Phys. 2008; 71(2):484–490 [37] Ang KK, Price RE, Stephens LC, et al. The tolerance of primate spinal cord to re-irradiation. Int J Radiat Oncol Biol Phys. 1993; 25(3):459–464 [38] Boden G. Radiation myelitis of the cervical spinal cord. Br J Radiol. 1948; 21 (249):464–469 [39] Marcus RB, Jr, Million RR. The incidence of myelitis after irradiation of the cervical spinal cord. Int J Radiat Oncol Biol Phys. 1990; 19(1):3–8 [40] McCunniff AJ, Liang MJ. Radiation tolerance of the cervical spinal cord. Int J Radiat Oncol Biol Phys. 1989; 16(3):675–678 [41] Leibel SG. Tolerance of the Brain and Spinal Cord to Conventional Irradiation. New York, NY: Raven Press; 1991 [42] Gibbs IC, Patil C, Gerszten PC, Adler JR, Jr, Burton SA. Delayed radiation-induced myelopathy after spinal radiosurgery. Neurosurgery. 2009; 64(2) Suppl:A67–A72

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Stereotactic Radiosurgery for Tumors of the Spine [43] Sahgal A, Weinberg V, Ma L, et al. Probabilities of radiation myelopathy specific to stereotactic body radiation therapy to guide safe practice. Int J Radiat Oncol Biol Phys. 2013; 85(2):341–347 [44] Rose PS, Laufer I, Boland PJ, et al. Risk of fracture after single fraction imageguided intensity-modulated radiation therapy to spinal metastases. J Clin Oncol. 2009; 27(30):5075–5079 [45] Boehling NS, Grosshans DR, Allen PK, et al. Vertebral compression fracture risk after stereotactic body radiotherapy for spinal metastases. J Neurosurg Spine. 2012; 16(4):379–386 [46] Sahgal A, Atenafu EG, Chao S, et al. Vertebral compression fracture after spine stereotactic body radiotherapy: a multi-institutional analysis with a focus on radiation dose and the spinal instability neoplastic score. J Clin Oncol. 2013; 31(27):3426–3431

[47] Hartsell WF, Scott CB, Bruner DW, et al. Randomized trial of short- versus long-course radiotherapy for palliation of painful bone metastases. J Natl Cancer Inst. 2005; 97(11):798–804 [48] Roos DE, Turner SL, O’Brien PC, et al. Trans-Tasman Radiation Oncology Group, TROG 96.05. Randomized trial of 8 Gy in 1 versus 20 Gy in 5 fractions of radiotherapy for neuropathic pain due to bone metastases (Trans-Tasman Radiation Oncology Group, TROG 96.05). Radiother Oncol. 2005; 75(1):54–63 [49] Steenland E, Leer JW, van Houwelingen H, et al. The effect of a single fraction compared to multiple fractions on painful bone metastases: a global analysis of the Dutch Bone Metastasis Study. Radiother Oncol. 1999; 52(2):101–109 [50] Ryu S, Pugh SL, Gerszten PC, et al. RTOG 0631 phase II/III study of imageguided stereotactic radiosurgery for localized (1–3) spine metastases: phase ii results. Int J Radiat Oncol Biol Phys. 2011; 81(2):S131–S132

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Part IV Surgical Techniques

17 Transoral and Transnasal Approaches to the Craniocervical Junction

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18 Posterior Cervical Microforaminotomy and Discectomy

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19 Posterior Cervical Approach

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20 Anterior Cervical Discectomy, Fusion, and Instrumentation

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21 Cervical Arthroplasty

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22 Cervical Case Studies

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23 Posterior Thoracic Microdiscectomy

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24 Anterior Thoracoscopic Sympathectomy

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25 Thoracoscopic Discectomy and Thoracoscopy-Assisted Tubular Retractor Discectomy 249 26 Anterior Thoracoscopic Vertebral Reconstruction and Instrumentation

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27 Minimally Invasive Deformity Correction 266

IV

28 Minimally Invasive Treatment of Thoracic and Thoracolumbar Idiopathic Scoliosis

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29 Kyphoplasty and Vertebroplasty

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30 Minimally Invasive Robotic-Assisted Thoracic Spine Surgery

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31 Minimally Invasive Spine Surgery: Thoracic Case Studies

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32 Endoscopic Spine Techniques: An Overview

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33 Muscle Preserving Lumbar Microdiscectomy

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34 Far-Lateral Microdiscectomy

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35 Minimally Invasive Laminectomy for Lumbar Stenosis

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36 Anterior Lumbar Interbody Fusion

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37 Percutaneous Pedicle Screw Placement for Spinal Instrumentation

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38 Transforaminal Lumbar Interbody Fusion 377 39 Transpsoas Anatomical Approach to the Spine

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40 eXtreme Lateral Interbody Fusion

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41 Trans-sacral Approach

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42 Stabilization of the Sacroiliac Joint with the Sacroiliac Bone Surgical Implant

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43 Lumbar Disc Replacement: The Artificial Disc

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44 Minimally Invasive Spine Surgery: Lumbar Case Studies

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Transoral and Transnasal Approaches to the Craniocervical Junction

17 Transoral and Transnasal Approaches to the Craniocervical Junction Matthew L. Rontal, Daniel Roy Pieper, and Mick J. Perez-Cruet Abstract This chapter discusses both the traditional transoral approach and the endoscopic transoral and transnasal approaches to the craniocervical junction or craniovertebral junction. These approaches are extremely versatile for the treatment of a variety of anterior pathology affecting the craniocervical junction. This chapter discusses the anatomy as well as operative nuances to help make these approaches safe and effective. Keywords: craniocervical junction, craniovertebral junction, rheumatoid pannus, nasopharyngeal carcinoma, chordoma, chondrosarcoma, osteogenesis imperfecta, Klippel–Feil syndrome, Down’s syndrome, achondroplasia, mucopolysaccharidoses, transoral, velopharyngeal insufficiency, transnasal

17.1 Introduction Management of disease of the craniocervical junction (CCJ), or craniovertebral junction (CVJ), is evolving.1,2 This evolution largely results from the simultaneous development of the technology and the techniques of approach and resection of disease. This chapter discusses both the traditional transoral approach and the endoscopic transoral and transnasal approaches to the CCJ.

17.1.1 Anatomy Approach to the CCJ is founded in an understanding of the correlated pharyngeal and spinal anatomy, the function of the CCJ and velopharynx, and the required surgical exposure.

The CCJ consists of the occipital bone, the atlas, and the axis. Together these bony structures house the junction of the brainstem and spinal cord and transmit the vertebral arteries and proximal derivatives of the spinal cord. The bony and ligamentous anatomy of the CCJ creates the structural basis of the majority of the flexion, extension, and rotation of the head. An understanding of the complex anatomy of the cranial vertebral junction, soft palate, and transoral approach is critical to safe and effective surgical intervention (▶ Fig. 17.1).

Occipital-C1 The junction of the occipital bone and atlas is an articulation of the occipital condyles of the occipital bone and the concave surfaces of the lateral masses of C1 which confers flexion and extension of the head. Just above this articulation are two discrete portions of the occipital bone: 1. Clivus, anteriorly. 2. Squamous portion of the occipital bone, posteriorly. The pontomedullary junction lies approximately 1 cm above the inferior tip of the clivus. The hypoglossal nerves exit through their canals in the squamous portion of the occipital bone just superior and medial to the condyles. The atlanto-occipital membrane (AOM) spans from the posterior aspect of the atlas ring to the occipital bone. The vertebral arteries ascend through their foramina in the lateral masses of the cervical vertebrae, and then run over the posterior ring of atlas and pierce the AOM to enter the foramen magnum. The AOM does not confer stability to the CCJ.

Fig. 17.1 Anatomical illustration of the craniocervical junction.

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C1–C2 The atlantoaxial junction is defined by the unique articulation of the odontoid process and C1, which permits rotation of the head. The dens extends superiorly from the anterior aspect of C2 and articulates with the posterior aspect of the anterior ring of C1. A complex arrangement of the transverse ligament and its vertically oriented superior and inferior crura (together comprising the cruciate ligament) and the alar ligaments restrict flexion/extension and rotation, respectively, stabilizing the CCJ. The role of the tectorial membrane, which fans upward from the anterior aspect of C2 to the dura mater within the anterior aspect of the foramen magnum, remains controversial. The anterior longitudinal ligament guards the anterior aspect of the CCJ and contributes stability, but does not confer any of the regions’ specialized range of movement. The longus colli and longus capitis muscles lie anterior to the anterior longitudinal ligament and just behind the mucosal, muscular, and fascial planes of the posterior pharyngeal wall. The velopharynx is the name given to the region at the junction of the nasopharynx and oropharynx that operates to restrict the flow of air through the nose during speech. It is composed of the soft palate, the lateral pharyngeal walls, and the posterior pharyngeal wall. The soft palate projects posteriorly from the posterior edge of the hard palate and then assumes a posteroinferiorly curved posture at rest. The midline aspect of the inferior-most edge of the soft palate extends further inferiorly as the bullet-shaped uvula. Deep to the mucosa and minor salivary glands of the soft palate are the muscles of the palate. Most important, the levator veli palatini is the principal elevator of the palate. It descends from the inferior aspect of the greater wing of the sphenoid to the lateral aspect of the palate and then turns 90 degrees to run transversely in the substance of the palate, inserting on the palatal aponeurosis. Contraction of the levator muscles elevates the palate in the coronal plane and creates a posterior superior movement in the sagittal plane such that the palate obturates against the posterior pharyngeal wall. The superior pharyngeal constrictor bounds the lateral and posterior aspects of the velopharynx. It takes its origin from the medial pterygoid plate, the mandible, and the pterygomandibular raphe. And it inserts on the midline raphe in the posterior pharyngeal wall and the pharyngeal tubercle at the base of the occipital bone. More superiorly, the posterior wall of the nasopharynx is created by the mucosal covering of the anterior aspect of the inferior portion of the clivus. Together the posterior superior movement of the palate and the purse-string movement of the superior constrictor function to close the velopharynx during swallowing and during speech. During swallowing, these movements are slow and large in amplitude, preventing the egress of food and liquids into the nasopharynx. During speech, these movements work to open and close the velopharynx several times per second, appropriately permitting and restricting nasal flow of air in the creation of particular phonemes of speech. Inadequacy in these movements results in hypernasal resonance and inability to create the sounds of the letters P, B, D, K, G, Z, and S. The consequence is a constellation of abnormal voice and misarticulations known as velopharyngeal incompetence (VPI).3 VPI

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is most commonly seen in some patients with cleft palate in whom palatal length and/or movement is insufficient to obstruct the velopharynx during speech. Correction of VPI involves adding partially obstructive tissue in the region of the velopharynx to aid in closure. The authors’ preferred technique is the superiorly based pharyngeal flap, which creates a myofascial-mucosal bridge from the posterior pharyngeal wall to the palate.4 Improved closure of the velopharynx is then accomplished by inward movement of the lateral pharyngeal walls up to the lateral margins of the bridge, without significant movement of the palate. The function of the velopharyngeal sphincter is essential to maintaining normal, intelligible speech, and should be preserved in approaching the CCJ.

17.1.2 Pathology Disease of the CCJ resulting in compression of the spinal cord and brainstem and/or instability of the complex bony and ligamentous anatomy threatens severe neurologic impairment. Historically, the most common presenting etiology has been compression due to a rheumatoid pannus involving the atlantoaxial junction.1,5,6,7,8,9,10,11 Other pathologies of the CCJ include neoplastic processes such as nasopharyngeal carcinoma, chordoma, and chondrosarcoma, infectious processes, and trauma. Congenital disease affecting craniofacial growth such as osteogenesis imperfecta,9 Klippel–Feil syndrome, Down’s syndrome,12 achondroplasia, and mucopolysaccharidoses may result in basilar invagination.13 Acquired diseases of bone such as rickets, osteogenesis imperfecta, cretinism, and parathyroid disease may result in softening of the occipital bone and basilar impression resulting from settling of the skull and a relative odontoid elevation.14 Interestingly Choi et al11 reported that with improved management of rheumatoid arthritis, the incidence of rheumatoid pannus of the CCJ is more recently markedly reduced and that resection of tumor has ascended to the most common indication.1,15 While most inflammatory and benign neoplastic presentations can be managed with piecemeal resection, some malignant processes indicate a need for en bloc resection. The required exposure and thus the chosen approach vary based on these indications16 (▶ Fig. 17.2).

17.1.3 Relative Anatomy Key to choosing an approach is understanding an individual patient’s CCJ anatomy relative to the structures of the palate. This provides an understanding of the angle of attack that may be expected through the nose and the mouth. On lateral cephalogram, the tip of the odontoid has long been compared to the level of the hard palate. McGregor’s line is drawn from the posterior aspect of the hard palate to the base of the occiput. Chamberlain’s line is drawn from the posterior aspect of the hard palate to the anterior lip of the foramen magnum. The tip of the dens is found at or below Chamberlain’s line in roughly 50% of individuals. Basilar invagination is said to be present if the tip of the dens is 4.5 mm above McGregor’s line or 6 mm above Chamberlain’s line. As the approach to the CCJ has evolved, CCJ anatomy relative to the hard palate has been studied with respect to the angle of attack in the transnasal approach (▶ Fig. 17.3).

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Transoral and Transnasal Approaches to the Craniocervical Junction

Fig. 17.2 Illustration of pathology affecting the odontoid process, which is typically a chordoma.

Fig. 17.3 Illustration showing Wackenheim’s, McRae’s, Chamberlain’s, and McGregor’s lines used to define craniovertebral junction anatomy and pathology.

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17.2 Transoral Approach The traditional transoral, transpalatal, and transpharyngeal approaches have been the gold standard approaches to the ventral CCJ for several decades. First described by Kanavel in 1917 as a method to remove a bullet from the CCJ, the first small series on

successful use of the transoral approach was published by Fang and Ong 1962.17 Over several years, further advances in instrumentation and technique have improved outcomes in the hands of Crockard et al,7 Menezes and VanGilder,6 and others,11,18,19 such that low rates of complications, especially infection, have been achieved (▶ Fig. 17.4).

17.2.1 Technique

Fig. 17.4 Illustration showing the exposure achieved using the traditional (A) transoral, (B) transpharyngeal, and (C,D) transpalatal approaches.

As the case is begun, fiberoptic intubation may be required due to very limited neck extension and a tracheostomy may be performed.20 The oral cavity and oropharynx are cleansed. A throat pack is placed. While neck extension could provide improved angle of attack to the lower clivus, instability of the cervical spine most often precludes significant extension. The posterior pharyngeal wall (and greater palatine foramen if indicated) is infiltrated with 1% lidocaine with 1:100,000 epinephrine. The transoral approach utilizes a retractor of the tongue and mandible. The retractor is released every 30 minutes for 5 minutes in order to allow the tongue to reestablish blood flow. This reduces the risk of severe tongue edema and necrosis. The spinal anatomy can be palpated in the posterior wall of the oropharynx. Determination as to the need for division of the palate is made(▶ Fig. 17.5). The soft palate may be retracted into the nasopharynx by inserting a red rubber tube into the nose, suturing to the uvula, and retracting gently. Debate exists as to the access obtained from retraction versus division of the soft palate. If division of the soft palate is required, the authors prefer a broken line incision through the palate in order to prevent shortening of the palate via straight-line scar contracture. The posterior surface of the hard palate may be resected for further superior exposure. If this is required, the authors prefer to offset the oral surface incision from the midline and from the muscular/nasal surface incision in order to prevent

Fig. 17.5 (a) Anterior and (b) sagittal illustrations of the anatomy of the transoral approach.

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Transoral and Transnasal Approaches to the Craniocervical Junction

Fig. 17.6 (a,b) Anatomy of the soft palate pertinent to the transoral approach.

fistula formation at the hard palate–soft palate junction. Understanding the anatomy of this area is critical to successful surgery(▶ Fig. 17.6). The posterior pharyngeal wall mucosa is then opened as a rectangular flap. Although others advocate an inferiorly based flap, the authors favor a superiorly based flap. This flap is designed as if it were to be used to reconstruct the velopharynx in the event of postoperative VPI, as described earlier. Thus, the flap is essentially delayed in the process of approaching the CCJ, and is ready to use in the future if it is required. Use of an inferiorly based flap in the initial procedure may compromise the vascularity of superiorly based flap, preventing its later use in the case of postoperative VPI.21 The longus colli and longus capitus muscles are divided in the midline fascial raphe. The anterior longitudinal ligament is divided. Thus, the disease process is then managed (odontoid, resection, etc.). The defect is then slightly overfilled with a fat graft, the longus colli and longus capitus muscles are reapproximated

in the midline if possible, and the superiorly based flap is rotated back into its native position and is closed with multiple interrupted 3–0 Vicryl sutures in horizontal mattress fashion. The palate is then closed in three layers, the nasal mucosal surface, the muscular plane, and the oral surface. The key aspect of the palatal closure is reconstruction of the divided levator muscle, ensuring adequate palatal function (▶ Fig. 17.7).

Extended Transoral Exposure Greater inferior exposure can be obtained by dividing the tongue in the midline. Even greater extension of the transoral technique is gained in dividing the mandible inferiorly and/or dividing the maxilla superiorly. Mandibular swing, LeFort I maxillotomies, and LeFort II maxillary swing procedures extend the potential exposure from C3 inferiorly to the anterior skull base superiorly. Detailed descriptions of these techniques are beyond the scope of this chapter.

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Fig. 17.7 The posterior pharyngeal wall mucosa is opened as a rectangular flap either (a) rostral or (b) caudal depending on the location of the pathology. (c,d) The longus colli and longus capitus muscles are divided in the midline fascial raphe. (e–g) The anterior longitudinal ligament is divided exposing the disease process (i.e., odontoid, resection, etc.). (h,i) The longus colli and longus capitus muscles are reapproximated in the midline if possible, and the superiorly based flap is rotated back into its native position and is closed with multiple interrupted 3–0 Vicryl sutures in horizontal mattress fashion.

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Transoral and Transnasal Approaches to the Craniocervical Junction

17.2.2 Complications to the Transoral Approach Airway Obstruction Edema of the tongue, pharyngeal wall, and palate, secondary dysphagia, and halo stabilization all predispose to difficulty in managing the postoperative airway. This may be more pronounced in obese patients, especially those with a known history of obstructive sleep apnea. In addition, there is evidence that, through either surgical fixation or disease, restriction in neck extension may inhibit full mouth opening.22 Lastly, more advanced presentations may preoperatively include lower cranial nerve deficits, further inhibiting the patient’s ability to manage secretions and protect the airway.16 Tracheostomy may be prudent in these patients in order to avoid prolonged intubation and difficult reintubation. Perioperative use of systemic steroids and steroid cream applied to the tongue intraoperatively may be useful.

Velopharyngeal Insufficiency VPI may result from any of the following changes in velopharyngeal anatomy21,23: 1. Fibrosis or scar contracture within the opened and repaired soft palate resulting in foreshortening of the palate, or dehiscence of the levator sling during wound healing. 2. Deepening of the posterior pharyngeal wall resulting from odontoid/disease resection. This may result in too great an AP diameter of the velopharynx such that the otherwise unaffected palate may be unable to successfully obturate against the posterior wall. 3. Change in relationship of the structures of the velopharynx resulting from change in the height and position of the spine and clivus secondary to surgical resection. 4. Loss of posterior pharyngeal wall movement resulting from scarring or denervation, again resulting in incomplete velopharyngeal closure.

Published rates of VPI are variable ranging from 25 to 45%.21,23 Broken-line palatal incisions may prevent foreshortening secondary to straight-line scar contracture and add little time or complexity. In addition, utilizing a wide, superiorly based flap for the approach should prepare the surgeon for secondary velopharyngeal reconstruction, if needed.

17.3 Transnasal Approach In order to avoid palatal division and with the advent of endoscopy in endonasal, oropharynx, and neurosurgical procedures, endoscopic approaches to the CCJ have been developed. The pedicled nasoseptal flap has allowed for closure of skull base and nasopharyngeal wounds in which a soft tissue deficit is created (▶ Fig. 17.8). Preoperative planning is partly focused on the degree of inferior exposure available through the endonasal approach. Multiple approximations of the inferior extent of endonasal endoscopic dissection have been based on the anatomy of the hard palate on sagittal images.24,25,26 While some methods seem to overestimate the inferior surgical exposure, La Corte et al suggested that the rhinopalatine line is perhaps most accurate.16 On a sagittal CT image, this line connects an anterior point, found two-thirds of the distance from the rhinion to the anterior nasal spine, to a posterior point at the posterior nasal spine and then intersects with the CCJ at the expected inferiormost exposure. Lesions above this point may be managed via endonasal approach alone. Lesions at this line may require both endonasal and endoscopic transoral approach; and lesions greater than 1 cm below this line may require only the endoscopic transoral approach.

17.3.1 Technique The patient is registered to the image guidance system. The nose is packed with oxymetazoline-soaked cottonoids for 3 to 5 minutes. The greater palatine foramen, the septum, spheno-

Fig. 17.8 Illustration of exposure achieved with (a) transnasal approach with (b) endoscope in place to improve visualization (inset, illustration showing endoscope medial to nasal turbinate).

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Surgical Techniques palatine region, axilla of the middle turbinate, inferior turbinates, and the posterior pharyngeal wall are injected with 1% lidocaine and 1:100,000 epinephrine. The inferior and middle turbinates are lateralized. A pedicled nasal septal flap is developed. The nasal septal mucosa is raised from anterior to posterior and the pedicle is then raised across the sphenoid rostrum from medial to lateral. The pedicle is then isolated by transverse incisions at the level of the sphenoid ostium and at the junction of the sphenoid rostrum and nasopharynx. In this manner, the septal branch of the sphenopalatine artery, coursing from the sphenopalatine foramen medially across the face of the sphenoid sinus to the posterior palate, is captured. Superior and inferior incisions in the septal mucosal flap are then made extending anteriorly from the sphenoid rostrum incisions to the vertical anterior septal incision and the creation of a pedicled, arterialized flap is completed. Once one or both leaves of the mucoperiosteum of the septum are raised as flaps, the posterior septum is removed, taking care not to fracture upward toward the skull base, and thus exposure of the posterior wall of the nasopharynx is achieved. If greater superior exposure is needed, the floor of the sphenoid sinus is removed. The posterior nasopharyngeal wall is then divided either vertically or in a U-shaped pattern. The transoral approach is carried out as an isolated dissection through the posterior pharyngeal wall with retraction of the palate. Importantly, angled telescopes allow for a view above the palate without dividing it. Dissection through the midline raphe and the anterior longitudinal ligament and resection of disease and/or odontoid are carried out with elongated, gently curved drills, microdebriders, and dissectors that can be inserted through the nose. The authors prefer a handheld CO2 laser for mucosal incisions and initial dissection in the posterior wall of the nasopharynx. Elongated dissectors, curettes, and suctions, such as those used in transsphenoidal surgery, image guidance, and three-hand or four-hand techniques, in combination with the skills of neurosurgical and ENT colleagues, are utilized. The endoscopic approach obviates the need for division of the palate. It provides a cone-out view with better illumination

than the cone-down view of the microscope, and it allows greater freedom of movement of instruments and combined dissection with two surgeons. The endonasal endoscopic approach allows significant inferior exposure with an angled telescope and angled instrumentation without placing the wound below the level of the soft palate. Proponents suggest that this more cephalad placement of the surgical dissection avoids dysphagia by avoiding dissection through the oropharyngeal aspect of the superior constrictor and by avoiding aggressive retraction of the tongue.23,27,28,29 Perhaps most importantly, the craniocaudal angle of attack via the endonasal endoscopic approach allows controlled odontoid resection without thinning or resection of the anterior ring of C128 (▶ Fig. 17.9). Still, the authorsworry that the transnasal approach and dissection through the upper aspect of the posterior pharyngeal wall still deepen the AP diameter of the velopharynx and predispose to VPI. Adequate statistical data on this question are not yet available.

17.4 Complications Concerns following endoscopic approaches are the same as those following the open transoral approach. These include airway obstruction requiring tracheostomy, prolonged dysphagia and need for gastrostomy tube, and VPI. The data available are found in small series with inadequate statistical power. However, there appears to be a trend toward reduced risk of all complications when the palate is not divided and the tongue is not compressed through a prolonged procedure.23

17.4.1 Clinical Case A 56-year-old female presents with axial neck pain. Contrastenhanced MRI revealed an anterior skull based lesion. A transoral approach was used to achieve gross total resection. The patient made an unremarkable recovery. Pathology revealed meningioma. Two-year follow-up contrasted MRI revealed no evidence of tumor recurrence (▶ Fig. 17.10).

Fig. 17.9 (a) Preoperative contrast-enhanced sagittal MRI showing (b) resection of large skull base meningioma using endoscopic transnasal approach.

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Transoral and Transnasal Approaches to the Craniocervical Junction

Fig. 17.10 (a) Intraoperative photo showing surgeon performing endoscopic surgery. (b) Preoperative sagittal and postoperative sagittal and preoperative axial and postoperative axial contrast-enhanced MRI showing gross total resection of skull base meningioma using a transoral approach.

17.5 Conclusion The choice of endoscopic versus open approach is ultimately dependent on the anatomical location and pathology of the presenting problem. Of course, primary importance is placed on obtaining as complete management of the disease as possible while avoiding morbidity. The marked reduction in patients presenting with rheumatoid disease has resulted in very few centers taking on large numbers of cases, and thus the lack of statistical power in current studies. In addition, the steep learning curve, specialized instrumentation, and angled two-dimensional images are relative deterrents to the endoscopic approaches for some. Certainly, the surgeons’ experience and comfort with each approach will dictate the choice of technique. However, it seems an unavoidable conclusion on the part of the authors that for those presentations that can be managed endoscopically, with reduced surgical/retraction trauma to the palate and tongue, the surgeon should strongly consider the endoscopic approach.

Clinical Caveats ●

●

●

●

The endoscopic transoral, transnasal, and transpalatal approaches offer excellent visualization for resection of anterior craniocervical junction pathology. The steep learning curve of these procedures requires adequate training achieved via cadaveric dissection labs, fellowships, and intraoperative experience with experts. Outstanding patient outcomes can be achieved with a thorough understanding of the cranial cervical anatomy. A team approach comprising expert ear, nose, and throat; neurosurgeon; and oral maxillary specialists helps assure outstanding patient outcomes.

References [1] Choi D, Crockard HA. Evolution of transoral surgery: three decades of change in patients, pathologies, and indications. Neurosurgery. 2013; 73(2):296– 303, discussion 303–304 [2] Dlouhy BJ, Dahdaleh NS, Menezes AH. Evolution of transoral approaches, endoscopic endonasal approaches, and reduction strategies for treatment of craniovertebral junction pathology: a treatment algorithm update. Neurosurg Focus. 2015; 38(4):E8 [3] Shprintzen RJ, Bardach J. Cleft Palate Speech Management: A Multidisciplinary Approach. St. Louis, MO: Mosby; 1995:xviii, 380 [4] Saman M, Tatum SA, III. Recent advances in surgical pharyngeal modification procedures for the treatment of velopharyngeal insufficiency in patients with cleft palate. Arch Facial Plast Surg. 2012; 14(2):85–88 [5] Menezes AH, VanGilder JC, Graf CJ, McDonnell DE. Craniocervical abnormalities. A comprehensive surgical approach. J Neurosurg. 1980; 53(4):444–455 [6] Menezes AH, VanGilder JC. Transoral-transpharyngeal approach to the anterior craniocervical junction. Ten-year experience with 72 patients. J Neurosurg. 1988; 69(6):895–903 [7] Crockard HA, Calder I, Ransford AO. One-stage transoral decompression and posterior fixation in rheumatoid atlanto-axial subluxation. J Bone Joint Surg Br. 1990; 72(4):682–685 [8] Ashraf J, Crockard HA, Ransford AO, Stevens JM. Transoral decompression and posterior stabilisation in Morquio’s disease. Arch Dis Child. 1991; 66 (11):1318–1321 [9] Menezes AH. Specific entities affecting the craniocervical region: osteogenesis imperfecta and related osteochondrodysplasias: medical and surgical management of basilar impression. Childs Nerv Syst. 2008; 24(10):1169–1172 [10] Menezes AH. Craniovertebral junction database analysis: incidence, classification, presentation, and treatment algorithms. Childs Nerv Syst. 2008; 24 (10):1101–1108 [11] Choi D, Melcher R, Harms J, Crockard A. Outcome of 132 operations in 97 patients with chordomas of the craniocervical junction and upper cervical spine. Neurosurgery. 2010; 66(1):59–65, discussion 65 [12] Menezes AH. Specific entities affecting the craniocervical region: Down’s syndrome. Childs Nerv Syst. 2008; 24(10):1165–1168 [13] Menezes AH. Craniocervical developmental anatomy and its implications. Childs Nerv Syst. 2008; 24(10):1109–1122 [14] Donald PJ. Surgery of the Skull Base. Philadelphia, PA: Lippincott-Raven; 1998:xvii, 678

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Surgical Techniques [15] Robinson AJ, Taylor DH, Wright GD. Infliximab therapy reduces periodontoid rheumatoid pannus formation. Rheumatology (Oxford). 2008; 47(2):225–226 [16] Hsu W, Wolinsky JP, Gokaslan ZL, Sciubba DM. Transoral approaches to the cervical spine. Neurosurgery. 2010; 66(3) Suppl:119–125 [17] Fang HSY, Ong GB. Direct anterior approach to the upper cervical spine. J Bone Joint Surg Am. 1962; 44-A(8):1588–1604 [18] Goel A, Bhatjiwale M, Desai K. Basilar invagination: a study based on 190 surgically treated patients. J Neurosurg. 1998; 88(6):962–968 [19] Goel A. Basilar invagination, Chiari malformation, syringomyelia: a review. Neurol India. 2009; 57(3):235–246 [20] Menezes AH. Surgical approaches: postoperative care and complications “transoral-transpalatopharyngeal approach to the craniocervical junction”. Childs Nerv Syst. 2008; 24(10):1187–1193 [21] Cantarella G, Mazzola RF, Benincasa A. A possible sequela of transoral approach to the upper cervical spine. Velopharyngeal incompetence. J Neurosurg Sci. 1998; 42(1):51–55 [22] Calder I, Picard J, Chapman M, O’Sullivan C, Crockard HA. Mouth opening: a new angle. Anesthesiology. 2003; 99(4):799–801 [23] Wu JC, Mummaneni PV, El-Sayed IH. Diseases of the odontoid and craniovertebral junction with management by endoscopic approaches. Otolaryngol Clin North Am. 2011; 44(5):1029–1042 [24] Nayak JV, Gardner PA, Vescan AD, Carrau RL, Kassam AB, Snyderman CH. Experience with the expanded endonasal approach for resection of the odontoid process in rheumatoid disease. Am J Rhinol. 2007; 21(5):601–606

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[25] de Almeida JR, Zanation AM, Snyderman CH, et al. Defining the nasopalatine line: the limit for endonasal surgery of the spine. Laryngoscope. 2009; 119 (2):239–244 [26] La Corte E, Aldana PR, Ferroli P, et al. The rhinopalatine line as a reliable predictor of the inferior extent of endonasal odontoidectomies. Neurosurg Focus. 2015; 38(4):E16 [27] Frempong-Boadu AK, Faunce WA, Fessler RG. Endoscopically assisted transoral-transpharyngeal approach to the craniovertebral junction. Neurosurgery. 2002; 51(5) Suppl:S60–S66 [28] Pillai P, Baig MN, Karas CS, Ammirati M. Endoscopic image-guided transoral approach to the craniovertebral junction: an anatomic study comparing surgical exposure and surgical freedom obtained with the endoscope and the operating microscope. Neurosurgery. 2009; 64(5) Suppl 2:437–442, discussion 442–444 [29] El-Sayed IH, Wu JC, Ames CP, Balamurali G, Mummaneni PV. Combined transnasal and transoral endoscopic approaches to the craniovertebral junction. J Craniovertebr Junction Spine. 2010; 1(1):44–48

Suggested Reading [1] Wu JC, Mummaneni PV, El-Sayed IH. Diseases of the odontoid and craniovertebral junction with management by endoscopic approaches. Otolaryngol Clin North Am. 2011; 44(5):1029–1042

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Posterior Cervical Microforaminotomy and Discectomy

18 Posterior Cervical Microforaminotomy and Discectomy Carter S. Gerard, Lee A. Tan, and Richard G. Fessler Abstract Posterior cervical microforaminotomy and discectomy is an effective minimally invasive surgical technique that can result in decompression of cervical nerve roots and improvement of cervical radiculopathy in patients with foraminal stenosis or lateral disc herniation. This chapter provides a step-by-step guide for this important minimally invasive technique, along with valuable clinical pearls from the senior author (R. G. F.). Keywords: posterior cervical, foraminotomy, discectomy, minimally invasive, tubular dilator, cervical disc herniation

18.1 Introduction Multiple degenerative pathologies of the cervical spine can be successfully treated with posterior decompressive techniques.1, 2,3,4 While anterior cervical procedures are well established as treatments for cervical disc herniation, posterior cervical laminoforaminotomy consistently shows symptom improvement of 90 to 97% for patients with foraminal stenosis or lateral disc herniation.3,5,6,7,8 Posterior decompressive procedures avoid the complications associated with anterior approaches such as esophageal injury, recurrent laryngeal nerve paralysis, dysphagia, and adjacent level disease after fusion.9,10,11,12 While standard open approaches achieve excellent decompression of the lateral recess and neural foramen and are effective, minimally invasive approaches have been developed in order to avoid the extensive subperiosteal stripping of paraspinal musculature, which can result in significant postoperative pain, muscle spasm, and dysfunction in 18 to 60% of patients.4,9, 13,14 Furthermore, preoperative loss of lordosis combined with long segment decompression can contribute to the risk of sagittal plane deformity, a known complication that often obliges fusion at the time of decompression.15,16,17,18 The use of a posterior fusion technique increases operative time, blood loss, surgical risk, and early postoperative pain, and potentially contributes to adjacent level disease. The principal tenet of minimal access techniques is to reduce approach-related morbidity. To that end, the advent of muscle-splitting tubular retractor systems and associated instruments has allowed for the application of minimally invasive techniques to posterior cervical decompressive procedures.14,19 The microforaminotomy/discectomy (MF/D) was first described in a cadaver model and has subsequently been shown to have clinical efficacy equal to open procedures in addition to having less blood loss, shorter hospital stay, and decreased postoperative pain.7,20,21,22,23,24,25

18.2 Indications Radicular symptoms in the upper extremities most commonly occur due to degenerative changes in the cervical spine such as disc herniation or osteophytes within the intervertebral foramen. Regardless of the pathology, it must be lateralized without significant canal stenosis to be amenable to MF/D. Patients with

persistent radicular pain refractory despite at least 6 weeks of effective nonoperative therapy, those with debilitating pain, or those who have developed muscle weakness are appropriate candidates for surgical intervention. The prototypical patient will present to the neurosurgeon with a history of neck pain and unilateral cervical monoradiculopathy, having already undergone initial pain management with first- and second-line analgesics. Determining the proper candidate for surgery is straightforward in patients who present with a clear history of isolated radicular pain in a classical distribution and imaging, which shows foraminal stenosis at the expected level. When the clinical evaluation is not supported by MRI findings, further testing including dynamic imaging or electromyography (EMG) may be helpful.

18.3 Contraindications Relative contraindications to the MF/D include those patients with central pathology or cervical instability.7,8 When an MF is properly performed, the surgeon gains access to the foramen and the most lateral portion of the spinal canal. Therefore, patients with central disc herniations and resulting myelopathy are best treated with an anterior approach. Patients with a progressive kyphotic deformity or suspected instability should not undergo MF/D. While recent series have failed to show an increased risk of postoperative instability in well-selected patients, patients with increased mobility are at elevated risk of frank destabilization and are unlikely to benefit from this procedure.22,23,24,25,26,27,28

18.4 Preoperative Evaluation A preoperative radiographic evaluation follows a detailed history and physical examination and should include magnetic resonance imaging (MRI) or postmyelographic computed tomography (CT), and anteroposterior (AP), lateral, and flexion/ extension cervical radiographs. Preoperative EMG and nerve conduction studies may also assist in the neurological localization of specific radiculopathy. Those patients with radicular symptoms that correlate with electrophysiologic and radiographic findings may be well suited for MF/D, depending on the underlying pathology. ▶ Fig. 18.1a shows a lateralized disc herniation without spinal cord compression on preoperative MR scan. In contrast, ▶ Fig. 18.1b shows moderate cord and nerve root compression due to a herniated disc. The former would be an ideal candidate for MF/D, while an anterior approach would be safer and more effective in the latter. Regardless of the pathology, whether a soft disc or an osteophyte, it must be lateralized without significant canal stenosis to be amenable to MF/D.

18.5 Surgical Technique and Instrumentation Appropriately selected patients, following routine presurgical evaluation and medical clearance, are brought to the operating

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Surgical Techniques

Fig. 18.1 Axial T2-weighted magnetic resonance imaging (MRI) scans of the cervical spine demonstrate: (a) laterally herniated disc to the right with compression of the exiting nerve root; (b) a centrally located disc/osteophyte causing both spinal cord and nerve root compression.

suite. Endotracheal intubation ensues under general anesthesia. Somatosensory and motor evoked potentials are recorded to follow intraoperative spinal cord integrity. Electromyograms of appropriate muscle groups can also be monitored as additional intraoperative feedback. Use of neuromuscular paralytic agents is minimized to better assess intraoperative nerve irritation. A single dose of antibiotics (either cephazolin or vancomycin) is routinely administered before skin incision. Intravenous steroids are not used routinely for patients undergoing micro-endoscopic discectomy/foraminotomy (MED/F). A Foley catheter is generally not needed. With the patient supine on the operating table, the head is secured with a Mayfield Skull Clamp (Integra LifeSciences) (this refers to the skull clamp with three pins that secure the head in place during the procedure) and the patient is brought to the semi-sitting position; the knees are level with the heart. The Mayfield Spine Table Adaptor (Integra LifeSciences) (this refers to the adapter that connects the skull clamp to the operating room [OR] table) is attached to the table between the hip and knees and arched back as necessary to accommodate the patient’s body habitus. Care is taken to maintain the neck in a comfortable, neutral position. The arms are folded and secured across the chest; pressure points are padded to prevent nerve palsies and pressure sores. The fluoroscope is positioned to obtain a lateral view of the cervical spine. Precordial Doppler monitoring is used to monitor the right atrium for air emboli; a central venous catheter is not necessary because of the brevity and minimal blood loss associated with the procedure. After segmental localization with fluoroscopy, a small incision (approximately 1.8 cm) is made 1 cm from midline on the symptomatic side. Soft tissue is bluntly dissected, and the underlying cervical fascia is sharply dissected with scissors or Bovey cautery. Failure to do this places undue strain on the cervical spine and makes serial tissue dilation difficult. The first dilator is then passed through this pathway and docked on the facet complex (▶ Fig. 18.2a). Docking onto the facet avoids the risk of slipping off the lamina into the canal and adds a margin of safety to the approach. Sequential tissue dilators are then passed to obtain a working corridor (▶ Fig. 18.2b,c) with each docking onto the facet. Note that use of a Steinmann pin to localize level is not recommended. Care is taken in advancing the Steinmann pin toward the spine to avoid passing it between the interlaminar space and into the spinal canal. The first dilator is passed using slow careful rotation toward the facet complex. Once the first dilator is passed, the Steinmann pin is removed to

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avoid migration during passage of subsequent dilators. The working channel is then passed over the final muscle dilator and adjusted to the desired position under fluoroscopy (▶ Fig. 18.2d). If the tubular retractor is not docked directly on the facet, dissection of the paraspinal muscle can be done under direct endoscopic or microscopic visualization and then advanced again using the serial muscle dilators. The tubular retractor is then fixed to the flexible arm, which is mounted to the operating table, opposite to the approach, and the endoscope is secured to the tubular retractor (▶ Fig. 18.3). Alternatively, a microscope can be used which provides excellent 3D visualization of the anatomy. Using the microscope, we typically perform the procedure in the sitting position. An arm rest can be used if arm support is helpful by bending the head rest down. A Bovie cautery unit on a long handle is used to circumferentially remove muscle from the operative field. We prefer to work from lateral to medial. The surgeon should always be cognizant of the interlaminar space. The bony anatomy is defined with a curette to appreciate the interlaminar space and facet relationship (▶ Fig. 18.4a). A 1- or 2-mm Kerrison rongeur is used to begin the hemilaminotomy (▶ Fig. 18.4b). After the hemilaminotomy is completed, the foraminotomy can be continued with either the Kerrison rongeur or the Midas Rex Legend Stylus high-speed surgical drill with the hooded telescoping attachment. In either case, the foraminotomy is usually completed using the drill. Whether drilling cephalad, caudal, or lateral to the nerve root, the root itself is protected by holding the hooded telescoping attachment toward the nerve to prevent any soft tissue surrounding the nerve from getting caught up in the rotating drill bit. The nerve is visualized well because of the 30-degree angle on the endoscope. When performing a posterior discectomy, drilling approximately 2 mm of the superior medial pedicle facilitates safe removal of herniated disc fragments and limits nerve root manipulation (▶ Fig. 18.4c–f). Once again the hooded telescoping attachment is used to protect the nerve root (located cephalad to the drill bit) and the medially located dura. The space created by drilling the pedicle also can be used to reduce anterior osteophytes contributing to foraminal stenosis with a down-angled curette. Radiographic and tactile confirmation of the extent of discectomy or foraminotomy is obtained before closing. The wound is copiously irrigated with an antibiotic saline solution. Local bleeding is controlled with Gelfoam and bone wax. Placing a pledget of Gelfoam soaked with methylprednisolone

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Posterior Cervical Microforaminotomy and Discectomy

Fig. 18.2 (a) Lateral intraoperative fluoroscopic image demonstrating initial placement of the first dilator on the facet just below the facet complex. (b,c) Sequential dilators are passed to enlarge the working space to 18 mm over which the tubular retractor is placed. (d) After the final muscle dilator is placed, the dilators are aimed toward the level of interest.

Fig. 18.3 Tubular retractor and endoscopic setup in place to perform MED/F.

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a

b

Cephalad

Medial

Lateral

c

Cephalad

Nerve root

Medial

Cephalad

Nerve root Medial

Lateral

Lateral

Axilla of nerve root

Ligamentum flavum

Caudal

Bone of pedicle

Caudal

Eggshell pedicle under nerve root

Caudal

d e

Facetectomy

f

Cephalad

Medial

HNP

Decompressed nerve root

Lateral

Caudal

Nerve hook delivers HNP

Pedicle Eggshell bone of pedicle under nerve root Fig. 18.4 Step-by-step technique for the minimally invasive posterior cervical foraminotomy/discectomy. (a) The laminofacet complex is identified by removing the overlying soft tissue with Bovie cautery and curettage. (b) A foraminotomy is then performed in standard fashion. (c,d) Drilling the medial superior aspect of the pedicle of the caudal vertebrae allows access to the disc, minimizing nerve root manipulation. Leaving a thin rim of bone between the pedicle and the nerve root during drilling avoids injury to the nerve root. This piece of bone is then removed with a pituitary rongeur. (e,f) The HNP is removed to decompress the root. HNP, herniated nucleus pulposus.

over the laminoforaminotomy is optional; we use it in select cases to help reduce postoperative nerve inflammation. The Gelfoam is removed according to the surgeon’s preference. The fascia and skin are closed with absorbable sutures. Dermabond is used for the final skin layer. The scar is small and cosmetically acceptable (▶ Fig. 18.5).

18.6 Postoperative Care After awaking from general anesthesia, the patient is brought to the postanesthesia care unit and mobilized as early as possible. No collar is necessary. If medically stable, patients are typically discharged home after 2 to 3 hours, although in some cases we have chosen to observe older patients, or those with additional comorbidities, overnight. Discharge medications generally include an opioid/acetaminophen combination pain reliever and a muscle relaxant. Nonsteroidal anti-inflammatory agents are also commonly used. The patient is instructed to remove OR dressing on postoperative day 2 and to return to the office 2 weeks after surgery.

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18.7 Management of Complications Although many complications are possible, our experience has been associated with few. Dural tears occurred in two patients during the senior author’s (R.G.F.) initial clinical experience.5 Direct suture repair of durotomy is rarely indicated. Most minor tears require no specific treatment. Alternative treatments include covering the durotomy with muscle, fat, Gelfoam, or dural substitute, followed by fibrin glue or synthetic. Using this approach, overnight bed rest is usually sufficient to seal the defect. If a larger dural tear occurs, 2 to 3 days of lumbar cerebrospinal fluid drainage could be elected. In our experience, no treatment was necessary and no long-term problems were encountered by these patients. Potential neurological complications include radicular injury from manipulation within the tight foramen or direct mechanical spinal cord injury during dilation or decompression. Vertebral artery injury can be avoided by early detection of dark venous bleeding from the venous plexus surrounding the artery

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Posterior Cervical Microforaminotomy and Discectomy that may arise from accidental dilation lateral to the facet or during overly aggressive dissection laterally in the foramen. Placing the patient in the seated position will aid in minimizing venous bleeding. When bleeding does occur, it can typically be controlled by packing with Gelfoam or other hemostatic product. Cord or root injury during dilation is avoided by incising the cervical fascia before passing the dilators. Postoperative surgical site infection is exceedingly rare after minimally invasive posterior cervical procedures and is exceedingly uncommon for foraminotomies.29 Though recurrent disease and postoperative instability are potential concerns, recent series have failed to show an increased risk.22,23,24,25,26,27,28

18.8 Clinical Case A 43-year-old college professor suffered the acute onset of radiating right arm pain 1 day after digging holes in his backyard. The pain began in his neck, radiated to his right scapula, and traveled down to his arm into the third and fourth digits of his right hand. The pain was intense, graded 10/10 on a visual analog scale without medication, and 2/10 with narcotic pain medication. He denied any bowel, bladder, balance, or sexual dysfunction. On examination, he had weakness (4/5) in finger flexion and wrist flexion of the right hand, and decreased sensation to pinprick in right C7 distribution. A cervical spine MRI demonstrated a right lateral disc herniation at C6–C7 (▶ Fig. 18.6a,b). The patient was taken to surgery for a right posterior MED, which was performed with the patient in the sitting position, as described earlier. A large disc fragment was removed in a stepwise manner as illustrated in ▶ Fig. 18.4. Surgery was completed in 75 minutes with an estimated blood loss of less than 10 mL. The patient was discharged 3 hours after surgery. Four weeks after surgery, he returned to work full-time. By 6 weeks after surgery, his radicular pain had resolved completely, his hand strength was normal, he was completely off narcotic pain medications, and the muscular pain from surgery was nearly resolved as a result of starting physical therapy.

18.9 Conclusion It is possible to effectively treat cervical radiculopathy via minimally invasive techniques. These approaches have several obvious advantages over more invasive open procedures.

Advantages of Minimally Invasive Spine Surgery to Treat Cervical Radiculopathy ● ● ● ●

Fig. 18.5 Typical postoperative incision after MEF/D.

●

Reduced operative time. Decreased hospital stay. Decreased postoperative pain and muscle spasm. Decreased postoperative need for narcotic pain medication. Earlier return to work and normal activities.

Fig. 18.6 (a) Sagittal T2-weighted MRI of the cervical spine shows multiple levels of cervical spondylosis with a disc herniation at C6–C7. (b) Axial imaging of the same patient shows an acute right-sided lateral disc herniation with foraminal compromise.

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Surgical Techniques The decision to use a minimally invasive posterior approach will partly depend on the surgeon’s familiarity with the technique. There is a learning curve associated with implementation of any new technique. We believe that posterior MF/D is associated with fewer operative risks than the anterior cervical foraminotomy or discectomy, and is quite effective in achieving excellent surgical results. With time, minimally invasive approaches will certainly be the preferred methods of treating spinal disorders; continued efforts toward this goal will make minimally invasive approaches possible for a wider spectrum of surgical lesions.

Clinical Caveats ●

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Patients with radiculopathy due to a lateralized osteophyte or disc herniation without cord compression, evidence of instability, or for those where an anterior approach is contraindicated are candidates for microendoscopic discectomy or foraminotomy (MF/D). Care is taken during the approach to the cervical spine especially with placement of the Steinmann pin and first muscle dilator. Gentle rotation toward the spine can pass the pin and serial muscle dilators safely. Final docking of the tubular retractor can be performed under direct visualization if needed. Durotomy is the most common reported complication of MF/D; however, due to the limited dead space, symptomatic cerebrospinal fluid leaks are exceedingly rare. Spinal cord and nerve injury can be avoided by incising the cervical fascia before passing the dilators and by removing the Steinmann pin after inserting the first dilator. MF/D offers the advantages of reduced blood loss, length of stay, postoperative pain and muscle spasm; preservation of motion segments; and decreased risk of iatrogenic sagittal plan deformity, in addition to equivalent efficacy.

References [1] Aldrich F. Posterolateral microdisectomy for cervical monoradiculopathy caused by posterolateral soft cervical disc sequestration. J Neurosurg. 1990; 72(3):370–377 [2] Crandall PH, Batzdorf U. Cervical spondylotic myelopathy. J Neurosurg. 1966; 25(1):57–66 [3] Henderson CM, Hennessy RG, Shuey HM, Jr, Shackelford EG. Posterior-lateral foraminotomy as an exclusive operative technique for cervical radiculopathy: a review of 846 consecutively operated cases. Neurosurgery. 1983; 13 (5):504–512 [4] Ratliff JK, Cooper PR. Cervical laminoplasty: a critical review. J Neurosurg. 2003; 98(3) Suppl:230–238 [5] Khoo L, Perez-Cruet M, Fessler R. Posterior cervical microendoscopic foraminotomy. In: Perez-Cruet M, Fessler R, eds. Outpatient Spinal Surgery. St. Louis, MO: Quality Medical Publishing, Inc.; 2006:71–93 [6] Holly LT, Moftakhar P, Khoo LT, Wang JC, Shamie N. Minimally invasive 2-level posterior cervical foraminotomy: preliminary clinical results. J Spinal Disord Tech. 2007; 20(1):20–24

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[7] Ruetten S, Komp M, Merk H, Godolias G. Full-endoscopic cervical posterior foraminotomy for the operation of lateral disc herniations using 5.9-mm endoscopes: a prospective, randomized, controlled study. Spine. 2008; 33 (9):940–948 [8] Jagannathan J, Sherman JH, Szabo T, Shaffrey CI, Jane JA. The posterior cervical foraminotomy in the treatment of cervical disc/osteophyte disease: a singlesurgeon experience with a minimum of 5 years’ clinical and radiographic follow-up. J Neurosurg Spine. 2009; 10(4):347–356 [9] Fessler RG, Khoo LT. Minimally invasive cervical microendoscopic foraminotomy: an initial clinical experience. Neurosurgery. 2002; 51(5) Suppl:S37–S45 [10] Hilibrand AS, Robbins M. Adjacent segment degeneration and adjacent segment disease: the consequences of spinal fusion? Spine J. 2004; 4(6) Suppl:190S–194S [11] Ishihara H, Kanamori M, Kawaguchi Y, Nakamura H, Kimura T. Adjacent segment disease after anterior cervical interbody fusion. Spine J. 2004; 4 (6):624–628 [12] Xia X-P, Chen H-L, Cheng H-B. Prevalence of adjacent segment degeneration after spine surgery: a systematic review and meta-analysis. Spine. 2013; 38 (7):597–608 [13] Hosono N, Yonenobu K, Ono K. Neck and shoulder pain after laminoplasty. A noticeable complication. Spine. 1996; 21(17):1969–1973 [14] Siddiqui A, Yonemura K. Posterior cervical mircoendoscopic diskectomy and laminoforaminotomy. In: Kim D, Fessler R, Regan JJ, eds. Endoscopic Spine Surgery and Instrumentation: Percutaneous Procedures. New York, NY: Thieme; 2005:66–73 [15] Albert TJ, Vacarro A. Postlaminectomy kyphosis. Spine. 1998; 23(24):2738–2745 [16] Kaptain GJ, Simmons NE, Replogle RE, Pobereskin L. Incidence and outcome of kyphotic deformity following laminectomy for cervical spondylotic myelopathy. J Neurosurg. 2000; 93(2) Suppl:199–204 [17] Perez-Cruet MJ, Samartzis D, Fessler RG. Microendoscopic cervical laminectomy. In: Perez-Cruet M, Khoo L, Fessler R, eds. An Anatomic Approach to Minimally Invasive Spine Surgery. St. Louis, MO: Quality Medical Publishing, Inc.; 2006:349–365 [18] Yonenobu K, Okada K, Fuji T, Fujiwara K, Yamashita K, Ono K. Causes of neurologic deterioration following surgical treatment of cervical myelopathy. Spine. 1986; 11(8):818–823 [19] Khoo L, Bresnahan L, Fessler R. Cervical endoscopic foraminotomy. In: Fessler R, Sekhar L, eds. Atlas of Neurosurgical Techniques: Spine and Peripheral Nerves. Vol. 1. New York, NY: Thieme; 2006:785–792 [20] Burke TG, Caputy A. Microendoscopic posterior cervical foraminotomy: a cadaveric model and clinical application for cervical radiculopathy. J Neurosurg. 2000; 93(1) Suppl:126–129 [21] Roh SW, Kim DH, Cardoso AC, Fessler RG. Endoscopic foraminotomy using MED system in cadaveric specimens. Spine. 2000; 25(2):260–264 [22] Kim K-T, Kim Y-B. Comparison between open procedure and tubular retractor assisted procedure for cervical radiculopathy: results of a randomized controlled study. J Korean Med Sci. 2009; 24(4):649–653 [23] Winder MJ, Thomas KC. Minimally invasive versus open approach for cervical laminoforaminotomy. Can J Neurol Sci. 2011; 38(2):262–267 [24] Lidar Z, Salame K. Minimally invasive posterior cervical discectomy for cervical radiculopathy: technique and clinical results. J Spinal Disord Tech. 2011; 24(8):521–524 [25] Lawton CD, Smith ZA, Lam SK, Habib A, Wong RHM, Fessler RG. Clinical outcomes of microendoscopic foraminotomy and decompression in the cervical spine. World Neurosurg. 2014; 81(2):422–427 [26] Minamide A, Yoshida M, Yamada H, et al. Clinical outcomes of microendoscopic decompression surgery for cervical myelopathy. Eur Spine J. 2010; 19 (3):487–493 [27] Yabuki S, Kikuchi S. Endoscopic partial laminectomy for cervical myelopathy. J Neurosurg Spine. 2005; 2(2):170–174 [28] Dahdaleh NS, Wong AP, Smith ZA, Wong RH, Lam SK, Fessler RG. Microendoscopic decompression for cervical spondylotic myelopathy. Neurosurg Focus. 2013; 35(1):E8 [29] O’Toole JE, Eichholz KM, Fessler RG. Surgical site infection rates after minimally invasive spinal surgery. J Neurosurg Spine. 2009; 11(4):471–476

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Posterior Cervical Approach

19 Posterior Cervical Approach Michael Y. Wang, Mick J. Perez-Cruet, Dino Samartzis, and Richard G. Fessler Abstract The posterior approach to the cervical spine is one of the most common approaches to the spine. Accessing the spinal column and its neural elements through the posterior musculature of the neck has been performed for nearly a hundred years. Nonetheless, there are important elements of preparation and technical nuances that have to be considered when performing the posterior cervical approach. This chapter summarizes these considerations. Keywords: neck, laminectomy, laminoplasty, musculature, posterior approach, cervical

19.1 Introduction Compression of the spinal cord from cervical spondylosis was first described in 1911 by Bailey and Casamajor1 and in 1928 by Stookey,2 who described a patient with quadriplegia resulting from spinal cord compression due to cervical spinal stenosis.

However, it was not until 1952, when Brain, Northfield, and Wilkinson described the role of vascular supply to the spinal cord and the manifestation of myelopathic symptoms, that cervical stenosis causing myelopathy was identified as a distinct entity. Lees and Turner3 further noted the lengthy clinical course of the disease accompanied by a long duration of nonprogressive disability. Cervical spondylosis may be the most common underdiagnosed spine disorder whose true incidence is unknown.4 Most patients present in the fifth decade of life, but the condition is not limited therein and is indiscriminate of age and degree of disease manifestation.5,6,7 Levels below C3–C4 are primarily affected, with predominance at C5–C6 followed by C6–C7 and C4–C5.8 Radiographically, spondylotic manifestations are evident in 25 to 50% of the population by age 50, and they are seen in as many as 85% of individuals by their mid-60 s.9,10 Treatment is performed using an anterior, posterior, or combined surgical decompression approach(▶ Fig. 19.1). A number of disorders may mimic the symptoms of cervical spondylosis and need to be differentiated for proper diagnosis.

Fig. 19.1 (a) Preoperative axial view; (b) preoperative sagittal CT/myelogram in patient presenting with weakness and myelopathy showing significant multilevel cervical stenosis. Patient has multiple bridging osteophytes consistent with the diagnosis of diffuse idiopathic skeletal hyperostosis (DISH). (c) Postoperative plain AP view; (d) postoperative lateral radiographs following multilevel posterior decompression, fusion, and lateral mass instrumentation. (e) Sagittal and (f) axial MRIs in a patient with myelopathy primarily from multiple anterior cervical disc herniations compressing spinal cord. (g) Postoperative lateral radiograph following multilevel anterior cervical decompression, fusion, and instrumentation.

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Differential Diagnosis: Cervical Spondylosis Disorders exhibiting some of the same symptomology include: ● Torticollis. ● Athetosis. ● Chronic dystonia. ● Cerebral palsy. ● Syringomyelia. ● Low-pressure hydrocephalus. ● Cerebral hemisphere lesions. ● Amyotrophic lateral sclerosis. ● Down’s syndrome. ● Multiple sclerosis. ● Neoplastic lesions.

Cervical spondylosis is an insidious, progressive disease process that presents with a number of symptoms that are frequently refractory to conservative nonoperative management. Nevertheless, controversy exists over the optimal choice of surgical treatment for this disorder. For patients with progressive symptoms, despite nonoperative treatment, posterior decompression is an appropriate treatment option. However, traditional methods of cervical decompressive laminectomy require stripping of the posterior cervical muscular, as well as ligamentous, attachments to the spine. In so doing, patients experience considerable postoperative pain from muscle spasms and muscle injury. Some patients will go on to develop iatrogenic swan neck deformity, which is particularly prevalent in younger individuals undergoing multilevel posterior cervical decompression.11,12 Relatively recent improvements in posterior spinal instrumentation, namely, lateral mass plates and/or screw-rod constructs, have made fusion more attractive. However, this method adds considerable cost to the procedure, does nothing to reduce iatrogenic muscle and ligamentous injury, and can result in considerable complications from misplacement of screws. The laminoplasty technique attempts to widen the diameter of the spinal canal by preserving the posterior spinal elements, namely, the spinous processes and laminae, while maintaining the dynamic motion of the cervical spine. However, this technique still requires extensive muscle dissection and retraction. Recent studies have shown that despite attempts to maintain spinal mobility using the laminoplasty technique, many patients develop progressive limitation of cervical range of motion similar to that seen after laminectomy and fusion and/or continue to experience significant axial neck pain.11 Cervical laminectomy may result in instability and progressive kyphotic deformity in some adults, particularly when extensive resection of the facets has been performed.12,13 In particular, progressive kyphotic deformity and cervical instability are common in children after laminectomy.12,14,15 Bone grafting and internal fixation using lateral mass plates have been reported to prevent the development of postlaminectomy instability and deformity.16 Some investigators believe that development of a postlaminectomy membrane may yield late deterioration after laminectomy with or without fusion.17

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To address many of the issues encountered with more traditional posterior cervical decompressive approaches, namely, significant muscle, ligament, and bone removal, postoperative pain, and iatrogenic instability, a minimally invasive microendoscopic cervical laminectomy technique was developed. The effectiveness of this technique was first tested in cadaveric specimens before being applied in the clinical setting (see Cadaveric Studies (p. 199) later in this chapter). This chapter will review both the results of the cadaveric study and recent surgical experiences with this technique. It should be emphasized that the clinical application of this technique portends a steep learning curve, and our initial clinical experience only includes those patients with one- to three-level stenosis, despite the effectiveness of applying this technique to four-level decompression in the cadaveric model.

19.2 Anatomy and Pathophysiology The cervical spine consists of seven vertebrae in which the first two vertebrae, the atlas and the axis, compose the high cervical region and are considered integral components of the craniovertebral junction. These vertebrae are unique in structure and are rarely involved in the degenerative process of cervical spondylosis. Cervical vertebrae C3 through C7, otherwise known as the subaxial spine, are distinguished from the high cervical vertebrae by the presence of uncovertebral joints and the morphology of the vertebral bodies. The lateral masses of the cervical spine are composed of superior and inferior articular processes, which are thinnest at the C6–C7 level and have dimensions that increase from depth to height to width.18 The spinal canal has a triangular configuration with a varied sagittal diameter of approximately 17 to 18 mm from C3–C6 to 15 mm at C7.19,20,21,22 In vitro biomechanical testing has determined that the anterior column of the cervical spine transmits 36% of the applied load, whereas each pair of facets transmits 32% of the total load, stressing the importance of the posterior structures in cervical stability.23 The diameter of the spinal cord is not uniform in the cervical spine region. At the C1 level, the spinal cord occupies one-half of the spinal canal. At the C5–C7 level, the cord expands and occupies three-fourths of the canal diameter, which increases the incidence of cord compression at the lower cervical spine. Cailliet24 determined that cervical spinal canal stenosis is more uniform and restrictive in the diagonal anteroposterior diameter than the transverse. The size of the spinal canal is a predisposing factor in symptomatic cervical stenosis. Those patients with congenitally smaller canals are potentially at increased risk. A canal anteroposterior diameter of less than 13 mm has been established as a diagnostic standard of medullary symptoms from spondylotic encroachment.24,25 The anterior spinal artery provides 60 to 70% of the vascular supply of the cervical spinal cord.26 Although the midsagittal position of the anterior spinal artery is at risk for direct compression from disc protrusion or degenerative hypertrophies, its segmental medullary feeders provide collateral blood flow

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Posterior Cervical Approach to enhance cord perfusion. Mannen27 and Jellinger28 also reported that the lower cervical arteries are also more predisposed to atherosclerotic changes. The normal cervical spine has a sagittal lordotic curvature mainly attributed to the intervertebral disc height, which accounts for 22% of the overall length of the cervical spine. The disc space height is greatest at the anterior aspect of the interspace and accounts for the natural lordotic curvature of the cervical spine. Motion is greatest at the intervertebral discs, and compressive and tensile forces are distributed throughout the cervical spine. Loss of cervical lordosis is often attributed to dehydration of the intervertebral discs and may contribute to altered biomechanical forces throughout the cervical spine, resulting in reactive hyperostotic changes in the adjacent vertebral endplates and development of a spondylotic bar due to posterior disc protrusion. Posterior disc herniation may contribute to impingement of the exiting nerve root and produce radiculopathic symptoms. In combination, these physiologic alterations may contribute to overriding of the uncinate processes leading to destruction of the uncovertebral joint space. Further progression of this degenerative process may lead to subsequent hypertrophy of the facet joints, ligamentum flavum, and ossification of the posterior longitudinal ligament. Moreover, manifestation of pain is attributed to compression or stretching of the sinuvertebral nerve, and altered integrity or distortion of the apophyseal facet joints, ligamentous elements, and cervical musculature.29 Superimposed hypermobility at the adjacent levels may further induce hypertrophy of the respective motion segment and threaten encroachment on the spinal cord and nerve roots. Additionally, the pincher phenomenon also contributes dynamically to instability in addition to physical cord encroachment. In flexion, the anteroposterior diameter decreases 2 to 3 mm, and the superior rim of the posterior vertebral body produces tension on the spinal cord. Although spinal cord tension is minimized in extension, the cord is still susceptible to compression by buckling of the ligamentum flavum. Lateral motion of the neck on the side of compression may further reduce foraminal diameter and produce or exacerbate symptoms. In addition, compensatory subluxation may develop above the level of the rigid spondylotic segment.

19.3 Surgical Approach Surgical treatment can be through either an anterior or posterior approach. The anterior approach consists of decompression and interbody or strut grafting with or without instrumentation.30,31,32,33 The posterior approach consists of laminoplasty or laminectomy with fusion with or without internal fixation (see ▶ Fig. 19.1). Selection of an approach is often dependent on: ● Surgeon preference. ● Source of the cord compression (i.e., either anterior or posterior). ● Age of patient. ● Number of vertebral levels involved. ● Maintenance of lordotic alignment. The anterior approach is recommended for patients with kyphotic curvature. The posterior approach is preferred in patients

with preserved lordosis and more than three levels of involvement. The principal advantage of the posterior approach is its relative ease and familiarity among spine surgeons. This approach has been clearly established as a safe and effective means of decompressing the cervical spinal cord and nerve roots.34,35,36 Nonetheless, the objective of any surgical approach is to maintain spinal stability and provide sufficient decompression without compromising sagittal balance.

19.4 Surgical Technique 19.4.1 Cadaveric Studies Five cadaveric specimens were imaged preoperatively and postoperatively with CT myelography. Approximately 50 mL of Omnipaque contrast agent was injected into the subdural space of the cervical spine followed by CT imaging. In the cadaver laboratory, the cadaver specimen was placed on a radiolucent table in the prone position with the lateral fluoroscopic C-arm in place. The approach to the posterior cervical spine was achieved by means of the microendoscopic approach previously described for treating herniated discs of the lumbar spine as well as lumbar stenosis.37 The C4–C5 level was first identified with a spinal needle and lateral fluoroscopic imaging, and a small incision was made approximately 2 cm lateral to the midline. A Kirschner wire (K-wire) was then passed under fluoroscopic visualization and docked on the C4–C5 laminofacet junction. The initial muscle dilator was passed over the K-wire, docked securely on bone, and then the K-wire was removed. Subsequent dilators were then passed, and an 18-mm-diameter tubular retractor was passed over the final dilator and locked in place. The muscle dilators were removed and the endoscopic assembly was white balanced, focused, and passed down the tube for visualization during the operation. Using a Bovie cautery, the soft tissue overlying the lamina and medial facet was removed. Fluoroscopic imaging both in the anteroposterior and lateral projections was used to aid in proper surgical orientation and location with wanding of the endoscopic assembly to perform a multilevel decompression (▶ Fig. 19.2). With the endoscopic assembly facing away from the surgeon, the ipsilateral lamina was removed using a highspeed drill and Kerrison punch (▶ Fig. 19.3a). This allowed for good visualization using the 30-degree angulation of the endoscope and also allowed for ipsilateral cervical foraminotomy as previously described.38,39 Wanding the tubular retractor–endoscope assembly rostrally and caudally, up to a four-level laminectomy was performed.19 Once the ipsilateral laminectomy (or laminectomies) was performed, the endoscope was repositioned facing the surgeon on the tubular retractor.19 This allowed for contralateral cervical decompression (▶ Fig. 19.3b). The spinous process was identified, and drilling of the underside of the spinous process and contralateral lamina was performed (▶ Fig. 19.3c). This maintains the bony integrity of the spinous process and contralateral lamina with no removal of any muscle or ligament (▶ Fig. 19.3d). Therefore, much of the bone, muscular, and ligamentous integrity was maintained. This may reduce the incidence of postoperative muscle pain, spasms, and iatrogenic instability that is seen in more traditional approaches. Postoperative CT myelography confirmed adequate cervical decompression (▶ Fig. 19.4a–d). Subsequent open cadaveric dissection revealed

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Fig. 19.2 Cadaveric setup showing endoscopic assembly and C-arm positioning for lateral fluoroscopic imaging. C2 to C7 decompression is achieved by wanding the endoscopic assembly in a caudal (a,b) and rostral (c,d) direction.

a

Undercut spinous process and contralateral lamina

b

Eggshell contralateral lamina

Fig. 19.3 Step-by-step technique for performing ipsilateral laminectomy. (a) Positioning of the endoscopic assembly. (b) Under drilling of spinous process and contralateral lamina. (c) Axial view illustrates drilling and decompression of the spinal cord. (d) Axial view demonstrating postoperatively the ipsilateral laminectomy with removal of the underside of the spinous process and contralateral lamina, achieving spinal cord decompression. This same technique is used for decompression of spinal stenosis in the lumbar spine (see Chapter 35).

Rotate scope to 6 o’clock position

c

d Ligamentum flavum Eggshell

Postoperative

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Posterior Cervical Approach

Fig. 19.4 Preoperative (a,b) and postoperative (c,d) CT-myelogram images showing adequate decompression of the cervical spinal cord. (e) Open cadaveric dissection showing extent of bone removal. Note the preservation of the spinous process and contralateral lamina achieved with under drilling of the spinous process and contralateral lamina.

adequate spinal cord decompression, while much of the posterior bony and muscular attachments of the cervical spine were preserved (▶ Fig. 19.4e).

19.4.2 Current Clinical Experience Dahdaleh et al40 have published a preliminary experience with this technique. This involved using a working channel through a 1.5-cm skin incision posteriorly. The procedure was similar to that described above for the cadaveric development of this technique. Somatosensory evoked potentials and motor evoked potentials are placed during general anesthesia prior to final positioning of the patient. The original skin incision was marked and localized with fluoroscopy 15 mm ipsilateral to the midline. After infiltration with a combination of 0.5% Marcaine and 1:200,000 epinephrine solution for local anesthesia and hemostasis, the 2-cm incision is made with a #15 scalpel blade.

Soft Tissue Dissection Monopolar electrocautery is used to extend the incision deep to the subcutaneous tissue. The trapezius and paraspinal

muscle fascia are opened under direct visualization with Metzenbaum scissors. Metz scissors are used to bluntly dissect the paraspinal muscles down to the laminofacet junction. The smallest tubular dilator is placed onto the ipsilateral laminofacet junction at the surgical level and confirmed with lateral fluoroscopy. Sequential serial muscle-splitting dilating tubes are placed until the final expandable tubular retractor is secured with the flexible arm attached to the operating table. Lateral fluoroscopy is used to confirm the final retractor tube is centered over the ipsilateral laminofacet junction (left C4–C6). The remainder of the soft tissue overlying the C4–C6 laminofacet is removed with monopolar and/or bipolar electrocautery. The endoscope is attached to the retractor for the bony decompression. An up-angled curette is used to define the sublaminar plane of C4–C6. A combination of Kerrison rongeurs and a pneumatic drill is used to perform the laminotomies and create the rostral and caudal surgical borders. Caution should be exercised to prevent inadvertent plunging of the pneumatic drill and potential injury to the dura and spinal cord below. After the ipsilateral bony decompression is complete, the tubular retractor is repositioned in a medial direction to facilitate the contralateral decompression from a unilateral approach. The

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Fig. 19.5 (a,b) Pre- and postoperative sagittal and (c,d) pre- and postoperative axial T2-weighted MRI images in patient undergoing multilevel minimally invasive cervical decompression for spinal stenosis. (e) Intraoperative endoscopic image showing orientation and decompression of the spinal cord.

pneumatic drill and Kerrison rongeurs are used to resect the ventral aspect of the overlying spinous processes as well as the contralateral lamina up to the contralateral pedicles. After completion of the bilateral bony decompression, an up-angled curette is used to separate the ligamentum flavum from the dura. The ligament is carefully resected with Kerrison rongeurs bilaterally until the thecal sac is completely decompressed (▶ Fig. 19.5). Hemostasis is achieved with a combination of Surgifoam (Ethicon, Johnson & Johnson company), bipolar electrocautery, and bone wax. Antibiotic irrigation is used and the surgical field is inspected for any residual bleeding or sites of CSF leakage prior to closure. A total of 10 patients were treated using this tubular decompression method. In this pilot series, the average age was 67 ± 7.7 years. All patients had myelopathy, but four also had radicular symptoms and received additional foraminotomies at the time of the index surgery. An average of 2.2 (range, 1– 4) segments were treated (▶ Table 19.1).40 The mean blood loss was 32.3 ± 12.5 mL, and the mean hospitalization time was 1.6 ± 0.5 days. The average follow-up time for the patients was 18.9 ± 32.1 months. The mean Nurick score was 1.6 ± 0.7 preoperatively and improved to 0.3 ± 0.7 postoperatively, which was a statistically significant difference (p = 0.0005). Postoperative Odom scores indicated excellent outcomes for four patients, good outcomes for three, fair outcomes for two, and poor outcome for one. None of the 10 patients experienced intraoperative or postoperative complications. While these outcomes were excellent, the patients were chosen for this procedure from a total of 248 patients treated for cervical myelopathy during the study accrual period(▶ Fig. 19.6).

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Table 19.1 Summary of surgical experience Mean ± standard deviation Age

67 ± 7.7 y

Number of levels treated

2.2 (range,1–4)

Blood loss

32.3 ± 12.5 mL

Hospitalization stay

1.6 ± 0.5 d

Follow-up

18.9 ± 32.1 mo

Pre-op Nurick score

1.6 ± 0.7

Post-op Nurick score

0.3 ± 0.7

Complications

0

19.5 Management of Complications 19.5.1 Postoperative Kyphosis Although cases of symptomatic postlaminectomy kyphosis are well described in the literature, their incidence and relevance are unclear.41 Addition of fusion to the laminectomy procedure obviates these concerns16,42 Three groups of patients are at significant risk of developing postlaminectomy instability or spinal deformity43: ● Individuals younger than 25 years. ● Trauma cases. ● Laminectomy combined with extensive facet dissection.

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Posterior Cervical Approach

Fig. 19.6 (a,b) Sagittal and axial preoperative T2-weighted MRI images showing central cord compression at the C3–C4 level (blue arrow). (c) View of the spinal dura through the endoscope after adequate decompression using the minimally invasive technique described.

Development of postlaminectomy kyphosis is a significant risk in younger patients.12,44,45 According to Cattel and Clark,12 children are predisposed to instability because of skeletal and ligamentous laxity, neuromuscular imbalance, and the formation of bone deformities as a consequence of osseous development. Adults may not be susceptible to similar patterns of spinal degeneration because of ligamentous changes with aging. Yasuoka et al15 report that 90% of patients younger than 15 years undergoing cervical or cervicothoracic laminectomy developed kyphotic spinal deformity. All patients younger than 15 years undergoing cervical laminectomy alone developed kyphosis. Significantly fewer patients older than 15 years developed a spinal deformity after laminectomy. Excluding cases of trauma and facetectomy, no adult patient developed a spinal deformity significant enough to require fusion.14 In adult patients, development of postlaminectomy spinal deformity clearly correlates with facet disruption or resection. In cadaver studies, resection of more than 50% of the facet joint and capsule is associated with acute instability.46,47 Herkowitz48 reported a 25% incidence of kyphotic deformity within 2 years after cervical laminectomy and partial bilateral facetectomy. Capsule resection alone also results in increased cervical motion in cadaver studies.49 Less severe destabilization of the cervical spine, perhaps yielding slowly progressive deformity in spinal alignment, may be expected with less severe facet joint and capsule injury. Many cases of symptomatic postlaminectomy cervical kyphosis have been reported. Development of instability and spinal deformity may produce late deterioration in postlaminectomy patients.50,51,52 Adams and Logue53 correlated late deterioration in laminectomy patients with increased postoperative cervical spine motion. Numerous series attest to a late deterioration in postlaminectomy patients, with some series reporting up to 50% of patients affected.16,53,54,55 However, kyphotic deformities may remain asymptomatic. Kaptain

et al56 reported a postlaminectomy kyphosis rate of 21%; no correlation was found between postoperative alignment and clinical outcome. Crandall and Gregorious,36 in their report of long-term follow-up of cervical laminectomy patients, found significant rates of early and late deterioration. They did not emphasize development of instability in their patient population, but offered only limited radiographic follow-up.

19.6 Alternate Surgical Procedures 19.6.1 Laminectomy with Fusion and Instrumentation Because of concerns over postoperative worsening of spinal alignment after laminectomy alone, fusion was added to the procedure to prevent delayed malalignment and loss of sagittal balance. A variety of fusion techniques have been offered in the literature, including facet wiring, lateral mass plate fixation, and polyaxial screw and rod fixation. All share the goal of immediate cervical fixation to promote bone fusion. Goel et al42 demonstrated, in a cadaver model, that posterior facet wiring limits the immediate instability generated by laminectomy. In a long-term follow-up of patients undergoing laminectomy with fusion, Kumar et al16 found no instability, progression of spinal deformity, or late clinical deterioration after laminectomy with lateral mass plate fusion. Appropriate application of lateral mass plating screws has been scrutinized in an attempt to obtain proper placement, avoid neural and vascular injury, and ascertain optimal fixation. Two widely used techniques, the Roy-Camille and the Magerl techniques, have been established as relatively safe and effective.57 However, in a comparison of these two techniques, Heller et al57 found a 10.8 and 26.8% risk of nerve root injury, respectively. Our

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Surgical Techniques experience with the Magerl technique indicated that screw length of 12 mm avoids nerve root injury and allows for adequate bone fixation (author M. J. P-C., personal experience). Moreover, the Magerl technique was noted to have fewer facet joint violations, although a proper screw trajectory was difficult to achieve at the cervicothoracic junction. To address such concerns, An et al18 proposed an alternative to these established screw placement techniques and noted that anatomic variations existed that accounted for inconsistent interfacet distances commonly implemented as markers in screw trajectory methods. Nonetheless, instrumentation-related complications are always a concern as is the potential for loss of cervical alignment, nerve injury, facet penetration, pseudarthrosis, and iatrogenic foraminal stenosis.58,59,60 However, lateral mass plating has the capability for restoring lordosis.37,61,62 Coupled with fusion, lateral mass plating further minimizes the risk of kyphotic deformity and instability. Kumar et al16 reported on 25 patients who had an average 47.5 months’ follow-up after laminectomy with lateral mass plate fusion. Most patients presented with gait difficulties, upper extremity and hand weakness, and sensory disturbances. Eighty percent of patients had a good outcome, and 76% of patients had improved myelopathy scores. None of the patients developed spinal deformities, and patients with preoperative kyphosis or Sshaped deformities remained stable. There were no instances of late deterioration.

19.6.2 Laminoplasty Cervical laminectomy has been an established procedure providing sufficient decompression. However, extensive cervical laminectomy induces alterations in sagittal curvature that may contribute to progressive kyphotic deformity, instability resulting in compromise or destruction of bony or ligamentous structures, and scar tissue or perineural adhesions. In an attempt to diminish the incidence of complications and poor outcomes associated with laminectomy, cervical laminoplasty was developed.19 Laminoplasty was first described in 1973 by Hattori,63 who demonstrated a Z-shaped method. The procedure generated an interest in this technique and led to numerous laminoplasty variations, primarily from Japan, which are best classified as Z-shaped, midline or bilateral, and unilateral. The laminoplasty technique preserves posterior bony elements and spinoligamentous structures, and minimizes muscle detachment to reduce the incidence of postoperative kyphotic deformity and instability often associated with laminectomy. Multilevel radiculopathy, myeloradiculopathy, and multilevel cervical spinal myelopathy are indications for laminoplasty. However, an anterior approach is preferred for bilateral radiculopathy. Laminoplasty is thought to be a viable option if cervical lordosis is maintained with minimal to no preexisting neck pain. Additional indications for using the laminoplasty technique might include involvement of more than three vertebral levels, cervical spinal myelopathy in younger patients, ossification of the posterior longitudinal ligament, and thickening of the ligamentum flavum. Although various laminoplasty techniques have been developed and vary based on the location of the “hinge” to maintain the opening, an “open-door” or unilateral laminoplasty is a

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common procedure whose initial exposure and intraoperative patient positioning is the same as that used in the aforementioned laminectomy technique. The unilateral laminoplasty involves removal of the tips of the spinous processes of the involved levels and bilateral thinning of the laminofacet junction to the inner cortex with a high-speed burr.64 An opening is selected based on the patient’s dominant symptomatic side, and a hinge is maintained by preserving the inner cortical laminar layer. A vertebral spreader is then used to open the canal by reflecting the ipsilateral cut lamina, spinous process, and contralateral “greensticked” lamina to the contralateral side in an open-hinged fashion. As the canal is opened, the ligamentum flavum and soft tissue adhesions are carefully resected. It is often necessary to cut the most caudal and rostral ligamentous attachments to freely hinge the posterior spinous structures. Once opened, bone grafts, struts, sutures, plating, or a combination of these is used to maintain the opening. Although the risks of instability remain, complications associated with laminectomy are reduced with laminoplasty. Matsunaga et al65 noted that laminectomy had a 33% incidence of a buckling type of alignment as compared to 6% after laminoplasty. Unlike laminectomy after fusion and instrumentation, range of motion has been reported to be preserved after laminoplasty.48,66 This may be an advantage when using the technique, particularly in younger patients with cervical spinal myelopathy. Nevertheless, complications exist with laminoplasty and may arise in the open-door setting, including epidural hematoma formation and nerve root injury.67

19.6.3 Skip Laminectomy for Muscle Attachment Preservation Respecting the principles of minimally invasive surgery as preservation of critical soft tissue structures, several Japanese groups, beginning with Shiraishi,68 have explored a mini-open approach for dorsal decompression. The reasoning is that the size of the skin incision is not the critical measure of how destructive a procedure is. Rather, preservation of muscular bellies and their attachments is the priority. These surgeons have innovated the concept of “skip laminectomy” whereby the critical attachments of the multifidus muscles to the spinous processes and lamina are preserved and the surgeon works through corridors free of muscle. This technique is essentially a fenestration procedure. Sivaraman et al69 investigated the use of this technique in comparison to standard laminoplasty. The study was prospective but not randomized, with 25 patients in each treatment group. All patients had cervical spondylotic myelopathy and were treated from C3–C7. Follow-up was a minimum of 2 years. The investigators found that skip laminectomy provided adequate cord decompression but was associated with less blood loss, neck stiffness, pain, and loss of motion. Yukawa and colleagues70 performed a randomized comparison study between skip laminectomy and double door laminoplasty, but they were unable to identify any benefits with the MIS procedure as compared to conventional laminoplasty with regard to blood loss, operative time, pain, and range of motion.

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Posterior Cervical Approach

Clinical Caveats ●

●

●

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As discussed in this chapter, there are a variety of methods to address cervical spinal stenosis. Optimal approach for each individual patient can be determined based on the pathology (i.e., anterior or posterior). CT/myelogram can be useful in combination with MRI to determine whether spinal stenosis is due to soft or calcified cervical disc. Minimally invasive techniques are being applied to address these issues that have the added benefit of preserving the normal anatomical integrity of the spine; they have a steep learning curve and should be applied judiciously.

19.7 Conclusion A number of techniques exist for the treatment of cervical stenosis. Posterior approaches afford the advantage of being familiar to spine surgeons. The techniques of laminectomy, laminectomy with fusion and instrumentation, and laminoplasty have advantages and disadvantages as reviewed earlier. However, these traditional techniques require extensive muscle dissection, resulting in muscle denervation, atrophy, and postoperative pain. The microendoscopic cervical laminectomy procedure described herein is a useful innovation in less invasive spinal techniques that result in quicker recovery times, less postoperative pain, maintenance of dynamic spinal motion, and reduced iatrogenic instability by maintaining the normal musculature, bone, and ligamentous anatomy of the cervical spine. Additional clinical studies are needed to assess the clinical efficacy of this technique for the treatment of cervical stenosis.

References [1] Bailey P, Casamajor L. Osteo-arthritis of the spine as a cause of compression of the spinal cord and its roots: With reports of five cases. J Nerv Ment Dis. 1911; 38:588–609 [2] Stookey B. Compression of the spinal cord due to ventral extradural cervical chordomas: diagnosis and surgical treatment. Arch Neurol Psychiatry. 1928; 20:275–291 [3] Lees F, Turner JWA. Natural history and prognosis of cervical spondylosis. BMJ. 1963; 2(5373):1607–1610 [4] Dillin WH, Watkins RG. Cervical myelopathy and cervical radiculopathy. Semin Spine Surg. 1989; 1(4):200–208 [5] Clarke E, Robinson PK. Cervical myelopathy: a complication of cervical spondylosis. Brain. 1956; 79(3):483–510 [6] LaRocca H. Cervical spondylotic myelopathy: natural history. Spine. 1988; 13 (7):854–855 [7] Crandall PH, Batzdorf U. Cervical spondylotic myelopathy. J Neurosurg. 1966; 25(1):57–66 [8] DePalma AF, Rothman R. The Intervertebral Disk. Philadelphia, PA: WB Saunders; 1970 [9] Friedenberg ZB, Miller WT. Degenerative disc disease of the cervical spine. J Bone Joint Surg Am. 1963; 45:1171–1178 [10] Payne EE, Spillane JD. The cervical spine: an anatomico-pathological study of 70 specimens (using a special technique) with particular reference to the problem of cervical spondylosis. Brain. 1957; 80(4):571–596 [11] Ratliff JK, Cooper PR. Cervical laminoplasty: a critical review. J Neurosurg. 2003; 98(3) Suppl:230–238 [12] Cattell HS, Clark GL, Jr. Cervical kyphosis and instability following multiple laminectomies in children. J Bone Joint Surg Am. 1967; 49(4):713–720

[13] Katsumi Y, Honma T, Nakamura T. Analysis of cervical instability resulting from laminectomies for removal of spinal cord tumor. Spine. 1989; 14 (11):1171–1176 [14] Yasuoka S, Peterson HA, MacCarty CS. Incidence of spinal column deformity after multilevel laminectomy in children and adults. J Neurosurg. 1982; 57 (4):441–445 [15] Yasuoka S, Peterson HA, Laws ER, Jr, MacCarty CS. Pathogenesis and prophylaxis of postlaminectomy deformity of the spine after multiple level laminectomy: difference between children and adults. Neurosurgery. 1981; 9(2):145–152 [16] Kumar VG, Rea GL, Mervis LJ, McGregor JM. Cervical spondylotic myelopathy: functional and radiographic long-term outcome after laminectomy and posterior fusion. Neurosurgery. 1999; 44(4):771–777, discussion 777–778 [17] LaRocca H, Macnab I. The laminectomy membrane. Studies in its evolution, characteristics, effects and prophylaxis in dogs. J Bone Joint Surg Br. 1974; 56B(3):545–550 [18] An HS, Gordin R, Renner K. Anatomic considerations for plate-screw fixation of the cervical spine. Spine. 1991; 16(10) Suppl:S548–S551 [19] Panjabi MM, Duranceau J, Goel V, Oxland T, Takata K. Cervical human vertebrae. Quantitative three-dimensional anatomy of the middle and lower regions. Spine. 1991; 16(8):861–869 [20] Burrows EH. The sagittal diameter of the spinal canal in cervical spondylosis. Clin Radiol. 1963; 14:77–86 [21] Chrispin AR, Lees F. The spinal canal in cervical spondylosis. J Neurol Neurosurg Psychiatry. 1963; 26:166–170 [22] Boijsen E. The cervical spinal canal in intraspinal expansive processes. Acta Radiol. 1954; 42(2):101–115 [23] Pal GP, Sherk HH. The vertical stability of the cervical spine. Spine. 1988; 13 (5):447–449 [24] Cailliet R. Neck and Arm Pain. 2nd ed. Philadelphia, PA: FA Davis; 1981 [25] Ferguson RJL, Caplan LR. Cervical spondylitic myelopathy. Neurol Clin. 1985; 3(2):373–382 [26] Parke WW. Correlative anatomy of cervical spondylotic myelopathy. Spine. 1988; 13(7):831–837 [27] Mannen T. Vascular lesions in the spinal cord of the aged. Geriatrics. 1966; 21:151–160 [28] Jellinger K. Spinal cord arteriosclerosis and progressive vascular myelopathy. J Neurol Neurosurg Psychiatry. 1967; 30(3):195–206 [29] Arnold JG, Jr. The clinical manifestations of spondylochondrosis (spondylosis) of the cervical spine. Ann Surg. 1955; 141(6):872–889 [30] Robinson RA, Smith G. Anterolateral cervical disc removal and interbody fusion for cervical disc syndrome. Bull Johns Hopkins Hosp. 1955; 96 (Suppl):223–224 [31] Böhler J, Gaudernak T. Anterior plate stabilization for fracture-dislocations of the lower cervical spine. J Trauma. 1980; 20(3):203–205 [32] Böhler J. Immediate and early treatment of traumatic paraplegias. Z Orthop Ihre Grenzgeb. 1967; 103(4):512–529 [33] Cloward RB. The anterior approach for removal of ruptured cervical disks. J Neurosurg. 1958; 15(6):602–617 [34] Benzel EC, Lancon J, Kesterson L, Hadden T. Cervical laminectomy and dentate ligament section for cervical spondylotic myelopathy. J Spinal Disord. 1991; 4 (3):286–295 [35] Carol MP, Ducker TB. Cervical spondylitic myelopathies: surgical treatment. J Spinal Disord. 1988; 1(1):59–65 [36] Crandall PH, Gregorious FK. Long-term follow-up of surgical treatment of cervical spondylotic myelopathy. Spine. 1977; 2:139–146 [37] Perez-Cruet MJ, Foley KT, Isaacs RE, et al. Microendoscopic lumbar discectomy: technical note. Neurosurgery. 2002; 51(5) Suppl:S129–S136 [38] Guiot BH, Khoo LT, Fessler RG. A minimally invasive technique for decompression of the lumbar spine. Spine. 2002; 27(4):432–438 [39] Roh SW, Kim DH, Cardoso AC, Fessler RG. Endoscopic foraminotomy using MED system in cadaveric specimens. Spine. 2000; 25(2):260–264 [40] Dahdaleh NS, Wong AP, Smith ZA, Wong RH, Lam SK, Fessler RG. Microendoscopic decompression for cervical spondylotic myelopathy. Neurosurg Focus. 2013; 35(1):E8 [41] Herman JM, Sonntag VKH. Cervical corpectomy and plate fixation for postlaminectomy kyphosis. J Neurosurg. 1994; 80(6):963–970 [42] Goel VK, Clark CR, Harris KG, Schulte KR. Kinematics of the cervical spine: effects of multiple total laminectomy and facet wiring. J Orthop Res. 1988; 6 (4):611–619 [43] Mehalic TF, Pezzuti RT, Applebaum BI. Magnetic resonance imaging and cervical spondylotic myelopathy. Neurosurgery. 1990; 26(2):217–226, discussion 226–227

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Surgical Techniques [44] Fager CA. Results of adequate posterior decompression in the relief of spondylotic cervical myelopathy. J Neurosurg. 1973; 38(6):684–692 [45] Haft H, Ransohoff J, Carter S. Spinal cord tumors in children. Pediatrics. 1959; 23(6):1152–1159 [46] Zdeblick TA, Zou D, Warden KE, McCabe R, Kunz D, Vanderby R. Cervical stability after foraminotomy. A biomechanical in vitro analysis. J Bone Joint Surg Am. 1992; 74(1):22–27 [47] Raynor RB, Pugh J, Shapiro I. Cervical facetectomy and its effect on spine strength. J Neurosurg. 1985; 63(2):278–282 [48] Herkowitz HN. A comparison of anterior cervical fusion, cervical laminectomy, and cervical laminoplasty for the surgical management of multiple level spondylotic radiculopathy. Spine. 1988; 13(7):774–780 [49] Zdeblick TA, Abitbol JJ, Kunz DN, McCabe RP, Garfin S. Cervical stability after sequential capsule resection. Spine. 1993; 18(14):2005–2008 [50] Albert TJ, Vacarro A. Postlaminectomy kyphosis. Spine. 1998; 23(24):2738–2745 [51] Yonenobu K, Fuji T, Ono K, Okada K, Yamamoto T, Harada N. Choice of surgical treatment for multisegmental cervical spondylotic myelopathy. Spine. 1985; 10(8):710–716 [52] Yonenobu K, Okada K, Fuji T, Fujiwara K, Yamashita K, Ono K. Causes of neurologic deterioration following surgical treatment of cervical myelopathy. Spine. 1986; 11(8):818–823 [53] Adams CB, Logue V. Studies in cervical spondylotic myelopathy. II. The movement and contour of the spine in relation to the neural complications of cervical spondylosis. Brain. 1971; 94(3):568–586 [54] Ebersold MJ, Pare MC, Quast LM. Surgical treatment for cervical spondylitic myelopathy. J Neurosurg. 1995; 82(5):745–751 [55] Mikawa Y, Shikata J, Yamamuro T. Spinal deformity and instability after multilevel cervical laminectomy. Spine. 1987; 12(1):6–11 [56] Kaptain GJ, Simmons NE, Replogle RE, Pobereskin L. Incidence and outcome of kyphotic deformity following laminectomy for cervical spondylotic myelopathy. J Neurosurg. 2000; 93(2) Suppl:199–204 [57] Heller JG, Carlson GD, Abitbol JJ, Garfin SR. Anatomic comparison of the RoyCamille and Magerl techniques for screw placement in the lower cervical spine. Spine. 1991; 16(10) Suppl:S552–S557

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[58] Heller JG, Silcox DH, III, Sutterlin CE, III. Complications of posterior cervical plating. Spine. 1995; 20(22):2442–2448 [59] Grob D, Dvorak J, Panjabi MM, Antinnes JA. The role of plate and screw fixation in occipitocervical fusion in rheumatoid arthritis. Spine. 1994; 19 (22):2545–2551 [60] Fehlings MG, Cooper PR, Errico TJ. Posterior plates in the management of cervical instability: long-term results in 44 patients. J Neurosurg. 1994; 81(3):341–349 [61] Cooper RP. Posterior stabilization of the cervical spine using Roy-Camille plates: a North American experience. Orthop Trans. 1988; 12:43–44 [62] Ebraheim NA, An HS, Jackson WT, Brown JA. Internal fixation of the unstable cervical spine using posterior Roy-Camille plates: preliminary report. J Orthop Trauma. 1989; 3(1):23–28 [63] Hattori S. A new method of cervical laminectomy. Centr Jpn J Orthop Traumatic Surg. 1973; 16:792–794 [64] Hirabayashi K, Watanabe K, Wakano K, Suzuki N, Satomi K, Ishii Y. Expansive open-door laminoplasty for cervical spinal stenotic myelopathy. Spine. 1983; 8(7):693–699 [65] Matsunaga S, Sakou T, Nakanisi K. Analysis of the cervical spine alignment following laminoplasty and laminectomy. Spinal Cord. 1999; 37(1):20–24 [66] Morio Y, Yamamoto K, Teshima R, Nagashima H, Hagino H. Clinicoradiologic study of cervical laminoplasty with posterolateral fusion or bone graft. Spine. 2000; 25(2):190–196 [67] Ozunal RM, Delamarter RB. Cervical laminoplasty for cervical myeloradiculopathy. Oper Tech Orthop. 1996; 6:38–45 [68] Shiraishi T. Skip laminectomy–a new treatment for cervical spondylotic myelopathy, preserving bilateral muscular attachments to the spinous processes: a preliminary report. Spine J. 2002; 2(2):108–115 [69] Sivaraman A, Bhadra AK, Altaf F, et al. Skip laminectomy and laminoplasty for cervical spondylotic myelopathy: a prospective study of clinical and radiologic outcomes. J Spinal Disord Tech. 2010; 23(2):96–100 [70] Yukawa Y, Kato F, Ito K, et al. Laminoplasty and skip laminectomy for cervical compressive myelopathy: range of motion, postoperative neck pain, and surgical outcomes in a randomized prospective study. Spine. 2007; 32 (18):1980–1985

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Anterior Cervical Discectomy, Fusion, and Instrumentation

20 Anterior Cervical Discectomy, Fusion, and Instrumentation Mick J. Perez-Cruet and Moumita S.R. Choudhury Abstract The anterior cervical approach to the spine can be performed in a muscle-sparing manner via fascial planes to reduce approachrelated morbidity, allowing the surgeon to preserve the muscle anatomy. Minimally invasive spine surgery is becoming increasingly popular over traditional techniques as a means of treating spine pathology. Typical indications for anterior cervical discectomy include patients with myelopathy or bilateral radicular symptoms attributed to a central disc herniation, large lateralized disc herniations, large bone osteophytes leading to radiculopathy, and collapsed disc causing bilateral foraminal stenosis. This approach allows for direct decompression of the spinal cord while allowing for restoration of disc and foraminal height and normal sagittal lordosis. When the level of neck pain can be identified, this approach provides for excellent fusion since the graft is placed under compression, which promotes arthrodesis. Though applying the term minimally invasive surgical (MIS) technique to anterior cervical discectomy, fusion, and instrumentation might be considered inappropriate, the anterior cervical discectomy and fusion respects all the aspects of MIS by sparing injury to normal anatomical structures. Keywords: cervical, discectomy, interbody implant, foraminal stenosis, autograft, , arthrodesis, osteophyte, annulotomy, corpectomy

20.1 Introduction Minimally invasive spine surgery is becoming increasingly popular as a means of treating spine pathology. The anterior cervical approach to the spine can be performed in a muscle-sparing manner via fascial planes to reduce approach-related morbidity. The anatomy of the approach allows the surgeon to perform this approach via a traditional technique and still preserve the muscle anatomy while having the benefits of direct visualization and reduced risk to anterior spinal structures. Autograft remains the standard of care for anterior cervical discectomy and fusion; however, patient dissatisfaction with iliac crest graft site morbidity remains a significant drawback of this graft option.1 Use of instruments developed to collect local bone graft (i.e., BoneBac Press, Thompson MIS) can eliminate graft site morbidity while using autograft.

20.2 Indications Typical indications for anterior cervical discectomy include patients with myelopathy or bilateral radicular symptoms attributed to a central disc herniation, large lateralized disc herniations, large bone osteophytes leading to radiculopathy, and collapsed disc causing bilateral foraminal stenosis and progressive kyphosis. This approach allows for direct decompression of the spinal cord while allowing for restoration of disc

and foraminal height and normal sagittal lordosis. When the level of neck pain can be identified, this approach provides for excellent fusion since the graft is placed under compression, which promotes arthrodesis.

20.3 Preoperative Planning After general anesthesia induction, the patient is placed in the supine position on the operating table. We prefer using a Jackson flat table that allows for the C-arm fluoroscopic unit to be pushed down toward the feet and out of the way of the surgeon. A small shoulder roll is placed under the shoulder if needed to aid in slight extension or neutral position of the neck. Care is taken to confirm that the neck is not placed in an overextended position. In those patients with significant myelopathy due to cord compression, fiberoptic intubation is performed after which the patient is asked to move all four extremities before induction. Next, the fluoroscope is set in place for a lateral image of the cervical spine. This image is used to identify the target disc space. At times, gentle caudal retraction of the shoulders by pulling the hands toward the feet or by taping the shoulders down is necessary for adequate cervical visualization in large or more muscular individuals. We have found it helpful to place a Kerlex loosely around each wrist. The arms can then be pulled down toward the feet during fluoroscopic imaging to view levels below C5 especially in patients with large shoulders to help properly identify the level of interest. The base of the fluoroscopic unit should be placed on the side opposite the surgeon so as not to encumber access to the spine. However, using a Jackson table allows for the fluoroscopic unit to be moved toward the patient’s feet and away from the operative field.

20.4 Surgical Instrumentation A variety of surgical instrumentation is available for the anterior cervical approach. More recently, zero profile implants have allowed for interbody implant to be secured within the disc space without the need for an anterior cervical plate. The advantage may potentially be less dysphagia as there is not a plate overlying the cervical vertebrae and under the esophagus (▶ Fig. 20.1). Polyetheretherketone (PEEK) cages allow for autograft from the surgical bed to be used and have the benefit of Xray visualization of fusion mass once it occurs. Expandable cage technology has facilitated reconstruction after vertebrectomy.

20.5 Surgical Technique Cloward2 and Robinson and Smith3 first described anterior surgical approaches in the 1950s as a method of neural decompression. Following discectomy, Cloward directly removed compressive structures and followed with fusion using a dowelshaped graft.2 Robinson and Smith3 fused the adjoining vertebrae using a horseshoe graft harvested from the iliac crest (IC),

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Surgical Techniques

Fig. 20.1 (a) Lateral and (b) AP X-ray radiographs showing zero profile implants used to perform C4–C5 and C5–C6 anterior cervical discectomy fusion and instrumentation.

but left decompression to occur secondarily. In 1960, Bailey and Badgley,4 who had performed the first anterior cervical fusion in 1952, described a fusion technique for patients with neoplasm and instability involving on-lay strut grafts, a concept now utilized following corpectomy.5 The neck is prepped and draped in normal surgical fashion. A transverse skin incision is made lateral to the midline in the upper neck crease to approach the C2–C3 to C4–C5 levels and in the lower neck crease to approach the C5–C6 to C7–T1 levels. The side of the incision is made per preference of the surgeons. Many right-handed surgeons make the incision on the right side of the neck to facilitate the approach and surgery. After the skin incision is made, a careful subcutaneous incision/dissection is performed exposing the platysma muscle and the superficial fascia. The platysma muscle is then opened 1.5 cm longitudinally or can be cut with Bovey cautery and reapproximated at the end of the case with interrupted absorbable sutures. The medial border of the sternocleidomastoid muscle is identified and the fascial plane followed medial to the sternocleidomastoid muscle in the areolar plane. The external jugular vein can be dissected laterally off the sternocleidomastoid muscle and pushed medially. A Weitlander retractor is used to hold open the skin. Holding the retractor up allows for easier visualization of the areolar plane between the muscles and facilitates the dissection. With an index finger or Metzenbaum scissor, dissection via fascial planes of the anterior cervical region is done in such a way that the neurovascular (carotid artery) bundle is identified by tactile feel and retracted laterally while the esophagus and trachea remain medial (▶ Fig. 20.2). The anterior vertebral body of the cervical spine is palpated. Kittner dissector can be used to gentle push the soft tissue to expose the anterior vertebral body and disc space. The longus colli muscle is dissected off the vertebral body at the level of the disc pathology using an insulated Bovey cautery tip. A 90-degree bent spinal needle, which prevents overpenetration of the disc space, is placed in the disc space and lateral fluoroscopic image taken to identify the disc space level. Distractor pins are placed in the appropriate vertebrae adjacent to the disc space of interest and retractors are placed medial to the longus colli muscles bilaterally. We prefer to use the thinnest toothed blades of the Trimline cervical retractor (Medtronic) as this can reduce retraction-related morbidity. The blades are positioned

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directly lateral to the disc space of interest. Because this region is less muscular than the posterior cervical and lumbar regions, the retractors can be easily moved, potentially resulting in retractor displacement relative to the disc space that is being operated on. For this reason, fluoroscopic imaging is used to verify the positioning of the retractor and distractor posts once in place(▶ Fig. 20.3). An annulotomy is made in the disc, and the disc is removed in a piecemeal fashion with pituitary rongeurs, curettes, and drill. A long, tapered drill is then used to remove osteophytes. The posterior longitudinal ligament can be removed after adequate discectomy to expose the dural and assure adequate distraction of the disc space. The posterior longitudinal ligament is removed starting laterally using an up-going microcurette to detach the ligament laterally. Next, a number 1 or 2 Kerrison punch is used to further remove the ligament and posterior osteophytes. The decompression continues to completely remove the disc herniation, posterior longitudinal ligament, and bone osteophytes (▶ Fig. 20.3). After adequate decompression is achieved, a trial is used to identify the proper implant size. The implant can then be filled with bone graft material, typically autologous bone graft harvested from the surgical site using the BoneBac Press (Thompson MIS) (see ▶ Fig. 20.3). This bone can be mixed with bone graft extenders if needed and completely eliminate the need for IC harvest and its associated morbidity. With the implant in place, distractor pins are removed to allow for implant and graft compression. Distractor pin bone holes are filled with bone wax to prevent any bone bleeding. We prefer zero profile cages. These cages are easier to implant and secure to adjacent vertebrae while potentially helping to reduce the incidence of plateinduced dysphagia (see ▶ Fig. 20.1).

20.5.1 Closure With complete hemostasis assured, the retractor blades are removed. The platysma muscle is reapproximated with 2–0 interrupted Vicryl suture. A subcutaneous suture is applied and the skin closed with either skin glue or Steri-Strips. Clean dressing is applied. At times, a drain is placed for multilevel approaches or cervical corpectomy and removed the following morning or shortly after.

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Anterior Cervical Discectomy, Fusion, and Instrumentation

Fig. 20.2 (a) A transverse incision is made in the appropriate neck crease. (b) The approach medial to the sternocleidomastoid muscle to palpate the carotid artery and gently (c) retract it laterally and the trachea and esophagus medially.

20.6 Avoiding Complications and Management of Complications 0Before any surgical intervention, those patients with cardiac risk factors should undergo a full cardiovascular evaluation including evaluation of the carotid arteries for stenosis. Manipulation of the carotid arteries with underlying carotid disease could result in complications. We generally use carotid Doppler evaluation in these cases. As in the traditional approach, discectomy should be performed to respect the lateral margins of the disc to prevent vertebral artery injury. Vertebral artery anomalies should be checked on preoperative imaging studies. Dissecting through the posterior longitudinal ligament should be done with a 1- or 2-mm Kerrison rongeur to avoid possible injury to the dura. This precaution is especially important in those patients presenting with a significant myelopathy

because the dura may be very adherent. A small up-going curette or nerve hook can also be useful in developing a plane between the dura and the posterior longitudinal ligament to facilitate removal. Hemostasis from venous bleeding is controlled with thrombin-soaked Gelfoam. However, we prefer to remove the Gelfoam before closure.

20.7 Clinical Cases 20.7.1 Case 1: Progressive Kyphosis and Spinal Cord Compression An elderly man presents with severe neck pain, stumbling gait, weakness in hand, and myelopathy. MRI images of the cervical spine reveal progressive kyphosis, spinal cord compression, and signal changes seen on T2-weighted images within the spinal cord (▶ Fig. 20.4).

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Fig. 20.3 (a) Placement of retractor blades medial to the longus colli muscles; (b) distractor pins in the adjacent vertebral bodies to open disc space; (c) disc annulotomy is performed; (d) disc material is removed in a routine fashion; (e) a long tapered drill is used to remove anterior osteophytes; (f) all drilled bone is collected using the BoneBac Press (Thompson MIS). The collected bone is used to fill the implant; (g) then, further disc material is used; (h) posterior osteophytes drilled or removed under microscope visualization to decompress the spinal canal and neural foramen; (i) the disc space is prepared for the implant; (j) the implant, filled with bone graft material, is placed; (k) anterior screw instrumentation is applied to secure the implant in place.

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Anterior Cervical Discectomy, Fusion, and Instrumentation

Fig. 20.4 (a) Sagittal MRI images at the (b) C3–C4; (c) C4–C5; (d) C5–C6; (e) C6–C7 disc space showing severe spinal cord compression and kyphosis; (f) intraoperative photo of implant filled with local autograft harvested using the BoneBac Press. (g) Postoperative lateral X-ray after C3–C4, C4–C5, C5–C6, and C6–C7 anterior cervical discectomy fusion and dynamic anterior cervical plate instrumentation achieving reduction of kyphosis. Patient made an uneventful recovery and returned to activities of daily living with resolution of myelopathic symptoms.

20.7.2 Case 2: Spinal Cord Compression A middle-aged man presents with severe neck pain, gait difficulty, and myelopathy (▶ Fig. 20.5). Patients with ossification of the posterior longitudinal ligament of the cervical spine (OPLL) are challenging cases. Anterior decompression and fusion demonstrated a benefit in neurological recovery and reduction of morbidity.6 Recognition of OPLL on preoperative MRI as illustrated in the above case and subsequent CT if needed can help assure adequate decompression of the spinal cord and improve patient outcomes.

Clinical Caveats ●

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20.8 Conclusion Anterior cervical approaches to the cervical spine can allow for excellent anterior spinal canal decompression of a variety of cervical pathology. Respecting anatomical planes allows this approach to be used in a minimally invasive fashion. This minimally invasive technique allows for adequate discectomy, removal of osteophytes, and fusion.

●

●

The skin incision is usually made in the neck crease. Upper neck crease for approaching the C3–C4 and C4–C5 levels and lower crease for approaching C5–C6 and C6–C7 levels. Holding a Weitlander retractor up can be helpful in exposing the areolar planes to allow for tissue dissection. A plane medial to the sternocleidomastoid muscle leads to the anterior cervical spine. The carotid artery is carefully retracted lateral and trachea and esophagus retracted medial. Bone graft material can be collected from the surgical site using the BoneBac Press and used for fusion material to avoid graft site morbidity. Adequate retraction of the longus colli muscles is necessary and achieved with a Bovie electrocautery before discectomy is initiated. Removal of the posterior longitudinal ligament assures adequate canal decompression and is started at the lateral margins of the ligament under microscopic visualization.

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Fig. 20.5 (a) Sagittal T2-weighted MRI of the cervical spine showing spinal cord compression at the C5–C6 and C6–C7 level but also (b) posterior to the C6 vertebrae by ossification of the posterior longitudinal ligament seen on axial MRI as a dark mass compressing the spinal cord. CT can also show ossification of the posterior longitudinal ligament; (c) a C5–C6 and C6–C7 discectomy as well as C6 corpectomy performed with anterior reconstruction performed using an expandable cage filled with the patient’s own autograft bone; (d) postoperative sagittal CT showing expandable cage reconstruction, use of local autograft bone fusion, and anterior plate reconstruction.

References [1] Silber JS, Anderson DG, Daffner SD, et al. Donor site morbidity after anterior iliac crest bone harvest for single-level anterior cervical discectomy and fusion. Spine. 2003; 28(2):134–139 [2] Cloward RB. The anterior approach for removal of ruptured cervical disks. J Neurosurg. 1958; 15(6):602–617 [3] Robinson RA, Smith GW. Anterolateral cervical disc removal and interbody fusion for cervical disc syndrome. Bull Johns Hopkins Hosp. 1955; 96:223–224

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[4] Bailey RW, Badgley CE. Stabilization of the cervical spine by anterior fusion. J Bone Joint Surg Am. 1960; 42-A:565–594 [5] Whitecloud TS, III. Modern alternatives and techniques for one-level discectomy and fusion. Clin Orthop Relat Res. 1999(359):67–76 [6] Wang X, Chen D, Yuan W, Zhang Y, Xiao J, Zhao J. Anterior surgery in selective patients with massive ossification of posterior longitudinal ligament of cervical spine: technical note. Eur Spine J. 2012; 21(2):314–321

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Cervical Arthroplasty

21 Cervical Arthroplasty K. Daniel Riew and Kevin R. O’Neill Abstract Compared with traditional fusion operations, cervical disc arthroplasty allows the same benefits of neural decompression while preserving motion and reducing stress on adjacent disc levels. Long-term studies now support the efficacy of cervical disc arthroplasty and have demonstrated reduced rates of breakdown of adjacent levels. This chapter reviews the evidence along with indications and contraindications of its use. A detailed and illustrated description of the procedure is provided along with several technical tips. A case example is then used to demonstrate a common clinical application. Keywords: cervical disc arthroplasty, cervical disc replacement, anterior cervical discectomy and fusion, cervical disc herniation, cervical radiculopathy, cervical myelopathy

21.1 Introduction Anterior cervical discectomy and fusion (ACDF) has proven to be a highly successful operation for the treatment of radiculopathy and myelopathy associated with anteriorly based nerve root or spinal cord compression.1,2,3,4,5,6,7,8 However, as with any surgical procedure, complications may occur. Symptomatic nonunion or pseudarthrosis occurs in approximately 5% and may require revision surgery.4,8,9 In addition, there are biomechanical data suggesting increased stress on motion segments adjacent to fusions, raising the concern for accelerated degeneration.10 Whether this process is indeed accelerated when next to a fusion or is the natural result of continued degeneration, adjacent segment pathology (ASP) following anterior fusion has been found to occur in 9 to 16% of patients with an incidence of 26% predicted at 10 years postoperatively.4,11,12,13,14 It has been shown that 61 to 82% of patients with ASP then undergo subsequent surgery.4,7,11 A more recent study has validated these estimates, finding that 18% of patients undergo surgery for ASP following anterior fusion by 10 years postoperatively.15

21.1.1 Evolution of Technique and Advantages and Disadvantages Anterior cervical discectomy with arthroplasty (ACDA) has been introduced as a method to provide the same successful decompression as an ACDF, but with retention of segmental motion across the disc space. With the intent of retained motion, this eliminates the concern over pseudarthrosis. In addition, this theoretically avoids the increased stress at adjacent levels caused by fusion, and therefore may reduce the incidence of ASP. To date, there have been several studies investigating ACDA versus ACDF, and several meta-analyses of those studies.16,17,18,19,20,21,22,23,24,25,26,27,28,29,30 The two procedures share the same surgical approach and similar decompression techniques. Some studies suggest statistically increased blood loss and operative time with ACDA, though the actual differences are not likely clinically significant.24,25,26 Neurologic success, defined

as maintained or improved motor or sensory function, is similar or slightly more favorable in the arthroplasty group.20,24,26,31 Not surprisingly, motion across the index surgical level was lower in the fusion group.26,32 Patient-reported outcomes, including visual analog scale (VAS) arm pain and neck pain and Neck Disability Index (NDI) scores, were also found to generally favor arthroplasty.16,19,28 Further, the compensatory increased motion at adjacent segments following fusion was not found to be present following ACDA, and several studies with follow-up of 2 to 5 years have demonstrated reduced rates of reoperation in those undergoing arthroplasty.16,19,22,32,33 With the longest follow-up period to date of 7 years, a recent study has demonstrated a significantly lower rate of ASP following ACDA (5%) compared with ACDF (12%).34

21.2 Anterior Cervical Discectomy with Arthroplasty 21.2.1 Indications The indications for ACDA are similar to those for ACDF, as they share the same approach and decompression maneuvers. The primary indication for both of these procedures is the treatment of radiculopathy or myelopathy caused by anterior compression at the disc level. While most studies have investigated single-level disease, arthroplasty can be considered for up to three disc levels.35,36 For an acute radiculopathy, nonoperative measures should be attempted for at least 6 weeks, and in most cases 3 months, prior to consideration of surgery, as symptoms often resolve over this period. For myelopathy, surgery may be considered sooner, especially when more severe neurologic deficits are present. Cross-sectional imaging should be obtained and demonstrate focal compression behind the disc space. Magnetic resonance imaging (MRI) provides excellent visualization of both the discs and neural elements, though computed tomography (CT) myelogram can be obtained when contraindications to MRI exist. Given that there is a high rate of disc pathology demonstrated in asymptomatic patients, it is important that imaging findings correlate appropriately with both the patients’ symptoms and physical exam findings.37,38

21.2.2 Contraindications There are several contraindications to arthroplasty. Because decompression is performed at the disc level, congenital or retrovertebral stenosis will not be alleviated by ACDA. Similarly, if neutral lateral radiographs show focal kyphosis, adequate decompression cannot be achieved with ACDA. When present, these pathologies are better addressed by anterior corpectomy, posterior decompression, or a combined approach. All patients should be evaluated with CT to determine if there is ossification of the posterior longitudinal ligament (OPLL), which is a contraindication. OPLL is often associated with retrovertebral stenosis that would not be alleviated by

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Surgical Techniques ACDA. In addition, continued motion following arthroplasty may lead to bone formation posterior to an arthroplasty device in patients with OPLL, which may result in worsening stenosis and neurologic deterioration. Finally, OPLL may predispose the motion segment to spontaneous fusion despite arthroplasty, eliminating the advantage of this procedure over ACDF. Similarly, the presence of diffuse idiopathic skeletal hyperostosis (DISH) and ankylosing spondylitis may predispose the level to spontaneous fusion and therefore failure of the arthroplasty, and these are therefore also contraindications. Posterior column instability is another important contraindication. In all cases, flexion-extension lateral radiographs should be obtained to rule out instability. Because the procedure involves resection of the anterior longitudinal ligament (ALL) and potentially the posterior longitudinal ligament (PLL), the additional presence of posterior instability may result in an unstable spinal column. Prior laminectomy is therefore considered a contraindication. Previous laminoplasty may also cause posterior instability, though this has not been investigated. The presence of fracture or posterior ligamentous disruption is an absolute contraindication. Finally, rheumatoid arthritis may result in laxity of posterior facet capsules and is considered a contraindication as well, except in rare cases with minimal rheumatoid involvement. The presence and severity of neck pain is an important consideration. A patient with predominantly axial neck pain is not an ideal candidate for arthroplasty. While a degenerative disc may be a cause of axial neck pain with the potential for pain relief from arthroplasty, this has not yet been demonstrated. Similarly, facet arthrosis with associated neck pain is considered a contraindication. Such arthritic facets will continue to experience motion and therefore generate pain following arthroplasty. In contrast, the presence of facet arthrosis alone, in the absence of significant neck pain, is not considered a contraindication. Finally, the quality of bone and local environment at the surgical level should be considered. Certainly, an active spine infection at the index surgical level is a contraindication. Introduction of the implant into an infected environment may make eradication more difficult and may lead to loosening and failure of the implant. Severe osteoporosis is also a contraindication as this too can lead to implant subsidence and failure.

21.2.3 Preoperative Planning Patients with stenosis associated with disc pathology causing radiculopathy or myelopathy are potential candidates for ACDA. It is important that physical exams findings correlate with areas of compression demonstrated on cross-sectional imaging. MRI provides excellent visualization of both the discs and neural elements and is the preferred imaging modality. If contraindications to MRI exist, CT myelogram can be obtained. Radiographic imaging should include AP, neutral lateral, flexion/extension lateral, and oblique views. A complete neurological exam should be performed, including evaluation of motor and sensory function and appropriate reflexes for each nerve root level. Additionally, tests for cervical myelopathy should be performed including evaluation of gait and tandem gait, Romberg’s sign, Hoffmann’s sign, Lhermitte’s sign, finger escape sign, grip and release test, sustained clonus, and Babinski test.

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Instrumentation Fernström39 implanted the first cervical artificial disc in 1966, which consisted of a stainless steel ball-bearing implant. Another stainlesssteel device with a ball-in-socket metal-on-metal design was introduced in 1989 by Cummins et al,40 but had a similar high failure rate. A redesign of this implant was introduced as the Frenchay artificial disc, which later became the Prestige Disc (Medtronic, Inc.).31 This metal-on-metal implant utilizes screw fixation to the vertebral bodies. In 1992, Bryan20 introduced another arthroplasty implant, consisting of titanium shells with a polyethylene core surrounded by a saline-filled polyurethane sheath. This utilizes a press-fit design that does not require screw fixation. The Pro-disc C (Synthes, Inc.) was introduced by Marnay,24 and utilizes a cobalt-chrome shell with a polyethylene articulating surface. This design included keels that are press fit into the vertebral bodies. Another cobaltchrome and polyethylene implant, the Porous Coated Motion Disc Prosthesis (Nuvasive, Inc.), was introduced by McAfee.41 This device has a calcium phosphate coating that allows bone ingrowth to the implant after an initial press fit. Numerous other designs have subsequently been described, with nine devices currently with FDA approval.41 It is essential that the surgeon be familiar and comfortable with the chosen arthroplasty implant system.

21.2.4 Surgical Technique Positioning The patient is positioned supine on the operating table. We prefer to use a Jackson table with radiolucent flat table, though any radiolucent table can be used. A shoulder roll is placed under the shoulders, and sheets and foam are placed under the head as necessary to achieve a neutral neck position. Unlike ACDF where a more extended position is often preferred, this should be avoided in ACDA. Placing the neck in an extended position can result in excessive posterior vertebral body resection while creating parallel endplates in preparation for the arthroplasty implant. In contrast, kyphotic positioning should also be avoided, as this makes exposure and decompression more difficult and can lead to excessive anterior loading on the implants. Shoulders are taped down to allow better radiographic visualization of the lower cervical levels, and the head is secured to the table using tape across the forehead to minimize neck rotation. Care is taken to insure that the anterior neck is prepped and draped, keeping the bottom of the chin and sternal notch exposed as an additional alignment reference.

Exposure The anterior cervical spine is exposed via the same interval described originally by Smith-Robinson3 (▶ Fig. 21.1). After exposure, the longus colli are used to initially identify midline on the vertebral bodies adjacent to the disc space, which is then marked with electrocautery. A combination of bipolar electrocautery and a Penfield #2 dissector is then used to elevate the longus colli bilaterally, exposing over the uncinate processes and foramen transversarium. Use of the Penfield to expose laterally minimizes potential risk of injury to the vertebral artery. A hemostat is utilized to clamp a small medial portion of the

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Cervical Arthroplasty

Fig. 21.1 (a) A transverse incision is most commonly utilized, utilizing a skin crease overlying the operative level. Either a left- or right-sided incision may be used. (b) The approach utilizes the intramuscular plane between the sternocleidomastoid muscle laterally and strap muscles medially. Deep to this, a plane is developed between the carotid sheath laterally and esophagus medially, exposing the spine and longus colli muscles. (c) After splitting the platysma, the approach utilizes the intramuscular plane between the sternocleidomastoid muscle (1) laterally and strap muscles (4) surrounding the trachea (3) medially. Deep to this, a plane is developed between the carotid sheath (2) laterally and esophagus (5) medially, exposing the spine and longus colli muscles. Note that the recurrent laryngeal nerves usually travel along the trachea and esophagus.

longus colli at the level of the disc space. Only a small portion is clamped in order to avoid injury to the sympathetic plexus. The correct level is then confirmed using a lateral fluoroscopic or radiographic view. The radiograph is also checked to insure that the correct patient is being operated on and that the segment is in proper alignment. Any anterior osteophytes are removed using a Leksell rongeur or burr such that it is smooth with the native vertebral body, which can be verified by digital palpation (▶ Fig. 21.2). Self-retaining retractors are then placed, which may be specific to the arthroplasty system being utilized. The retractor blades should be tucked under the previously elevated longus colli. Adequate elevation of longus colli and resection of osteophytes are key steps in allowing the retractors to be positioned appropriately.

Discectomy and Endplate Preparation The discectomy is performed next. A #15 blade is used to incise the disc, starting in the midline on the superior endplate of the caudal vertebral body, going out laterally to the uncinate, turning the knife blade cranially, and then following along the inferior endplate of the cranial vertebrae back to midline. Performing this maneuver bilaterally allows efficient disc removal and utilizes the uncinate to protect the vertebral artery when incising laterally. A pituitary is used to grossly remove disc material, followed by a small 2-mm curette to denude the endplates(▶ Fig. 21.3). Care should be taken not to go lateral to the uncinate and inadvertently injure the vertebral artery. Irrigation and suction tubing can be used to quickly remove disc fragments generated using the

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Fig. 21.2 (a) Longus colli muscles are present on either side of the anterior aspect of the spine. These can be used following the initial exposure to mark the midline of the vertebral bodies above and below the operative disc level. (b) The retractors are extended underneath the edges of the longus colli bilaterally, completing the exposure. Structures adjacent to the medial retractor blade include the trachea and surrounding strap muscles, esophagus, and longus colli. Structures adjacent to the lateral retractor blade include the sternocleidomastoid, carotid artery and sheath, and the longus colli.

Fig. 21.3 (a) After retractor placement and removal of anterior osteophytes, distractor pins are placed in the midline of the vertebral bodies cranial and caudal to the disc. For many of the arthroplasty systems, this is a critical step to ensure proper placement of these distractor pins. (b) Slight distraction can then be applied across the disc space to allow improved visualization.

curette. Clear identification of the uncinates is critically important, and allows for appropriate sizing of the implant and confirmation of the midline of each vertebral body. This then allows distraction pins to be placed precisely in the midline. Unlike during an ACDF, the position of pin placement is absolutely critical. If placed too close to the disc space, the procedure cannot be performed. In general, placing the pins far from the disc without violating the adjacent disc space is optimal. Pins that are placed off-center will result in asymmetric

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retraction and poor placement of the arthroplasty device. Note that some systems have specialized vertebral body retraction systems that would be utilized at this point. The burr is next used to remove the overhanging anterior endplate of the cranial vertebral body until it is flush with the more central endplate. The endplate is lightly decorticated extending laterally and posteriorly to the level of the PLL, with the goal of creating a smooth and flat surface. In a similar fashion, the caudal vertebral body endplate is decorticated between the uncinates

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Cervical Arthroplasty

a

Fig. 21.4 Complete resection of the intervertebral disc is performed. Care is taken to ensure complete spinal cord and nerve root decompression as necessary. Then, the vertebral body endplates are decorticated, taking care to avoid excessive decortication and violation of the endplates.

and posteriorly down to the PLL, creating parallel smooth endplates and “rectangular” disc space(▶ Fig. 21.4 and ▶ Fig. 21.5). It is important to avoid excessive decortication and violation of either endplate, as this can lead to implant subsidence and failure.

Decompression Central decompression is performed next. If a large disc herniation is present, the PLL can be resected to insure that no compressive disc fragments remain hidden behind the PLL. At this point, it is critical to remove any posterior osteophytes (▶ Fig. 21.6). Continued motion following arthroplasty can cause any remaining osteophytes to enlarge and cause worsening stenosis and neurologic deterioration. Following resection, bone wax can be used to help prevent bleeding and osteophyte recurrence. Foraminal decompression is then completed. It is critical to identify the lateral vertebral body and remain oriented to this when performing foraminal decompression in order to avoid vertebral artery injury. We prefer to perform the decompression using a matchstick burr. The tip of this burr does not cut as aggressively as the sides, and can gently rest momentarily against PLL or even dura without causing damage. The burr is then moved carefully laterally to perform the decompression, bearing in mind the anterior and inferior trajectory of the nerve root. Only a small portion of the uncinate is removed at a time. Care must be taken to avoid vertebral artery injury lateral to the uncinate. It is sometimes useful to identify the lateral uncinate by placing a Penfield 4 to enlarge the space, followed by a Penfield 2, over the lateral aspect of the uncinate. In some situations, it may be necessary to perform a partial or complete uncinatectomy for adequate decompression. However, bilateral complete uncinatectomy should be avoided, as the uncinate processes contribute significantly to the

b Fig. 21.5 (a) Intraoperative photograph demonstrating appropriate “rectangular” endplate preparation of the disc spaces for insertion of arthroplasty devices. Note that the uncinates are exposed bilaterally, identified by a Penfield dissector at the cranial disc space. This exposure and preparation are critical to obtaining a properly fitting and functioning arthroplasty. (b) Arthroplasty devices have been inserted. This particular device utilizes a keel into the vertebral bodies to stabilize the device.

stability of the motion segment. Similar to resection of posterior osteophytes centrally, it is critical that osteophytic compression of the foramen be removed as there is some potential that such osteophytes increase in size following arthroplasty. Any remaining spurs can result in continued or worsening nerve root irritation.

Device Implantation With the decompression and disc space preparation complete, most systems then require sizing of the space with trials. Retraction across the disc space should be released prior to sizing. When sizing, care must be taken to avoid creating a fit that is either too tight or too loose. Excessive tightness can cause ligamentous strain or hyperlordosis with increased load on the facets. This can cause increased neck pain, as well as increased load on the implant that can lead to subsidence. In contrast, excessive looseness can result in device extrusion, foraminal stenosis, and a poorly functioning device. Also, the footprint of

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Surgical Techniques the implant should be as large as possible in order to distribute the forces across a greater area, which may also minimize implant subsidence. It should also be placed as posteriorly as possible and occupy as much of the anteroposterior (AP) disc space as possible, without intruding into the spinal canal. The properly sized implant is then inserted, making sure of the appropriate implant orientation (see ▶ Fig. 21.5). Fluoroscopic guidance in both the AP and lateral planes is utilized for final placement (▶ Fig. 21.7, ▶ Fig. 21.8). Again, it is important to be familiar with whatever implant system is being utilized. Some implants then require screw fixation to be performed.

Closure The wound is then thoroughly irrigated. After the self-retaining retractors are removed, it is important that adequate hemostasis is achieved. We utilize commercially available hemostatic agents placed along and under the longus colli to provide additional protection from postoperative bleeding. A drain is generally not necessary. If bleeding from the endplates or other sources is thought to be an issue, we use a ¼-inch Penrose drain. Monofilament suture is used to reapproximate the platysma layer and close skin.

Fig. 21.6 Implant trials are used to determine the appropriate implant dimensions, per each manufacturer’s specific indications. Often, intraoperative fluoroscopy is used to check orthogonal views of the implant trial and verify the appropriate size arthroplasty device is selected.

a

b

21.2.5 Postoperative Care No postoperative immobilization is necessary, though some patients may prefer temporary use of a soft cervical collar. The incision is left open to air, and patients are allowed to gently

c

Fig. 21.7 (a) Lateral radiograph demonstrating an arthroplasty device that was placed minimally too anterior. Note that the device is not flush with the anterior vertebral body of C5. Although such placement is not likely to be clinically relevant, one should aim to place the device in a perfect position in every case. Too far anterior a placement can lead to abnormal kinematics which can lead to early failure. (b) AP radiograph showing an arthroplasty device inserted with a slightly tilted position. Although this degree of tilt is not likely to be clinically relevant, a device that is too tilted or placed offcenter can cause uneven loading of the device, and accelerated failure. (c) An appropriately positioned arthroplasty device, occupying the full anteroposterior width of the disc space without protruding into the spinal canal.

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Cervical Arthroplasty wash and dry their necks immediately. Patients are encouraged to walk postoperatively, but no therapy is generally prescribed. For 6 weeks postoperatively, patients are instructed to avoid overhead activities, lifting more than 25 pounds, pushing or pulling with their arms, or soaking their neck underwater. After 6 weeks, all restrictions are usually lifted.

21.2.6 Management of Complications As arthroplasty shares similar exposure and decompression maneuvers with ACDF procedures, early surgical complications are also similar and treated in the same manner.42,43 Additional early surgical complications described in ACDA include implant migration and subsidence, though these again can occur similarly with

grafts or cages in ACDF.44 Later complications in ACDA have also been described and include neurologic worsening, implant migration or subsidence, implant failure, heterotopic ossification, spontaneous fusion, and osteolytic bone loss.44,45 When reoperation is indicated, it is generally preferred to convert to a fusion procedure. This can be achieved either by removal of the arthroplasty device with anterior fusion or by posterior cervical fusion.

21.3 Clinical Case 21.3.1 Presentation An otherwise healthy 40-year-old female patient presented with several weeks of neck pain and radiating right arm pain. Her pain was exacerbated by neck rotation to the right. She additionally described numbness and tingling most significantly in her right middle finger, and subjective weakness of her hand and wrist. She had tried numerous conservative treatments including anti-inflammatories, narcotics, physical therapy, and chiropractic manipulations. Despite these treatments, she remained in significant pain.

21.3.2 Exam Her right upper extremity exam was notable for diminished sensation in a C7 distribution and 4/5 weakness of her triceps and wrist flexors. She had a positive Spurling’s sign to the right. Reflex testing revealed a diminished right triceps reflex, but symmetric biceps reflexes. Her left upper extremity and bilateral lower extremity exams were within normal limits. She had negative Hoffmann’s and Romberg’s signs, and was able to perform tandem gait.

21.3.3 Imaging

Fig. 21.8 Following device implantation, care is taken to irrigate any remaining debris and ensure complete hemostasis has been achieved.

Standing neutral radiographs revealed a relatively straight cervical spine, with some loss of normal lordosis (▶ Fig. 21.9). CT scan did not show any OPLL, but did demonstrate some spondylotic foraminal narrowing on the right side at C6–C7 (▶ Fig. 21.10). An MRI revealed a large right-sided disc herniation at C6–C7 causing compression of the C7 nerve root (▶ Fig. 21.11).

Fig. 21.9 (a) Standing anteroposterior and (b) lateral neutral radiographs of the cervical spine. Note the slight loss of normal lordosis on the lateral view.

a

b

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Fig. 21.10 CT images of the cervical spine. (a) Sagittal view; (b) axial view. There is no significant facet arthrosis present. At C6–C7, there is some spondylotic right-sided foraminal narrowing present. Ossification of the posterior longitudinal ligament (OPLL) is not present.

a

b

Fig. 21.11 MRI images of the cervical spine, demonstrating a large right parasagittal and foraminal disc herniation at C6–C7. (a) Sagittal view; (b) axial view.

a

b

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Cervical Arthroplasty

a

b

c

Fig. 21.12 Radiographs demonstrating appropriate implant position and retained motion across the disc arthroplasty. (a) Postoperative lateral flexion; (b) neutral; (c) extension.

21.3.4 Treatment and Outcome With imaging demonstrating a right-sided C6–C7 disc herniation and concordant signs and symptoms of a C7 radiculopathy that persisted several weeks despite conservative treatments, surgery was recommended. After discussing the risks and benefits, the patient agreed to undergo a C6–C7 ACDA. The surgery was performed successfully, and she was discharged from the hospital on the day after surgery without complication. At her most recent follow-up, she reported complete resolution of both her right arm radicular symptoms and neck pain. Radiographs demonstrated appropriate implant alignment with retained motion (▶ Fig. 21.12).

21.4 Conclusion Cervical disc arthroplasty is an effective alternative to fusion in select patients with radiculopathy or myelopathy caused by disc-based neural compression. The primary benefits of arthroplasty include motion preservation, lack of concern over achieving fusion, diminished stress on adjacent motion segments, and potentially reduced rates of adjacent segment disease. While ACDA shares several similarities with ACDF procedures, it is critically important to understand the important differences in technique and to be familiar and comfortable with the chosen implant system.

Clinical Caveats ●

●

●

Patient selection is important for successful outcomes of cervical arthroplasty, understanding both the indications for and contraindications against the procedure. Positioning the neck in neutral is important to avoid excessive bone resection and asymmetric loading of the implant. Utilizing multiple anatomic references to identify midline is critical to achieving a centered and horizontal implant. The most important of these is to expose both uncinates.

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●

●

Careful endplate preparation is mandatory, and may be unique to the chosen implant device. Adequate decompression and resection of central and foraminal osteophytes is essential for neurologic improvement and avoidance of postoperative neurologic deterioration. The surgeon must be familiar and comfortable with the chosen implant device and any associated tools for exposure, endplate preparation, and implant insertion.

References [1] Bailey RW, Badgley CE. Stabilization of the cervical spine by anterior fusion. J Bone Joint Surg Am. 1960; 42-A:565–594 [2] Cloward RB. The anterior approach for removal of ruptured cervical disks. J Neurosurg. 1958; 15(6):602–617 [3] Smith GW, Robinson RA. The treatment of certain cervical-spine disorders by anterior removal of the intervertebral disc and interbody fusion. J Bone Joint Surg Am. 1958; 40-A(3):607–624 [4] Bohlman HH, Emery SE, Goodfellow DB, Jones PK. Robinson anterior cervical discectomy and arthrodesis for cervical radiculopathy. Long-term follow-up of one hundred and twenty-two patients. J Bone Joint Surg Am. 1993; 75 (9):1298–1307 [5] Kaiser MG, Haid RW, Jr, Subach BR, Barnes B, Rodts GE, Jr. Anterior cervical plating enhances arthrodesis after discectomy and fusion with cortical allograft. Neurosurgery. 2002; 50(2):229–236, discussion 236–238 [6] Shapiro S, Connolly P, Donnaldson J, Abel T. Cadaveric fibula, locking plate, and allogeneic bone matrix for anterior cervical fusions after cervical discectomy for radiculopathy or myelopathy. J Neurosurg. 2001; 95(1) Suppl:43–50 [7] Gore DR, Sepic SB. Anterior discectomy and fusion for painful cervical disc disease. A report of 50 patients with an average follow-up of 21 years. Spine. 1998; 23(19):2047–2051 [8] Yue W-M, Brodner W, Highland TR. Long-term results after anterior cervical discectomy and fusion with allograft and plating: a 5- to 11-year radiologic and clinical follow-up study. Spine. 2005; 30(19):2138–2144 [9] Fraser JF, Härtl R. Anterior approaches to fusion of the cervical spine: a metaanalysis of fusion rates. J Neurosurg Spine. 2007; 6(4):298–303 [10] Eck JC, Humphreys SC, Lim T-H, et al. Biomechanical study on the effect of cervical spine fusion on adjacent-level intradiscal pressure and segmental motion. Spine. 2002; 27(22):2431–2434

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Surgical Techniques [11] Hilibrand AS, Carlson GD, Palumbo MA, Jones PK, Bohlman HH. Radiculopathy and myelopathy at segments adjacent to the site of a previous anterior cervical arthrodesis. J Bone Joint Surg Am. 1999; 81(4):519–528 [12] Hilibrand AS, Robbins M. Adjacent segment degeneration and adjacent segment disease: the consequences of spinal fusion? Spine J. 2004; 4(6) Suppl:190S–194S [13] Gore DR, Sepic SB. Anterior cervical fusion for degenerated or protruded discs. A review of one hundred forty-six patients. Spine. 1984; 9(7):667–671 [14] Baba H, Furusawa N, Imura S, Kawahara N, Tsuchiya H, Tomita K. Late radiographic findings after anterior cervical fusion for spondylotic myeloradiculopathy. Spine. 1993; 18(15):2167–2173 [15] Lee JC, Lee SH, Peters C, Riew KD. Risk-factor analysis of adjacent-segment pathology requiring surgery following anterior, posterior, fusion, and nonfusion cervical spine operations: survivorship analysis of 1358 patients. J Bone Joint Surg Am. 2014; 96(21):1761–1767 [16] Boselie TF, Willems PC, van Mameren H, de Bie RA, Benzel EC, van Santbrink H. Arthroplasty versus fusion in single-level cervical degenerative disc disease: a Cochrane review. Spine. 2013; 38(17):E1096–E1107 [17] Evaniew N, Madden K, Bhandari M. Cochrane in CORR®: arthroplasty versus fusion in single-level cervical degenerative disc disease. Clin Orthop Relat Res. 2014; 472(3):802–808 [18] Buchowski JM, Anderson PA, Sekhon L, Riew KD. Cervical disc arthroplasty compared with arthrodesis for the treatment of myelopathy. Surgical technique. J Bone Joint Surg Am. 2009; 91 Suppl 2:223–232 [19] Gao Y, Liu M, Li T, Huang F, Tang T, Xiang Z. A meta-analysis comparing the results of cervical disc arthroplasty with anterior cervical discectomy and fusion (ACDF) for the treatment of symptomatic cervical disc disease. J Bone Joint Surg Am. 2013; 95(6):555–561 [20] Heller JG, Sasso RC, Papadopoulos SM, et al. Comparison of BRYAN cervical disc arthroplasty with anterior cervical decompression and fusion: clinical and radiographic results of a randomized, controlled, clinical trial. Spine. 2009; 34(2):101–107 [21] Jiang H, Zhu Z, Qiu Y, Qian B, Qiu X, Ji M. Cervical disc arthroplasty versus fusion for single-level symptomatic cervical disc disease: a meta-analysis of randomized controlled trials. Arch Orthop Trauma Surg. 2012; 132(2):141–151 [22] McAfee PC, Reah C, Gilder K, Eisermann L, Cunningham B. A meta-analysis of comparative outcomes following cervical arthroplasty or anterior cervical fusion: results from 4 prospective multicenter randomized clinical trials and up to 1226 patients. Spine. 2012; 37(11):943–952 [23] Mummaneni PV, Burkus JK, Haid RW, Traynelis VC, Zdeblick TA. Clinical and radiographic analysis of cervical disc arthroplasty compared with allograft fusion: a randomized controlled clinical trial. J Neurosurg Spine. 2007; 6(3):198–209 [24] Murrey D, Janssen M, Delamarter R, et al. Results of the prospective, randomized, controlled multicenter Food and Drug Administration investigational device exemption study of the ProDisc-C total disc replacement versus anterior discectomy and fusion for the treatment of 1-level symptomatic cervical disc disease. Spine J. 2009; 9(4):275–286 [25] Riew KD, Buchowski JM, Sasso R, Zdeblick T, Metcalf NH, Anderson PA. Cervical disc arthroplasty compared with arthrodesis for the treatment of myelopathy. J Bone Joint Surg Am. 2008; 90(11):2354–2364 [26] Sasso RC, Anderson PA, Riew KD, Heller JG. Results of cervical arthroplasty compared with anterior discectomy and fusion: four-year clinical outcomes in a prospective, randomized controlled trial. J Bone Joint Surg Am. 2011; 93 (18):1684–1692

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[27] Upadhyaya CD, Wu J-C, Trost G, et al. Analysis of the three United States Food and Drug Administration investigational device exemption cervical arthroplasty trials. J Neurosurg Spine. 2012; 16(3):216–228 [28] Yin S, Yu X, Zhou S, Yin Z, Qiu Y. Is cervical disc arthroplasty superior to fusion for treatment of symptomatic cervical disc disease? A meta-analysis. Clin Orthop Relat Res. 2013; 471(6):1904–1919 [29] Yu L, Song Y, Yang X, Lv C. Systematic review and meta-analysis of randomized controlled trials: comparison of total disk replacement with anterior cervical decompression and fusion. Orthopedics. 2011; 34(10):e651–e658 [30] Riew KD, Schenk-Kisser JM, Skelly AC. Adjacent segment disease and C-ADR: promises fulfilled? Evid Based Spine Care J. 2012; 3 S1:39–46 [31] Burkus JK, Haid RW, Traynelis VC, Mummaneni PV. Long-term clinical and radiographic outcomes of cervical disc replacement with the Prestige disc: results from a prospective randomized controlled clinical trial. J Neurosurg Spine. 2010; 13(3):308–318 [32] Park DK, Lin EL, Phillips FM. Index and adjacent level kinematics after cervical disc replacement and anterior fusion: in vivo quantitative radiographic analysis. Spine. 2011; 36(9):721–730 [33] Delamarter RB, Zigler J. Five-year reoperation rates, cervical total disc replacement versus fusion, results of a prospective randomized clinical trial. Spine. 2013; 38(9):711–717 [34] Burkus JK, Traynelis VC, Haid RW, Jr, Mummaneni PV. Clinical and radiographic analysis of an artificial cervical disc: 7-year follow-up from the Prestige prospective randomized controlled clinical trial: clinical article. J Neurosurg Spine. 2014; 21(4):516–528 [35] Huppert J, Beaurain J, Steib JP, et al. Comparison between single- and multilevel patients: clinical and radiological outcomes 2 years after cervical disc replacement. Eur Spine J. 2011; 20(9):1417–1426 [36] Wu J-C, Huang W-C, Tsai T-Y, et al. Multilevel arthroplasty for cervical spondylosis: more heterotopic ossification at 3 years of follow-up. Spine. 2012; 37 (20):E1251–E1259 [37] Teresi LM, Lufkin RB, Reicher MA, et al. Asymptomatic degenerative disk disease and spondylosis of the cervical spine: MR imaging. Radiology. 1987; 164 (1):83–88 [38] Matsumoto M, Fujimura Y, Suzuki N, et al. MRI of cervical intervertebral discs in asymptomatic subjects. J Bone Joint Surg Br. 1998; 80(1):19–24 [39] Fernström U. Arthroplasty with intercorporal endoprothesis in herniated disc and in painful disc. Acta Chir Scand Suppl. 1966; 357:154–159 [40] Cummins BH, Robertson JT, Gill SS. Surgical experience with an implanted artificial cervical joint. J Neurosurg. 1998; 88(6):943–948 [41] Basho R, Hood KA. Cervical total disc arthroplasty. Global Spine J. 2012; 2 (2):105–108 [42] Bertalanffy H, Eggert HR. Complications of anterior cervical discectomy without fusion in 450 consecutive patients. Acta Neurochir (Wien). 1989; 99(1–2):41–50 [43] Fountas KN, Kapsalaki EZ, Nikolakakos LG, et al. Anterior cervical discectomy and fusion associated complications. Spine. 2007; 32(21):2310–2317 [44] Pickett GE, Sekhon LHS, Sears WR, Duggal N. Complications with cervical arthroplasty. J Neurosurg Spine. 2006; 4(2):98–105 [45] Hacker FM, Babcock RM, Hacker RJ. Very late complications of cervical arthroplasty: results of 2 controlled randomized prospective studies from a single investigator site. Spine. 2013; 38(26):2223–2226

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Cervical Case Studies

22 Cervical Case Studies Mick J. Perez-Cruet, Richard G. Fessler, and Michael Y. Wang Abstract This chapter reviews a number of cervical cases using a variety of minimally invasive approaches. These approaches include simple decompression, spinal fusion, and instrumentation for trauma and more complex reconstruction and tumor resection. It is hoped that these cases will spur additional interest in applying anatomy-preserving minimally invasive approaches, techniques, and technology to the cervical spine. Further refinements in instrumentation including robotics could expand indications and applications of minimally invasive approaches to the cervical spine. With proper application, these techniques and technologies can lead to faster recoveries and improved patient outcomes, ultimately leading to more cost-effective care. Keywords: cervical, minimally invasive, degenerative disease, trauma management, tumor management, MIS instrumentation and applications

22.1 The Evolution of Cervical Minimally Invasive Spine Surgery The cervical spine poses a unique environment for the surgeon. The biomechanics, anatomy, and function of this area are distinct from the thoracolumbar spine, and the evolution of MIS techniques has thus been quite different, as well. For most surgeons, the anterior approaches initially described by Cloward1 and Smith and Robinson2 are already minimally painful, and improvements in this arena have been challenging. Thus, most of the recent advances have been improvements in posterior cervical surgery. This chapter highlights case studies intended to introduce the reader to some of the practical applications of topics already covered in other areas of this textbook. Case studies offer significant illumination to areas that may be more murky in topic-oriented discussions. As such, they can provide unique insight for the reader. However, they are also limited by the inherent heterogeneity seen in the practice of spinal surgery, with regard to pathology, presentation, patient factors, and responses to treatment.

22.2 Case 1: Cervical Foraminotomy 22.2.1 Patient Profile A 47-year-old woman with a 5-year history of pain and dysesthesia located in the right anterior and lateral arm and shoulder and radiating to the right thumb and first and second finger. Increased by flexion. Improved with lying down. Failed physical therapy (PT), and epidural steroid injections. Imaging studies revealed a right C5/C6 disc/osteophyte causing foraminal stenosis (▶ Fig. 22.1).

22.2.2 Case Selection Although this could be done through an anterior or posterior approach, the laterality of this disc/osteophyte complex makes it a perfect case to approach posteriorly using minimally invasive technique.

22.2.3 Preoperative Notes The options were discussed with the patient in detail, including specific techniques, anticipated recovery and ultimate desired function, need versus no need for instrumentation, and risks.

22.2.4 Instrumentation Notes For this approach and procedure, no instrumentation is needed.

22.2.5 Surgical Approach and Technique Using fluoroscopy to identify the level, a 2-cm incision was made 1.5 cm right of midline. Under direct vision, dissection was performed to the facets using a Metz scissors. A mediumsized dilator was then placed onto the facets and further dilation was performed until an 18-mm working channel was positioned. Location was verified, and an endoscopic camera

Fig. 22.1 (a) Sagittal and (b) axial T2-weighted image showing right C5–C6 foraminal stenosis from disc/osteophyte complex. (Case courtesy of Dr. Richard G. Fessler.)

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Surgical Techniques was placed into the channel. Alternatively, a microscope can be used for visualization. Bovie cautery was used to remove a small amount of soft tissue. A hemilaminotomy was performed using a Kerrison punch. This was extended into a foraminotomy using both a drill and the Kerrison punch. Decompression was verified from pedicle to pedicle and to the lateral aspect of each pedicle.

22.2.6 Postoperative Care The patient was discharged in approximately 2 hours.

increases with flexion. Patient has failed PT, pain medication, epidural steroid injection. Right C4 selective nerve root block significantly relieved pain. MRI demonstrates cervical stenosis at C3–C4 level (▶ Fig. 22.2).

22.3.2 Case Selection This stenosis could be approached either anteriorly with an ACDF or posteriorly with laminectomy and decompression. Because this is limited to a single level, it is an easy case to perform using a minimally invasive technique and converts the operation into an outpatient procedure.

22.2.7 Management of Complications The most frequent complication is most likely cerebrospinal fluid (CSF) leak from a dural breach. In the cervical spine, this requires nothing more than Gelfoam and a dural sealant.

22.2.8 Operative Nuances Because the interlaminar space can be quite large, Kirschner wires (K-wire) should not be used here. Dissection should be performed under direct vision using a Metz scissors to create a free pathway for placement of a medium-sized dilation tube. In that way, nothing is ever pushed forcefully toward the spinal cord. Rather than using a Bovie cautery when removing soft tissue from the medial interlaminar space, the bipolar electrosurgery should be used.

22.2.9 Postoperative Results Published series demonstrate excellent to good results in 85 to 90% of patients with a very low complication rate.3

22.3 Case 2: Cervical Decompression 22.3.1 Patient Profile A 78-year-old man, 13 years s/p C5/C6. Anterior cervical discectomy and fusion (ACDF) with 2 years neck pain getting worse over time. It is primarily located in the posterior midline and

22.3.3 Preoperative Notes The options were discussed in detail with the patient. Anterior, open posterior, and MIS posterior options were described and pros and cons of each discussed. Because of the higher incidence of swallowing difficulties in the elderly following high cervical anterior procedures, the patient did not want ACDF. He selected the minimally invasive posterior approach.

22.3.4 Instrumentation Notes For this approach and procedure, no instrumentation is needed.

22.3.5 Surgical Approach and Technique Using fluoroscopy to identify the level, a 2-cm incision was made, 1.5 cm right of midline. Under direct vision, dissection was performed to the facets using a Metz scissors. A medium- size dilator was then placed onto the facets and further muscle dilation was performed using serial muscle dilators until an 18-mm working channel was positioned. Location was verified, and an endoscopic camera was placed into the channel. Alternatively, an operative microscope can be used. Bovie cautery was used to remove a small amount of soft tissue. A hemilaminotomy was performed using a Kerrison punch. This was extended into a foraminotomy using both a drill and Kerrison punch. Decompression was verified from pedicle to pedicle and to the lateral aspect of each pedicle. The tube was then angled to the Fig. 22.2 (a) Sagittal and (b) axial T2-weighted MRI showing C3–C4 cervical stenosis above the level of a prior anterior cervical fusion. (Case courtesy of Dr. Richard G. Fessler.)

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Cervical Case Studies contralateral side. Using a partially shielded drill, the base of the spinous process and ventral surface of the contralateral lamina were removed. Hemostasis was achieved with Surgifoam.

22.3.6 Postoperative Care The patient was discharged in approximately 2 hours.

is left in place while drilling to help protect the dura and prevent durotomy.

22.3.9 Postoperative Results Only a few published series exist, but all report excellent to good results in 85 to 90% of patients, with a very low complication rate.3

22.3.7 Management of Complications The most frequent complication is most likely CSF leak from a dural breach. In the cervical spine, this requires nothing more than Gelfoam and a dural sealant.

22.3.8 Operative Nuances Because the interlaminar space can be quite large, K-wires should not be used here. Dissection should be performed under direct vision using a Metz scissors to create a free pathway for placement of a medium-sized dilation tube. In that way, nothing is ever pushed forcefully toward the spinal cord. Rather than Bovie cautery, when removing soft tissue from the medial interlaminar space, the bipolar should be used. When drilling the contralateral side, care must be taken to drill the bone without compressing the dural sac/spinal cord. The ligamentum flavum

22.4 Case 3: Tubular Access for Instrumented Fusion 22.4.1 Patient Profile A 33-year-old man dove into a shallow pool, resulting in severe neck pain. He presented to the emergency department neurologically intact, but with axial pain 7/10. Imaging studies revealed a dislocation at the C3/C4 level (▶ Fig. 22.3).

22.4.2 Case Selection With the absence of a large anterior disc herniation in a neurologically intact patient, a posterior approach with reduction, fixation, and fusion is a reasonable treatment option.

Fig. 22.3 (a) C3/C4 dislocation following trauma in a 33-year-old patient. (b) Intraoperative view showing placement of cervical lateral mass screws bilaterally at C3–C4 through a 14-mm expandable tubular dilator retractor. (c) Postoperative lateral cervical spine X-rays showing reduction and fixation/fusion at the C3/C4 level. (d) Axial CT scan images showing anatomically appropriate lateral mass screw placement. (Case courtesy of Michael Wang.)

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Surgical Techniques

22.4.3 Preoperative Notes The patient was offered anterior versus posterior versus combined (360 degrees) approaches and he elected for a posterior approach, which was the most likely to achieve a successful reduction in a single-stage operation.

22.4.4 Instrumentation Notes Numerous fixation options are available and standard lateral mass screws are acceptable for insertion through a tubular dilator retractor.

22.4.5 Surgical Approach and Technique Through a midline incision caudal to the level of intervention a tubular dilator retractor was placed and docked on either the right or left side, centered on the facet joint at C3/C4. The facet joint was then entered and opened with curettes. This allowed for decortication of the fusion surfaces of the joint as well as to help with reduction of the perched facet joint. The joint was then packed with bone grafting material and then screws were placed using the Magerl technique (▶ Fig. 22.3b). The tubular retractor was then directed to the contralateral facet joint and the instrumentation and fusion were accomplished on that side (▶ Fig. 22.3c, d).

22.4.6 Postoperative Care The patient is managed postoperatively with standard pain management and bracing, similar to standard open surgery.

22.4.7 Management of Complications Routine antibiotic prophylaxis is used to minimize the risk of postoperative infections. Pseudarthrosis can be minimized with proper graft site preparation, use of appropriate graft materials, bracing, external bone stimulation, and the elimination of tobacco use.

22.4.8 Operative Nuances Because the incision is made caudal to the level of interest, targeting may be difficult in the lower cervical spine where adequate visualization of the level of instrumentation cannot be fully achieved due to the shoulders.

22.4.9 Postoperative Results In a series of patients treated in this manner for one- and twolevel fusions, there was a high fusion rate, as expected with effective fixation and facet joint fusions.

22.5 Case 4: Transfacet Screw Fixation 22.5.1 Patient Profile A 46-year-old male was involved in a high-speed motor vehicle accident. He presented to the emergency department with left

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triceps weakness and axial neck pain 5/10. Imaging studies revealed a C5/C6 disc disruption with neural entrapment and a facet fracture (▶ Fig. 22.4a, b).

22.5.2 Case Selection With the presence of an anterior disc herniation, the patient underwent a C5/C6 anterior cervical disc herniation with fusion and plating. The patient had a good neurological result, but he had persistent neck pain and imaging demonstrated posterior instability and ligamentous disruption. Thus, the patient was scheduled for posterior transfacet instrumentation and screw fixation.

22.5.3 Preoperative Notes The patient was offered transfacet screw fixation only after consideration of the location of the occiput, which can prevent a straight-line trajectory orthogonal and across the facet joint at C5/C6.

22.5.4 Instrumentation Notes While specific, commercially available options are limited for such an approach, cannulated orthopaedic extremity screws can be utilized.

22.5.5 Surgical Approach and Technique A midline 0.5-cm incision several levels cranial to the level of intervention is used. An incision is made in the dorsal muscular fascia and a drill guide is docked on the center of the lateral mass at C5. This is done under fluoroscopic views and without direct visualization. The trajectory is laterally and orthogonal to the facet in the sagittal plane (▶ Fig. 22.4c–e). K-wire placement must be done carefully to avoid overdrilling, which would result in deep placement near critical structures. Conversely, shallow placement risks inadvertent K-wire dislodgement. Cannulated tapping is followed by final cannulated screw placement.

22.5.6 Postoperative Care Standard postoperative care is instituted for a circumferential cervical spinal fusion procedure.

22.5.7 Management of Complications Routine antibiotic prophylaxis is used to minimize the risk of postoperative infections. Pseudarthrosis can be minimized with proper graft site preparation, use of appropriate graft materials, bracing, external bone stimulation, and the elimination of tobacco use.

22.5.8 Operative Nuances As previously stated, the major impediment inhibiting the trajectory is the patient’s own occiput. The lateral trajectory should be adequate to avoid critical structures at the distal

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Cervical Case Studies

Fig. 22.4 (a) Sagittal T2-weighted MRI image showing a C5/C6 acute traumatic disc herniation with posterior ligamentous disruption. (b) Axial CT image showing a facet fracture on the left. (c,d) Lateral and AP intraoperative fluoroscopic images showing a lateral view of placement of a Kirschner wire across the C5/C6 facet on the left. (e) Final lateral image showing the facet crossing the C5/C6 left facet joint to supplement an anterior construct. (Case courtesy of Michael Wang.)

screw end, which will generally be a 15- to 20-degree angle in the coronal plane.

22.5.9 Postoperative Results

22.6.2 Case Selection After discussion of approach selections with the patient, an anterior approach was selected to allow for direct removal of the calcified disc fragment that was compressing the spinal cord.

Because this technique has been newly introduced, clinical and radiographic outcomes from large case series and controlled trials have yet to be published.

22.6.3 Preoperative Notes

22.6 Case 5: Anterior Decompression and Expandable Cage Reconstruction

Patient was obese with a short neck. Cervical MRI showed a dark lesion causing cord compression. For better delineation, a CT myelogram of the cervical spine was ordered. These studies can reveal whether a disc is calcified or not and show the extent of spinal cord compression. An anterior approach was recommended based on the anterior compression of the spinal cord (▶ Fig. 22.5).

22.6.1 Patient Profile A 57-year-old man presented with severe axial neck pain. On examination he was found to have brisk reflexes, positive Hoffmann’s sign, clonus, and Babinski present. His gait was unsteady. On evaluation, he was found to have a large calcified extruded disc fragment compressing the spinal cord at the C2–C3 level (▶ Fig. 22.5).

22.6.4 Instrumentation Notes After a decompression, cervical corpectomy was performed and expandable titanium cage was packed with morselized autograft harvested from the same surgical incision. An anterior cervical plate was then applied extending from C2 to C4.

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Fig. 22.5 (a) Axial and (b) sagittal CT myelogram showing large calcified extruded disc fragment compressing the spinal cord at the C2–C3 level. (c) Postoperative plane X-ray showing anterior reconstruction using a titanium expandable cage and anterior plate instrumentation after removal of the calcified disc. (d) Axial postoperative CT showing removal of calcified disc and reconstruction. Note autologous bone graft placed circumferentially around expandable cage. (Case courtesy of Mick Perez Cruet.)

22.6.5 Surgical Approach and Technique The patient was fiberoptically intubated to prevent any neck extension. Physiologic monitoring was applied including EMG, SSEP, and MEP. A transverse incision was made just under the chin. The sternocleidomastoid muscle was identified and a fascial plane medial to this muscle was used to approach the disc space. Intraoperative fluoroscopy identified the proper level. In order to adequately and safely remove the calcified disc, a C3 corpectomy was performed. Under microscopic visualization, the calcified disc was completely removed. All drilled bone was collected using the Thompson MIS BoneBac Press (Thompson MIS, Salem, NH) and used as autologous bone graft fusion material. An expandable titanium cage was filled with bone graft material and placed extending from the base of C2–C4. An anterior cervical plate was applied. Wound was closed in a routine fashion.

22.6.6 Postoperative Care Because of the patient’s large body habitus and short, thick neck, the patient was initially observed in the intensive care unit. After an overnight stay, he was transferred to the floor and

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discharged on postoperative day 3. Patient experienced no postoperative dysphagia and made an unremarkable recovery. He regained full strength and gait.

22.6.7 Management of Complications If needed, a cervical drain can be left in place to help avoid a wound hematoma. The patient is placed in a hard cervical collar. The expandable cage allows for a “tight fit” of the anterior reconstruction and can be applied relatively easily in “hardto-get-to places” such as the high cervical spine in patients with large short necks. Care is taken not to overexpand the cage. Bone is placed around the cage to enhance arthrodesis. An anterior cervical plate is placed to provide further structural support and prevent cage migration. Patient used an external bone graft stimulator postoperatively to enhance fusion and prevent the need for further posterior cervical stabilization.

22.6.8 Operative Nuances The anterior cervical approach is a relatively minimally invasive procedure that can be performed through a small incision. Thin bladed tooth retractors are used that minimize retraction-related complications. Using bone harvested from

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Cervical Case Studies the same surgical incision can prevent graft site morbidity. Expandable cages are very effective in areas which are surgically challenging such as in this case.

22.6.9 Postoperative Results This patient made an excellent recovery. Complete arthrodesis was achieved in 3 months’ time and he has returned to work and normal activities of daily living.

22.7 Case 6: Intradural Tumor Resection 22.7.1 Patient Profile An 65-year-old female presented with neck pain and symptoms of myelopathy including unsteady gait and hyperreflexia, bilateral Hoffmann’s sign, clonus, and Babinski present. A contrast-enhanced cervical MRI revealed an intradural C4–C5 mass consistent with meningioma (▶ Fig. 22.6).

22.7.2 Case Selection The approaches to tumor were discussed with the patient. A left lateral muscle-splitting approach, tumor resection and instrumented fusion was selected.

22.7.3 Preoperative Notes Imaging studies were reviewed with the patient and family. Because of the age of the patient and medical comorbidities, surgical approach was discussed with patient and family that would limit tissue damage. The possibility of posterior lateral instrumented fusion was also discussed with patient and family members if greater than 50% of the facet needed to be removed to safely access and remove the tumor.

22.7.4 Instrumentation Notes Following gross total removal of the tumor and dural closure, unilateral (left-sided) lateral mass instrumented fusion was performed.

22.7.5 Surgical Approach and Technique The patient was intubated and placed in a Mayfield head holder. Intraoperative monitoring was placed including SSEP, MEP, and EMG. The patient was log rolled onto gel rolls and fixed into the Mayfield head holder. The level was then identified using lateral and AP fluoroscopy. With the level properly identified, small para-midline incision was made on the left side. Muscle-splitting approach was used exposing the lamina

Fig. 22.6 (a) Sagittal and (b) axial contrastenhanced MRI revealed an intradural contrastenhancing mass consistent with meningioma located on the left at the C4–C5 level. Postoperative (c) sagittal and (d) axial CT myelogram showing complete resection of the meningioma using muscle-sparing lateral approach with preservation of the spinous process. Lateral mass instrumented fusion was performed as greater than 50% of the facet was resected to safely remove the tumor. (Case courtesy of Mick Perez Cruet.)

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Surgical Techniques and facet complex on the left. Under microscopic visualization, the lamina was exposed. Using a high-speed drill, a leftsided laminectomy was performed overlying the tumor. The dura was opened laterally exposing the tumor, which was soft. The tumor was removed in a gross total fashion and confirmed by pathology as a meningioma. The dura was closed with 4–0 nurolon suture, and fibrin sealant placed. Since greater than 50% of the facet was removed to safely access the tumor, unilateral lateral mass screws were placed to supplement a posterolateral arthrodesis using locally harvested bone. The muscles were reapproximated and fascial sutures placed. Subcuticular sutures were applied and skin closed with a running locking nylon suture.

22.7.8 Operative Nuances

22.7.6 Postoperative Care

Less invasive approaches to tumor resection require careful patient selection. Further advances in surgical technique, retractors, and instrumentation will expand the indications for these types of cases.

Patient tolerated the procedure without complications. Postoperative CT/myelogram confirmed complete resection of the tumor (▶ Fig. 22.6c,d).

22.7.7 Management of Complications Careful patient selection is critical to performing safe less invasive intradural tumor resection. We felt that the focal lateral location of this tumor made this an ideal case. Dural closure was enhanced by fibrin glue with the addition of multilevel tissue closure and skin closure with a running locking nylon suture.

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A unilateral muscle-splitting approach with preservation of the spinous processes, intraspinous ligament, and contralateral muscles achieved a rapid recovery and avoidance of more extensive tissue resection.

22.7.9 Postoperative Results The patient was discharged on postoperative day 2 and made an unremarkable recovery. Further MRI imaging done 2 years after surgery has shown no tumor recurrence.

22.8 Conclusion

References [1] Cloward RB. The anterior approach for removal of ruptured cervical disks. J Neurosurg. 1958; 15(6):602–617 [2] Smith GW, Robinson RA. The treatment of certain cervical-spine disorders by anterior removal of the intervertebral disc and interbody fusion. J Bone Joint Surg Am. 1958; 40-A(3):607–624 [3] Lawton CD, Smith ZA, Lam SK, Habib A, Wong RH, Fessler RG. Clinical outcomes of microendoscopic foraminotomy and decompression in the cervical spine. World Neurosurg. 2014; 81(2):422–427

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Posterior Thoracic Microdiscectomy

23 Posterior Thoracic Microdiscectomy Robert E. Isaacs, Mick J. Perez-Cruet, and Steven H. Cook Abstract Posterior thoracic microdiscectomy via the transfacet pediclesparing and transpedicular approaches provides safe and minimally invasive access to disc herniations within the thoracic spine. These approaches have been developed to treat both radiculopathy and myelopathy in a manner that allows complication avoidance and relief of symptoms. The minimally invasive nature of the procedure allows access to a noncalcified herniated disc without traversing the thoracic cavity and reduction in soft tissue disruption. Intraoperative anatomic landmarks are critical to successful discectomy, and these are discussed in terms of both visual and radiographic appearances. Cerebrospinal fluid leak, spinal cord injury, and pneumothorax are known complications of this procedure; however, maneuvers for avoidance as well as treatment are provided. Outcomes from posterior thoracic microdiscectomy have improved dramatically in recent years with improvements in imaging, instrumentation, and techniques. Mastery of the skills and tools described within this chapter will allow surgeons to manage thoracic disc herniations via a minimally invasive approach. Keywords: thoracic herniated disc, microdiscectomy, transfacet pedicle sparing, transpedicular

23.1 Introduction Thoracic disc herniation is a relatively rare condition with an inconclusive incidence ranging from 1/1,000 to 1/1,000,000 patients per year and occurs in a central or centrolateral location without gender predilection.1,2,3 Theoretically, because of decreased flexion and increased stability of the costovertebral joints, the incidence of thoracic disc disease is low in comparison with disc pathology of the cervical and lumbar regions.4,5 Furthermore, between 10 and 37% of such herniations are asymptomatic.2,6,7,8,9,10 When symptomatic, the patient may present with a combination of pain and neurological symptoms. The most common reported symptom is pain, found in 76% of patients, followed by sensory impairment and paresis.3 In the thoracic region, the diameter of the spinal canal is less than in the cervical and lumbar region. In addition, vascular supply to the cord is limited in the thoracic region, making manipulation of the cord tenuous11; thus, proper visualization of the disc herniation must be established to avoid excessive or even minor cord manipulation. Although traditional approaches have been successful to some degree in reaching thoracic disc pathology, each procedure requires a relatively large skin incision and/or extensive bone resection that may subsequently cause significant postoperative morbidity or lead to the need for instrumentation and fusion.12,13,14,15 The numerous approaches developed to address thoracic disc herniation include: posterior (laminectomy),16 posterolateral (costotransversectomy),17,18 transfacet pedicle sparing,19 transpedicular,20 transversoarthropediculectomy,21 lateral (extracavitary),22 thoracotomy,17,23 transthoracic (transpleural and extrapleural),24,25,26 transsternal,27 and thoracoscopy.28,29,30

The first posterior approach described for thoracic discectomy was by laminectomy via a posterior approach.16,31 Outcomes from this approach were extremely poor, with the majority of patients failing to improve, with morbidity rates from 18 to 75% (including paraplegia) and in some cases mortality rates nearing 50%.16,17,32,33,34,35,36 Therefore, this approach was abandoned and should be avoided unless significant spinal stenosis exists from hypertrophy of posterior thoracic column elements. Posterolateral approaches were subsequently developed to allow visualization of discs without a midline approach; however, this was balanced with the resulting tissue disruption, devascularization, and possible kyphosis.37 With calcified and more centrally located discs, a lateral or anterior approach was desired as this allowed for direct visualization of surrounding anatomy without manipulation of the spinal cord, complete removal of calcified discs, and repair of the thecal sac in cases of dural erosion. However, these anterior approaches place the great vessels and thoracic cavity contents at risk along with the pain and healing concerns associated with the tissue disruption.14 Clinical studies have shown minimally invasive spine surgery to be associated with less disruption of normal tissue, less blood loss, and shortened procedural time when compared with traditional open approaches. This translates into patients experiencing reduced postoperative pain, hospitalization, and recovery time.12,38,39,40 In order to diminish the various potential complications and morbidities associated with more traditional surgical procedures used to treat a herniated thoracic disc, minimally invasive techniques such as the transfacet, pedicle-sparing and transpedicular approaches are becoming more frequently used. These two approaches will be discussed.

23.2 Indications and Contraindications Because of the infrequency of clinically significant thoracic disc herniation as well as the potential risks to the thoracic spinal cord, operative intervention should be limited to those patients with debilitating symptoms. A clear indication to perform a posterior microdiscectomy is in patients with soft thoracic disc herniations causing myelopathy in order to improve neurologic function and prevent further injury to the spinal cord.41,42 Isolated thoracic radiculopathy from disc herniation is typically a sharp, lancinating pain that radiates unilaterally in a dermatomal distribution around the chest cavity and usually responds to conservative management such as medications, intercostal nerve injection, extension bracing, or activity modification.17 Although a rarer presentation, lateralized foraminal discs need to be considered when reviewing imaging. Severe and refractory radiculopathy not responsive to treatment for at least 6 months is another indication for surgery. It remains controversial whether patients with localized back pain and axial pain without myelopathy require surgery; most surgeons do not recommend thoracic discectomy for isolated back pain unless it is associated with neurologic deficit.3,14,30,43,44

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Surgical Techniques A more absolute contraindication to this technique is large calcified midline thoracic discs that may require an anterior approach to reduce manipulation of the spinal cord to achieve adequate decompression. For more compressible centrally located discs, the experience of the surgeon would be the determining factor for using this approach safely and effectively.

23.3 Preoperative Planning The preoperative evaluation of the patient should include a thorough physical exam. This includes a neurological evaluation for signs of myelopathy or radiculopathy that will help guide surgical decision making. With thoracic disc herniations, myelopathy and radiculopathy can occur exclusively or concomitantly depending on extent of the disc herniation. A skin examination should note any prior incisions to assist in planning surgical approach. Radiographic evaluation should be performed with thoracic spine X-rays to visualize alignment and curvature of the spine. Preoperative chest X-ray view allows for identification of ribs for intraoperative localization. Additionally a preoperative AP and lateral X-ray of the thoracic and lumbar spine allows for identification of uncommon anatomical variations (i.e., four or six lumbar vertebrae). Computed tomography (CT) is recommended in order to determine the degree of calcification of the herniated disc as this will affect management of centrally located discs. Magnetic resonance imaging (MRI) should be performed to accurately localize the level of the disc herniation and whether it is located in a lateral or central position. This imaging is also helpful in noting the degree of compression on neural elements and ruling out any intradural or posterior lesions that may be contributing to symptoms. Given the reliance on intraoperative imaging for a successful surgical outcome, localizing levels (T1 or sacrum) should be clearly identifiable on imaging by the surgeon. To avoid wrong level surgery, there has been increasing interest in preoperativelevel marking with radiopaque materials.45

23.4 Instrumentation The instruments used are similar to those used to perform a microscopic lumbar discectomy with the system of tubular dilators.40

Required Instrumentation for Thoracic Microdiscectomy Imaging requirements: ● Fluoroscopy. ● Lead drape including thyroid shield for surgeon and operative personnel. ● Radiolucent table and frame that permits adequate anteroposterior and lateral fluoroscopic views of the spine. Surgical instruments: Tubular dilator set. ● Long tapered high-speed drill. ● Microsurgical instruments (curettes, probes, etc.). ● Microscope (endoscope use has been performed). ●

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23.5 Surgical Approach and Technique The approach for the transfacet, pedicle-sparing and transpedicular approaches relies on intra-operative imaging to delineate the docking point for tubular retraction. The differences lie in starting point for dilator placement and amount of bony removal. Both use a small paramedian incision with a medial direction of approach. Patient positioning and incision is similar for both the transfacet, pedicle-sparing and transpedicular approaches. After general endotracheal induction and placement of a Foley catheter, the patient is positioned prone on a radiolucent Wilson frame or Jackson table. All pressure points are padded adequately and the arms are placed above the patient unless an upper thoracic disc is being approached, making sure not to overextend at the shoulder beyond 90 degrees (▶ Fig. 23.1a). Somatosensory evoked potentials (SSEPs) are measured throughout the procedure, if desired. The fluoroscopic C-arm is positioned to allow for a lateral X-ray image of the operative area. (▶ Fig. 23.1b). The microscope is draped sterilely. The back is shaved, prepared, and draped in a routine surgical fashion. Under fluoroscopic guidance, a spinal needle is used to locate the level of the herniated thoracic disc. The exact location of the thoracic disc herniation is confirmed by counting from the sacrum below and/or from the C7–T1 junction above. Alternatively, the ribs can be counted from T1 or T12. Preoperative chest X-ray is helpful in identifying any variations in the ribs (i.e., small 12th rib). Once the correct level is identified, a craniocaudal incision of approximately 2 cm is made 3 cm lateral to the midline. Preoperative axial MRI can be helpful in identifying how lateral the incision should be placed. The center of this incision should be in same axial plane of the inferior border (superior endplate of inferior vertebral body) of the disc being approached. Larger and more muscular individuals require a more lateral approach for adequate visualization of the foramen and safe removal of the thoracic disc herniation without cord manipulation. The more central the herniation, the more lateral the incision. An initial dilator is placed at the center of the pedicle caudal to the disc herniation for the transpedicular route and at the medial aspect of the transverse process (at junction with rib head) caudal to the thoracic disc herniation for the transfacet route. Next, a series of tubular muscle dilators are placed under fluoroscopic guidance (▶ Fig. 23.2a, b). Finally, a tubular retractor is then placed over the final muscle dilator and then affixed to a flexible arm secured firmly to the operative table (▶ Fig. 23.2,c). At this point, confirmation of level should be obtained via imaging and reference to anatomic localizer (T1 or sacrum).

23.5.1 Transfacet Pedicle-Sparing Approach Adequate intraoperative imaging not only ensures that the operative level is identified, but can also be used if the surgical anatomy is distorted to help guide bone removal and delineate the disc space (▶ Fig. 23.2d). This can be facilitated by lateral and anteroposterior (AP) fluoroscopic images during the procedure. The lateral projectory of the tubular retractor through a

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Posterior Thoracic Microdiscectomy

Fig. 23.1 (a) Patient positioning, prone with arms extended on Wilson frame. (b) Fluoroscopy unit placed for intraoperative use and localization of the level.

transforaminal-type approach allows for extensive disc removal under the thoracic spinal cord and dura, enabling even midlinelocated thoracic disc herniations to be removed safely.46 The remainder of the procedure can be safely performed under microscopic visualization though the endoscopic-assisted procedure has been performed safely and described in the literature.46,47 If the facet junction with the transverse process cannot be seen or if a lateral to medial trajectory was not obtained, redilation via a different track should be performed to ensure an adequate starting point before proceeding to bone removal. If needed, AP and lateral fluoroscopic views can be used to reconfirm the level and location of the tubular retractor. The muscle and soft tissue overlying the proximal portion of the transverse process and lateral facet complex are removed using an insulated Bovie cautery. Careful probing with a ballended probe helps in defining the bone margins, and liberal use of fluoroscopic imaging also helps to orient the surgeon throughout the procedure. Once the bone architecture is defined,

access to the neural foramen and subsequent herniated disc fragment requires removal, via the use of a long tapered high-speed drill, of the proximal aspect of the transverse process as well as the lateral aspect of the facet complex (▶ Fig. 23.3a,b). The thoracic pedicle of the more caudal vertebral body is identified and followed to the appropriate disc level (the exiting nerve root can also be followed proximally if pedicle not identified). Drilling of the lateral aspect of the pedicle facilitates final access to the thoracic disc and the thecal sac (▶ Fig. 23.3c). If more exposure is needed at this point, the dorsal side of the rib may be drilled for bone removal. Once the exiting nerve root and thecal sac have been identified, the veins overlying the disc space may be cauterized with a bipolar cautery and the annulus incised. Any presenting lateral disc fragments can be removed safely. A bony trough, centered on the disc space, may then be drilled a few millimeters ventrally into the adjacent vertebral bodies. Once an adequate anterior trough ventral to the herniation is completed, one can decompress the

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Surgical Techniques

Fig. 23.2 (a,b) Surgical and fluoroscopic view of tubular dilator placement off midline with lateral to medial trajectory. (c) Attachment to flexible arm secured to bed. (d) Fluoroscopic view of probe confirming anatomy and operative level.

neural elements by displacing the herniated disc into the defect and removing it (▶ Fig. 23.3d,e). Complete removal of the disc may require gentle compression along the dorsal side and pressure to push the disc fragment ventrally into the disc space and trough. A micro down-going curette can be used to push disc material away from the dura and spinal cord. A number 1 or 2 Kerrison punch can be used to resect partly calcified lateral fragments. Once visual disc is removed, the disc space is irrigated and all accessible fragments are removed. In the case of a calcified lateral disc, drilling may need to be continued into the disc space leaving a thin layer of bone directly adjacent to the dura. This layer may then be disconnected from the vertebral bodies and dissected gently away from the dura into the ventral defect. After complete discectomy, further inspection underneath the dura and spinal cord using a combination of the Woodson elevator, Sypert impactor, and down-going curette ensures complete decompression (▶ Fig. 23.4a,b). The tubular retractor is removed, and sutures placed in the thoracodorsal fascia. Interrupted subcuticular sutures are then placed and the skin is closed with surgical adhesive.

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23.5.2 Transpedicular Approach Once the positioning of the tubular retractor over the pedicle is confirmed with fluoroscopy, the lateral edge of the lamina and medial facet should be identified. Overlying muscle and soft tissue can be removed with electrocautery in order to visualize bony landmarks. Drilling should begin along the rostral and lateral portion of the lamina, the medial portion of the facet, and pedicle. Drilling should continue until adequate exposure of the lateral disc space is obtained. This may require drilling of the pedicle to the vertebral body junction. Care should be taken to preserve tissue between drilling and the thecal sac to prevent CSF leaks and no retraction should be performed medially to prevent damage to the spinal cord. Nerve roots and traversing vessels should be avoided to prevent postoperative neuralgia and risk of ischemia. Once the disc space is clearly identified, the annulus is incised laterally to avoid manipulation of the spinal cord. Disc material may be removed through this opening or via a trough drilled in the vertebral body followed by gentle pressure applied to the herniated disc in order to push it into cavity created

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Posterior Thoracic Microdiscectomy

a

b

Medial

Vertebral body

Facet complex

Vertebral body Facet complex Caudal

Cephalad

Transverse process

Lateral

c

d

Medial Facet complex

Medial

Facet complex

Neural foramen

Cord

Pedicle Caudal

Cephalad Herniated nucleus pulposus

Transverse process

Transverse process Herniated nucleus pulposus Lateral

e

Medial

Facet complex Cord

Transverse process

Fig. 23.3 (a) Drilling of the cephalad proximal aspect of the transverse process, (b) lateral aspect of the facet joint, (c) and lateral aspect of the pedicle. (d,e) Removal of disc herniation, resulting in decompression of the spinal cord.

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Surgical Techniques

Fig. 23.4 (a) Removal of disc fragments, fluoroscopic view of rongeurs in disc space. (b) Intraoperative view of curette beneath the thecal sac pressing fragment into disc space.

ventrally before removal. Once visual disc is removed, the disc space is irrigated and all accessible fragments are removed. In the case of a calcified lateral disc, drilling may need to be continued into disc space leaving a thin layer of bone directly adjacent to dura. This layer may be then disconnected from the vertebral bodies and dissected gently away from the dura.

23.6 Postoperative Care Postoperative care includes early ambulation and pain control, which can usually be achieved with oral analgesia. Most patients will be ready for discharge within 24 hours and commonly treated on an outpatient basis. Follow-up should consist of neurological examination to ensure that symptoms are improving. If symptoms are not improved by 6 weeks postoperatively, or worsening, an MRI is recommended to look for residual disc fragments or persistent compression. Routine wound care can be performed and absorbable sutures negate the need for removal.

23.7 Management of Complications Complications of posterior thoracic microdiscectomy include a risk to the spinal and intrathoracic contents. If there is neurologic decline noted after the procedure, then adequate blood pressure should be maintained to facilitate spinal cord perfusion. MRI should be immediately obtained to look for any persistent or new cord compression that may require surgical exploration. If there is noted to be a breach of the pleural cavity, then attempt can be made to repair primarily. A chest tube should be inserted which can be removed as soon as postoperative radiograph demonstrates resolution of any pneumothorax. Cerebrospinal fluid leaks are a known complication of thoracic discectomy and a more commonly seen complication with calcified discs that can adhere to the dura. If the disc is seen to be eroded through the dura, complete removal should not be attempted and a decompression can be performed with subtotal removal leaving the shell of the calcified disc attached to the dura, much as is done with ossification of the posterior longitudinal ligament (OPLL) patients. If the disc is heavily calcified preventing removal, a more lateral or anterior approach may need to be performed for decompression. If a fluid leak is seen intraoperatively, then primary repair should be attempted with

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direct closure or plugging with muscle. If the surgeon is unable to obtain a primary closure, then a graft may be used with tissue sealant to avoid persistent leaks. A lumbar drain may be inserted if a leak is suspected after surgery, or for incomplete repair, for a few days to aid in closure. In the event of a CSF leak, the thoracodorsal fascia is meticulously closed and a running locking nylon suture applied to reapproximate the skin. If there is persistent CSF leak through the skin or nonresolving subcutaneous collection, then a more extensive surgical exploration may be needed for definitive closure.

23.8 Clinical Case A 48-year-old female presented with thoracic radiculopathy and myelopathy from a left minimally calcified disc herniation at T7–T8 level. Given the paracentral location, she underwent a left-sided T7–T8 microdiscectomy. Preoperative (▶ Fig. 23.5a–c) and postoperative (▶ Fig. 23.5e, f) MRI showed the extent of disc removal with adequate decompression of the thoracic spinal cord. Postoperatively, there were no complications and patient had resolution of symptoms and returned to activities of daily living.

23.9 Conclusion Transthoracic approaches for the treatment of thoracic disc herniation were first performed in the late 1950s, after which they became a standard procedure to manage thoracic disc herniations.24 This approach provides excellent visualization of the anterior aspect of the thoracic spine without the risk of spinal cord manipulation to yield optimal decompression.25,26,48 However, thoracotomy requires a large skin incision, extensive lung and rib retraction, and muscle dissection, all of which can contribute to postoperative pulmonary dysfunction, pain, and increased morbidity.13,47,49 This approach is still favored in cases of large midline calcified thoracic disc herniations. Thoracoscopic discectomy is an effective alternative to traditional open thoracotomy techniques because it has been shown to reduce the incidence of pulmonary morbidity, intercostal neuralgia, and shoulder girdle dysfunction.41,50,51,52 Although the procedure-associated morbidities are much less than with the open thoracotomy, the prevalence of pulmonary complications, such as postoperative atelectasis, pneumothorax, pleural effusion, and hemothorax, is considerable.14,53,54,55,56 In addition, although the complication rates of the open approach versus the thoracotomy approach may vary, the types of

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Posterior Thoracic Microdiscectomy

Fig. 23.5 (a) Preoperative CT scan showing minimal calcification of disc. Preoperative MRI (b) sagittal and (c) axial view of T7/T8 level. (d) Intraoperative fluoroscopy showing docking of tubular dilator. Postoperative (e) sagittal and (f) axial MRI views of same levels.

complications encountered are similar.57,58 Thoracoscopic surgery is technically demanding and requires attainment of new surgical skills and additional expensive operative technology. The lateral extracavitary approach provides many of the benefits of an anterior approach without the additional risks of entering the thoracic cavity.59,60,61,62 Unfortunately, the exposure for the open posterolateral extracavitary approach requires extensive muscle dissection and rib resection, violation of the costal neurovascular bundle, and pleural retraction that increase the risk of complications and can add to postoperative morbidity.13,48 A minimally invasive approach that can be performed from a posterior lateral position has been described by the author and others in which a dilator system is used extrapleurally or transpleurally, similar to how it is performed in the lumbar region. This has been proven to be safe and feasible for a number of thoracic disc pathologies, including central calcified discs with reduced risk of complications compared to an open procedure.63 The advantages of this technique include those related to minimally invasive techniques described elsewhere as well

as avoidance of the thoracic cavity while disadvantages are inability to visualize the spinal cord anteriorly.64 Posterolateral approaches, including the transpedicular and transfacet pedicle-sparing procedures, have been effective in treating thoracic disc herniation but require relatively extensive muscular and bone dissection during the approach.13,47 The posterior minimally invasive approaches to thoracic discectomy have a number of advantages over other traditional techniques including the following: avoidance of traversing through the thoracic cavity, minimal osseous and ligamentous removal, maintenance of the integrity of the disc, avoidance of the need for thoracic fusion, and avoidance of extensive posterior muscle dissection. In the treatment of thoracic disc herniations, the surgeon must choose the approach that can treat the pathology, is safe for the patient, and is within the skills of the surgeon. The posterior minimally invasive techniques described here rely on similar approaches to the lumbar spine that many surgeons are familiar with or can develop with minimal training. The ability

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Surgical Techniques to remove a majority of thoracic disc herniations through a minimally invasive approach allows for improved outcomes and decreased complications.

Clinical Caveats ●

●

●

●

●

●

Calcified disc herniations located centrally should be approached from a more lateral or anterior approach. Preoperative imaging including CT/myelogram is helpful in determining degree of calcification in central disc herniations. Preoperative chest X-ray, AP and lateral thoracic and lumbar plain films, and MRI or CT sagittal images showing sacrum to level of pathology can help prevent wrong level surgery. Knowledge of thoracic spine anatomy is critical for minimally invasive approach to minimize risk of injury and avoid spinal cord manipulation. Use of sequential steps in bone removal and removal of disc will allow for use of anatomical landmarks throughout case. Adequate localization prior to incision and bone removal is essential; anatomical reference of sacrum allows for intraoperative localization. Ensure adequate disc space or bony trough is present in order to remove herniated disc ventral to the thecal sac by pushing herniated disc fragment into ventral space.

References [1] Arce CA, Dohrmann GJ. Thoracic disc herniation. Improved diagnosis with computed tomographic scanning and a review of the literature. Surg Neurol. 1985; 23(4):356–361 [2] Brown CW, Deffer PA, Jr, Akmakjian J, Donaldson DH, Brugman JL. The natural history of thoracic disc herniation. Spine. 1992; 17(6) Suppl:S97–S102 [3] Stillerman CB, Chen TC, Couldwell WT, Zhang W, Weiss MH. Experience in the surgical management of 82 symptomatic herniated thoracic discs and review of the literature. J Neurosurg. 1998; 88(4):623–633 [4] Adams MA, Hutton WC. Prolapsed intervertebral disc. A hyperflexion injury 1981 Volvo Award in Basic Science. Spine. 1982; 7(3):184–191 [5] White AAI, Panjabi MM. Clinical Biomechanics of the Spine. Philadelphia, PA: Lippincott; 1990 [6] Awwad EE, Martin DS, Smith KR, Jr, Baker BK. Asymptomatic versus symptomatic herniated thoracic discs: their frequency and characteristics as detected by computed tomography after myelography. Neurosurgery. 1991; 28 (2):180–186 [7] Oppenheim JS, Rothman AS, Sachdev VP. Thoracic herniated discs: review of the literature and 12 cases. Mt Sinai J Med. 1993; 60(4):321–326 [8] Ross JS, Perez-Reyes N, Masaryk TJ, Bohlman H, Modic MT. Thoracic disk herniation: MR imaging. Radiology. 1987; 165(2):511–515 [9] Vanichkachorn JS, Vaccaro AR. Thoracic disk disease: diagnosis and treatment. J Am Acad Orthop Surg. 2000; 8(3):159–169 [10] Wood KB, Blair JM, Aepple DM, et al. The natural history of asymptomatic thoracic disc herniations. Spine. 1997; 22(5):525–529, discussion 529–530 [11] Dommisse GF. The blood supply of the spinal cord. A critical vascular zone in spinal surgery. J Bone Joint Surg Br. 1974; 56(2):225–235 [12] Birch BD, Desai RD, McCormick PC. Surgical approaches to the thoracolumbar spine. Neurosurg Clin N Am. 1997; 8(4):471–485 [13] Fessler RG, Sturgill M. Review: complications of surgery for thoracic disc disease. Surg Neurol. 1998; 49(6):609–618 [14] Rosenthal D, Dickman CA. Thoracoscopic microsurgical excision of herniated thoracic discs. J Neurosurg. 1998; 89(2):224–235 [15] Stillerman CB, Chen TC, Day JD, Couldwell WT, Weiss MH. The transfacet pedicle-sparing approach for thoracic disc removal: cadaveric morphometric analysis and preliminary clinical experience. J Neurosurg. 1995; 83(6):971–976 [16] Mixter WJ, Barr JS. Rupture of the intervertebral disc with involvement of the spinal canal. N Engl J Med. 1934; 211:210–215

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[17] Hulme A. The surgical approach to thoracic intervertebral disc protrusions. J Neurol Neurosurg Psychiatry. 1960; 23:133–137 [18] Simpson JM, Silveri CP, Simeone FA, Balderston RA, An HS. Thoracic disc herniation. Re-evaluation of the posterior approach using a modified costotransversectomy. Spine. 1993; 18(13):1872–1877 [19] Stillerman CB, Chen TC, Couldwell WT, et al. Transfacet pedicle-sparing approach. In: Benzel EC, Stillerman CB, eds. The Thoracic Spine. St Louis, MO: Quality Medical Publishing; 1999:338–345 [20] Patterson RH, Jr, Arbit E. A surgical approach through the pedicle to protruded thoracic discs. J Neurosurg. 1978; 48(5):768–772 [21] Lesoin F, Rousseaux M, Autricque A, et al. Dorsal disc herniation. 13 cases. Rev Chir Orthop Repar Appar Mot. 1986; 72:441–445 [22] Larson SJ, Holst RA, Hemmy DC, Sances A, Jr. Lateral extracavitary approach to traumatic lesions of the thoracic and lumbar spine. J Neurosurg. 1976; 45 (6):628–637 [23] Capener N. The evolution of lateral rhachotomy. J Bone Joint Surg Br. 1954; 36-B(2):173–179 [24] Crafoord C, Hiertonn T, Lindblom K, Olsson SE. Spinal cord compression caused by a protruded thoracic disc: report of a case treated with antero-lateral fenestration of the disc. Acta Orthop Scand. 1958; 28(2):103–107 [25] Perot PL, Jr, Munro DD. Transthoracic removal of midline thoracic disc protrusions causing spinal cord compression. J Neurosurg. 1969; 31(4):452–458 [26] Ransohoff J, Spencer F, Siew F, Gage L, Jr. Transthoracic removal of thoracic disc. Report of three cases. J Neurosurg. 1969; 31(4):459–461 [27] Sundaresan N, Shah J, Feghali JG. A transsternal approach to the upper thoracic vertebrae. Am J Surg. 1984; 148(4):473–477 [28] Mack MJ, Regan JJ, Bobechko WP, Acuff TE. Application of thoracoscopy for diseases of the spine. Ann Thorac Surg. 1993; 56(3):736–738 [29] Mack MJ, Regan JJ, McAfee PC, Picetti G, Ben-Yishay A, Acuff TE. Video-assisted thoracic surgery for the anterior approach to the thoracic spine. Ann Thorac Surg. 1995; 59(5):1100–1106 [30] Rosenthal D, Rosenthal R, de Simone A. Removal of a protruded thoracic disc using microsurgical endoscopy. A new technique. Spine. 1994; 19(9):1087–1091 [31] Zeidman SM, Rosner MK, Poffenbarger JG. Thoracic disc disease, spondylosis, and stenosis. In: Benzel EC, Stillerman CV, eds. The Thoracic Spine. St. Louis, MO: Quality Medical; 1999:297–303 [32] Hawk WA. Spinal compression caused by ecchondrosis of the intervertebral fibrocartilage: with a review of the recent literature. Brain. 1936; 59:204–224 [33] Logue V. Thoracic intervertebral disc prolapse with spinal cord compression. J Neurol Neurosurg Psychiatry. 1952; 15(4):227–241 [34] Love JG, Kiefer EJ. Root pain and paraplegia due to protrusions of thoracic intervertebral disks. J Neurosurg. 1950; 7(1):62–69, illust [35] Muller R. Protrusion of thoracic intervertebral disks with compression of the spinal cord. Acta Med Scand. 1951; 139(2):99–104 [36] Tove D, Strang RR. Thoracic intervertebral disk protrusions. Acta Chir Scand. 1960; 267:3–41 [37] Burke TG, Caputy AJ. Treatment of thoracic disc herniation: evolution toward the minimally invasive thoracoscopic technique. Neurosurg Focus. 2000; 9(4):e9 [38] Anand N, Regan JJ. Video-assisted thoracoscopic surgery for thoracic disc disease: classification and outcome study of 100 consecutive cases with a 2-year minimum follow-up period. Spine. 2002; 27(8):871–879 [39] Huang TJ, Hsu RW, Liu HP, et al. Video-assisted thoracoscopic treatment of spinal lesions in the thoracolumbar junction. Surg Endosc. 1997; 11 (12):1189–1193 [40] Perez-Cruet MJ, Smith MM, Foley KT. Microendoscopic lumbar discectomy. In: Perez-Cruet MJ, Fessler RG, eds. Outpatient Spinal Surgery. St Louis, MO: Quality Medical Publishing; 2002:171–183 [41] Kuklo TR, Lenke LG. Thoracoscopic spine surgery: current indications and techniques. Orthop Nurs. 2000; 19(6):15–22 [42] Oskouian RJ, Jr, Johnson JP, Regan JJ. Thoracoscopic microdiscectomy. Neurosurgery. 2002; 50(1):103–109 [43] Otani K, Yoshida M, Fujii E, Nakai S, Shibasaki K. Thoracic disc herniation. Surgical treatment in 23 patients. Spine. 1988; 13(11):1262–1267 [44] Peker S, Akkurt C, Ozcan OE. Multiple thoracic disc herniations. Acta Neurochir (Wien). 1990; 107(3–4):167–170 [45] Upadhyaya CD, Wu JC, Chin CT, Balamurali G, Mummaneni PV. Avoidance of wrong-level thoracic spine surgery: intraoperative localization with preoperative percutaneous fiducial screw placement. J Neurosurg Spine. 2012; 16 (3):280–284 [46] Isaacs RE, Podichetty VK, Sandhu FA, et al. Thoracic microendoscopic discectomy: a human cadaver study. Spine. 2005; 30(10):1226–1231 [47] Perez-Cruet MJ, Kim BS, Sandhu F, Samartzis D, Fessler RG. Thoracic microendoscopic discectomy. J Neurosurg Spine. 2004; 1(1):58–63

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Posterior Thoracic Microdiscectomy [48] Mulier S, Debois V. Thoracic disc herniations: transthoracic, lateral, or posterolateral approach? A review. Surg Neurol. 1998; 49(6):599–606, discussion 606–608 [49] Currier BL, Eismont FJ, Green BA. Transthoracic disc excision and fusion for herniated thoracic discs. Spine. 1994; 19(3):323–328 [50] Ferson PF, Landreneau RJ, Dowling RD, et al. Comparison of open versus thoracoscopic lung biopsy for diffuse infiltrative pulmonary disease. J Thorac Cardiovasc Surg. 1993; 106(2):194–199 [51] Fessler RG, Dietze DDJ, Jr, Millan MM, Peace D. Lateral parascapular extrapleural approach to the upper thoracic spine. J Neurosurg. 1991; 75 (3):349–355 [52] Hazelrigg SR, Landreneau RJ, Boley TM, et al. The effect of muscle-sparing versus standard posterolateral thoracotomy on pulmonary function, muscle strength, and postoperative pain. J Thorac Cardiovasc Surg. 1991; 101 (3):394–400, discussion 400–401 [53] Dickman CA, Rosenthal D, Regan JJ. Reoperation for herniated thoracic discs. J Neurosurg. 1999; 91(2) Suppl:157–162 [54] Dickman CA, Mican CA. Multilevel anterior thoracic discectomies and anterior interbody fusion using a microsurgical thoracoscopic approach. Case report. J Neurosurg. 1996; 84(1):104–109 [55] McAfee PC, Regan JR, Zdeblick T, et al. The incidence of complications in endoscopic anterior thoracolumbar spinal reconstructive surgery. A prospective multicenter study comprising the first 100 consecutive cases. Spine. 1995; 20 (14):1624–1632

[56] Roush TF, Crawford AH, Berlin RE, Wolf RK. Tension pneumothorax as a complication of video-assisted thorascopic surgery for anterior correction of idiopathic scoliosis in an adolescent female. Spine. 2001; 26(4):448–450 [57] Huang TJ, Hsu RW, Sum CW, Liu HP. Complications in thoracoscopic spinal surgery: a study of 90 consecutive patients. Surg Endosc. 1999; 13(4):346–350 [58] Perez-Cruet MJ, Fessler RG, Perin NI. Review: complications of minimally invasive spinal surgery. Neurosurgery. 2002; 51(5) Suppl:S26–S36 [59] Delfini R, Di Lorenzo N, Ciappetta P, Bristot R, Cantore G. Surgical treatment of thoracic disc herniation: a reappraisal of Larson’s lateral extracavitary approach. Surg Neurol. 1996; 45(6):517–522, discussion 522–523 [60] Graham AW, III, Mac Millan M, Fessler RG. Lateral extracavitary approach to the thoracic and thoracolumbar spine. Orthopedics. 1997; 20(7):605–610 [61] Maiman DJ, Larson SJ, Luck E, El-Ghatit A. Lateral extracavitary approach to the spine for thoracic disc herniation: report of 23 cases. Neurosurgery. 1984; 14(2):178–182 [62] Karikari IO, Nimjee SM, Hardin CA, et al. Extreme lateral interbody fusion approach for isolated thoracic and thoracolumbar spine diseases: initial clinical experience and early outcomes. J Spinal Disord Tech. 2011; 24(6):368–375 [63] Uribe JS, Smith WD, Pimenta L, et al. Minimally invasive lateral approach for symptomatic thoracic disc herniation: initial multicenter clinical experience. J Neurosurg Spine. 2012; 16(3):264–279 [64] Perez-Cruet MJ, Samartzis D, Fessler RG. Microendoscopic thoracic discectomy. In: Perez-Cruet MJ, ed. An Anatomic Approach to Minimally Invasive Spine Surgery. Boca Raton, FL: CRC Press; 2006:431–448

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Surgical Techniques

24 Anterior Thoracoscopic Sympathectomy Curtis A. Dickman and Hasan A. Zaidi Abstract Anterior thoracoscopic sympathectomy is used to treat patients with hyperhidrosis resulting from an idiopathic disorder of autonomic function. In elective cases, approaches that offer cosmesis are ideal in ablating the sympathetic plexus to relieve symptoms. The biportal endoscopic technique allows for improved visualization while minimizing approach-related morbidity. In this chapter, we describe our institutional experience in treating hyperhidrosis and suggest technical nuances. Keywords: endoscopic, minimally invasive, plexus, sympathectomy , thoracoscopic, thorax

24.1 Biportal Microsurgical Thoracoscopy 24.1.1 Definition of Problem In this chapter, we detail the technical aspects of a biportal microsurgical thoracoscopic technique for sympathectomy. The primary goal of sympathectomy is to remove or destroy the second sympathetic ganglion (T2). The sympathetic ganglia of T3 and T4 are also usually ablated.1 Hyperhidrosis, or excessive perspiration, results from an idiopathic disorder of autonomic function. Its cause is unknown and its reported incidence ranges from 0.15 to 1%.2,3,4,5,6 The palms of the hands are primarily affected (▶ Fig. 24.1), but the axillae and the plantar surfaces of the feet can also be involved. It rarely affects the scalp and face (craniofacial hyperhidrosis). Hyperhidrosis can also be generalized, affecting the entire body. The symptoms usually appear in childhood or early adulthood.

Hyperhidrosis significantly reduces quality of life.5,7,8 Patients with hyperhidrosis are affected socially, professionally, and psychologically in every activity of daily living. When palmar, axillary, or craniofacial hyperhidrosis is intractable to medical treatment, patients may consider surgical treatment by upper thoracic sympathectomy. Sympathectomy targets only the hands, axillae, and facial regions, and it is not used to treat hyperhidrosis of the whole body.

24.1.2 Evolution of Technique Prior to the 1990s, options for patients with hyperhidrosis included medical management, which was often ineffective in resolving symptoms, and open thoracotomy for sympathectomy, which was associated with significant morbidity. With the advent of the video-assisted thoracoscopy as a cardiothoracic subspecialty in the early 1990s, our group developed a minimally invasive approach to sympathectomy using modified thoracoscopic instruments.

24.1.3 Advantages and Disadvantages Open procedures are more invasive than thoracoscopic sympathectomy and thus are associated with increased morbidity. Minimally invasive thoracoscopic procedures permit direct visualization of the sympathetic ganglia and are associated with shorter operative times, shorter hospitalizations, and faster patient recovery.9,10,11,12,13 However, as with open thoracoscopy, minimally invasive procedures have inherent risks, such as pneumothorax, hemothorax, major vascular injury (e.g., to the aorta, inferior vena cava, and heart), cardiac arrhythmias, lung contusion, pneumonitis, transient atelectasis, compensatory hyperhidrosis, intercostal neuralgia, and Horner’s syndrome. Fig. 24.1 The hands of a patient with severe palmar hyperhidrosis. The palmar surfaces of the hands are saturated with sweat, which drips from the fingers and palms. This profound problem interferes with almost all activities of daily living. The sweat-soaked hands saturate everything and are apparent to anyone they touch. The problem permeates all aspects of the lives of patients: social, interpersonal, romantic, recreational, and vocational.

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Anterior Thoracoscopic Sympathectomy Table 24.1 Surgical indications and success rates for thoracoscopic sympathectomy Clinical disorder

Success rate, %

Essential hyperhidrosis ●

Palmar

95–100

●

Axillary

75–85

●

Craniofacial

90–95

Excessive craniofacial blushing

85–95

Hand ischemia due to Raynaud’s disease

50–60 (temporary)

Upper extremity reflex sympathetic dystrophy

30–70

a permanent cure via endoscopic sympathectomy is likely to be appealing to many patients.

24.2.2 Patient Profiles Patients who have undergone a previous thoracotomy and who have evidence of severe pleural adhesions may not be good candidates for this procedure, as the lung would not be able to be deflated to allow for adequate visualization. Patients with poor cardiac function and severe cardiovascular disease are also poor candidates for this elective procedure.

24.3 Preoperative Planning 24.3.1 Physical Examination

24.2 Indications and Contraindications Thoracoscopic sympathectomy is useful for the treatment of various problems (▶ Table 24.1). It is extraordinarily successful (in 75–100% of cases) for focal essential hyperhidrosis (i.e., palmar, axillary, or craniofacial) and excessive craniofacial blushing. Sympathectomy can also be used to treat reflex sympathetic dystrophy and hand ischemia caused by Raynaud’s disease. However, it is associated with lower success rates in patients being treated for pain and limb ischemia. Patients with upper-extremity reflex sympathetic dystrophy whose pain improves significantly with a stellate ganglion block have a 30 to 70% likelihood of further improvement in pain after a sympathectomy. Sympathectomy results in arterial vasodilation and thus can be a temporizing measure in patients with vascular ischemia due to Raynaud’s disease. However, because Raynaud’s disease is progressive, sympathectomy is not curative; it only delays progression to the need for amputation. Other than medical contraindications to surgery, absolute contraindications include known evidence of pleural adhesions and medically limiting cardiopulmonary disease, such as that evident on poor pulmonary function tests that would prevent intraoperative deflation of a lung.

24.2.1 Patient Selection Patients who have intractable and severe palmar, axillary, or craniofacial hyperhidrosis are the best candidates for sympathectomy. Thyroid function studies and general blood chemistries should be obtained to rule out endocrinological or metabolic abnormalities responsible for the hyperhidrosis. Patients must be able to tolerate single-lung ventilation during the procedure, and patients with severe pulmonary disease, extensive pleural adhesions, or tracheal stenosis should be excluded from consideration. Alternative nonsurgical treatments should be discussed with patients. These options include botulinum toxin type A injections in the hands, anticholinergic medications (e.g., Ditropan [oxybutynin chloride] and Robinul [glycopyrrolate]), topical antiperspirants (e.g., Drysol [topical aluminum chloride] and Certain Dri [aluminum chloride hexahydrate]), and iontophoresis (Drionic; General Medical Co., Pasadena, CA). These nonsurgical measures are temporizing, usually only partially effective, and often have adverse side effects. Therefore, the possibility of

Hyperhidrosis can be disabling to patients, disrupting their work and their social, personal, and recreational activities. Physical findings of patients with severe symptoms include sweat dripping spontaneously from the affected region. Hyperhidrosis results in considerable occupational, social, and psychological impairment. Numerous patients report that they do not leave home because of the embarrassing and disabling nature of the disease. Although palmar hyperhidrosis is the most common presentation, some patients present with primary axillary hyperhidrosis. In addition to primary axillary hyperhidrosis as their primary complaint, many patients also report less severe hyperhidrosis in the plantar or craniofacial regions.

24.3.2 Radiographic Work-up and Preoperative Imaging Anteroposterior chest radiographs should be obtained prior to surgical intervention. These are useful in evaluating the patient for any cardiopulmonary anomalies, such as atelectasis, pulmonary effusion, and pneumothorax.

24.4 Instrumentation A double-lumen endotracheal tube is required to secure the airway and allow the anesthesiologist to deflate the ipsilateral lung during surgical manipulation. Visualization is performed using a 5-mm thoracoscope (Karl Storz Endoscopy-America, Inc., El Segundo, CA). The sympathectomy is performed using endoscopic monopolar cautery scissors (or an ultrasonic scalpel [Harmonic Scalpel, Ethicon Endo-Surgery, Cincinnati, OH]).

24.5 Surgical Approach and Technique 24.5.1 Patient Positioning The patient is placed on the operating room table in the supine position. General anesthesia is administered, and the patient is intubated with a double-lumen endotracheal tube. Correct positioning of the endotracheal tube is confirmed with a bronchoscope by the anesthesiologist. Palmar cutaneous temperature monitors (Mallinckrodt, Juarez, Mexico) are applied bilaterally. An intraoperative increase of 1 °C or more indicates an adequate sympathectomy.

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Surgical Techniques The sympathectomy procedures are performed bilaterally in one operation. The patient is placed in a lateral decubitus position, and a unilateral sympathectomy is performed. An axillary roll is placed under the axilla. The dependent arm is supported on an arm board, and the nondependent arm is placed in an airplane splint in an abducted position to expose the axilla and thorax. The patient’s right arm and thorax are prepared and draped using routine techniques (▶ Fig. 24.2a). Patients are taped securely to the operating table with wide cloth tape to permit intraoperative rotation. The ipsilateral lung is deflated by the anesthesiologist using a double-lumen endotracheal tube. Rapid dense atelectasis is achieved when air is suctioned from the lumen of the endotracheal tube on the side without insufflation.

24.5.2 Incision Two 5-mm incisions are made after the skin is injected with 0.5% bupivacaine hydrochloride with epinephrine (▶ Fig. 24.2b). The endoscope is inserted in the fifth intercostal space in the posterior axillary line. The working portal (for tools, cautery scissors, and chest tube) is placed in the middle or anterior axillary line in the third intercostal space. An entry puncture over the superior surface of the underlying rib is made in the thoracic cavity with a hemostat. Through the first incision, a 6-mm-diameter trocar and stylet are inserted for the 5-mm thoracoscope (Karl Storz Endoscopy-America, Inc.), which is inserted into the chest cavity. Under direct endoscopic visualization, the lung and contents of the mediastinum are inspected. Through the

Fig. 24.2 Patient positioning for a right-sided sympathectomy. (a) A lateral decubitus position is used. The dependent axilla is padded with an axillary roll. The other arm is abducted and placed in an airplane splint. Abduction of the arm provides unobstructed access to the chest wall for the surgery. (b) Two small (5-mm) incisions are used for the endoscopic sympathectomy. They are placed in the middle and posterior axillary lines over the third and fifth intercostal spaces.

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Anterior Thoracoscopic Sympathectomy second portal site, a hemostat is placed through the inner pleura under direct visualization. The second 5-mm portal is placed into the chest under endoscopic visualization. The endoscopic monopolar cautery scissors (or an ultrasonic scalpel [Harmonic Scalpel, Ethicon Endo-Surgery]) are inserted through the second portal. The patient is rotated ventrally to allow gravity to retract the lung away from the surface of the spine.

24.5.3 Step-by-Step Surgical Technique Under direct thoracoscopic visualization, the sympathetic chain is identified and ablated (▶ Fig. 24.3a, b and ▶ Fig. 24.4a–c). The first rib and stellate ganglia are usually obscured by an apical fat pad, but the first rib can be palpated. The brachiocephalic or subclavian vessels can be visualized adjacent to the first rib. The second rib is identified at its articulation with the spine. The

Fig. 24.3 Intraoperative thoracoscopic photographs of the regional anatomy of the right upper thoracic cavity and mediastinum. (a) The second through fourth rib heads are visible with the sympathetic chain coursing over the rib heads. The second rib head is the first visible rib on the right. The upper intercostal and segmental veins (highest intercostal vein) form a tributary that drains directly into the azygos vein and the arch of the azygos vein. Medially, the phrenic nerve is visible over the brachiocephalic artery and vein. The esophagus, trachea, and vagus nerve are visible anterior to the surface of the spine (left=caudal, right=rostral, up=lateral, down=medial). (b) Intraoperative view of the upper sympathetic chain. The brachiocephalic vein and artery are visible as they course beneath the first rib on the lower right. The sympathetic chain is clearly seen over the second, third, and fourth rib heads. More rostrally, the sympathetic chain enlarges to become the stellate ganglion, which is obscured by a fat pad. The stellate ganglion is avoided to prevent postoperative Horner’s syndrome.

Fig. 24.4 Intraoperative photographs obtained during a right-sided thoracoscopic sympathectomy. (a) The sympathetic chain is visible over the second and third rib heads. The stellate ganglion is beneath the apical fat pad on the right. (b) The sympathetic chain was transected with cautery scissors over the second and third rib heads. A 10- to 15-mm gap was created in the sympathetic chain at each level. (c) The stump of the sympathetic chain is inspected to ensure that complete transection was achieved. The site is also inspected to assess for accessory sympathetic bundles (nerves of Kuntz). (d) An apical chest tube is inserted to suction the air as the lung is reventilated. The chest tube is removed at the completion of surgery.

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Surgical Techniques extent of sympathectomy is dictated by the symptoms of the patient. For palmar or craniofacial hyperhidrosis, the sympathetic chain is transected over the second and third rib heads to isolate the second sympathetic ganglia. For axillary hyperhidrosis, the sympathetic chain is transected over the second, third, and fourth rib heads to isolate the second, third, and fourth ganglia. The sympathetic chain ganglia are tented laterally and transected with cauterization to create a gap of 10 mm or more between the ends of the sympathetic chain. Care is taken to preserve the surrounding vascular structures.

After the sympathetic chain is transected, the surrounding soft tissue is inspected to confirm complete transection and to search for accessory sympathetic nerves (i.e., nerves of Kuntz). The monopolar scissors (or the Harmonic scalpel [Ethicon Endo-Surgery]) are removed, and a 20-French chest tube is inserted into the chest cavity through the working portal incision under endoscopic visualization (▶ Fig. 24.4d). Under direct thoracoscopic visualization, the lung is then reinflated by the anesthesiologist by ventilating through the double-lumen endotracheal tube. Reinflation of the lung is observed directly before removal of the thoracoscope.

24.5.4 Closure

Fig. 24.5 Intraoperative photograph during a left-sided thoracoscopy shows the regional anatomy. The aortic arch, subclavian artery, and descending aorta are prominent. A large venous tributary (highest intercostal vein) crosses over the arch of the aorta. In this patient, the sympathetic chain is positioned over the second rib head and courses slightly anteromedially to the third, fourth, and fifth rib heads. The position of the sympathetic chain can vary somewhat but is usually directly over the rib heads.

The two incision sites are closed with deep subcuticular sutures using 3–0 polyglactin 310 (Vicryl; Ethicon, Inc., Johnson & Johnson, Somerville, NJ) and then dressed with benzoin and SteriStrips (3 M Health Care, St. Paul, MN). The chest tube is secured with a 2–0 nylon purse-string suture. The chest tube is kept in the first side until completion of the second sympathectomy. The patient is then repositioned and the sympathectomy on the contralateral side is conducted using the same surgical technique (▶ Fig. 24.5 and ▶ Fig. 24.6). At the conclusion of the second sympathectomy, both chest tubes are removed in the operating room before the patient is extubated. While the chest tubes are removed, the anesthesiologist performs the Valsalva maneuver, and the surgeon applies direct pressure to the wound. The chest tube sites are closed with absorbable subcuticular sutures, and Steri-Strips (3 M Health Care) or bandages are applied to the incisions, which usually produces a good cosmetic result (▶ Fig. 24.7). The anesthesiologist records palmar temperature to confirm that an adequate sympathectomy has been achieved on each side. A sitting plain anteroposterior chest radiograph is obtained to confirm that there are no significant residual pneumothoraces before general anesthesia is discontinued and the patient is extubated.

Fig. 24.6 Intraoperative photographs obtained during a left-sided sympathectomy. (a) Cautery scissors are used to tent the sympathetic chain at the level of T2 laterally away from the subclavian artery. (b) In this patient, the sympathetic chain has been transected completely over the second and third rib heads to treat palmar hyperhidrosis. (c) The stump of the sympathetic chain is inspected to ensure that complete transection was achieved. (d) An apical chest tube is inserted to suction the air as the lung is reventilated.

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Anterior Thoracoscopic Sympathectomy the endotracheal tube and awakening the patient. If significant residual air is present, it can be evacuated with a 16-gauge angiocatheter and suction tube or with a chest tube, if necessary. A small residual apical air cap is typically present after surgery but does not require treatment. Compensatory hyperhidrosis is not a complication of surgery. Rather, it is an expected side effect of the procedure. The sympathectomy denervates the face, head, and arms. The nondenervated regions of the body (i.e., trunk, back, and legs) still sweat to dissipate body heat. To dissipate heat effectively, these nonexposed regions tend to increase sweating to cool the body effectively. Although most patients (80–90%) have tolerable symptoms, a few (10–20%) are substantially bothered by compensatory hyperhidrosis.

Fig. 24.7 Sympathectomy incisions 3 months after surgery. An excellent cosmetic result was achieved, and the patient’s palmar hyperhidrosis was relieved completely.

24.6 Postoperative Care Sympathectomy is performed as an outpatient procedure. Unless problems arise, patients are discharged home after a few hours. Patients return to normal activity within a few days of surgery. Postoperatively, all patients are prescribed an incentive spirometer and narcotic analgesic medication for 48 to 72 hours.

24.7 Management of Complications The most important method for avoiding complications with thoracoscopic sympathectomy is to ensure that the surgeon has developed adequate endoscopic skills through training and experience to be adept at thoracoscopic surgery. The surgeon should be prepared to convert immediately to a thoracotomy, if necessary, to treat vascular complications. The surgeon should also be well versed in techniques for endoscopic hemostasis and dissection. In addition, the surgeon should be able to detach focal pleural adhesions that occasionally tether the lung to the pleura. Adhesions must be detached carefully to avoid violating the lung parenchyma or causing excessive bleeding. An effective sympathectomy is achieved by measuring palmar temperature and by completely transecting the T2 and T3 sympathetic chain and the nerves of Kuntz. Horner’s syndrome is avoided by not manipulating the stellate ganglion and by not using cauterization near the stellate ganglion. Horner’s syndrome can be avoided by transecting the sympathetic chain in situ rather than by dissecting the chain completely. Atelectasis and pneumonia are avoided with vigorous postoperative incentive spirometry. If necessary, bronchodilator medication can also be prescribed. Pneumothorax is avoided by ensuring that there is no air leak from the lung (i.e., no violation of lung parenchyma) and that the chest tubes have satisfactorily evacuated the residual air from the thorax at the end of the procedure. At the end of the surgery, a postoperative chest radiograph should be obtained with the patient in a sitting position after the chest tubes have been removed prior to removing

24.8 Clinical Cases Between 1996 and 2008, the senior author (C. A. D.) performed bilateral thoracoscopic sympathectomies for hyperhidrosis in 322 patients. The long-term follow-up results for these patients have been published previously and are discussed in the following paragraphs.14,15 Of the 322 patients who underwent bilateral thoracoscopic sympathectomy, 104 were male and 218 were female (mean age, 27.6 years [range, 10–60 years]). The mean length of follow-up was 8 months. More than one-third (38.8% [n=125]) had a family history of hyperhidrosis. Most (66.1% [n=213]) reported lifelong hyperhidrosis. Eighty-four (26.1%) experienced the onset of symptoms during puberty, and 12 (3.7%) experienced onset during childhood. All 322 patients reported that their hyperhidrosis impaired dating, marriage, interpersonal relationships, recreational and other social activities, and school or work. Most patients reported psychological distress related to their hyperhidrosis; seven patients had severe depression or anxiety that they attributed to their condition. In addition to using standard deodorants or antiperspirants, most (95.3% [n=307]) of the 322 patients had attempted one or more unsuccessful nonsurgical treatments for hyperhidrosis before surgery. The most common nonsurgical treatments were Drysol, Drionics, prescribed medications (e.g., propranolol, clonidine, or an anticholinergic), biofeedback or homeopathic treatments, Robinul, and botulinum toxin type A. No patient had undergone a previous operation for hyperhidrosis. All 322 patients identified a primary area of hyperhidrosis, and most (82.6% [n=266]) presented with hyperhidrosis in more than one region. Fifty-six patients had hyperhidrosis isolated to a single region, either axillary or palmar. The hyperhidrosis was palmar in 301 patients, axillary in 186, plantar in 197, and craniofacial in 30 (▶ Table 24.2).15 A total of 104 of the 322 patients (32.3%) had hyperhidrosis in three locations (palmar, axillary, and plantar). Eighty-four patients (26.1%) had both palmar and plantar hyperhidrosis, 47 (14.6%) had both palmar and axillary hyperhidrosis, and 12 (3.7%) had both palmar and axillary hyperhidrosis. All other patients had a combination of palmar, axillary, plantar, and craniofacial hyperhidrosis. Intraoperatively, the estimated blood loss was minimal (< 50 mL) in all 322 patients. No patient required a blood transfusion or conversion to open thoracotomy.

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245

Surgical Techniques The surgical results of thoracoscopic sympathectomy for hyperhidrosis were evaluated by region (▶ Table 24.2). Most (99.7% [n=300]) of the 301 patients with palmar hyperhidrosis reported complete alleviation of symptoms, and 1 patient (0.3%) reported symptomatic improvement. Of the 186 patients who presented with axillary hyperhidrosis, most (95.7% [n=178]) experienced symptom relief after surgery. The axillary hyperhidrosis completely resolved in 136 of these patients (73.1%). Forty-two (22.6%) patients reported significant improvement but had some residual axillary sweating, and 1 patient (0.5%) had complete resolution unilaterally but sweating was not relieved on the contralateral side. Plantar hyperhidrosis was not anatomically targeted during the surgeries. Nonetheless, of the 197 patients who presented with plantar hyperhidrosis, 19 patients (9.6%) reported complete resolution and 124 (62.9%) reported improvement. For the 30 patients who presented with craniofacial hyperhidrosis, symptoms resolved completely in 27 (90%) and somewhat in 3 (10%). A total of 301 patients were followed for a mean of 33 weeks (range, 1–242 weeks); 21 patients were lost to follow-up. Axillary hyperhidrosis recurred bilaterally 6 months after sympathectomy in one patient with unilateral failure due to unknown factors. Postoperatively, no patient experienced excessive dryness or cracking of the skin of the hands despite the elimination of sympathetic-mediated hand sweating. Patients with palmar hyperhidrosis that was alleviated also experienced resolution of the accompanying erythema, edema, and diminished hand temperature. Postoperatively, patients often experienced persistent episodes of tingling in their hands, but without subsequent hand

sweating. The same sensation had occurred before surgery as a premonitory sign of an episode of severe hand sweating. None of the 322 patients sustained a vascular injury or excessive bleeding or required a blood transfusion or emergency conversion to thoracotomy. No patient had injuries to the lungs, heart, or mediastinal structures. Transient intraoperative cardiac asystole developed in one patient (0.3%) but resolved with medication without any long-term sequelae. No patient had deep vein thrombosis or life-threatening complications of surgery, and no patient died. The mean hospital stay was 0.5 days (range, 0–5 days). Most patients had the procedure performed as an outpatient; overnight admission was required in 8 of the last 150 patients (5.3%). Hospital stays longer than 1 day were caused by pleural adhesions that were detached surgically, requiring a chest tube in two cases; by mild postoperative pulmonary edema in one case; by residual pneumothorax requiring a chest tube in two cases; and by moderate pain in two cases. The most common side effect was a generalized increase in body perspiration (compensatory hyperhidrosis), which occurred in 201 of the 322 patients (62.4%)15(▶ Table 24.3). The rest of the patients (n=121 [37.6%]) noticed no alteration in sweating. More than one-half (n=181 [56.2%]) developed moderate compensatory hyperhidrosis. Three patients noted the spontaneous occurrence during rest. Twenty patients (6.2%) experienced symptoms of severe compensatory hyperhidrosis with exercise or heat, and they reported that the symptoms were bothersome but not disabling. The compensatory hyperhidrosis occurred in all regions of the body (typically the trunk and legs, sparing the arms, head, and face), except in the areas denervated by the sympathectomy; no area predominated.

Table 24.2 Surgical results of thoracoscopic sympathectomy for hyperhidrosis by region Hyperhidrosis

No. of patientsa

No. (%) of patients Complete resolution

Improved

Unchanged

Worse

Palmar

301

300 (99.7)

1 (0.3)

0

0

Axillary

186

136 (73.1)

42 (22.6)

7 (3.8)

1 (0.5)

Craniofacial

30

27 (90.0)

3 (10.0)

0

0

197

19 (9.6)

124 (62.9)

51 (25.9)

3 (1.5)

Plantarb

al.15

Source: From Wait et aThe sum of this column is more than 322 patients because most patients had multiple areas of hyperhidrosis. bBy itself, plantar hyperhidrosis is not an indication for surgery; it was always associated with palmar, axillary, or craniofacial hyperhidrosis.

Table 24.3 Self-reports of the severity of compensatory sweating according to the most caudal level of sympathectomy Most caudal sympathectomy level

No. of patients

T3

Compensatory sweating None, no. (%)

Moderate, no. (%)

Severe, no. (%)

155

58 (37.4)

89 (57.4)

8 (5.2)

T4

96

39 (40.6)

55 (57.3)

2 (2.1)

T5

71

24 (33.8)

37 (52.1)

10 (14.1)a

Total

322

121 (37.6)

181 (56.2)

20 (6.2)

Source: From Wait et al.15 (χ2 test for independence) indicating a T5 sympathectomy is significantly associated with the occurrence of severe compensatory sweating.

ap = 0.008

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Anterior Thoracoscopic Sympathectomy Overall, the 322 patients had few complications and none were life-threatening15 (▶ Table 24.4). Nine patients each had transient intercostal neuralgia, which resolved completely within 6 weeks of surgery, and residual air in the chest cavity (30–40% pneumothorax) that required insertion of a chest tube. Seven patients developed unilateral Horner’s syndrome after surgery. No patient had tension pneumothorax. Transient atelectasis occurred in three patients, and one patient each had chemical pneumonitis from aspiration, pulmonary edema, and transient intraoperative asystole. Table 24.4 Number and type of postoperative complications in 642 patients after sympathectomy Complications

No. (%)

Transient intercostal neuralgia

9 (1.4)

Pneumothorax requiring postoperative chest tube

9 (1.4)

Horner’s syndrome

7 (1.1)

Transient atelectasis

3 (0.5)

Chemical pneumonitis from aspiration

1 (0.2)

Pulmonary edema

1 (0.2)

Transient intraoperative cardiac asystolea

1 (0.2)

Source: From Wait et al.15 with medication; no long-term sequelae.

aResolved

24.9 Conclusion Compared to the often ineffective nonsurgical treatment of hyperhidrosis, surgical treatment offers many advantages to patients. Thoracoscopic sympathectomy procedures are associated with a success rate of 95 to 100% for relieving palmar hyperhidrosis.1,3,16,17,18,19,20 The results are usually permanent, and plantar, axillary, and craniofacial hyperhidrosis may also be relieved. An alternative to thoracoscopic sympathectomy is open sympathectomy, which includes the extrapleural or subpleural posterior approach, the transaxillary approach, the supraclavicular approach, and the anterior thoracotomy approach. However, thoracoscopic approaches are more efficient and less traumatic. They provide direct surgical access to the upper sympathetic chain to allow visualization and ablation of the upper sympathetic ganglia, and they result in shorter hospital stays and decreased morbidity. Our clinical technique uses two portals to transect the sympathetic ganglia with monopolar cautery scissors or an ultrasonic scalpel. Although the use of one incision and one portal produces the optimal cosmetic result, the use of two or three incisions and portals provides additional room for safer manipulation of the instruments in case of pulmonary adhesions or hemorrhage.1,9 Three portals are required to completely remove the sympathetic chain for histological confirmation. However, this step is unnecessary because an intraoperative increase in palmar temperature of 1 °C confirms that the sympathetic ganglia have been destroyed. It is also the best indicator of longterm success.7,9 Other series have demonstrated no added clini-

cal benefit to removing the ganglia compared to transecting the sympathetic chain in situ.21,22 The biportal approach provides appropriate visualization of the relevant anatomy to avoid damaging the stellate ganglia and causing Horner’s syndrome. It also minimizes the risk of intercostal neuralgia caused by injury to the intercostal nerves when ports are placed or by direct injury to the nerve during the procedure. In addition, the risk of neuralgia is avoided by using flexible portals rather than rigid portals within the intercostal spaces. Postoperative pneumothorax is avoided by not violating the lung parenchyma and by inspecting the lung for air leaks with the thoracoscope during lung reinflation. Overall, only a few procedures were associated with postoperative complications, and most complications were minor and transient. Biportal thoracoscopic sympathectomy is a safe, highly effective procedure to eliminate palmar, axillary, and craniofacial hyperhidrosis. It is usually conducted as an outpatient procedure and is associated with minimal blood loss and low morbidity. Compared to open thoracic sympathectomy, this minimally invasive surgery has unequivocal and substantial advantages.

Clinical Caveats Avoid Horner’s syndrome: ● Do not manipulate the stellate ganglion or use cauterization near the stellate ganglion. ● Transect the sympathetic chain in situ rather than dissecting it completely. Avoid atelectasis and pneumonia: Conduct vigorous postoperative incentive spirometry.

●

Avoid pneumothorax: Ensure that there is no air leak from the lung (no violation of lung parenchyma) and that the chest tubes have satisfactorily evacuated the residual air from the thorax at the end of the procedure. ● Obtain a postoperative chest radiograph with the patient in a sitting position after the chest tubes have been removed before removing the endotracheal tube and awakening the patient. ●

Be aware of compensatory hyperhidrosis: Expect compensatory hyperhidrosis as a side effect of sympathectomy but not as a complication of the procedure.

●

24.9.1 Note This entire chapter has been adapted from Han et al14 and Wait et al.15

References [1] Wong CW. Transthoracic video endoscopic electrocautery of sympathetic ganglia for hyperhidrosis palmaris: special reference to localization of the first and second ribs. Surg Neurol. 1997; 47(3):224–229, discussion 229–230 [2] Wilkinson HA. Percutaneous radiofrequency upper thoracic sympathectomy: a new technique. Neurosurgery. 1984; 15(6):811–814 [3] Noppen M, Herregodts P, D’Haese J, D’Haens J, Vincken W. A simplified T2T3 thoracoscopic sympathicolysis technique for the treatment of essential

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Surgical Techniques

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[7]

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hyperhidrosis: short-term results in 100 patients. J Laparoendosc Surg. 1996; 6(3):151–159 Chuang KS, Liou NH, Liu JC. New stereotactic technique for percutaneous thermocoagulation upper thoracic ganglionectomy in cases of palmar hyperhidrosis. Neurosurgery. 1988; 22(3):600–604 Adar R, Kurchin A, Zweig A, Mozes M. Palmar hyperhidrosis and its surgical treatment: a report of 100 cases. Ann Surg. 1977; 186(1):34–41 Mockus MB, Rutherford RB, Rosales C, Pearce WH. Sympathectomy for causalgia: patient selection and long-term results. Arch Surg. 1987; 122 (6):668–672 Kao MC, Tsai JC, Lai DM, Hsiao YY, Lee YS, Chiu MJ. Autonomic activities in hyperhidrosis patients before, during, and after endoscopic laser sympathectomy. Neurosurgery. 1994; 34(2):262–268, discussion 268 Shih CJ, Wang YC. Thoracic sympathectomy for palmar hyperhidrosis: report of 457 cases. Surg Neurol. 1978; 10(5):291–296 Vanaclocha V, Sáiz-Sapena N, Panta F. Uniportal endoscopic superior thoracic sympathectomy. Neurosurgery. 2000; 46(4):924–928 Weale FE. Upper thoracic sympathectomy by transthoracic electrocoagulation. Br J Surg. 1980; 67(1):71–72 Kao MC. Video endoscopic sympathectomy using a fiberoptic CO2 laser to treat palmar hyperhidrosis. Neurosurgery. 1992; 30(1):131–135 Edmondson RA, Banerjee AK, Rennie JA. Endoscopic transthoracic sympathectomy in the treatment of hyperhidrosis. Ann Surg. 1992; 215(3):289–293 Kux M. Thoracic endoscopic sympathectomy in palmar and axillary hyperhidrosis. Arch Surg. 1978; 113(3):264–266

[14] Han PP, Gottfried ON, Kenny KJ, Dickman CA. Biportal thoracoscopic sympathectomy: surgical techniques and clinical results for the treatment of hyperhidrosis. Neurosurgery. 2002; 50(2):306–311, discussion 311–312 [15] Wait SD, Killory BD, Lekovic GP, Ponce FA, Kenny KJ, Dickman CA. Thoracoscopic sympathectomy for hyperhidrosis: analysis of 642 procedures with special attention to Horner’s syndrome and compensatory hyperhidrosis. Neurosurgery. 2010; 67(3):652–656, discussion 656–657 [16] Byrne J, Walsh TN, Hederman WP. Endoscopic transthoracic electrocautery of the sympathetic chain for palmar and axillary hyperhidrosis. Br J Surg. 1990; 77(9):1046–1049 [17] Drott C, Göthberg G, Claes G. Endoscopic transthoracic sympathectomy: an efficient and safe method for the treatment of hyperhidrosis. J Am Acad Dermatol. 1995; 33(1):78–81 [18] Herbst F, Plas EG, Függer R, Fritsch A. Endoscopic thoracic sympathectomy for primary hyperhidrosis of the upper limbs: a critical analysis and long-term results of 480 operations. Ann Surg. 1994; 220(1):86–90 [19] Shachor D, Jedeikin R, Olsfanger D, Bendahan J, Sivak G, Freund U. Endoscopic transthoracic sympathectomy in the treatment of primary hyperhidrosis: a review of 290 sympathectomies. Arch Surg. 1994; 129(3):241–244 [20] Johnson JP, Obasi C, Hahn MS, Glatleider P. Endoscopic thoracic sympathectomy. J Neurosurg. 1999; 91(1) Suppl:90–97 [21] Plas EG, Függer R, Herbst F, Fritsch A. Complications of endoscopic thoracic sympathectomy. Surgery. 1995; 118(3):493–495 [22] Pillay PK, Thomas J, Mack P. Thoracoscopic ganglionectomy for hyperhidrosis. Stereotact Funct Neurosurg. 1994; 63(1–4):198–202

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Thoracoscopic Discectomy and Thoracoscopy-Assisted Tubular Retractor Discectomy

25 Thoracoscopic Discectomy and Thoracoscopy-Assisted Tubular Retractor Discectomy Hyun-Chul Shin, Jonathan B. Lesser, Robert E. Isaacs, and Noel I. Perin Abstract In patients with symptomatic, large, centrally located and calcified thoracic disc herniations with significant spinal cord compression, thoracoscopic surgery (video-assisted thoracoscopic surgery) is a viable minimally invasive alternative to open thoracotomy. Both thoracoscopic discectomy and tubular retractor– guided discectomy, while achieving the same results as an open thoracotomy, reduces postoperative pain and shoulder girdle dysfunction and provides better cosmetic results, shorter hospital stay, and earlier return to normal activity. Keywords: thoracoscopy, video-assisted thoracoscopic surgery, mean arterial blood pressure

25.1 Introduction Thoracic disc herniation is an uncommon but clinically important cause of incapacitating axial and/or radicular pain with or without neurologic deficits. The incidence of clinically significant thoracic disc herniation has been estimated to be approximately 1 patient per 1 million people (0.25–0.75% of all disc ruptures). The incidence of asymptomatic disc herniations in thoracic spines imaged with magnetic resonance imaging (MRI) is between 11.1 and 14.5% of the general population. Thoracoscopic discectomy can be performed on disc herniations from T2–T3 through T12–L1. A number of surgical approaches have been proposed for the treatment of symptomatic thoracic disc herniation. Posterior approaches include transpedicular and pedicle-sparing approaches. These approaches are most suitable for lateral and foraminal disc herniations. The costotransversectomy and lateral extracavitary approaches allow for posterolateral access to the more central and paracentral disc herniations, although anterior access is somewhat limited. Transthoracic and thoracoscopic approaches are most suitable for large central and calcified disc herniations with spinal cord compression and afford better unrestricted access to the anterior thecal sac than do posterior and posterolateral approaches. The transthoracic approach to thoracic disc herniation was first reported by several investigators in 1969.1 The transthoracic approach allows better visualization of the disc–dural interface, reducing the extent of spinal cord manipulation and its resultant complications. The major advantage of this approach is the improved visualization of the thecal sac and the relationship between the disc herniation and the dura. This is particularly helpful in the management of calcified midline disc herniations, especially when there is significant spinal cord compression and adherence to the dura. It is, however, an approach to the thoracic spine that is associated with significant postoperative morbidity and pain. The morbidity is related to extensive rib retraction and rib resection, and division of chest wall muscles, shoulder girdle muscles, and the diaphragm.

The thoracoscopic approach to thoracic disc herniation derives the same benefits as the transthoracic approach, with a reduction in postoperative pain and morbidity related to muscle dissection. The first reported application of the video-assisted thoracoscopic approach to thoracic disc herniation was in 1994.2 The advantages of the thoracoscopic approach include a substantial reduction in tissue trauma and thus a reduction in the postoperative pain and shoulder girdle dysfunction associated with an open thoracotomy. In addition, thoracic disc herniations in the lower thoracic spine (T8–L1) can be performed thoracoscopically without the need to take down the diaphragm, thus significantly reducing the morbidity. After thoracoscopic discectomy, the intensive care unit (ICU) stay and the hospital stay are shorter because patients can be mobilized much faster. Thoracoscopic surgery has a steep learning curve because of the lack of tactile feedback. Surgeons also need to familiarize themselves with working with long instruments through small openings in a two-dimensional videoscopic environment, and perfect the hand–eye coordination required as well. Although three-dimensional scope technology is available, it is expensive and cumbersome and may not afford a significant advantage. Operative times will be reduced with experience and become comparable to those associated with the open thoracotomy. To help reduce the learning curve associated with thoracoscopic approaches, the minimally invasive tubular retractor– guided transthoracic approaches are being utilized. This approach reduces the morbidity of the thoracotomy approach and overcomes the steep learning curve of thoracoscopy. We have combined thoracoscopy with the tubular retractor system and use of the operating microscope for excellent three-dimensional visualization.

25.2 Preoperative Assessment MRI scans are the mainstay in the preoperative work-up of patients with thoracic disc herniation. In the presence of a good MRI showing a thoracic disc herniation with neural compression, a myelogram is unnecessary. We usually obtain a computed tomography (CT) scan to assess the extent of calcification of the thoracic disc herniation. All patients undergo chest radiography with sufficient penetration to count ribs, and they undergo anteroposterior and lateral lumbar radiography as well. Particular note should be taken of the number of ribs on the chest radiographs, especially the presence of a cervical rib and if only 11 ribs are present. These radiographs and the location of the thoracic disc herniation on MRI must be closely correlated with the intraoperative localizing radiographs to avoid operating at the wrong level. Additionally, patients undergoing an anterior transthoracic approach can be admitted on the day before surgery so that a radiologist can place a metallic marker into the head of the rib at the appropriate level. All patients must have a preoperative medical evaluation with particular attention paid to pulmonary function; patients

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Surgical Techniques with severe emphysema and impaired lung function may not tolerate single-lung ventilation; patients with a prior history of empyema and/or pleurodesis are also not candidates for thoracoscopic discectomy.

25.3 Preoperative and Intraoperative Anesthetic Considerations After induction of general anesthesia, a double-lumen endobronchial tube is placed, and the correct position is verified with a fiberoptic bronchoscope. A 20-gauge radial artery catheter is usually inserted on the dependent side. Because motor and somatosensory evoked potentials are continuously evaluated during the surgical procedure, nondepolarizing muscle relaxants are allowed to completely wear off, and a total intravenous anesthetic, consisting of remifentanil and propofol, plus an air-oxygen mixture is administered to maintain anesthesia. Muscle relaxants are not used for the remainder of the surgical procedure. A phenylephrine infusion is used as needed to maintain adequate mean arterial pressure (above 80 mm Hg)

25.4 Surgical Technique 25.4.1 Patient Positioning The patient is positioned in the lateral decubitus position as for an open thoracotomy. The side selected for the approach depends largely on the side of the disc protrusion. However, if the disc is more or less in the midline, in the upper (T2–T5) or midthoracic (T5–T8) spinal area, a right-sided approach is selected. In the lower thoracic spine (T9–L1), a left-sided approach is preferable because the diaphragm may be up to the fifth intercostal space and retraction of the diaphragm with the underlying liver may be somewhat more difficult. An axillary roll is placed under the dependent chest to keep the axilla free. The lateral popliteal nerve area on the dependent leg is padded, a pillow is placed between the legs, and a rolled-up blanket is placed against the anterior abdominal wall. The patient’s hips are taped firmly to the table; tape is applied loosely around the knees and ankles to keep the legs from falling over when the table is rotated during surgery. The down arm is flexed at the elbow, padded, and positioned in front of the patient’s face on the operating table. This avoids an arm board, which might interfere with the surgeon’s ability to move freely, and allows adequate radiographs to be obtained. This is especially true when dealing with middle and upper thoracic herniations. The upper arm is supported on an elevated arm board with the arm abducted slightly more than 90 degrees and flexed over the patient’s head. The table is placed in steep reverse Trendelenburg position to allow the lung to fall away from the spine and the diaphragm and abdominal contents to fall caudally. In addition, the table is rotated toward the abdominal side of the patient allowing the lung to fall away from the spine.

25.4.2 Thoracoscopic Port Placement It is important to plan the location of the ports so that the retractor and the endoscope do not interfere with the instruments

250

being placed at the working ports. The anterior, middle, and posterior axillary lines are drawn on the patient. We obtain an anteroposterior plain radiograph of the thoracic spine with metallic markers on a strip of paper tape placed over the patient’s thoracic spine posteriorly in the midline. This allows the surgeon to roughly mark the level of the disc herniation and plan initial port placement. Contrary to most reports, the working port is not placed in the anterior axillary line. Instead, the initial port position is marked on the patient’s flank at and slightly posterior to the posterior axillary line, in line with the level of the herniated disc. The initial port serves as the working port. In individuals with large, rounded chests, port placement is even more critical. If the working port is too anterior, the direction of access is more posterior at the spine, instead of looking down at the pedicle. In both large and obese patients, a port placed more anteriorly will adversely change the angle of approach to the disc space. This will lead to a more horizontal approach to the disc, making it difficult to look down at the pedicle, instead looking directly back toward the rib, transverse process, and facet joint. The port site selected is marked with a marking pen, and the patient’s entire chest is prepared and draped as for a thoracotomy. Electrodes are placed for somatosensory and motor evoked potential monitoring prior to positioning, and baseline recordings are obtained after positioning is complete. As the chlorhexidine or Betadine preparation of the surgical site is initiated, the anesthesiologist collapses the lung on the ipsilateral side and applies suction to that lung. A 2-cm incision is made in the skin, and the incision is carried down to the chest wall muscles. A Kelly clamp is used to separate the chest wall muscles in the direction of the fibers toward the selected intercostal space. The clamp is directed along the upper border of the lower rib to avoid injuring the neurovascular bundle. By necessity, the initial entry into the chest cavity is blind. The Kelly clamp is pushed in a controlled fashion through the parietal pleura into the chest cavity; the anesthesiologist will hold the breathing for a few seconds during this maneuver. The clamp is opened along the length of the intercostal space to enlarge the entry port. A forefinger is inserted into the chest cavity and swept around the chest wall to release any adhesions. A soft, pliable Thoracoport (U.S. Surgical), 15 mm in diameter, is introduced into the pleural cavity. The length of the Thoracoport depends on the thickness of the chest wall as measured by placing the operator’s finger into the chest cavity. If the port extends too far into the chest cavity, it will impede visualization and interfere with the range of motion of the working instruments introduced via that port. If the port is cut too short, it will slip back into the chest wall muscles and interfere with the introduction of the working instruments. A 10-mm, 0-degree-angled endoscope is placed via this port, and an initial exploratory thoracoscopy undertaken. The second working port for suction/irrigation is placed in line with the first port, rostral or caudal to the first port depending on the level of the disc herniation. All ports after the initial working port are guided into the pleural cavity with continuous endoscopic visualization. A third port is placed in the anterior axillary line away from the working ports or in line with the working ports, for retraction of the lung and/or diaphragm. The third port is placed such that the long shaft of the fan retractor outside the chest is not in the path of the working instruments. A fan retractor is placed

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Thoracoscopic Discectomy and Thoracoscopy-Assisted Tubular Retractor Discectomy via this port to retract the lung and/or diaphragm away from the spine, and the retractor is held in position using a tablemounted retractor holder. Finally, an endoscopic port is placed posterior to the posterior axillary line to and away from the working ports, either rostral or caudal to the working ports depending on the level of the disc herniation. A 10-mm, 30-degree-angled endoscope is introduced via this port and held in position using a tablemounted scope holder (▶ Fig. 25.1).

25.4.3 Identification of the Disc Space The ribs are counted from the apex of the chest cavity downward. The highest rib visualized thoracoscopically is the second rib. The ribs are counted from the second rib to the rib corresponding to the appropriate disc space. The 1st and 2nd ribs articulate with the first and second vertebral bodies only; likewise, the 11th and 12th ribs articulate with their respective bodies only. All other ribs straddle the disc space, the 3rd rib with the T2–T3 disc, and the 10th rib with the T9–T10 disc space, respectively. It is important to count down to the appropriate rib corresponding to the disc to be operated on and mark the disc with the Bovie or Harmonic scalpel (Ethicon Endo-Surgery, Inc., Cincinnati, OH). A Steinmann pin is placed through one of the ports or directly through the chest wall into the identified disc space, and a cross-table radiograph of the thoracic spine is obtained to reconfirm the level. With very obese patients when we anticipate difficulty with identification, we have had the radiologist place a metallic marker into the head of the appropriate rib with fluoroscopic guidance the day before surgery. The marker is then readily identified in the operating room with a cross-table radiograph.

25.4.4 Exposure and Preparation of the Surgical Field Once the disc space and the overlying rib have been identified, the parietal pleura over the proximal 2 to 3 cm of the rib is opened to expose the corresponding rib and rib head at that level. The Harmonic scalpel with ultrasonic cutting and coagulating capabilities is used to open the pleura. The pleural opening is extended down the rib to the disc space and then at right angles along the vertebral body above and below the disc (inverted T). The use of the Harmonic scalpel instead of the cautery avoids charring locally, which can obscure tissue landmarks. The radicular artery and vein will be encountered over the middle of the vertebral bodies. Using right-angled dissectors, the artery and vein are freed from the vertebral body, and after an endoscopic clip applier (5-mm clips) is used to clip the vessels proximally and distally, these vessels are divided. This will prevent tearing of these vessels during the drilling phase of the operation that could lead to uncontrollable bleeding.

25.4.5 Resection of the Rib The head and neck of the rib with 2 cm of the shaft of the rib should be removed. The parietal pleura over the rib is divided as described above in an inverted T shape. Using angled curettes, the soft tissues along the upper and lower borders of the rib are dissected free. Care should be exercised to avoid injuring the neurovascular bundle along the lower border of the rib. If bleeding does occur, this is controlled with bipolar coagulation. The head of the rib is disarticulated at the costovertebral articulation. A Cobb elevator is insinuated into the joint space on all sides and rocked from side to side to release the costovertebral

a

b Scope

First working port

Suction irrigation Irrigation Fan Fan retracting lung tissue

Lung retracted

Level T10-11 Initial port (first working port)

Scope posterior and caudal Fig. 25.1 (a,b) Port placement for thoracoscopic approach to the spine.

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Surgical Techniques articulation (▶ Fig. 25.2a). The R attachment of the Midas Rex drill (Medtronic Sofamor Danek) with an adjustable sheath is used to drill the distal end of the rib. A trough is created in the shaft of the rib, drilling from rostral to caudal and deep to superficial. Once the rib has been detached at either end, it is rocked back and forth and freed from the remaining soft-tissue attachments using a nerve hook and angled curettes. The rib is removed from the chest cavity by aligning the rib lengthwise, grasping it with a large pituitary rongeur, and bringing it out of the port (▶ Fig. 25.2). If the port is not large enough for the rib to be brought out, the Thoracoport is removed and the rib is brought out directly through the chest wound. The rib may be used for interbody fusion if required.

25.5 Drilling of the Vertebral Bodies and Decompression of the Spinal Cord Once the head and neck of the rib at the level of the disc herniation have been removed, the soft tissue overlying the pedicle of the lower vertebral body is coagulated with the bipolar cautery. The pedicle is exposed, and its margins are identified. The disc space is clearly identified by removing some disc material using a small Cobb elevator in the disc space. We do not remove the pedicle once the rib is removed to expose the dura because the bone may be too thick, but instead start the drilling of the vertebrae. The drilling of the vertebral bodies straddling the disc is continued into the pedicle. With the R attachment on the Midas Rex drill fitted with an adjustable sheath, a coarse diamond drill bit is used to start the drilling of the vertebral bodies (see ▶ Fig. 25.2c). The coarse diamond bit used for drilling reduces bleeding by packing the bone dust into the bone, thus reducing the amount of bleeding. The drill is brought in through the working port in line with the target; the suction/irrigation can be rostral or caudal to the working port. A segment 1 to 1.5 cm of the vertebral bodies adjacent and on either side of the disc is drilled, starting 1 cm behind the spinal canal and working toward the canal. A trough is created anterior to the spinal canal; the shape of the trough may be triangular or rectangular depending on the extent of decompression required (see ▶ Fig. 25.2d). The drilling is extended posteriorly into the pedicle of the lower vertebral body at the level of the disc herniation, thinning the pedicle to a thin cortical shell. Bone bleeding is controlled with bone wax applied on the end of a peanut and then spread over the raw bone surface with small Cottonoids attached to long threads. The drilling is extended posteriorly until a thin shell of cortical bone is left against the anterior aspect of the spinal canal with the attached herniated disc. The thinned-out rostral edge of the pedicle and the floor of the spinal canal are identified with a nerve hook (see ▶ Fig. 25.2e), and a Kerrison rongeur is used to remove this pedicle in a piecemeal fashion, exposing the dura. Venous epidural bleeding can be troublesome and is controlled with bipolar coagulation and thrombin-soaked Gelfoam and FloSeal. The thin cortical shell of bone against the anterior surface of the dura with the attached herniated disc should be freed next. Disc and bone removal can

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be achieved with reverse-angled curettes and Kerrison rongeurs (see ▶ Fig. 25.2f, g). The shell of bone with the attached disc is gently pulled away from the thecal sac into the previously drilled anterior trough. Using a dissecting instrument, the attachment of the disc to the dura is gently freed as the disc is pulled forward into the trough. Once the main fragment of the disc has been removed and the cord decompressed, it should be determined if the decompression has extended across the midline to the opposite pedicle. It is not easy to do this visually because of the lack of depth perception. Thus, a cross-table anteroposterior chest radiograph should be obtained with an instrument placed in the area of the decompression. The tip of the instrument should be at the opposite pedicle. Once adequate decompression has been achieved, the wound is irrigated with antibiotic solution to remove bone dust and other debris. Hemostasis is achieved with bipolar coagulation, thrombin-soaked Gelfoam, and Floseal. In the event of a dural tear and spinal fluid leakage, a piece of fat harvested from one of the ports is placed over the defect and sealed with fibrin glue, a lumbar spinal drain is inserted, and the chest tube is left on water seal drainage without suction.

25.6 Thoracoscopy-Assisted Tubular Retractor–Guided Discectomy More recently, we have adopted the benefits of thoracoscopy in combination with the tubular retractors for our transthoracic discectomies. For thoracoscopy-guided tubular retractor approach, the working port/mini-thoracotomy site was placed in the intercostal space overlying the appropriate disc space, at and slightly behind the posterior axillary line (▶ Fig. 25.3a). In this combined approach, an exploratory thoracoscopy was performed via two 5-mm ports using a 5-mm zero-degree-angled endoscope. An exploratory thoracoscopy was carried out, minor pleural adhesions were released, and the disc space identified from within the chest cavity by counting the ribs and placing a K-wire in the disc, and cross-table X-rays were obtained to identify and mark the disc space. A fan retractor may be utilized to retract the lung and great vessels to expose the spine (▶ Fig. 25.3b). A harmonic scalpel was then used to open the parietal pleura overlying the disc space and rib, and if necessary the adjacent segmental vessels were dissected free, coagulated, and divided. Following these preparatory steps, the incision over the working port was enlarged to approximately 3 to 4 cm, and a tubular retractor (XLIF, Nuvasive, San Diego, CA) was safely deployed to the disc space under continuous endoscopic visualization. More recently, we started removing a 3-cm segment of rib at the working port to minimize the risk of rib fracture and intercostal neuralgia from forces generated by the retractor blades. (This rib segment was reattached with titanium mini-plates at the end of the operation.) Once the tubular retractor was docked on the disc space, the third blade was opened anteriorly, with additional plastic shims used as necessary to protect the lung. The microscope was then brought into position. The rest of the operation proceeds as described with the thoracoscopic approach, but in this case with the use of the operating microscope.

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Thoracoscopic Discectomy and Thoracoscopy-Assisted Tubular Retractor Discectomy

a

b

Drill rib trough Incised parietal pleura

Fig. 25.2 Steps taken in thoracoscopic discectomy, including (a) disarticulation of rib head and (b) proximal rib head harvest for grafting. (c) Drilling of rostral lateral portion of pedicle to expose lateral dural margin. (d) Removal of the pedicle continues with a rongeur. (e) Identification of the floor of the spinal canal with a nerve hook. (f) Disc and bone removal with reverseangled curettes and Kerrison rongeurs. (g) A dorsal cavity is created and the curette pushes the disc anteriorly into the cavity to facilitate removal. (h) After cord decompression, graft and instrumentation are placed.

Rib head used for grafting

Sympathetic chain ganglia

Costovertebral ligaments

Segmental vessels clipped at midportion of vertebral body

Cobb elevator

c

Pedicle (partial resection)

d

Dura Posterior longitudinal ligament Annulus (disc)

e

f

Probe or nerve hook

Dura Posterior longitudinal ligament

Dura Posterior longitudinal ligament

Disc space

g

Downgoing curette

Disc (herniated nucleus pulposus)

h

Dura Graft

25.7 Bone Fusion In most patients undergoing thoracoscopic discectomy, no fusion was performed. We have been performing stabilization and fusion when the disc herniation is at the apex of the thoracic kyphosis and when we had to remove more bone for the decompression to reduce incidence of progressive kyphosis and chronic axial pain. In the event that a large segment of bone has to be removed because of extension of the disc behind the adjacent bodies, a bone fusion may be indicated. If this is anticipated, care should be exercised when removing the rib at the outset of the operation so as to have bone for fusion. The height of the trough is measured with a plastic ruler cut to size and introduced on a string into the chest cavity. During height measurement, the assistant pushes on the back of the thoracic spine to distract the bodies. A narrow vertical trough is created with the drill on the inferior aspect of the superior vertebra and the superior aspect of the inferior ver-

tebra to accommodate the width of the rib graft. The piece of rib of appropriate size is introduced into the chest cavity through the Thoracoport or through the chest wound, tied to a string. The rib graft is manipulated into the vertical slots created with pressure applied on the posterior spine by one of the assistants (▶ Fig. 25.2h). Once the graft is seated, a long impactor is used to tap the graft into position. The mortise created keeps the rib graft from slipping back toward the spinal cord.

25.8 Wound Closure The wound is irrigated with antibiotic solution; blood, irrigating fluid, and bone dust are washed and suctioned out. Injection of 0.25% bupivacaine (Marcaine) along the intercostal bundles at each port site will reduce postoperative pain. A single chest tube 28 or 32 Fr is placed via one of the posterior ports, and the tip is guided endoscopically into the apex of the

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Fig. 25.3 (a,b) Thoracoscopy is used to visualize and protect the lung and great vessels as an expandable tubular retractor is deployed through minithoracotomy.

chest cavity. The tube is also manipulated to lie medially along the area of the decompression. The ports are removed and the lung is reinflated at this time. The wounds are closed with 3–0 Vicryl sutures subcuticularly, and Steri-Strips are applied to the skin. The chest tube is connected to wall suction.

25.9 Tubular Retractor–Guided Discectomy As discussed previously, once the tubular retractor is docked on the spine straddling the appropriate rib and disc space, the retractor is affixed to the table-mounted holder and the light source introduced. The medial blade of the 3-blade retractor is placed facing the chest cavity; plastic shims can be deployed down the blades to keep the lung out of the working space. The operating microscope is brought in with operative magnification; the rest of the operation is performed as described previously. After disarticulating the head of the rib from its costovertebral articulation, the Midas Rex drill with the “R” attachment is used to drill the neck of the rib and remove this segment of the rib. The vertebral bodies and the rostral third of the lower pedicle are drilled as discussed previously. The use of the operating microscope allows for better visualization and the ability to use familiar microscopic instruments while separating the herniated disc material from the dura. Once the decompression is complete, the remaining disc space anterior to the trough is cleared of all disc material and the end plates prepared for placement of a polyetheretherketone (PEEK) cage with local autograft bone. Thereafter, we utilize a plate screw system (Nuvasive Syst, San Diego, CA) across this segment of the disc and vertebral bodies to stabilize the construct.

the drainage is less than 50 mL in 24 hours. Most chest tubes can be removed in 24 to 48 hours. It has been our experience that thoracoscopic discectomy patients have less postoperative pain and less shoulder girdle dysfunction postoperatively compared with patients having an open thoracotomy. Length of stay in the ICU is reduced, thus reducing the overall hospital stay.

25.11 Conclusion Thoracoscopic discectomy for large central and calcified disc herniations is a viable and preferable alternative to thoracotomy. However, there is a steep learning curve to master this technique. Thoracoscopic discectomy in selected patients and in the hands of surgeons experienced in thoracoscopic surgery can be very successful. Longer operating times can be reduced with experience and become comparable to open thoracotomy, without the postoperative morbidity associated with thoracotomy. The adaptation of the thoracoscopy-guided approach to place a tubular retractor safely and use of the operating microscope have reduced the morbidity associated with the other transthoracic approaches even further.

Clinical Caveats ●

●

●

●

25.10 Postoperative Care All patients are admitted to the ICU, and pain is controlled with patient-controlled analgesia for 24 hours. The chest tube is started on wall suction of 20-cm water in the operating room. Once the lung has been fully inflated as noted on chest radiograph, the chest tube is changed to water seal drainage until

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●

Careful analysis of preoperative plain radiographic images can help prevent wrong-level thoracic surgery. In morbidly obese patients, preoperative radiographic placement of metal marker can help identify the proper surgical level. Rib head and subsequent pedicle removal leads to early identification of the dura and spinal canal location. A trough is created anterior to the thoracic disc herniation into which the disc herniation can be pushed away from the spinal cord to prevent cord manipulation. Tubular retractor system in combination with thoracoscopic techniques can help reduce the learning curve by allowing for use of standard microinstruments and improve visualization using the operative microscope.

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References [1] Ransohoff J, Spencer F, Siew F, Gage L, Jr. Transthoracic removal of thoracic disc. Report of three cases. J Neurosurg. 1969; 31(4):459–461 [2] Rosenthal D, Rosenthal R, de Simone A. Removal of a protruded thoracic disc using microsurgical endoscopy. A new technique. Spine. 1994; 19(9):1087–1091

Further Reading [1] Arce CA, Dohrmann GJ. Thoracic disc herniation. Improved diagnosis with computed tomographic scanning and a review of the literature. Surg Neurol. 1985; 23(4):356–361 [2] Benjamin V. Diagnosis and management of thoracic disc disease. Clin Neurosurg. 1983; 30:577–605 [3] Benson MKD, Byrnes DP. The clinical syndromes and surgical treatment of thoracic intervertebral disc prolapse. J Bone Joint Surg Br. 1975; 57(4):471–477 [4] Bloomberg AE. Thoracoscopy in perspective. Surg Gynecol Obstet. 1978; 147 (3):433–443 [5] Bohlman HH, Zdeblick TA. Anterior excision of herniated thoracic discs. J Bone Joint Surg Am. 1988; 70(7):1038–1047 [6] Carson J, Gumpert J, Jefferson A. Diagnosis and treatment of thoracic intervertebral disc protrusions. J Neurol Neurosurg Psychiatry. 1971; 34(1):68–77 [7] Chou SN, Seljeskog EL. Chapter 25. Alternative surgical approaches to the thoracic spine. Clin Neurosurg. 1973; 20:306–321 [8] Coltharp WH, Arnold JH, Alford WC, Jr, et al. Videothoracoscopy: improved technique and expanded indications. Ann Thorac Surg. 1992; 53(5):776–778, discussion 779 [9] Dickman CA, Karahalios DG. Thoracoscopic spinal surgery. Clin Neurosurg. 1996; 43:392–422 [10] Dickman CA, Mican CA. Multilevel anterior thoracic discectomies and anterior interbody fusion using a microsurgical thoracoscopic approach. Case report. J Neurosurg. 1996; 84(1):104–109 [11] Dickman CA, Rosenthal D, Regan JJ. Reoperation for herniated thoracic discs. J Neurosurg. 1999; 91(2) Suppl:157–162 [12] Fessler RG, Dietze DD, Jr, Millan MM, Peace D. Lateral parascapular extrapleural approach to the upper thoracic spine. J Neurosurg. 1991; 75(3):349–355 [13] Horowitz MB, Moossy JJ, Julian T, Ferson PF, Huneke K. Thoracic discectomy using video assisted thoracoscopy. Spine. 1994; 19(9):1082–1086 [14] Hulme A. The surgical approach to thoracic intervertebral disc protrusions. J Neurol Neurosurg Psychiatry. 1960; 23:133–137 [15] Kao MC, Tsai JC, Lai DM, Hsiao YY, Lee YS, Chiu MJ. Autonomic activities in hyperhidrosis patients before, during, and after endoscopic laser sympathectomy. Neurosurgery. 1994; 34(2):262–268, discussion 268 [16] Landreneau RJ, Dowling RD, Ferson PF. Thoracoscopic resection of a posterior mediastinal neurogenic tumor. Chest. 1992; 102(4):1288–1290 [17] Le Roux PD, Haglund MM, Harris AB. Thoracic disc disease: experience with the transpedicular approach in twenty consecutive patients. Neurosurgery. 1993; 33(1):58–66

[18] Lesoin F, Rousseaux M, Autricque A, et al. Thoracic disc herniations: evolution in the approach and indications. Acta Neurochir (Wien). 1986; 80(1)(–) (2):30–34 [19] Love JG, Kiefer EJ. Root pain and paraplegia due to protrusions of thoracic intervertebral disks. J Neurosurg. 1950; 7(1):62–69, illust [20] Love JG, Schorn VG. Thoracic-disk protrusions. JAMA. 1965; 191:627–631 [21] Love JG, Schorn VG. Thoracic disk protrusions. Rheumatism. 1967; 23(1):2–10 [22] Lyons MK, Gharagozloo F. Video-assisted thoracoscopic resection of intercostal neurofibroma. Surg Neurol. 1995; 43(6):542–545 [23] Mack MJ, Regan JJ, Bobechko WP, Acuff TE. Application of thoracoscopy for diseases of the spine. Ann Thorac Surg. 1993; 56(3):736–738 [24] Maiman DJ, Larson SJ, Luck E, El-Ghatit A. Lateral extracavitary approach to the spine for thoracic disc herniation: report of 23 cases. Neurosurgery. 1984; 14(2):178–182 [25] McAfee PC, Regan JR, Zdeblick T, et al. The incidence of complications in endoscopic anterior thoracolumbar spinal reconstructive surgery. A prospective multicenter study comprising the first 100 consecutive cases. Spine. 1995; 20 (14):1624–1632 [26] Otani K, Nakai S, Fujimura Y, Manzoku S, Shibasaki K. Surgical treatment of thoracic disc herniation using the anterior approach. J Bone Joint Surg Br. 1982; 64(3):340–343 [27] Patterson RH, Jr, Arbit E. A surgical approach through the pedicle to protruded thoracic discs. J Neurosurg. 1978; 48(5):768–772 [28] Perot PL, Jr, Munro DD. Transthoracic removal of midline thoracic disc protrusions causing spinal cord compression. J Neurosurg. 1969; 31(4):452–458 [29] Reif J, Gilsbach J, Ostheim-Dzerowycz W. Differential diagnosis and therapy of herniated thoracic disc. Discussion of six cases. Acta Neurochir (Wien). 1983; 67(3)(–)(4):255–265 [30] Robertson DP, Simpson RK, Rose JE, Garza JS. Video-assisted endoscopic thoracic ganglionectomy. J Neurosurg. 1993; 79(2):238–240 [31] Russell T. Thoracic intervertebral disc protrusion: experience of 67 cases and review of the literature. Br J Neurosurg. 1989; 3(2):153–160 [32] Sekhar LN, Jannetta PJ. Thoracic disc herniation: operative approaches and results. Neurosurgery. 1983; 12(3):303–305 [33] Stillerman CB, Chen TC, Couldwell WT, Zhang W, Weiss MH. Experience in the surgical management of 82 symptomatic herniated thoracic discs and review of the literature. J Neurosurg. 1998; 88(4):623–633 [34] Stillerman CB, Chen TC, Day JD, Couldwell WT, Weiss MH. The transfacet pedicle-sparing approach for thoracic disc removal: cadaveric morphometric analysis and preliminary clinical experience. J Neurosurg. 1995; 83(6):971–976 [35] Weder W, Schlumpf R, Schimmer R, Kotulek T, Largiadèr F. Thoracoscopic resection of benign schwannoma. Thorac Cardiovasc Surg. 1992; 40 (4):192–194 [36] Williams MP, Cherryman GR, Husband JE. Significance of thoracic disc herniation demonstrated by MR imaging. J Comput Assist Tomogr. 1989; 13 (2):211–214 [37] Wood KB, Garvey TA, Gundry C, Heithoff KB. Magnetic resonance imaging of the thoracic spine. Evaluation of asymptomatic individuals. J Bone Joint Surg Am. 1995; 77(11):1631–1638

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26 Anterior Thoracoscopic Vertebral Reconstruction and Instrumentation Francisco Verdú-López and Rudolf W. Beisse Abstract Anterior thoracoscopic surgery with vertebral reconstruction and instrumentation can be used to approach the anterior column of the spine in the area between the third thoracic vertebra and the third lumbar vertebra in most cases. Acute instability with structural damage to the anterior loadbearing spinal column and posttraumatic deformity represent the most frequent indications for surgery. The application potential includes anterior release procedures, with incision and resection of ligaments and intervertebral discs; removal of fragmented discs or sections of vertebrae, with anterior surgical decompression of the spinal canal; replacement of vertebral bodies with biologic or alloplastic materials for spinal fusion; and ventral stabilization procedures with implants designed for use in thoracoscopy. The thoracolumbar junction is the section of the truncal spine most often affected by traumatic injuries and spinal fractures. In most cases, it is necessary to partially detach the diaphragm to provide access to the retroperitoneal section of this region. The thoracoscopic trans-diaphragmatic approach described in this chapter opens up the whole thoracolumbar junction in a minimally invasive surgery, allowing one to perform all the procedures needed for a full reconstruction of the anterior column. Video-assisted thoracoscopic surgery decreases the morbidity associated with open thoracotomy such as significant pain and respiratory problems, substantial blood loss, poor cosmesis, and prolonged hospitalization. With an adequate learning curve of training, these procedures are safe and have low complication rates. Thoracoscopic surgery is in many cases an alternative to conventional open surgery. Keywords: diaphragm, minimally invasive surgery, spinal fracture, spinal fusion, surgical decompression, thoracoscopic surgery, thoracoscopy, video-assisted thoracoscopic surgery

26.1 Introduction Cord compression in the thoracic spine typically involves the anterior column and can potentially lead to neurologic deficits. These patients may benefit from decompression and reconstruction of the anterior weight-bearing column. However, traditional anterior approaches require extensive exposures that can cause significant morbidity and mortality including intercostal neuralgia and post-thoracotomy syndrome. Furthermore, those patients requiring diaphragmatic detachment to access pathology in the thoracolumbar region can develop visceral herniations into the chest.1,2 Much of the morbidity associated with the standard thoracotomy is related to chest wall injury.1,2,3 Thoracoscopic decompression with reconstruction and instrumentation provides a minimally invasive approach to reduce the iatrogenic injury to tissues seen with more traditional transthoracic approaches. Thoracoscopic techniques can be employed to gain access to the thoracic spine, including the thoracolumbar junction,

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by minimal thoracoscopic detachment of the diaphragm. This is made possible by an anatomic peculiarity of the pleural cavity and the diaphragmatic insertion whose lowest point, the costodiaphragmatic recess, is projected onto the spine perpendicularly just above the baseplate of the second lumbar vertebra.3,4,5 Thus, with a diaphragmatic opening of approximately 6 to 10 cm, the entire L2 vertebral body can be exposed, which is a much smaller opening than that required for conventional open techniques. As with traditional thoracotomy approaches, thoracoscopic techniques are based on the classic spine surgery principles of neural decompression, restoration of spinal alignment, reconstruction, and short-segment stabilization. When performed by well-trained surgeons, thoracoscopic spine surgery has a low rate of complications comparable to the open approaches, with good clinical outcomes and similar deformity correction. Advantages of thoracoscopic spine surgery over open procedures include less morbidity with faster postoperative recovery, less analgesia, shorter hospital stay, and better cosmetic result. Although an anterior thoracoscopic technique alone can be used to perform sympathectomies and thoracic discectomy or to treat compression fractures, a combined open posterior approach may be needed in those patients with three column spinal injuries. These techniques are more difficult in morbidly obese patients. Another disadvantage of thoracoscopic techniques is increased difficulty in handling complex dural injuries.

26.2 Indications With the advancement of the thoracoscopic spine surgery, the number of indications has also increased. These possible indications include the following: ● Anterior reconstruction of recent or old fractures or injuries of the thoracic and thoracolumbar regions that can present with instability, deformity, and/or stenosis.3 ● Spinal canal stenosis with a lesion anatomy that favors the anterolateral approach.6 ● Centrally located herniated thoracic disc.7 ● Surgery for deformities and scoliosis.8 ● Treatment of some tumors if spine stability is compromised after resection. ● Treatment of various infectious processes.9 ● Revision surgery (i.e., infection of the surgical bed, failure or loss of implant purchase, etc.). Good candidates for anterior thoracoscopic vertebral reconstruction and instrumentation are those with previous indications, whether or not the anatomy of the lesions is favored by the anterolateral approach. Thinner patients allow for easier surgeries. Obese patients, although more difficult to operate on, benefit the most from a thoracoscopic procedure. The procedure is essentially the same in obese patients as in thinner patients once the portals are set. Obesity therefore is not a contraindication. Adequate relaxation is required and preoperative purging is recommended. The patient should not have lung restriction or significant ventilatory

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Anterior Thoracoscopic Vertebral Reconstruction and Instrumentation problems because he or she must withstand selective ventilation in only one lung, which is aimed to collapse the other one.

26.3 Preoperative Planning A complete neurological assessment has to be done prior to surgery. Depending on the type of surgery that we plan to do, it is usually necessary to have anteroposterior (AP) and lateral thoracic and lumbar X-rays. CT scan or MRI is necessary to evaluate the characteristics of the soft tissue and bone. Typically, the fractured or deformed vertebrae are easy to locate under fluoroscopy. If in doubt, surgeons can resort to visually apparent osteophytes previously identified on radiographs and CT to assist in localization. Pay attention to patients with an abnormal number of ribs or lumbar vertebrae. We typically order and evaluate a lumbar and thoracic AP and lateral plain radiograph as well as a chest X-ray prior to surgery to assist in identifying the proper level(s) for surgery. It is important to assess the location of the great vessels and possible anatomical variables for surgery planning. Size of the vertebrae is another parameter that must be taken into consideration in choosing the optimal instrumentation. During the anesthetic assessment prior to surgery, pulmonary and respiratory functions should be checked. If there are any doubts, forced expiratory volume in 1 second (FEV1) and diffusion capacity for carbon monoxide (DLCO) allow surgeons to determine preoperatively whether the patient can tolerate selective ventilation of one lung during surgery, as well as postoperatively.

26.3.1 Instrumentation Standard video endoscopic and thoracoscopic instruments are used to perform the procedure. The image transmission system consists of a rigid endoscope angled at 30 degrees and linked to a three-chip camera. A xenon cold light source with high light-transmitting capacity is essential to illuminate the

entire thoracic spine. Instruments required for thoracoscopic dissection include osteotomes, hooks for dissection, hook probes, sharp and blunt rongeurs, Kerrison rongeurs, curettes, and so on. Thoracoscopic instruments for bone and soft-tissue resection should be long with large handles to work safely and securely within the thoracic cavity. Instruments should preferably have a scale marked on both sides for bone and intervertebral disc resection to gauge the depth of instrument insertion during decompression. We had used the Z-Plate (Medtronic Sofamor Danek, Memphis, TN) until October 1999 for reconstruction purposes. Ever since then, we have used the MACS TL system (Aesculap, Tuttlingen, Germany) exclusively because it is specially designed for endoscopic application. This system greatly facilitates the procedure and is now available in a second generation.

26.4 Surgical Approach and Technique 26.4.1 Anesthesia and Patient Positioning Thoracoscopic procedures are performed with the patient under general anesthesia with single-lung ventilation. The positioning of the double-lumen tube is controlled bronchoscopically. A Foley catheter, central venous line, and arterial line are placed in all cases. The operating room setup is shown in ▶ Fig. 26.1. The patient is placed in a stable lateral position on the right side and fixed with a four-point support at the symphysis, sacrum, scapula, and arms. The proper use of padded brackets is very important to secure and stabilize the surgical posture4 (▶ Fig. 26.2a). Below the corresponding hemithorax, an inflatable air bag is placed for maximum physiological opening of the intercostal spaces. It is useful to use a cushion shaped as an “inverted U”

Fig. 26.1 Operating room setup for thoracoscopic spine surgery.

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Fig. 26.2 (a) Surgical position in the lateral decubitus position. The level of injury is located using fluoroscopy. (b) The surgeon and the assistant holding the camera stand behind the patient. On the opposite side, another assistant surgeon manages the suction-irrigation and the retractor. (c,d) Location of different surgical portals: the black arrow indicates the working channel portal with exact projection on the level of injury, the white arrow indicates the portal for the endoscope, the black asterisk indicates the portal for suction-irrigation, and the white asterisk indicates the portal for the retractor. (Reproduced with permission from Elsevier Spain. Original source: Beisse R, Verdú-López F. Situación actual de la cirugía toracoscópica del raquis torácico y lumbar. Parte 1: Aspectos generales y tratamiento de las fracturas. Neurocirugía 2014;25(1):8–19. Copyright © 2012 Sociedad Española de Neurocirugía. Published by Elsevier España, S.L. All rights reserved.)

between the legs, which slightly flexes the upper hip to relax the upper aspect of the iliac psoas muscle. The side of approach is mainly decided according to the location of the great vessels, for which CT is best suited. Normally, a right-sided approach is preferred for upper and middle thoracic pathology, and a leftsided approach is preferred for lower thoracic spine and thoracolumbar junction pathology. The arm on the approach side is abducted and elevated to facilitate endoscopic placement and manipulation during the procedure. Before the operation is begun, the position and free tilt of the C-arm must be checked. Sterile draping extends posteriorly from the middle of the sternum anterior to the spinous processes as well as from the axilla down to approximately 8 cm caudal to the iliac crest. Both monitors are placed at the lower end of the operating table on opposite sides to allow the surgeon and the assistant an unrestricted view. The surgeon and the assistant holding the camera stand behind the patient. The

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C-arm intensifier is placed between the surgeon and the cameraman. The assistant and the C-arm monitor are placed on the opposite side (▶ Fig. 26.2b).

26.4.2 Port Placement Port placement is critical and will affect the ease of accessing the pathology. With the assistance of fluoroscopy, the targeted vertebrae are marked on the skin. First, an AP fluoroscopic projection is done at 0 degrees to verify that the column is not rotated. The surgical table may be slightly rotated to adjust the position. Second, the lateral projection is performed at 90 degrees, making sure that all margins (anterior, posterior, and upper and lower plates) of the vertebral bodies are appraised on fluoroscopy without double contours, which in this case represent the actual situation of injury. For this task, it is very helpful to use, as a rule, a Kirschner wire (K-wire).

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Anterior Thoracoscopic Vertebral Reconstruction and Instrumentation

Fig. 26.3 (a) Introduction of trocars through the intercostal space under endoscopic control. (b) Using the left thoracoscopic approach to access the thoracolumbar junction, the spine, aorta, lung, and diaphragm are shown. (c) Thoracoscopic view showing the line of diaphragmatic insertion. (d) Diaphragmatic opening with hook diathermy electrode. (Reproduced with permission from Elsevier Spain. Original source: Beisse R, Verdú-López F. Situación actual de la cirugía toracoscópica del raquis torácico y lumbar. Parte 1: Aspectos generales y tratamiento de las fracturas. Neurocirugía 2014;25(1):8–19. Copyright © 2012 Sociedad Española de Neurocirugía. Published by Elsevier España, S.L. All rights reserved.)

The working channel is centered exactly over the target vertebrae (12.5-mm diameter). The optical channel for the endoscope (10-mm diameter) is placed two or three intercostal spaces cranial to the target vertebrae for approaching the lower thoracic spine and thoracolumbar junction pathology. For pathology of the middle and upper thoracic spine, the optical channel is placed caudal to the target vertebrae. The ports for suction/irrigation (5-mm diameter) and the retractor (10-mm diameter) are placed approximately 5 to 10 cm anterior to the working port and optical channel (▶ Fig. 26.2c,d). The port for the diaphragm and/or lung retractors should be placed as far ventrally as possible to avoid instrument “fencing.” It is sometimes helpful to use two separate working ports directed above and below the segment to be instrumented. The operation begins with the most cranial approach (optical channel). Through a 1.5-cm skin incision above the intercostal space, small Langenbeck hooks are inserted. Muscles of the thoracic wall are crossed in a blunt, muscle-splitting technique, and the intercostal space is opened by blunt dissection, thus exposing the pleura and creating an opening into the thoracic cavity. The 10-mm trocar is inserted, and single-lung ventilation is begun. The 30-degree scope is inserted at a flat angle in the direction of the second trocar. Under direct endoscopic visualization, perforation of the thoracic wall is performed to admit the second, third, and fourth trocars4 (▶ Fig. 26.3a). The second portal is usually done for the retractor, allowing an initial inspection of the surgical area before introducing the next ports. Once the four trocars are placed, the endoscopic view of the surgical site must remain constant to avoid spatial disorientation.

With the main surgeon and the camera assistant behind the patient (as we do), the aorta is arranged horizontally above. Below are the vertebral bodies and intervertebral discs located perpendicular to the aorta (▶ Fig. 26.3b). Further down is the spinal canal, which hides behind the pedicles, neural foramina, and the heads of the ribs in the thoracic region. The cranial side is on the right and the caudal side on the left.

26.4.3 Prevertebral Dissection and Access to Thoracolumbar Junction The target area can now be exposed with the help of a fan retractor inserted through the anterior port. The retractor holds down the diaphragm and exposes the insertion of the diaphragm on the spine. The pathologic area is identified with a long spinal needle inserted through the thoracoscopic port under fluoroscopic guidance. The pleura is incised and mobilized over the proximal ribs of the involved vertebra and one level above and below the vertebra. The segmental vessels are ligated with an Endo-Clip (▶ Fig. 26.4a), coagulated with an endoscopic bipolar coagulator, and transected. As opposed to the traditional approach to the thoracolumbar junction, which requires extensive diaphragmatic detachment, the thoracoscopic approach requires minimal diaphragmatic detachment. Thus, with a diaphragmatic opening of approximately 6 to 10 cm, the entire L2 vertebral body can be exposed. In order to appreciate the anatomic orientation, the anterior circumference of the motion segment and the location and

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Fig. 26.4 (a) The segmental vessels are ligated with an Endo-Clip and then transected. (b) The K-wire should be inserted approximately 10 mm away from the posterior edge of the vertebral body and 10 mm away from the endplate. The correct placement of K-wires offers surgeons the correct orientation throughout the whole procedure. (c) Partial discectomy is performed to define the vertebral borders. The blade is sharp only on one side, and we always cut the disc down to avoid injury to the great vessels. (d,e) Reconstruction with the hydraulic device Hydrolift (Aesculap, Center Valley, PA), which allows a variable distraction and adaptation to the endplates. (f) The polyaxial screw, posterior screw first, is placed over the K-wire. (g) Detail of MACS TL system (Aesculap) fully assembled. (h,i) The retractor is rearranged, and the gap in the diaphragm is closed with staples or adaptive sutures using endoscopic techniques. (Reproduced with permission from Elsevier Spain. Original source: Beisse R, Verdú-López F. Situación actual de la cirugía toracoscópica del raquis torácico y lumbar. Parte 1: Aspectos generales y tratamiento de las fracturas. Neurocirugía 2014;25(1):8–19. Copyright © 2012 Sociedad Española de Neurocirugía. Published by Elsevier España, S.L. All rights reserved.)

course of the aorta are palpated with a blunt probe. The line of dissection for the diaphragm is “marked” with monopolar cauterization (▶ Fig. 26.3c,d). The diaphragm is then incised using endo-scissors. A rim of 1 cm is left on the spine to facilitate closure of the diaphragm at the end of the procedure. To facilitate diaphragmatic reconstruction, an incision is made that runs along the spine and the ribs parallel to the diaphragmatic insertion, which leaves a 1- to 2-cm cuff of diaphragmatic tissue for reapproximation. The diaphragm is thinner in this portion than at the bony insertion site and makes subsequent suturing easier. Retroperitoneal fat tissue is now exposed and mobilized from the anterior surface of the psoas muscle insertion. The psoas muscle is dissected very carefully from the vertebral bodies in order not to damage the segmental blood vessels “hidden” underneath. A retractor is then placed into the diaphragmatic gap.

26.4.4 Orientation and Kirschner Wire–Guided Screw Insertion Orientation Instrumentation starts with the correct placement of K-wires that allows surgeons the correct orientation throughout the

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whole procedure. We presently use the MACS TL system (Aesculap) because it was specially designed for endoscopic placement and greatly facilitates instrumentation. We have previously reported on our technique of thoracoscopic instrumentation3 (▶ Fig. 26.5).

Kirschner Wire–Guided Screw Insertion The K-wire is inserted in the distal cannulated end of the instrument and connected with the K-wire impactor. The K-wire is then positioned under fluoroscopic guidance. It is very important that the patient be placed in a true lateral position in order to expose the posterior edge of the corresponding vertebral body. Therefore, it is critical to confirm the patient’s perpendicularity to the fluoroscopic beam to ensure that the K-wire is driven into the vertebral body correctly.

Placement of Kirschner Wire If the instrument charged with the K-wire is well aligned, a dark inner point (the K-wire inside the cannulated instrument) and a concentric ring (the outer diameter of the cannulated instrument) will be observed, and the correct placement of the Kwire into the vertebral body will be ensured. If a line is observed

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Anterior Thoracoscopic Vertebral Reconstruction and Instrumentation

Fig. 26.5 Thoracoscopic instrumentation with the MACS TL system (Aesculap) and K-wire insertion. (a) K-wire insertion and decortication of cortical bone to prepare entry hole for the polyaxial screw. (b) Screw insertion over the K-wire. (c) Distraction maneuver using distraction ratchet and plate placement. (d) Final fixation of the polyaxial screw with the torque wrench applied to the nut driver and countertorque applied by using the handle on the insertion sleeve. (e) Final tightening of the polyaxial screw. (f) Insertion of the anterior screw. (g) Insertion of locking screws.

on the radiograph, then the K-wire is not positioned parallel, thereby posing a risk of injury to the spinal cord or visceral structures. After alignment, the K-wire is impacted until it is stopped by the gray ring of the instrument (20 mm).

Position of Kirschner Wire For safe screw implantation, the K-wire should be inserted approximately 10 mm away from the posterior edge of the vertebral body and 10 mm away from the endplate (▶ Fig. 26.4b). Afterward, the K-wire is released by turning the knob of the impactor counterclockwise. The cannulated instrument can then be pulled out with the K-wire remaining in place. Normally, after this step, we proceed with the corpectomy.

26.4.5 Thoracoscopic Corpectomy and Discectomy The extent of the planned partial vertebrectomy is defined with an osteotome. Partial discectomy is performed to define the vertebral borders (▶ Fig. 26.4c). The scalpel is designed in a manner that we can open it showing its blade once we have it in the desired disc. The blade is sharp only on one side, and we

always cut the disc down to avoid injury to the great vessels. It is important to avoid large movements of the knife within the cavity. After resection of the intervertebral disc(s), the fragmented parts of the vertebra are removed carefully with rongeurs and are saved for graft. The proximal rib head is removed with an osteotome or Kerrison rongeur. The depth of the osteotomy in its anterior limit should be about two-thirds the diameter of the vertebra. The surgeon can use the depth scale recorded on the tip of the osteotome. Bone resection is facilitated by the use of high-speed burrs. If decompression of the spinal canal is necessary, the lower border of the pedicle should first be identified with a blunt hook. The base of the pedicle is then resected caudally with a Kerrison rongeur so that the surgeon can identify the dura and avoid spinal cord injury. Finally, the posterior fragments within the spinal canal can be removed safely. In patients with tumors, more extensive dissection of the vertebral body, pedicles, and proximal rib head is required because tumorous lesions often extend into the pedicle, spinal canal, and surrounding structures over the vertebral body. We need to respect the endplates if we expect to implant titanium boxes to prevent subsidence. In fusion with monosegmental tricortical iliac bone graft, the endplate subchondral bone is removed to promote bone fusion.

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26.4.6 Vertebral Reconstruction with Bone Grafting and Cage Placement The preparation of the graft bed is completed by aggressive preparation of the adjacent endplates and complete removal of all soft tissues. The length and depth of the bone graft/spacer are measured with a caliper. For vertebral fracture replacement in only one segment, autologous iliac crest was used in most patients. In reconstructions involving two segments (i.e., replacement of vertebral body height), it is preferable to use a prosthetic device. Distractible titanium cages (Synthes, Paoli, PA) or Vertebral Body Replacement (VBR; Osteotech, Inc., Eatontown, NJ) was also used in some cases. In past years, we have used the hydraulic device Hydrolift (Aesculap, Center Valley, PA) in most of our surgeries, which allows for variable distraction and adaptation to the endplates (▶ Fig. 26.4d,e). The graft or cage is mounted on the graft holder and inserted through the working port incision. Longer bone grafts (> 2 cm) are inserted along their long axis through the opening and then mounted onto the graft holder inside the thoracic cavity. It is best to place the graft/cage under compression, which is facilitated using distractible titanium cages that can be expanded within the corpectomized segment.

Instrumentation: Decortication We use the previously inserted K-wires to guide the position of the screws. The entry point for the screw is easily decorticated using the sharp tip of the targeting device to facilitate placement of the polyaxial screw (▶ Fig. 26.5a).

Centralizer Attachment The twin screw, the polyaxial clamp and the centralizer, must be preassembled before insertion. In the new version of the MACS TL implant, the centralizer already contains the locking screw, which fixes the polyaxial screw at the end. The centralizer must be screwed into the inner thread. This is accomplished by using a special hex key for the centralizer that applies a torque of 5 Nm. For the rotational locking, the centralizer has two flanges that correspond to the slots of the clamp.

Assembly of Insertion Instrument The handle must be connected to the proximal end, the external hex, of the insertion sleeve. The cannulated screwdriver must be positioned through the insertion sleeve until it locks into position. The polyaxial screw and clamp should be aligned along the direction of the handle to facilitate orientation of the plate during placement. The polyaxial screw must be placed parallel to ensure proper attachment of the screwdriver.

Screw Insertion The polyaxial screw, posterior screw first, is placed over the Kwire (▶ Fig. 26.4f). A handle attached to the insertion sleeve controls the direction of the polyaxial clamp. The polyaxial clamp must be oriented so that the hole for the anterior stabilization screw comes to lie anteriorly. After a few turns of the screw into the vertebral body, the K-wire must be removed so that it is not advanced excessively to cause tissue perforation (▶ Fig. 26.5b).

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Kirschner Wire Removal After partial insertion of the polyaxial screws, the K-wire must be removed. The removal instrument is inserted through the insertion instrument and attached to the K-wire by turning the removal instrument clockwise and screwing it onto the wire. The K-wire can then be pulled out through the cannulated instrument.

Insertion Instrument Removal The instrument is released from the centralizer by pulling it backward. The segmental vessels of the fractured vertebra are mobilized, clamped with vascular clips, and dissected.

Distraction Maneuvers After discectomy or vertebrectomy and proper preparation of the graft bed, distraction can be optionally applied to the vertebral bodies in order to insert a graft that is slightly larger than the prepared disc space and to achieve graft compression. The distraction ratchet (▶ Fig. 26.5c) is placed over the centralizers using holding forceps. By measuring the distance between the centralizers, the surgeon selects the appropriate distraction bar. After placement of the distraction ratchets on the centralizers, the distraction forceps are engaged between the ratchet sleeves.

Plate and Rod Placement The measurement device is used to determine the distance between the polyaxial heads. If the plates are used, 30 mm must be added to select the proper plate length. The stabilization plate is then placed over the centralizer onto the polyaxial heads. The rounded side with the markings is the upper side of the plate.

Rod Insertion In cases of multisegmental assemblies, a rod connection must be chosen. Both rods should be contoured in the same fashion. The anterior border of the polyaxial plate is slightly lower than the posterior border; therefore, the posterior rod can be placed first and temporarily closed by slightly tightening the nut to avoid loosening of the rod. Placement of the anterior rod is then performed. For both types of clamps, a degree of freedom should be preserved to allow angulation of the polyaxial heads. Final screw insertion is performed after the plates are placed and tightened with fixation nuts.

Final Fixation The insertion sleeve must be attached on the centralizer. After the plate or rod is placed and the polyaxial plate is well aligned, the assembly can be closed by using a fixation nut. The nut should be placed with the smooth part against the stabilization plate. Using the cannulated nut driver, the nut can be placed over the centralizer. In order to apply countertorque when tightening the nut, the handle must be attached to the insertion sleeve. Prefixation can be achieved using the nut driver with the countertorque handle. For final fixation, the torque wrench is applied to the nut driver, and countertorque is again applied by using the handle on the insertion sleeve. Thus, no torque is applied to the spine. The tightening torque for final fixation is 15 Nm (▶ Fig. 26.5d).

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Anterior Thoracoscopic Vertebral Reconstruction and Instrumentation

Tightening of Polyaxial Screws Now the assembly must be brought into final position directly onto the surface of the vertebral bodies. To achieve this, the screws are finally inserted until the plate is flush with the vertebral body (▶ Fig. 26.5e).

Insertion of Anterior Screw The screw-guiding sleeve for the anterior stabilization screw must be attached to the centralizer. With the central punch, the cortex is then penetrated. After selection of the appropriate screw length, the anterior screw is fixed to the screwdriver with a retaining clip and then inserted through the guiding instrument into the vertebral body (▶ Fig. 26.5f). Finally, the guiding instrument can be removed.

Inserting Locking Screws To lock definitely the polyaxial mechanism, the locking instrument and screwdriver must be attached to the centralizer. The instrument must be positioned perpendicular to the plate/rod. The locking screw is finally tightened with a torque wrench with two audible clicks (▶ Fig. 26.5g). The centralizer can now be removed together with the fixation instrument.

Closure The retractor is rearranged, and the gap in the diaphragm is closed with staples or adaptive sutures using endoscopic techniques (▶ Fig. 26.4h,i). The thoracic cavity is irrigated, blood clots are removed, and a chest tube is inserted with the end of the tube placed in the costodiaphragmatic recess. A drain of 20 to 24 Fr is placed through the suction–irrigation portal, avoiding the working port, thus decreasing the possibility of infection of the wound or surgical site. All instruments are removed by endoscopic control. After consulting the anesthetist for lung expansion, it is checked thoracoscopically before the camera is removed. The ports are closed with sutures by planes after removal of the trocars. The drain is connected to a water seal chamber under a pressure of 15- to 25-cm H2O suction.

26.5 Postoperative Care Normally the patient is extubated immediately after the operation. AP and lateral radiographs of the target area are obtained postoperatively. In patients with advanced age, chronic obstructive pulmonary disease, or cardiovascular disease, artificial ventilation may be necessary for the first 24 hours after the operation. Low-dose, low-molecular-weight heparin is given for thromboembolic prophylaxis. The patient stays in the intensive care unit for 24 hours. The chest tubes can usually be removed on the first postoperative day. It is very important to give proper analgesia to the patient to avoid postoperative pain and facilitate mobilization of the chest. Conventional analgesia can be completed with epidural analgesia and/or thoracic paravertebral blockade. Mobilization and ventilation training begin on the first postoperative day. On the second postoperative day, physiotherapy is started (1 hour/day), using intensive deep breathing exercises. From the third postoperative

week, physiotherapy is intensified to 2 to 3 hours daily. A plain radiograph is obtained on the second postoperative day, after 9 weeks, and after 6 and 12 months. The patient is allowed to return to work after 12 to 16 weeks. It may be advisable to perform an early postoperative CT control scan to assess the spine, spinal canal, and instrumentation system, and to help rule out possible complications such as pleural effusion and pneumothorax.

26.6 Management of Complications In our series of more than 1,600 cases since 1996, access-related complications such as pleural effusion, pneumothorax, and intercostal neuralgia occurred in less than 5% of cases. No hernia or relaxation of the diaphragm has been recorded. One transient injury of the L1 root occurred during thoracoscopic detachment of the diaphragm. Injuries to major organs (lungs, heart), the aorta, and the vena cava are the most dangerous intraoperative complications. Distorted spine anatomy and insufficient preparation of the segmental vessels can result in accidental injury, bleeding, and loss of visual control. Other complications, such as dural tearing, peritoneum opening, lung injury, and nerve injury due to uncontrolled monopolar coagulation, can occur. Possible intraoperative complications are hemothorax, recurrent pleural effusion, intrathoracic adhesions, deep wound infection, and implant failure. Most of these complications occurred early in the series and were the result of technical difficulties. With experience and improvements in instruments designed specifically for endoscopic application, complication rates have decreased. Implant failure has been very rare, in our experience, since the introduction of the MACS TL system. Implant loosening occurred in two patients with advanced osteoporosis, where postoperative CT and radiographic images revealed shifting of the instrumentation within the vertebral body segments, which was reflective of poor bone quality. Thus, in patients with known or suspected osteoporosis, an extensive posterior and shorter anterior fixation should be considered. Some of these complications did require open thoracotomy and revision. In our series, four patients needed conversion to open surgery. Conversion was necessary in two of the initial five cases in the series; one of these was due to bleeding and the other was due to technical difficulties. The third conversion was the result of bleeding from the aorta. The fourth conversion was necessary because of technical difficulties in attempting to access pathology in the upper thoracic region. Thus, careful preoperative evaluation, operative approach preparation, and meticulous techniques are essential to ensure good patient outcomes and avoid complications. There is a steep learning curve for mastering this procedure, and it is advised that adequate thoracoscopic training be undertaken before performing this technique.

26.7 Clinical Case A 35-year-old male patient was seen after a motor vehicle accident with weakness and numbness in the lower extremities. Examination revealed grade 4 paraparesis and diminished sensations below the L1 dermatome. Radiographs

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Fig. 26.6 (a–c) CT scans of the thoracolumbar spine showing burst fracture of T12 vertebra with extension into the spinal canal. (d) Postoperative radiograph after anterior thoracoscopic decompression, reconstruction of anterior column with bone grafting, and anterior fixation (MAC STL system, Aesculap).

and reconstructed CT scans (▶ Fig. 26.6a–c) of the thoracolumbar spine revealed a T12 vertebral burst fracture with fracture fragments extending into the spinal canal. The patient underwent thoracoscopic decompression of the L1 vertebral body, reconstruction with autologous iliac bone grafting, and instrumentation with the MACS TL system. Postoperative radiographs (▶ Fig. 26.6d) revealed excellent correction of the deformity. At 3 months’ follow-up, he was neurologically intact.

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26.8 Conclusion Thoracic vertebral decompression, reconstruction, and instrumentation can be safely and effectively performed using thoracoscopic techniques. Even the entire thoracolumbar junction can be accessed safely with minimal opening of the diaphragm. Although the procedure is technically demanding, earlier functional recovery and postoperative pain reduction can be achieved compared with conventional open thoracotomy or thoracoabdominal approaches.

Clinical Caveats ●

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The operative side of the thoracoscopic approach is determined on the basis of the location of the spine pathology and the anatomical idiosyncrasies of the great vessels. Careful and secure lateral positioning of the patient is essential to prevent any rotation and dislocation of the body during the

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operative procedure, which is often hardly detectable but may cause inadequate or incorrect placement of instruments. The surgeon should take time to carefully mark the section of the spine and the entry points of portals on the lateral thoracic wall. Importantly, the entry point for the working portals should be placed exactly over the pathology to be treated. As the system mostly provides two-dimensional imaging, angles and depth cannot be easily defined. Placing K-wires or screws under fluoroscopic control improves orientation throughout the procedure and offers the surgeon information about relative movements of the instruments in order to create a three-dimensional working environment. If decompression (trauma or thoracic disc herniation) is necessary, the surgeon should complete the partial corpectomy first, dissecting (a part of) the ipsilateral pedicle and removing the posterior wall fragment in a dorsoventral direction, away from the dura to the front. In order to avoid postoperative diaphragmatic hernia, we recommend suturing every incision longer than 2 cm at the attachment of the diaphragm. In finishing up the procedure, the operative site and thoracic cavity should be irrigated to prevent postoperative pleural effusion and adhesions. After removal of the fan-shaped retractor, insertion of the chest tube, and reinflation of the lung, check to ensure full inflation of all lobes of the lung under endoscopic view before the endoscope is removed.

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Anterior Thoracoscopic Vertebral Reconstruction and Instrumentation

References [1] Dajczman E, Gordon A, Kreisman H, Wolkove N. Long-term postthoracotomy pain. Chest. 1991; 99(2):270–274 [2] Kalso E, Perttunen K, Kaasinen S. Pain after thoracic surgery. Acta Anaesthesiol Scand. 1992; 36(1):96–100 [3] Khoo LT, Beisse R, Potulski M. Thoracoscopic-assisted treatment of thoracic and lumbar fractures: a series of 371 consecutive cases. Neurosurgery. 2002; 51(5) Suppl:S104–S117 [4] Beisse R, Verdú-López F. Current status of thoracoscopic surgery for thoracic and lumbar spine. Part 1: general aspects and treatment of fractures. Neurocirugia (Astur). 2014; 25(1):8–19 [5] Beisse R, Potulski M, Temme C, Bühren V. Endoscopically controlled division of the diaphragm. A minimally invasive approach to ventral management of thoracolumbar fractures of the spine. Unfallchirurg. 1998; 101(8):619–627

[6] Beisse R, Mückley T, Schmidt MH, Hauschild M, Bühren V. Surgical technique and results of endoscopic anterior spinal canal decompression. J Neurosurg Spine. 2005; 2(2):128–136 [7] Verdú-López F, Beisse R. Current status of thoracoscopic surgery for thoracic and lumbar spine. Part 2: treatment of the thoracic disc hernia, spinal deformities, spinal tumors, infections and miscellaneous. Neurocirugia (Astur). 2014; 25(2):62–72 [8] Reddi V, Clarke DV, Jr, Arlet V. Anterior thoracoscopic instrumentation in adolescent idiopathic scoliosis: a systematic review. Spine. 2008; 33 (18):1986–1994 [9] Lü G, Wang B, Li J, Liu W, Cheng I. Anterior debridement and reconstruction via thoracoscopy-assisted mini-open approach for the treatment of thoracic spinal tuberculosis: minimum 5-year follow-up. Eur Spine J. 2012; 21 (3):463–469

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27 Minimally Invasive Deformity Correction Neel Anand, Zeeshan M. Sardar, Andrea Simmonds, and Eli M. Baron Abstract Minimally invasive deformity correction techniques are evolving rapidly to aid in surgical treatment of adult spinal deformities. These techniques involve a combination of minimally invasive interbody fusion methods and percutaneous posterior pedicle screw and rod placement. Achieving a balanced spine in the coronal and sagittal planes is the ultimate goal of such surgery while aiming to reduce complications and readmissions. Minimally invasive techniques have the potential to reduce the risk of postoperative infections since muscle dissection is limited. Additionally, they may play a role in reducing the incidence of proximal junctional kyphosis as the posterior musculo-ligamentous tension band is preserved. This chapter provides a systematic approach for surgical correction of spinal deformities using minimally invasive techniques. Preoperative planning, intraoperative surgical techniques, and postoperative management including complication management are discussed. Keywords: minimally invasive surgery, percutaneous pedicle screws, transpsoas lateral interbody fusion, minimally invasive transforaminal lumbar interbody fusion

27.1 Introduction Adult spinal deformity (ASD) is defined by the SRS-Schwab classification as being a deformity in the coronal plane or the sagittal plane or both.1 In the coronal plane, a Cobb angle of more than 30 degrees is considered significant, whereas in the sagittal plane significant deformity includes a pelvic tilt (PT) greater than 20 degrees, sagittal vertical axis (SVA) greater than 4 cm, or pelvic incidence–lumbar lordosis (PI-LL) mismatch greater than 10 degrees. Traditionally, these deformities were treated surgically with open approaches. However, with a better understanding of anatomy, minimally invasive surgical (MIS) techniques have been used to successfully treat patients with ASD.2,3,4,5,6 Commonly used MIS techniques for spine deformity correction currently include anterior lumbar interbody fusion (ALIF), transforaminal lumbar interbody fusion (TLIF), lateral lumbar interbody fusion (LLIF), axial lumbar interbody fusion (AxiaLIF), and MIS posterior instrumentation and fusion (PSIF).3, 5,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23 Considering the high prevalence of ASD in the elderly population, it is important to assess these less invasive techniques that may offer a reduced risk of adverse events.2

27.2 Indications and Contraindications The spectrum of ASD treated with MIS techniques includes adult idiopathic scoliosis, adult degenerative scoliosis, iatrogenic spinal deformity, and posttraumatic deformity. Surgical correction is indicated in these patients when they have exhausted nonoperative measures such as physical therapy, epidural injections, and facet

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blocks, and still continue to have mechanical back pain related to the spinal deformity. Surgery is also indicated in these patients if they suffer from lumbar radiculopathy or neurogenic claudication. Another relative indication is progressively worsening deformity with pain as the rib cage abuts the pelvis. At present, we do not recommend the use of MIS techniques for correction of ASD when the preoperative SVA is greater than 100 mm, or when the preoperative PI-LL mismatch is greater than 38 degrees.24 We also do not use the MIS techniques for curves with a Cobb angle greater than 90 degrees, rigid kyphotic deformities with fused segments, and osteoporosis with T-score at the femoral neck of less than –2.0. However, as the MIS techniques for correction of spinal deformity continue to evolve, the applicability of MIS techniques to treat greater deformities will also improve.

27.3 Preoperative Planning 27.3.1 Physical Examination Preoperative evaluation of the patient with ASD begins with a thorough history and physical examination. Patients are asked about the existence of back pain, leg pain, and symptoms of neurogenic claudication. The intensity of the pain and the disability caused by it is important to quantify. Additionally, patients should be questioned about the existence of scoliosis in adolescence to differentiate between idiopathic scoliosis and de novo scoliosis. Physical examination is of prime importance in these patients. The patients should be appropriately disrobed to allow for evaluation of the spinal deformity. Examination should begin with inspection of the patient in the standing position with their hips and knees extended. Their overall coronal and sagittal balance is observed, as is their ability to bend laterally. Patients should be assessed for leg-length discrepancy to rule that out as a confounding problem. A complete neurological examination should be performed. Special attention should be paid to any signs of myelopathy to ensure that cervical spine pathology is addressed appropriately if it exists. For patients with neurogenic claudication, the peripheral vessels should be palpated. Finally, the hips and knees are examined to rule them out as causative agents of the leg or back pain.

27.3.2 Radiographic Workup and Preoperative Imaging All patients require 36-inch standing posteroanterior (PA) and lateral radiographs (▶ Fig. 27.1). The lateral films must include adequate visualization of the auditory meatus proximally and the femoral heads distally. The lateral radiographs are used to measure the pelvic parameters and the sagittal profile of the spine as follows: ● Sacral slope (SS): The angle between the end plate of S1 and the horizontal axis.

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Minimally Invasive Deformity Correction

Fig. 27.1 (a,b) Preoperative 36-inch standing films of a patient with adult spinal deformity (ASD).

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Pelvic tilt (PT): The angle between a line drawn from the center of the femoral head to the center of the S1 end plate, and a vertical line drawn from the center of the femoral head. Pelvic incidence (PI): The angle between a line drawn from the center of the femoral head to the center of the S1 end plate, and another line drawn perpendicular to the S1 end plate at the center of the S1 end plate. PI is a morphological parameter that does not change with position and can also be calculated using the formula PI = SS + PT. Lumbar lordosis (LL): The angle between the superior end plate of L1 and the end plate of S1. Pelvic incidence–lumbar lordosis (PI-LL): The difference between PI and LL. Thoracic kyphosis (TK): The angle between the superior end plate of T4 and the lower end plate of T12. Sagittal vertical axis (SVA): Horizontal distance from the posterosuperior corner of S1 to the C7 plumb line. A negative value denotes that the C7 plumb line is posterior to the posterosuperior corner of S1.

The PA radiographs are used to measure the Cobb angles of the thoracic, thoracolumbar, or lumbar curves in the coronal plane. When choosing the levels to instrument, we include all levels within the Cobb angle of a curve. Additionally, when the fusion crosses the thoracolumbar junction, we choose the upper instrumented vertebra (UIV) to be the vertebra below

the first normal parallel disc irrespective of whether it is at L1, T12, T11, or T10. A CT scan is also obtained frequently to assess for preexisting fusion between spinal segments (▶ Fig. 27.2). This is especially important in patients who have had previous surgeries at the involved segments. We also obtain a bone density scan on all patients older than 50 years and reserve the use of MIS techniques for those patients whose T-score at the femoral neck is higher than –2.0. An MRI scan is obtained on all patients preoperatively to assess for stenosis of the spinal canal and neuroforamens. Furthermore, the MRI scan is used to assess the location of the vena cava, the descending aorta, and the lumbar plexus to ensure that these vital structures are not harmed during the lateral approach to the spine. Based on our experience, the lateral approach for interbody fusion is contraindicated in the presence of a high-grade spondylolisthesis, especially at the L4–L5 segment as the nerve root crosses more anteriorly and is thus in the direct path of the approach. When using the AxiaLIF approach to fixate the L5–S1 level, it is imperative to obtain an MRI of the sacrum as well to evaluate the presacral space for any adhesions as well as to rule out any aberrant vasculature that may cross the midline on the anterior surface of the sacrum. The AxiaLIF procedure is not a part of our current algorithm for MIS treatment of adult spinal deformities. Finally, we carefully evaluate our patients for medical comorbidities and involve our medical team for preoperative optimization of their medical conditions.

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Fig. 27.2 (a,b) Coronal and sagittal cut of the CT scan of a patient with adult spinal deformity showing bridging osteophytes and fusion at the L2–L3 level.

27.3.3 Instrumentation

27.4.2 Stage 2

We use the Medtronic CD Horizon Longitude for percutaneous pedicle screw and rod placement. In our experience, this system is useful for multilevel placement of percutaneous pedicle screws and rods as it allows for gradual reduction of the spinal deformity via reduction screw extenders.

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27.4 Surgical Approach and Algorithm Our current minimally invasive approach is composed of three main components for correction of spinal deformity: ● Lateral transpsoas approach for discectomy, release, and fusion from T10 to L5. ● ALIF versus TLIF at L5–S1 and sometimes at L4–L5. ● Posterior multilevel percutaneous pedicle screw and rod placement. In carefully selected patients as mentioned in the “Indications and Contraindications” section, we have not found the need to perform posterior-based osteotomies to obtain sagittal or coronal balance. Our algorithm for MIS correction of spinal deformity is as follows:

27.4.1 Stage 1 ●

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Lateral transpsoas approach for discectomy, release, and fusion from T10 to L5 using 12-degree cages placed anteriorly. Sometimes the L4–L5 level cannot be addressed via the lateral approach. In those cases, it is then addressed in the second stage along with the L5–S1 level. We usually wait 2 to 3 days to perform the second stage of the surgery and obtain 36-inch standing radiographs prior to second stage to reassess the sagittal and coronal alignment (▶ Fig. 27.3). The crux of the reduction of the deformity takes place in the second stage during posterior instrumentation.

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If SVA is less than 5 cm and PI-LL is less than 10 degrees: MIS TLIF at L5–S1 and at L4–L5 if needed. If SVA between 5 and 10 cm and PI-LL between 10 and –40 degrees: ALIF at L5–S1 and at L4–L5 if needed. If SVA is greater than 10 cm or PI-LL is greater than 40 degrees: Posterior osteotomies may need to be performed. We have not encountered the need to perform osteotomies in patients selected according to the criteria mentioned in the “Indications and Contraindications” section. This is followed by posterior multilevel percutaneous pedicle screw and rod placement.

27.5 Surgical Technique 27.5.1 Transpsoas Discectomy and Fusion Patient Positioning The patient is positioned on a radiolucent sliding table with a kidney rest in the right lateral decubitus position with the left side up. We almost exclusively perform the transpsoas approach through the left side as there is an increased risk of injury to the great vessels when approached from the right side, especially at L4–L5.25 The iliac crests of the patient are positioned just below the level of the kidney rest. The kidney rest is then elevated maximally to increase the distance between the rib cage and the iliac crest. An axillary pad is placed in the right axilla, while the left arm is secured on an elevated arm rest. The left hip is flexed to relax the psoas muscle and the femoral nerve. Extra padding is placed over the bony prominence of the fibular head to minimize risk of peroneal nerve palsy. Finally, the patient is secured to the table using bolsters and strapping tape (▶ Fig. 27.4).

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Minimally Invasive Deformity Correction

Fig. 27.3 Thirty-six-inch standing (a) anteroposterior and (b) lateral plain films of a patient after L1–L5 lateral interbody fusions.

Fig. 27.4 Back view of a patient positioned for the lateral interbody fusion technique.

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Incision

Step-by-Step Surgical Technique

A mini C-arm is then used in the lateral plane to localize the incision for accessing the appropriate disc space. We usually use one skin incision per two disc spaces. However, separate fascial incisions are used for each disc space to allow direct access. Using the C-arm, the skin is marked over the anterior third of the disc space of the two discs involved.26 An oblique incision is then planned in the direction of the external oblique muscle that connects the two marks to grant access to the two disc spaces (▶ Fig. 27.5 and ▶ Fig. 27.6).

We start the lateral interbody fusions with the L4–L5 level and then proceed proximally. The skin incision is marked as earlier and a scalpel is used to incise the skin. A monopolar cautery is then used to coagulate subcutaneous vessels. Blunt finger dissection is then used to identify Petit’s triangle at the top of the iliac crest. The retroperitoneal space is entered through Petit’s triangle and the inner table of the iliac crest can be felt. The retroperitoneal fat is then swept from posterior to anterior with swiping motions of the finger. The contents of the retroperitoneal space are thus displaced anteriorly and the space between the rib cage and iliac crest is cleared for insertion of retractors. The patient is monitored with continuous free-running electromyography (EMG) at all times. The percutaneous access kit (PAK) probe is then placed over the junction of the middle and anterior third of the disc space under fluoroscopic guidance. Once appropriate position is confirmed, the probe is advanced through the psoas muscle and placed over the disc space and the position is confirmed again with fluoroscopy. A guide wire is then placed through the probe into the disc space. A PA image is then taken to ensure proper positioning of the guide wire in the coronal plane. The guide wire is inserted to roughly 50% depth of the disc space under PA fluoroscopic guidance. Sequential dilators are then placed over the guide wire, followed by placement of an appropriately sized expanding tubular retractor. A stimulating probe with triggered EMG is then used to check the area visualized under the retractor. If a nerve is encountered directly in the path of the interbody cage placement, we abandon the procedure for that specific disc level. Once the disc is adequately visualized through the retractor, a discectomy is performed using a no. 15 blade for the initial annulotomy, followed by a series of Cobb elevators, rasps, curettes, and pituitaries to excise the disc and prepare the end plates. Care must be taken to avoid damaging the end plates. Serial trials are then performed and an appropriately sized polyetheretherketone (PEEK) 12-degree lordotic spacer packed with rhBMP-2/ACS (INFUSE, Medtronic Sofamor Danek, Memphis,

Fig. 27.5 Fluoroscopic image used to plan the skin incision for the lateral interbody fusion.

Fig. 27.6 Oblique skin incision for the lateral interbody fusion.

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Minimally Invasive Deformity Correction TN) and Grafton Putty demineralized bone matrix (DBM; Osteotech, Eatontown, New Jersey) is inserted into the disc space. We use about 3 mg of recombinant human bone morphogenetic protein-2 (rhBMP-2) in each spacer. The position of the spacer is then checked in the PA and lateral planes prior to removal of the insertion handle to allow for any last-minute adjustments to be made. We inject 1 mg of Decadron over the psoas at each disc space after insertion of the spacer to decrease muscle and nerve inflammation due to retraction. The retractor is then gradually removed under visualization to confirm lack of bleeding. This technique is repeated for each disc level as we proceed proximally. As mentioned earlier, two disc spaces are accessed per skin incision. The diaphragm may need to be displaced upward at the T12–L1 level, whereas at the T11–T12 level, the diaphragm may need to be displaced downward as the access is through the chest cavity. When working in the chest cavity, the anesthesiologist is asked to hold expirations until the retractors are in place. For closure on the pleura, a red tube catheter is inserted into the chest cavity and watertight closure is performed around it. A purse-string suture is lastly placed around the red tube catheter and the anesthesiologist is requested to perform a Valsalva maneuver as the red tube catheter, while on suction, is removed. A purse-string suture around the red rubber catheter is closed simultaneously with removal to prevent air leakage into the pleural cavity. Using this technique, we have not had to use a chest tube in our patients. However, we still get a chest X-ray postoperatively to ensure the absence of a significant pneumothorax.

Closure The fascia over the external oblique muscle is closed with interrupted absorbable sutures, followed by closure of the subcutaneous tissues and the skin.

27.5.2 Percutaneous Pedicle Screw and Rod Placement Patient Positioning The patient is positioned prone on a Jackson spinal table and the bony prominences are padded appropriately. The abdomen should be free hanging to prevent venous vascular congestion. This helps reduce surgical bleeding.

Incision Two options exist for making the skin incision in these cases: ● A single midline incision extending the entire length of the fusion. The subcutaneous tissues are then undermined to retract laterally. Individual fascial incisions are then made paramedian as needed for screw insertion. ● The second option is to use multiple paramedian skin and fascial incisions for percutaneous screw insertions.

Step-by-Step Surgical Technique The pedicle screws for the levels to be instrumented are placed using the percutaneous technique of your preference. In the past, we used fluoroscopy to percutaneously insert all the

Fig. 27.7 Cannulated pedicle screws in place with attached reduction screw extenders.

pedicle screws. However, we have recently switched to using the O-arm surgical imaging with StealthStation navigation for placement of pedicle screws. Regardless of the method of screw insertion used, a cannulated pedicle screw with an attached reduction screw extender is placed (▶ Fig. 27.7). We prefer to use tricortical fixation for sacral screws.27 In cases where the fusion extends down to the sacrum, we also prefer to use at least one iliac screw on the side of the concavity of the lumbar curve. The iliac screw can be placed using navigation or the teardrop view if using fluoroscopy. Once all the screws with the extenders are in place, the length of the rod is measured. We usually use the cord of the cautery to measure the rod length. Attention must be paid to choose the right length that would accommodate the curvature of the spine. Bending of the rod is then performed. Appropriate bending of the rod to recreate LL and TK is a critical step that will aid in correcting the deformity (▶ Fig. 27.8). Once the rod is measured and bent, it is introduced into the reduction screw extenders deep to the fascia in a proximal-to-distal fashion. The extenders can be controlled and manipulated as the rod makes its way through all the extenders. The length of the rod is again checked at this point. The extenders are then sequentially and gradually reduced, working from distal to proximal until the rod is completely reduced into the tulips of all screws. It is very important to maintain the rod in a strict sagittal orientation as the reduction maneuver is being performed to allow for correction of the spinal deformity. The extenders are also used to perform derotation of the vertebral segments as rod reduction is being performed. It is important to perform rod reduction under fluoroscopic guidance to ensure that the pedicle screws are not pulled out during this step, especially in osteoporotic patients. Once correction and fixation with the rods and screws has been achieved, bilateral facet joint fusion is performed for the segments that were not fused with an interbody device. This is typically performed in the thoracic and sometimes the thoracolumbar spine. To achieve facet fusion, a speculum device is introduced through the incisions for the pedicle screws to gain exposure to the facet joints. Decortication of the pars and facet joints at those levels is then performed. A total of 1 to 1.5 mg of rhBMP-2 mixed with Grafton putty is then placed along each joint.

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Fig. 27.8 Contouring of the rod to regain appropriate spinal balance.

Closure Closure of the incisions is then performed in a typical fashion using absorbable interrupted sutures for closure of the fascia, subcutaneous tissues, and finally the skin.

Postoperative Care

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In the immediate postoperative period, the patients are seen by physical therapy and occupational therapy in the hospital to gradually help them mobilize. A brace is not used by these patients. The use of narcotics is limited to avoid post-op ileus. In the first 4 to 6 weeks, the patients are advised against heavy lifting, or strenuous exercises. ●

Management of Complications MIS techniques offer the potential for reducing the morbidity associated with open surgeries. They have been shown to result in lower rates of infection, blood loss, and muscle dysfunction.28,29,30,31 However, MIS procedures are still associated with major complications. We recently performed a retrospective review of 214 patients with ASD treated by us with circumferential MIS techniques. We noted an 8.9% rate of major complications occurring in the 30-day period following surgery that included ureteropelvic junction injuries, incidental durotomies, iliac vein injury during ALIF, wound dehiscence, pedicle screw loosening or cutout requiring instrumentation revision, deep vein thrombosis, pulmonary embolism, cerebellar hemorrhage, and radiculopathy from foraminal stenosis. Complications specific to MIS techniques and their management are listed below.

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Ureteropelvic junction injury ○ This injury should be suspected if blood is seen in the urinary catheter postsurgery. The ureter and renal pelvis are susceptible to injury during the lateral transpsoas approach, especially in patients with idiopathic scoliosis who can have significant rotation of the vertebral segments, thus causing the ureter to be in close proximity to the approach. The diagnosis can be made with a CT urogram

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or a nuclear renal scan. These cases require urology consultation and are usually treated with placement of a temporary ureteral stent with no permanent sequelae. In the rare event of a complete transection of the ureter, a delayed ureteral reconstruction may need to be performed. Pleural effusions ○ It is not uncommon for patients to develop small pleural effusions if the lateral approach was above the thoracolumbar junction as the chest cavity is entered in these cases. In general, these small effusions are of little clinical significance. However, in rare cases a significant pleural effusion can develop and may need to be managed with thoracocentesis. Iliac vein injury ○ The iliac vein is susceptible to injury during the anterior approach. The anterior approach is generally performed by a vascular surgeon and if iliac vein injury is encountered, it is treated with vascular repair and control of the bleeding. Quadriceps Palsy ○ Quadriceps palsy is usually a transient neurapraxia due to stretching that resolves within 6 months. A course of physical therapy is recommended. Rarely, permanent damage can occur if direct injury to the nerve is caused during the approach.

27.6 Clinical Case A 56-year-old female teacher presented to the clinic complaining of mid and low back pain that had been worsening for 2 years. The patient had been diagnosed with scoliosis at age 20 years at which time the thoracic curve was 30 degrees. The patient described the pain as a severe sharp constant pain that was aggravated with any activity. She had tried nonoperative therapies such as physical therapy, heat therapy, and anti-inflammatory medications without good pain relief. On physical examination, she had a normal neurological examination. However, she had significant pain with flexion or extension of her back. She was noted to have a significant right-sided rib hump. Her right shoulder was slightly elevated compared to the left shoulder. She was also noted to have waistline asymmetry.

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Minimally Invasive Deformity Correction

Fig. 27.9 (a) Standing posteroanterior (PA) and lateral radiographs of a patient with adult spinal deformity prior to surgery. (b) Standing PA and lateral radiographs of the patient after T12–L5 lateral interbody fusion. (c) Final standing PA and lateral radiographs of the patient after correction of the deformity.

Standing 36-inch radiographs are displayed in ▶ Fig. 27.9a and show a right-sided thoracic curve and a left-sided lumbar curve. Decision was made to perform a fusion from T4 to L5. As the first stage, a lateral interbody fusion was performed from T12 to L5. Standing radiographs were obtained on postoperative day 2 (▶ Fig. 27.9b). As can be seen in the radiographs, the deformity in the coronal plane is not corrected after the lateral interbody fusion. The main goals of the lateral interbody fusion are to release the intervertebral space and to add a spacer for interbody fusion. The patient then underwent percutaneous pedicle screw placement and reduction using a rod on the third day. The second stage is where the reduction of the deformity is performed with the aid of properly contoured rods. The final standing radiographs demonstrating deformity correction are shown in ▶ Fig. 27.9c.

27.7 Conclusion Circumferential minimally invasive techniques are capable of surgically correcting adult spinal deformities effectively in wellselected patients. However, attention to detail is necessary in obtaining the desired outcomes.

Clinical Caveats ●

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We caution against using circumferentially minimally invasive techniques for correction of adult spinal deformities in osteoporotic patients with a T-value of less than –2.0. A left-sided approach is preferred for transpsoas discectomy and fusion to avoid injury to the major vessels. In the face of a high-grade spondylolisthesis, the transpsoas approach is not recommended, especially at the L4–L5 levels. Rod contouring and reduction is critical in obtaining reduction of the spinal deformity.

References [1] Schwab F, Ungar B, Blondel B, et al. Scoliosis Research Society-Schwab adult spinal deformity classification: a validation study. Spine. 2012; 37 (12):1077–1082 [2] Haque RM, Mundis GM, Jr, Ahmed Y, et al. International Spine Study Group. Comparison of radiographic results after minimally invasive, hybrid, and open surgery for adult spinal deformity: a multicenter study of 184 patients. Neurosurg Focus. 2014; 36(5):E13 [3] Anand N, Baron EM, Khandehroo B. Does minimally invasive transsacral fixation provide anterior column support in adult scoliosis? Clin Orthop Relat Res. 2014; 472(6):1769–1775 [4] Anand N, Baron EM, Khandehroo B, Kahwaty S. Long-term 2- to 5-year clinical and functional outcomes of minimally invasive surgery for adult scoliosis. Spine. 2013; 38(18):1566–1575 [5] Anand N, Baron EM. Minimally invasive approaches for the correction of adult spinal deformity. Eur Spine J. 2013; 22 Suppl 2:S232–S241 [6] Bach K, Ahmadian A, Deukmedjian A, Uribe JS. Minimally invasive surgical techniques in adult degenerative spinal deformity: a systematic review. Clin Orthop Relat Res. 2014; 472(6):1749–1761 [7] Wong AP, Smith ZA, Stadler JA, III, et al. Minimally invasive transforaminal lumbar interbody fusion (MI-TLIF): surgical technique, long-term 4-year prospective outcomes, and complications compared with an open TLIF cohort. Neurosurg Clin N Am. 2014; 25(2):279–304 [8] Terman SW, Yee TJ, Lau D, Khan AA, La Marca F, Park P. Minimally invasive versus open transforaminal lumbar interbody fusion: comparison of clinical outcomes among obese patients. J Neurosurg Spine. 2014; 20(6):644–652 [9] Schwender JD, Holly LT, Rouben DP, Foley KT. Minimally invasive transforaminal lumbar interbody fusion (TLIF): technical feasibility and initial results. J Spinal Disord Tech. 2005; 18 Suppl:S1–S6 [10] Park Y, Ha JW, Lee YT, Sung NY. Minimally invasive transforaminal lumbar interbody fusion for spondylolisthesis and degenerative spondylosis: 5-year results. Clin Orthop Relat Res. 2014; 472(6):1813–1823 [11] Nandyala SV, Fineberg SJ, Pelton M, Singh K. Minimally invasive transforaminal lumbar interbody fusion: one surgeon’s learning curve. Spine J. 2014; 14 (8):1460–1465 [12] Luo P, Wu J, Mao GY. Pedicle screw fixation in minimally invasive transforaminal lumbar interbody fusion. Neurosurg Focus. 2014; 36(6):1 [13] Kimball J, Yew A, Getachew R, Lu DC. Minimally invasive tubular surgery for transforaminal lumbar interbody fusion. Neurosurg Focus. 2013; 35(2) Suppl:Video 19 [14] Yuan PS, Rowshan K, Verma RB, Miller LE, Block JE. Minimally invasive lateral lumbar interbody fusion with direct psoas visualization. J Orthop Surg. 2014; 9:20

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Surgical Techniques [15] Youssef JA, McAfee PC, Patty CA, et al. Minimally invasive surgery: lateral approach interbody fusion: results and review. Spine. 2010; 35(26) Suppl: S302–S311 [16] Kotwal S, Kawaguchi S, Lebl D, et al. Minimally invasive lateral lumbar interbody fusion: clinical and radiographic outcome at a minimum 2-year followup. J Spinal Disord Tech. 2015; 28(4):119–125 [17] Amin BY, Mummaneni PV, Ibrahim T, Zouzias A, Uribe J. Four-level minimally invasive lateral interbody fusion for treatment of degenerative scoliosis. Neurosurg Focus. 2013; 35(2) Suppl:Video 10 [18] Ahmadian A, Verma S, Mundis GM, Jr, Oskouian RJ, Jr, Smith DA, Uribe JS. Minimally invasive lateral retroperitoneal transpsoas interbody fusion for L4–5 spondylolisthesis: clinical outcomes. J Neurosurg Spine. 2013; 19(3):314–320 [19] Alimi M, Hofstetter CP, Cong GT, et al. Radiological and clinical outcomes following extreme lateral interbody fusion. J Neurosurg Spine. 2014; 20(6):623–635 [20] Tobler WD, Melgar MA, Raley TJ, Anand N, Miller LE, Nasca RJ. Clinical and radiographic outcomes with L4-S1 axial lumbar interbody fusion (AxiaLIF) and posterior instrumentation: a multicenter study. Med Devices (Auckl). 2013; 6:155–161 [21] Aryan HE, Newman CB, Gold JJ, Acosta FL, Jr, Coover C, Ames CP. Percutaneous axial lumbar interbody fusion (AxiaLIF) of the L5-S1 segment: initial clinical and radiographic experience. Minim Invasive Neurosurg. 2008; 51(4):225–230 [22] Wang MY. Percutaneous iliac screws for minimally invasive spinal deformity surgery. Minim Invasive Surg. 2012; 2012:173685 [23] Kepler CK, Yu AL, Gruskay JA, et al. Comparison of open and minimally invasive techniques for posterior lumbar instrumentation and fusion after open anterior lumbar interbody fusion. Spine J. 2013; 13(5):489–497

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[24] Anand N, Baron EM, Khandehroo B. Limitations and ceiling effects with circumferential minimally invasive correction techniques for adult scoliosis: analysis of radiological outcomes over a 7-year experience. Neurosurg Focus. 2014; 36(5):E14 [25] Kepler CK, Bogner EA, Herzog RJ, Huang RC. Anatomy of the psoas muscle and lumbar plexus with respect to the surgical approach for lateral transpsoas interbody fusion. Eur Spine J. 2011; 20(4):550–556 [26] Moro T, Kikuchi S, Konno S, Yaginuma H. An anatomic study of the lumbar plexus with respect to retroperitoneal endoscopic surgery. Spine. 2003; 28 (5):423–428, discussion 427–428 [27] Lehman RA, Jr, Kuklo TR, Belmont PJ, Jr, Andersen RC, Polly DW, Jr. Advantage of pedicle screw fixation directed into the apex of the sacral promontory over bicortical fixation: a biomechanical analysis. Spine. 2002; 27(8):806–811 [28] Anand N, Baron EM, Bray RS, Jr. Benefits of the paraspinal muscle-sparing approach versus the conventional midline approach for posterior nonfusion stabilization: comparative analysis of clinical and functional outcomes. SAS J. 2007; 1(3):93–99 [29] Parker SL, Adogwa O, Witham TF, Aaronson OS, Cheng J, McGirt MJ. Post-operative infection after minimally invasive versus open transforaminal lumbar interbody fusion (TLIF): literature review and cost analysis. Minim Invasive Neurosurg. 2011; 54(1):33–37 [30] O’Toole JE, Eichholz KM, Fessler RG. Surgical site infection rates after minimally invasive spinal surgery. J Neurosurg Spine. 2009; 11(4):471–476 [31] Anand N, Baron EM, Khandehroo B. Is circumferential minimally invasive surgery effective in the treatment of moderate adult idiopathic scoliosis? Clin Orthop Relat Res. 2014; 472(6):1762–1768

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Minimally Invasive Treatment of Thoracic and Thoracolumbar Idiopathic Scoliosis

28 Minimally Invasive Treatment of Thoracic and Thoracolumbar Idiopathic Scoliosis Peter F. Picetti, Alexander R. Vaccaro, Zachary D. Patterson, David L. Downs, and George D. Picetti III Abstract This chapter will describe a new minimally invasive approach for treating single overhang thoracic and thoracolumbar curves. The authors describe the evolution of this new technique through a detailed description of preoperative planning, the actual surgical procedure, and the postoperative care. Case reports and the initial series are included, which demonstrate improved results and decreased complications as the technique has evolved. Keywords: thoracoscopic minimally invasive scoliosis, one-lung ventilation

28.1 Introduction Minimally invasive techniques have permitted access to the anterior spinal column without a thoracotomy and its associated potential risk. Surgical approaches may change, but the technical procedure and operative goals remain the same. Thoracoscopic treatment of lung diseases has been used since Jacobaeus’ work in the early 1900s.1 In the early 1990s, Regan et al2 presented their work on thoracoscopic treatment of spinal disease in Dublin, Ireland. Rosenthal et al3 were the first in print with their technique of thoracic discectomy in 1994. Pollock et al4 evaluated the efficacy of thoracoscopic release and posterior fusion versus open release and posterior fusion, and found no statistical difference in correction of Cobb angle. Other studies followed with expanded indications for thoracoscopic surgery in deformity.5 Development of endoscopic treatments for spinal disorders began in 1993.2,3 Initial efforts focused on techniques for release and fusion for kyphosis and scoliosis, followed by an endoscopic technique for hemiepiphysiodesis and hemivertebrectomy for congenital scoliosis. After having performed more than 150 endoscopic procedures for release and fusion for spinal deformities in the mid1990s, we set out to develop an endoscopic technique for the instrumentation, correction, and fusion of primary thoracic scoliosis. We performed our first entirely endoscopic instrumentation, correction, and fusion for thoracic scoliosis in October 1996. The goal of this technology in the surgical treatment of idiopathic scoliosis is to perform a safe, reproducible, and effective procedure that results in spinal alignment improvement and balance in all planes and axial derotation comparable to, or better than, that obtained with an open procedure. Over time, the surgical technique and times have progressively improved with curve correction outcomes similar to open methods, but with the benefits of less soft-tissue disruption and less time to functional recuperation. Once this was accomplished, our next goal was to develop a minimally invasive approach for the treatment of thoracolumbar scoliosis. Challenges to this technique include endoscopically crossing the diaphragm, maintaining

retroperitoneal exposure, and attaining and maintaining lumbar lordosis with the use of structural grafting.

28.2 Indications and Preoperative Planning The endoscopic technique is indicated for single-overhang primary thoracic scoliosis, Lenke type 1A or 1B curve pattern for the direct thoracoscopic technique, and Lenke type 5C curve pattern for the minimally invasive combined approach. These curve patterns can be safely addressed as an isolated fusion without the risk of spinal imbalance.6 However, if the patient is kyphotic with this curve pattern, then this technique should not be performed. Because the anterior growth plates are removed with the discectomy and fusion, no further growth can take place. In contrast, the posterior elements continue to grow and an exaggerated kyphosis will result. The technique is contraindicated for double major curves. Finally, this procedure should not be attempted in patients who are not able to tolerate single-lung ventilation. Patients are selected on the basis of progressive scoliosis and curve type. All curves should be Lenke type 1A, 1B, or 5C.6 Patients are evaluated for pelvic obliquity, waist crease, shoulder height difference, degree of rotation, flexibility, and sagittal balance. Complete histories are obtained and all patients undergo physical examination; in addition, 36-inch posteroanterior, lateral, and lateral bending radiographs are obtained. Cobb angles are marked in the standard fashion.

28.3 Surgical Technique Patient positioning and port placement and anesthesia are the same for both procedures. Early on, we struggled with selecting the optimal location for port placement. In planning for a long fusion, accurate port placement is critical. If placed inappropriately, the port sites are levered against the ribs, and a significant amount of pressure and trauma may be inflicted on the intercostal neurovascular bundle. Patients may complain of postoperative dysesthesia over the anterior chest wall, which can last from weeks to 6 months. Early in the series, port placement was determined by visually compensating for the angle of rotation, which results in suboptimal locations. With the use of Carm fluoroscopy, ports can be placed with great accuracy. As our port placement improved, we no longer saw cases of chest wall numbness and wound issues. General anesthesia is administered by means of double-lumen intubation in children weighing more than 45 kg. Children weighing less than 45 kg often require selective intubation of the ventilated lung. The patient is then placed in the direct lateral decubitus position, with the arms forward and elevated at 90 degrees and the elbows flexed at 90 degrees. Hips and shoulders are taped to

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Surgical Techniques the operating table, which helps maintain the patient’s correct position throughout the procedure. The C-arm is then used to mark the levels, port sites, and the mini-open site below the diaphragm for the thoracolumbar approach. Port site placement is key for the procedures. The ports are placed to enable the surgeon to reach the superior and inferior levels of the spine to be instrumented. The C-arm is used to identify the levels as well as to assist in positioning in the anteroposterior plane, correcting for spinal rotation (▶ Fig. 28.1). Thoracic surgery assistance is required initially. Two endoscopic monitors are used: one monitor faces the patient and the other monitor is placed posterior to the patient and spine surgeon to allow visualization for the thoracic surgeon. The spine surgeon is positioned at the patient’s back. This positioning allows all instruments to be directed away from the spinal cord. Standing behind the patient also orients the surgeon in the same direction as the endoscopic view, thereby avoiding the necessity to navigate the external landmarks of the ribs and spine to a mirror image on the screen. Patient positioning is checked to confirm a direct lateral decubitus position, with the concave side of the curve down. The orientation provides a reference to gauge the anteroposterior and lateral direction of guide wires and screws. After lung deflation, the initial port is usually placed in the sixth or seventh interspace in line with the spine for the thoracic curves and positioned according to the amount of spinal rotation. The superior-most portal is selected first for the thoracolumbar curves. Preoperatively, the initial skin incision mark is placed with the aid of the C-arm. Inserting the first port at this level will avoid injury to the diaphragm, which is normally more caudal. Once the port is placed, digital inspection of the port is made to ensure that the lung is deflated and no adhesions exist. The endoscope is then inserted into the chest, and additional ports are placed under direct visualization. Port incisions are usually made directly over the ribs, two interspaces apart. This allows port placement above and below the rib at each level, enabling a surgeon to reach two levels through a single skin incision. Three or four incisions are used for the thoracic curves and three for the thoracolumbar, depending on the number of levels to be instrumented. The ports are 10.5 to 11.0 mm in size.

28.3.1 Exposure and Discectomy The pleura is incised longitudinally along the entire length of the spine to be instrumented. The pleura is dissected off the spine (vertebral bodies and discs) from the anterior longitudinal ligament anteriorly to the rib heads posteriorly (▶ Fig. 28.2). Next, the electrocautery is used to incise the disc annulus. The disc is removed in standard fashion using various endoscopic instruments. Once the disc is completely removed, the anterior longitudinal ligament is thinned from within the disc with a pituitary rongeur. The ligament is thinned to a flexible remnant that is no longer structural but is still able to contain the bone grafts. The disc and annulus are removed posteriorly to the rib head. Once the disc is evacuated and the end plate is completely removed, the disc space is inspected directly with the endoscope (▶ Fig. 28.3). The end plates are then rasped to a homogeneous bleeding surface, and the disc space is packed with Surgicel to control end-plate bleeding. All of the thoracic discs are removed in this fashion. For the thoracolumbar curves, the T12–L1 disc can be removed from the thoracic cavity depending on where the diaphragm inserts. If the diaphragm inserts below the T12–L1 disc space, the

Fig. 28.2 Intraoperative view through the endoscope showing the hooked Bovie incising the pleura cephalad to caudad along the axis of the spine over the middle of the vertebral bodies.

Fig. 28.1 (a) The C-arm is placed in the posteroanterior plane at the distal level to be instrumented with a rod as a marker. A skin marker is used to mark the levels to be instrumented. (b) Posteroanterior C-arm image of the rod marker parallel to the end plates of the distal level. (c) The C-arm in position in the lateral plane using the rod marker to determine the port location.

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Minimally Invasive Treatment of Thoracic and Thoracolumbar Idiopathic Scoliosis exposure of the disc does not require taking down the diaphragm. Conversely, if the diaphragm inserts above the disc space, then the disc is removed from the retroperitoneal approach below the diaphragm. The lumbar retroperitoneal approach is next performed for the thoracolumbar curves. This is accomplished via an 11th rib approach. In cases where the instrumentation is planned to extend down to L2, the skin is marked over the L1–L2 disc space. This allows for surgical access from the T12–L1 disc space to the L2 vertebral body. If the instrumentation is planned to extend down to L3, the skin is marked over the center of the L2 vertebral body. This allows for surgical access from the L1 disc vertebral body to the L2 vertebral body. If the instrumentation is to extend only to L1, a retroperitoneal approach may be performed to access the T12–L1 disc space and the L1 vertebral body. The surgical approach to L1 is usually initially attempted through the thoracic cavity. This, however, can lead to extensive retraction of the diaphragm.

In performing the retroperitoneal approach, a 3-cm incision is performed over the previously determined skin incision site to expose the 11th rib. The 11th rib is exposed by mobilizing the incision as far anteriorly and posteriorly as possible. Once the rib has been subperiosteally dissected, it is removed with the endoscopic rib cutter. This is accomplished by freeing the rib anteriorly from the soft tissue and placing the jaw of the rib cutter under the rib and the foot over the top and sliding the rib cutter as posteriorly as possible. Once this is done, the rib is amputated. Using this technique, almost the entire rib can be harvested for bone graft (▶ Fig. 28.4). Dissection is then carried under the T12 rib, through the oblique muscles into the retroperitoneal space and onto the psoas, spine, and diaphragm. Spinal retractors are placed. A plane is developed between the line of the crus of the diaphragm and the psoas. The psoas is retracted posteriorly, and the discs and end plates are exposed and removed in the standard fashion. Once all the discs have been removed, more graft may be harvested via the thoracic portals.

28.3.2 Graft Harvest

Fig. 28.3 Intraoperative view through the endoscope of a completed discectomy; the opposite side annulus is visible, and the complete cartilaginous end plate removal of both vertebral bodies is seen.

Ports are removed after completion of the discectomies. Next, the rib graft is harvested. Handheld retractors are used to expose each rib to be harvested. The port site is retracted anteriorly as far as possible, and the rib is dissected subperiosteally. Dissection is carried posteriorly as far as the port site can be retracted. Using the endoscopic rib cutter, two incisions 8 to 10 cm apart are made on the superior aspect of the rib. These incisions are perpendicular to the rib and extend only halfway across the rib. An osteotome is used to cut through the rib along the longitudinal axis until the perpendicular incisions are connected. The rib section is removed and morselized. Other rib sections are removed until sufficient bone graft has been harvested. This technique produces adequate amounts of graft and preserves the lower half of each rib, thus protecting the intercostal nerve and decreas-

Fig. 28.4 (a) The 3-cm incision is made over the 11th rib. (b) The rib is subperiosteally dissected. (c) The rib has been amputated anteriorly and is ready for removal with the endoscopic rib cutter.

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Surgical Techniques ing postoperative pain. The graft harvest is performed at this time to limit the stress placed on the remaining rib. For the thoracolumbar curves, the disc spaces of the lower thoracic and lumbar are sized for structural graft application. Femoral rings are cut and contoured into a tapered shape to produce the desired lordosis, kyphosis, or neutral alignment at each level. The contoured grafts are packed with the morselized rib graft and impacted into the respective disc spaces (▶ Fig. 28.5). The degree of lumbar graft angulation or taper is decreased as they are placed at more proximal levels. At times, the lower thoracic vertebrae are of a size that accommodates a smaller structural graft such as a humeral ring rather than a femoral ring. An alternative to allograft is metal or synthetic cages. These also provide anterior column support and can be used to produce the desired degree of lordosis or kyphosis.

28.3.3 Screw Placement The segmental vessels, which have not been disturbed until now, are grasped at midvertebral body level and cauterized with the electrocautery. The Kirschner wire (K-wire) guide is placed onto the vertebral body just anterior to the rib head. The position is then checked with the C-arm to be sure the wire will be parallel to the end plates and in the center of the body. Next, the inclination of the guide is checked in the lateral plane by examining the chest wall and rotation (▶ Fig. 28.6a, b). The guide should be in a slightly posterior to anterior inclination; this will direct the K-wire away from the spinal canal. If any concern arises as to the K-wire placement in the lateral plane, a lateral image with the C-arm can be obtained to confirm the location. Once the guide is correctly aligned, the K-wire is inserted into the appropriate cannula and drilled into the vertebral body parallel to the end plates to the opposite cortex. Care must be taken when

placing screws transcortically to avoid segmental vessel injury on the opposite side. The position is confirmed with C-arm fluoroscopy as the wire is being inserted. The length of the K-wire in the vertebral body can be determined by a scale on the upper section of the K-wire at the top of the guide. The guide is removed, and the staple awl guide is placed over the K-wire. The awl is used to make a starting point in the vertebral body and the staple is tapped and placed over the K-wire. The K-wire is grasped and held to prevent migration. The staple awl guide is removed and the tap is placed over the K-wire and the near cortex of the vertebral body is tapped as the K-wire is held in place. The appropriate-sized screw is placed over the K-wire and advanced. The wire is again grasped to keep it from advancing while the screw is being inserted. The wire is removed when the screw is approximately three-fourths of the way across the vertebral body. The screw direction can be checked with the Carm as it is advanced and seated against the vertebral body (▶ Fig. 28.7a–c). The screw should penetrate the opposite cortex for bicortical purchase. Using the rib heads as a reference for subsequent screw placement helps ensure that the screws are in line and yield proper spinal rotation. If each screw is placed in the same position and orientation on each vertebral body, also accounting for rotation, the screws will align in a V pattern and will aid in derotation of the spine during rod placement. If a screw is inserted more than a few millimeters deeper than the rest of the screws, reduction of the rod into the screw head may be difficult. Once all the screws have been placed, the Surgicel is removed and the graft is inserted in those discs that do not already contain a structural graft. This is the most important part of the operation. A small amount of graft is inserted into the disc space, and the rasp is then used to push the graft all the way to the opposite side. The disc is completely “backfilled” in this fashion. The periosteum is elevated on the edges of the vertebral bodies, and a

Fig. 28.5 (a) The femoral ring allograft has been cut, contoured, filled with morselized autograft, and placed into the T12–L1 disc space; the diaphragm is to the left of the graft. (b) The graft is now in its final position.

Fig. 28.6 (a) Intraoperative view through the endoscope of the K-wire guide positioned on the vertebral body parallel to the end plate ready for the K-wire to be inserted. (b) Intraoperative view through the endoscope of the K-wire inserted into the vertebral body.

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Minimally Invasive Treatment of Thoracic and Thoracolumbar Idiopathic Scoliosis

Fig. 28.7 (a) Intraoperative view through the endoscope of the K-wire guide positioned on the vertebral body. (b) Intraoperative C-arm image of the K-wire in the vertebra body. (c) Intraoperative view through the endoscope of the staple awl guide over the K-wire onto the vertebral body. (d) Intraoperative view of the tap over the K-wire. (e) Intraoperative view through the endoscope of the dual-head screw over the K-wire ready for insertion.

Fig. 28.8 (a) Intraoperative view through the endoscope showing a small amount of graft inserted into the disc space before using the rasp to push the graft all the way to the opposite side. (b) The disc is completely filled, the periosteum has been elevated, and a mound of graft is placed over the disc space and the edges of the vertebral bodies.

mound of graft is placed over the disc space and the edges of the vertebral bodies (▶ Fig. 28.8). Rod length is determined with the endoscopic rod measurer, which is a cable that slides through a fixed end that is used as a scale. The free end of the cable is placed into the proximal screw and the fixed end is placed in the inferior screw. As the cable is pulled tight, a reading is taken from the provided scale to determine rod length (▶ Fig. 28.9). In treating thoracolumbar curves, the procedure is performed on both sides of the diaphragm. To obtain the rod length and perform the remainder of the procedure, the diaphragm needs to be crossed. With the endoscope in the chest cavity, a right angle clamp is inserted into the retroperitoneal incision. The right angle clamp is next used to make a small opening under the diaphragm mid vertebral body. The opening is made under direct visualization with the endoscope, and made only large enough for the passage of the rod.

The rod length is determined by placing the fixed end of the endoscopic rod measuring device into the saddle of the distalmost screw. The measuring cable is then guided through the small opening under the diaphragm using a pituitary as an assistive tool to the proximal-most screw (▶ Fig. 28.10). The 4.5-mm rod is cut to length and inserted into the chest cavity through the inferior-most port. The rod has slight flexibility and is not bent before insertion. For the thoracic curves, the rod is manipulated into the inferior screw just beyond flush with the saddle into the posterior saddle of the dual-head screw (▶ Fig. 28.11). This is done to prevent a section of rod from protruding and puncturing the diaphragm. Once the rod is in place, the plug introduction tube is placed over the screw to guide the plug and hold the rod in position. The plug is inserted into the screw and tightened. The rod is then sequentially reduced into each successive screw head with the rod pushers. The plugs are inserted into

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Surgical Techniques

Fig. 28.9 (a,b) Intraoperative view through the endoscope showing the endoscopic rod measurer, with the fixed ball in the distal screw and the cable pulled through all the screws and the free end in the most proximal screw.

Fig. 28.10 (a) Intraoperative view through the endoscope demonstrating the right-angle clamp through the small opening under the diaphragm. (b) Intraoperative view through the endoscope demonstrating the endoscopic rod measurer introduced under the diaphragm. (c) Intraoperative view through the endoscope showing the endoscopic rod measurer pulled through all the screws and the free end into the posterior head of the superior screw.

Fig. 28.11 (a) Intraoperative view through the endoscope demonstrating the posterior rod inserted into the distal screw and (b) at the proximal end of the construct with all the plugs in place.

the screws as the rod is reduced and provisionally tightened. For the thoracolumbar curves, the right angle clamp is inserted into the retroperitoneal incision and under the diaphragm. The rod is grasped into the jaws of the right angle clamp and pulled under the diaphragm into the retroperitoneal space (▶ Fig. 28.12). The rod is inserted into the posterior saddle of the inferior-most screw. Once the rod is appropriately placed, a plug is inserted and tightened. Rod is sequentially reduced with rod pushers into each screw with plugs inserted and provisionally tightened. After the posterior rod is placed, the second rod is inserted in a similar fashion into the anterior saddles.

28.3.4 Compression Once the rods have been seated and all plugs inserted, compression between the screws is performed. The compressor instrument is inserted into the chest cavity or the retroperitoneal

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incision depending on the levels being corrected. The compressor fits over the screw heads onto the rod, and compression is accomplished by turning the compressor driver clockwise and by compressing the two screws together. Compression is started at the inferior end of the construct following tightening of the plugs in the distal screw. Compression is sequentially performed from caudal to cranial until all levels have been compressed (▶ Fig. 28.13). For the thoracolumbar curves when the diaphragm is reached with the compressor, the endoscope is reinserted into the thoracic cavity, and the long arm is manipulated under the diaphragm and over the next screw head. Compression is performed at this level. The compressor is removed from the retroperitoneal incision and inserted into the thoracic cavity. Compression is then sequentially performed superiorly until all the remaining levels are compressed. As each level is compressed, both plugs are torqued.

Perez-Cruet et al, An Anatomic Approach to Minimally Invasive Spine Surgery, 2nd Ed. (ISBN 978-1-62623-643-1), copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.

Minimally Invasive Treatment of Thoracic and Thoracolumbar Idiopathic Scoliosis A 20-Fr chest tube is placed through the inferior port, and the incisions are closed in the standard fashion. Anteroposterior and lateral radiographs are obtained, and the patient is transferred to recovery. The patient stays in the intensive care unit overnight and is then transferred to a regular floor. He or she is fitted for a custom thoracolumbosacral orthosis (TLSO), which must be worn for 3 months. The chest tube is removed when the drainage is less than 75 mL per shift. The patient becomes ambulatory the day the chest tube is removed and is discharged when independent with ambulation. Patients are seen, and radiographs are obtained and assessed at 1, 3, 6, and 12 months postoperatively.

28.4 Thoracic Clinical Cases To date, we have performed several hundred endoscopic procedures. The first was performed in October 1996. The technique, instruments, and implants have undergone several modifications. A review of our first consecutive 100 patients with the diagnosis of primary thoracic scoliosis who underwent endoscopic instrumentation, correction, and fusion documents the evolution. Patients were seen at 1, 3, 6, and 12 months postoperatively and yearly thereafter. Patients were evaluated by physical examination and radiography. Fusion and maintenance

of correction were determined radiographically by an independent evaluator. All patients underwent successful endoscopic scoliosis correction and instrumentation. None required conversion to an open procedure. Patients included 81 females and 19 males, who ranged in age from 9 to 40 years. The average age at the time of surgery was 12.2 years. The average follow-up was 43 months with a range of 48 to 92 months. The average preoperative Cobb measurement was 58.1 degrees with a range of 44 to 98 degrees. The average coronal Cobb measurement of the compensatory curve was 39 degrees with a range of 22 to 59 degrees. Levels instrumented ranged from T2 to T12. The average number of levels instrumented per patient was 7.5 (range 6–9). Blood loss averaged 259.3 mL (range of 100–700 mL), with no transfusions required. On average, chest tubes were removed on postoperative day 2.3 (range 1–6 days). Hospital stays averaged 3.2 days (range 2–7 days). Curve correction averaged 50.1%, in the first 10 cases, with a range of 37.5 to 96%. The average curve correction for the last 10 cases was 71.8% (▶ Fig. 28.14). Patients with hypokyphosis averaged 24.2 degrees of correction with a range of 11 to 39 degrees. Operative time averaged 6 hours 6 minutes for the first 30 cases, with a range of 2 hours 22 minutes to 8 hours 30 minutes. The operative time for the last 10 cases was 2 hours 22 minutes to 2 hours 56 minutes. Successful fusion was determined by the presence of bridging bone between the end plates confirmed on the anteroposterior and lateral radiographs. There were a total of 15 nonunions. The first 15 patients had the bone graft substitute Grafton used for their fusions, and 9 of them exhibited nonunion. The next 85 patients underwent rib graft harvesting for their fusion, with 6 of them developing a nonunion. All the patients in this study were off all pain medication by the first postoperative visit. Children participating in the study returned to school between 2 and 4 weeks after surgery (▶ Fig. 28.15).

28.4.1 Management of Complications Fig. 28.12 Intraoperative view through the endoscope demonstrating the rod as it is pulled under the small opening under the diaphragm.

Poor screw placement was seen in many initial cases. Several of these screws did not have bicortical purchase, and the screw heads were not well seated against the vertebral body. Many of the superior-most screws in the construct were placed at an

Fig. 28.13 (a) Intraoperative view through the endoscope with the endoscopic compressor on the rod compressing two screws together. (b) The endoscopic compressor’s small arm under the diaphragm compressing two screws at the diaphragm level.

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Fig. 28.14 (a,b) Anteroposterior and lateral preoperative radiographs of a 14-year-old girl with a 71-degree thoracic (T6–T12) and 48-degree lumbar (T12–L3) curve. (c,d) Postoperative posteroanterior and lateral radiographs of the same patient after an endoscopic instrumentation, correction, and fusion.

Fig. 28.15 (a–d) A 7-year-old girl with 57-degree T9–L3 curve. (e–g) Pre- and postoperative X-rays. Postoperative standing, bending, and incisions.

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Minimally Invasive Treatment of Thoracic and Thoracolumbar Idiopathic Scoliosis angle into the vertebral body. Oblique screw placement may contribute to screw pullout. Development of mucous plugs in the ventilated lung has been the most common complication. During surgery, the ventilated lung becomes hyperemic and increases its mucous output. Pooling of secretions can also occur because of the dependent position of the lung. The secretion eventually becomes organized and forms a mucous plug. To avoid this complication, the ventilated lung is fiberoptically suctioned before extubation. This new routine has completely eliminated this complication. There were a total of 40 complications, none considered serious. Fifteen patients developed pseudarthrosis, 9 in the Grafton group and 6 in the autologous group. One patient had a screw pullout of the superior vertebral body with loss of correction and went on to a posterior instrumentation and fusion. Three patients experienced transient chest wall numbness. Five patients developed postoperative airway obstruction by mucus, and three patients underwent bronchoscopy to remove the plugs. Two patients developed plug separation from screws. In both cases, the plugs had completely separated, one at the superior screw and the other at the inferior screw. Both patients lost some correction, and one went on to a nonunion but remains asymptomatic and is under observation. One patient required wound revision. Two of the Grafton nonunion patients fractured their rods. The majority of these complications occurred in the first 50 cases. In the last 50 patients, significant issues were pseudarthrosis and loss of correction at follow-up. This was thought to be secondary to the flexibility of the rod and lack of total construct stiffness. In 2002, we developed a unique dual-head screw design, a single shaft with a fixed dual head. This design has several advantages. A single flexible rod is still used to reduce the deformity. This does not stress the bone–screw interface. The second rod acts as a stabilizing rod. A single large screw can resist pullout and is easier to place in the vertebral body than two smaller screws, especially in the smaller proximal vertebral bodies. Our nonunion rate has dramatically reduced since we have used this system. We have no rod fractures to date.

28.5 Thoracolumbar Clinical Cases A total of 45 patients underwent minimally invasive instrumentation, correction, and fusion for thoracolumbar scoliosis, Lenke type 5C. The average curve size was 51.6 degrees, with a range of 40 to 64 degrees. None of the patients were converted to an open procedure. There were 43 females and 2 males, an average age of 13.96 years with a range of 11.11 to 17.4 years. The levels ranged from T7 to L3. Blood loss averaged 385 mL with a range of 150 to 550 mL. Chest tubes were removed on average after 1.6 days with a range of 1 to 6 days. Operative time averaged 5 hours and 46 minutes with a range of 3 hours and 48 minutes to 6 hours and 55 minutes. There were three nonunions. These occurred in the thoracic discs prior to December 2002 with the conversion to the dualhead screw. The average curve correction was 83.4% with an average postoperative Cobb angle of 3.9 degrees. To date, all curves have maintained correction. Sagittal balance was maintained or improved through anterior column distraction using femoral ring structural allograft filled with the patient’s own rib graft that was harvested during the procedure.

28.5.1 Management of Complications There were three complications. One patient developed transient chest wall numbness that resolved by the third month. Two patients developed a mucus plug that required bronchoscopy.

28.6 Discussion Spine surgery for the treatment of thoracic and thoracolumbar scoliosis has evolved over the last several decades. Posterior spinal fusion (PSF) with the Harrington system was the standard in the 1970s and 1980s. However, technology evolved; anterior approaches using instrumentation as well as combined approaches became more popular. With continued improvement in surgical techniques and safety, deformity surgery is now consistently performed in an efficacious manner from an anterior and posterior approach with frequent instrumentation failure or pseudarthrosis.7 Anterior surgical techniques have evolved with the ability now to perform minimal access approaches to allow for anterior soft-tissue release and improved curve correction. The anterior approach to idiopathic scoliosis correction has advanced due to the observed benefits of requiring fewer segments fused, and equal curve correction and derotation as compared with posterior instrumented spinal fusion techniques.7,8 There have been many documented benefits of the use of thoracoscopy for the treatment of spinal deformities. This includes improved visualization with enhanced access to the extremes of the curves, shorter hospital stays, and shorter recuperative periods with a reduction in postoperative pain. Additionally, this approach is less invasive and lacks the potential risks associated with an open thoracotomy or thoracolumbar approach. A significant disadvantage to the open anterior approach includes alterations in pulmonary function testing.8,9 Several studies have documented a significant short-term reduction and questionable long-term reduction in pulmonary function following anterior fusion techniques in open thoracotomy procedures.10,11,12,13 Studies have documented reduction in postoperative pain, improved muscle function, and improved early postoperative pulmonary function,14 as well as reduced morbidity, shorter hospital stays, and decreased overall costs.14,15,16 Pollock et al4 evaluated the efficacy of video-assisted thoracoscopy (VATS) versus open thoracotomy for the correction of scoliosis and found no difference in the correction of the Cobb angle at the time of surgery and at 1-year follow-up. Newton et al17 likewise evaluated the two approaches and found the percentage of curve correction to be similar. The authors also demonstrated in an animal model that both thoracoscopic and open anterior release techniques with disc excision result in similar efficacy.18 Picetti et al19,20,21,22 documented in several studies that the thoracoscopic procedure may be as efficacious as open procedures, as determined in a biomechanical study demonstrating that both surgeries achieve approximately the same degree of correction of 68.6% in endoscopic-treated scoliosis. With regard to the treatment of thoracolumbar scoliosis Lenke type 5C, Geck et al23 reported on comparing open anterior approach to posterior approach. Of 42 patients, 21 matched patients Lenke type 5C (▶ Table 28.1). Norton et al22 reported on 45 patients with Lenke type 5C treated with minimally invasive instrumentation, correction, and fusion (▶ Table 28.2).

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Surgical Techniques Table 28.1 Comparison of thoracolumbar scoliosis treatments Age

Length of stay

Preoperative Cobb angle

Postoperative Cobb angle

% correction

ASF

15.1

6.5

48.9

11

78.3

PSF

15

4.3

49.8

6.2

87.5

Abbreviations: ASF, anterior spinal fusion; PSF, posterior spinal fusion. Source: Geck et al.23

Table 28.2 Minimally invasive outcomes

MIASF

Age

Length of stay

Preoperative Cobb angle

% correction

13.96

2.9

51.6

83.4

Source: Norton et al.22 Abbreviation: MIASF, minimally invasive anterior spinal fusion.

Geck et al23 noted PSF had better correction; however, this was felt possibly secondary to inability in the anterior spinal fusion (ASF) group surgeons to “reach” the target level for adequate correction. The PSF group had better correction and shorter hospital stay. However, when compared to minimally invasive studies, the correction rates are comparable between PSF and minimally invasive surgery (MIS) approaches. With the MIS approach, the upper end of the curve can always be reached and the dual-head screw can always be placed in the proximal level. The hospital stay is also shorter for the MIS group. Advantages of minimally invasive treatment of scoliosis are listed in the following text box.

such as large curves and the thoracolumbar techniques, requires differing levels of technical skill and experience when performed thoracoscopically.

Clinical Caveats ●

●

●

Advantages of Minimally Invasive Treatment of Idiopathic Scoliosis ● ● ● ● ● ● ● ● ●

Faster rehab (return to school 2–4 weeks). Shorter hospital stay: 2.9 days. Greater than 80% curve correction. Costs less. All patients off pain medication by 4 weeks. Can reach ends of the construct. Desired cosmetic result. No adversity to pulmonary functions. No blood transfusions required.

●

●

●

The spine surgeon is positioned at the patient’s back. This positioning allows all instruments to be directed away from the spinal cord and facilitates surgical orientation and viewing of the monitor. In treating thoracolumbar curves, the procedure is performed on both sides of the diaphragm. Adequately performed autologous rib graft harvest can help reduce pseudoarthrosis rates and maintains correction of scoliosis while reducing intercostal nerve pain. Compression of the rod to correct spinal alignment is started at the inferior end of the construct and sequentially performed from caudal to cranial until all levels have been compressed. Pooling of secretions can occur in the dependent lung and lead to mucous plug postoperatively. To avoid this, the ventilated lung is fiberoptically suctioned before extubation. A unique dual-head screw design comprised of a single shaft screw with a fixed dual head allows single flexible rod deformity correction and two-rod final system to strengthen the final construct, reducing nonunion rates and maintaining correction.

28.7 Conclusion Minimally invasive instrumentation, correction, and fusion for adolescent idiopathic scoliosis (AIS) is a very effective procedure with results equal to or better than the open anterior or posterior approaches. However, the minimally invasive approach for the treatment of scoliosis is technically demanding in terms of required surgical expertise and has a significant learning curve in terms of required technical skills, both of which contribute to lengthier operative times and subsequent increased operative costs.18 This technique limits the availability of this procedure to be performed only by a surgical team that has invested significant time with endoscopic procedures in order to become comfortable and efficient enough to perform this procedure in a safe and effective manner. Furthermore, specific spinal deformity correction,

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References [1] Jacobaeus HC. Possibility of the use of the cystoscope for investigation of serious cavities. Munch Med Wochenschr. 1910; 57:2090–2092 [2] Regan JJ, Mack MJ, Picetti GD III. A comparison of VAT to open thoracotomy in thoracic spinal surgery. Presented to the Scoliosis Research Society, Dublin, Ireland, September 18–23, 1993 [3] Rosenthal D, Rosenthal R, de Simone A. Removal of a protruded thoracic disc using microsurgical endoscopy. A new technique. Spine. 1994; 19(9):1087–1091 [4] Pollock ME, O’Neal K, Picetti GD, III, Blackman R. The results of video-assisted exposure of the anterior thoracic spine in idiopathic scoliosis. Ann Thorac Surg. 1996; 62:1818–1823 [5] Picetti GD III. Video-assisted thoracoscopy (VATS) in the treatment of congenital hemivertebra. Presented at the Spine Society of Australia Annual Scientific Meeting, Cairns, Australia, September 1996

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Minimally Invasive Treatment of Thoracic and Thoracolumbar Idiopathic Scoliosis [6] Lenke L. A new classification of idiopathic scoliosis: predicting and assessing treatment. The Sixth International Meeting on Advanced Spine Techniques, Vancouver, BC, July 1999 [7] Shimamoto N, Kotani Y, Shono Y, et al. Static and dynamic analysis of five anterior instrumentation systems for thoracolumbar scoliosis. Spine. 2003; 28 (15):1678–1685 [8] Potter BK, Kuklo TR, Lenke LG. Radiographic outcomes of anterior spinal fusion versus posterior spinal fusion with thoracic pedicle screws for treatment of Lenke Type I adolescent idiopathic scoliosis curves. Spine. 2005; 30 (16):1859–1866 [9] Mardjetko S. Anterior surgery in the management of scoliosis. 1. Introduction and anterior release. Contemp Spine Surg. 2006; 6:6–13 [10] Wong CA, Cole AA, Watson L, Webb JK, Johnston ID, Kinnear WJ. Pulmonary function before and after anterior spinal surgery in adult idiopathic scoliosis. Thorax. 1996; 51(5):534–536 [11] Vedantam R, Lenke LG, Bridwell KH, Haas J, Linville DA. A prospective evaluation of pulmonary function in patients with adolescent idiopathic scoliosis relative to the surgical approach used for spinal arthrodesis. Spine. 2000; 25(1):82–90 [12] Graham EJ, Lenke LG, Lowe TG, et al. Prospective pulmonary function evaluation following open thoracotomy for anterior spinal fusion in adolescent idiopathic scoliosis. Spine. 2000; 25(18):2319–2325 [13] Chen SH, Huang TJ, Lee YY, Hsu RW. Pulmonary function after thoracoplasty in adolescent idiopathic scoliosis. Clin Orthop Relat Res. 2002(399):152–161 [14] Landreneau RJ, Hazelrigg SR, Mack MJ, et al. Postoperative pain-related morbidity: video-assisted thoracic surgery versus thoracotomy. Ann Thorac Surg. 1993; 56(6):1285–1289

[15] DeCamp MM, Jr, Jaklitsch MT, Mentzer SJ, Harpole DH, Jr, Sugarbaker DJ. The safety and versatility of video-thoracoscopy: a prospective analysis of 895 consecutive cases. J Am Coll Surg. 1995; 181(2):113–120 [16] Ferson PF, Landreneau RJ, Dowling RD, et al. Comparison of open versus thorascopic lung biopsy for diffuse infiltrative lung disease. J Am Coll Surg. 1995; 181:113–120 [17] Newton PO, Cardelia JM, Farnsworth CL, Baker KJ, Bronson DG. A biomechanical comparison of open and thoracoscopic anterior spinal release in a goat model. Spine. 1998; 23(5):530–535, discussion 536 [18] Newton PO, Wenger DR, Mubarak SJ, Meyer RS. Anterior release and fusion in pediatric spinal deformity. A comparison of early outcome and cost of thoracoscopic and open thoracotomy approaches. Spine. 1997; 22(12):1398–1406 [19] Picetti GD, III, Pang D, Bueff HU. Thoracoscopic techniques for the treatment of scoliosis: early results in procedure development. Neurosurgery. 2002; 51 (4):978–984, discussion 984 [20] Picetti G, Blackman R, O’Neil K. Preliminary results of endoscopic procedure on the anterior spine. J Bone Joint Surg Br. 1997; 79:289 [21] Picetti GD, III, Ertl JP, Bueff HU. Anterior endoscopic correction of scoliosis. Orthop Clin North Am. 2002; 33(2):421–429 [22] Norton RP, Patel D, Kurd MF, Picetti GD, Vaccaro AR. The use of thoracoscopy in the management of adolescent idiopathic scoliosis. Spine. 2007; 32 (24):2777–2785 [23] Geck MJ, Rinella A, Hawthorne D, et al. Anterior dual rod versus posterior pedicle fixation surgery for the treatment in Lenke 5C adolescent idiopathic scoliosis: multicenter, matched case analysis of 42 patients. Spine Deform. 2013; 1(3):217–222

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29 Kyphoplasty and Vertebroplasty Sina Rajamand and Daniel K. Fahim Abstract Vertebroplasty and kyphoplasty are useful vertebral augmentation surgeries that can be performed in an inpatient or outpatient setting to effectively treat acute pathologic or traumatic compression fractures of a vertebral body causing intractable pain. When indicated, the fairly simple procedures of vertebroplasty and kyphoplasty are extremely effective in reducing the debilitating pain associated with vertebral body compression fractures especially in the osteoporotic elderly population. Patients are able to return to their baseline functional level of activity postprocedure due to the reduction of pain. With the utilization of modern imaging techniques including X-ray, CT scans, MRI studies, and bone scintigraphy, the clinician is able to quickly identify and intervene in patients with acute compression fractures of a vertebral body to limit debility and the potential comorbidities that can be associated with it. Keywords: vertebroplasty, kyphoplasty, compression fracture, vertebral body, vertebral augmentation, pathologic compression fracture

29.1 Introduction Vertebroplasty was first performed in France in 1987 for painful vertebral body hemangioma treatment. Shortly thereafter, it was used to treat osteoporotic compression fractures. It was later introduced in the United States in 1993. A subsequent modification of the original procedure, involving fracture reduction with the use of a balloon, was introduced in 1998.1,2,3 Osteoporotic vertebral compression fractures affect more than 700,000 Americans per year, and approximately 10 million people are affected by osteoporosis in the United States.4 Vertebral compression fracture may be the first symptom of osteoporosis, and clinicians must be vigilant in correctly diagnosing this potentially devastating disease. Although vertebroplasty and kyphoplasty are used in other pathologies resulting in painful compression fractures (such as metastatic disease), they are most frequently utilized in osteoporotic vertebral compression fractures. Vertebroplasty is a minimally invasive procedure where polymethyl methacrylate (PMMA) is injected into the vertebral body to treat pain associated with a compression fracture of that segment.5 Kyphoplasty is similar, except a balloon tamp is inserted prior to injection of the cement and a cavity is created within the vertebral body into which PMMA is subsequently injected.6 Kyphoplasty is the more expensive and technically demanding of the two. However, relative benefits of kyphoplasty are the ability to restore height by virtue of the balloon and the compaction of the cancellous bone in the vertebral body resulting in greater strength along the cortical walls.7,8 The creation of a cavity by the balloon is also thought to lessen the chance of cement migration or leakage during cement injection, which is a complication more frequently observed with vertebroplasty. The cavity helps loculate and contain the cement and the compaction of the cancellous bone will theoretically tamp off the

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previous channels and pores created from the original fracture. The cement acts like an internal cast that stabilizes that segment. Pain relief is thought to be a function of both the stabilization of the vertebral body and denervation of the bone matrix due to the cytotoxicity of the cement to the nerve tissue, as well as free oxygen radical production and heating during cement polymerization.9,10

29.2 Indications and Contraindications 29.2.1 Indications Indications for kyphoplasty are osteoporotic compression fractures, traumatic compression fractures, and compression fractures secondary to metastases to the vertebral body that are limiting the mobility and functional capacity of the patient.11,12, 13 Guidelines from the Society of Interventional Radiology and the Cardiovascular and Interventional Radiological Society of Europe state the indications for vertebroplasty are as follows14: ● Osteoporotic vertebral compression fractures refractory to 3 weeks of analgesic therapy. ● Primary or secondary benign or malignant bone tumor resulting in painful vertebrae. ● Painful osteonecrotic vertebral compression fracture. ● Reinforcement of a vertebral segment prior to surgical intervention. ● Chronic traumatic vertebral compression fractures with nonunion. Even a short period of pain limiting activity may be unacceptable and deleterious to an elderly individual with already limited mobility. The comorbidities of substantially decreased daily activity and prolonged bed rest due to pain can lead to detrimental adverse outcomes such as deep venous thrombosis, pulmonary embolism, pressure ulcers and sores, decreased muscle mass, and further decreased bone density. Decreased bone density or osteoporosis is one of the main factors in vertebral body compression fractures. Further decrease in bone density due to decreased stress on the bones of the body from limited daily activity and prolonged bed rest can progress to long bone fractures and compression fractures of other vertebral levels, leading to further decrease in activity resulting in a downward spiral with the eventual demise of the patient due to irrecoverable insults to the body and the morbidity and mortality attributable to prolonged bed rest. Suitability for vertebral augmentation surgery can be evaluated with proper imaging. Plain radiographs of the spine are often the starting point due to the nature of the disease. Patients are often discovered to have a compression fracture at their primary doctor’s office or in the emergency department where a plain radiograph is inexpensive and easily obtained. CT scans and MRIs are more definitive and are often the next step in diagnostic imaging. Bone scans can also be useful in evaluating compression fractures of vertebral bodies.15,16,17 CT scan is excellent at identifying vertebral fractures or osseous destruction; however, it is less helpful in

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Kyphoplasty and Vertebroplasty evaluating the acuity of the injury. MRI is useful to identify the chronicity versus acuity of a compression fracture by evaluating the presence or lack of edema. Alternatively, bone scintigraphy can identify which levels to treat as increased uptake generally indicates acute fracture of the vertebral body. The vertebral segment with increased uptake has been shown to respond well to vertebral augmentation with kyphoplasty or vertebroplasty.15,16,17 However, bone scans have continued to show increased uptake up to 1 year after an injury, making it difficult to discern acute injuries from chronic injuries with this modality alone. In this situation, vertebral augmentation surgery may have limited benefits as it is recommended to treat compression fractures less than 8 weeks old for the best results.15 As the number of patients with metastases to the spine increases, there is a rapidly growing body of literature on vertebral body compression fractures in this patient population. Although a painful vertebral body compression fracture secondary to a metastatic lesion is a well-established indication for kyphoplasty, the indications for “prophylactic” vertebral body augmentation are under investigation.18,19,20 Patients with spine metastases frequently undergo radiation therapy. Increasingly, these patients are undergoing stereotactic radiosurgery. Multiple studies have identified risk factors for the development of compression fractures in patients receiving radiation for treatment of spine metastases. There is growing discussion about offering prophylactic vertebral body augmentation for patients with increased risk of developing compression fractures during their radiation treatment.21,22,23

29.2.2 Contraindications Contraindications include nonpainful or asymptomatic vertebral compression fractures, adequate pain control with oral analgesics, sepsis or active systemic infection, epidural abscess, infection in the soft tissue or skin overlying the approach trajectory, severe or uncorrectable coagulopathy, cord compression from retropulsion of bone resulting in myelopathy, complete collapse of the vertebral body (vertebra plana), allergy to PMMA, and severe posterior vertebral body wall destruction.24,25,26 Relative contraindications include radicular pain, vertebral compression fractures greater than 70% of vertebral body height, and advanced tumor extension into the central canal. Osteomyelitis presents an interesting challenge as this disease entity can result in painful compression fractures that can sometimes be effectively treated with PMMA mixed with an antimicrobial agent (in addition to the requisite intravenous [IV] antibiotics).

29.3 Surgical Technique The procedure can be performed in the outpatient setting with conscious sedation and local anesthesia in a location with the proper imaging tools. Usually patients can return to their normal daily activity that day, and often patients have almost immediate pain relief.

29.3.1 Patient Positioning The patient is sedated and then positioned prone with arms above their head. An imaging apparatus is then properly set up for a biplane image. The procedure can be performed in either a

biplane angiography suite or with two C-arm fluoroscopy machines. Anteroposterior (AP) and lateral fluoroscopic images are obtained to localize the fractured vertebral level. The patient is prepped and draped in the usual fashion. The skin is marked approximately 1 cm lateral to the lateral and superior border of the pedicle. Next, the skin surface is anesthetized with a small gauge needle, creating a wheal with lidocaine. Once the skin surface has been anesthetized, a longer needle with local anesthetic is inserted down to the periosteal level of the proposed trocar entry site at the pedicle and anesthetic is injected while withdrawing the needle.

29.3.2 Procedure A small stab skin incision is made at the proper level and a trocar needle is introduced to localize the pedicle. An AP image and a lateral image are obtained to assure proper alignment. The AP image should show the tip of the trocar at the lateral superior edge of the pedicle. Care must be taken not to cross the medial border of the pedicle prior to entering the body of the vertebrae. Early medialization can result in entering the central canal and damaging the cord or nerve roots. If a parapedicular approach is chosen, the trocar is placed on the transverse process of the chosen vertebral level and walked superiorly and laterally just above the transverse process.27,28 The trocar is then advanced with biplane guidance to enter the vertebral body just lateral to the pedicle at the pedicle body interface. The pedicle body interface can best be visualized with the lateral X-ray. The trocar needle should be passed until it resides near the center of the vertebral body. A bipedicular approach results in the most uniform cement injection; however, a unipedicular approach can result in sufficient cement placement, as well.29,30,31,32,33 There are also instruments with articulating heads for the balloon-tapping portion of a kyphoplasty that will help facilitate obtaining a midline deployment of the balloon. Once the proper position is reached and confirmed with AP and lateral images, the trocar introducer needle portion is taken out leaving behind the dilator. Injection of cement is then performed. The cement used is usually PMMA with contrast material premixed into the preparation. The PMMA is mixed to the consistency of toothpaste before injection. Injection is performed under fluoroscopic guidance with frequent images to visualize the placement of the cement insuring there is no extravasation through venous tributaries or posterior leakage into the spinal canal, which can have detrimental consequences. Enough cement is usually injected under direct fluoroscopic guidance to fill the anterior 2/3 of the vertebral body. The introducer needle is left in place for a few minutes to allow cement setting. Marcaine without epinephrine is injected along the paraspinal muscles for postoperative analgesia. The needle is then removed and the incision sites are closed, usually with a skin adhesive.

29.4 Postoperative Care The patient can be left prone for another 10 to 15 minutes to allow the cement to further harden. The patient is then returned to the supine position and observed in the recovery room until he or she is sufficiently awake and stable to be discharged home, hopefully with much less pain.

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29.5 Management of Complications Complications include failure to obtain pain relief or worsening of symptoms, osteomyelitis, vertebral fracture, pedicle fracture, retropulsion or spillage of cement into the spinal canal or neural foramen, paralysis, nerve root irritation or damage, venous embolism, and fatal anaphylactic reaction to PMMA (very rare but reported).34,35,36,37,38,39,40

29.6 Clinical Case A 95-year-old female was brought to the emergency department with a status post fall from standing 10 days before. Since that time, the patient had been bedridden secondary to severe lower back pain. CT scan and MRI demonstrated an L3 compression fracture. Due to the severe morbidity and mortality associated with prolonged bed rest in a 95-year-old, including deconditioning, potential for deep venous thrombosis, urinary tract infections, skin breakdown and ulceration leading to infection, and pneumonia, a decision was made with the patient and family that a percutaneous kyphoplasty would be an appropriate procedure. All risks of the procedure were also discussed with the patient and family (▶ Fig. 29.1).

29.7 Conclusion Kyphoplasty is a safe and effective treatment for painful vertebral body compression fracture etiology, even in patients of advanced age. It can routinely be performed with local anesthetic and sedation on an outpatient basis.

Clinical Caveats ●

●

●

●

Osteoporotic vertebral compression fractures affect around 700,000 Americans per year. Vertebral augmentation surgery is useful for the treatment of painful acute or pathological compression fractures of the vertebral body. Vertebroplasty and kyphoplasty are vertebral augmentation surgeries that can be performed in the inpatient or outpatient setting with local anesthetic and sedation. Compression fractures can be debilitating, especially in the elderly osteoporotic population. Vertebral augmentation through vertebroplasty or kyphoplasty can prevent the comorbidities associated with pain limiting activity in this population by decreasing the pain associated with these fractures and returning them to functional daily activities sooner.

Fig. 29.1 (a) The patient had an acute compression fracture as seen on MRI short tau inversion recovery sequences. (b) The patient underwent balloon kyphoplasty. A bipedicular approach was chosen for more uniform cement injection. (c,d) The final outcome of cement injection. Notice there is no cement extravasation. The patient did very well and was discharged home 3 days postprocedure with great pain relief.

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Kyphoplasty and Vertebroplasty

References [1] Crowley RW, Yeoh HK, McKisic MS, Oskouian RJ Jr, Dumont AS. Osteoporotic fractures: evaluation and treatment with vertebroplasty and kyphoplasty. In: Winn HR, ed. 6th ed. Youmans Neurological Surgery. Philadelphia, PA: Elsevier; 2011:3255–3265 [2] Chen L-H, Lai P-L, Chen W-J. Current status of vertebroplasty for osteoporotic compression fracture. Chang Gung Med J. 2011; 34(4):352–359 [3] Galibert P, Deramond H, Rosat P, Le Gars D. Preliminary note on the treatment of vertebral angioma by percutaneous acrylic vertebroplasty. Neurochirurgie. 1987; 33(2):166–168 [4] Gangi A, Sabharwal T, Irani FG, Buy X, Morales JP, Adam A, Standards of Practice Committee of the Society of Interventional Radiology. Quality assurance guidelines for percutaneous vertebroplasty. Cardiovasc Intervent Radiol. 2006; 29(2):173–178 [5] Yu S-W, Yang SC, Kao YH, Yen CY, Tu YK, Chen LH. Clinical evaluation of vertebroplasty for multiple-level osteoporotic spinal compression fracture in the elderly. Arch Orthop Trauma Surg. 2008; 128(1):97–101 [6] Zampini JM, White AP, McGuire KJ. Comparison of 5766 vertebral compression fractures treated with or without kyphoplasty. Clin Orthop Relat Res. 2010; 468(7):1773–1780 [7] Teng MMH, Wei CJ, Wei LC, et al. Kyphosis correction and height restoration effects of percutaneous vertebroplasty. AJNR Am J Neuroradiol. 2003; 24 (9):1893–1900 [8] McArthur N, Kasperk C, Baier M, et al. 1150 kyphoplasties over 7 years: indications, techniques, and intraoperative complications. Orthopedics. 2009; 32(2):90 [9] Moreau MF, Chappard D, Lesourd M, Monthéard JP, Baslé MF. Free radicals and side products released during methylmethacrylate polymerization are cytotoxic for osteoblastic cells. J Biomed Mater Res. 1998; 40(1):124–131 [10] Nelson DA, Barker ME, Hamlin BH. Thermal effects of acrylic cementation at bone tumour sites. Int J Hyperthermia. 1997; 13(3):287–306 [11] Fransen P, Collignon F. Balloon kyphoplasty for treatment of vertebral osteoporotic compression fractures. Rev Med Brux. 2007; 28(3):159–163 [12] Shin JJ, Chin DK, Yoon YS. Percutaneous vertebroplasty for the treatment of osteoporotic burst fractures. Acta Neurochir (Wien). 2009; 151(2):141–148 [13] Zoarski GH, Snow P, Olan WJ, et al. Percutaneous vertebroplasty for osteoporotic compression fractures: quantitative prospective evaluation of long-term outcomes. J Vasc Interv Radiol. 2002; 13(2 Pt 1):139–148 [14] McGraw JK, Cardella J, Barr JD, et al. SIR Standards of Practice Committee. Society of Interventional Radiology quality improvement guidelines for percutaneous vertebroplasty. J Vasc Interv Radiol. 2003; 14(7):827–831 [15] Maynard AS, Jensen ME, Schweickert PA, Marx WF, Short JG, Kallmes DF. Value of bone scan imaging in predicting pain relief from percutaneous vertebroplasty in osteoporotic vertebral fractures. AJNR Am J Neuroradiol. 2000; 21(10):1807–1812 [16] Karam M, Lavelle WF, Cheney R. The role of bone scintigraphy in treatment planning, and predicting pain relief after kyphoplasty. Nucl Med Commun. 2008; 29(3):247–253 [17] Masala S, Schillaci O, Massari F, et al. MRI and bone scan imaging in the preoperative evaluation of painful vertebral fractures treated with vertebroplasty and kyphoplasty. In Vivo. 2005; 19(6):1055–1060 [18] Furtado N, Oakland RJ, Wilcox RK, Hall RM. A biomechanical investigation of vertebroplasty in osteoporotic compression fractures and in prophylactic vertebral reinforcement. Spine. 2007; 32(17):E480–E487 [19] Hart RA, Prendergast MA, Roberts WG, Nesbit GM, Barnwell SL. Proximal junctional acute collapse cranial to multi-level lumbar fusion: a cost analysis of prophylactic vertebral augmentation. Spine J. 2008; 8(6):875–881

[20] Oakland RJ, Furtado NR, Wilcox RK, Timothy J, Hall RM. The biomechanical effectiveness of prophylactic vertebroplasty: a dynamic cadaveric study. J Neurosurg Spine. 2008; 8(5):442–449 [21] Boehling NS, Grosshans DR, Allen PK, et al. Vertebral compression fracture risk after stereotactic body radiotherapy for spinal metastases. J Neurosurg Spine. 2012; 16(4):379–386 [22] Sahgal A, Atenafu EG, Chao S, et al. Vertebral compression fracture after spine stereotactic body radiotherapy: a multi-institutional analysis with a focus on radiation dose and the spinal instability neoplastic score. J Clin Oncol. 2013; 31(27):3426–3431 [23] Cunha MVR, Al-Omair A, Atenafu EG, et al. Vertebral compression fracture (VCF) after spine stereotactic body radiation therapy (SBRT): analysis of predictive factors. Int J Radiat Oncol Biol Phys. 2012; 84(3):e343–e349 [24] Denaro L, Longo UG, Denaro V. Vertebroplasty and kyphoplasty: reasons for concern? Orthop Clin North Am. 2009; 40(4):465–471, viii [25] Manson NA, Phillips FM. Minimally invasive techniques for the treatment of osteoporotic vertebral fractures. J Bone Joint Surg Am. 2006; 88 (8):1862–1872 [26] Mueller CW, Berlemann U. Kyphoplasty: chances and limits. Neurol India. 2005; 53(4):451–457 [27] Mathis JM. Percutaneous vertebroplasty. JBR-BTR. 2003; 86(5):299–301 [28] Mathis JM. Percutaneous vertebroplasty: complication avoidance and technique optimization. AJNR Am J Neuroradiol. 2003; 24(8):1697–1706 [29] Kim AK, Jensen ME, Dion JE, Schweickert PA, Kaufmann TJ, Kallmes DF. Unilateral transpedicular percutaneous vertebroplasty: initial experience. Radiology. 2002; 222(3):737–741 [30] Chung HJ, Chung KJ, Yoon HS, Kwon IH. Comparative study of balloon kyphoplasty with unilateral versus bilateral approach in osteoporotic vertebral compression fractures. Int Orthop. 2008; 32(6):817–820 [31] Hoh BL, Rabinov JD, Pryor JC, Hirsch JA. Balloon kyphoplasty for vertebral compression fracture using a unilateral balloon tamp via a uni-pedicular approach: technical note. Pain Physician. 2004; 7(1):111–114 [32] Hu MM, Eskey CJ, Tong SC, et al. Kyphoplasty for vertebral compression fracture via a uni-pedicular approach. Pain Physician. 2005; 8(4):363–367 [33] Ortiz AO, Zoarski GH, Beckerman M. Kyphoplasty. Tech Vasc Interv Radiol. 2002; 5(4):239–249 [34] Choe DH, Marom EM, Ahrar K, Truong MT, Madewell JE. Pulmonary embolism of polymethyl methacrylate during percutaneous vertebroplasty and kyphoplasty. AJR Am J Roentgenol. 2004; 183(4):1097–1102 [35] Quesada N, Mutlu GM. Images in cardiovascular medicine. Pulmonary embolization of acrylic cement during vertebroplasty. Circulation. 2006; 113(8): e295–e296 [36] Barragán-Campos HM, Vallée JN, Lo D, et al. Percutaneous vertebroplasty for spinal metastases: complications. Radiology. 2006; 238(1):354–362 [37] Chung S-E, Lee SH, Kim TH, Yoo KH, Jo BJ. Renal cement embolism during percutaneous vertebroplasty. Eur Spine J. 2006; 15 Suppl 5:590–594 [38] Kim M-H, Lee AS, Min SH, Yoon SH. Risk factors of new compression fractures in adjacent vertebrae after percutaneous vertebroplasty. Asian Spine J. 2011; 5(3):180–187 [39] Kim SY, Seo JB, Do KH, Lee JS, Song KS, Lim TH. Cardiac perforation caused by acrylic cement: a rare complication of percutaneous vertebroplasty. AJR Am J Roentgenol. 2005; 185(5):1245–1247 [40] Nussbaum DA, Gailloud P, Murphy K. A review of complications associated with vertebroplasty and kyphoplasty as reported to the Food and Drug Administration medical device related web site. J Vasc Interv Radiol. 2004; 15 (11):1185–1192

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30 Minimally Invasive Robotic-Assisted Thoracic Spine Surgery Mick J. Perez-Cruet and Jorge Mendoza-Torres Abstract This chapter discusses the minimally invasive assisted robotic spine surgery (MARSS) for resection of paraspinal tumors. This advanced minimally invasive robotic-guided technique for removal of thoracic tumors is particularly ideal for patients with well-circumscribed apical lung tumors that can be difficult to resect using traditional thoracotomy approaches. Additionally, MARSS avoids the morbidity of open thoracotomy approaches and the technical limitations of thoracoscopic techniques. This chapter reviews the preoperative workup and approach developed that facilitates removal of thoracic tumors. This technique does require specialized training and equipment including use of the da Vinci robotic surgical system. With further refinements in instrumentation, this approach will expand in its indications and ultimately result in improved patient outcomes. Keywords: MARSS, da Vinci robot, thoracic tumors, minimally invasive

30.1 Introduction The da Vinci robotic surgical system has been in use since its Food and Drug Administration (FDA) approval in 2000 and was initially approved for use in general, urologic, and gynecologic laparoscopic procedures.1 During this time period, the da Vinci System has also been indicated for thoracic surgeries of the lungs, mediastinum, and esophagus. These include lung resection, parathyroid gland resection, and thymectomy among others.2 Furthermore, we have described use of the da Vinci system in combination with minimally invasive surgery (MIS) posterior approach for the resection of complex paraspinal schwannomas with thoracic extension.3 Minimally invasive robotic surgery has also been shown to potentially provide patients with better outcomes and fewer complications, as well as a cost-effective alternative to traditional open procedures.4 In this chapter, we will describe our technique that we call minimally invasive assisted robotic spine surgery (MARSS) for resection of paraspinal tumors using the da Vinci robotic system. However, the da Vinci robot could potentially be used for sympathectomies for palmar hydrosis, trauma, and degenerative disc conditions. The main limitation of this system for expanded indications is the lack of the necessary surgical tools needed by the surgeon.

30.2 Indications and Contraindications As described earlier, the initial use of the da Vinci robotic surgical systems covered the following: ● General surgery.5 ● Urologic surgery.5 ● Gynecologic laparoscopic procedures.5

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Thoracic surgery of the lungs, mediastinum, and esophagus, including the following: ○ Lung resection, parathyroid gland resection, and thymectomy.2 ○ Minimally invasive resection of complex paraspinal schwannomas with thoracic extension.3

A lack of long-term outcomes and quality of life data for da Vinci robotic procedures in the spine precludes a meaningful comparison with open approaches. Thus, few contraindications to using the da Vinci system have been defined, though contraindications are expected to be similar to thoracoscopic procedures and include significant pleural scarring that may precludes a safe approach. Additionally, use of the da Vinci robotic system requires specialized surgeon training.

30.3 Preoperative Planning Patients typically present with apical thoracic lesions. An “ideal” patient in our opinion has well-circumscribed lesions such as schwannomas. As better instrumentation for spinal surgery using the da Vinci system is developed, the indications should expand. For patients presenting with apical thoracic schwannomas, imaging studies include contrasted thoracic spinal MRI. Contrast-enhanced CT is also useful for accurately identifying the level of origin and determining the neural foramen from which the tumors originate (▶ Fig. 30.1). This is critical to the resection of the tumor attached to the exiting nerve root to avoid traction injury to the spinal cord and/or root evulsion. A sagittal CT starting at the sacrum can help accurately determine the level of the lesion. For proper surgical level determination, the following images are ordered: chest X-ray and thoracic and lumbar anteroposterior (AP) and lateral images. Intraoperative fluoroscopy is used to accurately determine the level by counting vertebral bodies starting at the sacrum or ribs on the AP chest view. In the case of removal of thoracic schwannomas, no implant instrumentation is needed.

30.4 Surgical Technique The patient is initially positioned in the prone position on a Jackson table or Wilson frame with all pressure points adequately padded. Double-lumen intubation is done to allow collapsing of the lung on the thoracic approach side. Intraoperative electrophysiologic monitoring is used to measure somatosensory evoked potentials and motor evoked potentials. AP and lateral fluoroscopy is used to help localize the level. An incision is then made lateral to the midline based on preoperative image analysis (▶ Fig. 30.2). A muscle dilating technique is used to approach the spine over which a tubular retractor is placed. Under microscopic visualization, the ipsilateral lamina and facet are exposed. A bone cutting drill with an M8 cutting

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Fig. 30.1 Tumor extending out of the right T2–T3 neural foramen into the right chest cavity. (a) Axial CT. (b) Chest radiography. (c) Coronal view. (d) Sagittal view. (e) Axial contrast-enhanced MRI.

burr is used to perform an adequate ipsilateral laminectomy and facetectomy, exposing the tumor within the neural foramen and the dura. The contralateral aspect of the spine is not dissected. The drilled bone is collected using a BoneBac Press (Thompson MIS; ▶ Fig. 30.3). The sheath of the tumor is opened and the tumor is removed in a piecemeal fashion. If the exiting nerve root is infiltrated in tumor, it is ligated with silk ties. To prevent potential cerebral spinal leakage into the thoracic cavity, the area can be covered with Gelfoam and thrombin sealant. Once complete hemostasis is achieved, the facet and laminectomy defects are reconstructed using the morselized autograft that was collected in the BoneBac Press (▶ Fig. 30.4). Gross total removal of the tumor extending into the spinal canal is achieved (▶ Fig. 30.5). The tubular retractor is removed, allowing the paraspinous muscles to return to their normal anatomic position. The fascia is closed using 2–0 interrupted Vicryl suture. A subcuticular interrupted suture is applied and the skin incision is closed with skin glue.

The patient is then repositioned in the lateral position on a sandbag to allow for adequate unilateral thoracic approach to the tumor. A thoracoscope can then be used for proper port placement (▶ Fig. 30.6). Thoracoscopic ports are placed and the da Vinci robot is positioned adequately. Instruments are placed in the da Vinci robot for retraction of the tumor and cautery removal of the tumor from the chest cavity. A separate port is used to place a suction to remove cautery smoke. Detaching the tumor from its spinal canal attachment allows for gross total removal and limits potential traction injury to the spinal cord. Once the tumor is resected, it can be placed into a gallbladder bag and removed via one of the thoracoscopic ports. The thoracic ports are moved, a chest tube is placed, and the incisions are closed in a routine fashion. Reinflation of the lung is performed before the final closure. Patients are typically transferred to the intensive care unit for at least an overnight stay.

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Fig. 30.2 (a) Axial contrast-enhanced MRI used to identify skin incision location 3 cm lateral to the midline. (b) Patient in the prone position for first stage of the procedure. (c) Use of tubular retractor to remove the posterior portion of the tumor extending from the spinal canal into the thoracic cavity.

30.5 Clinical Cases 30.5.1 Case 1: Schwannoma Lesion The patient presented with symptoms of upper thoracic chest pain and discomfort. Imaging studies revealed a right apical thoracic mass, which extended out of the right T2–T3 neural foramen (▶ Fig. 30.1). The tumor was biopsied and found to be a schwannoma. The patient was in his 70 s and had a history of cerebral stroke and had multiple other medical comorbidities, making him a poor surgical candidate. The patient initially underwent focused radiation to the tumor; however, the tumor continued to grow and the patient’s symptoms increased. He was deemed a good candidate for a minimally invasive spinal approach using the da Vinci robot since his medical condition precluded an open thoracotomy. The patient was initially placed prone on a radiolucent Jackson table (Mizuho OSI), and

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the tumor level was determined with AP thoracic fluoroscopy, counting from the first rib to the location of the tumor. A 2-cm incision parallel to the spinous processes was made approximately 3 cm lateral to the midline, based on preoperative MRI imaging (▶ Fig. 30.2). Serial muscle dilation was used to dock a tubular retractor on the right T2–T3 facet complex using fluoroscopic guidance. A small amount of soft tissue was removed using a Bovie cautery to expose the facet complex and ipsilateral lamina. Laminectomy and facetectomy were performed to expose the intraspinal portion of the tumor. All drilled bone was collected using the BoneBac Press (Thompson MIS) and used to reconstruct the lamina and facet after tumor resection (▶ Fig. 30.3). The tumor sheath was cut, and the tumor was debulked in a piecemeal fashion. Duragen (Integra LifeSciences) and Tisseel (Baxter) were placed over the dura to prevent cerebrospinal fluid leakage into the thoracic cavity. Morselized autologous bone collected during the procedure with the BoneBac Press

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Fig. 30.3 (a) Intraoperative image showing surgeon use of the (b) BoneBac Press to (c) collect drilled autograft separated from the blood providing (d) morselized autograft used for (e) posterior fusion, laminar, and facet reconstruction illustrated with postoperative CT.

(Thompson MIS) was used to perform a posterolateral arthrodesis at the T2–T3 level (▶ Fig. 30.4). The intraspinal component of the tumor was gross totally removed (▶ Fig. 30.5). The retractor was removed, and the incision closed in a routine manner. The patient was then repositioned on a surgical beanbag in the lateral position with the right side up. All pressure points were adequately padded. The patient was then prepped and draped in surgical fashion. A thoracoscope was then used to assist in docking ports into the thoracic cavity (▶ Fig. 30.6a). Using the MARSS technique, the da Vinci robot was then draped in a sterile manner and positioned into the thoracic ports (▶ Fig. 30.6b–e). The robot was then used to resect the tumor using an arm that retracted the tumor off the inner thoracic wall and the other arm was equipped with electrocautery to resect the tumor at its base (▶ Fig. 30.6f,g). Once removed, the tumor was placed into a gallbladder bag and removed via one of the thoracic ports in a gross total manner. Postoperative contrast-enhanced MRI revealed complete tumor removal (▶ Fig. 30.6i,j). The patient made an unremarkable recovery. He was discharged on postoperative day 3, and had a well-healed incision at 2-week follow-up (▶ Fig. 30.6k,l).

Outcome Our patient experienced a very good outcome with resection of a paraspinal schwannoma with intrathoracic extension using a combined minimally invasive anterior and posterior approach. Intraoperative blood loss was minimal, and gross total resection of the tumor was accomplished. The MARSS technique can be used safely and effectively to perform minimally invasive spine surgery.

30.5.2 Case 2: Tumor (Right T2–T3 Neural Foramen) A 66-year-old female presented with finding on chest X-ray of right upper lung field mass. CT revealed a tumor coming from the right T2–T3 neural foramen (▶ Fig. 30.7a–c).

Surgical Approach Posterior Approach The patient was intubated with double lumen endotracheal tube to allow collapsing of the right lung. She was then placed in the prone position on gel rolls. Using fluoroscopy, the level was identified by counting ribs down and up to the level. An incision was made approximately 2 cm lateral to the midline at the level of the right T2–T3 neural foramen. A series of muscle dilators were used to approach the spine over which an 18-mm tubular retractor was placed. The lamina and facet complex on the right side were exposed. Using a high-speed drill, laminectomy and facetectomy were performed with all bone dust collected using the Thompson MIS BoneBac Press. The tumor was extending into and out of the right T2–T3 neural foramen. The nerve root from which the tumor arose was identified and suture ligature was applied around the root and then cut so that the tumor could be safely removed from the thoracic cavity (▶ Fig. 30.8). Fibrin glue was applied and the tubular retractor was removed, allowing the paraspinous muscles to return to their normal anatomical position. The fascia was reapproximated using 2–0 interrupted Vicryl suture. A subcuticular suture was applied, followed by skin glue.

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Fig. 30.4 (a) Anatomy of thoracic spine with tumor in place. (b) Posterior view with resection of lamina and facet. (c) Tubular retractor in place. (d,e) Final resection of tumor. (f) Collection of drilled autograft bone using BoneBac Press. (g) Final reconstruction of lamina and facet with collected drilled autograft bone.

Fig. 30.5 Posterior minimally invasive surgery resection of a tumor. (a) Pretumor removal after laminectomy, facetectomy, and exposure of spinal cord and tumor. (b) Tumor bed after gross total removal.

Anterior Approach The da Vinci robot was prepared and draped. A thoracic endoscope was then used to identify the proper incision location for placing the robotic ports (▶ Fig. 30.9a). The robot was then introduced into the thoracic cavity. Four robotic arm ports were applied and included suction, camera, Bovie, and grip retractor arm. Using the da Vinci surgeon console (▶ Fig. 30.9b), the arms were used to remove the tumor in a gross total fashion by circumferentially coagulating and resecting at the base of the tumor (▶ Fig. 30.9c). The arms and ports were removed and the

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incision was closed in a routine fashion. The patient made a quick recovery and was discharged on postoperative day 2. Postoperative MRI 2 years after surgery showed no residual tumor (▶ Fig. 30.9d, e).

30.6 Postoperative Care Patients are typically observed in the intensive care unit (ICU) for the first night postoperatively. A chest tube is usually placed and it is removed once fluid output is limited. Patients are ambulated

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Fig. 30.6 (a) Thoracoscopy used to help guide port placement. (b,c) da Vinci robot. (d) Ports and thoracoscopic arms in place. (e) A da Vinci robot console with surgeon operator. (f) Intraoperative view of tumor resection. (Continued)

the day after surgery and the Foley is removed. Once stable, ambulating, tolerating oral intake, and voiding regularly, the patient is discharged. If needed, physical therapy is generally started 2 weeks after surgery during the first postoperative visit. Patients with any sign of infection (e.g., significant wound draining, high fever, etc.) are asked to return to the hospital. In the case of tumor, an initial postoperative contrast MRI is ordered. This study can be repeated in 6 months to a year to assure no recurrence of tumor. This can be repeated in the second year to assure no recurrence of tumor pathology.

30.7 Management of Complications Complication avoidance is enhanced with proper surgical training with the use of the da Vinci robot system. This technique for the treatment of intrathoracic pathology is rapidly evolving and will improve with refinements of technique and instrumentation. The proper level location can be identified with careful preoperative workup including scout CT or MRI from the sacrum to the level of the pathology to aid in intraoperative vertebral body counting. Additionally, AP and posterior lumbar and thoracic plane films as well as chest X-ray are ordered to aid in proper level identification. Dural tears and/ or injury to the spinal cord can be avoided by first removing the intraspinal component of the tumor. Placement of fibrin glue sealant can help avoid a possible cerebral spinal fluid leak into the chest cavity. If needed, a chest tube can be placed at completion of the thoracic portion of the procedure to avoid hemothorax. Patients are ambulated soon after surgery to prevent postoperative atelectasis.

30.8 Conclusion Recent advances in retractor systems have led to new, minimally invasive approaches to the spine.6 Though there are few examples in the literature, these posterior MIS approaches can be combined with anterior approaches using the da Vinci robotic system to access complex lesions while providing excellent outcomes for our patients. It is important that as surgeons, we continue to train and familiarize ourselves with new technology and techniques. It is also vital that we collect clinical data on patient outcomes, and publish them in a timely manner. In this way, we can provide an extremely high level of care to our patients using MARSS techniques and improve patient outcomes while pushing the boundaries of surgical technology. Minimally invasive approaches to complex lesions have provided patients with better outcomes and fewer complications, including reduced intraoperative blood loss, less postoperative pain, shorter hospital stays, and better quality of life.6,7 As we push forward with new minimally invasive techniques, it is important to keep in mind that our goal is to perform the complete surgery. MIS is not minimal surgery. We must provide our patients with all of the benefits of traditional open surgical approaches without the added morbidity associated with large incisions, excessive muscle dissection, and neurovascular compromise. The da Vinci robotic surgical system presents new challenges to surgeons and requires extensive specialized training. Operating at a console can be disorienting, and requires the surgeon to respond to a different set of cues. The surgeon tactile feedback of using instruments is lost in exchange for reduced approach-related morbidity. The robotic system translates the surgeon’s gross hand movements into the subtle movements of instruments inside of the body cavity. Touch and pressure stimuli present when

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Fig. 30.6 (continued) (g,h) Illustrations showing thoracic removal of tumor. (i) Preoperative MRI. (j) Postoperative contrast-enhanced MRI showing gross total tumor resection. (k) Two weeks postoperatively showing thoracic posterior surgical incisions. (l) Patient made an uneventful recovery and remains tumor free 2 years postoperatively.

operating directly on the patient are not available while using the da Vinci system. Thus, it is imperative that surgeons undergo proper training in courses and cadaver laboratories in order to learn the nuances of the system. These resources are currently available to educate surgeons and improve patient outcomes. With the use of MARSS techniques, we can potentially reduce the morbidity associated with open thoracotomy, and drastically improve quality of life in our patients. The da Vinci robotic system provides other technical advantages to the surgeon. The system’s four arms, which are controlled with two hand controllers and two foot pedals, can be interchanged with cameras and various other instruments. The system provides the operator with great visualization of the operative field with its ability to navigate around corners and within tight corridors. The da Vinci system also allows for range of motion exceeding that of the human hand, and provides a tremor-reduction and motionscaling algorithm to further refine hand movements.1

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Clinical Caveats ● ●

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Proper da Vinci robot training is required. Level identification can be difficult in high thoracic level pathology. Preoperative image preparation and analysis prior to surgery are critical. Detachment of the tumor from a posterior approach first facilitates safe tumor resection from the anterior thoracic approach. Reconstruction of the facet complex using local bone autograft can eliminate the need for more extensive instrumented fusion. Thoracoscopic visualization of port placement can reduce lung or visceral injury. Appreciation of anatomical variation in individual patients by studying images preoperatively can reduce complications.

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Minimally Invasive Robotic-Assisted Thoracic Spine Surgery

Fig. 30.7 (a) Coronal and (b) axial CT and (c) coronal and (d) axial MRI showing a mass coming out of the right T2–T3 neural foramina extending into the apical chest cavity.

Fig. 30.8 (a) Intraoperative image showing exposure of tumor within the spinal canal arising from the exiting thoracic nerve root, (b) suture ligation of nerve root, and (c) section of the nerve root leading to tumor so that the tumor could be safely removed via the anterior thoracic approach.

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Fig. 30.9 (a) Intraoperative image showing use of thoracic endoscope to identify da Vinci port location on thoracic chest. (b) Photograph of work station of a da Vinci robotic surgeon. (c) Intraoperative video monitor view showing use of da Vinci robotic arms to resect tumor from chest wall. (d) Two-year postoperative contrast-enhanced coronal and (e) axial MRI showing complete resection of tumor with no evidence of recurrence. Small amount of enhancement seen on axial image represents surgical scar.

References [1] Obasi PC, Hebra A, Varela JC. Excision of esophageal duplication cysts with robotic-assisted thoracoscopic surgery. JSLS. 2011; 15(2):244–247 [2] Ismail M, Swierzy M, Ulrich M, Rückert JC. Application of the da Vinci robotic system in thoracic surgery. Chirurg. 2013; 84(8):643–650 [3] Perez-Cruet MJ, Welsh RJ, Hussain NS, Begun EM, Lin J, Park P. Use of the da Vinci minimally invasive robotic system for resection of a complicated paraspinal schwannoma with thoracic extension: case report. Neurosurgery. 2012; 71(1) Suppl Operative:209–214

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[4] Yang MS, Kim KN, Yoon DH, Pennant W, Ha Y. Robot-assisted resection of paraspinal Schwannoma. J Korean Med Sci. 2011; 26(1):150–153 [5] Kajiwara N, Kakihana M, Usuda J, et al. Training in robotic surgery using the da Vinci® surgical system for left pneumonectomy and lymph node dissection in an animal model. Ann Thorac Cardiovasc Surg. 2011; 17(5):446–453 [6] Perez-Cruet MJ, Khoo LT, Fessler RG, eds. An Anatomical Approach to Minimally Invasive Spine Surgery. St. Louis, MO: Quality Medical Publishing; 2006 [7] Perez-Cruet MJ, Beisse R, Pimenta L, Kim DH, eds. Minimally Invasive Spine Fusion: Techniques and Operative Nuances. St. Louis, MO: Quality Medical Publishing; 2011

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Minimally Invasive Spine Surgery: Thoracic Case Studies

31 Minimally Invasive Spine Surgery: Thoracic Case Studies Mick J. Perez-Cruet, Richard G. Fessler, and Michael Y. Wang Abstract Minimally invasive spine (MIS) approaches to the thoracic spine allow many advantages by preserving the normal anatomic integrity of the thoracic spine. These techniques ultimately result in less tissue damage, faster patient recoveries, and quicker return to improved quality of life. However, it must be cautioned that many of these approaches require specialized training including MIS fellowships, cadaveric workshops, and/or MIS surgeon expert-guided intraoperative training. The thoracic spine is perhaps the most delicate segment of the spine, and overaggressive manipulation can result in permanent neurological deficits. This chapter illustrates a number of thoracic cases that will show the benefits of mastering these challenging but greatly patient-rewarding approaches and techniques to treat trauma, tumor, and degenerative pathology. Keywords: thoracic pathology, minimally invasive, trauma, tumor, degenerative

31.1 The Evolution of Thoracic Minimally Invasive Spine Surgery Thoracic minimally invasive spine (MIS) surgery has a long and rich history. This is due in part to the fact that access through the pleural cavity affords the use of endoscopic as well as minimally invasive techniques in a body cavity and thus is a natural extension of general surgical endoscopic and MIS approaches. While the use of thoracoscopy to access the anterior thoracic vertebral column was a natural development, its adoption has been limited by the different and unique skill set that is not part and parcel with traditional spinal surgery.

31.2 Case 1: Retropleural Thoracic Discectomy 31.2.1 Patient Profile A 60-year-old female with osteoporosis developed a low-energy L1 fracture. She had developed progressive pain in the upper back with a progressive spinal deformity. The pain was associated with mechanical loading, and her symptoms were progressive (▶ Fig. 31.1a–f).

31.2.2 Case Selection With severe osteoporosis, the patient was started on pharmacologic treatment to improve her bone density. Extensive counseling was undertaken to inform the patient of the risks and benefits of surgical versus conservative management. The decision was made to perform a MIS anterior and posterior operation to most optimally correct her deformity without performing a long segment fusion.

31.2.3 Preoperative Notes Extensive discussion was undertaken regarding the length of the construct, given her coronal and sagittal imbalance. The patient refused to have a long segment fusion, for example, a T5 iliac, as a first attempt to correct her problem; therefore, a more parsimonious approach was chosen. The patient was also counseled on the off-label use of recombinant human bone morphogenetic protein (rhBMP-2) as well as the potential risks of pleural violation and the need for a chest tube.

31.2.4 Instrumentation Notes Numerous cage reconstruction and fixation options are available and it was decided that an expandable cage would give the best option for restoring anterior column height. Use of a polyetheretherketone (PEEK) cage more closely matched the patient’s bone modulus and thus might reduce the likelihood of significant settling.

31.2.5 Surgical Approach and Technique In the direct lateral approach, the L1 vertebral body was targeted. A small 2-cm flank incision allowed dissection of the retropleural space, which allowed entry through a 3-cm direct lateral incision to place a tubular retractor. This then allowed cutting of the disc spaces above and below the L1 body with Cobb elevators and osteotomes (▶ Fig. 31.1g–j). Once L1 was removed, temporary distractors elevated the interbody height. This was followed by cage placement and expansion (▶ Fig. 31.1h–p). The patient underwent percutaneous screw fixation and further sagittal correction under the same anesthetic (▶ Fig. 31.1q,r). This resulted in a significant improvement, likely possible without employing a longer construct.

31.2.6 Postoperative Care The patient is managed postoperatively with standard pain management and bracing, similar to standard open surgery. There was no chest tube necessary and chest X-rays did not demonstrate a pneumothorax.

31.2.7 Management of Complications Routine antibiotic prophylaxis is used to minimize the risk of postoperative infections. Pseudarthrosis can be minimized with proper graft site preparation, use of appropriate graft materials, bracing, external bone stimulation, and the elimination of tobacco use.

31.2.8 Operative Nuances Great care is taken at the level of the diaphragm to minimize its disruption. Careful direct visualization of the retropleural space is also necessary given the ease with which the pleura is violated.

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Fig. 31.1 (a) Sagittal CT reconstruction showing an L1 chronic compression fracture with deformity. (b) The spine shown on MRI, (c) flexion, and (d) extension lateral X-rays. (e) Thirty-six-inch anteroposterior scoliosis X-rays. (f) Thirty-six-inch lateral scoliosis X-rays. (g) Intraoperative lateral imaging to target the center of the L1 vertebral body. (h) A Cobb elevator cutting across the T12/L1 disc space. (i) Osteotomy cuts at the top. (j) Bottom of the L1 body. (k) Distraction of the fracture site with a temporary expandable cage on the right and (l) left sides of L1. (m) Initial placement of a radiolucent expandable cage using a shim to reduce the likelihood of end plate violation. (n) Following cage expansion.

31.2.9 Postoperative Results

31.3.2 Case Selection

This approach is being employed more commonly given the significant morbidity associated with thoracoabdominal and thoracotomy approaches.

With the absence of a large anterior disc herniation in a neurologically intact patient, a posterior approach with reduction, fixation, and fusion is a reasonable treatment option.

31.3 Case 2: Percutaneous Thoracic Fixation for Trauma

31.3.3 Preoperative Notes

31.3.1 Patient Profile A 46-year-old woman was involved in a high-speed motor vehicle accident (MVA), resulting in severe back pain. She was presented to the emergency department neurologically intact, but with axial pain 9/10. Imaging studies revealed a dislocation-dislocation at the T6–T7 level (▶ Fig. 31.2a, b).

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The patient was neurologically intact with good alignment, so she was a good candidate for percutaneous fixation. On the other hand, this fracture was likely too unstable to be treated only with external bracing.

31.3.4 Instrumentation Notes Numerous fixation options are available for thoracic percutaneous screw fixation. In this case, extension tab screws were chosen

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Fig. 31.1 (continued) (o) Sagittal CT reconstruction showing height restoration at L1. (p) Axial CT showing central cage placement. (q) AP and (r) lateral final 36-inch standing films showing improvement in coronal and sagittal alignment.

for ease of bringing the rod to the screw saddles while requiring a very small skin and fascial incision for placement.

31.3.5 Surgical Approach and Technique The patient is positioned prone on a Jackson table with care not to overextend her and further disrupt the alignment. Screws are placed through 6-mm individual incisions. Pedicle targeting is achieved using the anteroposterior (AP) fluoroscopic view to enter the pedicle 2 cm without passing the medial wall of the pedicle to ensure the canal is not violated. Kirschner’s wires (K-wires) allow passage of an awl and tap under lateral fluoroscopic views, and screws are then placed. The rod is bent appropriately and then passed subfascially and connected to the screws using set screws (▶ Fig. 31.2c, d). The reduction portion of the screw extensions makes this an efficient process and also allows for correction of kyphosis. The facets can also be drilled, decorticated, and packed with graft materials for fusion. Wound closure is with a single stitch at each incision (▶ Fig. 31.2e).

31.3.6 Postoperative Care If a fusion is not performed, the patient should be counseled on the possibility of needing a delayed hardware retrieval after bony fusion has occurred.

31.3.7 Management of Complications Routine antibiotic prophylaxis is used to minimize the risk of postoperative infections.

31.3.8 Operative Nuances Use of AP targeting minimized radiation exposure for the surgeon, and frequently four bilateral spinal levels can be targeted with a single fluoroscopic view.

31.3.9 Postoperative Results Given the nature of polytrauma, such percutaneous approaches may be used for “internal bracing” and as “damage

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Fig. 31.2 (a) CT and (b) MRI sagittal reconstructions showing a T6–T7 disruption consistent with a ligamentous chance fracture. (c,d) Following placement of percutaneous screws, a rod bent into the appropriate kyphosis is introduced and passed subfascially. (e) Postoperative anteroposterior X-ray.

control surgery” to allow a patient to survive an injury without taking as much risk as in an open surgical procedure.

31.4 Case 3: Minimally Invasive Trans-facet Thoracic Discectomy 31.4.1 Patient Profile The patient is a 56-year-old woman status post MVA. Immediately after the MVA, her legs “felt like jelly.” Since then she has had pain located below her bra line, radiating bilaterally around to her anterior chest. She has attempted physical therapy, has had 12 thoracic epidural steroid injections, and is on chronic narcotic pain medication without significant relief. MRI revealed T7/T8 herniated disc with compression and deviation of the spinal cord (▶ Fig. 31.3a, b).

31.4.2 Case Selection This patient presents with a traumatic thoracic disc herniation and has failed 4 years of aggressive nonsurgical therapy. Because she has significant radiculopathy that correlates with her disc herniation level, she is an excellent candidate for thoracic discectomy.

31.4.3 Preoperative Notes Other than mild distal right lower extremity weakness, the patient is neurologically intact. She does not have evidence of

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myelopathy. To ensure identification of the correct operative level, preoperative thoracic (to count ribs) and lumbar (to verify five normal lumbar vertebrae) X-rays are necessary. Furthermore, an MRI scout showing the herniation and the sacrum or C2 in the same cut is needed.

31.4.4 Instrumentation Notes When a minimally invasive technique is used, instrumentation is not necessary.

31.4.5 Surgical Approach and Technique The patient was induced with general anesthesia, intubated endotracheally, and turned into the prone position onto chest rolls. Using lateral fluoroscopy, an appropriate incision to approach the right T7/T8 level was identified and marked 1.5 cm off midline. The correct level was identified by counting vertebrae from S1 to the surgical level using continuous fluoroscopy. A no. 10 scalpel was then used to incise the skin over approximately 2 cm and a K-wire was placed through the incision and advanced to the T7/T8 facet. A series of dilators was placed over the K-wire, the K-wire was then removed, and the working channel was positioned, angled medially, and locked in place. Bovie cautery was used to remove a small amount of residual tissue at the bottom of the working channel. An angled curette was then used to define the sublaminar space below T7 and T8.

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Minimally Invasive Spine Surgery: Thoracic Case Studies

Fig. 31.3 (a) Sagittal and (b) axial T2-weighted MRI showing T7/T8 disc herniation with compression and deviation of the spinal cord.

Kerrison’s punch was used to perform a hemilaminotomy of T7/ T8. This was extended into a medial facetectomy using a drill. An angled curette was then used to define the plane between the ligamentum flavum and dura. Ligamentum flavum was removed using a Kerrison punch. The disc space was then readily visible and palpable. A no. 15 blade scalpel was used to incise the disc space lateral to the dura. A series of curettes and pituitary rongeurs was then used to perform a lateral discectomy. Using down-pushing curettes, the disc bulge was pushed into the disc space and removed laterally using pituitary rongeurs. Exploration with a right-angled spatula revealed that the ventral dura was well decompressed. Hemostasis was obtained with Surgifoam and bone wax.

31.5 Case 4: Intradural/ Extramedullary Tumor

31.4.6 Postoperative Care

Intradural/extramedullary tumors with focality, such as schwannomas or neurofibromas, are excellent candidates for resection through an MIS approach.

Skin is closed with Dermabond, routine recovery is several hours of observation, and the patient may then be discharged home. Bracing is not necessary. Physical therapy is begun between 3 and 6 weeks postoperatively.

31.4.7 Management of Complications Routine antibiotic prophylaxis is used to prevent wound infection. Cerebrospinal fluid (CSF) leak, if encountered, is sealed with DuraSeal, and the patient is kept lying flat overnight and discharged the next morning. Lumbar drainage is not necessary.

31.4.8 Operative Nuances Maintaining straight to lateral trajectory of the K-wire will protect against inadvertent entrance into the spinal canal. Absolute diligence in level identification (preoperative X-rays, MRI, and repeated and accurate intraoperative counting) will minimize risk of incorrect level surgery. Removal of 50% of facet will enable entrance into the lateral disc space without retracting the dura.

31.4.9 Postoperative Results Excellent relief of radicular pain is seen in the majority of thoracic disc herniation patients. However, thoracic discectomy is generally less effective for central back pain.

31.5.1 Patient Profile The patient is a 56-year-old female with a 6-month history of progressive weakness in the lower extremities. On examination it is found that she has 4/5 iliopsoas weakness and a subjective sensory level to pinprick just below the level of the breasts. MRI reveals an intradural/extramedullary tumor, ventral to the spinal cord, located at T6/T7 (▶ Fig. 31.4a,b).

31.5.2 Case Selection

31.5.3 Preoperative Notes To ensure identification of the correct operative level, preoperative thoracic (to count ribs) and lumbar (to verify five normal lumbar vertebrae) X-rays are necessary. Furthermore, an MRI scout showing the herniation and the sacrum or C2 in the same cut is needed.

31.5.4 Instrumentation Notes Using minimally invasive technique, the supraspinous ligament is kept intact. Therefore, instrumentation is generally not necessary.

31.5.5 Surgical Approach and Technique The patient is induced with general anesthesia, intubated endotracheally, and turned into the prone position on chest rolls. Using lateral fluoroscopy, an appropriate incision to approach the T6/T7 level is identified by counting vertebrae from S1 to the surgical level using continuous fluoroscopy. The skin is incised over approximately 4 cm, 1.5 cm lateral to midline, and a K-wire is placed through the incision and advanced to the T6/T7 facet. A series of dilators is placed over the K-wire, the K-wire is then

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Fig. 31.4 (a) Sagittal and (b) axial MRI reveals an intradural/extramedullary tumor, ventral to the spinal cord, located at T6/T7.

removed, and the working channel is positioned, angled medially, and locked in place. Bovie cautery is used to remove any residual tissue at the bottom of the working channel. An angled curette then defines the sublaminar space below T7 and T8. A hemilaminotomy is created from the bottom of T7 and extending to the top of T6. This is extended into a medial facetectomy using a drill. The tube is then angled medially, and the drill is used to remove the ventral portion of the spinous process and contralateral lamina all the way to the contralateral pedicle. An angled curette is then used to define the plane between the ligamentum flavum and dura. Ligamentum flavum is removed using a Kerrison punch. Hemostasis in the lateral gutters is assured using Surgicel and Surgifoam. Under microscopic guidance, the dura is opened in the midline and the edges are tacked back. After cutting the dentate ligament, the tumor is identified. Traversing nerves were dissected free of the tumor and the tumor was removed either piecemeal or intact. After assuring hemostasis, routine wound closure is performed.

31.5.6 Postoperative Care Skin is closed with Dermabond; routine recovery is several hours of observation, and 1 to 2 days of hospitalization. Bracing is not necessary. Physical therapy is begun between 3 and 6 weeks postoperatively.

31.5.7 Management of Complications Routine antibiotic prophylaxis is used to prevent wound infection. Because the dura was opened, the dural incision can be sealed with Duraseal. In either case, the patient is kept lying flat overnight, and elevated slowly the next morning. Lumbar drainage is not necessary.

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31.5.8 Operative Nuances Maintaining straight to lateral trajectory of the K-wire will protect against inadvertent entrance into the spinal canal. Absolute diligence in level identification (preoperative X-rays, MRI, and repeated and accurate intraoperative counting) will minimize risk of incorrect level surgery. Removal of 50% of facet will enable excellent exposure of the tumor without risking instability. With that additional resection, most often the tumor can be slid to the side of the spinal cord and removed without causing any harm to the cord.

31.5.9 Postoperative Results Reported results have demonstrated total resection of intradural/extramedullary schwannomas and neurofibromas without neurologic compromise, and with more rapid discharge from the hospital.

31.6 Case 5: Rotatory Thoracic Levo-Dextroscoliosis 31.6.1 Patient Profile An 84-year-old male presents with progressive paraparesis status post long construct open thoracic–lumbar fusion and instrumentation. He is only able to ambulate with the use of a walker and has 4/5 leg strength bilaterally and brisk lower extremity reflexes. He has had multiple prior lumbar fusion and instrumentation with the last fusion extending to the lower thoracic region. He has multiple medical comorbidities and is a high-risk surgical candidate. MRI revealed a high-grade T10–T11 spinal stenosis (▶ Fig. 31.5). His plain films revealed that he had a rotatory levodextroscoliosis in the thoracic and lumbar spine.

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Minimally Invasive Spine Surgery: Thoracic Case Studies

Fig. 31.5 (a) Sagittal and (b) axial MRI showing high-grade T10 –T11 spinal stenosis (blue arrow).

31.6.2 Case Selection, Preoperative, and Instrumentation Notes Patient had significant medical comorbidities; thus, a posterior minimally invasive approach was chosen. He had no other areas of stenosis, and his symptoms were felt to be due to the focal T10– T11 stenosis. The hypertrophy of the ligamentum flavum and signal seen within the facets joints implied an unstable segment that might lead to restenosis or become grossly unstable with decompression alone; thus, a posterolateral fusion and minimally invasive percutaneous pedicle screws were applied. No attempt was made to correct the deformity, as this was not felt to be causing his symptoms. Patient was informed that his leg strength might not improve or might possibly worsen with surgical intervention.

31.6.3 Surgical Approach and Technique The patient was intubated and monitoring was placed including somatosensory evoked potential (SSEP) and MEP. The patient was carefully log rolled into the prone position onto a radiolucent Jackson table. All pressure points were padded. The level was identified with lateral fluoroscopy. An incision was made 2 cm lateral to the midline and the fascia cut. A series of muscle dilators were placed to approach the spine over which an 18-mm tubular retractor was placed. An ipsilateral laminectomy was performed. The patient was tilted 5 degrees away from the surgeon and the spinous process and contralateral lamina were undercut with a long tapered drill using an M8 burr. All bone was collected using the Thompson MIS BoneBac Press (Thompson MIS, Salem, MA) and used for fusion material. Once adequate bony decompression was achieved, the ligamentum flavum on the ipsilateral side was removed, followed by the ligamentum flavum on the contralateral side. The bed was placed flat again and a discectomy performed to allow for additional space in the canal. The facets were then decorticated through the tube and autograft placed within the facet complexes bilaterally. Complete hemostasis was achieved and the tubular retractor removed, allowing the paraspinous muscles to return to their normal anatomical position.

Using AP and lateral fluoroscopy, percutaneous pedicle screws were placed in a routine fashion via two 2-cm-long paraspinal incisions (▶ Fig. 31.6).

31.6.4 Postoperative Care Patient was transferred to the floor and used a brace when ambulating. He gradually began to regain his leg strength and with physical therapy was able to walk independently.

31.6.5 Management of Complications Adjacent level disease, particularly with prior long construct instrumentation, is a frequently seen problem. We feel this is in large part due to resection of the normal anatomical integrity of the spine that leads to relative instability at adjacent levels and response seen in facet and ligamentum flavum hypertrophy. When treating elderly patients with degenerative scoliosis, we prefer an approach that treats the symptomatic level. In many cases, these patients can be treated with a focused minimally invasive decompression, fusion, and instrumentation without the need to correct the deformity. This can lead to marked improvement in the quality of life without the risk of major spinal deformity correction surgery or the need for further spine surgery as much of the normal anatomy is preserved.

31.6.6 Operative Nuances ●

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When treating elderly patient with deformity, try to identify the cause of the current symptoms. CT/myelogram can often reveal where symptomatic focal canal or foraminal stenosis exists in patients with degenerative levo-dextroscoliosis. In many elderly patients with deformity, simple minimally invasive decompression and posterolateral fusion supplemented with percutaneous instrumentation can lead to return to activities of daily living with minimal surgical risk or need for further surgical intervention.

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Fig. 31.6 (a) Postoperative lateral and (b) anteroposterior plain X-rays showing instrumentation in place at the T10 –T11 level. Note prior traditional surgical intervention with long construct fusion and pedicle screw instrumentation.

Fig. 31.7 (a) Sagittal and (b) axial thoracic CT/myelogram showing a large partially calcified T10 –T11 right-sided thoracic disc herniation with marked spinal cord compression.

31.7 Case 6: Thoracic Disc Herniation with Spinal Cord Compression 31.7.1 Patient Profile A 48-year-old obese female presented with severe right leg pain and paraparesis. CT/myelogram of the thoracic spine reveals a large partly calcified right-sided T10–T11 thoracic disc herniation with marked spinal cord compression (▶ Fig. 31.7).

31.7.2 Case Selection Because of the location and marked compression of the spinal cord by a partly calcified thoracic disc herniation as well as the presentation of severe bilateral leg weakness, an anterior approach was chosen. To reduce postoperative pain and discomfort, a minimally invasive thoracotomy approach was chosen. The patient was informed of the gravity of the case and that her leg weakness might not improve or she might become paraplegic even with surgical intervention. She chose to proceed with the surgery.

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31.7.3 Preoperative Notes MRI of the thoracic spine showed a marked compression and signal changes in the spinal cord from the T10–T11 disc herniation. Plain X-rays of the thoracic and lumbar spine as well as chest X-ray were evaluated for proper intraoperative localization of the thoracic disc herniation. Additionally, a CT/myelogram of the thoracic spine showed the extent of spinal cord compression and that the midline partly calcified disc herniation warranted an anterior approach. A scout film showing the sacrum to the level of the thoracic pathology was taken to aid in proper intraoperative localization (▶ Fig. 31.7).

31.7.4 Instrumentation Notes A unique retractor (Alexis O, Applied Medical, Rancho Santa Margarita, CA) was used, through which the procedure was performed (▶ Fig. 31.8 and ▶ Fig. 31.9). An expandable cage filled with morselized autograft harvested from the same surgical incision using the BoneBac Press (Thompson MIS) was used. A two-bolt anterior thoracic plate construct (Medtronic, Memphis, TN) was used to secure the cage in place and add to the final construct strength.

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Minimally Invasive Spine Surgery: Thoracic Case Studies

Fig. 31.8 (a) Intraoperative photos showing the use of the Alexis retractor (b) to perform minimally invasive spine thoracotomy.

31.7.5 Surgical Approach and Technique Patient was intubated and monitoring placed including SSEP and MEP. The patient was placed on a beanbag and secured in the lateral position with the right side up. The level was then identified with fluoroscopy counting from the sacrum to the level of pathology as well as counting rib heads. The incision was made directly over the T10–T11 disc space and the retractor placed (▶ Fig. 31.8). Microscope was brought into the operative field. The pleura was taken down over the T10 and T11 vertebrae as well as the T10 rib head. A long tapered drill (Stryker TPS, Kalamazoo, MI) was used to drill the rib head and underlying pedicle in order to enter the spinal canal and identify the location of the spinal cord. Once confirmed, a partial corpectomy of T10 and T11 was performed as well as a T10–T11 discectomy. With adequate space created ventral to the disc herniation, the large disc herniation was pushed away from the spinal cord into the ventral surgical defect. Brisk bleeding was controlled with Gelfoam, Surgifoam, and cottonoid pledget. Complete decompression of the spinal cord was achieved. An expandable cage was then filled with morselized autograft collected from the same surgical field and positioned to fill the defect. An anterior thoracic plate was applied as well but first the screw bolts were applied and the plate was locked in place. Additional morselized autograft bone was placed around the construct. A chest tube was left in place. The rib was reconstructed with a rib plate and the incision closed in a routine fashion (▶ Fig. 31.9).

compression stockings and pneumatic compression device on her legs bilaterally. Careful monitoring and care of bladder and bowel function was performed. Patient wore a thoraco-lumbar brace while ambulating.

31.7.7 Management of Complications Large calcified thoracic disc patients presenting with paraparesis can lead to paraplegia even with surgical intervention. To avoid manipulation of the spinal cord, we prefer an anterior approach. To help reduce or avoid post-thoracotomy pain symptoms, we use a soft retractor system and reconstruct the thoracic rib with a plate. Anticipate brisk venous bleeding when resecting these lesions, and hemostatic agents are critical. Early mobilization of these patients can help reduce DVTs.

31.7.8 Operative Nuances ●

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31.7.6 Postoperative Care The patient was initially managed in the intensive care unit (ICU) with chest tube in place. Early ambulation was encouraged. Patient was started on physical therapy soon after surgery with deep vein thrombosis (DVT) prophylaxis including

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Careful preoperative workup can help in the approach decision-making process. We prefer CT/myelogram as it helps define whether the disc is calcified or not. Sagittal reconstructive CT or MRI from sacrum to the level of pathology can help accurately identify the level. Removal of the rib head and pedicle at the level of the pathology will identify the location of the spinal canal and helps orient the surgeon during surgery. Hemostatic agents are necessary as brisk venous bleeding is expected. Expandable cage technology filled and surrounded by autograft bone helps assure a solid final construct. Anterior plate instrumentation leads to further construct strength and avoidance of the need for additional posterior instrumentation. Chest tube placement can avoid the need for thoracentesis post-op.

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Fig. 31.9 Illustrations showing steps to perform thoracic discectomy including (a) illustration of thoracic anatomy, (b) drilling off rib head, (c) exposure of underlying lateral aspect of pedicle, (d) drilling rostral two-thirds of pedicle, (e) exposure of dura, (f) creating a trough in the disc space and adjacent vertebrae to (g) push the disc fragment into.

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Minimally Invasive Spine Surgery: Thoracic Case Studies

Fig. 31.9 (continued) (h) Removal of disc fragment compressing spinal cord, (i) preparation of corpectomy site (j,k) for expandable cage, and (l) anterior plate placement.

Fig. 31.9 (continued) (m) Intraoperative microscopic view of large herniated thoracic disc and (n) after decompression of the spinal cord. (o) Intraoperative view of expandable cage filled with and surrounded by morselized autograft bone harvested from the surgical site and (p) plate in place.

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Fig. 31.9 (continued) (q) Postoperative reconstructive axial CT showing spinal cord decompression, (r) postoperative incision. (s) Postoperative plane anteroposterior and (t) lateral views showing plate reconstruction of rib to help reduce post-thoracotomy pain.

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31.7.9 Postoperative Results

31.8 Conclusion

The patient was managed with chest tube following surgery and started to ambulate soon after surgery. Patient made an unremarkable recovery and was managed with physical therapy. The patient wore a thoracic brace while ambulating up to 3 months following surgery. Subsequent imaging studies after 3 months showed complete fusion of the segment instrumented.

A variety of pathology of the thoracic spine can be treated in a minimally invasive fashion and includes degenerative conditions, trauma, and neoplasm. With refinements in technique and technology, the indications for treatment of thoracic conditions will expand. The advantages of MIS in thoracic cases to patients are quicker recoveries and less iatrogenic tissue damage.

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Endoscopic Spine Techniques: An Overview

32 Endoscopic Spine Techniques: An Overview Nima Salari, Christopher Yeung, and Anthony T. Yeung Abstract Posterolateral endoscopic discectomy provides excellent access to the epidural space from pedicle to pedicle facilitating removal of herniated disc fragments. It is the least invasive visualized surgical procedure for treating lumbar disc herniations. Literature demonstrates equivalent or better results compared to standard posterior microscopic discectomy. It is an excellent minimally invasive surgical approach to many disc herniations. Ideal indications include foraminal/extraforaminal disc herniations, upper lumbar and lower thoracic herniations, revision cases, foraminal stenosis, and as a treatment of discitis. This chapter will discuss the historical development of the procedure, relevant literature with results, and indications and contraindications, and describe the step-by-step surgical technique. Keywords: endoscopic discectomy, foraminoplasty, posterolateral discectomy, YESS, herniated disc, minimally invasive discectomy

32.1 Introduction The pathogenesis of disc degeneration and herniation is complex and multifactorial, but surgical management for the condition has seen little change since the introduction of the operating microscope.1,2 The microscopically assisted technique became the gold standard; however, it requires retraction of the dural tube and nerve, periosteal stripping of the muscle and ligaments, removal of laminar bone, and regional or general anesthesia. As outlined in previous chapters, tubular retractors utilize tissue dilation rather than cutting, and minimize the superficial tissue destruction, but the technique still requires

the same amount of bone removal and neural manipulation as the standard microscopic posterior discectomy.3 This can cause muscle atrophy and scarring around the sensitive nerve roots even in a technically perfect operation. The evolution of the surgical endoscope brought about significant change in many fields of medicine, predominantly in the realm of abdominal surgery and joint arthroscopy. Knee arthroscopy in many cases replaced the classic arthrotomy that was performed in the past. Adoption of endoscopy in spinal surgery has seen slower growth. In the early 1970s, Kambin, Gellman,4 and Hijikata5 separately defined posterolateral approaches for percutaneous central nucleotomy in the lumbar spine. The intervertebral disc space was later visualized with a modified arthroscope by Forst and Housmann.6 These developments along with Kambin’s anatomic description of the neural foramen for the purposes of posterolateral endoscopic access through the “triangular zone”7,8 (▶ Fig. 32.1) became the cornerstones in the development of the endoscopic transforaminal approach. Yeung9 introduced a rigid rod-lens, flow-integrated, multichannel, wide-angle operating spinal endoscope that allowed visualized access to the disc space. The endoscope configuration and the complementary instrument system with specialized slotted and bevel-ended tubular access cannulas allowed for same-field viewing of the intradiscal space, annular wall, and epidural space (▶ Fig. 32.2). The design allows for improved access to the posterior disc for visualized fragmentectomy, improved access to the undersurface of the superior articular facet for foraminoplasty, and protection of the neural structures by rotating the cannula. Several commercially available systems have been introduced to the market (Richard Wolf GmbH, Knittlingen, Germany; Joimax GmbH, Karlsruhe, Germany; Karl Storz, Tuttlingen, Germany;

Fig. 32.1 The reader should be familiar with Kambin’s “triangular zone” as best seen during a transforaminal interbody fusion approach to the disc space. The traversing and exiting nerve roots constitute the medial and superior borders of the triangle, respectively, while the inferior border is lined by the superior end plate of the lower lumbar vertebra.

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Fig. 32.2 The configuration of the endoscope and the bevel-ended tubular access cannulas allow for same-field viewing of the intradiscal space, posterior annular wall and longitudinal ligament, and epidural space. A, herniation; B, foraminal ligament (extension of ligamentum flavum); C, ligamentum flavum; D, posterior longitudinal ligament; E, beveled cannula; F, disc; G, annulus; H, traversing nerve root.

Max-MoreSpine, Unterföhring, Germany) and the technique has seen some changes. Imaging quality has improved over the years with higher definition cameras and monitors allowing for better visualization of the surgical field. Furthermore, the quality and assortment of instrumentation has seen refinement, with addition of holmium: yttrium aluminum garnet (Ho:YAG) laser, larger working channels, angled instruments, Kerrison rongeurs, and articulating reamers facilitating easier surgical access. Broader use of the technique has led to publication of multiple studies, which demonstrate the efficacy of the surgical approach.10,11,12,13,14,15,16,17 Quality studies suggest that outcomes are favorable in direct comparison to traditional microdiscectomy, all while minimizing approach-related morbidity. In their prospectively randomized clinical trial, Ruetten et al14 demonstrated benefits in posterolateral endoscopic surgery over microdiscectomy with similar patient satisfaction. The study cited shorter duration of operation time, more rapid rehabilitation, lower cost of care, and reduced trauma. Systematic reviews of the literature further this sentiment, indicating at least equally good outcomes for patients undergoing posterolateral endoscopic discectomy as compared to traditional microdiscectomy, although a long learning curve for this technique has been emphasized.10,11,12,13, 14,15,16,17,18 Prior experience with discography, epidural injections, and joint arthroscopy will help reduce the learning curve for the budding endoscopic spine surgeon.

32.2 Indications for Endoscopic Spine Techniques Any intervertebral disc herniation contiguous with the disc space not sequestered and migrated is amenable to endoscopic

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disc excision. The sizes and types of herniations chosen by the surgeon are dependent on their skill and experience level. Perhaps the ideal lesion for the technique is the far lateral extraforaminal disc herniation. The approach accesses the disc through the foramen where the cannula is easily inserted at the herniation site. Other opportune circumstances include the following: ● Targeting upper lumbar and lower thoracic disc herniations. ● Recurrent disc herniations after a standard microdiscectomy. ● Posterior annular tears. ● Foraminal bony stenosis. ● Discitis. ● A novel approach for interbody fusion.

32.2.1 Herniations Herniations in the upper lumbar segments require more aggressive laminotomies when approached posteriorly because of laminar shingling and overlap in relation to the disc space. Furthermore, more sagittal orientation of the facet joints may increase the chance for postoperative instability. Any potential destabilization is avoided via a posterolateral approach, and safe removal of disc herniations can also be achieved in the lower thoracic segments without the need to manipulate the spinal cord or conus medullaris. The posterior laminotomy defect and epidural scarring add a level of difficulty and require more technical skill to achieve safe outcomes in cases of recurrent disc herniations. It is not uncommon for the formed scar tissue to limit the migration of the recurrent herniated disc fragment. This makes the posterolateral endoscopic approach more advantageous as it avoids the scar tissue and allows for safer access to the disc fragment. Radiofrequency energy can be applied to annular tears under direct visualization to contract the collagen and ablate ingrown

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Endoscopic Spine Techniques: An Overview granulation tissue, neoangiogenesis, and sensitized nociceptors. This and the use of saline irrigation, which helps flush the neurotoxic chemicals and metabolites causing chemical irritation, can help reduce pain generated from this region. Frequently, interpositional nuclear tissue is seen within the fibers of the annular tear preventing the tear from healing. This tissue can be removed to allow the tear to heal, providing a minimally invasive alternative to a condition that may otherwise be treated with fusion or total disc replacement. Endoscopic foraminoplasty can be readily achieved with bone trephines/rasps, specially designed articulating burrs, Kerrison rongeurs, and the side-firing Ho:YAG laser. The roof of the foramen is formed by the undersurface of the superior articular facet. This is easily visualized and accessed via the endoscope. The side-firing Ho:YAG laser and bone trephines strip the facet capsule and remove bone to enlarge the foraminal opening. Synovial cysts can also be visualized and removed.

32.2.2 Discitis Discitis can be treated with posterolateral endoscopic discectomy and debridement. Current methods rely on needle aspiration, followed by prolonged antibiotic treatment. Needle aspirations are not as reliable as tissue samples from endoscopic debridement, and are often negative even in the face of bacterial discitis. Surgeons are often hesitant to perform open debridement because of the morbidity of the open approach, creation of dead space and devascularized tissue, and the concern for spreading the infection in the spinal canal. Endoscopic excisional biopsy and thorough debridement via the posterolateral portal has provided almost immediate pain relief and a much more reliable tissue sample for laboratory analysis and culture. Since only tissue dilation is used, no dead space is created that would allow the infection to spread.

32.2.3 Interbody Fusion With the growing popularity of interbody fusion and development of expandable interbody implants for the purpose of spinal realignment, the posterolateral endoscopic technique has the potential to become the least invasive method to achieve these results. With the use of specialized flexible shavers and direct visualization of the interspace via the endoscope, a more efficient discectomy is affordable. Further, previously inaccessible levels such as an L5/S1 interspace become amenable to minimally invasive posterolateral fusion via the approach. Similarly, lateral access to other levels of the lumbar spine is easily gained without dilation through the iliopsoas muscle or excessive traction on the individual nerve roots and/or the sensitive nerve plexus.

32.3 Contraindications for Endoscopic Spine Techniques Contraindications are relative and depend on the location of disc herniation, the patient’s anatomy, and surgeon experience. Sequestered herniations and highly migrated extruded herniations can be successfully treated from the posterolateral approach, but are more easily removed via a traditional posterior approach. Patients with a high iliac crest and a more horizontal

sacral slope present a challenge for the posterolateral endoscopic approach. A steeper, more medialized trajectory is needed, making it more difficult to reach herniations in the posterior quadrant of the disc space. In degenerative scoliosis, access through the neuroforamen on the concave side of the curve presents yet another challenge. Although these barriers are not insurmountable for the experienced surgeon, the surgeons first learning the technique should attempt more accessible foraminal herniations. As they become more familiar with the technique and their endoscopic surgical skills improve, they can successfully treat more difficult-to-reach herniations. In order to overcome anatomic constraints at L5/S1, for example, the more experienced endoscopic spine surgeon will attempt to remove the ventral portion of the superior articular process to allow for a shallower approach trajectory to the posterior aspect of the disc space.

32.4 Preoperative Planning A careful preoperative history, physical examination, and meticulous review of the plain radiographs and MRI are essential before attempting a posterolateral endoscopic discectomy regardless of the pathology being addressed. Attention to specific anatomic relationships is important to determine whether the approach is safe and feasible, and to ensure that there are no contraindications. Note the level of the iliac crest in relation to the disc space being accessed to determine the optimal needle trajectory. A high narrow pelvis may make it difficult to access the L5/S1 disc space. Furthermore, review the axial MRI images to evaluate the relationship of the lateral facets to the disc space and the location of retroperitoneal structures in order to obtain a better understanding of the planned trajectory (▶ Fig. 32.3). Also, severe degenerative scoliosis or the presence of spondylolisthesis may make the endoscopic procedure less predictable. Some endoscopic spine surgeons may elect to perform their own transforaminal epidural steroid injections. As a diagnostic tool, it is invaluable as a selective nerve root block to isolate the pathology to a unilateral and singular level. It may also provide the patient with therapeutic relief of symptoms, if only for a short period of time. More importantly, it may serve as a “trial run” to determine the ease of endoscopic instrument access to the pathologic lesion.

32.4.1 Instrumentation There are a number of endoscopic systems in clinical use today with similar instrumentation (▶ Fig. 32.4). At heart, they consist of an endoscope, video camera, light source with cable, a video processing unit, and a tower. The endoscopes typically employ a rigid rod-lens design connected to a body, which has a working channel and several attachments for irrigation fluid, suction, and a video source. The system used by the authors consists of the Yeung Endoscopic Spine Surgery System (YESS)/Vertebris system (Richard Wolf GmbH.) with the following instruments: ● Multichannel, 20-degree oval spinal endoscope with a 2.7-, 3.1-, or 4.1-mm working channel and integrated continuous irrigation (inflow and outflow) ports. ● Multichannel, 70-degree oval spinal endoscope. ● Access cannulas of 7 and 8 mm with various open slotted, beveled, and tapered tips.

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Fig. 32.3 While posteroanterior and lateral fluoroscopic imaging should aid the surgeon in triangulating the tip of the needle to the desired position after the patient has been positioned, close attention should also be paid to preoperative imaging. This axial view shows proposed needle trajectory as it traverses the erector spinae (ES) in relation to the quadratus lumborum (QL), psoas muscle (P), and the peritoneal cavity. Axial MRI imaging should also allow the surgeon to estimate the distance of the skin entry point from the midline (L) and the angle of the needle trajectory off of the horizontal plane.

Fig. 32.4 Basic instrument set includes the endoscope with a working channel for discectomy and probing tools utilized under direct visualization.

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Endoscopic Spine Techniques: An Overview ●

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Guide wire and tissue dilator/obturator cannulated with a central channel and an eccentric channel to accommodate a needle for local annular anesthetic (eccentric channel) while simultaneously positioned over the guide wire (central channel). Specialized single and double action rongeurs for visualized fragmentectomy through the endoscope working channel. Larger straight and hinged rongeurs that fit through the access cannulas for biportal fragmentectomy and fluoroscopically guided uniportal discectomy. Cutting tenotomy type forceps to release annular fibers. Trephines for annulotomy and removal of bone for foraminal enlargement (foraminoplasty). Micro-rasps, curettes, and Penfield probes. Annulotomy knife. Flexible bipolar radiofrequency probe (Elliquence) for hemostasis, thermal contraction of the annular collagen, and thermal ablation of the annular nociceptors.

Adjunctive equipment includes the following: Straight and flexible suction-irrigation shavers for discectomy. ● Pump suction-aspirator to connect to the suction-irrigation shavers for stronger suction than standard wall suction. ●

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Side-firing Ho:YAG laser for fine tissue and bone vaporization/dissection. Endoscopic high-speed drill and alternatively an articulating burr for foraminoplasty. Fluid pump for consistent and continuous irrigation.

32.5 Surgical Approach The process of posterolateral endoscopic discectomy started out as an inside-out approach. This means the disc fragments are extracted from within the disc space, which may be accessed through a lateral portal created in the annulus. Over time and with the introduction of new instruments and expansion of systems, the approach underwent several modifications. These modifications include the use of special reamers to widen the intervertebral foramen so that the herniated material could be accessed directly from inside the spinal canal, yet posterior to the disc space. An additional outside-in approach uses an extreme lateral approach accessing the foramen via a more horizontal trajectory. All three approaches still employ the transforaminal space for access, and each offers a small subset of advantages and disadvantages (▶ Fig. 32.5). Foraminal and extraforaminal disc herniations are easily accessed by all methods. An additional

Fig. 32.5 (a) With the inside-out approach, disc fragments are extracted from within the disc space, which may be accessed through a lateral portal created in the annulus. (b) With the use of special reamers to widen the intervertebral foramen, herniated disc material can also be accessed directly from inside the spinal canal without entering the disc space. This outside-in approach still employs the transforaminal space for access. (c) Alternatively, a more horizontal trajectory can afford access to the spinal canal without entering the disc space. Careful study of preoperative imaging is necessary to ensure safe passage to the intervertebral foramen.

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Fig. 32.6 (a,b) The tip of the endoscope and pituitary forceps can be levered and directed dorsally to remove disc fragments or to better visualize the ventral epidural space. This is best achieved via sufficient widening of the access portal into the disc space, or if necessary, by way of a foraminoplasty. (c) A demonstration of the fixed entry point and the ability to lever the tip of the cannula more dorsally.

lateral portal or fenestration is not required and the disc space can be targeted and accessed via the herniation site. The herniated material will shift the exiting nerve root further cranially, making the approach through Kambin’s triangle safer. In cases of contained central or paracentral disc herniations, the additional portal site via an inside-out approach may help spare the already weakened dorsal annulus. With the help of the flexible bipolar radiofrequency probe, energy can be applied to the annular tissue under direct visualization to contract the collagen. Interpositional nuclear tissue, seen frequently within the fibers of the annular tear, can be removed to allow the tear to heal. Furthermore, the visualization of the disc from within is suggested to be important for the decompression of disc space and removal of loose fragments in order to reduce the number of reherniations. The inside-out technique affords this advantage. Although studies do indeed indicate lower rates of reherniation, they also urge caution that too aggressive a discectomy may lead to disc space narrowing and higher rates of subsequent back pain.19 In cases of migrated disc extrusion and sequestration, visualization of the entire disc material in the epidural space from inside the disc space is not possible. Direct visualization and access of the spinal canal are hence more appropriate for an adequate decompression. Furthermore, visualization of the nerve roots and neural structures is more easily afforded via an outside-in approach. The outside-in approach frequently necessitates removal of bony stenosis created by the superior articular process in the entry, middle, and exit zones of the neuroforamen. The concomitant foraminoplasty often helps alleviate the bony lateral recess and foraminal stenosis. The starting point and skin incision need to be appropriately adjusted in such cases as well. To access a cranially migrated herniation, the surgeon would position the starting incision more caudally in order to position the access cannula in a trajectory that approximates the herniation in the ventral epidural space. Conversely, with a caudally migrated herniation, the starting incision is positioned more cranially to allow a trajectory to reach the herniation.

32.5.1 Surgical Technique The authors’ philosophy is to use the inside-out technique as a safe starting point. This approach can be modified based on the

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pathology. It is easiest to orient oneself via the disc space and should access to the epidural space be necessary, a foraminoplasty can be easily performed to allow for a shallower trajectory dorsal to the annulus (▶ Fig. 32.6). The following further discusses the inside-out technique with use of the YESS system.

32.5.2 Setup and Exposure The operating room setup requires a video tower system with the endoscopic equipment, one C-arm machine, and a radiolucent table with an antilordotic frame. The patient is positioned prone on the table (▶ Fig. 32.7). Some surgeons utilize the lateral position; however, the prone position is preferred as it allows easier visual orientation of the video image in relation to the patient and more ergonomic manipulation of the operating instruments. The prone position also allows a biportal (bilateral) approach. While one channel may be used for real-time visualization and use of smaller instruments through its working channel, the accessory cannula may allow for larger and more flexible working instruments during discectomy. It is also important to position the patient and C-arm in such a way as to facilitate a perfect posteroanterior (PA) and lateral view for fluoroscopic imaging. The surgical level must be centered to avoid parallax error. Local anesthetic and intravenous sedation with Versed and fentanyl are the preferred agents for anesthesia versus general anesthesia. This allows for real-time nerve monitoring utilizing the patient’s pain response to avoid any injury to the exiting or traversing nerve root. One-half percent lidocaine is the preferred local anesthetic since this can anesthetize the area enough to avoid pain, but does not prevent a painful response when the nerve roots are stimulated. The anesthesiologist should avoid using propofol for intravenous sedation since this can induce general anesthesia and prevent the patient from responding to a maneuver that could cause a nerve root injury.

32.5.3 Protocol for Optimal Needle Placement Optimal needle placement is critical as all subsequent instrumentation follows this trajectory. The needle entry point typically starts about 10 to 13 cm from the midline and is positioned to allow entry into the disc parallel to the end plates

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Endoscopic Spine Techniques: An Overview

Fig. 32.7 The proper operating room setup allows the surgeon visual access to the video feed via the endoscope and further feedback from the fluoroscopy machine.

to allow intradiscal positioning without damaging the end plates. The patient’s body habitus will determine just how far lateral from the midline one will have to start. A good estimate can be made by laying a metal rod transversely on the patient’s back and marking a point 1 inch lateral to the point where the rod does not touch the skin. After determining the lateral extent of the incision site on the PA view, you will then check a lateral image and position the incision in line with the disc inclination. To obtain the most accurate needle placement customized to the patients’ individual body habitus, a thin metal rod is utilized as a radio-opaque marker and ruler to draw lines on the skin to mark surface topography for guidance in free-hand biplane Carm needle placement. These surface markings help identify and target three key landmarks for needle placement: ● The anatomic disc center. ● The annular foraminal window (centered within the medial and lateral borders of the pedicles). ● Skin window (needle entry point/skin incision).

the PA view. The intersection of these 2 lines marks the anatomic disc center (▶ Fig. 32.8, a). 2. On the lateral view, draw a line with the rod tip at the anterior border of the disc positioned parallel to the end plates and bisecting the disc. This represents the disc inclination plane and determine the cephalad/caudal position of the needle entry point (▶ Fig. 32.8, b). To avoid parallax and measurement error, the rod should be held perpendicular to the fluoroscopy beam and should not be leaning away from or toward the patient. 3. The distance from the rod tip to the plane of the posterior skin is measured by grasping the rod at the point where the posterior skin plane intersects it. 4. This distance is then measured on the posterior skin from the midline along the transverse plane line. At the lateral extent of this measurement, a line parallel to the midline is drawn to intersect the disc inclination plane line. This intersection marks the skin entry point or skin window for the needle (▶ Fig. 32.9).

32.5.4 Step-by-Step Surgical Technique

The skin window’s lateral location from the midline determines the trajectory angle into the foraminal annular window. This method for determining the lateral needle starting point will produce a safe starting point and an approach trajectory of approximately 20 to 30 degrees off of the horizontal plane (see ▶ Fig. 32.9).

1. Utilizing a metal rod as radio-opaque marker and ruler, draw a longitudinal line over the spinous processes to mark the midline on the PA view and draw a transverse line bisecting the targeted disc space to mark the transverse disc plane on

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Surgical Techniques the optimal skin window more cephalad from the transverse plane line, which helps avoid the iliac crest. A flatly inclined L5/ S1 disc will position the optimal skin window with the iliac crest obstructing the trajectory of the needle. The skin window will have to start more medial to avoid the iliac crest and sometimes this creates a steep approach trajectory that makes it difficult to access the herniation. This can often be overcome by resecting the ventral–lateral aspect of the superior articular facet with the trephine and bone drill to allow a shallower approach into the disc to access the targeted herniation. If an acceptable trajectory is not possible to access the herniation, then this surgical approach is not indicated and a posterior approach is preferred. The first neutrally aligned disc inclination plane is usually at L4/L5 or L3/L4. A neutrally aligned disc inclination plane is in the same plane as the transverse plane line; thus, the skin window is in line with the transverse plane line. A negatively inclined disc, often at L1/L2 and L2/L3, places the skin window caudal to the transverse plane line.

Needle Placement

Fig. 32.8 (a) With the patient positioned prone, the posteroanterior fluoroscopic view allows for topographic drawing of lines indicating midline and transverse plane lines of target discs and their respective disc centers. (b) Draw a line with the rod tip at the anterior border of the disc positioned parallel to the end plates and bisecting the disc on the lateral view. Not only does this represent the disc inclination line and determines the cephalad/caudal position of the needle entry point, but it also allows for measurement of the distance from the rod tip to the plane of the posterior skin.

To optimize the approach trajectory to access the specific herniation type, the entry point can usually be adjusted a little more medial (for foraminal or extraforaminal herniations) or lateral (for central and some paracentral herniations). Typically one would want to start as lateral as possible to create a shallow entry trajectory to the disc to target the base of the typical paracentral herniations and central herniations. However, starting too far lateral risks injury to the abdominal contents and the trajectory should never be zero degrees. Preoperative measurements can also be performed on the axial MRI images to estimate the most optimal and safe lateral starting point to access the offending pathology. The positive disc inclination plane of the L5/S1 disc is noteworthy. A steep positive inclination line (lordosis) will position

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Once the starting point and needle trajectory are determined, the skin window and subcutaneous tissue is infiltrated with 0.5% lidocaine. A 6-inch-long, 18-gauge needle is then inserted from the skin window at the desired trajectory and passed anteromedially toward the anatomic disc center marked on the posterior skin. Infiltrating the needle tract with 0.5% lidocaine as you are advancing the needle will anesthetize the tissue tract, avoiding pain when the dilator is passed later in the procedure. The needle is advanced to the annulus while monitoring it in the PA Ferguson view (angled in the disc inclination plane to provide a true PA view of the disc space). You should check a lateral view before advancing the needle tip medial to the medial border of the pedicle to confirm appropriate trajectory and avoid inadvertent dural puncture in the case of an overly shallow trajectory. The needle tip should be centered in the foraminal annular window on the PA Ferguson view and just touching the posterior annular surface on the lateral view. Then the needle can be advanced to the midline while monitoring the PA Ferguson view. Then check the lateral view again. Ideally, the needle tip will be in the posterior 25% of the disc, indicating adequate posterior needle placement needed to access the paracentral disc herniations. The needle tip can even be located slightly posterior to the posterior border of the vertebral bodies on the lateral view if the herniation is large with extensive posterior migration. If you are operating on a foraminal disc herniation, then the needle tip can be in the center of the disc, indicating a 45-degree trajectory into the disc. This is appropriate since the surgeon would not need to access the posterior epidural space as much to remove the foraminal herniation.

Evocative Chromo-discography Perform confirmatory contrast discography at this time. The following contrast mixture is used: 9 mL of Isovue 300 contrast with 1 mL of methylene blue dye. Indigo carmine blue dye was used in the past, but it is no longer manufactured so it has been substituted with methylene blue dye. This combination of contrast ratio gives readily visible radio-opacity on the discography

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Endoscopic Spine Techniques: An Overview

Fig. 32.9 The distance determined on the lateral using the rod tip is then measured from the midline along the respective transverse plane line for each disc. At the end of this measure, a line parallel to the midline is drawn to intersect the respective disc inclination line and mark the skin entry point for needle placement. The needle is then inserted and triangulated at an angle of 20 to 30 degrees off of the horizontal plane to the desired disc space.

images, and intraoperative light blue chromatization of pathologic nucleus and annular fissures, which help guide the targeted fragmentectomy. The annular fibers do not readily accept dye, so this can help differentiate the visualized tissue. If the dye is seen leaking into the epidural space on the fluoroscopic images, then one will know that the herniation is not contained, but extruded, and this helps the surgeon plan the endpoint of the discectomy. With an extruded paracentral herniation, one should always visualize the decompressed traversing nerve root from inside the annulotomy that the nucleus herniated through. If it is a contained herniation with attenuated posterior annulus still present, thorough nucleus removal is usually accomplished without visualizing the traversing nerve root since the intact posterior annular fibers will obscure visualization of the traversing nerve root. If complete decompression is questioned, one can always cut the remaining annular fibers medially to be able to visualize the traversing nerve root, but this makes the surgically created annulotomy larger.

Instrument Placement Insert a long thin guide wire through the 18-gauge needle channel. Advance the guide wire tip, 1 to 2 cm deep into the annulus; then, remove the needle and make a small transverse stab incision. Slide the bluntly tapered tissue dilating obturator over the guide wire until the tip of the obturator is firmly engaged in the annular window. An eccentric parallel channel in the obturator allows for circumferential annular infiltration with small volumes of 0.5% lidocaine, enough to anesthetize the annulus, but not the exiting and traversing nerve roots. Hold the obturator firmly against the annular window surface and remove the guide wire. Advance the obturator bluntly through the annulus with a mallet. Annular fenestration is the most painful step of the entire procedure. Advise the anesthetist to heighten the sedation level just prior to annular fenestration. Advance the obturator tip deep into the annulus and confirm on the C-arm views. Now slide the beveled access cannula over the obturator toward the

disc. Advance the cannula until the beveled tip is deep in the annular window. Remove the obturator and insert the endoscope to get a view of the disc nucleus and annulus. Alternatively if you are worried about further extruding a large disc herniation or you want to inspect the outer annular fibers before fenestrating the annulus, the surgeon can engage the outer annulus with the blunt obturator. Then the beveled cannula is advanced over the obturator to the annulus. The obturator is removed and the endoscope is inserted. The outer annular fibers can be inspected to ensure that no neural structures are in the path of the cannula prior to the annulotomy. Then an annulotomy knife or a cutting trephine can be used for the annular fenestration under direct vision. Prominent disc tissue can be removed prior to entering the disc with the cannula. This is often the best way to attack foraminal and extraforaminal herniations. The foraminal annular window is an easily identifiable C-arm and intraoperative anatomic landmark and is the starting location for endoscopic disc excision. Through the endoscope, the surgeon may see various amounts of blue-stained nucleus pulposus. The general-purpose access cannula has a bevel hypotenuse of 12 mm and outside diameter of 7 mm. When the cannula is slightly retracted to the midstraddle position in relationship to the annular wall, the wide-angle scope visualizes the epidural space, annular wall/posterior longitudinal ligament, and the intradiscal space in the same field.

Performing the Discectomy The basic endoscopic method to excise a paramedian extruded lumbar herniated disc via a uniportal technique is described here. Most of the time with accurate needle targeting, the opening of the cannula is already within the actual herniated nucleus fragment and is immediately visualized with the endoscope. The radiofrequency bipolar probe is used to coagulate any small bleeders to achieve hemostasis and clear visualization. The endoscopic rongeurs can be utilized immediately to begin removing the herniation. If there are annular fibers between the

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Fig. 32.10 Endoscopic view of the decompressed traversing nerve root after removal of the herniated nucleus pulposus. The nerve probe is retracting the posterior annulus/posterior longitudinal ligament and pressing it ventrally.

opening of the cannula and the herniation, then enlarge the annulotomy medially to release the base of the herniation with cutting forceps. This connects the surgical annulotomy with the annulotomy from the herniation. The side-firing Ho:YAG laser can also be utilized to enlarge and widen the annulotomy. This is performed to release the annular fibers at the herniation site that may pinch off or prevent the extruded portion of the herniation from being extracted. Directly under the herniation apex, a large amount of blue-stained nucleus is usually present, likened to the submerged portion of an iceberg. The nucleus here represents migrated and unstable nucleus. The endoscopic rongeurs are used to extract the blue-stained nucleus pulposus under direct visualization. If needed, the larger straight and hinged rongeurs can be used directly through the cannula after the endoscope is removed. This step is best guided under fluoroscopy and surgeon’s feel for the instrument. By grabbing the base of the herniated fragment, one can usually extract the extruded portion of the herniation. After removing the readily visualized herniated nucleus pulposus, perform a small debulking decompression by using a straight and flexible suction-irrigation shaver to create the working cavity. This step requires shaver head C-arm localization before power is activated to avoid nerve/dura injury and anterior annular penetration. The debulking process allows better intradiscal visualization, removes the unstable nucleus material to prevent future reherniation, and allows any residual herniated disc tissue to follow the path of least resistance into the cavity. The working cavity is inspected for persistent herniated fragments. If a noncontained extruded disc fragment is still found to be present by finding blue-stained nucleus material posteriorly, then these fragments are teased into the working cavity with the endoscopic rongeurs and the flexible radiofrequency trigger-flex bipolar probe and removed. The flexible radiofrequency bipolar probe is also used to contract and thicken the annular collagen at the herniation site and to maintain hemostasis throughout the case. Complete herniation removal is verified by visualizing the decompressed traversing nerve root (▶ Fig. 32.10). One should

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Fig. 32.11 Endoscopic view of the exiting nerve root in the right-sided neuroforamen.

note, however, that if the herniation is a contained paracentral herniation, you would not expect to see the decompressed traversing nerve. You would see the undersurface of the thinned out annulus from within the disc. Prior to removing the endoscope, we also routinely visualize and confirm the exiting nerve root (▶ Fig. 32.11) or the perineural fat encasing the nerve root is uninjured. At the end of the case, we inject 1 mL of 80-mg methylprednisolone in the foramen to help decrease inflammation and reduce the incidence of dysesthesia. The majority of herniations can be treated via the uniportal technique. A biportal (bilateral access) technique is indicated for large extruded central herniations and at L5/S1 when the approach trajectory is not shallow enough to position the end of the cannula at the base of the herniation.

Wound Closure Only small adhesive strips are needed to close the skin and a sterile 2 × 2 gauze. A single suture may be used to close the 8mm incision, but sutures are not necessary. Most bleeding is stopped by tissue pressure, and cauterization of the wound incision is not necessary.

32.5.5 Postoperative Care The postoperative protocol is similar to a traditional posterior discectomy wherein the patient is instructed to avoid bending, lifting, and twisting for 4 to 6 weeks after surgery. Despite the less invasive skin and muscle dissection, the annulotomy at the disc does require time to heal. The limitations may reduce the chance of recurrent disc herniation from the foraminal access portal and from the annular defect produced by the disc herniation. A lumbar corset for a couple of weeks can make the patient feel more comfortable. Physical therapy is not required, but can be considered on an individual basis. Patients are instructed to use their pain as a guide after the 6-week period.

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Endoscopic Spine Techniques: An Overview

32.5.6 Management of Complications

32.6 Clinical Case

As with any spine surgery, there are the usual risks of infection, nerve injury, dural tears, bleeding, and scar-tissue formation. The most common postoperative complaint is transient dysesthesia and occurs in approximately 5 to 15% of cases. It may be related to nerve recovery, operating adjacent to the dorsal root ganglion of the exiting nerve, or hematoma formation adjacent to the ganglion of the exiting nerve. Using blunt techniques to dilate the annular fibers and routine injection of 80-mg methylprednisolone decreases the incidence of dysesthesia, but it cannot be avoided completely. Transient dysesthesia is not unique to this technique and it is shown in transforaminal lumbar interbody fusion (TLIF) techniques even when no adverse intraoperative events were present and continuous electromyogram (EMG) and somatosensory evoked potentials (SSEP) did not show any nerve irritation. We do not use intraoperative neuromonitoring as the awake patient is our real-time indication of any nerve irritation. Postoperative dysesthesia is treated with transforaminal epidurals, sympathetic blocks, and the off-label use of pregabalin or gabapentin. Minimally invasive techniques carry their own subset of iatrogenic complications including the off-chance of wrong-level surgery and the misplacement of instrumentation. It is always important to study the preoperative imaging and meticulously plan the upcoming surgery. Fluoroscopic identification of the index level is paramount to this technique and should help avoid wrong-site surgery. Furthermore, great care must be taken when inserting and removing the instrumentation. Plunging with the guide wire too deeply may penetrate the anterior annulus and cause vascular or visceral injury. Aggressive penetration and blind use of pituitaries and shavers may cause similar injuries and endanger the neural elements and dural tube. Avoidance of complications is enhanced by the ability to visualize normal and patho-anatomy clearly, as well as through the use of local anesthesia and conscious sedation rather than general or spinal anesthesia. Adopting the “inside-out” technique will give the surgeon more leeway in planning his surgical approach, since direct targeting to the herniation based on imaging studies may provide some “surprises” when visualization is not as clear as anticipated. This may occur in the presence of bleeding. Staying inside the disc space or returning to the disc space when visualization is obscured to reorient the surgeon is an important factor to consider. In experienced hands, some surgeons have safely utilized general anesthesia when circumstances make it safer for the patient. The patient, under a local anesthetic, usually remains comfortable during the entire procedure, with the exception of periods such as during evocative chromo-discography, during annular fenestration, or when instruments are manipulated past the exiting nerve. Local anesthesia of 0.5% lidocaine permits generous use of this diluted anesthetic for pain control but allows the patient to feel pain when the nerve root is manipulated. Nerves can also be adherent to the annulus or nucleus. Pain experienced by the patient is very helpful to the surgeon when probing or operating in the foramen, as he or she can then look to document or free these adhesions before removing the herniation.

A 37-year-old man with a 2-month history of low back pain and progressively worsening right lower extremity pain presented for evaluation in crutches and unable to bear weight. He proportionalized his pain to 30% back and 70% right lower extremity. He complained of a worsening weakness, tingling, and constant numbness over the anterolateral aspect of the ankle and dorsum of his right foot. The pain radiated through the buttock down to the posterolateral thigh and into the great right toe. He was unable to sleep supine and had to sleep in a recliner to minimize the pain. He had not been able to return to work since the pain started. He denied bowel or bladder incontinence, but had constipation for the last 12 days. Physical examination revealed an antalgic gait, limited lumbar extension, positive straight leg raising (SLR) and Lasègue’s tests on the right, blunted right patellar deep tendon reflex, decreased sensation to light touch over the dorsum of the foot, and weakness. The right-sided weakness was graded as 4 + /5 anterior tibialis, and 4–/5 extensor hallucis longus (EHL). The remainder of the examination was normal. MRI revealed a large right foraminal extruded nucleus pulposus at L5/S1 causing compression of the exiting L5 nerve root. Surgery was recommended due to the progressive nature of his pain and neurologic deficits, along with failure of conservative measures including oral and epidural steroid injections along with several sessions of physical therapy. After a full discussion of his risks, benefits, and alternatives, the patient elected to undergo outpatient posterolateral endoscopic discectomy. The patient experienced over 80% pain relief immediately postoperatively. He had almost complete resolution of pain upon his 2-week postoperative visit and had returned to work shortly after his surgery. Six weeks after his operation, he had complete resolution of pain and weakness.

32.7 Conclusion Posterolateral endoscopic discectomy provides excellent access to the epidural space from pedicle to pedicle facilitating removal of herniated disc fragments. Prior experience with discography, epidural injections, and joint arthroscopy is helpful in reducing the learning curve. The technique is performed with tissue dilatation to accommodate a 7-mm working cannula; it avoids significant trauma of muscle stripping, muscle retraction, bony resection, and nerve root retraction associated with standard open surgery. As the patient is conscious throughout the procedure, the procedure is safe preventing nerve root injury. Limited need for anesthetics allows for better integration of these procedures in ambulatory surgery centers. Minimized approach-related morbidity does not limit future surgical options if necessary. It is an excellent minimally invasive approach to any disc herniation, and excels at cases involving foraminal disc herniations, upper lumbar and lower thoracic herniations, revision cases, foraminal stenosis, treatment of discitis, and as a potential means of achieving interbody fusion.

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Clinical Caveats ●

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Avoid radiographic parallax error and misplacement of the needle, cannula, and endoscope by positioning the patient such that true anteroposterior and lateral fluoroscopic views can be obtained. Use of a general anesthetic such as propofol is not recommended. To avoid nerve injury, the patient should remain awake and alert during needle insertion, and dilator and cannula passage. Initial needle trajectory and placement is essential because it will ultimately determine the endoscopic field of view. Careful review of the preoperative MRI and X-rays is recommended. Unless there are anatomic restraints, start the endoscopy via the inside-out approach for safety reasons and improved orientation. Beginning the endoscopy before reaching the disc annulus can make recognition of foraminal anatomy more difficult and can increase the likelihood of nerve root injury. Fluoroscopy should be used to confirm location if there is any uncertainty about anatomy or location during endoscopy.

References [1] Yasargil MG. Microsurgical operation of herniated lumbar disc. In: Wullenweber R, Brock M, Hamer J, Klinger M, Spoerri O, eds. Advances in Neurosurgery. Vol. 4. Berlin: Springer-Verlag; 1977:81–94 [2] Williams RW. Microlumbar discectomy: a conservative surgical approach to the virgin herniated lumbar disc. Spine. 1978; 3(2):175–182 [3] Perez-Cruet MJ, Foley KT, Isaacs RE, et al. Microendoscopic lumbar discectomy: technical note. Neurosurgery. 2002; 51(5) Suppl:S129–S136 [4] Kambin P, Gellman H. Percutaneous lateral discectomy of the lumbar spine: a preliminary report. Clin Orthop Relat Res. 1983; 174:127–132 [5] Hijikata S. Percutaneous nucleotomy. A new concept technique and 12 years’ experience. Clin Orthop Relat Res. 1989(238):9–23

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[6] Forst R, Hausmann B. Nucleoscopy: a new examination technique. Arch Orthop Trauma Surg. 1983; 101(3):219–221 [7] Kambin P, Schaffer JL. Percutaneous lumbar discectomy. Review of 100 patients and current practice. Clin Orthop Relat Res. 1989(238):24–34 [8] Kambin P, O’Brien E, Zhou L, Schaffer JL. Arthroscopic microdiscectomy and selective fragmentectomy. Clin Orthop Relat Res. 1998(347):150–167 [9] Yeung AT. Minimally invasive disc surgery with the Yeung Endoscopic Spine System (YESS). Surg Technol Int. 1999; 8:267–277 [10] Hermantin FU, Peters T, Quartararo L, Kambin P. A prospective, randomized study comparing the results of open discectomy with those of video-assisted arthroscopic microdiscectomy. J Bone Joint Surg Am. 1999; 81(7):958–965 [11] Tsou PM, Yeung AT. Transforaminal endoscopic decompression for radiculopathy secondary to intracanal noncontained lumbar disc herniations: outcome and technique. Spine J. 2002; 2:41–48 [12] Yeung AT, Tsou PM. Posterolateral endoscopic excision for lumbar disc herniation: surgical technique, outcome, and complications in 307 consecutive cases. Spine. 2002; 27(7):722–731 [13] Choi G, Lee SH, Bhanot A, Raiturker PP, Chae YS. Percutaneous endoscopic discectomy for extraforaminal lumbar disc herniations: extraforaminal targeted fragmentectomy technique using working channel endoscope. Spine. 2007; 32(2):E93–E99 [14] Ruetten S, Komp M, Merk H, Godolias G. Full-endoscopic interlaminar and transforaminal lumbar discectomy versus conventional microsurgical technique: a prospective, randomized, controlled study. Spine. 2008; 33 (9):931–939 [15] Nellensteijn J, Ostelo R, Bartels R, Peul W, van Royen B, van Tulder M. Transforaminal endoscopic surgery for symptomatic lumbar disc herniations: a systematic review of the literature. Eur Spine J. 2010; 19(2):181–204 [16] Gibson JN, Cowie JG, Iprenburg M. Transforaminal endoscopic spinal surgery: the future “gold standard” for discectomy? A review. Surgeon. 2012; 10 (5):290–296 [17] Jasper GP, Francisco GM, Telfeian AE. Clinical success of transforaminal endoscopic discectomy with foraminotomy: a retrospective evaluation. Clin Neurol Neurosurg. 2013; 115(10):1961–1965 [18] Wang H, Huang B, Li C, et al. Learning curve for percutaneous endoscopic lumbar discectomy depending on the surgeon’s training level of minimally invasive spine surgery. Clin Neurol Neurosurg. 2013; 115(10):1987–1991 [19] Carragee EJ, Spinnickie AO, Alamin TF, Paragioudakis S. A prospective controlled study of limited versus subtotal posterior discectomy: short-term outcomes in patients with herniated lumbar intervertebral discs and large posterior anular defect. Spine. 2006; 31(6):653–657

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Muscle Preserving Lumbar Microdiscectomy

33 Muscle Preserving Lumbar Microdiscectomy Mick J. Perez-Cruet and Moumita S.R. Choudhury Abstract Herniated lumbar disc was perhaps the first indicated pathology for the minimally invasive surgery (MIS) muscle preserving approach. This approach allows spine surgeons to reliably decompress a symptomatic lumbar nerve root using a microscope while preserving the normal anatomical integrity of the spine. This technique has been expanded to perform cervical foraminotomy, lumbar laminectomy for stenosis, and more complex fusion and instrumentation. It offers many advantages over other MIS lumbar discectomy techniques by reducing tissue trauma, allowing direct visualization of the nerve root and disc pathology, and enabling bony decompression with instruments designed specifically for use in a small working space. The approach used is anatomically familiar to spine surgeons and excellent clinical results have been achieved on an outpatient basis. The potential complications with the use of the tubular system are not significantly different from those encountered when performing standard microdiscectomy. Prospective multicenter clinical study has shown the efficacy of this system in treating lumbar disc disease. The approach described allows the development of expanded application beyond lumbar nerve root decompression and the tubular retractor system developed for use with an endoscope has been modified for use with a microscope, which allows excellent three-dimensional visualization and improved image quality. Surgeons familiar with the microscope have more readily adopted this latter technique. Keywords: minimally invasive spine, muscle-sparing approach, muscle-splitting approach, One-Step Dilator, BoneBac Press, tubular retractor, microdiscectomy

33.1 Introduction The microdiscectomy procedure is considered the gold standard for patients who require surgery for symptomatic lumbar disc herniation causing radiculopathy that has not improved with conservative measures.1 Lumbar disc herniation is the most common cause of nerve root pain and yet responsible for less than 5% of all lower back problems.2 Except when there is a considerable or emergent neurologic deficit, conservative medical management is approached preferred for at least 6 weeks since the onset of symptoms. If there is no improvement in 6 weeks, surgical intervention is considered. Microdiscectomy is the gold standard treatment for uncomplicated disc herniation. Surgical discectomy for carefully selected patients with sciatica due to lumbar disc herniation provides faster relief from the acute attack than conservative management, although any positive or negative effects on the lifetime natural history of the underlying disc disease are still unclear.3 A qualitative and quantitative analysis was performed on articles published between January 1975 and December 2012, relating to the optimum time of surgery in patients with lumbar disc herniation. The results indicated that longer duration of sciatica led to poorer patient outcomes.4

Removal of a herniated disc using the operative microscope was first performed by Yasargil in 1977.5 Microscope use during spinal procedures became more prevalent during the late 1980s.6 By the 1990s, many spinal surgeons adopted the routine practice of microdiscectomy abandoning the open non-microscope visualization method.7 In 1997, the microendoscopic discectomy (MED) system was introduced, which allowed spine surgeons to reliably decompress a symptomatic lumbar nerve root via an endoscopic, minimally invasive surgical (MIS) approach.8,9 This system offered many advantages over other MIS lumbar discectomy techniques by reducing tissue trauma, allowing visualization of the nerve root and disc pathology, and enabling bony decompression.10,11, 12,13,14 In addition, the system came with long, tapered, bayonetted instruments designed specifically for use in a small working tubular retractor (▶ Fig. 33.1). The approach used is anatomically familiar to spine surgeons and excellent clinical results have been achieved on an outpatient basis. Unlike percutaneous approaches, the METRx Microdiscectomy System (Medtronic, Memphis, TN) allows surgeons to address not only contained lumbar disc herniations, but also sequestered disc fragments, lateral recess stenosis, and bone and ligamentous compression. Prospective multicenter clinical study has shown the efficacy of this system in treating lumbar disc disease.15 The modularity of the METRx system also allows the development of expanded application beyond lumbar nerve root decompression.16,17,18,19,20 In addition, the tubular retractor system developed for use with an endoscope has been modified for use with a microscope, which allows three-dimensional visualization and improved image quality. Surgeons familiar with the microscope have more readily adopted this latter technique. The evolution of many tubular retractor systems including expandable tubes has further facilitated the muscle-splitting approach to the spine. The endoscopic technique appears to be replaced by the microscope, which provides improved visualization and potentially reduced cost. Additionally, we have found that the need to clean the endoscope during the case causes undesirable delays. Other even less invasive techniques to perform microdiscectomy, such as the transforaminal endoscopic approach, have been described. However, Nellensteijn et al,21 in a comparative analysis between transforaminal endoscopic and microdiscectomy, found no statistically significant variation in techniques when comparing leg pain reduction, overall patient improvement, reoperation rate, and complications.

33.2 Surgical Approach 33.2.1 Patient Positioning and Operating Room Setup Microdiscectomy can be successfully performed on an ambulatory basis with the patient under spinal or general anesthesia. The patient is positioned prone with the spine flexed to aid in intraoperative exposure of the interlaminar space typically using a Wilson frame. Alternatively, a Jackson table can be used.

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Surgical Techniques

Fig. 33.1 Photos of microendoscopic discectomy (MED) system showing (a) K-wire, sequential muscle dilators, and tubular retractors; (b) endoscopic assembly; (c) bayonetted instruments. (d) Long tapered drill used in the MED procedure.

Abdominal compression is avoided by properly positioning the patient on a frame, Jackson table, or rolls to reduce intraoperative venous bleeding (see ▶ Fig. 8.3). The table and frame should be compatible with lateral fluoroscopy to allow for fluoroscopic viewing of the spine. A set of fine-bayonetted instruments and a long tapered drill help optimize the working space within the tubular retractor. We typically use a cutting matchstick M8 burr on the drill. The drilled bone is collected using the BoneBac Press (Thompson MIS, Salem, MA) and used to reconstruct the laminotomy defect after completion of the microdiscectomy. We have found that this may help reduce perineural scar formation by removing the dead space created by the laminotomy defect. Thus, this technique may potentially improve patient outcomes (▶ Fig. 33.2). Postoperative imaging studies after laminectomy with autologous bone graft reconstruction have shown excellent healing after decompression with restoration of the lamina defect and reduced perineural scar formation (▶ Fig. 33.3). The operating room should be large enough to comfortably accommodate the fluoroscopic unit, fluoroscopic monitor, and microscope. The microscope is typically set up on the opposite side of the table to the surgeon after being properly balanced.

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nates the Kirschner wire (K-wire) and muscle dilators that can potentially enter the canal and cause neural injury (▶ Fig. 33.4).

Benefits of Muscle-Sparing Approach Using One-Step Dilator This approach to spine surgery without K-wire or sequential muscle dilators: ● Facilitates and makes safer MIS surgery. ● Is easy to use. ● Reduces approach-related complications. ● Is more efficient.

On redo operations where scar is present, the One-Step Dilator is docked above the spine and the approach completed under direct microscope visualization. This helps avoid penetration of the canal and neural injury or dural tear. A tubular retractor is placed to establish an operative corridor to the lamina and interlaminar space. Fluoroscopy confirms appropriate positioning (▶ Fig. 33.5).

33.3 Surgical Technique

33.3.1 Soft-Tissue Removal and Laminar Identification

The patient’s back is prepped and draped in standard surgical fashion. With the patient in the prone position on a radiolucent Wilson frame, the level is identified with a spinal needle and lateral fluoroscopic image. An incision is made directly overlying the disc space of interest and lateral to the midline approximately one finger-breadth. The fascia is cut with a Bovie cautery. A muscle-splitting approach system has been developed that elimi-

It is essential to remove sufficient soft tissue exposed in the operative corridor to maximize the working space within the tubular retractor. The soft tissue over the lamina is removed using Bovie electrocautery, which prevents bleeding from the soft tissue during removal. A final confirmatory lateral fluoroscopic image can be taken to assure the proper disc space and tubular retractor location.

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Fig. 33.2 (a) BoneBac Press. (b) Autograft collected from surgical site. (c) Intraoperative view of BoneBacPress. (d) CT showing reconstruction of lamina.

Fig. 33.3 A 6-month postoperative MRI showing reconstruction of laminar defect using BoneBac Press autograft, normal anatomic distribution of cauda equine nerve roots, and no perineural scar formation following lumbar laminectomy (blue arrow). Note preservation of paraspinal muscles.

The soft tissue is removed circumferentially from the edge of the tubular retractor to maximize the working area and to prevent bleeding. Starting at the lateral aspect, bony landmarks are identified and soft tissue is removed by keeping the Bovie tip on the bone and turning the soft tissue inward toward the center of the tube. Final removal of soft tissue is achieved using a pituitary rongeur. In this manner, the medial facet and lamina are adequately exposed. A frequent on-and-off Bovie technique and use of sucker in the tube prevents smoke accumulation that can obscure visualization.

33.3.2 Laminar and Interlaminar Space Identification A hemilaminotomy/medial facetectomy is then performed with a Kerrison punch and/or high-speed drill. We prefer to use an M8 cutting burr and collect all drilled bone for bone reconstruction of the laminotomy defect at the completion of the case using the BoneBac Press (▶ Fig. 33.2). The smooth tip of the cutting M8 matchstick burr allows for bone to be removed safely over the

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Surgical Techniques

Fig. 33.4 (a) Intraoperative photograph of surgeon showing minimally invasive muscle-sparing approach to the spine using the One-Step Dilator (Thompson MIS). (b) One-Step Dilator closed, (c) opened. (d) Intraoperative photograph.

ligamentum flavum. Bone removal via drilling is started at the lateral caudal aspect of the lamina where the ligamentum flavum protects the dura. With the ligamentum flavum exposed laterally, the drilling can proceed safely over the ligament to remove the more rostral and then medial aspect of the lamina (▶ Fig. 33.6). After the hemilaminotomy is completed, the facetectomy can be extended. This maneuver is performed by removing 1 to 3 mm of the medial facet leaving a ventral “shelf” 1- to 3-mm thick. The remaining shelf of bone can then be easily removed with the Kerrison rongeur. Lateral recess and/or foraminal stenosis can be addressed in this fashion (▶ Fig. 33.7).

33.3.3 Ligamentum Flavum Removal Enough lamina is removed to expose the superior (rostral) end of the ligamentum flavum. A hint of epidural fat at the rostral medial aspect tells the surgeon that adequate laminar bone is

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removed to proceed to the next step of ligamentum flavum removal (▶ Fig. 33.8). An up-going angled microcurette opens the ligamentum flavum. The curette is placed under the remaining superior lamina where the ligament is thin or absent. The ligament is penetrated or detached with the curette using a twisting motion and peeled back caudally and dorsally, and then resected with a no. 2 Kerrison punch. The microscope is positioned to keep the surgical view in the center of the image while maintaining an ergonomically favorable position for the surgeon. There is an initial tendency to “cone” the exposure down to the final target. Inadequate exposure restricts the already confined working space of the tubular retractor. To avoid this tendency, complete soft tissue, bone, and ligament exposure at each level should be performed before proceeding into the epidural space. In this manner, the available working space within the tubular retractor is optimized.

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Fig. 33.4 (continued) (e,f) One-Step Dilator advanced through the fascial opening to the spine in a muscle-splitting fashion, (g) opened. (h,i) Tubular retractor placed over it. (j) Dilator removed with tubular retractor in place. (Images b, c, and d are provided courtesy of Thompson MIS.)

33.3.4 Nerve Root Exploration and Retraction The dura and traversing nerve root are identified. The nerve root is retracted medially using a Penfield dissector or suction retractor. The volar epidural space is then explored. If necessary, epidural veins are cauterized with bipolar forceps and divided with microscissors. Hemostatic agents and cotton patties are also used to obtain hemostasis (▶ Fig. 33.9). If the pathology is beyond the confines of the tubular retractor, the retractor is moved or angled over the pathology by a process known as wanding. While downward pressure is placed on the tubular retractor, the pneumatic arm is unlocked simply by pressing a button, allowing the tubular retractor to be pivoted over to the desired location. When the retractor is in the proper location, the flexible arm is locked in place and downward pressure is released. In this fashion, wanding achieves pedicle-to-pedicle access through the original incision. Wanding also allows the surgeon to place objects of interest in the center of the operative corridor. By placing objects in the center of the tubular retractor, visualization is enhanced and working access is maximized.

33.3.5 Discectomy and Closure If an annulotomy is necessary, it is accomplished with a sheathed micro-knife or bayonet annulotomy no. 11 blade knife while protecting the nerve root with the suction retractor (▶ Fig. 33.10). The herniated disc is then removed with micropituitary straight and angled rongeur in a standard fashion. Intradiscal and extradiscal dissection is performed in a routine fashion. At this point, the nerve root is explored to ensure the decompression is complete using a right- or left-angled ballended probe (▶ Fig. 33.11). When the nerve root is decompressed, the disc space is irrigated thoroughly. The laminar defect can then be reconstructed using the drilled bone collected with the BoneBac Press (▶ Fig. 33.2). Care is taken to lay the bone plug over the defect and not push it into the canal where compression of neural elements can occur (▶ Fig. 33.12). In this manner even the bone of the lamina can regrow to its original anatomic fashion potentially reducing perineural scar formation (▶ Fig. 33.3). The pneumatic arm assembly is loosened and the tubular retractor is removed slowly. Any bleeding in the paraspinal musculature is controlled with the bipolar forceps.

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Surgical Techniques The fascia is reapproximated with interrupted absorbable sutures. The subcutaneous tissue is closed in an inverted manner. Mastisol skin adhesive (Ferndale Laboratories) and Steri-Strips are applied to the wound and covered with a sterile adhesive dressing. Alternatively, Dermabond (Ethicon Endo-Surgery, Inc.) can be applied to reapproximate the skin edges.

33.4 Postoperative Care Patient’s neurological status is evaluated in the postoperative area and sent to the ambulatory ward with instructions on operative

findings, wound care, and further follow-up. When patients are able to ambulate and void, they can be discharged home with a family member or friend. The patient is seen approximately 2 weeks after surgery to ensure proper wound healing. Preoperative instructional classes are offered to patients and have been found to improve outcomes, reduce patient anxiety, improve satisfaction, and reduce postoperative returns to the hospital since they know better what to expect. Additional wound care and other instructions are given to patients upon discharge from the hospital. Typically, patients are discharged with oral pain medications and muscle relaxers and asked to take as needed. All patients are instructed to call and/or return on significant signs of wound infection (i.e., significant drainage or puss from wound) or changes in neurological condition.

33.5 Management of Complications The muscle-sparing tubular retractor system is very effective in performing lumbar microdiscectomy on an ambulatory basis. However, there is a learning curve associated with using the system efficiently and safely. With repeated use, the surgeon becomes more proficient, operative times decrease, and overall satisfaction with this system increases. When the surgeon is comfortable performing tubular lumbar microdiscectomy, further indications for the use of this technique include lumbar laminectomy for stenosis,20 posterior cervical laminoforaminotomy and discectomy,8,22 thoracic discectomy, far lateral lumbar discectomy, and interbody lumbar fusion.18,19 Increasingly more complex procedures are being performed using this technique including deformity correction, tumor resection, and intradural approaches. In our experience, patient satisfaction has been high with MIS procedures.

33.5.1 Avoiding Complications Fig. 33.5 Docking site of tubular retractor on laminar facet junction.

The potential complications with the use of the tubular system are not significantly different from those encountered

Fig. 33.6 (a,b) Use of cutting burr to perform laminotomy.

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Fig. 33.7 (a,b) Use of Kerrison punch to complete laminotomy and expose rostral edge of the ligamentum flavum.

Fig. 33.8 Exposure of the rostral edge of the ligamentum flavum.

when performing standard microdiscectomy.23 The most frequently stated risks are wound infection, dural tears, bleeding, and neurologic damage. In the early learning period, there may be a slightly higher incidence of dural tears, but these can be avoided with careful attention to operative technique. Dural tears are difficult to repair primarily through the working tube. A small piece of DuraGen dural graft matrix (Integra NeuroSciences) or Durepair Regeneration Matrix (Medtronic Neurologic Technologies) covered with fibrin glue

Fig. 33.9 Retraction of the traversing nerve root and bipolar cautery of epidural vessels overlying the disc space.

can be applied through the tubular retractor. In many cases, placing a small piece of Gelfoam over the durotomy and applying pressure will suffice. Alternatively, a lumbar drain can be placed percutaneously above or below the operative site and left in place for 2 to 3 days postoperatively. When a dural tear occurs, the fascia is closed meticulously and the skin can be closed with a running nylon locking type suture technique. The muscle-sparing approach facilitates durotomy healing and in our experience has not led to a postoperative pseudomeningocele

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Surgical Techniques requiring reexploration and closure. This is one of the advantages to preserving the muscles and soft tissue using this approach. Thus, in our experience, effective management of a small dural tear and cerebrospinal fluid leak could be managed with placement of a small piece of Gel-foam or DuraGen followed by the application of tissue sealant (i.e., Tisseel) and meticulous fascial and water tight wound closure. Additional risks include instrument malfunction such as bending, fragmentation, loosening, and breakage (whole or

Fig. 33.10 Annulotomy.

partial). These are delicate instruments and need to be used as such. The micro-pituitary rongeurs can break if overly torqued. Thus, hand positioning when using these instruments should be mastered to successfully perform these procedures and reduce instrument breakage.

Fig. 33.11 Discectomy performed in a routine fashion.

Fig. 33.12 (a) Reconstruction of the laminar bone using autograft bone collected using the (b) BoneBac Press.

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Muscle Preserving Lumbar Microdiscectomy

33.6 Clinical Cases With the development of newer techniques and instrumentation, patients and physicians are demanding more refined approaches to the spine. In addition to tubular lumbar microdiscectomy, a number of minimally invasive techniques have been developed for lumbar discectomy to meet this demand, including percutaneous nucleotomy,20 percutaneous laser disc decompression (PLDD),11,12,13,15 percutaneous endoscopic laser discectomy,9 and endoscopy.10,24 This technique has been expanded to perform cervical foraminotomy,8,22 lumbar laminectomy for stenosis,25 and fusion. Outcome studies are in progress to validate the clinical efficacy of these new techniques and to show that they are at least as effective as or better than traditional methods. Percutaneous approaches to the lumbar spine for the treatment of disc disease have limited indications primarily because the technique is restricted to patients with contained lumbar disc herniation.26,27 A review of randomized and quasirandomized trials of the surgical management of lumbar disc herniation identified three trials of percutaneous discectomy, revealing moderate evidence that it produces poorer clinical outcomes than standard discectomy or chymopapain.17 In this same review, three trials showed no difference in clinical outcomes between microdiscectomy and standard discectomy. Cochrane methodology used for meta-analysis of randomized controlled trials showed that microdiscectomy produced better results than percutaneous discectomy.16 A systematic review of the literature on percutaneous endoscopic laser discectomy showed that the level of evidence for safety and efficacy was low; there are currently no published controlled, blinded, or randomized studies.9 There was no statistical difference in postoperative infection, dural tear, or length of stay between the nonobese and obese groups. Recurrent symptomatic disc prolapse was seen in 27 patients (9.5%) confirmed by MRI. Nineteen (10.0%) were in the nonobese group and eight (8.6%) in the obese group (p > 0.8).28 Patients undergoing minimally invasive discectomy were found to have comparable perioperative results as those undergoing open microdiscectomy.29 Koebbe et al30 analyzed 3,000 microdiscectomies and had produced good to excellent clinical results in nearly 90% of patients, with the majority returning to work within 1 month. The complication rate of dural tears, discitis, or root injury was shown to be less than 2%, with a reoperation rate of 5%.30 Discectomy performed using the tubular muscle-sparing system produces less tissue trauma than a microdiscectomy and certainly much less than a standard discectomy.31 Using this method, 150 patients ranging in age from 18 to 76 years, with a mean age of 44 years, underwent this procedure.24 Eleven of the herniated discs were of the far lateral type. The male-to-female ratio was 93:57. Fourteen patients were receiving workers’ compensation. The levels of surgery included the following: 3 at L2–L3, 12 at L3– L4, 53 at L4–L5, and 82 at L5–LS1. The versatility of this technique was seen in its ability to treat various lumbar disc pathologies including far lateral disc herniations, concomitant lateral recess stenosis, and noncontained disc herniation. Significant savings were reflected in reduced operative times with case proficiency (75 minutes for the last 30 cases), reduced hospital stays (mean 7.7 hours), and short return-to-work time (mean 17 days).24

Complications were few and included eight patients with dural tears that were all repaired intraoperatively or with lumbar drainage; one patient had a delayed pseudomeningocele formation. One patient had a superficial wound infection that was treated with oral antibiotics. No deep wound infections occurred. Four patients returned with a recurrent herniated disc and were treated with a repeat MED procedure. Patient outcomes were graded using the modified MacNab criteria. According to the modified MacNab criteria, at an average follow-up of 12 months (range 3–24 months), the outcomes were as follows: 77% excellent, 17% good, 3% fair, and 3% poor.24

33.7 Conclusion The tubular muscle-sparing approach is safe and effective for performing minimally invasive lumbar microdiscectomy. Postoperative leg pain and neurological deficits, residual symptoms, intraoperative nerve root lesion, missed pathology, foreign bodies, early recurrent disc herniation, lesions from intraoperative positioning, postoperative cauda equina syndrome (CES), abdominal symptoms, thromboembolic symptoms, infection, and spondylodiscitis are known to be the perioperative complications.32 However, the outcome of lumbar disc surgery depends greatly on proper patient selection. Also, careful attention to surgical technique will ensure that complications are minimized and will optimize patient outcomes. Superficial wound infections and dural tears were the most frequently recognized complications and are reduced with increased experience with this surgical technique. In essence, this approach provides a conduit to the numerous benefits of minimally invasive spine surgery.

Clinical Caveats ●

●

●

●

●

The approach should be directly over the disc space of interest and confirmed with lateral fluoroscopy. Technologies have been developed that eliminate use of K-wires and sequential dilators to approach the spine in a muscle-sparing fashion. The operating microscope allows for excellent three-dimensional visualization of the operative field. Sufficient soft tissue is removed within the tubular retractor to expose the lamina and medial facet. Drilling of bone is performed with a cutting burr with all drill bone collected and used to reconstruct the laminotomy defect, potentially reducing postoperative perineural scar formation.

References [1] Riesenburger RI, David CA. Lumbar microdiscectomy and microendoscopic discectomy. Minim Invasive Ther Allied Technol. 2006; 15(5):267–270 [2] Manchikanti L, Singh V, Falco FJ, et al. An updated review of automated percutaneous mechanical lumbar discectomy for the contained herniated lumbar disc. Pain Physician. 2013; 16(2) Suppl:SE151–SE184 [3] Gibson JN, Waddell G. Surgical interventions for lumbar disc prolapse. Cochrane Database Syst Rev. 2007(2):CD001350 [4] Sabnis AB, Diwan AD. The timing of surgery in lumbar disc prolapse: a systematic review. Indian J Orthop. 2014; 48(2):127–135 [5] Yasargil MG. Microsurgical operation of herniated lumbar disc. Adv Neurosurg. 1977; 7:81

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Surgical Techniques [6] McCulloch JA. Principles of Microsurgery for Lumbar Disc Disease. New York, NY: Raven Press; 1989 [7] Postacchini F, Postacchini R. Operative management of lumbar disc herniation: the evolution of knowledge and surgical techniques in the last century. Acta Neurochir Suppl (Wien). 2011; 108:17–21 [8] Foley KT, Smith MM. Microendoscopic discectomy. Tech Neurosurg. 1997; 3:301–307 [9] Perez-Cruet MJ, Smith M, Foley K. Microendoscopic lumbar discectomy. In: Perez-Cruet MJ, Fessler RG, eds. Outpatient Spinal Surgery. St Louis, MO: Quality Medical Publishing; 2002:171–183 [10] Boult M, Fraser RD, Jones N, et al. Percutaneous endoscopic laser discectomy. Aust N Z J Surg. 2000; 70(7):475–479 [11] Choy DS. Percutaneous laser disc decompression (PLDD): twelve years’ experience with 752 procedures in 518 patients. J Clin Laser Med Surg. 1998; 16(6):325–331 [12] Gangi A, Dietemann JL, Ide C, Brunner P, Klinkert A, Warter JM. Percutaneous laser disk decompression under CT and fluoroscopic guidance: indications, technique, and clinical experience. Radiographics. 1996; 16(1):89–96 [13] Marks RA. Transcutaneous lumbar diskectomy for internal disk derangement: a new indication. South Med J. 2000; 93(9):885–890 [14] Maroon JC, Onik G, Vidovich DV. Percutaneous discectomy for lumbar disc herniation. Neurosurg Clin N Am. 1993; 4(1):125–134 [15] Brayda-Bruno M, Cinnella P. Posterior endoscopic discectomy (and other procedures). Eur Spine J. 2000; 9 Suppl 1:S24–S29 [16] Adamson TE. Microendoscopic posterior cervical laminoforaminotomy for unilateral radiculopathy: results of a new technique in 100 cases. J Neurosurg. 2001; 95(1) Suppl:51–57 [17] Gupta S, Foley K. Endoscopic far-lateral lumbar microdiscectomy. In: PerezCruet MJ, Fessler RG, eds. Outpatient Spinal Surgery. St Louis, MO: Quality Medical Publishing; 2002:185–195 [18] Isaacs RE, Khoo LT, Perez-Cruet MJ, et al. Minimally invasive microendoscopic posterior lumbar interbody fusion with instrumentation. Presented at the Annual Meeting of the American Association of Neurosurgical Surgeons, Chicago, April 2002 [19] Khoo LT, Khoo KM, Isaacs RE, et al. Endoscopic lumbar laminotomy for stenosis. In: Perez-Cruet MJ, Fessler RG, eds. Outpatient Spinal Surgery. St Louis, MO: Quality Medical Publishing; 2002:197–215

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[20] Khoo LT, Perez-Cruet MJ, Laich DT, et al. Posterior cervical microendoscopic foraminotomy. In: Perez-Cruet MJ, Fessler RG, eds. Outpatient Spinal Surgery. St Louis: Quality Medical Publishing; 2002:71–93 [21] Nellensteijn J, Ostelo R, Bartels R, Peul W, van Royen B, van Tulder M. Transforaminal endoscopic surgery for symptomatic lumbar disc herniations: a systematic review of the literature. Eur Spine J. 2010; 19(2):181–204 [22] Kotilainen E, Valtonen S. Long-term outcome of patients who underwent percutaneous nucleotomy for lumbar disc herniation: results after a mean follow-up of 5 years. Acta Neurochir (Wien). 1998; 140(2):108–113 [23] Siebert W. Percutaneous nucleotomy procedures in lumbar intervertebral disc displacement. Current status. Orthopade. 1999; 28:598–608 [24] Perez-Cruet MJ, Foley KT, Isaacs RE, et al. Microendoscopic lumbar discectomy: technical note. Neurosurgery. 2002; 51(5) Suppl:S129–S136 [25] Perez-Cruet MJ, Fessler RG, Perin NI. Review: complications of minimally invasive spinal surgery. Neurosurgery. 2002; 51(5) Suppl:S26–S36 [26] Gibson JN, Grant IC, Waddell G. Surgery for lumbar disc prolapse (Cochrane review). Cochrane Database Syst Rev. 2000; 3:CD001350 [27] Gibson JN, Grant IC, Waddell G. The Cochrane review of surgery for lumbar disc prolapse and degenerative lumbar spondylosis. Spine. 1999; 24 (17):1820–1832 [28] Quah C, Syme G, Swamy GN, Nanjayan S, Fowler A, Calthorpe D. Obesity and recurrent intervertebral disc prolapse after lumbar microdiscectomy. Ann R Coll Surg Engl. 2014; 96(2):140–143 [29] German JW, Adamo MA, Hoppenot RG, Blossom JH, Nagle HA. Perioperative results following lumbar discectomy: comparison of minimally invasive discectomy and standard microdiscectomy. Neurosurg Focus. 2008; 25(2):E20 [30] Koebbe CJ, Maroon JC, Abla A, El-Kadi H, Bost J. Lumbar microdiscectomy: a historical perspective and current technical considerations. Neurosurg Focus. 2002; 13(2):E3 [31] Sahlstrand T, Lönntoft M. A prospective study of preoperative and postoperative sequential magnetic resonance imaging and early clinical outcome in automated percutaneous lumbar discectomy. J Spinal Disord. 1999; 12(5):368–374 [32] Kraemer R, Wild A, Haak H, Herdmann J, Krauspe R, Kraemer J. Classification and management of early complications in open lumbar microdiscectomy. Eur Spine J. 2003; 12(3):239–246

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Far-Lateral Microdiscectomy

34 Far-Lateral Microdiscectomy Lee A. Tan, Carter S. Gerard, Mick J. Perez-Cruet, and Richard G. Fessler Abstract Far-lateral lumbar disc herniations are much less common than paramedian disc herniations and they are often missed. They are estimated to account for about 2 to 12% of all symptomatic lumbar disc herniations. They are characterized by the presence of herniated disc fragments in the foraminal or extraforaminal space, which causes impingement of exiting nerve roots at the same level. This feature is in contrast to the more common paramedian disc herniations, in which the descending nerve roots are often affected and the exiting nerve roots are spared. Minimally invasive approach for far-lateral disc herniations can achieve excellent clinical outcome with minimal soft tissue and bone resection, decreased blood loss, quicker recovery, and shorter hospital stay. In this chapter, the minimally invasive technique is described in detail along with a case illustration and various clinical pearls. Keywords: far-lateral, disc herniation, microdiscectomy, lumbar spine, minimally invasive

levels compared to paramedian disc herniations, with L4–L5 being the most common comprising 30 to 60% of cases.5 MRI can often reveal the herniated disc fragments in the foraminal or extraforaminal space (▶ Fig. 34.2), whereas these lesions can often be missed on CT or myelography.2 Surgical management of FLLDHs can be technically challenging due to the difficulty in gaining access to the foraminal and extraforaminal space, largely due to the important biomechanical roles the adjacent bony structures play in maintaining spinal stability. Traditional surgical approaches include midline approach, paramedian muscle-splitting or Wiltse’s approach, as well as the combined approach. The use of percutaneous approaches to FLLDH has also been described previously,6,7 but the efficacy of these procedures has been questioned.8,9 The advantages of the traditional midline approach include the familiar local anatomy by most spine surgeons and good visualization of the foraminal and extraforaminal space after removing the facet and/or pars interarticularis.1,10,11,12 However, varying degrees of bony resection required for exposure using this approach can often lead to destabilization of the spinal

34.1 Introduction Far-lateral lumbar disc herniations (FLLDHs) were first described by Abdullah et al in 19741 and are estimated to account for 2 to 12% of all symptomatic lumbar disc herniations.2 They are characterized by the presence of herniated disc fragments in the foraminal or extraforaminal space, which causes impingement of exiting nerve roots at the same level (▶ Fig. 34.1). This feature is in contrast to the more common paramedian disc herniations, in which the descending nerve roots are often affected and the exiting nerve roots are spared. Patients with FLLDHs often present with severe, acute onset radicular leg pain, which is thought to be due to direct compression of the dorsal root ganglion by the herniated disc fragment.3 The pain is often described by patient as excruciating, severe, lancinating, and burning pain that is most likely due in part to compression of the dorsal root ganglion. The peak incidence of FLLDHs is in the sixth decade of life.4 They tend to occur at more proximal

Exiting nerve root L3-4 disc

Fig. 34.1 Presence of herniated disc fragments in the foraminal space, which causes impingement of exiting nerve roots at the same level.

Fig. 34.2 (a) Axial and (b) sagittal views demonstrating the herniated disc fragments in the foraminal space with severe foraminal stenosis.

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Surgical Techniques segment.13,14 The Wiltse’s approach15,16 offers a more direct approach to the neuroforamen that spares the facet. However, this muscle-splitting approach is less familiar to many spine surgeons and it lacks the usual anatomical landmarks known from traditional midline approaches. Therefore, the paramedian approach has not gained wide acceptance. The combined approach allows the surgeon to work both medially and laterally to the foramen, therefore making the removal of the pars and facet unnecessary.13,14 However, the combined approach requires extensive stripping and lateral retraction of the paraspinal muscles, which equates to larger incisions and more soft-tissue injuries. The paraspinal muscular dysfunction and disability resulting from midline posterior spinal exposures have been well documented by various authors.17,18,19,20,21,22 With the advancement in minimally invasive surgery (MIS) in recent years, MIS techniques have been utilized to treat FLLDHs with excellent results.2,23,24 The MIS approach, utilizing either endoscope or microscope, provides direct access to the foraminal and extraforaminal space with little need for softtissue/muscle dissection, little bony removal, and minimal blood loss, and it does not destabilize the spine. We prefer the endoscope because the 30-degree viewing angle of the lens allows one to view beyond the confines of the tubular retractor. However, the microscope allows for excellent three-dimensional visualization and may be more readily adopted by surgeons. This muscle-splitting technique, which was initially developed to approach standard lumbar disc herniations, is also ideal for application to far-lateral disc herniations.9

34.2 Indications and Contraindications As a general principle for any surgical procedure, proper patient selection is paramount to a good clinical outcome. The management scheme for FLLDHs is similar to paramedian disc herniations. Symptomatic patients with corresponding MRI findings should undergo a trial of conservative treatment including nonsteroidal anti-inflammatory drugs (NSAIDs), oral steroids, physical therapy, and epidural steroid injection.25 Patients with persistent and intractable radicular pain or progressive weakness after a course of conservative management should be considered for microdiscectomy.5,26 Patients with significant stenosis, degenerative spondylolisthesis, and concurrent FLLDHs should be considered for laminectomy, full facetectomy, discectomy, and interbody fusion.23 Good or excellent clinical outcomes after the surgical management of FLLDH range from 68 to 100%.27,28,29 The MIS technique has been demonstrated to have comparable clinical outcomes with open approaches, with the added benefits of reduced blood loss, less soft-tissue injury, faster recovery, and shorter hospital stay.2,23

34.2.1 Preoperative Planning Far-lateral disc herniations often present more severe radicular symptoms than back pain. The symptom onset is usually acute. There are often absent knee-jerk reflex, dermatomal sensory loss, positive straight leg raise test, positive femoral stretch test, and reproduction of pain and/or paresthesia by lateral bending to the side of the lesion.5,26 MRI is the imaging modality of

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choice; CT and myelography can often give false-negative results which can occur in as much as 25% of cases.26 Flexion–extension X-rays can also be helpful to rule out instability at the level in question.

34.3 Surgical Technique 34.3.1 Patient Positioning The patient is brought into the operating room and placed in the prone position after undergoing general endotracheal anesthesia. Wilson’s frame can be used to place the spine in flexion, therefore widening the interlaminar space. A C-arm fluoroscope is draped into the sterile field for lateral visualization during the approach.

34.3.2 Technique After the operative field has been prepared and draped, a tubular retractor holder consisting of an articulating arm is attached to the operating table rail ipsilateral to the disc herniation. The midline is identified and a 2-cm incision is made 4 to 5 cm lateral to the midline at the ipsilateral side of disc herniation. The target area for docking the tubular retractor is at the junction of the transverse process and pars interarticularis of the vertebra rostral to the disc herniation (e.g., the L4 vertebra for a far-lateral disc herniation at L4–L5). The preoperative MRI images can be helpful in measuring the approximate distance of the incision from the midline and planning the trajectory of the tubular dilators. The appropriate spinal level is localized and confirmed using fluoroscope. A Kirschner wire (K-wire) is inserted through the incision and the lumbodorsal fascia, directed toward the junction of the transverse process and pedicle of the superior vertebra (▶ Fig. 34.3a). The initial cannulated dilator is then placed over the wire through the lumbodorsal fascia and then the Kwire is withdrawn (▶ Fig. 34.3b). The initial dilator is docked on the base of the cephalad transverse process at its junction with the pars. Medial–lateral orientation is determined by palpating the bony landmarks with the tip of the dilator. Anteroposterior (AP) X-rays can be used to confirm the medial–lateral placement of the tube if necessary. Sequential dilators are passed, followed by placement of the tubular retractor (▶ Fig. 34.3c–f). Particular care must be taken to stay docked on bone during the insertion of the dilators and the tubular retractor. The dilators are then removed and the tubular retractor system is connected to the articulating arm holder. It is important to maintain firm downward pressure on the tubular retractor while it is connected to the articulated arm and when the arm is tightened. This maneuver prevents soft tissue from flowing underneath the edges of the tubular retractor. The endoscope used for microendoscopic discectomy (MED) is a 25-degree rod-lens endoscope with contained illumination and variable magnification. It is connected to a coupler, a camera, and the light source. The endoscope is then inserted into the tubular retractor and secured with an attached ring clamp (▶ Fig. 34.4a). The endoscope can be positioned anywhere within the 360-degree arc of the retractor and can be advanced or withdrawn within the tubular retractor, allowing for variable magnification. Typically, the endoscopic assembly is placed at

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Far-Lateral Microdiscectomy

Fig. 34.3 (a) A Kirschner wire (K-wire) is inserted through the incision and the fascia, directed toward the junction of the transverse process and pedicle of the superior vertebra at the desired level. (b–d) Placement of sequential dilators. (e) Tubular dilator is placed in place. (f) Caudal angulation of the tubular dilator toward the far-lateral aspect of the disc space.

a

b

c

L3

L4

Transverse process

L3

L4

Drilling starts on caudal, proximal transverse process

Fig. 34.4 (a) Intraoperative photograph of tubular retractor and endoscopic assembly. (b) Location of tubular retractor. (c) Drilling of the inferomedial aspect of the transverse process and lateral margin of the pars.

the 12 o’clock position on the tubular retractor. Once the endoscope has been inserted into the tubular retractor, the video image on the monitor must be oriented to correspond with the underlying anatomy. Conventionally, medial anatomy should appear at the top of the video screen and lateral anatomy should appear at the bottom. In order to facilitate proper orientation, a suction tip can be placed in a lateral anatomic position

within the tubular retractor. The camera and coupler may then be rotated until the video image shows the instrument at the bottom of the video screen; this will properly orient the tubular retractor over the transverse process (▶ Fig. 34.4b). An operating microscope can be used for visualization through the tubular retractor rather than an endoscope. The procedure steps are essentially identical.

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Surgical Techniques Residual soft tissue is cleared from the base of the transverse process and the pars using monopolar cautery, curette, and pituitary rongeur. There is a pars artery that should be identified, coagulated, and divided early in the dissection. Next, soft tissue is separated from the undersurface of the lateral pars using the small, angled curette. This maneuver will detach the medial edge of the intertransverse ligament from the pars and allows for entry into the neuroforamen. A small portion of bone is then removed along the inferomedial aspect of the transverse process and the most lateral aspect of the pars using an angled Kerrison rongeur or a modified high-speed drill (▶ Fig. 34.4c). This opens the lateral aspect of the neuroforamen and allows for palpation of the pedicle with the ball-tipped probe. Straightforward identification of the exiting nerve root can be made as the nerve root rounds the pedicle. After the nerve root has been definitively identified at the level of the pedicle, dissection is carried out laterally and inferiorly along the root, following its caudal course toward the disc. The disc herniation is identified and the nerve root is decompressed (▶ Fig. 34.5). In order to follow the nerve root along its course, it is often necessary to wand the tubular retractor. This is accomplished by loosening the flexible arm, pivoting the tubular retractor within the small

Medial

a

skin incision, and retightening the arm. Pedicle-to-pedicle access may then be achieved through the initial skin incision. In patients with facet degenerative disease, an overhanging, hypertrophied superior articular process may hinder access to the disc space medial to the exiting root. The lateral margin of the articular process can be removed using either the Kerrison rongeur or the drill, further exposing the distal course of the nerve root. It is important to identify the dorsal root ganglion, which will be obvious as the enlargement of the exiting nerve root just lateral and inferior to the neuroforamen. Take care with the ganglion as excessive manipulation may result in significant postoperative pain and/or dysesthesia. After definitive identification and exposure of the exiting nerve root, the root is explored for compressive pathology (▶ Fig. 34.6a). Herniated disc fragments can be identified and removed with the various instruments such as a micropituitary rongeur (▶ Fig. 34.6b). If necessary, the disc space may be entered for further disc removal. Finally, the nerve root should be reexplored to confirm that it has been fully decompressed (▶ Fig. 34.6c). The wound should be copiously irrigated with antibiotic solution through the tubular retractor and a meticulous inspection made for hemostasis. The flexible arm is then loosened and the

b

Medial

Pars

Rostral

Caudal

Rostral

Exiting root

Intertransverse ligament

Transverse process

Disc Lateral

Lateral

c

Caudal

d

Medial

Rostral

Caudal

Lateral

Disc herniation (in this case, displacing the root medially)

Medial

Rostral

Caudal

Lateral

Decompressed nerve root

Fig. 34.5 Illustration of endoscopic far-lateral microdiscectomy showing overall anatomy. (a) Detachment of medial edge of intertransverse ligament from the par. (b) Removal of bone from inferomedial aspect of transverse process and lateral aspect of the pars. (c) Removal of disc material. (d) Decompression of the nerve root.

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Far-Lateral Microdiscectomy

Fig. 34.6 (a) Intraoperative endoscopic view showing identification of exiting nerve root, which is tented by the underlying disc herniations. (b) Removal of large far-lateral disc herniation. (c) Decompressed nerve root.

tubular retractor removed along with the endoscope. As the retractor is withdrawn, the surgical corridor closes spontaneously when the paraspinous muscles resume their normal anatomic position. Residual “dead space” is minimized. The fascia is closed with a single suture. If a deep subcutaneous fat layer precludes fascial closure, the suture is placed as deep into the subcutaneous tissue as possible. The subcutaneous tissues are then closed with an inverted suture. The skin edges can then be approximated with skin glue. Alternatively, an approach to the far-lateral herniated disc can be performed from the caudal aspect. In this technique, the lateral edge of the facet over the disc space is identified through the tubular retractor and is drilled to identify the rostral aspect of the pedicle just below the disc space of interest. Lateral fluoroscopy can help identify the location. The disc is then entered after an annulotomy is performed. Disc material is removed in a routine fashion with a micro-pituitary rongeur. Then using a ball-ended probe, the extruded fragment extending into the superior or rostral aspect of the neural foramen can be removed. The disadvantage of this approach is that frequently the exiting nerve root is never visualized. However, with careful inspection, the far-lateral disc herniation can be successfully removed with minimal tissue dissection.

34.4 Postoperative Care Routine postoperative care similar to paramedian disc herniation is usually adequate. Most patients can be discharged the same day after MIS microdiscectomy. Oral pain medications and stool softener are usually prescribed.

34.5 Management of Complications Unintended durotomy is a potential complication of MIS FLLDH microdiscectomy. We prefer to repair the durotomy primarily with an MIS dural repair kit as described previously.30 Wound closure with a running locking 2–0 nylon can help prevent any cerebrospinal fluid (CSF) leak. Usually, only overnight bed rest

is necessary in patients with durotomy.30 Infection is rare with the MIS approach as we have demonstrated in a previous study.31 Wrong-level or wrong-side surgery can be avoided with careful review of preoperative films and intraoperative fluoroscope. Excessive bone removal can lead to segmental instability, and lumbar fusion may be needed in these cases.

34.6 Clinical Case A 45-year-old woman with past medical history including anxiety and hepatitis C presented with low back pain with radiation to the left anterior thigh for 3 months. She was evaluated by her primary care physician and MRI lumbar spine was obtained 2 months ago, which revealed a left far-lateral disc herniation at L3–L4 (▶ Fig. 34.7). She had undergone 6 weeks of conservative management including oral pain medication, physical therapy, and epidural steroid injection with minimal improvement. She presented to the emergency department for worsening pain in her left anterior thigh and increasing difficulty with ambulation due to pain. Her physical examination was unremarkable except for decreased sensation in the left L3 dermatome. Given her persistent symptoms and failure of conservative management, she was taken to the operating room for MIS left L3–L4 far-lateral microdiscectomy. Intraoperatively, a large herniated disc fragment was identified and removed in the left L3 foramen without complication, and the L3 nerve root was decompressed at end of the case. Postoperatively, her left anterior thigh pain improved significantly and she was discharged on postoperative day 1 after physical therapy clearance. At 6-week follow-up, her left thigh pain has completely resolved.

34.7 Conclusion Minimally invasive approach for far-lateral disc herniations can achieve excellent clinical outcome with minimal soft tissue and bone resection, decreased blood loss, quicker recovery, and shorter hospital stay. This technique avoids significant musclerelated trauma, the risk of muscle denervation caused by extensive exposure, and potential spinal destabilization due to excessive bone resection.

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Fig. 34.7 MRI lumbar spine sagittal (a) and axial (b) views demonstrating a left far-lateral disc herniation at L3 –L4.

Clinical Caveats ●

● ●

●

●

Carefully review pre- and intraoperative images to avoid wrong-level or wrong-side surgery. Avoid excessive bony removal to maintain spinal stability. Patients with concurrent significant stenosis or spondylolisthesis should be considered for fusion. Incidental durotomy can be repaired with MIS dural repair kit and running locking nylon wound closure without need for prolonged bed rest. Proper patient selection is key to ensure a good clinical outcome.

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Far-Lateral Microdiscectomy [23] Liu T, Zhou Y, Wang J, et al. Clinical efficacy of three different minimally invasive procedures for far lateral lumbar disc herniation. Chin Med J (Engl). 2012; 125(6):1082–1088 [24] Salame K, Lidar Z. Minimally invasive approach to far lateral lumbar disc herniation: technique and clinical results. Acta Neurochir (Wien). 2010; 152 (4):663–668 [25] Rust MS, Olivero WC. Far-lateral disc herniations: the results of conservative management. J Spinal Disord. 1999; 12(2):138–140 [26] Tessitore E, de Tribolet N. Far-lateral lumbar disc herniation: the microsurgical transmuscular approach. Neurosurgery. 2004; 54(4):939–942, discussion 942

[27] Maroon JC. Current concepts in minimally invasive discectomy. Neurosurgery. 2002; 51(5) Suppl:S137–S145 [28] O’Hara LJ, Marshall RW. Far lateral lumbar disc herniation. The key to the intertransverse approach. J Bone Joint Surg Br. 1997; 79(6):943–947 [29] Postacchini F, Montanaro A. Extreme lateral herniations of lumbar disks. Clin Orthop Relat Res. 1979(138):222–227 [30] Tan LA, Takagi I, Straus D, O’Toole JE. Management of intended durotomy in minimally invasive intradural spine surgery: clinical article. J Neurosurg Spine. 2014; 21(2):279–285 [31] O’Toole JE, Eichholz KM, Fessler RG. Surgical site infection rates after minimally invasive spinal surgery. J Neurosurg Spine. 2009; 11(4):471–476

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35 Minimally Invasive Laminectomy for Lumbar Stenosis Mick J. Perez-Cruet, Ronnie I. Mimran, R. Patrick Jacob, and Richard G. Fessler Abstract Lumbar spinal stenosis is the most common spinal pathology that a surgeon treats. Knowing how to treat this common condition with a minimally invasive approach can result in marked improvements in patient outcomes and surgical cost. This chapter will review what we believe to be the most effective way of treating lumbar spinal stenosis. The chapter will also review some of the latest techniques and technology so that a direct approach to decompression of the neural elements can be performed while maintaining much of the normal anatomy of the spine. Our clinical outcomes using this technique have resulted in fast recoveries and reduced cost, and have minimized the incidence of recurrent stenosis and need for additional surgery. In addition, this technique results in minimal scar formation at the surgical site, ultimately leading to improved outcomes for our patients. Keywords: spinal stenosis, lumbar, neurogenic claudication, laminectomy, in situ fusion, local bone harvest, minimally invasive

and the anterior margin of the superior articular process (lateral recess stenosis); or in a combination of both areas. Spinal stenosis may be congenital or acquired. Congenital stenosis, which is usually associated with a shortened pedicle length or hereditary syndromes (i.e., achondroplasia), typically presents at a younger age than acquired or spondylotic spinal stenosis. Congenital stenosis is rarely symptomatic in childhood or young adult life and typically presents in the third or fourth decade as degenerative changes are superimposed. The bone in patients with congenital spinal stenosis tends to be relatively hard, making decompression tedious. Acquired forms of the disease may arise in a developmentally normal canal when degenerative changes occur, hallmarked by facet arthropathy, ligamentous hypertrophy, osteophytic growth, and intervertebral disc bulging. These acquired forms of lumbar spinal stenosis are the most common forms of the condition, most often implicated in cases leading to surgery.2,3 Canal stenosis may also be secondarily associated with other degenerative conditions, such as spondylolisthesis or scoliosis.

35.1 Introduction

35.2 Evolution of Techniques

Lumbar spinal stenosis is the most commonly diagnosed spinal disorder in the elderly population of the United States today. It is a major cause of lower back pain, leg pain, activity limitation, and disability in this population, causing an increasing number of patients to consider surgery. In fact, rates of surgery for lumbar stenosis have increased up to eightfold in recent years.1 Anatomically, spinal stenosis is defined as a reduced cross-sectional area of the vertebral canal, usually resulting in compression of neural structures. This may occur in the central portion of the spinal canal (termed central stenosis); in the lateral recesses of the canal, between the posterior margin of the vertebral body

The most commonly performed surgical procedure for treating lumbar stenosis, until recently, was an open laminectomy. To perform a standard open laminectomy, resection of the spinous process, the interspinous and supraspinous ligaments, bilateral laminae, the ligamentum flavum, and often varying amounts of the facet complex is required. This method allows complete decompression of the spinal canal, including the lateral recess and intervertebral foramen, but can potentially lead to poor patient outcomes and need for additional surgery for adjacent segment disease (ASD4,5; ▶ Fig. 35.1). This wide resection may be considered excessive for forms of lumbar stenosis occurring solely at

Fig. 35.1 (a-c) Potential problems with traditional open laminectomy include adjacent segment disease (ASD), which can result in 13% reoperation rate at 4-year follow-up.4 The removal of the spinous process can lead to facet hypertrophy causing ASD after multilevel traditional laminectomy, fusion, and instrumentation. This is felt to occur due to stresses placed on the adjacent facet and ligamentum flavum. (Adapted from Perez-Cruet and Mendoza-Torres 2015.5)

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Minimally Invasive Laminectomy for Lumbar Stenosis the level of the disc space, which occurs in the vast majority of cases. These forms of the disease, mainly caused by intervertebral disc pathology and a combination of thickened ligaments and hypertrophic facets, are accessible through a widened interlaminar space. This knowledge, combined with an effort to preserve midline posterior element structures, led to the introduction of the hemilaminotomy, initially performed bilaterally, to treat degenerative lumbar stenosis.6,7,8 Young et al9 introduced the concept of the unilateral approach for performing a bilateral decompressive laminotomy in which the ipsilateral side of the canal is decompressed first and the contralateral canal, lateral recess, and intervertebral foramen are decompressed under the midline structures. This approach offered the advantage of preserving the spinous processes and midline ligamentous structures and simultaneously allowed the surgeon to access both sides of the spinal canal to address the main points of compression. With the recent advent of endoscopic and minimally invasive approaches for removal of herniated lumbar discs, it became a natural progression to apply the technique to decompressive laminectomy and laminotomy. In addition to the benefits associated with preserving the midline structures, this new method provided a smaller skin incision, less tissue trauma, and improved visualization. After Guiot et al10 reported the feasibility of the technique in cadavers, Khoo and Fessler11 later demonstrated that it was a safe, effective surgical procedure for the decompression of the stenotic lumbar spine.

35.3 Indications and Contraindications 35.3.1 Patient Selection

claudication will reproduce their pain symptoms. The neurologic examination at rest may be fairly benign until very late stages of the disease when fixed motor or sensory deficits become evident. Sphincter disturbance is a late symptom of the condition and is usually associated with severe compression of the cauda equina, which is sometimes the result of an acute disc herniation superimposed on preexisting spinal stenosis.

35.3.3 Radiographic Workup Radiographic imaging usually begins with plain films, which often reveal degeneration of the motion segments, loss of disc space height, narrowed neural foramina, and hypertrophy of the facet joints. MRI scanning is the study of choice and will, with rare exception, provide diagnostic images. Typical findings include degenerative disc disease, ligamentous and facet hypertrophy, and a triangularly shaped trefoil spinal canal (▶ Fig. 35.2). Additionally, spinal stenosis occurs at the level of the disc space; therefore, focused surgical treatment can help preserve those anatomical structures not causing neural compression. For the occasional patient who is not a candidate or is uncomfortable with an MRI, myelography combined with a CT scan can be obtained. Myelography will show constrictions or blocks in the dye column, and the CT scan can be used for accurate measurements of canal diameter. The CT/myelogram study is especially helpful in identifying lumbar stenosis in those patients having undergone previous instrumented fusion surgery as the artifact created by the hardware prevents adequate canal visualization using MRI (▶ Fig. 35.3). Lumbar stenosis occurs at the level of the disc space and is caused in most situations from a combination of facet and ligamentum flavum hypertrophy. Thus, focused minimally invasive laminectomy can achieve

With the increasing incidence of lumbar stenosis, appropriate patient selection for the minimally invasive approach becomes the first essential step toward a good outcome. Reoperative cases are relatively more difficult and should not be attempted until the surgeon has gained a great deal of experience with minimally invasive approaches. Morbid obesity increases the working distance from the skin to the spine and increases the technical difficulty for the surgeon. These cases are best deferred until a high level of experience and comfort with tubular retractor systems is achieved.

35.3.2 Preoperative Planning Patients presenting with lumbar stenosis characteristically complain of bilateral or unilateral leg pain, weakness, and/or paresthesias. Many patients (~50%) also suffer from neurogenic claudication, a type of leg pain that is typically aggravated by standing and walking and relieved by sitting or lying down.1,3 Symptomatic relief with lumbar flexion is often a reliable characteristic that helps distinguish so-called neurogenic spinal claudication from vascular claudication (caused by arterial insufficiency). The bicycle test, in which the patient is leaning over riding a stationary bike, can also help distinguish the two forms. Patients with neurogenic claudication can ride without pain because they are in a flexed position, which helps open the spinal canal and relieve symptoms, whereas those with vascular

Fig. 35.2 Preoperative MRI showing triangularly shaped “trefoil” canal caused by hypertrophy of the ligamentum flavum and facet complex.

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Surgical Techniques

Fig. 35.3 (a–c) Adjacent segment disease (ASD) after open laminectomy, fusion, and instrumentation. Note facet hypertrophy and stenosis seen on sagittal and axial CT requiring reoperation.

adequate neural decompression while preserving much of the supporting anatomy of the spine (▶ Fig. 35.4). Following minimally invasive laminectomy, postoperative MRI shows adequate healing of the paramuscular muscle afforded by the muscle-dilating approach with adequate decompression of the spinal canal. We have noted that there is minimal scar formation, which may ultimately improve patient outcomes (▶ Fig. 35.5).

35.3.4 Operative Setup and Instrumentation Minimally invasive lumbar laminectomy is performed in a standard operating room with routinely available equipment. Fluoroscopy is used for the initial approach and confirmation of the correct surgical level. The procedure can be performed using a series of muscle dilators to approach the spine over which a tubular retractor is placed and is marketed by several different manufacturers. Recent developments like the Thompson MIS One-Step-Dilator (Thompson MIS, Salem, NH), eliminate the need for multiple muscle dilators and thus facilitate the procedure and reduce the risk of passing a dilator into the canal (▶ Fig. 35.6). Muscle damage and dissection are minimized. The tubular retractors are available in several working diameters and in various lengths to accommodate variability in the depth of soft tissues. Standard spinal surgery instruments are not ideal for use with tubular retractor systems because of the confined space of the retractors. If the surgeon is using a microscope for magnification and illumination, either the surgeon’s hands or the back of the instrument tends to obscure the visual pathway. If an endoscope is used, then the tube tends to become clogged with the scope, suction, and instrument. For these reasons, a full set of bayonetted instruments, including Kerrison rongeurs, curettes, probes, and dissectors, is essential for adequate visualization during the surgery. A long tapered drill facilitates bony decompression (▶ Fig. 35.6).

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The operative microscope is employed for excellent illumination and stereoscopic visualization through the dilated working channel. Surgeons using the operative microscope accomplish this by altering the angle of the working retractor (i.e., tilt the operative table slightly away from the surgeon when performing the contralateral decompression to undercut the spinous process and contralateral lamina). The microscope technique allows for excellent three-dimensional (3D) visualization of the operative anatomy (▶ Fig. 35.7).

Lumbar Facet Anatomy to Determine Surgical Approach Lumbar facet anatomy can play an important role in determining spinal stability and whether decompression alone versus decompression and more extensive instrumented fusion is necessary. Anatomical changes in the facet may represent the consequences of spinal instability not detected or appreciated on dynamic plain radiographs. The facet joint, with opposing cartilaginous surfaces, facilitates low friction movement between adjacent vertebral bodies. Together with the disc, the bilateral facet joints transfer loads, and guide and constrain motions in the spine due to their geometry and mechanical function. The facet joints may account for 15 to 40% of low back pain.5 However, there are few studies illustrating how morphometric analysis of the facet can help determine the most favorable surgical approach.5 We conducted an analysis of facet morphology in the following study to determine the relationship between surgical approach and preoperative facet anatomy visualized on axial MRI images.

Methods Twenty patients having undergone minimally invasive decompression with or without instrumentation for stenosis were retrospectively analyzed. Morphometric analysis of the lumbar facets at the index level was analyzed in the preoperative lumbar

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Minimally Invasive Laminectomy for Lumbar Stenosis

Fig. 35.4 Lumbar stenosis occurring at the (a) level of the disc space (L2–L3, L3–L4, and L4–L5 levels in this patient) and primarily caused by hypertrophy of the ligamentum flavum and facet joint as seen here at the corresponding axial MRI of (b) L2–L3, (c) L3–L4, and (d) L4–L5 levels. Minimally invasive laminectomy provides focused decompression at the level of compression as seen in these immediate postoperative corresponding (e) sagittal, (f) L2–L3 level, (g) L3–L4 level, (h) L4–L5 level axial, and (i–k) coronal postoperative reconstructive CT images showing minimally invasive laminotomy with autologous morselized bone graft laminar reconstruction and in situ facet fusion.

MRI at the mid-disc space level using a longitudinal measurement of the superior and inferior facets12 (▶ Fig. 35.8, ▶ Fig. 35.9, ▶ Fig. 35.10, and ▶ Table 35.1). Preoperative inspection of the MRI can help determine whether minimally invasive laminectomy alone or a more extensive procedure such as decompression with instrumented fusion is necessary (i.e., minimally invasive transforaminal lumbar interbody fusion and percutaneous pedicle screw fixation [MITLIF]12,13; see ▶ Fig. 35.9, ▶ Fig. 35.10, ▶ Fig. 35.11, ▶ Fig. 35.12, ▶ Fig. 35.13). Those patients who underwent decompression alone had an average longitudinal facet morphology of 11.1-mm length of

the superior facet of inferior vertebral body and 16.3-mm length of the inferior facet of the superior vertebral body. This compared with an average longitudinal facet morphology in spondylolisthesis patients of 24.7-mm length of the superior facet of inferior vertebral body and 30-mm length of the inferior facet of superior vertebral body. Patients with spinal stenosis and elongation of facets underwent MITLIF, whereas those patients with stenosis and relatively normal facet ratios underwent decompression alone. Therefore, facet morphology may be an important preoperative analysis to determine the need for decompression alone versus more extensive decompression, fusion, and spinal instrumentation.

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Fig. 35.5 Twelve-month (a) postoperative sagittal MRI in a patient having undergone right (b) L3–L4 and (c) L4–L5 minimally invasive laminectomy for stenosis with biological laminar reconstruction using morselized autograft. Note preservation of paraspinal muscular anatomy, spinous process, laminar reconstruction, and normal anatomic distribution of cauda equina nerve roots with adequate canal decompression and minimal scar formation.

35.4 Surgical Technique: MIS Laminectomy and In Situ Posterior Fusion Traditional surgical treatment for lumbar stenosis includes detachment of paraspinal musculature from midline boney anatomy and removal of the spinous process and lamina bilaterally to achieve decompression. This can potentially increase the incidence of adjacent-level pathology (ALP) and need for reoperation (see ▶ Fig. 35.1, ▶ Fig. 35.3). A study was conducted to evaluate whether minimally invasive laminectomy and in situ posterior fusion (MIL-ISF) can improve patient outcomes while reducing ALP and need for reoperation.

Complications occurred in nine (5.8%) cases and included superficial wound infection (n = 2, 1.3%) and pulmonary embolism (n = 1, 0.6%). Additional transient complications included urinary retention and atelectasis. Reoperation occurred in five (3.2%) cases due to new-onset or persistent symptoms with four (2.6%) cases requiring the same level surgery and one (0.6%) case adjacent segment surgery. VAS scores improved from 6.5 to 2.4 (p > 0.001) and ODI improved from 58 to 19 (p > 0.001). Preoperative facet anatomy and plain films determined optimal candidates.

Minimally Invasive Laminectomy for Lumbar Spine Stenosis: Case Review ●

35.4.1 Methods

●

Between April 2009 and September 2013, 280 MIL-ISF of the facets using local autograft (▶ Fig. 35.14, ▶ Fig. 35.15) were performed in 155 consecutive patients for lumbar spinal stenosis refractory to nonoperative treatments.5 Charts were reviewed retrospectively and outcome scales (Oswestry Disability Index [ODI] and Visual Analogue Scale [VAS]) were answered prospectively preoperatively and over a 5-year follow-up period. Facet anatomy was documented as well as stability seen on preoperative dynamic plain films. Complication and reoperation rates were analyzed.5

●

●

●

280 Laminectomies ● ● ● ●

Patients (n = 155) were followed over a 5-year period with an average 2.3-year follow-up. MIL-ISF was most commonly performed at the L3–L4 (n = 123, 44%) and L4–L5 (n = 98, 35%) levels.

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L2–L3: 15%. L3–L4: 24%. L4–L5: 44%. L5–S1: 35%.

Symptoms ●

Results

155 patients. M: 84/F: 61. Median age: 55 years. Years of symptoms: 1 month to 30 years. Follow-up: 2 months to 5 years.

● ● ● ●

Low back pain. Neurogenic claudication. Leg pain. Buttock pain. Difficulty in walking.

Perez-Cruet et al, An Anatomic Approach to Minimally Invasive Spine Surgery, 2nd Ed. (ISBN 978-1-62623-643-1), copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.

Minimally Invasive Laminectomy for Lumbar Stenosis positioned on a frame to allow flexion of the hips and lumbar spine. This maneuver reverses the lumbar lordosis, widens the interspinous and interlaminar distances, and places the vertebral canal in its widest arrangement. A Wilson frame can be used to accomplish this. In addition, the abdomen is kept dependent, which decreases venous backpressure and reduces epidural venous bleeding.14 Positioning for minimally invasive procedures is accomplished in a manner similar to standard open cases with the same precautions. Intraoperative C-arm fluoroscopy is positioned to provide lateral images during the procedure. When not in use, the fluoroscopy unit is moved out of the way toward the feet of the patient. We find a Jackson table with a Wilson frame on it to be helpful since there is no base in the middle of the operative table to interfere with the C-arm.

Incision

Fig. 35.6 (a) Intraoperative photograph showing use of One-StepDilator (b) approaching the spine by turning clockwise through the muscle (c) opening the blades by turning counterclockwise and (d) passing a tubular retractor and removing the dilator to create a working channel. (e) A long tapered drill with M8 cutting burr used to perform the minimally invasive surgery (MIS) laminectomy (Stryker TPS, Kalamazoo, MI).

Conclusion MIL-ISF for lumbar stenosis is a safe and effective technique with excellent clinical outcomes, low complication rates, and very low rate of ASD. This low rate of ASD can be attributed to proper patient selection for noninstrumented decompression and preservation of normal anatomical structures of the spine while allowing for adequate neural decompression.

35.4.2 Surgical Technique Patient Positioning and Operative Preparation After routine preoperative preparations and induction of general anesthesia, the patient is transferred to a fluoroscopy-compatible operating table in the prone position. Patients are

Under fluoroscopic guidance, an 18-gauge spinal needle is inserted approximately 1 to 2 cm lateral to midline to identify the appropriate level. The target is the lamina overlying the disc space of interest. When proper incision level has been attained, a 4- to 5-cm area around the incision site can be subcutaneously infiltrated with a solution of 0.25% bupivacaine and 1:200,000 epinephrine. This solution reduces bleeding around the track of the dissection and provides postoperative pain control. An incision is made directly over the level of interest. This is critical to assure the tubular retractor is directly over the level of surgery to facilitate the procedure. The total size of the incision should match the size of the intended final tubular retractor. Typically, an 18-mm-diameter tubular retractor is used. Once the skin incision is made, a Bovie cautery is used to make an incision parallel and lateral to the spinous process in the lumbodorsal fascia to facilitate subsequent muscle dilator insertion. When the incision is completed, a guide wire is docked on the laminar facet junction. Care is taken using fluoroscopic guidance not to enter the spinal canal with the Kirschner wire (K-wire). Remaining dorsal to the lamina and facet complex with the K-wire and subsequent serial muscle dilators assures a safe approach to the spine. The first dilator is placed over the guide wire (▶ Fig. 35.16a); subsequently, the guide wire is removed to reduce the risk of inadvertent dural puncture. Serial muscle dilators are placed and docked firmly against the lamina (▶ Fig. 35.16b). Care is taken not to push the dilators but to rotate them toward the spine during the approach, especially the first and second dilators, to avoid inadvertent entrance into the spinal canal. To create the shortest possible channel and to improve visualization and illumination, the tubular retractor chosen should be as short as possible to reach the lamina; the outer rim of the retractor should sit flush on the patient’s skin (▶ Fig. 35.16c). The appropriate tubular retractor is secured using the flexible arm assembly, which is fastened to the side rail of the operating table, out of the path of the fluoroscopy unit (▶ Fig. 35.16d). At times, especially in redo operations, the dilators and subsequent tubular retractor can be placed just dorsal to the spine. The microscope can then be brought into the surgical field to perform an approach to the bony anatomy of the spine under direct visualization. The operating microscope or surgical loupes and a headlight are used for enhanced illumination and visualization. At this point, fluoroscopy should be used

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Fig. 35.7 The microscope can be used to allow for excellent three-dimensional visualization of the operative anatomy while performing minimally invasive laminectomy.

Fig. 35.8 Facet morphology and back pain to define glacial instability and level requiring minimally invasive laminectomy alone or a more extensive instrumented fusion (i.e., minimally invasive transforaminal lumbar interbody fusion [MITLIF]). (a) Sagittal MRI showing (b) normal facet anatomy at the L3–L4 level. Note relatively symmetric ratio of inferior and superior articular facets. (c) Abnormal facet anatomy seen at the L4–L5 spondylolisthesis level. Note elongation of the facets due to translational force imparted on the facets from subluxation of the L4 vertebrae on the L5 vertebrae. The L4–L5 level was treated with MITLIF and percutaneous pedicle screw instrumentation.

to definitively confirm the level of operation (▶ Fig. 35.16f). Alternatively, the One-Step-Dilator (Thompson MIS, Salem, NH) has been developed to eliminate the need for guide wire and subsequent muscle dilators. This system allows for a bloodless muscle-sparing approach to the spine (▶ Fig. 35.6).

Laminectomy The remaining soft tissue on the laminar/facet surface is then removed with monopolar Bovie cautery. The edges of the inferior lamina and medial aspect of the facet should now be seen. Using a cutting M8 matchstick cutting burr, an ipsilateral laminotomy is performed with the drill, burring through the lamina to the thickened ligamentum flavum. All drilled bone is collected using the BoneBac Press (Thompson MIS, Salem, NH) and used to perform posterior lateral in situ fusion and reconstruction of laminar defect

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(see ▶ Fig. 35.14, ▶ Fig. 35.15). The approach to the ligamentum flavum should be performed on the caudal lateral aspect of the lamina to reduce the risk of dural tear since the ligamentum flavum underlies the lamina in this location (▶ Fig. 35.17). Once the ligamentum flavum is exposed in this area, further removal of the lamina is performed until the epidural fat pad is exposed on the rostral aspect of the ligamentum flavum of the ipsilateral lamina (▶ Fig. 35.18). The tubular retractor can be repositioned, or wanded, to alter the surgeon’s view and to complete the hemilaminotomy. Any bleeding from the bone edges is easily controlled with bone wax. When the ipsilateral hemilaminectomy is completed (▶ Fig. 35.19), the ligamentum flavum is left in place to protect the dura and neural elements during decompression of the contralateral side. The lateral recess is then decompressed with as much removal of the medial facet as necessary. The tubular

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Minimally Invasive Laminectomy for Lumbar Stenosis

Fig. 35.9 (a) Using preoperative MRI to measure the (b) inferior facet of superior vertebrae and (c) superior facet of inferior vertebrae. The surface areas on axial MRI of the inferior and superior facet were also analyzed.

2.5

Fig. 35.10 Facet ratios of normal and abnormal segments of the spine that underwent minimally invasive transforaminal lumbar interbody fusion (MITLIF) for the treatment of spondylolisthesis are shown here. (Adapted from Perez-Cruet et al 2014.12)

2

1.5 Normal Pathological

1

0.5

0

L5/S1

L4/5

L3/4

retractor can be angled in a medial to lateral orientation to view the medial facet more effectively, allowing the surgeon to undercut the facet and widen the lateral recess by removing bone. Once adequate ipsilateral decompression is achieved, the operative table can be tilted slightly away from the surgeon and the tubular retractor repositioned by wanding laterally to expose the base of the spinous process. Care is taken not to overtilt the table. Typically 5 to 10 degrees of table tilt is all that is needed to achieve adequate visualization of the base of the spinous process. A Bovie cautery is used to remove soft tissue to expose the base of the spinous process. The key maneuver in this procedure is angling the distal aspect of the tubular retractor medially, to visualize the base of the spinous process to achieve adequate contralateral decompression by undercutting the spinous process and contralateral lamina (see ▶ Fig. 35.19). The angle of the tubular retractor is approximated by the medial to lateral slope of the contralateral lamina. The operating microscope is similarly positioned to view down the tubular retractor. The ligamentum flavum is maintained during bony decompression as a protective layer over the dura, and the high-speed drill is used to extend the bone resection toward the contrala-

teral side. This process is not a complete laminectomy in the same manner as the ipsilateral side because the dorsal surface of the lamina is left in place. The bony removal is an undercutting of the lamina, intended not only to decompress the neural elements, but also to facilitate visualization of the contralateral lateral recess and neural foramen. Visualization of the contralateral side enables drilling under the spinous process and contralateral lamina (▶ Fig. 35.20a–c). The ligamentum flavum is left in place during drilling to protect the dura. A thin rim of bone can also be left between the dura and the drill. This bone is removed with a pituitary rongeur when drilling is completed. However, tilting the table away from the surgeon allows excellent 3D visualization of the surgical field without the need to clean the endoscope during the procedure. The ipsilateral ligamentum flavum is removed first with an up-biting Kerrison punch. After ipsilateral ligamentum flavum removal is completed, the contralateral ligamentum flavum can be removed. This facilitates contralateral decompression. We have used a CO2 laser to facilitate removal of the contralateral ligamentum flavum.15 Alternatively, a Cavitron ultrasonic surgical

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Surgical Techniques aspirator (CUSA) can be used. The intent is to remove enough contralateral ligamentum flavum that a no. 1 or 2 Kerrison punch can be safely placed to decompress the lateral recess safely and prevent durotomy. The CO2 laser or CUSA shrinks the contralateral ligamentum flavum and facilitates removal with a no. 1 or 2 Kerrison punch.15 If the contralateral recess is still very constricted or tight, wand the tubular retractor to the ipsilateral side and remove additional medial facet and ligamentum flavum to allow additional room to decompress the contralateral side. In this manner, we have almost completely eliminated the risk of durotomy during decompression. This is especially useful in cases of high-grade spinal stenosis with lateral recess stenosis and has significantly reduced the risk of durotomy while providing for adequate contralateral decompression. A medial facetectomy is carried out to decompress the lateral recess, with care being taken to first identify and then protect the contralateral nerve root as it exits the foramen. The superior articular process is typically the area of greatest compression and should be addressed if present. The full bilateral decompression is now complete (▶ Fig. 35.21). Table 35.1 Normal and abnormal facet ratios Normal (cm)

Abnormal (cm)

Mean

1.21

1.86

Median

1.20

1.79

Range

0.98–1.5

0.58–3.29

Mean

1.60

2.27

Median

1.61

2.03

Range

1.2–2.2

0.50–6.41

Mean

1.44

2.24

Median

1.42

2.23

Range

1.1–1.9

0.76–4.3

L5/S1 level

L4/L5 level

L3/L4 level

Source: Perez-Cruet et al 2014.12 Note: Normal and abnormal facet ratios seen at L5–S1, L4–L5, and L3–L4 levels. Note the higher values in facet ratios seen in elongated facets typically seen in patients with spondylolisthesis.

After adequate neural decompression, inspection is done with a ball-ended probe (▶ Fig. 35.22). We have found that in situ fusion of the facets can be performed to potentially reduce restenosis of the decompressed segment. This can be performed by decorticating the contralateral facet and placing morselized autograft through the tube to pack the facet. Once adequate contralateral decompression with ball-ended probe inspection is performed, the table is placed flat by tilting it toward the surgeon and the ipsilateral facet is decorticated. Morselized autograft is then placed into the drilled facet complex (▶ Fig. 35.23, ▶ Fig. 35.24). The adjacent levels of stenosis can be decompressed by removing the tubular retractor and similarly approaching the spine through the same skin incision using the technique previously described. In this manner, multilevel lumbar stenosis can be treated (▶ Fig. 35.25, ▶ Fig. 35.26).

Closure When a full decompression of the vertebral canal, lateral recesses, and nerve root foramina is complete, a broad inspection is performed and meticulous hemostasis is obtained using bipolar cautery, bone wax, and thrombin-soaked Gelfoam. The wound can be irrigated with antibiotic solution. A subfascial drain can be placed when performing multilevel decompression and the patient placed on postoperative antibiotics. Muscular hemostasis is ensured as the tubular retractor is withdrawn. Closure is accomplished with absorbable sutures in the fascia and subcutaneous layers and skin glue or Steri-Strips with wound dressing.

Postoperative Care Postoperatively, the patient is transferred to the floor to recover. Drains can usually be removed within 24 hours. Patients are ambulated on postoperative day 1 and discharged when able to void, tolerate oral food and drink, and ambulate. Patients are advised of wound care and to return in case of any sign of infection or changes in neurological status. Patients are typically seen 2 weeks after surgery and at 3 and 6 months postoperatively. If needed, physical therapy is usually started 2 weeks after surgery.

Avoiding Complications ●

Correct identification of the surgical level is dependent on fluoroscopy because unlike open procedures in which familiar landmarks can be identified, exposure can be limited.

Fig. 35.11 Preoperative inspection of the facet complex on MRI can help determine whether or not to decompress with minimally invasive laminectomy versus decompression with minimally invasive transforaminal lumbar interbody fusion (MITLIF). (a) Preoperative T2-weighted MRI image in which a minimally invasive lumbar laminectomy decompression was performed versus a (b) preoperative T2-wieghted MRI in which there is elongation of the facets. Thus, decompression with MITLIF was performed. (Adapted from Perez-Cruet et al 201412.)

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Minimally Invasive Laminectomy for Lumbar Stenosis

Fig. 35.12 Preoperative analysis of facet anatomy can help dictate the procedure of choice at each individual segment on a particular patient. (a,b) Minimally invasive surgery (MIS) laminectomy with in situ posterior fusion was performed at the L3/L4 level, while a (c,d) minimally invasive transforaminal lumbar interbody fusion (MITLIF) was performed at the L4/L5 level where elongation of the facets is seen. (Adapted from PerezCruet et al 201412.)

●

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Initial opening of the ligamentum flavum is often the most difficult portion of the procedure. This is a likely time for a dural tear to occur. Careful use of up-going curettes can limit the risk. Suture repair of a dural tear through the tube is possible, although very tedious. Small durotomies can usually be treated with a small pledget of Gelfoam and the skin closed with a running locking nylon suture. Careful identification of the midline and the ipsilateral facet will help maintain correct orientation. It is easy to enter the spinal canal on the opposite side if the tubular retractor is angled too medially during the initial bone drilling. Slightly tilt the operative table away from the surgeon and wand the tubular retractor to view the base of the spinous process to perform the contralateral decompression.

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Shrinking the contralateral ligamentum flavum with a CO2 laser or CUSA can facilitate removal with a Kerrison punch and reduce the risk of durotomy. When working toward the opposite side, the smooth heel of the Kerrison rongeur should be kept against the dura to reduce the risk of dural laceration. Before closure, fluoroscopy is used to identify the most rostral and caudal extent of the decompression to ensure that the entire segment is adequately treated. Approach each level separately when treating patients with multilevel stenosis. This allows for direct visualization and facilitates adequate decompression. Cadaveric training and teaching observation of the procedure by an experienced minimally invasive spine surgeon can be very useful in learning this technique.

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Fig. 35.13 Preoperative (a) sagittal and (b) axial T2-weighted MRI showing stenosis at the L3/L4 level. (c) Sagittal and (d) axial T2-weighted MRI showing L4/L5 spondylolisthesis with stenosis. Postoperative (e) sagittal and (f) axial CT showing minimally invasive surgery (MIS) laminectomy with posterolateral in situ fusion with local autograft performed at the L3–L4 level. Postoperative (g) sagittal and (h) axial CT showing MIS laminectomy with minimally invasive transforaminal lumbar interbody fusion (MITLIF) performed at the L4–L5 level based on facet morphology. (Adapted from Perez-Cruet et al 2014.13)

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Minimally Invasive Laminectomy for Lumbar Stenosis

Fig. 35.14 (a) Intraoperative use of BoneBac Press (Thompson MIS) to (b) harvest local bone autograft from the surgical field. Intraoperative (c) separation of blood from (d) bone graft to (e) yield soft morselized autograft bone graft material. (f) Postoperative axial CT showing fusion using local autograft to perform in situ posterior fusion after minimally invasive surgery (MIS) laminectomy.

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Fig. 35.15 Biologic restoration of lamina using locally harvested bone to reduce perineural scar formation. (a) Preoperative L4–L5 stenosis. (b) Intraoperative view after decompression. (c) Postoperative skin incision. (d,e) Postoperative T2-weighted MRI showing adequate decompression with restoration of lamina and minimal perineural scar formation using autologous biologic bone laminar reconstruction. (Adapted from Perez-Cruet and Mendoza-Torres 2015.5)

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Minimally Invasive Laminectomy for Lumbar Stenosis

Fig. 35.16 Surgical steps for minimally invasive laminectomy approach. (a) The initial muscle dilator is placed over the surface of the lamina and facet of interest. Care is taken to ensure that the dilator is docked on bone. (b) With all dilators in place, an adequately sized channel is created in the soft tissues. (c) The final tubular retractor is placed. (d) Muscle dilators are removed and tubular retractor fixed to the flexible arm. (e) Tubular retractor in place to view ipsilateral laminectomy. (f) A final lateral fluoroscope image is taken to confirm the proper level of the tubular retractor.

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Fig. 35.17 (a,b) Ipsilateral hemilaminotomy using cutting burr to expose the ligamentum flavum. It is recommended to start bone drilling on the lateral caudal aspect of the lamina. (c,d) As the leading or rostral edge of the ligamentum flavum is exposed, use a Kerrison punch.

Fig. 35.18 (a,b) Adequate bone decompression achieved with visualization of the epidural fat pad at the rostral aspect of the hemilaminotomy.

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Minimally Invasive Laminectomy for Lumbar Stenosis

Fig. 35.19 (a) Wanding of the tubular retractor to achieve (b,c) visualization of the base of the spinous process and (d,e) contralateral decompression by undercutting the spinous process and contralateral lamina. The ligamentum flavum is maintained to help protect the dura.

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Fig. 35.20 (a,b) Undercutting of the contralateral lamina with endoscopic visualization. (c) Bilateral decompression is achieved with preservation of the spinous process and much of the contralateral lamina.

Fig. 35.21 (a) Bony decompression is complete exposing both the ipsilateral and the contralateral sleeves of the ligamentum flavum. (b) Ipsilateral ligamentum flavum is removed first, followed by removal of the (c,d) contralateral ligamentum flavum with the aid of a CO2 laser to shrink the contralateral ligamentum flavum.

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Minimally Invasive Laminectomy for Lumbar Stenosis

Fig. 35.22 (a) Dural suction retractor (Thompson MIS, Salem, NH) can help protect the dura during decompression. (b) Preoperative axial MRI image showing lumbar stenosis. (c) Intraoperative image after decompression. (d) Postoperative axial MRI after minimally invasive laminectomy with arrow showing the surgical approach.

Fig. 35.23 (a) Contralateral facet decortication to perform (b) ipsilateral and (c) contralateral in situ autograft posterolateral fusion.

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Fig. 35.24 (a) Preoperative and (b) postoperative MRI showing the extent of resection after minimally invasive laminectomy with preservation of much of the bone and ligamentous/ muscular anatomy of the spine.

Fig. 35.25 Preoperative sagittal and corresponding axial T2-weighted MRI at (a,b) L2–L3, (c,d) L3–L4, and (e,f) L4–L5 showing stenosis at the L2–L3, L3–L4, L4–L5 levels, and (g) grade I spondylolisthesis at the L4–L5 level.

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Minimally Invasive Laminectomy for Lumbar Stenosis

Fig. 35.25 (continued) Postoperative axial and corresponding sagittal CT at the (h,i) L2–L3, (j,k) L3–L4, and (l,m) L4–L5 levels showing multilevel minimally invasive surgery (MIS) laminectomy transforaminal lumbar interbody fusion (TLIF) at the L4–L5 level, and multilevel percutaneous pedicle screw instrumentation. Note restoration of sagittal alignment.

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Fig. 35.26 (a) Six-month postoperative axial and (b) coronal CT showing restoration of the lamina and adequate facet fusion. This process allows for maintenance of neural decompression while improving the integrity of the normal anatomical structures of the spine and reducing perineural scar formation. We feel this method can lead to very low rates of observed adjacent segment disease (ASD).

35.5 Conclusion With the ubiquity of the disease and the frequency of operations performed to correct it, lumbar stenosis represents an incredible opportunity to improve existing tenets of surgery using the minimally invasive laminectomy technique. When performed properly, the procedure is a safe and effective method of decompressing the stenotic lumbar spinal canal that offers patients a smaller incision, less postoperative pain, and an overall quicker recovery. Additional benefits include long-term excellent outcomes and extremely low rate of additional surgical intervention at the operative or adjacent levels. This is a very cost-effective technique for the management of a commonly seen surgical disorder.

Clinical Caveats ●

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Relatively normal facet ratio can help assure that decompression and posterolateral arthrodesis will reduce need for additional surgery. Gentle rotation of muscle dilators toward spine helps reduce complication. Maintain ligamentum flavum during bone drill decompression to protect dura and neural elements. Removal of ipsilateral ligamentum flavum first, then contralateral ligamentum flavum helps reduce durotomy. A small Gelfoam pledget combined with meticulous closure of fascia and running locking nylon skin closure can help avoid complications with small durotomy.

[3] Turner JA, Ersek M, Herron L, Deyo R. Surgery for lumbar spinal stenosis. Attempted meta-analysis of the literature. Spine. 1992; 17(1):1–8 [4] Smorgick Y, Park DK, Baker KC, et al. Single- versus multilevel fusion for single-level degenerative spondylolisthesis and multilevel lumbar stenosis: four-year results of the spine patient outcomes research trial. Spine. 2013; 38 (10):797–805 [5] Perez-Cruet MJ, Mendoza-Torres J. Minimally invasive laminectomy with insitu posterolateral fusion for the treatment of lumbar stenosis. Poster presentation, American Association of Neurological Surgeons meeting, Washington, DC, May 2015 [6] Aryanpur J, Ducker T. Multilevel lumbar laminotomies: an alternative to laminectomy in the treatment of lumbar stenosis. Neurosurgery. 1990; 26 (3):429–432, discussion 433 [7] Lin PM. Internal decompression for multiple levels of lumbar spinal stenosis: a technical note. Neurosurgery. 1982; 11(4):546–549 [8] Postacchini F, Cinotti G, Perugia D, Gumina S. The surgical treatment of central lumbar stenosis. Multiple laminotomy compared with total laminectomy. J Bone Joint Surg Br. 1993; 75(3):386–392 [9] Young S, Veerapen R, O’Laoire SA. Relief of lumbar canal stenosis using multilevel subarticular fenestrations as an alternative to wide laminectomy: preliminary report. Neurosurgery. 1988; 23(5):628–633 [10] Guiot BH, Khoo LT, Fessler RG. A minimally invasive technique for decompression of the lumbar spine. Spine. 2002; 27(4):432–438 [11] Khoo LT, Fessler RG. Microendoscopic decompressive laminotomy for the treatment of lumbar stenosis. Neurosurgery. 2002; 51(5) Suppl:S146–S154 [12] Perez-Cruet MJ, Mendoza-Torres J, Choudhury M. Morphometric analysis of lumbar facet anatomy to determine surgical approach. Poster presentation, Congress of Neurological Surgeons meeting, Boston, MA; 2014 [13] Perez-Cruet MJ, Hussain NS, White GZ, et al. Quality-of-life outcomes with minimally invasive transforaminal lumbar interbody fusion based on longterm analysis of 304 consecutive patients. Spine. 2014; 39(3):E191–E198 [14] Park CK. The effect of patient positioning on intraabdominal pressure and blood loss in spinal surgery. Anesth Analg. 2000; 91(3):552–557 [15] Hussain NS, Perez-Cruet M. Application of the flexible CO2 laser in minimally invasive laminectomies: technical note. Cureus. 2016; 8(6):e628

Suggested Readings References [1] Ciol MA, Deyo RA, Howell E, Kreif S. An assessment of surgery for spinal stenosis: time trends, geographic variations, complications, and reoperations. J Am Geriatr Soc. 1996; 44(3):285–290 [2] Katz JN, Lipson SJ, Chang LC, Levine SA, Fossel AH, Liang MH. Seven- to 10year outcome of decompressive surgery for degenerative lumbar spinal stenosis. Spine. 1996; 21(1):92–98

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[1] Alimi M, Hofstetter CP, Pyo SY, Paulo D, Härtl R. Minimally invasive laminectomy for lumbar spinal stenosis in patients with and without preoperative spondylolisthesis: clinical outcome and reoperation rates. J Neurosurg Spine. 2015; 22(4):339–352 [2] Allen RT, Garfin SR. The economics of minimally invasive spine surgery: the value perspective. Spine. 2010; 35(26) Suppl:S375–S382 [3] Ang CL, Phak-Boon Tow B, Fook S, et al. Minimally invasive compared with open lumbar laminotomy: no functional benefits at 6 or 24 months after surgery. Spine J. 2015; 15(8):1705–1712

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Minimally Invasive Laminectomy for Lumbar Stenosis [4] Arai Y, Hirai T, Yoshii T, et al. A prospective comparative study of 2 minimally invasive decompression procedures for lumbar spinal canal stenosis: unilateral laminotomy for bilateral decompression (ULBD) versus muscle-preserving interlaminar decompression (MILD). Spine. 2014; 39(4):332–340 [5] Dangelmajer S, Zadnik PL, Rodriguez ST, Gokaslan ZL, Sciubba DM. Minimally invasive spine surgery for adult degenerative lumbar scoliosis. Neurosurg Focus. 2014; 36(5):E7 [6] Deer T. Minimally invasive lumbar decompression for the treatment of spinal stenosis of the lumbar spine. Pain Manag. 2012; 2(5):457–465 [7] Ee WW, Lau WL, Yeo W, Von Bing Y, Yue WM. Does minimally invasive surgery have a lower risk of surgical site infections compared with open spinal surgery? Clin Orthop Relat Res. 2014; 472(6):1718–1724 [8] Hofstetter CP, Hofer AS, Wang MY. Economic impact of minimally invasive lumbar surgery. World J Orthop. 2015; 6(2):190–201 [9] Hussain NS, Perez-Cruet MJ. Complication management with minimally invasive spine procedures. Neurosurg Focus. 2011; 31(4):E2 [10] Issack PS, Cunningham ME, Pumberger M, Hughes AP, Cammisa FP, Jr. Degenerative lumbar spinal stenosis: evaluation and management. J Am Acad Orthop Surg. 2012; 20(8):527–535 [11] Jang JW, Park JH, Hyun SJ, Rhim SC. Clinical outcomes and radiologic changes following microsurgical bilateral decompression via a unilateral approach in patients with lumbar canal stenosis and grade I degenerative spondylolisthesis with a minimum 3-year follow-up. Clin Spine Surg. 2016; 29(7):268–271 [12] Johans SJ, Amin BY, Mummaneni PV. Minimally invasive lumbar decompression for lumbar stenosis: review of clinical outcomes and cost effectiveness. J Neurosurg Sci. 2015; 59(1):37–45 [13] Komp M, Hahn P, Oezdemir S, et al. Bilateral spinal decompression of lumbar central stenosis with the full-endoscopic interlaminar versus microsurgical laminotomy technique: a prospective, randomized, controlled study. Pain Physician. 2015; 18(1):61–70 [14] Kshettry VR, Benzel EC. Interpreting incidental durotomy rates in minimally invasive versus traditional techniques in retrospective studies: a word of caution. World Neurosurg. 2015; 83(3):311–312 [15] Lønne G, Johnsen LG, Rossvoll I, et al. Minimally invasive decompression versus x-stop in lumbar spinal stenosis: a randomized controlled multicenter study. Spine. 2015; 40(2):77–85 [16] Lingreen R, Grider JS. Retrospective review of patient self-reported improvement and post-procedure findings for mild (minimally invasive lumbar decompression). Pain Physician. 2010; 13(6):555–560 [17] Minamide A, Yoshida M, Yamada H, et al. Endoscope-assisted spinal decompression surgery for lumbar spinal stenosis. J Neurosurg Spine. 2013; 19 (6):664–671

[18] Mobbs RJ, Li J, Sivabalan P, Raley D, Rao PJ. Outcomes after decompressive laminectomy for lumbar spinal stenosis: comparison between minimally invasive unilateral laminectomy for bilateral decompression and open laminectomy: clinical article. J Neurosurg Spine. 2014; 21(2):179–186 [19] Müslüman AM, Cansever T, Yılmaz A, Çavuşoğlu H, Yüce İ, Aydın Y. Midterm outcome after a microsurgical unilateral approach for bilateral decompression of lumbar degenerative spondylolisthesis. J Neurosurg Spine. 2012; 16 (1):68–76 [20] Nomura H, Yanagisawa Y, Arima J, Oga M. Clinical outcome of microscopic lumbar spinous process-splitting laminectomy: clinical article. J Neurosurg Spine. 2014; 21(2):187–194 [21] Nomura K, Yoshida M. Microendoscopic decompression surgery for lumbar spinal canal stenosis via the paramedian approach: preliminary results. Global Spine J. 2012; 2(2):87–94 [22] Payer M. “Minimally invasive” lumbar spine surgery: a critical review. Acta Neurochir (Wien). 2011; 153(7):1455–1459 [23] Parker SL, Adogwa O, Davis BJ, et al. Cost-utility analysis of minimally invasive versus open multilevel hemilaminectomy for lumbar stenosis. J Spinal Disord Tech. 2013; 26(1):42–47 [24] Samartzis D, Shen FH, Perez-Cruet MJ, Anderson DG. Minimally invasive spine surgery: a historical perspective. Orthop Clin North Am. 2007; 38(3):305– 326, abstract v [25] Snyder LA, O’Toole J, Eichholz KM, Perez-Cruet MJ, Fessler R. The technological development of minimally invasive spine surgery. BioMed Res Int. 2014; 2014:293582 [26] Song D, Park P. Primary closure of inadvertent durotomies utilizing the U-clip in minimally invasive spinal surgery. Spine. 2011; 36(26):E1753–E1757 [27] Stadler JA, III, Wong AP, Graham RB, Liu JC. Complications associated with posterior approaches in minimally invasive spine decompression. Neurosurg Clin N Am. 2014; 25(2):233–245 [28] Usman M, Ali M, Khanzada K, et al. Unilateral approach for bilateral decompression of lumbar spinal stenosis: a minimal invasive surgery. J Coll Physicians Surg Pak. 2013; 23(12):852–856 [29] Wada K, Sairyo K, Sakai T, Yasui N. Minimally invasive endoscopic bilateral decompression with a unilateral approach (endo-BiDUA) for elderly patients with lumbar spinal canal stenosis. Minim Invasive Neurosurg. 2010; 53 (2):65–68 [30] Wong WH. mild Interlaminar decompression for the treatment of lumbar spinal stenosis: procedure description and case series with 1-year follow-up. Clin J Pain. 2012; 28(6):534–538

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36 Anterior Lumbar Interbody Fusion Manish K. Kasliwal, Carter S. Gerard, Lee A. Tan, and Richard G. Fessler Abstract Anterior lumbar interbody fusion (ALIF) is a well-known surgical technique utilized by many spine surgeons to treat various degenerative lumbar pathologies. This chapter describes the indications, contraindications, preoperative evaluation, surgical techniques, and complications associated with ALIF in detail. A discussion regarding surgical nuances is provided along with clinical pearls and a review of pertinent literature. Proper patient selection remains the key to achieve successful clinical outcome. Keywords: anterior lumbar interbody fusion, degenerative disc disease, lumbar spine

36.1 Introduction Spinal fusions are often performed to treat various lumbosacral pathologies including degenerative conditions, tumor, trauma, infection, and spinal deformity. There has been a steady rise in the number of lumbar fusions performed in the United States between 1992 and 2003 in patients older than 65 years.1 This is not surprising given that low back pain (LBP) is the most common health problem in men and women between the ages of 20 and 50 years in the United States with approximately 13 million visits to physicians and is associated with significant loss in productivity.2 There has been an evolution of surgical treatment for lumbar degenerative disease over the last several decades, and various interbody fusion techniques had grown increasingly more popular as an alternative or supplement to the traditional posterolateral fusion (PLF).3 The common theme for various interbody fusion techniques is placement of the bone graft or a cage in the disc space. Since the anterior and middle spinal columns support 80% of the axial load, the interbody fusion techniques are biomechanically superior and can result in higher fusion rates with improved patient outcomes compared with PLF techniques.3 In addition, the restoration of intervertebral height and segmental lordosis is possible with interbody fusion devices, which is correlated with favorable clinical outcomes.4 However, there is not yet conclusive evidence regarding the superiority in terms of clinical and radiographic outcomes with various interbody fusion techniques.4,5 Surgical treatment of disabling back pain with spinal fusion has been shown to be superior to conservative treatment in a landmark prospectively randomized study, conducted by a Swedish lumbar spine study group.6 A variety of techniques are available for the application of interbody grafts—anterior lumbar interbody fusion (ALIF), transforaminal lumbar interbody fusion (TLIF), and extreme lateral interbody fusion (XLIF)—and each technique has its advantages and disadvantages. Currently, there is no randomized study demonstrating the superiority of one fusion technique over another for surgical management of back pain.6 The choice of a specific fusion technique depends on multiple factors including age, gender, medical morbidities, the specific

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pathology, presence of scar tissue from previous surgery, the surgeon’s preference, and anatomic considerations.5 The first attempted anterior approach to the lumbar spine was performed by Muller in 1906, where he used a transperitoneal approach to debride tuberculosis of the lumbar spine.7 Previously, most anterior lumbar approaches were performed through extensive transperitoneal exposures. In 1944, Iwahara et al8 performed an interbody fusion using a retroperitoneal approach to treat lumbar degenerative disease, which was then further described by Southwick and Robinson in 1957.9 Technical challenges and device limitations initially restricted the application of interbody procedures until the advent of newer interbody fixation devices, which significantly increased the technical ease and efficacy.10 The modern concept of interbody fixation was introduced by Wagner and coworkers following the implantation of a bonefilled cage in horses with Wobbler’s syndrome.11 The intervertebral disc space was distracted by placement of an oversized, perforated, stainless-steel cylinder (the Bagby basket) filled with autogenous bone graft, ultimately yielding a reported fusion rate close to 88%.12 Subsequent material evolution and physical modifications of the Bagby basket led to the production of the Bagby and Kuslich (BAK) implant.13 There was a tremendous increase in the number of graft options available over the last few years including the autologous iliac crest graft, structural allograft, bone chips within metallic cages, titanium mesh cages, carbon fiber cages, and polyetheretherketone (PEEK) cages.10,14,15,16 Even though anterior interbody fusion technique has been traditionally considered a predominant technique to treat discogenic back pain, there has been an increasing enthusiasm and resurgence in the applications of ALIF technique to restore segmental lordosis, secondary to improved understanding of spinal alignment and the possibility of achieving increased fusion, especially at the L4/L5 and L5/S1 with ALIF for long thoracolumbar constructs.17,18 The anterior approach provides direct access to the ventral surface of the vertebral bodies and disc spaces. It also provides a direct and more complete view of the anterior surface of the lumbar spine from L3 to S1.19,20,21 Various advantages of ALIF are listed in the following text box.

Advantages of ALIF ●

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Efficient and direct access for reconstruction of the anterior spinal column. The ability to avoid paraspinal muscle trauma and denervation, and posterior tension band compromise (in stand-alone ALIF or ALIF with minimally invasive posterior fixation), resulting in significantly decreased postoperative pain and subsequently decreased length of postoperative hospital stay.22 The ability to undertake indirect decompression of the intervertebral foramen. Avoidance of dural or posterior neural structure manipulation. Improves sagittal balance.

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Anterior Lumbar Interbody Fusion The increasing familiarity with the posterior instrumentation and the utilization of posterior osteotomy techniques and TLIFs have led to a greater number of surgeries being performed with all posterior approaches for adult spinal deformity. However, ALIF at L4/L5 and L5/S1 can be very useful in patients who have had previous radiation, large posterior bony resection with laminectomy and destabilization, or significant osteoporosis.18 One recent study compared ALIF with TLIF, and showed an increased ability of ALIF to improve foraminal height, local disc angle, and lumbar lordosis.23 Other studies have demonstrated decreased rate of adjacent segment degeneration with ALIF compared to posterior lumbar interbody fusion (PLIF). Nevertheless, ALIF has certain disadvantages including possible need for an access surgeon, potential for increased risk of deep vein thrombosis (DVT), increased risk for vascular injury secondary to vessel retraction, and retrograde ejaculation (RE) associated with hypogastric plexus injury.3,7,24,25,26,27,28 In addition, in cases requiring subsequent posterior instrumentation and fusion, ALIF is associated with increased operating time and blood loss, as well as prolonged recovery time. There is also a potential risk of muscular atony of the abdominal wall and abdominal hernias.

36.2 Indications Traditionally, ALIF has been performed most commonly for patients with discogenic back pain. Lumbar disc degeneration encompasses a dynamic process with overlapping findings at individual and adjacent levels; although the exact role of degenerative disc disease (DDD) is controversial in patients with back pain, disc degeneration has been shown to be a pain generator.29,30 Determining the ideal candidate for surgical management of DDD can be more challenging than performing the procedure itself because of the unclear relationship between patient symptoms, diagnostic studies, and surgical outcomes. Due to the lack of a “gold standard” test, attempts to identify the source of a patient’s LBP in the absence of neurological deficit can be frustrating for both the patient and the treating physician. Hence, before embarking on surgical intervention in patients with LBP, a trial of conservative management, including oral medication, lifestyle modification, and active rehabilitation, is imperative. Nevertheless, ALIF has been shown to result in significant improvement in a subgroup of patients with discogenic back pain.6 The ideal candidate for ALIF has chronic, disabling back pain of discogenic origin for one or two levels with loss of height, stability, and mobility of the diseased segment or neurological deficit.13,17,21,31 Though often considered to be a procedure performed for discogenic LBP, ALIF is a versatile technique with much wider application and can be performed for various other indications.

Indications for ALIF ● ● ● ● ● ●

Lumbar degenerative disc disease. Anterior column support in long fusion constructs. Restoring lumbar lordosis. Pseudarthrosis following posterior lumbar fusion. Lumbar fusions at high risk for nonunion. Tumor and trauma.

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Spondylolisthesis (usually grade I or II). Intervertebral foraminal stenosis secondary to loss of disc height, in conjunction with the need for interbody fusion.

In our experience, ALIF is the best at achieving L5–S1 interbody arthrodesis. At L5–S1, unlike the L4–L5 interspace, excessive retraction of the iliac vessels is typically unnecessary. The ideal patients for mini-ALIF are those with DDD limited to L5–S1 or those patients with DDD in combination with low-grade L5–S1 spondylolisthesis. Similarly, anterior lumbar fusions should be avoided in young men or in men who wish to have children because of the risk of RE.32 We also avoid ALIF in patients with a history of extensive abdominal surgery, in which tissue scarring in the retroperitoneal space can make the exposure difficult with potential for increased complications.26,33

36.3 Contraindications Relative contraindications for ALIF include advanced atherosclerosis of the major vessels and morbid obesity.3,13,26,28,34,35 Some consideration should be given to patients who have previously undergone abdominal surgery or have inflammatory diseases because these conditions create significant scarring that may increase the risk of approach-related complications.33 A transperitoneal approach may be performed as an alternative in these patients. Other relative contraindications for lumbar interbody fusion in general may include multilevel (three levels) disc disease (in patients without lumbar spinal deformities).3 Male patients may have a 2 to 5% risk for RE with the anterior lumbar approach.34

36.4 Preoperative Planning The preoperative evaluation of patients who will undergo ALIF for LBP first requires careful selection of those patients likely to have a successful outcome after an anterior fusion. Studies have shown the following to be associated with a good outcome after ALIF in patients with discogenic LBP6,13,17,36,37: ● Axial back pain aggravated by spinal loading and fusion. ● Radiographic studies consistent with disc degeneration. ● Provocative discography that produces pain only at the affected levels. ● Dynamic studies demonstrating motion/sagittal deformity on sagittal views. Though provocative discography had been used in the past during preoperative evaluation of patients with LBP for performing lumbar fusion, the current status of its use remains controversial at most. Even though lumbar discography can still be used in the evaluation of a patient presenting with chronic LBP based on level II evidence, treatment decisions should not be based on discography alone in patients with LBP and abnormal imaging studies.5,37 More recently, there are data from both animal and human studies suggesting that diagnostic disc injections may lead to iatrogenic injury to the disc and accelerated disc degeneration.38 A preoperative MRI should be obtained in all patients, especially in those with suspected DDD in the presence of neurological

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Surgical Techniques symptoms or deficits. A CT myelogram may need to be performed if MRI cannot be obtained. A standing lateral radiograph of the lumbar spine should be obtained to assess the sacral slope to ensure the L5–S1 disc space can be accessed through the anterior approach. If the sacral slope is too steep (often in cases of L5–S1 spondylolisthesis), access to the disc can be very difficult. The degree of sagittal imbalance should also be assessed on preoperative imaging in patients with deformity to allow appropriate graft selection. Preoperative evaluation by the exposure surgeon is advisable with special attention paid to patients with elevated body mass index (BMI) due to potential for increased vascular complications in this subgroup of patients.26

36.5 Surgical Approach Various techniques have been described to gain access to the anterior lumbar spine (transperitoneal, laparoscopic, open and mini-open retroperitoneal).25 In 1932, Capener was the first to describe using ALIF in the treatment of spondylolisthesis.39 Harmon40 described a left extraperitoneal approach to the lumbar spine with subsequent modification of the basic approach, which over time led to the development of mini-open and laparoscopic approaches aiming toward decreasing postoperative morbidity, reducing hospitalization time, and shortening rehabilitation time.25,41 The introduction of laparoscopic techniques represents minimally invasive modification of the ALIF. Developed in the 1990s, laparoscopic ALIF achieved early success with its pioneers.42 Laparoscopic ALIF was reported to be less invasive with less blood loss and faster recovery; however, later reports contradicted these findings, noting that there were no identifiable advantages, but with added technical challenge, and increased specific complications such as RE.25,27,41 More recently, mini-open retroperitoneal approach, a modification of conventional retroperitoneal approach, has been found to be superior to laparoscopic approaches and has become the “workhorse” approach, with mini-open transperitoneal and open procedures saved for revision or salvage procedures.3,20,25,41 Retroperitoneal and transperitoneal corridors allow complete exposure of the ventral surface of the spine and placement of a single large interbody implant that matches the vertebral end plate. Avoidance of the posterior musculature reduces postoperative pain and disability associated with extensive muscle stripping, denervation, and devascularization, often noted as a cause of failed back syndrome.6,20,21,28,43 The mini-open retroperitoneal approach is described in detail in this chapter.

36.5.1 Surgical Technique The patient is positioned supine on a radiolucent operating room table with the arms positioned at the sides in an abducted position on arm rests to allow lateral imaging. Alternatively, they can be positioned across the chest with adequate padding of all bony prominences. A bolster can be placed under the lumbar spine to accentuate lumbar lordosis. Obtaining fluoroscopic images before prepping the patient can be helpful to ensure that all views are obtainable without obstruction from the table or patient’s extremities. A lateral fluoroscopic image is used to localize and mark the level of incision. A radiopaque rod or pin is used to mark the angle of the disc and the corresponding trajectory to

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Fig. 36.1 A Pfannenstiel incision is more cosmetically appealing and provides good access to the L5–S1 level, although a direct midline or paramedian incision is preferable for multilevel exposures. In this patient, a Thompson Retractor was used to maintain adequate exposure.

the abdominal wall. The incision site can be adjusted to give optimum access to the intended disc space. A transverse or longitudinal incision is made a few centimeters lateral to midline at the corresponding disc level, in line with the angle of the disc space. While a Pfannenstiel incision is more cosmetically appealing and provides good access to the L5–S1 level (▶ Fig. 36.1), direct midline or paramedian incision may be preferable for multilevel exposures as they can be easily extended distally along the anterolateral portion of the flank toward the abdomen and the lateral border of the rectus abdominis muscle. Attention should be paid to identifying the correct disc level to be addressed in cases in which there is transitional lumbosacral anatomy. Use of electrocautery should be avoided as it may help minimize the risk of iatrogenic injury of the hypogastric plexus and resultant RE; using bipolar cautery or hemostatic agents to achieve hemostasis is recommended. Once the skin and subcutaneous tissue are divided, the anterior rectus sheath is entered and the rectus muscles retracted medially. The transversalis fascia is identified underneath the muscle, which is then stripped off of its insertion into the abdominal wall and the plane of dissection to the retroperitoneum is entered. When dissecting toward the upper lumbar spine, it may be necessary to detach the left crus of the diaphragm from the anterior longitudinal ligament at L2. Once the retroperitoneum is reached, continue careful blunt finger dissection posteriorly and then start pushing medially trying to elevate the peritoneum away from the psoas muscle. The genitofemoral nerve can be easily identified over the psoas muscle. The ureter can also be easily seen and is lifted away and swiped medially toward the right, carefully preserving it from any injury. For exposing the L4/L5 level, the iliolumbar vein

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Anterior Lumbar Interbody Fusion

Fig. 36.2 (a) A table-mounted retractor is then set up to maintain the exposure of the surgical level required. (b) At this point, it should be possible to identify the spine and appreciate the convexities of the disc spaces and concavities of the vertebral bodies.

must be ligated and cut along with exposure of the entire length of the common and external iliac arteries, mobilizing them as far distally as possible to prevent stretch and avulsion injury when retracted. All prevertebral tissues are mobilized together and retracted toward the contralateral side along with the vascular structures which are also ultimately swept from left to the right. The prevertebral tissues, including the hypogastric plexus, are identified and mobilized laterally. It is often possible to reach the L5/S1 disc space without mobilizing the great vessels, although the middle sacral artery and vein may need to be ligated and divided to gain access to the L5/S1 disc space. Bleeding should be controlled with pressure, bipolar cautery, and vascular clips; monopolar cautery increases risk of damage to the sympathetic plexus and should best be avoided. A table-mounted retractor is then set up to maintain the exposure to the spine. At this point, it should be possible to identify the spine and appreciate the convexities of the disc spaces and concavities of the vertebral bodies (▶ Fig. 36.2). In cases of multilevel surgery, segmental vessels may have to be divided to minimize any bleeding during the procedure. The correct operative level should be confirmed with fluoroscopy before incising the disc. Once confirmed, the anterior annulus is incised with a longhandled no. 11 scalpel. It is important to point the sharp edge of the blade away from the vascular structures when incising the disc margins to avoid inadvertent vascular injury. A Cobb elevator is then used to develop the interval between the subchondral bone and the cartilaginous end plate. Disc rongeurs are used to remove large disc fragments. Long-handled curettes are used to gently scrape the end plates of any remaining pieces of cartilage and to expose bleeding bone. The importance of developing a proper plane between the subchondral bone and the cartilaginous end plate cannot be overemphasized to allow complete and efficient disc excision. In patients with severe disc degeneration with collapsed discs, paddled distractors of progressive heights can be inserted to slowly distract the collapsed disc space to allow for viscoelastic expansion and restoration of disc height and to maintain distraction for improved visualization of the posterior margins of the vertebral bodies. It also allows for opening of the posterior longitudinal ligament when necessary. The end plates are then prepared for arthrodesis by

using curettes to obtain bleeding surfaces; it is important to preserve the subchondral bone to decrease the chances of implant subsidence.

36.5.2 Instrumentation An interbody device is often placed after performance of a discectomy during ALIF. An interbody device helps restore disc height, create lordosis through the segment, maintain sagittal balance, distract the neuroforaminal space, and restore anatomic load bearing to the anterior column.3,10,44 The number of various interbody grafts has dramatically increased over the last few decades and presently includes autograft iliac crest, cortical allograft (donor) or synthetic bone, threaded cylindrical titanium cages, impact titanium cages, carbon fiber reinforced or plain PEEK polymer, and impacted carbon fiber reinforced PEEK wedges.10,14,15,16 Osteoinductive materials have also evolved over this time period, from iliac crest bone to recombinant human bone morphogenetic protein 2 (rhBMP-2).45 In fact, the use of bone morphogenetic protein (rhBMP) for anterior lumbar fusion in LT-Cage (Medtronic Sofamor Danek, MN, USA) is the only Food and Drug Administration (FDA) approved indication for use of rhBMP.36 No interbody graft device is perfect, and there are various advantages and disadvantages of different interbody grafts or devices; the surgeon can use one depending on their preference.14,15,16,17,31 Risk of infection, modulus of elasticity, cost, and overall fusion rates are the various determinants of choice of interbody graft/device for ALIF. A trial implant or sizing device is used to determine the appropriate-sized graft or cage. An implant is selected that corresponds to the correct trial implant. The implant is packed with bone graft/osteoinductive material depending on surgeon’s preference, and then inserted into the disc space. The insertion device distracts the disc space as the implant is inserted. It is important to ensure the implant is inserted parallel to the end plates to avoid implant settling and loss of lordosis. Similarly, overaggressive insertion or impaction of the implant can cause fracture and displacement of the posterior vertebral body and subsequent thecal sac or nerve root impingement. Fluoroscopic imaging is used to ensure correct positioning of the implant.

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Surgical Techniques At present, the ALIF technique is usually followed by some form of internal fixation. Although not conclusive, many surgeons believe that anterior implants alone are not stable enough to obtain a successful fusion. However, for DDD at L5– S1, Burkus et al36 demonstrated that ALIF performed with rhBMP-2–filled (Infuse) LT-Cage (Medtronic Sofamor Danek) results in a fusion rate greater than 94%, making routine use of fixation following ALIF for DDD controversial. On the other hand, in patients with low-grade spondylolisthesis at L5–S1, use of supplemental posterior fixation is helpful in preventing cage migration and increasing chances of fusion.3,46,47 Various biomechanical studies have shown that instrumented ALIF with either anterior plate, integrated fixation, or posterior instrumentation is more stable than stand-alone cages, which is clinically relevant when anterior lumbar fusions are performed for indications other than DDD in the presence of an unstable spine.47,48,49 There are various options available to prevent the graft from backing out. While the use of plates and screws had been very common in the past, many available interbody implants now incorporate screw fixation into the implant itself, obviating the need for plate fixation.43,44,45,46,47 These are becoming more popular as they need lesser exposure and are simple to use and are our preference too. Following insertion of the interbody device, a drill guide is attached to the implant and drill holes are made for screw insertion. The appropriate-length screws depending on patients’ anatomy and fluoroscopy guidance are then inserted through the implant, through the superior and inferior end plates and into the vertebral body. After interbody graft placement and instrumentation, if performed, the retractor blades are sequentially removed. The right-sided retractor blade should be removed last. The wound is then irrigated copiously, meticulous hemostasis is achieved, and integrity of all the vascular structures is carefully examined. It should be ensured that the pulse oximeter in the feet shows normal oxygen saturation throughout the procedure. The peritoneum and its contents are returned to their normal anatomic position, and the fascial layer is then closed ensuring the anterior rectus sheath is well approximated. Subcutaneous tissues and skin are closed per surgeon’s preferences. Depending on the indication for the surgical procedure, augmentation of the interbody implant with pedicle screw fixation may be added to further the fusion success in comparison to standalone graft, especially in patients with spondylolisthesis.

36.6 Postoperative Care A patient can be extubated immediately after surgery if the patient is hemodynamically stable and there are no anesthesia concerns. A neurological evaluation should be performed as soon as the patient is awake and cooperative. Patient-controlled analgesia can be instituted for pain control and weaned to oral pain medications depending on pain control, bowel function, and oral tolerance. Patients are started on clear liquids, and their diets are advanced as tolerated. They are mobilized on postoperative day 1 and encouraged to ambulate as tolerated. The use of thromboembolic stockings and sequential compression devices should be continued throughout the recovery period. We routinely start pharmacologic DVT prophylaxis with subcutaneous heparin, 5,000 units twice daily, on postoperative day 1. Patients may need physical therapy, including ambulation training and mobilization,

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depending on their preoperative status. The use of nonsteroidal anti-inflammatory drugs is avoided early in the postoperative period. For single-level anterior fusions, hospital stay is typically 1 to 3 days, based on patient-specific factors and the surgery performed. The use of bracing is variable and dependent on stability of fixation and surgeon specific, ranging from an abdominal binder for comfort to a rigid thoracolumbosacral orthosis. The addition of instrumentation and bone morphogenetic proteins has obviated the routine need of rigid bracing and it should be decided on a case-by-case basis. We prefer not to use any bracing for routine single-level anterior lumbar fusion. Activity should include limited bending and twisting motions, and lifting initially should be limited to less than 10 to 20 lbs. Return to activities of daily living is progressively allowed and encouraged. Return to work and sports depends on the patient and surgeon, based on the patient’s requirements, status of fusion, and fixation method.

36.7 Management of Complications Although anterior lumbar fusion surgery is typically very safe, mobilization of abdominal structures does place the abdominal viscera, nerve roots, ureter, and great vessels at some risk for iatrogenic injury.27 In particular, the mobilization of the iliac vessels, which is required to adequately expose the disc spaces, can carry significant potential complications. The risk of vascular injury in contemporary literature ranges from 1 to 24%.26 There is a risk of DVT, which ranges from 0.7 to 5%.19 Clear identification of the disc space before discectomy must be obtained and maintained during the operation. The common iliac vein, which is compressible and dorsal to the artery, can be mistaken for soft tissue during the approach. The iliolumbar vein is at risk during the approach to the L4–L5 interspace and should be controlled as dictated by the amount of exposure necessary with a belief among some vascular surgeons that this vessel should be routinely ligated during exposures of the L4–L5 interspace to minimize the risk of tearing during retraction. Arterial or venous lacerations are more likely to occur in revision cases or in patients with preexisting vascular diseases, and may result from direct manipulations or retractor placement during instrumentation.33 Apart from the risk of hemodynamic instability due to excessive blood loss intraoperatively, there is also a delayed risk of retroperitoneal hematomas, pseudoaneurysms, and arteriovenous fistulas secondary to a vascular injury.26 In addition, thromboembolic phenomenon is particularly common after ALIF and is thought to be associated with prolonged retraction of great vessels. It can be reduced by releasing the retractors intermittently and utilizing pulse oximetry on the lower extremities to monitor lower extremity perfusion. Finally, there is also a risk of RE with trials to date. Kuslich and colleagues34 reported a 4% rate in 591 patients. Although RE after ALIF has typically been described as a complication specific to the anterior surgical approach, a recent study suggested that RE is instead attributable to the use of rhBMP-2 in ALIF procedures. This finding was not substantiated in various other studies.24,32,50 Nevertheless, the risk of RE after anterior lumbar spine surgery always exists whether BMP is used or not, and is inherent to the approach and the related anatomy. The

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Anterior Lumbar Interbody Fusion preaortic (prevertebral) sympathetic plexus runs along the anterolateral edge of the vertebral bodies, adjacent to the psoas, and then traverses over the aortic bifurcation and common iliac vessels forming the hypogastric plexus. Blunt dissection to mobilize the more cephalad prevertebral plexus before the hypogastric plexus can aid the exposure. Similarly, aggressive electrocautery must be minimized during the approach in this area and during the disc space preparation. Arterial injury and/or thrombosis from aggressive retraction have also been reported. Injury to the alimentary tract can be minimized by packing the peritoneum behind self-retaining retractors. Postoperative ileus may occur and can be effectively managed with restricted oral intake, proper fluid hydration, and gastric suction as indicated. Damage to the ureter, which is rare in primary cases, can be minimized with proper identification and the placement of preoperative ureteral stents if needed. Implant-related complications, such as graft subsidence, malposition,

extrusion, and pseudarthrosis, can be minimized with careful patient selection, careful implant selection, and meticulous discectomy to optimize the fusion bed without disrupting the structural integrity of the subchondral bony end plates. As with any instrumented spinal fusion, implant malposition may lead to incidental durotomy or nerve impingement. An inadequate closure of the fascia, subcutaneous tissue, or skin layers may predispose to wound infection and potential incisional hernias.

36.8 Clinical Case: Bulging Disc with a Broad-Based Disc Protrusion A 34-year-old woman presented with persistent, chronic back pain for several years. The patient worked as a surgical nurse, and had trouble with prolonged standing at work. The physical examination was unremarkable with no sensorimotor deficit. Imaging showed a diffuse bulging disc with a broad-based disc protrusion causing mild narrowing of both lateral recesses at L5–S1 (▶ Fig. 36.3). She had little relief with multiple oral medications, and had failed multiple sessions of physical therapy and steroid injections. After a thorough discussion, the patient elected to undergo ALIF for surgical management of her LBP. The patient tolerated the procedure well with no complication. The patient was discharged home from the hospital on postoperative day 3 after physical therapy clearance. The patient was slowly weaned from her pain medications and reported significant improvement in her back pain at the 3month postoperative visit. Imaging showed satisfactory placement of the interbody cage, lordosis was maintained, and the disc space was restored (▶ Fig. 36.4).

36.9 Conclusion

Fig. 36.3 At L5–S1, there is diffuse bulging disc with a broad-based disc protrusion causing mild narrowing of both lateral recesses.

Spinal fusion has dramatically evolved over the past few decades with various interbody fusion techniques available in the spine surgeon’s armamentarium. ALIF has experienced several advances, particularly in the last decade with various technical modifications. The mini-open technique as described in this chapter has become the preferred portal of exposure as it is associated with minimal morbidity. Placement of interbody grafts from the front provides improved anterior column support while maximizing the likelihood of bony fusion; the availability

Fig. 36.4 (a) Anteroposterior (AP) and (b) lateral X-rays show satisfactory placement of the interbody cage, preservation of lordosis, and the restoration of the disc space.

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Surgical Techniques of lordotic interbody grafts allows restoration of lumbosacral lordosis and correction of sagittal imbalance. Integrated interbody grafts with fixation have allowed surgeons the option of single-approach stand-alone anterior constructs with excellent radiographic and clinical outcomes. Careful patient selection remains the key to achieve successful clinical outcome.

Clinical Caveats ●

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Careful patient selection is key to successful surgery and maximization of outcomes, especially in patients with discogenic LBP. Preoperative standing lateral radiograph of the lumbar spine should be assessed to ensure the adequate angle for accessing the L5/S1 disc. Knowledge of the retroperitoneal anatomy is essential. Calcified great vessels on preoperative imaging should be retracted carefully to minimize the chances of a thrombotic event. Incomplete discectomy can result in retropulsion of disc fragments into the canal and should be avoided. Meticulous disc space preparation that avoids end plate violation is important for proper fit of the implant. Selection of an implant depends on the disc space anatomy to allow the best fit and contact with end plates. An implant of the proper height should be selected to restore “normal” disc height avoiding overdistraction. A laterally/posteriorly placed implant can result in neural foramen impingement. Chances of postoperative complications are significantly high in patients with prior abdominal surgery and should be kept in mind before considering ALIF in such patients.

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[11] DeBowes RM, Grant BD, Bagby GW, Gallina AM, Sande RD, Ratzlaff MH. Cervical vertebral interbody fusion in the horse: a comparative study of bovine xenografts and autografts supported by stainless steel baskets. Am J Vet Res. 1984; 45(1):191–199 [12] Bagby GW. Arthrodesis by the distraction-compression method using a stainless steel implant. Orthopedics. 1988; 11(6):931–934 [13] Bagby G. The Bagby and Kuslich (BAK) method of lumbar interbody fusion. Spine. 1999; 24(17):1857 [14] Brantigan JW, Steffee AD. A carbon fiber implant to aid interbody lumbar fusion. Two-year clinical results in the first 26 patients. Spine. 1993; 18 (14):2106–2107 [15] Jost B, Cripton PA, Lund T, et al. Compressive strength of interbody cages in the lumbar spine: the effect of cage shape, posterior instrumentation and bone density. Eur Spine J. 1998; 7(2):132–141 [16] Vadapalli S, Sairyo K, Goel VK, et al. Biomechanical rationale for using polyetheretherketone (PEEK) spacers for lumbar interbody fusion-A finite element study. Spine. 2006; 31(26):E992–E998 [17] Burkus JK, Gornet MF, Schuler TC, Kleeman TJ, Zdeblick TA. Six-year outcomes of anterior lumbar interbody arthrodesis with use of interbody fusion cages and recombinant human bone morphogenetic protein-2. J Bone Joint Surg Am. 2009; 91(5):1181–1189 [18] Dorward IG, Lenke LG, Bridwell KH, et al. Transforaminal versus anterior lumbar interbody fusion in long deformity constructs: a matched cohort analysis. Spine. 2013; 38(12):E755–E762 [19] Brau SA. Mini-open approach to the spine for anterior lumbar interbody fusion: description of the procedure, results and complications. Spine J. 2002; 2 (3):216–223 [20] Mobbs RJ, Loganathan A, Yeung V, Rao PJ. Indications for anterior lumbar interbody fusion. Orthop Surg. 2013; 5(3):153–163 [21] Sacks S. Anterior interbody fusion of the lumbar spine. Indications and results in 200 cases. Clin Orthop Relat Res. 1966; 44(44):163–170 [22] Shim JH, Kim WS, Kim JH, Kim DH, Hwang JH, Park CK. Comparison of instrumented posterolateral fusion versus percutaneous pedicle screw fixation combined with anterior lumbar interbody fusion in elderly patients with L5S1 isthmic spondylolisthesis and foraminal stenosis. J Neurosurg Spine. 2011; 15(3):311–319 [23] Kim J-S, Kang B-U, Lee S-H, et al. Mini-transforaminal lumbar interbody fusion versus anterior lumbar interbody fusion augmented by percutaneous pedicle screw fixation: a comparison of surgical outcomes in adult low-grade isthmic spondylolisthesis. J Spinal Disord Tech. 2009; 22(2):114–121 [24] Burkus JK, Dryer RF, Peloza JH. Retrograde ejaculation following single-level anterior lumbar surgery with or without recombinant human bone morphogenetic protein-2 in 5 randomized controlled trials: clinical article. J Neurosurg Spine. 2013; 18(2):112–121 [25] Escobar E, Transfeldt E, Garvey T, Ogilvie J, Graber J, Schultz L. Video-assisted versus open anterior lumbar spine fusion surgery: a comparison of four techniques and complications in 135 patients. Spine. 2003; 28(7):729–732 [26] Garg J, Woo K, Hirsch J, Bruffey JD, Dilley RB. Vascular complications of exposure for anterior lumbar interbody fusion. J Vasc Surg. 2010; 51(4):946–950, discussion 950 [27] Kaiser MG, Haid RW, Jr, Subach BR, Miller JS, Smith CD, Rodts GE, Jr. Comparison of the mini-open versus laparoscopic approach for anterior lumbar interbody fusion: a retrospective review. Neurosurgery. 2002; 51(1):97–103, discussion 103–105 [28] Tay BB, Berven S. Indications, techniques, and complications of lumbar interbody fusion. Semin Neurol. 2002; 22(2):221–230 [29] Freemont AJ, Peacock TE, Goupille P, Hoyland JA, O’Brien J, Jayson MI. Nerve ingrowth into diseased intervertebral disc in chronic back pain. Lancet. 1997; 350(9072):178–181 [30] Weinstein J, Claverie W, Gibson S. The pain of discography. Spine. 1988; 13 (12):1344–1348 [31] Burkus JK, Sandhu HS, Gornet MF, Longley MC. Use of rhBMP-2 in combination with structural cortical allografts: clinical and radiographic outcomes in anterior lumbar spinal surgery. J Bone Joint Surg Am. 2005; 87(6):1205–1212 [32] Lindley EM, McBeth ZL, Henry SE, et al. Retrograde ejaculation after anterior lumbar spine surgery. Spine. 2012; 37(20):1785–1789 [33] Osler P, Kim SD, Hess KA, et al. Prior abdominal surgery is associated with an increased risk of postoperative complications after anterior lumbar interbody fusion. Spine. 2014; 39(10):E650–E656 [34] Kuslich SD, Ulstrom CL, Griffith SL, Ahern JW, Dowdle JD. The Bagby and Kuslich method of lumbar interbody fusion. History, techniques, and 2-year follow-up results of a United States prospective, multicenter trial. Spine. 1998; 23(11):1267–1278, discussion 1279

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Anterior Lumbar Interbody Fusion [35] Sasso RC, Kitchel SH, Dawson EG. A prospective, randomized controlled clinical trial of anterior lumbar interbody fusion using a titanium cylindrical threaded fusion device. Spine. 2004; 29(2):113–122, discussion 121–122 [36] Burkus JK, Gornet MF, Dickman CA, Zdeblick TA. Anterior lumbar interbody fusion using rhBMP-2 with tapered interbody cages. J Spinal Disord Tech. 2002; 15(5):337–349 [37] Carragee EJ, Lincoln T, Parmar VS, Alamin T. A gold standard evaluation of the “discogenic pain” diagnosis as determined by provocative discography. Spine. 2006; 31(18):2115–2123 [38] Carragee EJ, Don AS, Hurwitz EL, Cuellar JM, Carrino JA, Herzog R. 2009 ISSLS Prize Winner: does discography cause accelerated progression of degeneration changes in the lumbar disc: a ten-year matched cohort study. Spine. 2009; 34(21):2338–2345 [39] Capener N. Spondylolisthesis. Br J Surg. 1932; 19:374–386 [40] Harmon P. Anterior extraperitoneal lumbar disc excision and vertebral body fusion. Clin Orthop. 1960:169–173 [41] Saraph V, Lerch C, Walochnik N, Bach CM, Krismer M, Wimmer C. Comparison of conventional versus minimally invasive extraperitoneal approach for anterior lumbar interbody fusion. Eur Spine J. 2004; 13(5):425–431 [42] Regan JJ, Yuan H, McAfee PC. Laparoscopic fusion of the lumbar spine: minimally invasive spine surgery. A prospective multicenter study evaluating open and laparoscopic lumbar fusion. Spine. 1999; 24(4):402–411 [43] Lammli J, Whitaker MC, Moskowitz A, et al. Stand-alone anterior lumbar interbody fusion for degenerative disc disease of the lumbar spine: results with a 2-year follow-up. Spine. 2014; 39(15):E894–E901

[44] Weiner BK, Fraser RD. Spine update lumbar interbody cages. Spine. 1998; 23 (5):634–640 [45] Burkus JK, Heim SE, Gornet MF, Zdeblick TA. Is INFUSE bone graft superior to autograft bone? An integrated analysis of clinical trials using the LTCAGE lumbar tapered fusion device. J Spinal Disord Tech. 2003; 16 (2):113–122 [46] Cagli S, Crawford NR, Sonntag VK, Dickman CA. Biomechanics of grade I degenerative lumbar spondylolisthesis. Part 2: treatment with threaded interbody cages/dowels and pedicle screws. J Neurosurg. 2001; 94(1) Suppl:51–60 [47] Oxland TR, Lund T. Biomechanics of stand-alone cages and cages in combination with posterior fixation: a literature review. Eur Spine J. 2000; 9 Suppl 1:S95–S101 [48] Gerber M, Crawford NR, Chamberlain RH, Fifield MS, LeHuec JC, Dickman CA. Biomechanical assessment of anterior lumbar interbody fusion with an anterior lumbosacral fixation screw-plate: comparison to stand-alone anterior lumbar interbody fusion and anterior lumbar interbody fusion with pedicle screws in an unstable human cadaver model. Spine. 2006; 31 (7):762–768 [49] Kornblum MB, Turner AWL, Cornwall GB, Zatushevsky MA, Phillips FM. Biomechanical evaluation of stand-alone lumbar polyether-ether-ketone interbody cage with integrated screws. Spine J. 2013; 13(1):77–84 [50] Carragee EJ, Mitsunaga KA, Hurwitz EL, Scuderi GJ. Retrograde ejaculation after anterior lumbar interbody fusion using rhBMP-2: a cohort controlled study. Spine J. 2011; 11(6):511–516

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Surgical Techniques

37 Percutaneous Pedicle Screw Placement for Spinal Instrumentation Steven H. Cook, Robert E. Isaacs, Hyun-Chul Shin, Jonathan B. Lesser, Moumita S.R. Choudhury, and Mick J. Perez-Cruet Abstract Percutaneous pedicle screw placement for spinal instrumentation is an important procedure for spine surgeons to treat a wide variety of spinal pathologies. The indications, necessary equipment, and procedure are explained in detail in this chapter. Modifications to include reduction of radiation exposure are discussed while stressing the importance of imaging for safe and efficient pedicle screw placement. Tips on complication avoidance and management are also presented.

A current disadvantage for percutaneous placement is radiation exposure to the patient and surgeon with use of imaging during the procedure.14 With advancements in protective equipment and imaging techniques, and changes in pulse/dosing, these radiation risks can be lowered.15 Recent developments in percutaneous pedicle screw targeting techniques and instrumentation have resulted in minimal radiation exposure to the surgeon (▶ Fig. 37.1).

Keywords: pedicle screw, percutaneous, fusion, internal fixation, minimally invasive

37.1 Introduction There are multiple spinal pathologies in the thoracolumbar spine that require internal fixation ranging from deformity to traumatic injuries. Pedicle screws have historically been placed using a midline incision and further lateral dissection, resulting in extensive muscle retraction and concern for tissue disruption. More recently, the use of minimally invasive procedures allows for safe placement of pedicle screws through smaller bilateral incisions with less tissue damage. Percutaneous pedicle screw placement was first described by Magerl in 19821 as part of an external fixation device first used in the thoracolumbar spine for treatment of traumatic injuries and osteomyelitis. In 2001, the Sextant (Medtronic) system was developed by Foley et al to safely pass a rod using percutaneous methods.2 In subsequent years, there has been further development of intraoperative imaging and spinal instrumentation as well as refinement of percutaneous techniques to allow for accurate and safe placement of pedicle screws in a minimally invasive manner. Comparisons of percutaneous pedicle screws to open techniques have identified advantages of minimally invasive procedures, including reduced damage to paraspinal musculature,3,4 reduced blood loss,5 decreased operative time,6 and improved injury reduction in fractures.7 There has been a concern for increased risk of facet violation or medial misplacement in the percutaneous approach, which could lead to increased risk of adjacent segment disease or neurological injuries. Recent studies imply a concern that percutaneous pedicle screw placement increases the risk of superior facet violation compared to open procedures,8,9 but malposition of screws has been shown to be as low as 0.3% in the lumbar spine and 4.4% in the thoracic spine, which is comparable to open reported rates.10,11 Additionally, accurate placement of pedicle screws has been shown to be as high as 98% in traumatic injuries.12 The instrumentation for percutaneous placement can present a higher initial cost but combined with shorter hospital stay and decreased blood transfusions, the total cost can be lower than or comparable to open minimally invasive procedures.13

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Fig. 37.1 (a–c) Intraoperative image showing use of MinRad arm (Thompson MIS, Salem, NH) used to hold the Jamshidi needle in place so that the surgeon can step away from the operative field during use of fluoroscopy while performing percutaneous pedicle screw placement.

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Percutaneous Pedicle Screw Placement for Spinal Instrumentation

37.2 Indications and Contraindications Indications for pedicle screw placement have been increasing. Degenerative disease, traumatic injuries, and infection have all been shown to have good results with percutaneous pedicle screw placement. Contraindications are not exclusive to this technique but are in line with other techniques of spine fusion, and patients who are poor candidates for fusion should be carefully reviewed. The only direct contraindication is inability to adequately arrange the screw within the confines of the pedicle. Patients with severe rotational scoliotic deformity have been a relative contraindication; however, improved techniques and experience has made this less so.16

37.3 Preoperative Planning The preoperative evaluation of the patient should include a thorough physical examination. This includes a neurological evaluation for signs of myelopathy or nerve root compression, which may alter your surgical plan. A skin examination should note any prior incisions to assist in planning surgical approach and placement of incisions for percutaneous screws. Radiographic evaluation should be performed with lumber spine Xrays at a minimum but usually to include either CT or MRI for visualization of pedicles to accurately determine size of pedicle screws to be placed and any abnormal anatomy.

37.3.1 Instrumentation Notes The surgical tools needed for percutaneous pedicle screws can be divided into imaging requirements and spinal instrumentation: ● Fluoroscopy. ● Lead drape including thyroid shield for surgeon and operative personnel. ● Radiolucent table and frame that permits adequate anteroposterior (AP) and lateral fluoroscopic views of the spine. ● Cannulated instruments for pedicle screw placement. ● Kirschner’s wire (K-wire) and K-wire driver. ● Rod instrumentation device.

37.4 Surgical Technique This chapter briefly describes two different techniques that have been used safely and effectively for accurate percutaneous pedicle screw placement for spinal instrumentation using fluoroscopic guidance. The patient is positioned prone on a radiolucent frame while maintaining a good sagittal balance (▶ Fig. 37.2a). Next, electrophysiologic monitoring can be applied (electromyography, somatosensory evoked potentials, or combination may be employed). The K-wires and pedicle screws are stimulated intraoperatively to assure placement is not impinging upon a nerve. Action potential of less than 8 mA warrants that the Kwire or pedicle screw be repositioned. The fluoroscope is brought into field to plan entry sites. AP images are taken at each vertebral level where pedicle screws will be placed to obtain a Ferguson angle, delineating the superior end plate of the body. Next, a true AP view is obtained so that the spinous process is centered between the pedicles. Heavyset individuals may require manipulation of the contrast mode of the fluoroscopic unit to adequately visualize these landmarks. This measurement is marked at each vertebral level with a transverse line that is parallel to the end plate and bisects bilateral pedicles using a radiopaque instrument and also recorded on fluoroscope for later use (▶ Fig. 37.2b). Next, 10 to 25 degrees off-angle oblique views are obtained through the pedicles (owl’s eye view) on each side and recorded on the fluoroscope. A craniocaudal line is marked on the skin that bisects all the pedicles on each side of levels receiving instrumentation (▶ Fig. 37.2c). Once adequately positioned, the two pedicles on the vertebral body should be clearly visible. It is especially important to view the medial border of the pedicle because violating this border by either a K-wire or Jamshidi needle can result in neural element injury. Looking at the pedicles on the vertebral bodies above and below helps delineate the anatomy of the targeted pedicle, particularly when targeting the sacrum (S1) where the pedicle can be hard to visualize. The patient is then sterilely draped and the C-arm is likewise draped to provide AP and lateral images without contaminating the field when repositioning the fluoroscopic unit intraoperatively. Local anesthetic may be instilled along the planned incision, which incorporates the craniocaudal line that bisects the

Fig. 37.2 (a) Patient in supine position, lateral view. (b) Radiopaque marker used to obtain level of bilateral pedicles using the Ferguson angle and centered spinous process. (c) Radiopaque marker used to identify craniocaudal axis for pedicles on each side.

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Fig. 37.3 (a,d) The Jamshidi needle is placed at the transverse process–facet junction (black arrow) in the oblique view, consistent with the middle portion of the pedicle on fluoroscopy. (b,c) The appropriate depth of the Jamshidi needle is demonstrated graphically. The Jamshidi needle is advanced under fluoroscopic imaging in a slight lateral-to-medial trajectory; the medial border of the pedicle should not be crossed before reaching the base of the pedicle–vertebral body junction. (e) The wire is passed down the center of the pedicle until seated in bone and then the Jamshidi needle removed; the wire visualized here lies within borders of the pedicle on oblique view. (f) A lateral view may be obtained after wires are placed to ensure they are at appropriate depth, extending beyond the pedicle but not violating anterior vertebral body cortex.

pedicles on either side of the spine. The skin is incised and the fascia may be opened sharply or with electrocautery with care taken not to disrupt underlying musculature.

37.4.1 Pedicle Access Using Oblique Images (Owl’s Eye) The C-arm is positioned using the predetermined measurements so that the surgeon is able to look straight down the targeted pedicle starting at the most rostral level undergoing fusion giving the truest en face view (10–25 degrees off-center depending on previous measurement). A Jamshidi needle is placed at the radiographic center of the pedicle. The procedure is performed by fluoroscopic visualization as the Jamshidi needle is aligned to beam axis of the fluoroscope and advanced through the pedicle with gentle tapping of a mallet (▶ Fig. 37.3a,d). The Jamshidi needle is advanced through the pedicle, making sure not to cross the medial border of the pedicle until the junction between the pedicle base and the vertebral body is reached (▶ Fig. 37.3b,c). (A similar technique is used when performing vertebroplasty or kyphoplasty.)

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The Jamshidi needle is placed into the pedicle until it enters the vertebral body. Lateral views are used to visualize the K-wire placement. Bone marrow can be removed by aspirating up to 2 mm from the Jamshidi needle if needed for later fusion. A Kwire is passed down the Jamshidi needle to seat it into bone, ensuring that it does not advance into the anterior half of the vertebral body. The Jamshidi needle is carefully removed while leaving the K-wire in place (▶ Fig. 37.3e,f). An assistant can hold the K-wire to ensure that it is not pulled out of the vertebral body. The fluoroscope is used to perform the contralateral pedicle at that level. The process is then repeated at each level undergoing fusion.

37.4.2 Pedicle Access Using the Anteroposterior View This technique utilizes the same positioning and image preparation as the oblique view. At the time of placement of Jamshidi needles, however, the fluoroscope remains in AP view so that bilateral pedicles may be cannulated simultaneously (▶ Fig. 37.4a). The Jamshidi needles are placed at the lateral

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Percutaneous Pedicle Screw Placement for Spinal Instrumentation

Fig. 37.4 (a) Operative view of wire placement through Jamshidi needle. Note the medial trajectory of the Jamshidi needle and preoperative skin markings delineating the pedicle at each level. (b) The Jamshidi needle is placed bilaterally near the lateral border of the pedicle on fluoroscopy (note the centered spinous process and flat superior end plate). The Jamshidi needle is advanced under fluoroscopic imaging in a slight lateral-to-medial trajectory; the medial border of the pedicle should not be crossed before reaching the base of the pedicle–vertebral body junction. (c) Cadaveric image demonstrating appropriate depth of Jamshidi needles on axial view. (d,e) The wire is passed through the Jamshidi needle until it exits the end and seats into the vertebral body. The Jamshidi needle is then removed.

Fig. 37.5 (a) Operative view of dilation over wire to be used for screw tapping by the surgeon on the left side. View of cannulated screw placement by the surgeon on the right. (b) Lateral view of wires prior to tapping. Care should be taken to ensure wire does not advance during tapping or screw placement; multiple images may be needed during these steps. (c) The tapping screw is placed over wire and advanced to depth beyond the pedicle–vertebral junction and then removed. (d) Cannulated screws are placed over the wire and advanced approximately two-thirds of the distance through vertebral body; Kirschner’s wire (K-wire) may be removed once the screw advances into the vertebral body.

edge of the pedicle and position confirmed with the fluoroscope (▶ Fig. 37.4b). They are then advanced through the pedicle in a medial trajectory ensuring that they do not cross the medial border of pedicle until entry in the vertebral body. Stimulation can be applied during this step. Once the needle is confirmed within the body at a depth of approximately 3 cm or anterior half of the vertebral body (▶ Fig. 37.4c), a K-wire is placed and the Jamshidi needle is removed (▶ Fig. 37.4d,e). This process is repeated at each level undergoing fusion. This method allows for simultaneous placement of screws bilaterally at each level but should be used only when good visualization of pedicles is obtained on the AP view. Oblique views are used only if confirmation is needed.

37.4.3 Screw Placement A series of cannulated muscle dilators are then passed over the Kwire to prevent the soft tissue from going into the threads of the tap screw as it is passed down the K-wire. The pedicle is tapped ensuring that direction is in line with the K-wire until just beyond the pedicle base (▶ Fig. 37.5a–c). Intraoperative monitoring can be performed throughout the tapping process via stimulation of screw to ensure there are no pedicle breaches. (Alternatively, stimulation can be performed on K-wire or after screw placement.) The ends of the K-wires may then be secured out of the field so that subsequent levels may be performed and the C-arm adjusted. Once all K-wires have been placed at levels to be fused

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Fig. 37.6 (a,b) Fluoroscopic view of final screw placement and rod positioning.

and tapping performed, the pedicle screws are placed. The appropriate-sized cannulated screw is placed over the K-wire and advanced until it enters vertebral body (~3 cm but varies by patient) and then the K-wire is withdrawn. We typically use a screw that measures 6.5 mm in diameter by 45 mm in length for instrumenting L3–S1 pedicles. Proper alignment of screw with K-wire during insertion is critical to ensure that the wire tip is not trapped within the vertebral body. Using fluoroscopic guidance, the pedicle screw is advanced approximately two-thirds of the depth of the vertebral body with the head resting adjacent to the posterior elements without impingement on them (▶ Fig. 37.5d). An AP view can be obtained to confirm that the screws maintain their medial trajectory. Various systems may be used for rod placement, but all entail accurate measurement so that rod extends at least 2.5 mm beyond the final screws of the construct. This is secured with screw caps. Depending on technique, the fascia may need to be incised further. Because the procedure does not allow open visualization of the rod secured in the screw heads, the rod can inadvertently slip lateral to the screw head. Before final tightening of the rod to the screw heads, take additional AP and lateral fluoroscopic views to ensure that the rod is indeed seated properly in the screw heads (▶ Fig. 37.6). The fascia is reapproximated and a subcuticular suture placed for skin closure.

37.5 Postoperative Care Postoperative hospital care includes early ambulation, pain control, and images for future comparison. Routine follow-up should consist of similar images at designated intervals to assess fusion and instrumentation. Percutaneous pedicle screw placement as part of minimally invasive spinal surgery trend has been shown to decrease hospital stays and postoperative analgesic requirement.14

37.6 Management of Complications Many of the complications that may arise from percutaneous pedicle screw placement can be prevented by adequate patient positioning, radiographic planning, or electrophysiologic monitoring. The most significant complications consist of damage to

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neural tissue (spinal nerves or spinal cord) via a pedicle breach or injury to adjacent viscera or blood vessels. With intraoperative imaging and monitoring, a medial breach can be identified at multiple points during the procedure. At any time that it is identified, the instrumentation should be removed from that pedicle and a new Jamshidi needle placed via fluoroscopy in an attempt to advance through the pedicle. If the pedicle is too sclerotic or too small (< 3 mm), then the procedure may need to be converted to an open procedure for direct visualization,17 but the same limitations will be encountered. The great vessels, peritoneal contents, or pleural cavity can be encountered if there is a lateral or anterior breach of the vertebral body. This is usually caused by poor trajectory or deep placement of the K-wire. Using a lateral view on fluoroscopy while advancing should prevent this complication. However, if encountered, corrective measures would include consultation with general or vascular surgeons for possible repair. In the event of a pneumothorax, a postoperative chest tube may be required.

37.7 Clinical Case: Foraminal Stenosis and Mobile Spondylolisthesis A 71-year-old woman presented with mechanical back pain for greater than a 6-month period with some radiation to her posterior thighs. She had minimal relief with conservative medical management. On examination, she was noted to have mild weakness on her distal right lower extremity with no other deficits. Imaging revealed severe right-sided foraminal stenosis and mobile spondylolisthesis at L3/L4 and L4/L5 levels. Given the concern for foraminal stenosis and need for spinal fusion, she had an L3/L4 and L4/L5 lateral interbody fusion performed with placement of percutaneous pedicle screws bilaterally from L3 to L5. She was discharged home after 1 day in the hospital and at follow-up has had almost full resolution of back pain and improvement in right lower extremity strength. Postoperative films including dynamic images show no mobility and good indirect decompression (▶ Fig. 37.7).

37.8 Conclusion Percutaneous pedicle screw instrumentation can be performed safely and effectively. The benefits to patients are reduced tissue

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Percutaneous Pedicle Screw Placement for Spinal Instrumentation

Fig. 37.7 (a) Lateral and (b) anteroposterior views of the lumbar spine demonstrating multilevel spondylolisthesis and neuroforaminal stenosis. (c,d) Postoperative images showing fusion construct consisting of interbody placement at L3/L4 and L4/L5 with posterior pedicle screws.

dissection and blood loss, preservation of normal anatomic supporting structures of the spine, and quicker recoveries. Mastering radiographic targeting of the pedicle can be done with a thorough appreciation of the bony anatomy of the spine and those landmarks critical in performing safe and accurate percutaneous pedicle screw placement.

Clinical Caveats ●

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●

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Plan trajectories at start of surgery for each level to be fixated. This will help in determining if AP or oblique views need to be used at certain levels. Percutaneous screws can be safely placed from AP views simultaneously; however, if there is any concern for pedicle wall breach, an oblique view needs to be obtained to ensure correct trajectory. Electromyogram (EMG) can be easily used for safe placement of screws if intraoperative fluoroscopy does not delineate anatomy sufficiently (in cases of obesity, prior fusion, or severe degenerative changes). Be cautious of K-wire depth during tapping maneuver and screw placement to prevent damage to structures anterior to the vertebral body.

References [1] Magerl FP. Stabilization of the lower thoracic and lumbar spine with external skeletal fixation. Clin Orthop Relat Res. 1984(189):125–141 [2] Foley KT, Gupta SK, Justis JR, Sherman MC. Percutaneous pedicle screw fixation of the lumbar spine. Neurosurg Focus. 2001; 10(4):E10 [3] Regev GJ, Lee YP, Taylor WR, Garfin SR, Kim CW. Nerve injury to the posterior rami medial branch during the insertion of pedicle screws: comparison of mini-open versus percutaneous pedicle screw insertion techniques. Spine. 2009; 34(11):1239–1242 [4] Kim DY, Lee SH, Chung SK, Lee HY. Comparison of multifidus muscle atrophy and trunk extension muscle strength: percutaneous versus open pedicle screw fixation. Spine. 2005; 30(1):123–129 [5] Grass R, Biewener A, Dickopf A, Rammelt S, Heineck J, Zwipp H. [Percutaneous dorsal versus open instrumentation for fractures of the thoracolumbar border. A comparative, prospective study]. Unfallchirurg. 2006; 109(4):297–305 [6] Grossbach AJ, Dahdaleh NS, Abel TJ, Woods GD, Dlouhy BJ, Hitchon PW. Flexion-distraction injuries of the thoracolumbar spine: open fusion versus percutaneous pedicle screw fixation. Neurosurg Focus. 2013; 35(2):E2 [7] Wang H, Zhou Y, Li C, Liu J, Xiang L. Comparison of open versus percutaneous pedicle screw fixation using the sextant system in the treatment of traumatic thoracolumbar fractures. Clin Spine Surg. 2017; 30(3):E239–E246 [8] Babu R, Park JG, Mehta AI, et al. Comparison of superior-level facet joint violations during open and percutaneous pedicle screw placement. Neurosurgery. 2012; 71(5):962–970 [9] Jones-Quaidoo SM, Djurasovic M, Owens RK, II, Carreon LY. Superior articulating facet violation: percutaneous versus open techniques. J Neurosurg Spine. 2013; 18(6):593–597

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Surgical Techniques [10] Powers CJ, Podichetty VK, Isaacs RE. Placement of percutaneous pedicle screws without imaging guidance. Neurosurg Focus. 2006; 20(3):E3 [11] Hardin CA, Nimjee SM, Karikari IO, Agrawal A, Fessler RG, Isaacs RE. Percutaneous pedicle screw placement in the thoracic spine: a cadaveric study. Asian J Neurosurg. 2013; 8(3):153–156 [12] Tinelli M, Matschke S, Adams M, Grützner PA, Münzberg M, Suda AJ. Correct positioning of pedicle screws with a percutaneous minimal invasive system in spine trauma. Orthop Traumatol Surg Res. 2014; 100(4):389–393 [13] Lucio JC, Vanconia RB, Deluzio KJ, Lehmen JA, Rodgers JA, Rodgers W. Economics of less invasive spinal surgery: an analysis of hospital cost differences between open and minimally invasive instrumented spinal fusion procedures during the perioperative period. Risk Manag Healthc Policy. 2012; 5:65–74

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[14] Bindal RK, Glaze S, Ognoskie M, Tunner V, Malone R, Ghosh S. Surgeon and patient radiation exposure in minimally invasive transforaminal lumbar interbody fusion. J Neurosurg Spine. 2008; 9(6):570–573 [15] Srinivasan D, Than KD, Wang AC, et al. Radiation safety and spine surgery: systematic review of exposure limits and methods to minimize radiation exposure. World Neurosurg. 2014; 82(6):1337–1343 [16] Ahmad FU, Wang MY. Use of anteroposterior view fluoroscopy for targeting percutaneous pedicle screws in cases of spinal deformity with axial rotation. J Neurosurg Spine. 2014; 21(5):826–832 [17] Mobbs RJ, Sivabalan P, Li J. Technique, challenges and indications for percutaneous pedicle screw fixation. J Clin Neurosci. 2011; 18(6):741–749

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Transforaminal Lumbar Interbody Fusion

38 Transforaminal Lumbar Interbody Fusion Mick J. Perez-Cruet, Moumita S.R. Choudhury, Esam A. Elkhatib, and Jorge Mendoza–Torres Abstract The minimally invasive transforaminal lumbar interbody fusion (MI-TLIF) approach and technique is one of the most versatile surgical treatment options for a variety of lumbar spinal disorders. The approach offers a muscle-sparing technique that can directly decompress the neural elements while providing optimal fusion and posterior instrumentation. The approach can also provide complete reduction of spondylolisthesis, which restores sagittal alignment, and foraminal and canal diameter. This chapter will illustrate this technique and some of the new innovative technology developed to facilitate the approach and improve patient outcomes. Keywords: minimally invasive, TLIF, lumbar, spondylolisthesis, stenosis, chronic back pain

degenerative scoliosis, and postlaminectomy spondylolisthesis (▶ Fig. 38.2).10,11,12 These conditions can often result in foraminal stenosis causing compression of the exiting nerve root. Restoration of disc height, sagittal alignment, and foraminal circumference can be achieved using the MI-TLIF procedure. Patients with osteoporosis, bleeding disorders, and active infection can be considered relative contraindications. However, since the MI-TLIF procedure is performed with minimal tissue destruction and blood loss, these patients can also be treated using this technique. Obese patients experienced clinically and statistically significant improvement in both pain and function after undergoing MI-TLIF. Since there is less tissue destruction, obese patients and those with medical comorbidities can be ambulated faster and they tend to recover quicker as well.12

38.3 Preoperative Planning 38.1 Introduction Minimally invasive transforaminal lumbar interbody fusion (MI-TLIF) is a surgical technique used to stabilize the lumbar spine. The technique is extremely versatile and allows treatment of a variety of pathology including degenerative disc disease, spondylolisthesis with and without lumbar stenosis, and scoliosis. The posterior approach permits direct decompression of the neural elements and, collection of local autograft bone for fusion material, and promotes arthrodesis by placing bone graft material in the interspace between adjacent vertebrae (▶ Fig. 38.1). Comparative studies have shown the superiority of MI-TLIF to the similar open technique.1,2,3,4,5,6,7 The technique represents an evolution in spine surgery by preserving normal anatomical structures and improving patient outcomes.8

38.2 Indications MI-TLIF is used for conditions such as the following: ● Degenerative disc disease. ● Spondylolisthesis with or without stenosis. ● Instability due to trauma or tumors. ● Discogenic pain disorder. ● Stabilization after osteotomy. ● Pars interarticularis defect. ● Stabilization of degenerative discs or recurrent disc herniations. ● Scoliosis correction and stabilization. These conditions are known to produce refractory chronic back pain disorders and can be considered indications for spinal fusion. Additionally, MI-TLIF is designed to replace the disc space with bone graft material to treat: isthmic spondylolisthesis (grades 1–4),9 junctional degeneration adjacent to a fusion mass, recurrent disc herniations with significant back pain, terminal end of long fusion constructs requiring interbody fusion,

Thorough preoperative evaluation including physical examination is necessary to achieve optimal clinical outcome and to reduce the need for a revision operation and complications. Radiographic workup typically includes plain X-rays with AP, lateral, flexion, and extension views. MRI of the lumbar spine is performed. In revision operations with hardware in place or patients with significant scoliosis, CT with myelogram is helpful. In those patients with no clear neurological compression, discography with postdiscography CT is useful in determining the possible source of the patient’s chronic back pain.

38.3.1 Decompression Alone versus Decompression with MI-TLIF Determining the most appropriate surgical approach can help improve patient outcomes while providing focused treatment and unnecessary surgical time and intervention. We conducted a retrospective analysis of facet anatomy in a large series of patients and determined that facet could assist in identifying optimal surgical approach. Those patients found to have lumbar stenosis and facet lengths (i.e., length of superior and inferior facets) similar to nonpathological segments could be treated with decompression. In those patients with elongated facets and stenosis, decompression in combination with MI-TLIF provided excellent patient outcomes and reduced the incidence for subsequent surgical intervention. Conversely, the surface area of patients with elongated facet was also greater than nonpathological segments. Elongation of the facet complex occurs frequently in patients with spondylolisthesis, whereby the subluxation of one vertebra relative to the other over an extended period of time (i.e., years) results in facet elongation. The MI-TLIF procedure allows for solid stabilization of the segment and restoration of disc and foraminal height, and thus eliminates the process by stabilizing the spine segment, preventing recurrence of stenosis, and further subluxation of the vertebrae (▶ Fig. 38.3).

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Fig. 38.1 Preoperative (a) sagittal and (b) axial T2-weighted MRI images showing L4–L5 grade 1 spondylolisthesis with associated stenosis. Postoperative (c) sagittal, (d) axial CT, and (e) postoperative incision following minimally invasive transforaminal lumbar interbody fusion approach showing restoration of normal sagittal alignment, adequate interbody graft, and central canal decompression while maintaining anatomical structures of the spine (i.e., spinous process and contralateral facet complex).

38.4 Surgical Technique

38.4.2 Spinal Approach

38.4.1 Patient Positioning

Incision

After the patient is intubated, a Foley catheter is placed and the patient is log-rolled onto a Jackson table (see ▶ Fig. 8.3). All pressure points are padded adequately. The Jackson table is helpful because it allows unencumbered fluoroscopic visualization of the spine and easy removal of the fluoroscopic unit, when not being used, away from the operative field toward the foot of the bed.

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The patient is positioned prone with appropriate padding, prepped and draped in sterile surgical fashion. The midline is marked to help orient the surgeon. An 18-gauge spinal needle and lateral fluoroscopy is used to identify the level. An incision is then made 3 cm lateral to the midline directly over the disc space in which the MI-TLIF is to be performed in association with canal decompression. This distance from the midline allows access to

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Transforaminal Lumbar Interbody Fusion

Fig. 38.2 (a) Lateral radiograph and (b) illustrations of spondylolysis or pars interarticularis defect (note foraminal compromise with subluxation of the vertebrae).

the base of the spinous process for adequate minimally invasive laminectomy if decompression for stenosis is performed. If no decompression is required, we find that 3.5 cm from the midline is adequate and facilitates interbody implant positioning within the disc space. The fascia is cut parallel to the spinous processes and the One-Step-Dilator (Thompson MIS, Salem, NH) is used to approach the spine (▶ Fig. 38.4). The dilator is supported by a holder and is advanced under fluoroscopic guidance in a clockwise fashion. Once docked on the facet, counterclockwise rotation opens the flanges of the dilator, separating the muscle tissue, and a tubular retractor of the appropriate length is placed. The procedure is then performed under direct microscopic visualization through the tubular retractor. The approach is bloodless and does not require Kirschner’s wire (Kwire) or a series of muscle dilators, thus helping avoid inadvertent passage into the spinal canal and potential dural tear and/ or nerve injury (see ▶ Fig. 38.4).

Lumbar Exposure and Decompression With the tubular retractor in place, the microscope is brought into the surgical field. Soft tissue is removed circumferentially to expose the facet complex laterally and the ipsilateral lamina medially. If needed, AP and/or lateral fluoroscopic views can confirm the proper location of the tubular retractor. With the ipsilateral lamina exposed, a high-speed drill and M8 cutting burr is used to drill the lamina. All drilled bone is collected using the

BoneBac Press (Thompson MIS, Salem, NH). This bone is used for fusion material, avoids graft site morbidity, has exceptional handling characteristics, and can be mixed with other types of bone graft material if needed (▶ Fig. 38.5). If significant spinal stenosis exists, a minimally invasive laminectomy is performed initially (see Chapter 37 for technique).

Interbody Fusion Once adequate decompression is achieved, the tubular retractor is positioned to expose the facet complex. A high-speed cutting burr is used to perform an ipsilateral facetectomy overlying the disc to be fused. The disc space is identified once again with lateral fluoroscopy and an annulotomy performed to enter the disc space. A series of disc space reamers, curettes, and rongeurs are used to adequately prepare the disc space for interbody arthrodesis. Care is taken to adequately prepare the adjacent vertebral end plates to remove the cartilage and expose the bony end-plates adequately (▶ Fig. 38.6). Once the disc space is properly prepared, the BoneBac TLIF device (Thompson MIS, Salem, NH) is filled with morselized autograft. The size of the implant is determined by trials. The most commonly used implant size is 7 mm wide, 11 mm tall, and 26 mm long. This size appears to be appropriate in majority of cases and provides for adequate disc and foraminal height restoration. Lateral fluoroscopy identifies proper location of the implant within the disc space.

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Fig. 38.3 Graph showing facet length and surface area analysis in the lumbar spine at the L4–L5 level in normal (control group) patients, in patients undergoing minimally invasive transforaminal lumbar interbody fusion, and in patients undergoing decompression without interbody fusion or instrumentation. Elongation of the facet complex is felt to be secondary to subluxation forces placed on the facet complex typically seen in patients with spondylolisthesis.

Once the implant is within the disc space, the tubular retractor is wanded lateral to help seat the implant within the center of the disc space. The implant is then rotated 90 degrees, thus restoring disc space and foraminal height (▶ Fig. 38.6). This unique design allows for easier access to the disc space and then rotation to restore disc space height. Thus, larger size implants can be used while minimizing nerve root retraction or possible injury. With the implant positioned properly, BoneBac TLIF bullets are filled with morselized autograft collected using the BoneBac Press and the implant holder loaded. The bone is then pushed down the handle of the implant to exit on either side of the device within the disc space. Typically, 10 to 12 bullets are used to completely fill the disc space with morselized autograft, the “Gold Standard” of fusion material. If more graft material is needed, the morselized autograft is mixed with additional bone graft material (i.e., allograft, demineralized bone matrix; ▶ Fig. 38.7). With the disc space packed with bone graft, the implant is released and deployed into the disc space. The disc space is inspected with a ball-ended probe to assure that no bone graft is outside the disc space. Additionally, bone graft material is used to reconstruct the resected facet complex. With complete hemostasis, the tubular retractor is removed, allowing the paraspinous

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muscles to return to their normal anatomical position. Postoperative CT confirms adequate filling of disc space with morselized autograft. The Thompson MIS BoneBac TLIF system allows for optimal loading of bone graft material harvested from the surgical site by placing bone graft outside the implant, and contained circumferentially by the annulus fibrosus. In this manner, almost 100% fusion rates have been achieved with very little evidence of implant subsidence (▶ Fig. 38.8).

Percutaneous Pedicle Screw Instrumentation Once adequate decompression, interbody fusion, and complete hemostasis are performed, the tubular retractor is removed, allowing the paraspinous muscles to return to their normal anatomical position. An incision is made on the contralateral side the same distance from the midline as was performed earlier for the interbody fusion. AP and lateral fluoroscopy are used to target the pedicles for percutaneous pedicle screw fixation. Alternatively, image guidance navigation can be used. The vertebra targeted is placed in the center of the fluoroscopic image to avoid parallax distortion, the end plate is made as one line, and the spinous process centered between the pedicles (see percutaneous

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Transforaminal Lumbar Interbody Fusion

Fig. 38.4 (a) Intraoperative image showing use of One-Step-Dilator to approach the spine and (b) eliminate Kirschner’s wire (K-wire) and multiple muscle dilators. (c) Retractor used to approach the spine in a muscle sparing fashion.

screw targeting in Chapter 37, ▶ Fig. 37.1). Intraoperative electrophysiologic monitoring with electromyogram (EMG) is performed. Once placed, K-wires and pedicle screws are stimulated with a probe to ensure adequate position. A stimulation threshold less than 8 mA requires repositioning of K-wire and/or pedicle screw. We typically place percutaneous pedicle screws bilaterally at each MI-TLIF segment to assure adequate fixation to promote arthrodesis. To help reduce radiation exposure to the surgeon, operative staff, and patient we utilize the MinRad arm (Thompson MIS, Salem, NH) to hold the Jamshidi needle. This method also facilitates percutaneous pedicle screw placement as the MinRad arm allows for small adjustments of the pedicle targeting needle, thus improving pedicle screw placement accuracy. If there is a subluxation between the vertebrae as seen in spondylolisthesis, attempts are made to reduce the spondylolisthesis and restore normal sagittal alignment. The advantage is that this technique significantly increases the size of the neural foramen and canal diameter plus increases the fusion surface area between the adjacent vertebrae. The unique design of the Thompson MIS BoneBac TLIF device with curved ends that correspond to the vertebral end plates helps facilitate reduction of the spondylolisthesis (▶ Fig. 38.9). The wound is irrigated and the fascial layer is closed using 2– 0 Vicryl in an interrupted fashion. A subcuticular stitch is applied and the skin is closed with skin glue. No drain or wound dressing is used routinely and the infection rate is negligible. Excellent long-term clinical outcomes using the MI-TLIF technique described have been achieved13 (▶ Table 38.1). Adjacent segment disease over a 5-year postoperative period has been approximately 2% compared to 13.6% in traditional open lumbar arthrodesis series.13,14

38.5 Postoperative Care Patients typically stay in the hospital for 3 days after surgery and ambulate the day after the surgery. Postoperative pain is managed initially with self-administered patient-controlled analgesia (PCA) pain pump and quickly switched to oral analgesics and muscle relaxers as needed. Consultation with physical therapist or occupational therapist is arranged before discharge. Patients are discharged with postoperative care guidelines and follow-up plans. The follow-up is performed at 2 weeks, 1 month, 3 months, 6 months, 1 year, and yearly thereafter from the day of surgery. Patients are advised to wear a lumbosacral orthosis (LSO) brace when ambulating for the first 3 months.

38.6 Management of Complications In general, patients tolerate MI-TLIF procedure very well. Potential perioperative complications include infection, hematoma, instrumentation malposition or failure, neurologic injury, and cerebrospinal fluid leakage. Perioperative antibiotics, meticulous wound closure, and dressing changes can help prevent wound infections. Proper use of fluoroscope and stimulation of K-wires and pedicle screws will minimize the risk of instrumentation malposition and nerve root impingement. A small durotomy can be successfully treated with Gelfoam (Pfizer Injectables, New York, NY) to cover the defect, followed by fibrin glue. Complications can be limited by adequate surgical training and critical patient selection.

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Fig. 38.5 (a) Intraoperative illustration showing use of microscope. (b,c) Intraoperative photographs showing decompression of lamina with high-speed cutting burr and (d) collection of drilled morselized bone graft material using the BoneBac Press.

38.7 Clinical Case: MI-TLIF with Decompression and Spondylolisthesis Reduction A 64-year-old man having undergone previous lumbar laminectomy presented with severe debilitating back pain, neurogenic claudication symptoms, and progression of spondylolisthesis to grade 2. The patient underwent MI-TLIF with decompression and spondylolisthesis reduction. His symptoms completely resolved after surgery and he returned to activities of daily living (▶ Fig. 38.10).

of fusion and low rates of complication. From a clinical prospective, these patients show an extremely high rate of satisfaction in the treatment of their chronic back pain disorders. In fact, the majority of these patients are completely pain free and have returned to work or activities of daily living full-time.

Clinical Caveats ● ●

●

38.8 Conclusion The MI-TLIF approach seems to provide both short- and longterm statistically significant outcome improvements in patients experiencing debilitating low back pain. In addition, long-term benefits observed in this study include a reduced rate of adjacent segment disease requiring reoperation while providing high rates

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●

Facet anatomy can help determine optimal surgical approach. Decompression for stenosis can be performed via the posterior approach and provides adequate autologous bone graft material for arthrodesis using the BoneBac Press. The unique BoneBac TLIF device can provide for adequate disc space height and neural foramen restoration while filling the disc space with bone graft material and helping facilitate spondylolisthesis reduction. Percutaneous pedicle screw systems that allow for spondylolisthesis reduction can improve patient outcomes by restoring adequate sagittal alignment, foraminal height, and canal diameter.

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Transforaminal Lumbar Interbody Fusion

Fig. 38.6 (a,b) Disc space preparation after facetectomy, (c) interbody placed within disc space, (d) device rotated to restore disc and foraminal height, (e) passage of autograft down implant holder, and (f) filling disc space with morselized autograft using Thompson MIS BoneBac TLIF System. The implant is designed to enter the disc space easily, restore the disc height by simple rotation, and allow bone to be passed down the implant holder and fill the disc space around the implant.

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Fig. 38.7 Intraoperative images showing (a) decompressed neural elements, (b) preparation of disc space and retraction of traversing nerve root for (c) placement of BoneBac TLIF device, (d) lateral fluoroscopic image with device in place, (e) rotation of device to restore disc height, foraminal height, and injection of bone graft material.

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Transforaminal Lumbar Interbody Fusion

Fig. 38.8 (a–c) Postoperative CT images showing MIS laminectomy decompression and filling of disc space with morselized autograft. This promotes loading of bone, not implant to promote arthrodesis.

Fig. 38.9 (a) Intraoperative lateral fluoroscopic images using unique design of the BoneBac TLIF device to reduce grade 1 spondylolisthesis to grade 0 and thus (b) restore foraminal height (inset MRI shows compressed exiting nerve root before reduction) allowing adequate decompression of the exiting nerve root. (c,d) Reduction of multisegmental spondylolisthesis with percutaneous reduction screws (Longitude system, Medtronic, Memphis, TN).

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Surgical Techniques Table 38.1 Long-term results of MI-TLIF technique Baseline

Follow-up time 12 moa

24 moa

47 moa

Back pain visual analog scale

7.0 ± 2.4

4.2 ± 3.0 (2.8, 40%)

4.5 ± 3.0 (2.5, 35.7%)

3.5 ± 2.8 (3.5, 50%)

Oswestry Disability Index

43.1 ± 15.7

29.7 ± 18.8 (13.4, 31.1%)

30.2 ± 20.4 (12.9, 29.9%)

28.2 ± 21.7 (14.9, 34.6%)

SF-36 physical component score

30.6 ± 7.8

38.3 ± 11.3 (7.7, 25.2%)

38.1 ± 11.7 (7.5, 24.5%)

39.6 ± 11.7 (9, 29.4%)

SF-36 mental component score

43.8 ± 11.0

48.3 ± 13.0 (4.5, 10.3%)

49.7 ± 12.9 (5.9, 13.5%)

49.7 ± 11.2 (5.9, 13.5%)

< 0.001

< 0.001

< 0.05

p

Abbreviations: MI-TLIF, minimally invasive transforaminal lumbar interbody fusion; SF-36, Short Form 36. Source: Perez-Cruet et al 2014.12 Note: Excellent long-term patient-generated outcome results have been achieved using the MI-TLIF technique described. The values are given as the mean and the standard deviation. aNet change and percent improvement from baseline, respectively, are in parenthesis.

Fig. 38.10 (a,b) Preoperative sagittal and axial MRI showing prior traditional laminectomy with grade 2 spondylolisthesis. Sequential intraoperative fluoroscopic views showing (b) use of OneStep-Dilator to approach the spine in a musclesparing fashion, (c) opening dilator and placing tubular retractor over it, (d) use of chisel and (e) reamers to enter and prepare disc space, (f) placement of BoneBac TLIF device, (g) placement and (h) prereduction of spondylolisthesis with (i) postreduction percutaneous pedicle screws, and (j) initial preoperative and (k) postoperative films with construct in place.

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Transforaminal Lumbar Interbody Fusion

References [1] Villavicencio AT, Burneikiene S, Roeca CM, Nelson EL, Mason A. Minimally invasive versus open transforaminal lumbar interbody fusion. Surg Neurol Int. 2010; 1:12 [2] Habib A, Smith ZA, Lawton CD, Fessler RG. Minimally invasive transforaminal lumbar interbody fusion: a perspective on current evidence and clinical knowledge. Minim Invasive Surg. 2012; 2012:657342 [3] Scheufler KM, Dohmen H, Vougioukas VI. Percutaneous transforaminal lumbar interbody fusion for the treatment of degenerative lumbar instability. Neurosurgery. 2007; 60(4) Suppl 2:203–212, discussion 212–213 [4] Dhall SS, Wang MY, Mummaneni PV. Clinical and radiographic comparison of mini-open transforaminal lumbar interbody fusion with open transforaminal lumbar interbody fusion in 42 patients with long-term follow-up. J Neurosurg Spine. 2008; 9(6):560–565 [5] Peng CWB, Yue WM, Poh SY, Yeo W, Tan SB. Clinical and radiological outcomes of minimally invasive versus open transforaminal lumbar interbody fusion. Spine. 2009; 34(13):1385–1389 [6] Schizas C, Tzinieris N, Tsiridis E, Kosmopoulos V. Minimally invasive versus open transforaminal lumbar interbody fusion: evaluating initial experience. Int Orthop. 2009; 33(6):1683–1688 [7] Wang J, Zhou Y, Zhang ZF, Li CQ, Zheng WJ, Liu J. Comparison of one-level minimally invasive and open transforaminal lumbar interbody fusion in degenerative and isthmic spondylolisthesis grades 1 and 2. Eur Spine J. 2010; 19(10):1780–1784

[8] Samartzis D, Shen FH, Anderson G, Perez-Cruet MJ. The history of minimally invasive spinal fusion technologies. In: Perez-Cruet MJ, Beisse RW, Pimenta L, Kim DH, eds. Minimally Invasive Spine Fusion Techniques and Operative Nuances. New York, NY: Thieme; 2011:3–22 [9] Meyerding HW. Spondylolisthesis. Surg Gynecol Obstet. 1932; 54:371–377 [10] Albert TJ, Fleischut PM. Transforaminal and posterior lumbar interbody fusion. In: Albert TJ, Vaccaro AR, eds. Spine Surgery: Tricks of the Trade. 2nd ed. New York, NY: Thieme; 2009:133–135 [11] Perez de la Torre RA, Kelkar PS, Beier A, et al. Decompression, transforaminal lumbar interbody fusion, reduction, and percutaneous pedicle screw fixation. In: Perez-Cruet MJ, Beisse RW, Pimenta L, Kim DH, eds. Minimally Invasive Spine Fusion: Techniques and Operative Nuances. St. Louis, MO: Quality Medical Publishing; 2011:345–367 [12] Terman SW, Yee TJ, Lau D, Khan AA, La Marca F, Park P. Minimally invasive versus open transforaminal lumbar interbody fusion: comparison of clinical outcomes among obese patients. J Neurosurg Spine. 2014; 20 (6):644–652 [13] Perez-Cruet MJ, Hussain NS, White GZ, et al. Quality-of-life outcomes with minimally invasive transforaminal lumbar interbody fusion based on longterm analysis of 304 consecutive patients. Spine. 2014; 39(3):E191–E198 [14] Sears WR, Sergides IG, Kazemi N, Smith M, White GJ, Osburg B. Incidence and prevalence of surgery at segments adjacent to a previous posterior lumbar arthrodesis. Spine J. 2011; 11(1):11–20

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39 Transpsoas Anatomical Approach to the Spine Steven L. Gogela and William D. Tobler Abstract This chapter discusses in detail the anatomy and clinical nuances of operative technique based on our ongoing refinements and deeper understanding of this complex anatomy. Although a lateral lumbar interbody fusion can be fraught with risks of complications and neuromuscular injury, mastery of the anatomy and technique can make this a valuable operation with minimal morbidity. The lateral transpsoas approach is an elegant, albeit unfamiliar, surgical corridor for many practicing surgeons, especially those trained before the approach became mainstream. Therefore, information is divided into five categories: abdominal wall with its neuromuscular structures, retroperitoneal cavity and contents, psoas muscle, lumbar plexus, and vertebral column. This minimally invasive procedure (using a shallow docking technique) affords excellent passage for interbody grafting, and credible clinical experiences have been well established. A relative decrease in morbidity compared with other approaches may be achieved with utilization of a natural anatomical corridor and use of the “shallow docking,” our preferred technique for dissecting the psoas under direct visualization. When indicated, properly prepared surgeons should not hesitate to approach the L4–L5 disc space laterally despite the robust psoas muscle and risk of injury to the lumbar plexus at this level. Further modification and experience with the lateral transpsoas approach will inevitably continue into the future. Keywords: anatomy, operative technique, lateral lumbar interbody fusion, lateral transpsoas approach, abdominal wall with its muscular and neural structures, retroperitoneal cavity, lumbar plexus, vertebral column, shallow docking technique

39.1 Introduction The minimally invasive lateral transpsoas approach to the lumbar spine has rapidly grown in popularity since its original description in 1998.1 The approach gave new options and advantages compared with standard posterior or anterior surgical corridors. One primary advantage relates to robust restoration of coronal balance at one or multiple segments. Other benefits include the preservation of stabilizing structures, such as the anterior and posterior longitudinal ligaments, facet joints, and other posterior elements, and improved graft–host interface with a larger interbody device spanning the entire ring hypophysis. Restoration of disc and foraminal height can provide indirect decompression of neural elements. With its overall ease of access, this minimally invasive approach has led to decreased blood loss and shorter hospital stays.2,3,4,5,6,7 For the inexperienced surgeon, the anatomy encountered during a lateral lumbar interbody fusion (LLIF) can be entirely new and fraught with risks of complication and neuromuscular injury. However, mastering the anatomy and clinical nuances of the approach will make this a valuable operation with minimal morbidity. In this chapter, we detail the relevant anatomy and

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our operative technique, which reflects our ongoing refinements as we gained greater understanding and experience with this complex anatomy.

39.2 Relevant Anatomy In reviewing the anatomy of this approach, we divided the information into five categories: ● Abdominal wall with its muscular and neural structures. ● Retroperitoneal cavity and contents. ● Psoas muscle. ● Lumbar plexus. ● Vertebral column.

39.2.1 Abdominal Wall The wall of the abdomen begins with the skin and subcutaneous fat superficial to the lateral abdominal musculature. The external oblique, encased by a fascial layer, overlies the internal oblique and transversus abdominis superficial to the retroperitoneum. Nerves commonly encountered in this territory are as follows (▶ Fig. 39.1, ▶ Fig. 39.2, ▶ Fig. 39.3): ● Subcostal nerve. Receiving innervation from T12, the subcostal nerve is responsible for sensation of the anterior gluteal skin and motor supply to the rectus abdominis and external oblique (see ▶ Fig. 39.1). It courses inferior to the 12th rib and anterior to the quadratus before perforating the transversus to travel between it and the internal oblique. The nerve then courses inferomedially until it perforates the rectus abdominis. Injury to this subcostal nerve can occur either during the approach or more commonly during harvesting of the iliac crest near the anterior superior iliac spine (ASIS). The effect varies depending on which portion of the nerve is injured: notalgia paresthetica with injury to the dorsal cutaneous branch, rectus abdominis syndrome with the anterior cutaneous branch, or abdominal wall weakening and potential hernia formation. ● Iliohypogastric nerve. With input primarily from L1 (and lesser T12), this nerve supplies sensation to the gluteal and hypogastric skin via the lateral and anterior cutaneous branches, respectively (see ▶ Fig. 39.2). It also contributes to the innervation of the transversus and internal oblique muscles. The nerve emerges along the superolateral psoas and travels anteriorly until it perforates the transversus above the iliac crest, traveling between that muscle and the internal oblique like the subcostal nerve. Branching about 3 cm medial to the ASIS, the iliohypogastric nerve then divides into lateral and anterior cutaneous branches. Injury to the nerve can cause painful paresthesias and/or paresis of the abdominal wall, causing either abdominal wall or direct inguinal hernias depending on the location of injury. ● Ilioinguinal nerve. Innervated primarily by L1 (lesser T12, L2), this nerve transmits sensation to the anterosuperomedial thigh as well as the root of the penis and scrotum in males or the labia majora in females. It also supplies motor innervation

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Transpsoas Anatomical Approach to the Spine

Fig. 39.1 Illustration of the relationship between the psoas muscle, lumbar plexus, and vertebral column. The genitofemoral nerve emerges from the psoas muscle at the L2–L3 disc space where it is prone to injury. The femoral nerve is predisposed to injury at the L4–L5 disc where the psoas travels anteriorly. (Reproduced with permission from Mayfield Clinic.)

●

to the lower transversus and internal oblique muscles. The nerve emerges from the psoas at the level of L1 just caudal to the iliohypogastric; it pierces the transversus to run between it and the internal oblique, giving off muscle branches to both. It continues toward the pubic symphysis, with its sensory branch traveling through the inguinal canal and past the superficial inguinal ring. Injury to this nerve is most common on approach and may cause painful paresthesias and/or paresis of the abdominal wall, resulting in either direct inguinal or abdominal wall hernias. Lateral femoral cutaneous nerve (LFCN). The LFCN receives its greatest contribution from L2 and L3 (lesser L1). This purely sensory nerve supplies sensation to the lateral thigh in a wellknown distribution. After emerging from the lateral psoas around the level of L4, this nerve travels underneath iliac fascia, across the anterior iliacus, and through the retroperitoneum en route to the ASIS. It then dives under the inguinal ligament roughly 1 cm medial to the ASIS. Injury results in meralgia paresthetica.

39.2.2 Retroperitoneal Cavity The borders of the retroperitoneum are the psoas muscle and vertebrae medially, peritoneum and internal organs anteriorly, quadratus lumborum and iliacus posteriorly, diaphragm superiorly, and pelvic structures inferiorly. Contents vary depending on the craniocaudal level, but may include the kidneys and/or adrenal glands, ureters, aorta, inferior vena cava, ascending and descending colon, rectum, duodenum, and pancreas.8

39.2.3 Psoas Muscle The psoas muscle is the major flexor of the hip and principal anterior stabilizer of the lumbar spine (see ▶ Fig. 39.1 and ▶ Fig. 39.2). The deep portion originates from the transverse processes of the T12–L4 vertebral bodies, with a superficial and anterior psoas minor component originating from the lateral bodies and discs between those vertebrae. The muscle belly significantly increases in mass as it travels inferiorly from T12, becoming quite large at the L4–L5 level where it begins to move anteriorly to the spine as it courses into the pelvis. Extensive study of the psoas muscle is a must before surgery because its shape and configuration varies among patients: it may be asymmetric, making one side more approachable in many cases. As the psoas moves anteriorly, the femoral nerve courses through the muscle and exits anteriorly, where it is at risk of injury at the L4–L5 level (▶ Fig. 39.4). Above this point, the L3 contribution to the lumbar plexus tends to be far posterior in the psoas and at lesser risk of damage on approach.

39.2.4 Lumbar Plexus Genitofemoral Nerve Generally supplied by L2 (lesser L1), the genitofemoral nerve has two components: a genital branch going to the scrotum in males and the mons pubis and labia majora in females, and a femoral branch supplying skin over the femoral triangle. Notably, this nerve also supplies motor innervation to the cremaster muscle in males, which may be monitored during surgery (see ▶ Fig. 39.1).

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Fig. 39.2 Lateral view of lumbar plexus anatomy in relation to the psoas muscle, vertebral column, and iliac bones. Note that the genitofemoral nerve travels anteriorly through the psoas muscle and pierces the surface at the L3–L4 disc space. (Reproduced with permission from Mayfield Clinic.)

The nerve travels anteriorly between the two bellies of the psoas muscle at the L2–L3 level before piercing the psoas around the L3–L4 disc and traveling down the anterior or middle third of the muscle belly.9,10 Risk of injury to the nerve is greatest at L2–L3, below which it is usually not visualized because it lies more anterior. It then branches, with the genital branch traversing the inguinal ligament and the femoral branch remaining deep to the ligament. Injury results in numbness and potentially paresthesias of the supplied areas and loss of the cremaster reflex in males (see ▶ Fig. 39.3).

Femoral Nerve The femoral nerve, which receives input from the L2–L4 trunks, is the largest branch of the lumbar plexus and carries the most important motor function placed at risk in the transpsoas approach. Supplying the quadriceps muscles, the femoral nerve is almost entirely responsible for knee extension. It also supplies a portion of the iliacus and pectineus muscles that assist in hip flexion. Through the sartorius muscle, it is involved in flexion, adduction, and rotation of the hip. The femoral nerve supplies sensation to the anteromedial thigh via the anterior femoral cu-

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taneous branch and the medial leg and foot via the saphenous branch. The nerve travels deep in the belly of the psoas and gradually moves anteriorly within the muscle as it progresses inferiorly. It crosses the L4–L5 disc space in the posterior middle quadrant, where the nerve is at greatest risk for injury.11 At this level, the femoral nerve is large and can be easily visualized (▶ Fig. 39.4b, c). Injury may result in anesthesia or paresthesias in its sensory territory, weakness of hip flexion, knee extension, and lateral thigh rotation, and loss of the patellar reflex. Injury to this nerve can result in profound and permanent disability, which is a major topic of concern cited by surgeons who are reluctant to use this approach, especially at the L4–L5 level.

Obturator Nerve The obturator nerve, chiefly supplied from L3 (lesser L2, L4), supplies sensation to the medial thigh. Unlike the genitofemoral nerve, it has significant motor function. The nerve emerges from the medial psoas and travels inferiorly over the sacral ala en route to the obturator canal, where it exits to supply the hip joint and muscles of hip adduction.8 This nerve is at lower relative risk during the transpsoas approach because its origin from

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Transpsoas Anatomical Approach to the Spine

Cutaneous nerve distribution

Spinal nerve distribution T11 T12 L1 L2

L3

Iliohypogastric (T12-L1) Ilioinguinal (L1) Genitofemoral (L1-L2) • Femoral br. • Genital br. Lateral femoral cutaneous (L2-L3) Anterior femoral cutaneous (L2-L4)

L4

Obturator (L2-L4)

Lateral sural L5

Saphenous

Superficial peroneal

S1

© Mayfield Clinic Fig. 39.3 Graphical illustration showing the spinal and cutaneous nerve distribution of the lumbar plexus. (Reproduced with permission from Mayfield Clinic.)

the femoral nerve is usually far anterior to the psoas muscle and not typically in the surgical corridor.

Sympathetic Trunk The sympathetic trunk runs deep to the medial border of the psoas along the anterior one-third of the vertebral bodies throughout the lumbar spine. Injury during this approach rarely occurs but may have broad-ranging autonomic effects, typically resulting in a warm, dry leg.

39.2.5 The Spine As at all levels in the spine, lumbosacral intervertebral discs are surrounded by an annulus fibrosus with a central nucleus pulposus. They are buttressed by the anterior and posterior longitudinal ligaments, but laterally are exposed. Although safe working zones have been described,12 others have shown that aberrant anatomy in these zones can place the lumbar plexus at

risk up to 37% of the time, especially when blindly dilating the psoas.9,13 In general, considering all published cadaveric studies and experience, the center of the disc space provides a relatively safe target provided that the surgeon dissects the psoas under direct visualization and, in most cases, utilizes neuromonitoring with continuous electromyogram (EMG) and direct stimulation of the operative field.9,12,13,14,15,16,17,18

39.3 Surgical Technique The lateral transpsoas approach to the lumbar spine is an elegant approach. Our operative technique is detailed, from positioning through stepwise dissection to the desired disc space, neuromonitoring, and appropriate imaging studies. Finally, we give some pearls of lessons learned and comment on some ongoing refinements in technique for approaching this complex anatomy.

39.3.1 Positioning The patient is positioned in the lateral decubitus position on a table and firmly secured with silk tape; the head faces toward anesthesia. The table must be capable of flexing with the break of the bed at the hips. Flexion of the table should optimize access between the patient’s iliac crest and the lower limits of the rib cage. However, extreme flexion of the operating table is strictly avoided to prevent undue tension on the lumbar plexus and psoas muscle, which places these structures at greater risk of ischemic injury during retraction for the approach. The ipsilateral hip is flexed significantly to relax the psoas, and thus helps mitigate this potential complication. Access to the upper lumbar levels may necessitate an intercostal approach. An axillary roll is placed and all bony prominences are padded, including the contralateral side, where positioning-related injury to the peroneal and superior gluteal nerve has been reported.19 Using fluoroscopy, the surgeon obtains true orthogonal anteroposterior (AP) and lateral images with the C-arm locked at 0 and 90 degrees, respectively (▶ Fig. 39.5). Minor adjustments of the table can be made, but any major adjustments should be avoided because the side rails can interfere with imaging. After the disc(s) of interest are localized with orthogonal lateral Xrays, the incision is marked on the skin at approximately the middle third of the targeted disc space.

39.3.2 Approach The patient is prepped and draped in sterile fashion. After skin incision, monopolar cautery may be used until the abdominal fat is encountered. The fat is then bluntly dissected until the external oblique muscle fascia is reached and incised sharply. Muscle layers are split longitudinally using gentle dissection with a finger or blunt instrument, taking care to mobilize any encountered neural structures en route to the retroperitoneal space. The iliohypogastric and ilioinguinal nerves flow through these muscular layers and must not be damaged. The retroperitoneum is identified by the presence of fatty tissue and a palpable sense of entering a cavity of free space. After locating the posterior wall (quadratus lumborum and iliacus), the retroperitoneal contents are swept bluntly with a finger

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Fig. 39.4 MRI of the lumbar spine from a healthy volunteer. (a) T1-weighted coronal image shows the gradual increase in psoas muscle mass moving inferiorly and the relation to the vertebral bodies. (b) Coronal STIR image. Note the psoas muscle (asterisk) and the femoral nerve (arrow) at the level of the L4–L5 disc. (c) T1-weighted axial image depicts the robust psoas muscle belly (asterisk) and the lumbar plexus (arrow) at the level of the L4–L5 disc. (Reproduced with permission from Mayfield Clinic.)

Fig. 39.5 (a) Typical positioning for the lateral transpsoas approach. Note the break of the table at the hips, ipsilateral knee flexion, and orthogonal positioning. (b) Orthogonal lateral X-ray positioning. (Reproduced with permission from Mayfield Clinic.)

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Transpsoas Anatomical Approach to the Spine

Fig. 39.6 The shallow docking technique, whereby a common retractor tube is advanced to the surface of the psoas muscle. Neuromonitoring confirms safe trajectory between the lumbar nerve roots posteriorly and the genitofemoral nerve anteriorly. The psoas muscle is then split under direct visualization and the disc space entered. (Reproduced with permission from Mayfield Clinic.)

from a posterior to anterior and cephalad to caudad direction. The vertebral transverse processes and psoas muscle are identified by finger palpation, while taking care not to probe into the neuroforaminal areas. Patients with scarring secondary to prior diverticulitis, radiation, or abdominal or retroperitoneal surgery may not be candidates for the lateral approach

39.3.3 Monitoring Continuous real-time monitoring of the patient’s lumbar plexus is common at many institutions. Generally, free-running EMG of multiple muscle groups innervated by L2–S2 is monitored for disturbance of neural structures; often this includes the vastus medialis, tibialis anterior, biceps femoris, and medial gastrocnemius, among others.13,20 Stimulated EMG using a probe is also utilized throughout the case to identify neural structures in close proximity to the field that may be placed at risk. Despite the use of free-running and stimulated EMG, nerve injury can occur that is not detected with monitoring. The use of transcortical motor-evoked potentials has provided added benefit. Recently, we are monitoring the cremaster muscle in men to signal proximity to the genitofemoral nerve with good results. Use of these various monitoring techniques should be an adjunctive tool

to aid the surgeon in protecting neural structures; it is not a substitute for a thorough mastery of the anatomy.

39.3.4 Opening the Psoas The most common retractor systems are advanced over a series of dilators; adjustable blades allow for altering of the exposure in any direction. We recommend advancing the dilators to the surface of the psoas muscle (▶ Fig. 39.6). X-rays are then obtained to confirm proper trajectory to the middle of the desired disc space (▶ Fig. 39.7). After the dilators are removed, the light source is connected. Under direct visualization, the surface of the psoas is inspected for traversing nerves, blood vessels, peritoneal contents, ureter, or other critical structures. At this point, the stimulator probe is used to “scout out” the area for EMG activity by nerves not visualized at this initial point. The psoas is then carefully divided vertically with a Penfield dissector in midposition of the muscle belly under direct visualization, stimulating anything suspicious for a traversing nerve. Using handheld retractor blades, the psoas is retracted to fully expose the annulus of the disc. Alternatively, we have used a radiolucent tubular retractor for suprapsoas “shallow docking” to which the deep retractor

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Fig. 39.7 (a) Suprapsoas docking of a tubular retractor. (b) Fluoroscopic confirmation of lateral disc target through radiolucent tube. (c) Manual insertion of deep retractor blades that are then fixed to the tube. (d) Fluoroscopic image of shallow-docked radiolucent tube and deep retractor blades. (Reproduced with permission from Mayfield Clinic.)

Fig. 39.8 (a) Anteroposterior and (b) lateral X-rays following placement of a lateral interbody graft. (Reproduced with permission from Mayfield Clinic.)

blades are fixed that traverse the psoas. With the more common modular retractors, the psoas is inspected superficially. Next, serial dilators can be advanced through the retracted muscle, with EMG testing of each successive dilator before the modular retractor is advanced to the spine. AP and lateral X-rays are again taken to confirm the level and location within the disc space (▶ Fig. 39.8). Once exposed, the annulus fibrosus is incised sharply and the disc removed with pituitary rongeurs, curettes, and various scrapers. Notably, the contralateral annulus is opened superiorly and inferiorly with a sharp periosteal elevator, which sometimes requires significant force for ligamentous release. This step allows for symmetric disc height expansion and ligamentotaxis. Next, the interbody graft size is determined and placed under fluoroscopy. Multiple options exist per surgeon preference and

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each patient’s clinical situation. These include pure polyetheretherketone (PEEK), coated PEEK, carbon fiber, and titanium, among others. The cages vary in size, generally ranging from 18- to 26-mm width by 8- to 15-mm height by 45- to 60-mm length. Recently, hyperlordotic cages (12 to 15 degrees) have been introduced for aggressive correction of sagittal plane deformity that may require anterior longitudinal ligament release. Either autograft—often iliac crest—or recombinant human bone morphogenetic protein-2 (rhBMP-2) is typically used to pack the cage before insertion to stimulate bony fusion. If multiple interbody grafts are placed, the retractor blades are removed and the psoas again dissected under direct visualization after radiographic localization; disc space preparation and grafting proceed as before. After completing the interbody fusion(s), the operative field is copiously irrigated with antibiotic solution,

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Transpsoas Anatomical Approach to the Spine the retractors are withdrawn, and the psoas muscle can be directly inspected. Muscle layers may be loosely approximated, but tight closure should be strictly avoided to prevent injury to sensory nerves, specifically the ilioinguinal and iliohypogastric nerves traversing between the transversus abdominis and internal oblique muscles. The external oblique fascia is then sutured, followed by dermal and subcuticular layers, and skin glue superficially. If a stand-alone construct is used, various plates are available for lateral fixation. This may be appropriate for patients at significant medical risk for surgery, especially at the lower-stress levels in the upper lumbar spine. The procedure maintains the anterior and posterior longitudinal ligaments, facet joints, and all posterior elements that may provide stability. More commonly, posterior pedicle screw fixation and fusion is performed with or without decompression at the level(s) that were grafted using open or minimally invasive techniques.

39.4 Potential Complications Enthusiastic early publications likely underreported complications related to the transpsoas approach, while more recent publications more realistically convey the incidence of thigh symptoms and weakness. This more accurate portrayal of procedural-related morbidity has elevated the degree of concern and respect for the difficulty inherent in the approach.2,3,4,5,7,8, 10,15,18,21,22,23,24,25 The most commonly reported complication remains weakness of the traversed psoas muscle, which limits hip flexion postoperatively. This condition is generally recognized as a result of direct trauma to the psoas muscle during the procedure. Although it can substantially limit postoperative mobilization and require rehabilitation, weakness of hip flexion without sensory deficit is generally expected to recover fully over 3 to 6 months or even up to 1 year. It rarely results from injury to intrinsic short motor roots to the psoas, which may not fully resolve.3,19,26,27 A more disabling and concerning complication of the transpsoas approach is injury to the femoral nerve. Most often, injury to this nerve results from trauma to the lumbar plexus while traversing the psoas with dilators and retractor blades. This iatrogenic injury is thought to result from direct mechanical compression, stretch, or traction injury from positioning or retractors, lacerated nerves, or indirect ischemia.2,28 Estimates of nerve injury have varied from 0.7 to 23%, leading to several modifications in technique in an effort to limit the substantial functional disability resulting from this complication.3,7,13,27,29 Sensory deficit can be significant as well, with high rates of dysesthesias or paresthesias reported in some series. Most prominent is the concern of injury to the genitofemoral nerve at the level of the psoas. Alternatively, injury to the iliohypogastric or ilioinguinal nerves may occur during either the exposure or closure of the abdominal wall. In a study of 919 consecutively treated levels, Lykissas et al19 reported a 9.3% incidence of sensory deficit and motor injury in 3.2%, noting that these rates may be higher with rhBMP-2 use. Furthermore, anesthesia, paresthesia, and abdominal wall paresis may result from injury to the subcostal, iliohypogastric, ilioinguinal, or genitofemoral nerves. Paresis may leave the patient with either an abdominal wall hernia or a direct inguinal hernia, which may or may not

be amenable to surgical repair. Anterior thigh dysesthesias are reported to affect 5.8 to 36%, which can be a troubling symptom for patients.4,19 Various other potential complications include visceral (bowel) and vascular injury, with a 0.08 and 0.10% incidence, respectively, according to a survey of surgeons who had performed more than 13,000 lateral fusions.30 The rate of vascular injury in the lateral transpsoas approach is rare, owing to the more common anterior position of the great vessels. The most at risk of these is the inferior vena cava during right-sided approaches. Aberrant anatomy and surgical risk may be easily assessed with preoperative imaging and may dictate the side of approach. Coronal deformities are typically approached from the concave side of the curve, especially in multilevel deformity correction. However, one must carefully evaluate the position of vascular structures in rotational deformities, where the vena cava may be much more exposed and at risk. Not only is the thickness of the psoas important, but also its position relative to the vertebral column must be noted. In a patient with significant spondylolisthesis or other positive sagittal deformity, the psoas may be displaced anteriorly from the vertebrae. In these cases, the femoral nerve is more likely to be exposed at the L4–L5 level and is at higher risk of injury. Careful evaluation of axial and coronal MRI sequences is vital for understanding these anatomical variants. Infection represents a well-known and feared surgical complication, but rates are significantly decreased with the lateral technique when compared with other minimally invasive lumbar approaches. Incidences of superficial and deep wound infections have been reported as 0.27 and 0.14% for LLIF, 0.8 to 9.2% overall for transforaminal lumbar interbody fusion and posterior lumbar interbody fusion (TLIF/PLIF), and 0.4 to 7.1% for an anterior lumbar interbody fusion (ALIF).30

39.5 Avoiding Complications Technological innovations have advanced the development and refinement of this approach. Furthermore, a better understanding of the functional surgical anatomy has allowed for successful surgical outcomes and has decreased morbidity substantially. Based on the cumulative experience to date and tempered by our own observations, we recommend the following “pearls” for this approach. Shallow, suprapsoas docking with dissection of the psoas under direct visualization reduces the rate of plexus injury and is our preferred technique.31 The psoas muscle is very small and devoid of nerves above the L2–L3 interspace, decreasing risk of injury. As it travels down to lower levels, the psoas increases in size and varies substantially in shape between individuals. The genitofemoral nerve will be directly visualized in many instances and injury may be avoided.10 Shallow docking and careful separation of the muscle fibers become most critical at the L4– L5 level. Notably, the placement of percutaneous Kirschner’s wires (K-wires) is strictly avoided because of its significant risk of nerve injury, with an incidence reported as high as 25%.9 Neuromonitoring should be used as an important adjunct, but alone it is not enough to prevent nervous injury. Even without any EMG changes, nerve damage can occur either in cases of direct nerve trauma or as a result of prolonged retraction–related

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Surgical Techniques nerve ischemia that is silent on EMG.2,28 Thus, we do not advocate blindly dilating and advancing the retractor through the psoas and docking against bone, relying solely on neuromonitoring for safety. Despite its limitations, both continuous EMG and direct operative field stimulation may be used to prevent avoidable injury. At the T12–L1–L2 levels, neuromonitoring is of doubtful benefit. During the transpsoas approach, the surgeon must understand the role of stimulated and free-running EMGs, transcortical motor-evoked potentials, and the possibility of genitofemoral monitoring in men. Cage subsidence, a well-reported complication of all fusion techniques, has been documented with the LLIF. Injury to the vertebral end plate because of either disc space preparation or pedicle screw placement should be strictly avoided. Pedicle screw fixation should augment the interbody graft if there is intraoperative concern for immediate subsidence. Reported rates of pseudoarthrosis are conflicting and the overall accuracy of reporting has been questionable. This risk is thought to be highest in the lower lumbar levels because of greater biomechanical stress and in those with significant risk factors, such as smoking, osteoporosis, vitamin D deficiency, or prior pseudoarthrosis. The incidence of pseudoarthrosis is decreased with pedicle screw augmentation, which should be routinely performed for patients with these comorbidities. When approaching the upper lumbar levels, and specifically T12–L1, one may occasionally encounter the pleural cavity. Although this may make a right-sided approach more favorable at this level given the elevated hemidiaphragm on this side, positioning will typically deflect the diaphragm superiorly. If entered, the lung should be inflated with a Valsalva maneuver and closed primarily. A postoperative chest X-ray can rule out a pneumothorax, which typically will not require a chest tube in this scenario.

39.6 Conclusion The lateral transpsoas approach to the lumbar spine is an elegant, albeit unfamiliar, surgical corridor for many practicing surgeons, especially for those trained over a decade ago. Spine surgeons are afforded an excellent passage for interbody grafting, and credible clinical experiences are now being reported. As evidenced by the well-known complications affecting the various structures described in this chapter, it is imperative for the surgeon to become extensively familiar with the relevant surgical anatomy before performing this minimally invasive procedure. When indicated, knowledgeable and properly prepared surgeons should not hesitate to approach the L4–L5 disc space laterally where the lumbar plexus is at greatest risk of injury and the psoas muscle is robust. Further modification and experience with the lateral transpsoas approach will inevitably continue into the future.

Clinical Caveats ●

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Substantial anatomy is placed at risk during the lateral transpsoas approach, including nerves, visceral organs, vasculature, and muscles. With in-depth understanding of this anatomy, the surgeon should also become extremely familiar with the structures in

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the surgical corridor. Practice in the laboratory setting before attempting the procedure will help prevent injury. Although there is no completely safe corridor for entry, perhaps the center of the disc space remains the safest target. This target should be slightly more posterior for the L2–L3 level (genitofemoral nerve runs anteriorly along psoas). Posterior placement is to be strictly avoided at the L4–L5 level where the lumbar plexus moves anteriorly. Shallow, suprapsoas docking of a retractor with dissection of the psoas muscle under direct visualization may decrease the degree of trauma to the psoas muscle and prevent potential nerve injury. The use of both direct stimulation and continuous EMG monitoring should be routinely utilized for recognition and prevention of impending nerve injury. Transcortical motorevoked potentials and cremaster muscle monitoring are useful adjuncts. Once mastered, the lateral transpsoas approach provides an excellent, biomechanically sound corridor for interbody grafting and spinal reconstruction. Although the anatomy is delicate and variable, the surgeon who adopts the aforementioned protective measures will ensure patient safety and allow for excellent clinical outcomes.

References [1] McAfee PC, Regan JJ, Geis WP, Fedder IL. Minimally invasive anterior retroperitoneal approach to the lumbar spine. Emphasis on the lateral BAK. Spine. 1998; 23(13):1476–1484 [2] Benglis DM, Elhammady MS, Levi AD, Vanni S. Minimally invasive anterolateral approaches for the treatment of back pain and adult degenerative deformity. Neurosurgery. 2008; 63(3) Suppl:191–196 [3] Isaacs RE, Hyde J, Goodrich JA, Rodgers WB, Phillips FM. A prospective, nonrandomized, multicenter evaluation of extreme lateral interbody fusion for the treatment of adult degenerative scoliosis: perioperative outcomes and complications. Spine. 2010; 35(26) Suppl:S322–S330 [4] Kotwal S, Kawaguchi S, Lebl D, et al. Minimally invasive lateral lumbar interbody fusion: clinical and radiographic outcome at a minimum 2-year followup. J Spinal Disord Tech. 2015; 28(4):119–125 [5] Oliveira L, Marchi L, Coutinho E, Pimenta L. A radiographic assessment of the ability of the extreme lateral interbody fusion procedure to indirectly decompress the neural elements. Spine. 2010; 35(26) Suppl:S331–S337 [6] Ozgur BM, Aryan HE, Pimenta L, Taylor WR. Extreme Lateral Interbody Fusion (XLIF): a novel surgical technique for anterior lumbar interbody fusion. Spine J. 2006; 6(4):435–443 [7] Sharma AK, Kepler CK, Girardi FP, Cammisa FP, Huang RC, Sama AA. Lateral lumbar interbody fusion: clinical and radiographic outcomes at 1 year: a preliminary report. J Spinal Disord Tech. 2011; 24(4):242–250 [8] Viswanathan A, Kim DH, Reid N, Kline DG. Surgical management of the pelvic plexus and lower abdominal nerves. Neurosurgery. 2009; 65(4) Suppl:A44–A51 [9] Banagan K, Gelb D, Poelstra K, Ludwig S. Anatomic mapping of lumbar nerve roots during a direct lateral transpsoas approach to the spine: a cadaveric study. Spine. 2011; 36(11):E687–E691 [10] Tender GC, Serban D. Genitofemoral nerve protection during the lateral retroperitoneal transpsoas approach. Neurosurgery. 2013; 73(2) Suppl Operative:ons192–ons196, discussion ons196–ons197 [11] Benglis DM, Jr, Vanni S, Levi AD. An anatomical study of the lumbosacral plexus as related to the minimally invasive transpsoas approach to the lumbar spine. J Neurosurg Spine. 2009; 10(2):139–144 [12] Uribe JS, Arredondo N, Dakwar E, Vale FL. Defining the safe working zones using the minimally invasive lateral retroperitoneal transpsoas approach: an anatomical study. J Neurosurg Spine. 2010; 13(2):260–266

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Transpsoas Anatomical Approach to the Spine [13] Tohmeh AG, Rodgers WB, Peterson MD. Dynamically evoked, discrete-threshold electromyography in the extreme lateral interbody fusion approach. J Neurosurg Spine. 2011; 14(1):31–37 [14] Bina RW, Zoccali C, Skoch J, Baaj AA. Surgical anatomy of the minimally invasive lateral lumbar approach. J Clin Neurosci. 2015; 22(3):456–459 [15] Cahill KS, Martinez JL, Wang MY, Vanni S, Levi AD. Motor nerve injuries following the minimally invasive lateral transpsoas approach. J Neurosurg Spine. 2012; 17(3):227–231 [16] Dakwar E, Vale FL, Uribe JS. Trajectory of the main sensory and motor branches of the lumbar plexus outside the psoas muscle related to the lateral retroperitoneal transpsoas approach. J Neurosurg Spine. 2011; 14(2):290–295 [17] Kepler CK, Bogner EA, Herzog RJ, Huang RC. Anatomy of the psoas muscle and lumbar plexus with respect to the surgical approach for lateral transpsoas interbody fusion. Eur Spine J. 2011; 20(4):550–556 [18] Regev GJ, Chen L, Dhawan M, Lee YP, Garfin SR, Kim CW. Morphometric analysis of the ventral nerve roots and retroperitoneal vessels with respect to the minimally invasive lateral approach in normal and deformed spines. Spine. 2009; 34(12):1330–1335 [19] Lykissas MG, Aichmair A, Hughes AP, et al. Nerve injury after lateral lumbar interbody fusion: a review of 919 treated levels with identification of risk factors. Spine J. 2014; 14(5):749–758 [20] Uribe JS, Vale FL, Dakwar E. Electromyographic monitoring and its anatomic implications in minimally invasive spine surgery. Spine. 2010; 35 Suppl 26:S372 [21] Ahmadian A, Deukmedjian AR, Abel N, Dakwar E, Uribe JS. Analysis of lumbar plexopathies and nerve injury after lateral retroperitoneal transpsoas approach: diagnostic standardization. J Neurosurg Spine. 2013; 18(3):289–297 [22] Papanastassiou ID, Eleraky M, Vrionis FD. Contralateral femoral nerve compression: an unrecognized complication after extreme lateral interbody fusion (XLIF). J Clin Neurosci. 2011; 18(1):149–151

[23] Sofianos DA, Briseño MR, Abrams J, Patel AA. Complications of the lateral transpsoas approach for lumbar interbody arthrodesis: a case series and literature review. Clin Orthop Relat Res. 2012; 470(6):1621–1632 [24] Taher F, Lebl DR, Hughes AP, Girardi FP. Contralateral psoas seroma after transpsoas lumbar interbody fusion with bone morphogenetic protein-2 implantation. Spine J. 2013; 13(2):e1–e5 [25] Moller DJ, Slimack NP, Acosta FL, Jr, Koski TR, Fessler RG, Liu JC. Minimally invasive lateral lumbar interbody fusion and transpsoas approach-related morbidity. Neurosurg Focus. 2011; 31(4):E4 [26] Cummock MD, Vanni S, Levi AD, Yu Y, Wang MY. An analysis of postoperative thigh symptoms after minimally invasive transpsoas lumbar interbody fusion. J Neurosurg Spine. 2011; 15(1):11–18 [27] Pumberger M, Hughes AP, Huang RR, Sama AA, Cammisa FP, Girardi FP. Neurologic deficit following lateral lumbar interbody fusion. Eur Spine J. 2012; 21 (6):1192–1199 [28] Houten JK, Alexandre LC, Nasser R, Wollowick AL. Nerve injury during the transpsoas approach for lumbar fusion. J Neurosurg Spine. 2011; 15(3):280–284 [29] Rodgers WB, Gerber EJ, Patterson J. Intraoperative and early postoperative complications in extreme lateral interbody fusion: an analysis of 600 cases. Spine. 2011; 36(1):26–32 [30] Uribe JS, Deukmedjian AR. Visceral, vascular, and wound complications following over 13,000 lateral interbody fusions: a survey study and literature review. Eur Spine J. 2015; 24 Suppl 3:386–396 [31] Acosta FL, Jr, Drazin D, Liu JC. Supra-psoas shallow docking in lateral interbody fusion. Neurosurgery. 2013; 73(1) Suppl Operative:48–51, discussion 52

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40 eXtreme Lateral Interbody Fusion Luiz Pimenta, Rodrigo Amaral, Luis Marchi, and Leonardo Oliveira Abstract eXtreme lateral interbody fusion (XLIF) is a less invasive alternative for the treatment of different pathologies of the spine above L5. Minimally invasive surgery provides the opportunity to reduce surgical duration and patient length of stay, minimize damage to adjacent tissue, and improve patient satisfaction and quality of life. This is particularly relevant to spinal conditions like low back pain, sciatica, and other intervertebral disc degenerations, as they are currently associated with severe morbidity and elevated costs to the society. The lateral approach allows the access of the intervertebral disc laterally through the psoas muscle. Proper patient positioning and concomitant lumbar plexus monitoring are mandatory for the success of the procedure. The technique preserves primary segmental stabilizing structures of the spine while also permitting a wide discectomy with bilateral annular release. Thus, the approach allows the placement of a large implant that reaches the ring apophysis bilaterally, promoting a more rigid construction without the need of posterior supplementation in some cases. Disc height restoration and ligamentotaxis also generate an indirect decompression of the neural elements, which help recover coronal and sagittal balance. Spinal fusion and improvement in self-assessment questionnaires have been described in the literature. Intraoperative bleeding and damage of adjacent structures are minimal and patients are encouraged to walk on the same day, being discharged after an overnight hospital stay, on average. Transient plexopathies and hip flexor weakness are the most commonly reported complication associated with lateral access surgery, but the majority are resolved within 6 months. Lateral transpsoas approach has been shown to be a safe and effective surgical option in the treatment of spinal pathologies. Keywords: low back pain, sciatica, intervertebral disc degenerations, spinal fusion, minimally invasive surgery

40.1 Definition of Problem Chronic low back pain has been described as a complex disorder that is also associated with high morbidity rates.1,2 However, patients who suffer from a painful lumbar motion segment that is not resolved with conservative management can benefit from lumbar fusion.3 Minimally invasive surgical techniques have been demonstrated to provide a range of benefits including less tissue trauma, preservation of anatomical structures, and faster recovery.4,5 As a less invasive alternative, lateral access surgery strongly avoids the vascular, visceral, and sympathetic risks associated with traditional direct anterior approaches, and the morbidity associated with bone removal, muscle damage, and ligamentous dissection of traditional posterior approaches. This technique has been utilized in a variable number of indications, varying from singlelevel degenerative conditions to multilevel complex deformity corrections, also including the treatment of traumatic fractures, infections, tumor removal, revisions of prior surgeries, and total disc replacement.

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40.2 Evolution of Technique The first description of the technique was presented in Brazil in 2001 on what was then called the LETRA (Lateral Endoscopic Transpsoas Retroperitoneal Approach).6 The procedure involved the use of blunt finger dissection of the retroperitoneal space using tubular portals with endoscopic visualization, but without electromyographic (EMG) monitoring. The first report presented the results of 85 patients and showed a 14% incidence of postoperative psoas weakness and 3.5% incidence of slight thigh atrophy.7 Thereafter, the MaXcess Retractor System (Nuvasive, Inc. San Diego, CA. USA) was developed to overcome the disadvantages of working through tubular portals, generating a direct visualization of the anatomical structures. Also, the EMG nerve monitoring prevented inadvertent pressure on nerves to protect their integrity. Presently, the lateral access surgery is defined as a 90-degree true lateral, retroperitoneal approach to access the anterior column with minimal muscular disruption or trauma to adjacent structures. By using a blunt finger for dissection of the retroperitoneal space and tactile guidance of an initial dilator to the psoas muscle, with subsequent EMG-guidance of the coming dilators through the psoas, it is possible to insert an expandable split-blade retractor system that provides a customizable working channel that provides direct visualization of disc space and placement of a large interbody implant that spans the ring apophysis for maximized correction and greatest biomechanical construction.

40.3 Advantages and Disadvantages Minimally invasive lateral surgery offers an adequate access to the disc space, with the added benefit of reduced iatrogenic injury to abdominal vascular structures (aorta and vena cava), sympathetic plexus (reducing the incidence of retrograde ejaculation), and neural structures (such as the spinal nerves that cross the posterior aspect of the psoas muscle). The technique utilizes tissue dilation through the divulsion of the psoas muscle fibers in an area of approximately 3 cm in diameter. Thus, the procedure realigns the end plates to a horizontal position through bilateral annular release, placement of a large implant across the disc space spanning the ring apophysis, and by ligamentotaxis. The cage insertion also restores disc and foraminal heights, indirectly decompressing the neural elements, and promotes stabilization through an anterior intervertebral fusion.8 In contrast, approaching the L5–S1 level is disadvantageous due to the elevated risk of iliac vessels damage as well as the position of iliac crest in the access pathway that prevents direct approach to this specific disc level.

40.4 Indications and Contraindications The lateral approach was first indicated for the treatment of low back pain associated with degenerative changes above the

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eXtreme Lateral Interbody Fusion L5 level.9 Recently, new indications have emerged, demonstrating that indirect decompression of the neural structures can be achieved by disc height restoration,8 while derotation of the vertebral body and coronal alignment are obtained by ligamentotaxis.10

40.4.1 Patient Selection The lateral approach, with or without posterior supplementation, can be applied to patients who have failed prior decompressive surgery (as in discectomy and/or laminectomy) and require interbody fusion, or in cases of adjacent-level disease after prior fusion surgery, as the scar tissue must limit the ability to safely perform a traditional fusion surgery by the same approach. Other applications of the technique are adjacent-level disease, pseudoarthrosis, trauma, infection, sagittal alignment, and spondylolisthesis.11,12,13,14,15 Revisions of failed interbody fusions or failed lumbar total disc replacements have also been treated using the eXtreme lateral interbody fusion (XLIF) approach for retrieval and revision surgeries.16,17

40.5 Patient Profiles This approach has been used successfully for levels spanning T4–T5 through L4–L5. Approaching the L5–S1 level by means of this technique is not recommended because of the risk of damage to the iliac blood vessels as well as the difficulty of accessing the disc space due to the iliac crest. For the L5–S1 level, patients may benefit from a posterior lumbar interbody fusion (PLIF) or a transforaminal lumbar interbody fusion (TLIF) combined with subsequent posterior decompression and pedicle screw supplementation.18,19

40.6 Preoperative Planning 40.6.1 Physical Examination Physical examination is not different from that performed for all patients with spinal disorders. Spine assessment must include a three-dimensional evaluation of the coronal, sagittal, and spinopelvic parameters, as well as the neurological status.

40.6.2 Radiographic Workup and Preoperative Imaging The initial X-ray workup begins with long-standing posteroanterior and lateral views. A focused lumbar or thoracic view might be helpful to evaluate disc height, disc asymmetry, and lateral listhesis, which are very common in degenerative scoliosis, for example. Also, lateral bending radiographs are used to evaluate the flexibility of the curve. Flexion and extension films can be used, if necessary, to determine the amount of sagittal instability or kyphosis flexibility. A CT myelogram is utilized to evaluate central and foraminal stenosis, while MRI is useful to evaluate disc degeneration and foraminal stenosis, as well as soft tissues. Other ancillary tests such as discography and facet blocks are done to elucidate the pain source.

40.6.3 Instrumentation Notes The instruments necessary for performing the XLIF procedure are as follows: ● MaXcess System of dilators and split-blade retractors (NuVasive, Inc.), which include a bifurcated light cable, articulating arm, retractor system with blades of various lengths, and blade-extension shims. ● NeuroVision System for MaXcess-compatible stimulated and continuous EMG monitoring of nearby nerves (NuVasive, Inc.). ● Set of interbody instruments such as curettes, rongeurs, and dissectors of different sizes (NuVasive, Inc.) ● Xenon light source for attachment to MaXcess bifurcated light cable. ● Radiolucent surgical table with a flexible middle section and rail for articulating arm attachment. ● C-arm fluoroscope and image intensifier.

40.7 Surgical Approach Lateral spine approaches lead to maintenance of the anterior and posterior longitudinal ligaments, which can help correct vertebral rotation and coronal and sagittal deformities, without the risks, comorbidities, and complications related to standard open surgeries.13 For example, in spondylolisthesis, the in-depth discectomy itself partially reduces vertebral slippage. The maintenance of the anterior and posterior portions of the disc, keeping intact the longitudinal ligaments, allows ligamentotaxis, which is partly responsible for slippage reduction.20 Disc height restoration has been proven to indirectly decompress the neural structures, without the need of posterior laminectomy or pedicle screw supplementation, minimizing muscle splitting, blood loss, hospital stay, and operative time, and improving patient’s recovery and satisfaction with the procedure.8,21 Moreover, several clinical reports have emerged demonstrating the safety and effectiveness of the technique in comparison to other conventional surgical approaches, with the same or better clinical and radiological results.14,22,23,24,25,26,27,28,29,30

40.7.1 Surgical Technique Patient Preparation In the preoperative room, the patient is linked to the EMG monitoring, which is mandatory in safely traversing the psoas muscle, avoiding the lumbar plexus that passes within it. Four muscle groups per side are monitored using the EMG system. These four muscles are easily palpated and represent spinal nerve distributions from L2 to S2: the vastus medialis, the anterior tibialis, the biceps femoris, and the medial gastrocnemius (▶ Fig. 40.1). A reference electrode is also placed on the upper lateral thigh, and an anode return electrode is placed superior to the operative site, for example, on the latissimus dorsi muscle. Proper skin preparation must be performed to ensure good electrical conductivity. This entails cleaning the electrode site and applying a light abrasive to remove dead skin cells. Electrodes are placed in pairs by simply removing the adhesive backing and applying to the skin. Electrical conductivity can be measured with a handheld impedance meter. These surface electrodes are connected to the system by snap-on

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RIGHT

LEFT

LEFT

BLUE Vastus medialis Channel 1 L2, L3, L4

RED Vastus medialis Channel 1 L2, L3, L4

YELLOW Biceps femoris Channel 3 L5, S1, S2

GRAY Biceps femoris Channel 3 L5, S1, S2

VIOLET Tibialis anterior Channel 2 L4, L5

ORANGE Tibialis anterior Channel 2 L4, L5

GREEN Medial gastrocnemius Channel 4 S1, S2

WHITE Medial gastrocnemius Channel 4 S1, S2

ANTERIOR

POSTERIOR

RIGHT

Fig. 40.1 Placement of recording electrodes for NeuroVision electromyographic monitoring.

Fig. 40.2 Lateral decubitus positioning of the patient with elongation of the space between the ribs and iliac crest by positioning the patient slightly flexed over the bent table. The patient is also taped just below the iliac crest (a) over the thoracic region (b) and from the greater trochanter to the knee (c). The patient is then secured to the table with padding placed between knees and taped from the table to the knee, past the ankle (d) and secured to the table.

cables that can be threaded under or through small holes in compression stockings.

Patient Positioning The surgical table must be radiolucent because of the fluoroscopic imaging that is mandatory for the safety of the procedure. General anesthesia is administered, and the patient is placed in lateral decubitus position at a 90-degree angle to the table (▶ Fig. 40.2). It is critical that the patient be maintained in this position to ensure that the disc is being accessed truly laterally and instruments are not displaced anteriorly or posteriorly. The surgical table must be bent, with the patient’s iliac crest taped

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securely and used as a fulcrum, thereby increasing the distance between the iliac crest and ribs, providing full access to the spine. The left arm is then supported in a sling. Fluoroscopic images should be obtained to confirm a true lateral 90-degree position.

Skin Incision and Retroperitoneal Dissection After skin asepsis, a mark is made on the patient’s upper lateral side, overlying the area to be accessed. The exact location of the mark is guided via fluoroscopy with the use of two Kirschner’s wires held over the skin to target the disc being approached (▶ Fig. 40.3a). One line is drawn in an anteroposterior direction, over the center of the index level. Another line is drawn in a

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eXtreme Lateral Interbody Fusion

Fig. 40.3 (a) Fluoroscopic localization of the lateral incision site. Operative target is the center of the intervertebral disc. (b) Skin markings show the correct incision site for dilators insertion and initial retroperitoneal finger dissection.

Fig. 40.4 Retroperitoneal finger dissection. (a) Blunt approach to the retroperitoneal space through the layers of the lateral musculature. (b) Sweeping of the retroperitoneal space both deep and back toward the direct lateral incision site.

superoinferior direction, crossing the center of the adjacent vertebral bodies. The skin incision is made at the intersection of markings, and through this opening the initial dilator will be inserted. It is indicated to mark the anterior and posterior limits of the vertebral body, for better visualization (▶ Fig. 40.3b). A second incision is made into the fascia or into the skin posterior to the initial incision for the guidance of the initial dilators accomplished by the surgeon’s index finger (▶ Fig. 40.4a). The layers of the lateral abdominal muscles are identified and opened in sequence (external oblique, internal oblique, transversus, and transversal fascia) until the retroperitoneal fat is reached. This dissection is performed with the help of scissors and by palpating the muscle layers at each level. After accessing the retroperitoneal space, the index finger is used to dissect through the retroperitoneal fat, sweeping the finger both deep and back up toward the skin (▶ Fig. 40.4b), opening the retroperitoneal space above the psoas muscle. Special care should be taken to avoid perforating the peritoneum. Placement of the

first dilator over the psoas muscle is guided by the surgeon’s index finger, which is already in the retroperitoneal space, to avoid injuring vascular or intestinal tissues (▶ Fig. 40.5a). The dilators reach the portion of the psoas muscle overlying the disc space to be operated on. To confirm this position, anteroposterior and lateral fluoroscopy are performed (▶ Fig. 40.5b,c). Once the disc is reached, another confirming fluoroscopic image is obtained and the position is held by placing a Kirschner wire through the initial dilator into the disc space. After confirmation of the proper positioning of the wire, the delicate sequence of dilators may be introduced through the psoas fibers, using neural guidance attached to the dilators for evoked EMG monitoring of relative distance of nerves (▶ Fig. 40.5d). EMG guidance must confirm that the nerves are posterior to the dilators. It is important to rotate the dilators into position to determine not just proximity, but also the relative direction of nerves. A mark at the proximal end of the dilator corresponds to the location of an isolated electrode at the distal end. If low thresholds are found,

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Fig. 40.5 Access to the disc space. (a) Retroperitoneal finger gently guides the initial dilator to the surface of the psoas muscle, protecting the peritoneum from impingement. (b,c) Placement of the initial dilator over the disc is confirmed by fluoroscopy in both lateral and anteroposterior views. (d) The initial dilator is connected to the electromyographic (EMG) monitoring before advancement through the psoas muscle. Low EMG thresholds indicate nearby nerves; higher thresholds indicate safe distance from nerves. Markings on the initial dilator indicate the size of the appropriate length blades to be attached to the retractor.

Fig. 40.6 (a) An articulating arm is attached to the retractor at the posterior blade and to the table, holding the retractor in place and preventing posterior excursion of the working portal during aperture, protecting the nerves within psoas muscle from injury. (b) Lateral fluoroscopy evidencing the proper positioning of the retractor. (c) Direct visualization of the disc space provided by the opening of the working portal.

the dilator should be moved slightly farther away from the direction of the nerve until higher thresholds are achieved. Both anteroposterior and lateral fluoroscopy should be used to ensure correct targeting of the disc space. This tissue dilation process produces only fiber divulsion of the psoas muscle and minimizes the potential transitory psoas weakness.31 Thereafter, larger dilators are then introduced, gradually and bluntly spreading the psoas muscle until the expandable

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retractor is inserted, which can be selectively adjusted to the desired aperture size and shape. The retractor is connected to the suspension arm to prevent unwanted movement (▶ Fig. 40.6a). This arm is attached to the posterior blade of the retractor, preventing expansion posteriorly and thereby protecting the nerves in the posterior region of the psoas muscle from compression injury. A bifurcated light cable is attached to the retractor for an optimal visualization of the exposure. This approach allows a direct

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eXtreme Lateral Interbody Fusion

Fig. 40.7 (a) Lateral fluoroscopic view showing a long implant device that provides optimal surface area for fusion. (b) Anteroposterior view showing the anterior placement of the cage that reaches the ring apophysis generating greater biomechanical support and stability.

view of the disc space without the need of magnifying glasses or endoscopic camera for disc space preparation and implant/graft placement (▶ Fig. 40.6b,c).

Disc Space Preparation With the working portal in place, the remainder of the surgery is conventional—disc removal, end plate preparation, and implant insertion. Any tissue debris on the lateral surface of the disc is retracted or coagulated. The disc annulus is opened, and the nucleus pulposus is removed with rongeurs. The disc space must be prepared appropriately for fusion, including meticulous preparation of the disc space with removal of all disc material and scraping of the cartilaginous end plates, which may hinder the fusion between the implant and the vertebral bodies. A Cobb elevator can be used to disrupt the contralateral annulus, which enables parallel end plate distraction and placement of a large implant to the far side of the ring apophysis.

Device Implantation After proper discectomy, the device is ready to be inserted. Initially, the adjacent vertebrae are distracted and the dimensions of the implant are determined by inserting a series of templates to find out the better cage that will generate proper correction. The implant is introduced from a lateral direction into the disc space. This entire process is guided by fluoroscopic imaging. A larger implant that expands across the disc space provides end plate coverage on the periphery of the ring apophysis, enhancing biomechanical support, allowing stand-alone constructions in a large series of cases20,23,24,32 (▶ Fig. 40.7). Implants must be filled with cancellous bone graft from the iliac crest, bone morphogenetic protein, or any osteoinductive agent of choice.

Postoperative pain and somatosensory symptoms tend to be minimal, and the majority of patients are discharged after only an overnight hospital stay.26 Painful dysesthesias and motor disturbance are rare, but possible. In these cases, a CT scan is recommended to rule out a psoas hematoma. If a hematoma is found, draining it should improve symptoms. All these side effects can be minimized through gentle muscle manipulation during psoas traverse, with the use of EMG guidance and careful nerve retraction when necessary.

40.9 Management of Complications Literature evidences low rates of complication at the postoperative period, which includes hip flexion weakness or numbness ipsilateral to the surgical approach (psoas weakness) and, less frequently, sensory changes in the lower limb; all of them resolved within 6 months.13,29,33 Transient plexopathies (motor or sensory) and hip flexor weakness are the most commonly reported complication associated with lateral access surgery.34,35 Psoas access is obviously the cause of hip flexor weakness in the absence of neurological injury. Thus, inhibition of the muscular contraction is expected postoperatively even without any intraoperative neural damage. Subsidence is another complication found in anterior lumbar interbody fusion. In lateral access, it is usually related to standalone constructs, and has been correlated to instability at the index level.36 The implantation of wider interbody spacers by lateral approach has been shown to maximize end plate support with a lower incidence of severe cage subsidence, preventing acute pain onset, and preserving surgical achievements.32

Closure

40.10 Clinical Cases

After device insertion, the retractor is closed and removed slowly to observe the psoas muscle and confirm hemostasis. Deep layers and skin are sutured in a standard fashion.

A 47-year-old man with a history of back pain 5 years prior to presentation, with worsening of symptoms during the last 1 year. Currently, the patient complains of back pain, being unable to stand for 15 minutes or longer (visual analogue scale [VAS] for back pain: 10), in addition to failed nonoperative treatment. On clinical examination, he presents with no neurological deficits, but with severe sitting and standing intolerance. Imaging studies have shown loss of disc height at L4–L5 without instability, with presence of sclerotic bone at both superior and inferior end plates

40.8 Postoperative Care Patients should be encouraged to walk on the same day to accelerate their recovery and muscle function, also avoiding deep venous thrombosis and pulmonary thromboembolism.

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Fig. 40.8 (a) Preoperative anteroposterior (AP) X-ray showing disc collapse at L4–L5. (b) Lateral X-ray showing loss of disc height and sclerotic bone lesions at both superior and inferior end plates at L4–L5. (c,d) Dynamic X-rays showing no instability at L4–L5 that enables a stand-alone construction. (e) Sagittal MRI in T1 (right) and T2 (left) evidencing degenerative changes at the intervertebral disc at L4–L5, with disc bulging and Modic changes type II at both end plates. (f) Axial MRI confirming central and bilateral stenosis at L4–L5. (g,h) AP and lateral X-rays 12 months after surgery showing gain in disc height and bone formation within the cage in a stand-alone construction. (i) CT scan confirming solid fusion 12 months after surgery.

(▶ Fig. 40.8a–d). Also, on T2 sagittal MRI, it is possible to see a L4–L5 disc bulging narrowing the central canal, besides Modic type II changes on both superior and inferior end plates (▶ Fig. 40.8e). On axial view, the central canal, as well as bilateral foraminal stenosis, was confirmed (▶ Fig. 40.8f). The patient underwent lateral access surgery for lumbar discectomy and fusion, without the need of pedicle screw supplementation (▶ Fig. 40.8g,h). The surgery was performed in 40 minutes with less than 50 mL of blood loss, and the patient was discharged 24 hours after surgery without complications. The patient was last seen at the 12-month follow-up visit, presenting resolution of symptoms with only little discomfort during sitting or standing for long periods. At CT scan, it is possible to see solid fusion at the index level (▶ Fig. 40.8i).

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40.11 Conclusion The results found in the literature have shown that the technique is feasible, safe, and effective for the treatment of several pathologies at the thoracolumbar spine. The complication rates are lower than traditional surgery. Psoas weakness is the most common complication and is resolved within 6 months. This technique has been successfully performed aiming to achieve spinal fusion through a minimally invasive lateral approach, decreasing pain, indirectly decompressing neurological structures as it restores disc height, reducing vertebral slippage in spondylolisthesis, and stopping the curve progression in coronal spinal deformity, which makes the lateral approach a favorable alternative for thoracolumbar access surgery.

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eXtreme Lateral Interbody Fusion

Clinical Caveats ●

●

●

●

When positioning the patient and throughout the procedure, it is critical to maintain a 90-degree position, which helps ensure proper disc space access and correct placement of instruments. Initial dissection with the index finger should be done in a careful manner to avoid perforation of the peritoneum. During the procedure, fluoroscopic images are necessary to ensure appropriate level and instrument trajectory and placement. Postoperative rehabilitation conditioning of the psoas muscle is conducted to reduce transitory psoas weakness.

References [1] Dunn KM, Hestbaek L, Cassidy JD. Low back pain across the life course. Best Pract Res Clin Rheumatol. 2013; 27(5):591–600 [2] Golob AL, Wipf JE. Low back pain. Med Clin North Am. 2014; 98(3):405–428 [3] Benz RJ, Garfin SR. Current techniques of decompression of the lumbar spine. Clin Orthop Relat Res. 2001(384):75–81 [4] Arts M, Brand R, van der Kallen B, Lycklama à Nijeholt G, Peul W. Does minimally invasive lumbar disc surgery result in less muscle injury than conventional surgery? A randomized controlled trial. Eur Spine J. 2011; 20(1):51–57 [5] McAfee PC, Phillips FM, Andersson G, et al. Minimally invasive spine surgery. Spine. 2010; 35(26) Suppl:S271–S273 [6] Pimenta L. Lateral Endoscopic Transpsoas Retroperitoneal Approach for Lumbar Spine Surgery. Minas Gerais, Brazil: Belo Horizonte; 2001 [7] Pimenta L, Figueiredo F, DaSilva M, McAfee P. The Lateral Endoscopic Transpsoatic Retroperitoneal Approach (LETRA): A New Technique for Accessing the Lumbar Spine. AANS/CNS Joint Section on Disorders of the Spine and Peripheral Nerves, San Diego, CA, March 17–20, 2004 [8] Oliveira L, Marchi L, Coutinho E, Pimenta L. A radiographic assessment of the ability of the extreme lateral interbody fusion procedure to indirectly decompress the neural elements. Spine. 2010; 35(26) Suppl:S331–S337 [9] Ozgur BM, Aryan HE, Pimenta L, Taylor WR. Extreme Lateral Interbody Fusion (XLIF): a novel surgical technique for anterior lumbar interbody fusion. Spine J. 2006; 6(4):435–443 [10] Castro C, Oliveira L, Amaral R, Marchi L, Pimenta L. Is the lateral transpsoas approach feasible for the treatment of adult degenerative scoliosis? Clin Orthop Relat Res. 2014; 472(6):1776–1783 [11] Mundis GM, Akbarnia BA, Phillips FM. Adult deformity correction through minimally invasive lateral approach techniques. Spine. 2010; 35(26) Suppl: S312–S321 [12] Isaacs RE, Hyde J, Goodrich JA, Rodgers WB, Phillips FMA. A prospective, nonrandomized, multicenter evaluation of extreme lateral interbody fusion for the treatment of adult degenerative scoliosis: perioperative outcomes and complications. Spine. 2010; 35(26) Suppl:S322–S330 [13] Marchi L, Oliveira L, Amaral R, et al. Anterior elongation as a minimally invasive alternative for sagittal imbalance-a case series. HSS J. 2012; 8(2):122–127 [14] Amaral R, Marchi L, Oliveira L, et al. Minimally invasive lateral alternative for thoracolumbar interbody fusion. Coluna/Columna. 2011; 10(3):239–243 [15] Patel VC, Park DK, Herkowitz HN. Lateral transpsoas fusion: indications and outcomes. Sci World J. 2012; 2012:893608

[16] Pimenta L. Removal of a keeled TDR prosthesis via a lateral transpsoas retroperitoneal approach. Proceedings of the twenty second annual meeting of the North American Spine Society, Austin, TX, 2007 [17] Pimenta L, Díaz RC, Guerrero LG. Charité lumbar artificial disc retrieval: use of a lateral minimally invasive technique. Technical note. J Neurosurg Spine. 2006; 5(6):556–561 [18] Karikari IO, Isaacs RE. Minimally invasive transforaminal lumbar interbody fusion: a review of techniques and outcomes. Spine. 2010; 35(26) Suppl: S294–S301 [19] Brislin B, Vaccaro AR. Advances in posterior lumbar interbody fusion. Orthop Clin North Am. 2002; 33(2):367–374 [20] Marchi L, Abdala N, Oliveira L, Amaral R, Coutinho E, Pimenta L. Stand-alone lateral interbody fusion for the treatment of low-grade degenerative spondylolisthesis. Sci World J. 2012; 2012:456346 [21] Rodgers WB, Gerber EJ, Patterson J. Intraoperative and early postoperative complications in extreme lateral interbody fusion: an analysis of 600 cases. Spine. 2011; 36(1):26–32 [22] Dakwar E, Cardona RF, Smith DA, Uribe JS. Early outcomes and safety of the minimally invasive, lateral retroperitoneal transpsoas approach for adult degenerative scoliosis. Neurosurg Focus. 2010; 28(3):E8 [23] Marchi L, Oliveira L, Amaral R, et al. Lateral interbody fusion for treatment of discogenic low back pain: minimally invasive surgical techniques. Adv Orthop. 2012; 2012:282068 [24] Oliveira L, Marchi L, Coutinho E, Abdala N, Pimenta L. The use of rh-BMP2 in Standalone eXtreme Lateral Interbody Fusion (XLIF®): Clinical and Radiological Results After 24 Months Follow-up. WSCJ. 2010; 1(1):19–25 [25] Ozgur BM, Agarwal V, Nail E, Pimenta L. Two-year clinical and radiographic success of minimally invasive lateral transpsoas approach for the treatment of degenerative lumbar conditions. SAS J. 2010; 4(2):41–46 [26] Pimenta L, Marchi L, Oliveira L, Coutinho E, Amaral R. A prospective, randomized, controlled trial comparing radiographic and clinical outcomes between stand-alone lateral interbody lumbar fusion with either silicate calcium phosphate or rh-BMP2. J Neurol Surg A Cent Eur Neurosurg. 2013; 74(6):343–350 [27] Pimenta L, Pesántez CFA, Oliveira L. Silicon matrix calcium phosphate as a bone substitute: early clinical and radiological results in a prospective study with 12-month follow-up. SAS J. 2008; 2(2):62–68 [28] Rodgers W, Cox C, Gerber E. Minimally invasive treatment (XLIF) of adjacent segment disease after prior lumbar fusions. Internet J Minim Invasive Spinal Technol. 2008; 3(4):1–7 [29] Rodgers WB, Cox CS, Gerber EJ. Early complications of extreme lateral interbody fusion in the obese. J Spinal Disord Tech. 2010; 23(6):393–397 [30] Rodgers WB, Gerber EJ, Rodgers JA. Lumbar fusion in octogenarians: the promise of minimally invasive surgery. Spine. 2010; 35(26) Suppl:S355–S360 [31] Ahmadian A, Deukmedjian AR, Abel N, Dakwar E, Uribe JS. Analysis of lumbar plexopathies and nerve injury after lateral retroperitoneal transpsoas approach: diagnostic standardization. J Neurosurg Spine. 2013; 18(3):289–297 [32] Pimenta L, Turner AWL, Dooley ZA, Parikh RD, Peterson MD. Biomechanics of lateral interbody spacers: going wider for going stiffer. Sci World J. 2012; 2012:381814 [33] Rodgers WB, Cox C, Gerber E. Experience and early results with a minimally invasive technique for anterior column support through eXtreme Lateral Interbody Fusion (XLIF®). US Musculoskelet Rev. 2007; 2:28–32 [34] Cummock MD, Vanni S, Levi AD, Yu Y, Wang MY. An analysis of postoperative thigh symptoms after minimally invasive transpsoas lumbar interbody fusion. J Neurosurg Spine. 2011; 15(1):11–18 [35] Le TV, Burkett CJ, Deukmedjian AR, Uribe JS. Postoperative lumbar plexus injury after lumbar retroperitoneal transpsoas minimally invasive lateral interbody fusion. Spine. 2013; 38(1):E13–E20 [36] Marchi L, Abdala N, Oliveira L, Amaral R, Coutinho E, Pimenta L. Radiographic and clinical evaluation of cage subsidence after stand-alone lateral interbody fusion. J Neurosurg Spine. 2013; 19(1):110–118

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41 Trans-sacral Approach William D. Tobler Abstract This chapter highlights the features of this distinctive surgical approach (trans-sacral approach) for lumbar fusion. Its anatomic corridor in the presacral space provides a unique access to the spine. The surgeon prepares the disc space with looped/flat cutters using fluoroscopic guidance and the biomechanics for the fixation device use a novel large threaded rod for one- or two-level fusions. Initially, some of these unique features became a barrier to its adoption, and publicized complications led to concerns about overall safety. Subsequently, refinements in patient selection and technique strategies achieved satisfactory outcomes. The trans-sacral fusion is minimally invasive, offering a sound option for select patients who have degenerative disc disease, multiple recurrent disc herniations, or spondylolisthesis. The chapter details its benefits (e.g., patient prone requires no repositioning, no access surgeon needed, preservation of muscles or supporting ligaments, superior stabilization, suitable for obese patients) and disadvantages (e.g., unrecognized bowel perforation, interspace distraction, and lordosis). A well-illustrated step-by-step guide leads the reader with tips for patient selection, preoperative imaging and examination, surgical technique from incision to closure, and complication management. Case examples discuss the principles for successful presacral interbody lumbar fusion. With specialized training, this presacral technique should be an option for surgeons dedicated to minimally invasive spine fusion. Keywords: lumbar interbody fusion, AxiaLIF, presacral approach, minimally invasive fusion, surgical technique, patient selection, two-level presacral approach

41.1 Introduction The trans-sacral (or presacral) approach is a minimally invasive surgical technique to achieve lumbar interbody fusion at L5–S1, or both L4–L5 and L5–S1. Using the unique trans-sacral access to the L5–S1 disc, the surgeon crosses through the space anterior to the sacrum, starting distally at the tip of the coccyx, and enters the sacrum at the S1–S2 junction to access the interspace in an axial plane (▶ Fig. 41.1). This new operation was introduced as a one-level device in 2005 with Food and Drug Administration clearance for use at L5–S1.1,2 Its initial FDA clearance also required stabilization posteriorly with facet or pedicle screws; clearance has not yet been obtained for the two-level device. This new trans-sacral operation introduced features distinct from any other interbody surgical approach. First, the anatomic corridor in the presacral space provides access to the spine previously not used for interbody fusion.3,4,5 Second, the methodology of interspace preparation uses looped/flat cutters to remove the disc, without direct visualization of the interbody space by the surgeon (▶ Fig. 41.2). Third, the biomechanics of the fixation device itself are unique: this large threaded rod crosses through the disc space oriented vertically aligned with the axis of the spine, starting at the sacral interface and extending across L5–S1 into L5. In cases of a two-level fusion, a longer device also crosses the L4–L5 interspace, extending up to the L4 vertebra. Some of these unique features of the presacral approach at times became a barrier to its adoption. The technique was unfamiliar to surgeons, and publicized complications led to concerns about its overall safety.6,7,8 Fusion outcomes have been

Fig. 41.1 Axial lumbar interbody fusion (AxiaLIF) corridor of approach. (a) Approach begins adjacent to the coccyx, moves midline along the avascular sacrum through the presacral fat to access the sacral promontory, and continues trans-sacral through bone to the L5–S1 disc space. (b) Titanium rod is composed of three parts: the S1 segment, inner distraction collar, and tapered L5 segment. When inserted, the distraction rod is adjusted to restore the height of the disc space and indirectly decompresses the neural foramen. (c) Facet screws inserted percutaneously achieve a 360°-stabilization of the motion segment. (Reproduced with permission of Mayfield Clinic.)

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Trans-sacral Approach

Fig. 41.2 (a) Loop cutters to debulk nucleus and lightly abrade end plates. (b) Brushes to evacuate the disc material. (c) Flat cutters designed to debulk nucleus in tight disc spaces (< 2.5 mm). (d) End plate rasps to lightly abrade end plates. (Reproduced with permission of Quandary Medical.)

controversial, perhaps not well understood, or sometimes studied inadequately. Several studies reporting poor outcomes fueled apprehensions about the approach itself (especially the two-level technique) when, in fact, these outcomes were possibly related to poor surgical technique.9,10 Subsequently, others refined patient selection and technique strategies, and satisfactory outcomes after the presacral two-level fusion also followed.3,11,12,13

41.1.1 Advantages The presacral technique provides unique benefits and advantages compared with other traditional methods of lumbar fusion at L5–S1. First, its anterior approach to the interbody at L5–S1 gives access to the disc space anterior to the sacrum and is achievable with the patient positioned prone. This is an advantage when compared with the typical anterior lumbar interbody fusion (ALIF) with its transabdominal approach to L5–S1. Unlike the two-stage positioning for the ALIF (i.e., supine for the initial part of the procedure and repositioned prone for posterior stabilization), the presacral approach requires no repositioning. Second, unlike the typical ALIF, no access surgeon is needed for the presacral approach. Third, in contrast with the opening and retraction of the abdominal wall musculature for ALIF, no muscles or supporting ligaments are divided with the presacral approach. Unlike the traditional transforaminal lumbar interbody fusion (TLIF) or posterior lumbar interbody fusion (PLIF) approaches, the surgeon performing a presacral approach does not disturb, manipulate, or retract the dural sac or the exiting and traversing nerve roots when preparing the disc space and inserting the interbody fixation device.14 The biomechanics of the presacral device offer advantages of initial superior stabilization over other techniques using interbody devices. Patients with a spondylolisthesis and high pelvic incidence face a high risk of construct failure because of the strong shear-force vector acting against the fixation of spinal fusion; most interbody devices are wedged into the disc space and do not provide resistance against such forces.15,16,17

Finally, the presacral fusion technique can be suitable for obese patients; this is unlike the greater technical challenges of exposing the spine during anterior or posterior approaches when division through deep layers of soft tissues is needed. With higher obesity, these surgical procedures (ALIF and TLIF) become increasingly difficult and thus pose higher risks for patients, whereas the presacral approach does not. Rather, the distance from the tip of the coccyx/entry point to the L5–S1 disc space does not adversely change in obese patients. In fact, the procedure can actually be easier to perform in overweight patients who were not candidates to undergo other traditional approaches. For example, obese patients typically have a large presacral fat pad, which makes access safer because the rectum is not too close to the sacrum.

41.1.2 Disadvantages Concerns about protecting the rectum have been the perceived disadvantages of the procedure. However, careful technique and evaluation of the rectum before and after the presacral approach have reduced the risk of unrecognized bowel perforation to very low rates.6,8,18 Another potential disadvantage of the device concerns interspace distraction and lordosis. The original device was engineered with the capability to distract the interspace when inserted. Differential thread counts on the L5 and S1 segments of the rod utilized a reverse Herbert method. The distracting force of the threaded device required a strong bone–device interface that often failed, especially in patients with osteopenia, leading to subsidence and failure to maintain distraction. Creation of lordosis is possible with the presacral device, but not predictable. Therefore, the presacral approach should not be used in a patient with significant positive sagittal balance that requires interbody fusion and significant restoration of lordosis at L5–S1.

41.1.3 Evolution of the Technique The second-generation presacral device incorporated improvements that resolved the stresses placed on the vertebral end

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Surgical Techniques plates imposed by the original design’s reverse Herbert technique. This newer modular design consists of L5 and S1 segments and an inner threaded collar that are assembled before insertion (see ▶ Fig. 41.1). Distraction of the interspace occurs after the device is advanced and positioned across the disc space. A torque rod is inserted into the second-generation device, and the inner collar is maximally extended to distract the space. With additional refinement, the upper end of the device is now tapered. Application of a porous bead coating has improved fixation and promoted arthrodesis. Introducing these changes subsequently eliminated the radiographic halo effect seen around the upper end of the L5 rod, which was often mistaken on X-ray and CT imaging for loosening of the device or pseudarthrosis.

A presacral access kit was introduced to protect the bowel. This inflatable, soft plastic mattress can be advanced into the presacral space and inflated with saline to create a barrier between the instrumentation and retroperitoneal contents during the procedure (▶ Fig. 41.3). A soft rubber gasket is added to the tip of the exchange cannula; this large-diameter tube is required to advance the device into the spine. The rubber gasket forms a soft seal at the distal sacrum; fixed with two small Steinmann pins, it stabilizes the exchange cannula during device insertion and prevents any soft tissue (e.g., rectum) from becoming entrapped inside it. Evaluation of the bowel integrity is encouraged before and after the approach. Injecting air into the bowel before the procedure locates the position of the rectum in the surgical position. After

Fig. 41.3 Presacral access. (a) Begins with blunt dissection to free Waldeyer’s fascia. (b) Presacral access kit is inserted against the sacral surface. Inflation with saline forms a mattress-like device to deflect soft tissues away from the sacrum, making a protective barrier between the bowel and instruments. Fluoroscopic image shows the deployed protective access kit. (Reproduced with permission of Quandary Medical.)

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Trans-sacral Approach the procedure, saline can be injected and aspirated from the rectum; any blood found in the aspirate raises a concern for a bowel perforation. Injected contrast into the rectum at the close of the procedure can demonstrate a fistula. Finally, a rigid scope can be inserted in the rectum to directly inspect the rectal wall. These various options, in conjunction with meticulous surgical technique, can reduce the incidence of bowel perforation to less than 1%.18 Intraoperative identification and immediate repair of a perforation can prevent infection and eliminate the need for colostomy.

patients at risk of osteoporosis. However, dual energy X-ray absorptiometry (DEXA) scan results do not always correlate with the hardness of the shell of the bone, which is necessary for fixation of the implant. As in any surgical planning, medical evaluation will identify any other medical contraindications to a surgical procedure.

Patient Profiles

This surgical procedure is indicated for a lumbar fusion at L5– S1 or L4–L5 and L5–S1, typically in skeletally mature patients who have degenerative disc disease, multiple recurrent disc herniations, or spondylolisthesis. The classic course is at least 6 to 12 months of symptoms that fail to respond to or be managed by therapy, anti-inflammatory agents and injection therapy, and lifestyle modification. Most patients who have undergone hysterectomies or bladder or other abdominal surgeries that do not violate the presacral space can also undergo the presacral approach. Contraindications include significant scarring in the presacral space that makes mobilization of the rectum and soft tissues impossible. Other contraindications are after surgical intervention or radiotherapy in the presacral space, and in cases of significant inflammatory bowel disease.6,19

Ideal candidates for a presacral fusion have a modest build, low pelvic incidence, and a classic-shaped sacrum. In patients with degenerative disc disease undergoing the presacral fusion, Modic end plate changes without spondylolisthesis represent the best case for good outcomes and minimal technical challenges. Although grade I or II spondylolisthesis is a more difficult scenario, patients can usually achieve excellent technical results. However, a grade III or higher spondylolisthesis is far more difficult; the procedure is only recommended if the slip can be reduced intraoperatively to obtain the required alignment and trajectory before final placement of the presacral device. This can be accomplished in most cases with posterior osteotomies and the powerful reduction capabilities of most pedicle screw systems. With the patient positioned prone, the surgeon can simultaneously perform portions of the presacral procedure and the posterior portion to achieve reduction of the spine. The presacral approach may be contraindicated for spondylolisthesis that does not spontaneously reduce or cannot be surgically reduced; in these cases, the rod would advance too posteriorly at L5 and could be misdirected into the spinal canal (▶ Fig. 41.4d).

41.3 Preoperative planning

41.3.2 Physical Examination

41.3.1 Patient Selection

There are no special aspects during the patient’s physical examination before a presacral fusion. Complete musculoskeletal and neurological examinations are required. Gait observation is extremely important to evaluate sagittal balance. Of note, 1 week before the procedure, patients should discontinue all nonsteroidal anti-inflammatory drugs (NSAIDs), antiplatelet agents, minerals, and vitamin supplements.

41.2 Indications and Contraindications

Potential candidates for interbody fusion at L5–S1 or L4–L5 and L5–S1 can be evaluated for the presacral approach. When the usual conservative measures fail, MRIs of the lumbar spine and pelvis as well as standing lateral/flexion–extension X-rays are routinely obtained. Bone density studies are important for

Fig. 41.4 Sacral anatomy and trajectory evaluation. (a) Typical sacrum and the trajectory for the approach perpendicular to the angle of the S1 end plate (red line). (b) Illustration of the optimal zone (green) for placement of the axial rod and the entry point relative to the sacrococcygeal ligament and coccyx. (c) A hooked or hyperlordotic sacral curve has an unsatisfactory trajectory that would result in axial rod placement in the spinal canal; this is unsuitable for presacral fusion. (d) The template used to plan for a two-level trajectory through S1–L5–L4. (Reproduced with permission of Mayfield Clinic.)

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41.4 Radiographic Workup and Preoperative Imaging Once the decision has been made for spinal fusion, consideration of the presacral approach requires evaluation of the presacral space (see ▶ Fig. 41.4). Standing lumbar films with exposure to the tip of the sacrum establish the extent of the patient’s lordosis and define the sacral morphology. Evaluation of the lumbosacral anatomy is required for trajectory planning, especially when considering a two-level presacral fusion. An MRI of the entire presacral space will show any unexpected pathology (e.g., neoplasm), and more importantly, define the vascular anatomy of the iliac vessels. Confirmation that there is no vascular anomaly is extremely important, particularly an aberrant iliac vein at the S1–S2 junction. This junction is the typical entry point into the sacrum. The small subperiosteal veins often seen in the sacrum are not problematic. Important image sequences are sagittal and parasagittal T2-weighted images and axial T2 images from the L5–S1 disc down to at least the midportion of the sacrum (see ▶ Fig. 41.4). The presence and thickness of the presacral fat pad can be identified on the T2-weighted sagittal image. Of note, absence of a presacral fat pad in a thin person does not contraindicate the surgery; this space devoid of fat will be dissected open early in the procedure. Overlaying a template onto the X-ray or MRI helps depict the trajectory. Using a straight rod or pin, examine the path from the tip of the coccyx to the midportion of the L5–S1 disc to determine if the procedure is feasible. Templating for a two-level procedure is even more critical because of the longer device used (see ▶ Fig. 41.4d). Additionally, if a patient appears to have a sagittal imbalance issue, complete scoliosis films are indicated.

41.4.1 Instrumentation Notes The inflatable part of the presacral access kit (described earlier) may be inserted to protect the working corridor. A series of long instruments and tubes advanced to the spine include sequential dilators up to 12-mm diameter. Once the disc space is accessed, nitinol-looped cutters and firm flat cutters are used for the discectomy, and soft wire brushes evacuate the disc material (see ▶ Fig. 41.3). Finally, a large exchange cannula will help safely advance the presacral rod into position. After packing grafting material into the disc space using a beveled bone graft inserter, the surgeon will use a series of bone drills and trilator to compress and compact the bone in the L5 vertebra where the rod is advanced.

41.5 Trans-sacral Approach With the patient prone on the operating table with legs spread apart, positioning is directed toward maximizing lordosis at L5–S1. A 3-inch strip of silk tape on each buttock will provide lateral retraction of each side. A plastic adherent barrier is draped just above the anus. A rectal catheter inserted into the rectum remains in place during the procedure.20

41.5.1 Surgical Technique Fluoroscopy Setup Two fluoroscopy units are preferred: one is placed across from the operating surgeon for lateral views and the other is set up at a 45-degree angle on the same side as the surgeon for the anteroposterior images (▶ Fig. 41.5). Air can be injected to outline the position of the rectum before sterile prep.

Fig. 41.5 Operating room set up for a presacral fusion. (a) Patient position and draping. (b) Room set up with two fluoroscopy units positioned in the anteroposterior (AP) and lateral projections. (Reproduced with permission of Mayfield Clinic.)

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Trans-sacral Approach

Making the Incision

Measuring and Placing the Interbody Device

With completion of the routine prep of the entire operative field, including the lumbar region, a 20-mm incision is made in the paracoccygeal area, preferably on the right side. The incision, off the midline at the tip of the coccyx, can be left or right sided depending on the surgeon’s preference. The trajectory will be just inferior to the sacrococcygeal ligament. Plunging too deeply with a knife or Bovie can lacerate the rectum, which is superficial at this level. Waldeyer’s fascia, deep to the subcutaneous layer, can usually be bluntly opened by finger dissection on entering the presacral space (see ▶ Fig. 41.3). With its oily texture, the periosteum on the sacrum is easily identified. Once the space is opened, the presacral access kit can be placed and inflated with saline.

After the disc is packed, a small drill is advanced to the L5 end plate and the cortex is drilled open. A trilator (blunt measuring rod), advanced partially into the L5 vertebra, compacts the bone around the L5 channel rather than drilling it out (see ▶ Fig. 41.6d). Measurements taken from this rod will determine the lengths of the L5 and S1 segments of the device; the device is assembled before insertion. After the 12-mm cannula is removed, the larger two-piece inner and outer exchange cannula is advanced to the sacrum and secured with two Steinmann pins, thus securing the exchange cannula to the sacrum. The inner cannula of the exchange cannula is removed and the larger Steinmann pin is left in place. The preassembled device is advanced along the Steinmann pin into the sacrum, across the L5–S1 disc and into the L5 vertebra. The ideal position of the distal tip is three-fourths of the distance from the L5 end plate at L5–S1 toward the end plate at the top of L5 at the L4–L5 disc space. A small portion of the proximal rod should protrude from the sacrum. After device placement, the antitorque and torque rods are inserted into it. Distraction of the disc space can be completed by rotating the torque wrench and visualizing distraction on the fluoroscope. After the torque rods are removed, insertion of a locking pin completes the procedure.

Accessing and Preparing the Disc Space The guide probe is advanced to the entry point usually at the L5–S1 interspace as identified on fluoroscopy. A series of dilators are advanced into the sacrum. With a final 12-mm dilator placed and its sheath left in place, a channel is drilled into the L5–S1 space. Various looped nitinol and firm flat cutters are used to morselize the disc; the end plates are scraped and rasped for fusion (▶ Fig. 41.6). After wire brushes completely evacuate the disc material, the space can be irrigated with antibiotic solution. Bone grafting material is then packed radially into the disc space using a beveled cannula. Choice of materials for grafting varies and is determined by surgeon and patient preferences.

Closure The wound is irrigated and a multilayered closure is performed. Dermabond is usually placed over the incision.

Fig. 41.6 Sequential intraoperative images that show the loop cutter (a), the flat cutter (b), the beveled bone graft inserter (c), and the trilator (d) in place. The notches allow for direct measurement of the implant to be placed. (Reproduced with permission of Mayfield Clinic.)

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41.5.2 Surgical Technique for a Two-Level Presacral Approach The two-level procedure is performed similarly to the one-level procedure until the disc space is packed at L5–S1. Now a 9.5mm channel is drilled across the L5 vertebra into the L4–L5 space and the L4–L5 disc is evacuated with the cutters similarly to L5–S1. However, use caution with the cutting instruments at L4 because access in the L4–L5 is often far anterior at the annulus; the instrument could sweep anteriorly into the space where the aorta and vena cava lie. The L4–L5 disc is packed with grafting material. The end plate of L4 is opened with a small drill and the trilator is passed into L4. The two-level device is composed of an L4–L5 segment and S1 segment. Measurements for these two components are similar to the L5–S1 technique. After assembly, the two-level rod is inserted in the same manner, but distraction can only be applied at L5–S1. The Steinmann pins and exchange cannula are removed. The wound is irrigated, a multilayered closure is performed, and Dermabond is usually placed over the incision.

41.6 Postoperative Care Routine pain management is provided with the intent of rapid mobilization. Attention is paid to bowel and bladder management. Inspection of the paracoccygeal wound and rectum is undertaken; in the rare circumstance of any bloody discharge from the rectum, immediate evaluation is required. The presacral approach at L5–S1 has been performed with same-day discharge. Patients and their families are informed about good hygiene measures related to healing of the presacral wound.

41.7 Management of Complications Since the introduction of the AxiaLIF device, refinements have been reported in patient selection, operative technique, the device itself, and radiographic assessments.19,20,21,22 At times, an alternative technique may be needed to achieve interbody lumbar fusion in the event of pseudarthrosis after AxiaLIF.23 The most concerning complications operatively or immediately after surgery are bowel or vascular injuries. Profuse bleeding is rare, especially when preoperative evaluation of the vasculature shows no vascular anomalies. Despite this, brisk venous bleeding can occur, caused by drilling out the sacral channel during the discectomy. Placement of the device tamponades the bleeding from the sacrum. Making certain that a small portion of the device protrudes from the sacrum adds another point of cortical fixation and seals off any further sacral bleeding. Compression by Flo-Seal or Gelfoam against the sacral entry point can effectively stop bleeding. In the rare event of continued bleeding or development of cardiovascular instability, an emergent vascular consultation is indicated. Any evidence of a bowel perforation (i.e., rectal bleeding, blood in the rectal aspirate, demonstration of a fistula after contrast injection) warrants a consultation with a colorectal surgeon in the operating room. A rectal tear can be primarily repaired under direct visualization with a rigid scope. A small perforation may be treated medically if advised by the consultant.

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Immediate recognition and treatment of a bowel perforation can avoid the serious consequences of developing a presacral abscess or peritonitis and the need for a diverting colostomy. Prompt recognition of a bowel perforation can avoid these delayed complications and, importantly, the possible infection that would require removal of the hardware. Such safeguards have reduced the risk of bowel perforation to less than 1%.18

41.8 Clinical Cases 41.8.1 Case 1: Spondylolisthesis—L5–S1 Examination A physically active 73-year-old man with a 12-month history of progressive back and lower extremity pain (right more than left side) noted left-sided pain radiating into his calf and heel. His pain was worsening with standing and walking, increasing in frequency and intensity. Physical therapy and two epidural steroid injections brought no lasting relief. On examination, the patient was thin, was well-built, and had normal gait. Mobility of the spine was normal and neurological examination disclosed no deficits.

Imaging Findings Flexion and extension views disclosed a mobile spondylolisthesis at L5–S1. His normal sacral curve was favorable for the presacral trajectory. MRI findings were nearly normal, showing normal alignment of his spine in the supine position.

Fusion A presacral fusion was performed at L5–S1 with placement of bilateral pedicle screws at L5–S1 and posterior facetectomy at L5–S1 on the right side. Postoperative CT showed excellent alignment and placement of bone graft material in the L5–S1 space. This case demonstrates a typical application of the presacral fusion device in a patient with dynamic instability of the spine (▶ Fig. 41.7).

41.8.2 Case 2: Degenerative Disc Disease L4–S1 with Long-Term Follow-Up Examination and History This 29-year-old woman presented in 2008 with a third-time noncompressive recurrent disc herniation at L5–S1, located centrally and on the left side. Marked degenerative changes were seen at L5–S1. She was disabled from work and all physical activities because of mechanical back pain that failed conservative care. On examination, no mechanical restriction was found on straight leg lifting; she had an absent ankle reflex but no motor or sensory deficits.

Fusion A presacral fusion included posterior stabilization with percutaneously placed facet screws. Surgery was uncomplicated; she made an excellent recovery and returned to all of her activities, including work and bowling.

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Trans-sacral Approach

Fig. 41.7 Case example of spondylolisthesis at L5–S1. (a) Flexion view demonstrates instability. (b) Extension view shows incomplete realignment. (c) MRI does not disclose the instability. (d) Postoperative CT shows ideal device placement, realignment, good lordosis, and full packing of the disc space. (Reproduced with permission of Mayfield Clinic.)

Imaging Findings at 5-Year Follow-Up Five years later, she returned to the clinic with new-onset back and left lower extremity pain. Multiple radiographic studies including MRI, plain lumbar films, and CT with thin-section reconstructed images showed a broad disc herniation at L4–L5 above the level of her presacral fusion. CT images showed solid fusion of the L5–S1 segment with the presacral device and facet screws. The adjacent L4–L5 segment was successfully treated with a TLIF and pedicle screw fixation; hardware from the presacral fusion was not removed (▶ Fig. 41.8).

41.8.3 Case 3: Two-Level Presacral Fusion for Spondylolisthesis at L4–L5 and Degenerative Disc Disease at L5–S1 Examination and History In this 53-year-old school teacher, back and bilateral neurogenic symptoms progressed despite 1 year of physical therapy and

NSAIDs. Imaging studies showed grade 1 spondylolisthesis with spinal stenosis at L4–L5, and degenerative disc disease with a broad L5–S1 disc protrusion.

Fusion Two-level presacral fusion was successful with posterior decompression at L4–L5 and bilateral pedicle screw placement (▶ Fig. 41.9).

41.9 Conclusion Presacral fusion at L4–L5 and L5–S1 is a viable surgical procedure for interbody fusion, with long-term follow-up now available since the first surgical procedure was performed in 2005. Improved technique, careful patient selection, and introduction of other safeguards have decreased the risk of bowel perforation to less than 1%, the most concerning complication. Compared with other fusion surgeries, the presacral approach offers distinctive advantages. Specifically, the fusion, which is anterior to

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Fig. 41.8 Long-term follow-up after a presacral fusion. (a) Anteroposterior (AP) image showing the presacral device and facet screws for treatment of an L5–S1 degenerative disc. (b) Six years postoperatively, sagittal CT showing solid arthrodesis with ectopic bone formation in the presacral space, which is asymptomatic. (c) MRI demonstrates herniated disc at L4–L5 above the L5–S1 presacral fusion. (d) Postoperative CT shows L4–L5 discectomy and fusion with pedicle screws and rods. (Reproduced with permission of Mayfield Clinic.)

Fig. 41.9 Two-level presacral fusion. (a) Preoperative MRI; dynamic film showed spondylolisthesis and stenosis at L4–L5. CT imaging postoperative (b) and at 1-year follow-up (c). (Reproduced with permission of Mayfield Clinic.)

the L5–S1 segment and performed with the patient positioned prone, eliminates the need for an approach surgeon and is especially suited for obese patients who were not candidates for other fusion approaches. The presacral device achieves exceptional biomechanical stability for patients with spondylolisthesis.

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As a new surgical procedure unfamiliar to many spine surgeons, specialized training can refine the technical expertise that will ensure proper preparation of the disc for fusion. The presacral fusion technique should be an option for surgeons dedicated to minimally invasive spine fusion. Clinical outcomes are comparable to those reported for other interbody techniques.

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Trans-sacral Approach

Clinical Caveats ●

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Given that this new surgical procedure is unfamiliar to many spine surgeons, specialized training in the trans-sacral approach will provide the technical expertise needed to perform this minimally invasive one- or two-level interbody fusion. The presacral (or AxiaLIF) corridor of approach begins adjacent to the coccyx, moves midline along the anterior margin of the sacrum through the presacral fat to the sacral promontory, and continues trans-sacral through bone to the L5–S1 disc space. The novel device can provide superior mechanical fixation in spondylolisthesis, especially if it can be reduced intraoperatively. The procedure works well in an outpatient setting and can be suitable for obese patients. The presacral approach should not be used in a patient with significant positive sagittal balance that requires interbody fusion and significant restoration of lordosis at L5–S1. The second-generation presacral device incorporated improvements that resolved the stresses placed on the vertebral end plates imposed by the original design’s reverse Herbert technique.

References [1] Cragg A, Carl A, Casteneda F, Dickman C, Guterman L, Oliveira C. New percutaneous access method for minimally invasive anterior lumbosacral surgery. J Spinal Disord Tech. 2004; 17(1):21–28 [2] Marotta N, Cosar M, Pimenta L, Khoo LT. A novel minimally invasive presacral approach and instrumentation technique for anterior L5-S1 intervertebral discectomy and fusion: technical description and case presentations. Neurosurg Focus. 2006; 20(1):E9 [3] Tobler WD, Ferrara LA. The presacral retroperitoneal approach for axial lumbar interbody fusion: a prospective study of clinical outcomes, complications and fusion rates at a follow-up of two years in 26 patients. J Bone Joint Surg Br. 2011; 93(7):955–960 [4] Ledet EH, Tymeson MP, Salerno S, Carl AL, Cragg A. Biomechanical evaluation of a novel lumbosacral axial fixation device. J Biomech Eng. 2005; 127 (6):929–933 [5] Ledet EH, Carl AL, Cragg A. Novel lumbosacral axial fixation techniques. Expert Rev Med Devices. 2006; 3(3):327–334

[6] Lindley EM, McCullough MA, Burger EL, Brown CW, Patel VV. Complications of axial lumbar interbody fusion. J Neurosurg Spine. 2011; 15(3):273–279 [7] Gebauer G, Anderson DG. Complications of minimally invasive lumbar spine surgery. Semin Spine Surg. 2011; 23:114–122 [8] Botolin S, Agudelo J, Dwyer A, Patel V, Burger E. High rectal injury during trans-1 axial lumbar interbody fusion L5-S1 fixation: a case report. Spine. 2010; 35(4):E144–E148 [9] Hofstetter CP, Shin B, Tsiouris AJ, Elowitz E, Härtl R. Radiographic and clinical outcome after 1- and 2-level transsacral axial interbody fusion: clinical article. J Neurosurg Spine. 2013; 19(4):454–463 [10] Marchi L, Oliveira L, Coutinho E, Pimenta L. Results and complications after 2level axial lumbar interbody fusion with a minimum 2-year follow-up. J Neurosurg Spine. 2012; 17(3):187–192 [11] Tobler WD, Gerszten PC, Bradley WD, Raley TJ, Nasca RJ, Block JE. Minimally invasive axial presacral L5-S1 interbody fusion: two-year clinical and radiographic outcomes. Spine. 2011; 36(20):E1296–E1301 [12] Bohinski RJ, Jain VV, Tobler WD. Presacral retroperitoneal approach to axial lumbar interbody fusion: a new, minimally invasive technique at L5-S1: clinical outcomes, complications, and fusion rates in 50 patients at 1-year followup. SAS J. 2010; 4(2):54–62 [13] Mazur MD, Duhon BS, Schmidt MH, Dailey AT. Rectal perforation after AxiaLIF instrumentation: case report and review of the literature. Spine J. 2013; 13 (11):e29–e34 [14] Whang PG, Sasso RC, Patel VV, Ali RM, Fischgrund JS. Comparison of axial and anterior interbody fusions of the L5-S1 segment: a retrospective cohort analysis. J Spinal Disord Tech. 2013; 26(8):437–443 [15] Hussain NS, Perez-Cruet MJ. Complication management with minimally invasive spine procedures. Neurosurg Focus. 2011; 31(4):E2 [16] Tender GC, Miller LE, Block JE. Percutaneous pedicle screw reduction and axial presacral lumbar interbody fusion for treatment of lumbosacral spondylolisthesis: a case series. J Med Case Reports. 2011; 5:454 [17] Bartolozzi P, Sandri A, Cassini M, Ricci M. One-stage posterior decompression-stabilization and trans-sacral interbody fusion after partial reduction for severe L5-S1 spondylolisthesis. Spine. 2003; 28(11):1135–1141 [18] Gundanna MI, Miller LE, Block JE. Complications with axial presacral lumbar interbody fusion: a 5-year postmarketing surveillance experience. SAS J. 2011; 5(3):90–94 [19] Issack PS, Kotwal SY, Boachie-Adjei O. The axial transsacral approach to interbody fusion at L5-S1. Neurosurg Focus. 2014; 36(5):E8 [20] Whang PG, Sasso RC, Patel VV, Ali RM, Fischgrund JS. Comparison of axial and anterior interbody fusions of the L5-S1 segment: a retrospective cohort analysis. J Spinal Disord Tech. 2013; 26(8):437–443 [21] Tobler WD, Melgar MA, Raley TJ, Anand N, Miller LE, Nasca RJ. Clinical and radiographic outcomes with L4-S1 axial lumbar interbody fusion (AxiaLIF) and posterior instrumentation: a multicenter study. Med Devices (Auckl). 2013; 6:155–161 [22] Zeilstra DJ, Miller LE, Block JE. Axial lumbar interbody fusion: a 6-year singlecenter experience. Clin Interv Aging. 2013; 8:1063–1069 [23] Louwerens JK, Groot D, van Duijvenbode DC, Spruit M. Alternative surgical strategy for AxiaLIF pseudarthrosis: a series of three case reports. Evid Based Spine Care J. 2013; 4(2):143–148

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42 Stabilization of the Sacroiliac Joint with the Sacroiliac Bone Surgical Implant Fred H. Geisler and Jake P. Heiney Abstract This chapter summarizes both the surgical technique of minimally invasive surgical (MIS) sacroiliac joint (SIJ) fusion and the clinical literature. Low back pain (LBP) in the United States is the second most common reason for primary care visits after the common cold. LBP, in addition to physical disability and lost income, increases the risk of falls in the elderly. The SIJ is a known cause of pain referred to the lumbar–pelvic region that often presents as clinically similar to pain presentation from the lumbar spine or hip regions. The SIJ is the largest joint and has high shear forces with a relatively small amount of translation and rotation. There is extensive evidence that suggests the SIJ can be a pain generator, possibly the primary one, in 15 to 30% of LBP-diagnosed patients. Patients failing to achieve postoperative pain and mobility goals after lumbar spinal arthrodesis may have an SIJ pain generator. Known etiologies of SIJ pain include degenerative sacroiliitis, residual adjacent segment degeneration, and misdiagnosis after a spinal fixation procedure. Although there is only modest evidence that nonsurgical treatments are effective for any length of time, they comprise the predominant form of current clinical care. In recent years, MIS methods have become available for treatment of SIJ pain. Compared to open SIJ surgery, minimally invasive techniques involve less blood loss, shorter hospital stays, and less perioperative morbidity. Reports of MIS SIJ fusion support the improved clinical outcomes, earlier postoperative weight bearing, and improved patient satisfaction compared to open surgical techniques. Keywords: sacroiliac joint, minimally invasive surgery, sacroiliac joint arthrodesis, degenerative sacroiliitis, sacroiliac joint disruption, sacroiliac joint dysfunction, low back pain, sacroiliac joint pain, pelvic girdle pain, titanium sacroiliac implant, previous spine surgery

42.1 Introduction Low back pain (LBP) is a common health issue and one of the top three health issues in developed countries.1 In the United States, after the common cold, LBP is the second most common reason for visits to primary care physicians.2 Annual expenditures for chronic back pain have been estimated to exceed $100 billion per year in the United States.3 In addition to pain, disability, and lost income, LBP has also been noted to increase falls in the elderly; falls can cause hip and/or spinal fractures with an increase in morbidity and mortality.4

42.2 Indications and Contraindications Pain in the lumbopelvic region can result from pathology in the lumbar, hip, or sacroiliac (SI) joint. Not only do the clinical

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symptoms of these areas overlap, but also often a patient has degenerative changes in more than one of these three areas. The SI joint is the largest joint in the human body and is subject to shear forces of up to 4800 N, with rotational movement of up to 4 degrees and translation capacity of 1.6 mm.5 Studies in healthy volunteers have helped to validate the SI joint as a cause of pain and define its innervation.6,7 Substantial evidence suggests that the SI joint may be the pain generator in 15 to 30% of patients diagnosed with LBP.8,9,10,11 Etiologies of SI joint pain include degenerative sacroiliitis, inflammatory arthritis, SI joint disruptions from trauma or related to pregnancy, anatomical abnormalities such as leg length inequality and scoliosis, adjacent segment degeneration as a result of lumbar and lumbosacral spinal fixation procedures, infection, tumor, gout, and idiopathic causes.12,13 Unfortunately, persistent or significant residual pain and disability are common after lumbar surgical procedures. There tends to be a higher frequency and severity of these problems after a lumbar spinal arthrodesis than after a simple lumbar decompression. Degeneration and dysfunction of the SI joint with pain can be the cause of either the reported postoperative pain or the failure to improve as a result of possible misdiagnosis or the presence of additional pain generators. It is interesting to note that the SI joint is the inferior adjacent segment for the L5S1 lumbar level.14,15,16,17 Radiographic evidence of SI degeneration has been reported in up to 75% of lumbar spinal fusion patients.18 The SI joint has also been reported to be the pain generator in 43% of patients with new onset or persistent pain after lumbar spinal fusion.19 The conclusion of a literature review on the correlation of LBP and SI joint pain indicates that the SI joint not only plays an important role in LBP, but also appears to be under-diagnosed. The mainstay of care for SI degenerative pain, as with degenerative pain elsewhere in the body, is nonsurgical care. Nonsurgical treatments for SI joint pain include anti-inflammatory medication, pain medication, activity modification, weight loss, physical therapy, chiropractic care, radiofrequency ablation and SI joint steroid injections.8,20,21 However, there is only modest evidence that any of these nonsurgical treatments is curative or effective for a long period of time.22 When these measures fail to provide significant and lasting symptom relief and the patient has persistent disabling pain, surgical options may be considered. Surgical treatment for persistent SI joint pain was first reported in the early 1900s.23 However, mainly due to challenges including blood loss, extended hospital stay, wound size, and difficulty with mobilization (e.g., non-weight bearing status), open surgical repair is typically reserved, even now, for only the most severe cases.24,25 A major shift in philosophy about surgical management has recently occurred after the development of minimally invasive surgical methods. Compared to

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Stabilization of the Sacroiliac Joint with the Sacroiliac Bone Surgical Implant open surgery, minimally invasive techniques are typically associated with far less blood loss, shorter hospital stay, and less perioperative morbidity. The better patient post-operative experience after minimally invasive SI joint fusion techniques is attributable to smaller surgical incisions and less soft tissue dissection. Reports of MIS SI joint fusion confirm these postop patient benefits as well as showing improved clinical outcomes, earlier post-operative weight bearing, and overall improved patient satisfaction compared to open surgical techniques.26,27,28 There are several published studies regarding minimally invasive fusion of the SI joint.29,30 The literature describes two significantly different approaches to achieve this goal: a dorsal joint distraction and a lateral transarticular approach. In the dorsal approach, the SI joint is distracted and a structural material (either implant or allograft) is placed posterior to anterior within the joint on decorticated bony surfaces. Using the lateral approach, structural implants are placed across the SI joint with the lateral portion of the implant residing in the ilium and the medial end in the sacrum. Thus, the two techniques differ markedly with respect to the biomechanical stabilization and bony arthrodesis of the SI joint. By far the most common approach reported in the literature is the lateral transarticular approach. With this technique, the SI joint is accessed laterally through a small incision made into the lateral buttocks. This approach typically involves placement of one or more implants across the joint, spanning the ilium and sacrum, under fluoroscopic guidance. SI joint implant systems using both triangular-shaped and screw-based implants have been proposed. The surgical goal is to provide immediate fixation of the joint with subsequent arthrodesis that leads to a mature bony fusion over the long term. Cadaveric and finite element biomechanical studies have demonstrated marked reduction in SI joint motion after lateral, transarticular placement of a series of triangularshaped implants. No biomechanical studies are known to support stabilization of the SI joint with a dorsal joint distraction technique.

42.2.1 Literature Review A systematic review with a quantitative meta-analysis (MA) of operative measures and clinical outcomes reported in published prospective or retrospective studies of MIS SI joint fusion using a lateral transarticular technique has been recently performed.31 This review was conducted according to PRISMA (Preferred Reporting Items for Systematic Reviews and MetaAnalyses) guidelines.32 The databases PubMed (http://www. ncbi.nlm.nih.gov/pubmed) and Embase (http://www.embase. com) were searched using the terms “sacroiliac joint” AND “fusion.” In addition to database reviews, the bibliographies of previously published systematic reviews were evaluated in an effort to identify any articles not retrieved in the database searches.33 This review only included articles that were: ● In English. ● Original prospective or retrospective studies. ● Included at least five patients. ● Describing operative and clinical outcomes after MIS SI joint fusion using a lateral transarticular approach for SI joint dysfunction. It excluded articles that reported: Dorsal distraction approach. ● Open surgical technique. ● Fusion of the pubic symphysis. ● Single case reports. ● No clinical data or very limited follow-up. ● Traumatic pelvic ring injuries. ● Ankylosing spondylitis. ● Infection or tumor. ● Studies that solely evaluated imaging. ●

In all included studies, patients were diagnosed with SI joint pain using a common approach based on history, physical examination findings34 (▶ Fig. 42.1), and diagnostic SI joint block. All of the included studies reported on patients with degenerative sacroiliitis (i.e., osteoarthritic degeneration of the SI joint)

Fig. 42.1 Provocative tests were used in the clinical examination that correlated with sacroiliac joint (SIJ) painful dysfunction. Most authors want three of five tests to be positive to justify proceeding with diagnostic injections of the SI joint for definitive diagnosis. (Adapted from SI-BONE 2017.34)

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Fig. 42.2 Multiple authors have studied the visual analog scale (VAS) pain relief after the SI-Bone procedure. There are two noteworthy points in the composite presentation of these reported outcomes. First, there is uniform agreement that a profound initial drop in the VAS in time coincidence with the surgery appears to last as long as the follow-up period. The second point is that there is a low level of residual pain remaining after this operation, which could be due to either degenerative joint disease sources other than the treated sacroiliac joint (SIJ) or the SIJ fusion only relieved a significant portion of the pain in the treated SIJ. (Adapted from Heiney et al 2015.31)

Fig. 42.3 Multiple authors have reported a significant decrease in the Oswestry Disability Index, a clinical scale known to correlate with increased function.

or SI joint disruptions (i.e., joint disruption as a result of isolated SI trauma, pregnancy, or other causes). Search results yielded 241 records from PubMed and 297 from Embase that were examined. Of these, the study design and number are as follows: ● Ten retrospective single-center case series.12,35,36,37,38,39,40,41,42,43 ● Two prospective single-center case series.44,45 ● One multicenter retrospective case series.46 ● One single center.27 ● Two multicenter26,28 comparative cohort studies. ● One prospective single-arm study.24 ● One prospective multicenter randomized controlled trial.47 Two types of implants are represented: (1) 3 studies reported the use of a single hollow modular anchorage (HMA) screw packed with demineralized bone matrix and (2) 15 described the placement of a series (typically 3) of triangular, porous titanium plasma spray (TPS) coated implants (iFuse Implant System, SI-BONE, Inc., San Jose, CA). After eliminating the overlap in patient cohorts across studies described earlier, the sum of the literature represents 12 unique studies from 4 different countries with a total of 432 patients: 368 patients from 10 cohorts using

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triangular TPS-coated implants and 64 patients from 2 cohorts using HMA screws. Reported operative parameters were procedure time, estimated blood loss (EBL), and hospital length of stay (LOS). The random effects meta-analysis (RMA) mean (95% confidence interval [CI]) procedure time was 59 minutes (50.9–66.9; range 27–78 minutes), with substantial heterogeneity across studies. The RMA mean EBL was 36.9 mL (31.4–42.38), with moderate heterogeneity across studies. Mean hospital LOS, reported in nine studies, ranged from 0.78 to 6.9 days (range 0–7 days). The RMA mean LOS was 1.7 days (1.2–2.2), with significant heterogeneity across studies. Pain severity was reported in all studies. These are summarized in ▶ Fig. 42.2 for the iFuse triangular implant series and the HMA screw results. Outcomes at 36 months, where available, were significantly different (p < 0.0001) by implant type: mean (standard deviation [SD]) score was 2.0 (1.9) for the triangular implant and 4.6 (2.5) for the HMA screw. ODI was used in several studies and is summarized in ▶ Fig. 42.3. Although both groups were similar in terms of baseline disability, the triangular implant cohort showed an improvement of 2.7 times that of the HMA screw cohort

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Stabilization of the Sacroiliac Joint with the Sacroiliac Bone Surgical Implant (baseline: 59, 54.1; 36-month: 16, 45 for the HMA screw and triangular implant, respectively). Minimally invasive fusion of the SI joint has been performed with several types of implants using either a dorsal joint distraction technique (titanium cages packed with bone morphogenic protein,48 allograft bone dowels,49 or autograft iliac bone plugs50) or, more commonly, through a lateral transarticular approach using either HMA screws packed with demineralized bone matrix12,37,44 or triangular TPS-coated implants.24,26,35,36,38,42 As the two techniques are fundamentally different and the body of literature supporting the latter approach is comparatively more substantial, the presented systematic review focused on the lateral transarticular approach only. Compared to open SI joint fusion, MIS SI joint fusion as reported herein is associated with less blood loss, a shorter hospital stay, and improved clinical responses.26,51,52,53 Not surprisingly, the use of minimally invasive fusion for SI joint pathology has overtaken open approaches.54 The analysis of intraoperative outcomes showed mean procedure times of approximately 1 hour, mean EBL of 50 mL, and a mean LOS of approximately 1 day. These procedure-related variables compare favorably to open surgical SI joint fusion

cohorts, which reported mean procedure times of 128 to 163 minutes, EBL of 288 to 682 mL, and mean hospital LOS of 3.3 to 5.2 days.26,27,51 In comparison to the modest changes in pain and disability in similar patients treated with nonsurgical management,47 improvements after minimally invasive SI joint fusion using a lateral transarticular approach appear to be substantial and clinically important. It is encouraging to see that studies with longer term outcomes consistently showed sustained positive outcomes on visual analog scale (VAS) and Oswestry Disability Index (ODI) over time.40,45

42.3 Preoperative Planning Preoperative planning is essential in SI joint surgery. The OsiriX software is an example of a three-dimensional planning program that is relatively inexpensive and can be loaded onto a personal Apple- or Windows-based computer (OsiriX MD 6.5). This computer program allows synthesis of the inlet and outlet views (▶ Fig. 42.4), which aids in lining up identical intraoperative views. This program can also make three-dimensional

Fig. 42.4 (a) Inlet and (b) outlet fluoroscopy images synthesized using the OsiriX program. These images are shown to the radiology technician as an example of what is desired for intraoperative images. Once shown these images, it is often easy for the technician to match them in a short number of exposures and time.

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Fig. 42.5 (a,b) Three-dimensional surface reconstructions are often helpful in the visualization of the sacroiliac (SI) joint and the surrounding bone.

surface reconstructions (▶ Fig. 42.5) to help guide in the planning of the surgery. The OsiriX program allows the axis to be rotated so that one of the axes is parallel to the posterior cortical lining in the upper part of the sacrum, thus often allowing the planning to be reduced to a two-dimensional problem (▶ Fig. 42.6). Green lines in ▶ Fig. 42.6a show the planned implant positions, and ▶ Fig. 42.6b shows the starting point as determined on the lateral X-ray. There are many other medical imaging programs that perform these functions and aid in the organization and planning of MIS surgery. Typically, the radiologist already has such a program integrated in the hospital radiology system, or the surgeon has access to one of the spinal operating room (OR) computer guidance systems (e.g., Medtronic Stealth, BrainLab, Stryker, etc.). The essential point is the importance of preoperative planning, not the particular computer program. OsiriX MD is highlighted as a low-cost alternative in the event hospital programs are unavailable.

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The operating room is set up with the patient prone with pressure point areas padded and the lateral portion of the buttocks exposed in the surgical area. While one C-arm is required, two C-arms reduce operating time by quickly providing alternating views in the anteroposterior (AP) and lateral planes. Dual C-arms are set up such that one provides imaging in the pelvic inlet and outlet views and the other provides the lateral view (▶ Fig. 42.7). As an alternative to the dual fluoroscopies, an intraoperative CT scan with three-dimensional navigation can be used for radiologic guidance. The skin is marked using a plumb line draped over the patient to define true vertical, and a Kirschner wire (K-wire) to define the posterior line of the sacrum (▶ Fig. 42.8). These are both imaged on the lateral fluoroscopy with the rotation of the image adjusted so that the plumb line wire images are vertical on the screen and superimposed, verifying a true lateral without a rotation component (▶ Fig. 42.9). As the skin is a tethering point for the implant

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Stabilization of the Sacroiliac Joint with the Sacroiliac Bone Surgical Implant

Fig. 42.6 The trajectory and length of the implants can be estimated from the preoperative planning. (a,b) The superior implant. (c,d) The inferior implant.

placement instruments, it is important to place the skin incision in the correct position to minimize its size, and to facilitate surgery.

42.4 Surgical Technique for MIS Fusion of the SI Joint

42.3.1 Instrumentation Notes

The iFuse Implant System lateral minimally invasive surgical technique has been described previously by one of the authors (FHG). This technique of stabilization of the SI joint is a true minimally invasive surgical technique performed through an initial small skin incision using a cannulated system with the aid of fluoroscopy in three orthogonal axes; one axis is parallel to the posterior sacral cortical line at the S1 to S2 region. The procedure includes the following steps: 1. Preoperative planning, using intraoperative fluoroscopy, of the desired implant trajectories to account for the anatomic variations (see section “Preoperative Planning”).

The procedure is performed with the assistance of fluoroscopy in all three imaging planes: lateral, and inlet and outlet views. The iFuse implants (SI-BONE, Inc.) are made of titanium and are triangular in cross-section. Furthermore, they are coated with a porous TPS, which is known to aid in osseointegration in hip and dental applications. The goal of the procedure is immediate stabilization, and fixation of the implants to the ilium and sacrum, as well as in the long term fusion of the SI joint after its prolonged immobilization.

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Fig. 42.7 Operating room setup. Note the two fluoroscopy display units at the foot of the bed and the wall monitor with the preoperative planning images. This arrangement has all the imaging in one direction, which aids the surgeon in comparing the three images.

Fig. 42.8 Before the patient is prepped and draped, the lateral image of the sacrum is obtained with a plumb line, and a Steinmann pin marking the posterior margin of the sacrum is placed and the skin marked. A disposable plumb line can easily be made by tying two 2-lb weights to an electrical cord such as a Bovie.

2. Placement of three Steinmann pins at these trajectories across the SI joint starting in a small skin incision (see section “Instrumentation Notes”). 3. Drilling, broaching, and then placement of the implant as a cannulated system. Before making the skin incision, the optimal inlet and outlet views are obtained and the centers of the laser aimer on the inlet and outlet are marked on the drapes to aid in exactly reproducing the same images when alternating between the inlet and outlet views (▶ Fig. 42.10). The skin incision area is first injected with local anesthetic (▶ Fig. 42.11a). The skin and subcutaneous fat layers are opened sharply and with unipolar electrocautery, respectively. Bipolar cautery is utilized where necessary. Typically, during this initial opening and hemostasis stage, self-retaining retractors are used (▶ Fig. 42.11b). The fascia over the muscle is approached in the electrocautery fat opening but is not visualized. Hemostasis is obtained and the self-retaining retractors are removed to facilitate a clear view on intraoperative fluoroscopy. Next, a Steinmann pin is tapped in 2 to 3 mm, just deep enough to hold the position, aimed at the starting point on the outside iliac cortex that matches the point on the lateral image as determined in preplanning. The pin is moved after lateral imaging until the

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desired position is obtained (▶ Fig. 42.11c). Now the three-dimensional placement geometry problem has been reduced to two angles as a point on a surface has been matched. Once the first pin is put in, the second pin is placed parallel to first, displaced to allow space for the implant size. If the exact position of one of these pins is not optimal, then the pin which is slightly adjacent to the optimal position is left and a more optimal pin is placed adjacent to the nonoptimal pin using the other pins for visual reference. The pin that will not be used for implant insertion is removed. The system is cannulated; all of the instruments are placed over the Steinmann pin. Thus, accurate pin placement is critical. After pins are in place, placement is verified in all views under fluoroscopy. A parallel pin guide is provided in the system that may be used instead of this freehand method. Once all three pins are placed in the outer cortex of the ilium and verified to be parallel to each other, they are tapped in across the SI joint as seen in the inlet and outlet views, and the lateral inlet and outlet views are all compared to make sure they match the preop planning on the OsiriX program (▶ Fig. 42.12). This is done sequentially, doing midcourse directional corrections and checking on the X-ray images in all three views. After all three pins are in the desired trajectories and depths (▶ Fig. 42.13), start placing the implants from a rostral to caudal

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Stabilization of the Sacroiliac Joint with the Sacroiliac Bone Surgical Implant

Fig. 42.9 The vertical line is verified by placing a sterile Steinmann pin on the markings (a) and rotating the projected image (b) on the monitor to be directly vertical. This direct vertical orientation on the lateral fluoroscopic image greatly aids in repositioning the starting point of the Steinmann pin for implant placement.

direction. The drill is slid over the pin, being careful to maintain the exact alignment with the axis of the pin. An unintended angle between the portion of the pin in the bone and the drill over the pin outside the bone will cause the pin to bend and can lead to binding of the drill on the pin. Free turning of the drill and cutting the bone verifies the alignment. This exact alignment can be verified with fluoroscopy if any question arises. The cannulated drill is placed over the pin and then pushed through the muscle to contact the outer cortex of the ilium; then the drill guides are slid in place and pushed until they also contact the bone (▶ Fig. 42.14). These maneuvers cause the sharp nonturning drill bit to make an initial rent in the fascia, which is subsequently enlarged with the coaxially placed drill guide. This forms the working channel for each implant through the fascia and the muscle layer directly over the implant entrance site. It is notable that the drill is not turned on until the drill guide is firmly placed against the outer table of the ilium and can act as a shield preventing the muscle from contacting the rotating drill bit. The angle at which the drill is pointed is closely matched to the other two pins as a visual trajectory guide in order to minimize downward hand drift, during which the weight of the drill tends to lower the surgeon’s hand and bend the pin at the entrance of the outer cortex of the ilium. The drill is advanced across the SI joint (▶ Fig. 42.15). The cortex on both sides of the SI joint is noticeably harder to drill

than the cancellous portion of the ilium or sacrum. This difference results in a tactile sign for the surgeon as a landmark of crossing the SI joint. The drill depth is a combination of measurement on the drill guide outside the wound and the images of the three planes of fluoroscopy. Often the sharp Steinmann pin used initially is replaced with a blunt pin. This is easily accomplished with drill still in the bone and holding the exact trajectory. Once the drilling is performed across the SI joint to the desired depth, the cannulated broach is placed on the pin (▶ Fig. 42.16a) and then hammered coaxially over the Steinmann pin past the SI joint. The broach converts the circular slot in the bone into a triangle. The broach is hammered across the SI joint, but not all the way into the sacrum (▶ Fig. 42.16b,c). The implant will make the final path into the sacrum, as the sacral cancellous bone is weaker. It is just the drill hole that is used as the pilot. Care is taken in exact rotation of the implants; they have three-pole symmetry as they are triangles, and clocking the implants relative to one another is important to avoid any collision and provide the maximum amount of remaining bone surface area for fixation and fusion. The triangularly cut bone produced by the broach determines the special rotational orientation of the implant. The implant is next coaxially placed over the Steinmann pin (▶ Fig. 42.17a). The exact rotation of the implant needs to

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Fig. 42.10 (a,b) Once the optimal inlet and outlet fluoroscopy views are obtained, the location of the aiming red laser stop on the drapes is marked. This simple step greatly aids in the repositioning of the fluoroscopy unit that alternates between the inlet and outlet views.

match the broach cut rotation. This is easily accomplished by holding the broach guide fixed between the broaching and implant insertion steps. The Steinmann pin is typically placed slightly deeper than the drilling or the broaching and remains fixed at the bottom during the implant insertion step. The Steinmann pin, along with the bone cut of the broach, determines the implant trajectory. The implant and the pins are monitored with fluoroscopy for the exact depth of implant placement and to verify that the pin is not driven deeper by the implant insertion. The SI-Bone implant is placed approximately with half in the ilium and half in the sacrum, with the SI joint at the middle of the implant (▶ Fig. 42.17b-d). The exact position is across the SI joint, matching the planned position on the OsiriX or other preplanning imaging program. This particular case is after a prior lumbar fusion. The second implant is inserted using the same technique as the first. Note that the drill is again placed against the outer cortex of the ilium and then the drill guide is pushed down against the bone to act as a muscle shield while drilling to prevent winding of any muscles (▶ Fig. 42.18a-c). Once the initial contact point is verified on fluoroscopy, the pilot hole is drilled in the desired trajectory and depth with fluoroscopy guidance. The video shows that the drilling step is often an in-and-out motion of about half an inch. This motion verifies that the drill is not bound on the Steinmann pin and can more easily drill the cortical bone.

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There are markings on the drill bit to aid in determining the drill depth. The initially placed Steinmann pin, which the drill goes over, is a longer pin. Occasionally, during the drilling process the pin will catch on the inside of the drill and is then inadvertently removed from the wound along with the drill when the latter is taken from the drill guide. A different pin is then placed, typically with a blunt tip. It is relatively easy to find the same trajectory, as the drill guide is left in place and the replacement pin easily slides into and down the drill track. After the drilling, the internal guide is removed; this step converts the drill guide into a broach guide (▶ Fig. 42.19). The broach is being inserted in preparation for placement of the second implant. Notice how the broach is lined up in relation to the other pins and then held in place for the broach impaction trajectory (▶ Fig. 42.20a,b). The broach is rotated, or clocked in machining terms, such that final placement of the implants will not cause surfaces to collide, and to preserve sufficient bone for fixation and ultimate fusion. During the broaching and implant placement, a long blunt pin is pushed down the center hole to hold the shorter pin at full depth, as it tends to elevate out of the bone during the hammering. Care is taken to hold the guide at the exact same position as the triangle, and the implant needs to be clocked to match the broach bone cuts in use to impact the SI-Bone implant into the ilium and sacrum crossing the SI joint. The implant is gradually tamped to final position (▶ Fig. 42.21a-c). The

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Fig. 42.11 (a) The skin is infiltrated with Marcaine before it is incised. (b) The skin and superficial adipose tissue are opened sharply and hemostasis is obtained with coagulation. (c,d) A preliminary pin is placed at the approximate location of the superior implant just a few millimeters into the ilium. A second pin is then used for the true path of the superior implant, using not only the fluoroscopy images, but also the visual correction necessary from the first pin. Leaving the first pin before placing the next pin converts the trajectory of the true pin to be a difference from the first. It is often easier to find the true position this way rather than removing the first pin and starting over to find the true trajectory with only fluoroscopy guidance.

author prefers to take multiple films as the implant is being advanced. If the implant is placed deeper than planned, there is a tool that can be screwed into the implant and pulled backward toward the ilium to adjust the final position. After the first two implants have been placed, the third implant is inserted in a similar manner. In many cases, the third implant is clocked to match the first implant. The handle position can be drawn on the surgical drapes to aid in the clocking of the implants. Using the handle position, the insertion guide is now clocked to approximately match the position of the first implant. Depth is drilled to the size of the planned implant (▶ Fig. 42.22a,b). Right there, you can see I am just getting up to the SI joint; I am feeling it, and then I am going to drill just a little further to cross the joint. The pin is put in the back, holding the other pin in place. The inner drill guide is taken out of the outer guide and

the broach is placed down. In this case, the pin slightly slides out of the boney hole and the blunt pin is put in place down the same track. The broach has been put in and tapped into place, just crossing the joint. Marks aid in the depth along with fluoroscopy (▶ Fig. 42.22c-e). Once the broach is across the joint, the impaction hammer is used to pull it out. Note that we left the other Steinmann pins in place; we find them useful in holding the alignment of the trajectory for the drill, broach, and implant insertion. The third implant is then put in (▶ Fig. 42.22fh). The length of all of the implants had been previously determined by measurements on the OsiriX program and then verified on fluoroscopy as they were implanted. At the end of the procedure, the implants are verified to all be in good positions on all three of the views, both with the Steinmann pins in (▶ Fig. 42.23a,b) and, then, with the pins out (▶ Fig. 42.23c-e). Notice that on the lateral, the clocking works

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Fig. 42.12 (a,b) The second and third pins are then placed parallel to the first and most superior pin. In this image, the third pin is being set on the ilium for placement parallel to the other two pins.

to prevent collision of the implants and preserve bony thickness in the ilium and sacrum between the implants. Once all three implants have been placed and their positions verified, hemostasis and closure is performed (▶ Fig. 42.24a). First, self-retaining retractors are replaced and the wound is irrigated with antibiotic irrigation. The three muscle holes with the implants at the bottom can be palpated with the surgeon’s index finger. With the surgeon’s index finger on the superior implant, 3 mL of the contents of a 10-mL syringe of powdered Gelfoam and thrombin mixture is placed directly on top of the implant and in the muscle dissection leading to the implant (▶ Fig. 42.24b). Sliding the cannula on the syringe down the

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side of the index finger and having the tip contact the implant before making the 3-mL injection facilitates this step. The same placement of thrombin–Gelfoam mixture is performed at the other two implant sites. The self-retaining retractors are then removed. The wound is then pressed with the surgeon’s hand over the surgical area for a full 5 minutes (▶ Fig. 42.24c,d). Standing bent slightly toward the patient so some of the surgeon’s body weight pushes on the hand at the wound site makes this maneuver more effective. Any excess thrombin–Gelfoam mixture is removed with additional antibiotic irrigation. Several sutures are placed in the deep adipose fascial layer but not tied initially.

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Stabilization of the Sacroiliac Joint with the Sacroiliac Bone Surgical Implant

Fig. 42.13 (a,b) The third pin is now placed in the desired trajectory and depth.

Marcaine is placed in the deep wound (▶ Fig. 42.25) to aid in immediate postoperative pain relief. Immediately after the Marcaine is placed, the untied deep adipose fascial sutures are all pulled tight to trap the Marcaine in the deep portion of the wound. They are then tied and the rest of the wound is closed in layers in standard fashion. It is notable that no attempt is made to close the muscle layer or its overlying deep fascial layer, as they have not been visualized during the procedure. Plastic closure is done on the skin. The patient is then sent to the recovery room for further management and care; a decision is made for going home the same day or being a 23-hour admit with discharge the next day. Crutch walking to avoid leg pressure with SI joint forces is taught in the hospital before discharge.

42.5 Postoperative Care The patient is initially ambulated with crutch walking for 6 weeks to avoid forces across the instrumented SI joint. In many cases, crutch walking begins a few hours after surgery and continues for the remainder of the following day. After a 6-week period of limited weight bearing on the operative side, the patient starts physical therapy and gradually increases the ambulation distance, with a goal of unlimited ambulation in 4 weeks. Patients with a preoperative history of prolonged pain and disability often have general disuse atrophy, which can take 6 to 12 months to resolve. Pain medication is continued at preoperative levels initially and then tapered as soon as possible in the postoperative course.

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Fig. 42.14 (a,b) This is a cannulated system where first a cannulated drill is placed over the superior pin. While the drill tip is NOT ROTATING, the tip is advanced to (1) contact the muscle deep fascia, (2) puncture the deep fascia, and (3) dilate through the muscle layer to contact the ilium. It is important to do this step without the drill rotating, as a rotating drill bit will wind muscle fibers if not protected by the drill guide.

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Stabilization of the Sacroiliac Joint with the Sacroiliac Bone Surgical Implant

Fig. 42.15 (a,b) With the drill against the ilium, the drill guide is first pushed down to the deep fascia over the muscle layer, as shown in the image, and then pushed deeper to contact the ilium (the position in ▶ Fig. 42.16) and the drilling begun. (b) shows the guide tube pushed against the ilium and the drill having passed through the sacroiliac (SI) joint.

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Fig. 42.16 (a) After the hole has been drilled to the desired depth of the implant, the inner drill guide is removed and the cannulated broach is placed over the pin. Note the lower position of the guide tube, as it is now in contact with the ilium. (b) The trajectory of the broach is verified both visually and with fluoroscopy to be in line with the other two pins. (c) The triangular broach is tapped through the ilium and both cortical surfaces of the sacroiliac (SI) joint. The triangular nature of the broach determines exactly how the implant is “clocked” as it passes the SI joint.

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Stabilization of the Sacroiliac Joint with the Sacroiliac Bone Surgical Implant

Fig. 42.17 (a) The cannulated SI-Bone implant is then slid over the pin while holding the guide tube fixed. It is important not to rotate the guide tube handle after the broaching step, as the triangular implant needs to match the triangular broach cut. (b) A cannulated impact tool is then slid onto the pin to advance the SI-Bone implant. (c,d) A hammer is used to drive the SI-Bone implant to the desired depth, crossing the sacroiliac (SI) joint as determined by fluoroscopy. The surface of the implant is rough and thus provides both immediate fixation and osteointegration potential for the contacting bony surface to adhere to the titanium of the implant.

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Fig. 42.18 (a) Once the first implant is in the final position, the second or middle pin is drilled in a like manner to the first pin. (b) Drill guide on the deep fascia and drill on the ilium. The drill is not turned on until the drill guide is contacting the ilium to prevent the drill bit from winding muscle. (c) With the drill guide firmly pressed against the ilium, the drilling is started and the cannulated drill follows the path of the pin. It is notable that drilling is more difficult at the cortical bone of the sacroiliac (SI) joint than in the cancellous bone of the ilium or sacrum.

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Stabilization of the Sacroiliac Joint with the Sacroiliac Bone Surgical Implant

Fig. 42.19 After the drill step is completed, the drill is removed and the inner part of the guide is switched from a drill guide to a triangular broach guide. In this image, the inner part of the guide tube is being removed over the pin. In this step as well as other steps in which an instrument or part of the guide is removed, an additional pin is inserted into the distal end of the cannulated instrument to keep the guiding pin at the bottom of the wound and prevent its removal. If the pin does come out of the ilium/sacrum, then it is easy to replace as the bony hole is directly at the bottom of the guide. Often an elective replacement is performed to convert the sharp pin to a dull pin after the drill step at each implant site to lessen the chance of the sharp pin advancing with instrument movement down the pin.

Fig. 42.20 (a) In this image, the cannulated broach is being slid over the middle pin. (b) Broach impacted across the sacroiliac (SI) joint. Note the additional longer blunt pin being pushed in the back of the broach instrument to hold the guide pin in the ilium and sacrum.

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Fig. 42.21 (a) The second cannulated implant is being slid onto the middle guide wire. (b) The cannulated impact instrument is slid over the middle guide wire with the guide tube held in position against the ilium. (c) The middle SI-Bone implant is impacted across the sacroiliac (SI) joint under fluoroscopy guidance.

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Stabilization of the Sacroiliac Joint with the Sacroiliac Bone Surgical Implant

Fig. 42.22 (a,b) The third or inferior SI-Bone implant is inserted similarly to the first two, with the drill guide firmly held against the ilium before the drilling is begun. Note on the image on the right that the first two implants have been placed and the drill guide is placed against the ilium. In this image, the guide pin is not yet at the bottom of its trajectory and was later pushed down to the bottom. (c) The inner drill guide is removed in preparation for the broach. (d) The cannulated broach is slid over the guiding pin for the third or inferior implant. (e) The path for the third implant is broached with the guide tube firmly held against the ilium. (f) The third SI-Bone implant is slid over the guide wire and then the impaction tool is placed on the guide pin. (g,h) The third implant is impacted into position with fluoroscopy guidance. In the image on the right, the implant is not fully impacted into final position and the guide wire is deeper than planned. The guide pin was withdrawn about an inch and the implant placed in the final position.

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Fig. 42.23 (a,b) Final position of the implants with the guide pins still in place. (c–e) These three images show the final lateral and inlet and outlet fluoroscopy images. Note the clocking of the implants to avoid a collision within the ilium or sacrum.

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Stabilization of the Sacroiliac Joint with the Sacroiliac Bone Surgical Implant

Fig. 42.24 (a) After the fluoroscopy verification of the position of the three implants, the guide wires are removed and the wound irrigated with antibiotic solution. (b) Thrombin–Gelfoam mixture is then placed directly over the implant and in the separated muscle by palpating the implant with an index finger and then sliding the injection nozzle on the syringe down the side of the finger on the implant. An injection of about 3 mL of thrombin–Gelfoam mixture is made over each implant. (c,d) Immediately after the thrombin– Gelfoam injection, firm pressure is applied to the wound with the palm of the hand for a clock time of 5 minutes. The excess thrombin–Gelfoam mixture is then removed with additional antibiotic irrigation.

Fig. 42.25 Marcaine (10 mL) is then injected into the wound cavity and trapped in place with sutures in the deeper layer of adipose tissue. The remainder of the wound is closed in layers, finishing with a plastic closure on the skin layer.

42.6 Management of Complications Adverse-event reporting rates were calculated in the literature search as the number of events divided by the total number of patients. In the 10 cohorts represented (432 patients treated), the most common events were surgical wound problems (17 events, 3.9% rate), trochanteric bursitis (8 events, 2.2%), facet pain (3 events, 0.8%), recurrent SI pain (i.e., initial improvement in SI joint pain, followed by pain recurrence, 3 events, 0.8%), and toe/foot numbness (2 events, 0.5%; ▶ Table 42.1). Nerve root impingement requiring revision occurred in 9 subjects (2.1%). There were no deaths. It is important to note that serious adverse events related to the device and placement procedure appeared to be uncommon.55 Two ongoing prospective clinical trials included in this systematic review collect all negative changes in health as adverse events according to an international clinical trial standard

(ISO 14155:2011) definition.24,47 Of 18 studies included in the systematic review, 83% described the use of a series of triangular TPS-coated implants. This uniquely designed implant system works on the well-accepted principle of joint stabilization, followed by long-term fusion. The porous coating of the device is similar to that used in total joint replacement surgery. These types of coatings are designed to promote biological fixation of the bone to the implant and promote a biomechanically sound construct. The immediate solid fixation is akin to that afforded in press fit total joints. Fusion of the SI joint using these implants has been demonstrated in two long-term studies.40,45 SI joint dysfunction is associated with a significant burden of disease,56 similar to that observed with other prominent orthopedic conditions such as hip and knee osteoarthritis, spinal stenosis, and degenerative spondylolisthesis, all of which are treated surgically. Therefore, it is reasonable to consider surgical treatment for cases of SI pain that do not respond to nonoperative therapy.

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Surgical Techniques Table 42.1 List of reported adverse events Complication

Number of patients

Surgical wound problems (including hematoma, 17 wound infection, cellulitis) Iliac fracture

1

Hairline ilium fracture at caudal implant

1

Pulmonary embolism

1

Nerve root impingement requiring revision

9

Transient postoperative radiculopathic pain

3

Buttock pain

1

Low back pain

2

Trochanteric bursitis

8

Piriformis syndrome

3

Facet pain

3

Contralateral SIJ pain

2

Recurrent pain

3

Leg pain

1

Toe/foot numbness

2

Bladder incontinence

1

Total

57/432 (4.6%)

Revision rate

9/432 (2.1%)

Abbreviation: SIJ, sacroiliac joint.

Clinical Caveats ●

●

●

●

●

SI joint pain is often the cause of residual pain after a lumbar fusion surgery. Nonoperative care of SI dysfunction should be tried before considering SI joint surgery. Mechanical physical examination tests that provoke SI joint pain are verified by SI joint injections for pain relief with an anesthetic agent for the diagnosis of SI joint dysfunction. The minimally invasive characteristics of the lateral transarticular SI joint procedure were confirmed, as evidenced by minimal blood loss, a short operative time, and brief LOS in multiple studies. The lateral transarticular approach is the current preferred technique over open surgical approaches.

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Stabilization of the Sacroiliac Joint with the Sacroiliac Bone Surgical Implant [31] Heiney J, Capobianco R, Cher D. A systematic review of minimally invasive sacroiliac joint fusion utilizing a lateral transarticular technique. Int J Spine Surg. 2015; 9:40 [32] Liberati A, Altman DG, Tetzlaff J, et al. The PRISMA statement for reporting systematic reviews and meta-analyses of studies that evaluate health care interventions: explanation and elaboration. Ann Intern Med. 2009; 151(4): W65–W94 [33] Zaidi HA, Montoure AJ, Dickman CA. Surgical and clinical efficacy of sacroiliac joint fusion: a systematic review of the literature. J Neurosurg Spine. 2015; 23(1):59–66 [34] SI-BONE, Inc. Sacroiliac Joint Pain. Diagnostic Algorithm for SI Joint Pain. Available at: www.si-bone.com/risks; 2017 [35] Cummings J, Jr, Capobianco RA. Minimally invasive sacroiliac joint fusion: one-year outcomes in 18 patients. Ann Surg Innov Res. 2013; 7(1):12 [36] Gaetani P, Miotti D, Risso A, et al. Percutaneous arthrodesis of sacro-iliac joint: a pilot study. J Neurosurg Sci. 2013; 57(4):297–301 [37] Khurana A, Guha AR, Mohanty K, Ahuja S. Percutaneous fusion of the sacroiliac joint with hollow modular anchorage screws: clinical and radiological outcome. J Bone Joint Surg Br. 2009; 91(5):627–631 [38] Rudolf L. Sacroiliac joint arthrodesis-mis technique with titanium implants: report of the first 50 patients and outcomes. Open Orthop J. 2012; 6:495–502 [39] Rudolf L. MIS Sacroiliac (SI) Joint Fusion in the Context of Previous Lumbar Spine Fusion: 50 Patients with 24 Month Follow up. Paper presented at: International Society for the Advancement of Spine Surgery, Vancouver, BC, Canada, 2013 [40] Rudolf L, Capobianco R. Five-year clinical and radiographic outcomes after minimally invasive sacroiliac joint fusion using triangular implants. Open Orthop J. 2014; 8:375–383 [41] Sachs D, Capobianco R. One year successful outcomes for novel sacroiliac joint arthrodesis system. Ann Surg Innov Res. 2012; 6(1):13 [42] Sachs D, Capobianco R. Minimally invasive sacroiliac joint fusion: one-year outcomes in 40 patients. Adv Orthop. 2013; 2013:536128 [43] Schroeder JE, Cunningham ME, Ross T, Boachie-Adjei O. Early results of sacroiliac joint fixation following long fusion to the sacrum in adult spine deformity. HSS J. 2014; 10(1):30–35

[44] Mason LW, Chopra I, Mohanty K. The percutaneous stabilisation of the sacroiliac joint with hollow modular anchorage screws: a prospective outcome study. Eur Spine J. 2013; 22(10):2325–2331 [45] Vanaclocha V, Verdú-López F, Sánchez-Pardo M, et al. Minimally invasive sacroiliac joint arthrodesis: experience in a prospective series with 24 patients. J Spine. 2014; 03(5):185 [46] Sachs D, Capobianco R, Cher D, et al. One-year outcomes after minimally invasive sacroiliac joint fusion with a series of triangular implants: a multicenter, patient-level analysis. Med Devices (Auckl). 2014; 7:299–304 [47] Whang P, Cher D, Polly D, et al. Sacroiliac joint fusion using triangular titanium implants vs. non-surgical management: six-month outcomes from a prospective randomized controlled trial. Int J Spine Surg. 2015; 9:6 [48] Wise CL, Dall BE. Minimally invasive sacroiliac arthrodesis: outcomes of a new technique. J Spinal Disord Tech. 2008; 21(8):579–584 [49] McGuire RA, Chen Z, Donahoe K. Dual fibular allograft dowel technique for sacroiliac joint arthrodesis. Evid Based Spine Care J. 2012; 3(3):21–28 [50] Giannikas KA, Khan AM, Karski MT, Maxwell HA. Sacroiliac joint fusion for chronic pain: a simple technique avoiding the use of metalwork. Eur Spine J. 2004; 13(3):253–256 [51] Buchowski JM, Kebaish KM, Sinkov V, Cohen DB, Sieber AN, Kostuik JP. Functional and radiographic outcome of sacroiliac arthrodesis for the disorders of the sacroiliac joint. Spine J. 2005; 5(5):520–528, discussion 529 [52] Güner G, Gürer S, Elmali N, Ertem K. Anterior sacroiliac fusion: a new videoassisted endoscopic technique. Surg Laparosc Endosc. 1998; 8(3):233–236 [53] Schütz U, Grob D. Poor outcome following bilateral sacroiliac joint fusion for degenerative sacroiliac joint syndrome. Acta Orthop Belg. 2006; 72(3):296–308 [54] Lorio MP, Polly DW, Jr, Ninkovic I, Ledonio CG, Hallas K, Andersson G. Utilization of minimally invasive surgical approach for sacroiliac joint fusion in surgeon population of ISASS and SMISS membership. Open Orthop J. 2014; 8:1–6 [55] Miller LE, Reckling WC, Block JE. Analysis of postmarket complaints database for the iFuse SI Joint Fusion System®: a minimally invasive treatment for degenerative sacroiliitis and sacroiliac joint disruption. Med Devices (Auckl). 2013; 6:77–84 [56] Cher D, Polly D, Berven S. Sacroiliac joint pain: burden of disease. Med Devices (Auckl). 2014; 7:73–81

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43 Lumbar Disc Replacement: The Artificial Disc Fred H. Geisler Abstract Lumbar spinal arthroplasty was first reported in clinical settings nearly 30 years ago in patients with lumbar degenerative disc disease. The early device underwent several mechanical improvements, including changes in its sterilization procedure to ensure long-term viability, and evolved into its final configuration of the CHARITÉ III. The CHARITÉ III artificial lumbar disc was studied in a Food and Drug Administration (FDA) investigational device exemption (IDE) randomized controlled trial (RCT) that compared arthroplasty to anterior lumbar interbody fusion. This trial was reported in 2005 and, since then, multiple other lumbar arthroplasty devices have been developed and are undergoing or completing clinical trials both in the United States and in Europe. Because lumbar total disc replacements require successful completion of RCT prior to market approval in the United States, lumbar arthroplasty devices have undergone more scrutiny and clinical evaluation than any other spinal medical devices. Although the randomized studies were initially planned for 2year follow-up, the total follow-up was extended to 5 years in all the studies. These prospective randomized clinical trials have generated a large body of evidence on the safety and efficacy of arthroplasty for lumbar spine. Additionally, significant insights were developed regarding the impact of lumbar arthroplasty on sagittal alignment and motion, possible adverse events and reoperation, and optimal patient selection and indication. Health economics papers have been presented to understand the societal impact of this new technology. This review chapter is aimed at providing an overview of the surgical technique and clinical data related to spinal arthroplasty. Keywords: lumbar arthroplasty, total disc replacement, lumbar artificial disc, clinical trial, statistical analysis, lumbar spine, revisions, reoperations, lumbar fusion, randomized study, FDA IDE randomized controlled trial, arthrodesis, prior surgery, effect of age

43.1 Introduction Multiple intervertebral disc procedures have been developed to deal with abnormalities in the intervertebral disc. These include herniation of the nucleus pulposus, degenerative disc disease (DDD), and segmental instability. In recent years, the diagnostic accuracy and description of these abnormalities have been aided by the development of water-soluble myelography, MRI, provocative discograms, diagnostic blocks, and high-resolution CT scanning techniques with both intravenous and intrathecal contrast. Over the past 15 years, multiple therapeutic advances have also occurred to aid in managing intervertebral disc disease. These have included rigid segmental pedicle screw fixation (which has been shown to enhance the fusion rate over a noninstrumented fusion), carbon fiber–reinforced polymer cages, and allograft spacers placed in the anterior column to promote anterior column fusion; demineralized bone matrix, platelet-derived autologous growth factors (AGF), bone morphogenetic proteins (BMP), and numerous bone graft extenders to eliminate or minimize iliac crest bone graft harvested during a lumbar fusion procedure.

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There has also been recognition over the past decade that interbody stabilization and arthrodesis, in addition to posterior instrumentation and arthrodesis, enhances the total lumbar joint fusion rate. Interbody fusion can be accomplished either anteriorly through a separate incision or posteriorly via a posterior lumbar interbody fusion or transforaminal lumbar interbody fusion approach. Laparoscopic surgery has also been used in spine surgery for anterior cage insertion, and minimally invasive techniques posteriorly and posterolaterally have been developed. There are also several intradiscal therapies with internal decompression of the disc center or heating of the posterior annulus to minimize the patient’s surgical discomfort while potentially relieving some symptoms of low back disorder.

43.2 Advantages of an Artificial Disc All of the above-mentioned techniques, however, either mask the true disease process or eliminate the joint motion and its normal physiologic function. With lumbar artificial disc technology, we now have the ability to fix the problem and restore normal anatomy and physiologic motion rather than simply fuse the back.1,2,3,4 Fusion works in many instances because the motion of the joint itself causes pain through its inability to comfortably support the weight of the body. Thus, when it is fused, it no longer moves and hence the motion cannot cause pain. The fusion does, however, cause stress and increased motion in the joints adjacent to the fused level as a direct effect of eliminating motion at the fused level. The theory behind an artificial disc in the lumbar area is not only to preserve the motion but also to correct the abnormal motion that would be present in the degenerative disc and restore the disc height, lordosis, and a normal instantaneous axis of rotation. By doing so, the joints adjacent to the dynamically stable segment would not be subject to abnormal loads and motions. It is hoped with this new technology of the artificial lumbar disc that the good results that have followed the introduction of artificial knees and hips will likewise be seen in the lumbar spine.5 The advantage of the artificial lumbar disc as compared with a lumbar fusion is that it reproduces the biomechanics of the normal disc. Additionally, it reduces the mechanical forces transmitted to the adjacent segments. It has the promise of slowing or halting degenerative changes at adjacent levels. Performing a total discectomy eliminates the chance of disc herniation and will hopefully retard spondylosis, stenosis, and instability at the dynamically stabilized segment. By restoring the anatomic disc height, the artificial disc increases the exiting foraminal height and prevents compression on the exiting nerve roots at the level stabilized. The typical diseased lumbar segment considered for artificial lumbar disc treatment is often collapsed in vertical height and exhibits loss of normal lordosis, modic end plate changes in adjacent vertebral bodies, and little motion on flexion–extension. Modic end plate changes in the bodies adjacent to the affected disc space, and little motion on flexion–extension. Because of

Perez-Cruet et al, An Anatomic Approach to Minimally Invasive Spine Surgery, 2nd Ed. (ISBN 978-1-62623-643-1), copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.

Lumbar Disc Replacement: The Artificial Disc the mechanical changes in the degenerative condition in the disc space, this natural disease process is already placing more forces on the adjacent levels. The application of an artificial lumbar disc will restore normal motion, height, and lordosis, and the forces on the adjacent level will be decreased. Thus, an artificial lumbar disc may have beneficial effects compared to the natural history of the nonoperated degenerative state.

43.3 Artificial Lumbar Disc Design The design of a lumbar artificial disc has many very strict requirements. These devices must have superb mechanical strength and endurance. They are designed to last several decades, as many of these devices will be implanted in young individuals. Mechanical testing of 5,000,000 motion cycles over a 40-year life span would be a typical design criterion. The base materials need to be biocompatible with no significant surrounding inflammatory reaction either due to the base material reaction or secondary to any debris. The devices need to induce no organotoxic or carcinogenic reaction from the base material or potential debris. The biomechanical functional movement requirements of an artificial lumbar disc are quite strict, as they need to replicate the full biomechanics of a normal disc. This normal motion includes translation and rotation in all three planes of motion—X, Y, and Z axes. The implant geometry and materials would determine the statistical configuration, dynamic motion, schematics, and any constrained nature of the motion. The exact placement of the lumbar artificial disc in the disc space is determined by its biomechanical design. Different designs will require different placement accuracy—the “sweet spot” for the implant. Fixed pivot devices may need a higher placement precision than devices that use a sliding core or an elastopolymer. The history of the lumbar artificial disc goes back 35 years to Fernström, who first placed spherical metal balls in the disc space. It was noted that a majority of these patients had ball migration into the vertebral body with subsequent collapse of the

disc space. Relatively recently, a nucleus pulposus replacement with a hygroscopic gel or fluid-filled cylindrical sacs has been developed for use after a standard discectomy in which the annulus is still holding the disc space to a normal height. These gels are currently under development and have not yet begun U.S. Food and Drug Administration (FDA) trials. Replacements of the entire disc after severe degenerative changes have included a variety of designs, such as mechanical bearing devices and a rubber/silicone/polymer nucleus between metal end plates made out of either cobalt-chromium or titanium, with the potential for bony ingrowth surfaces at the end plates. Although many different spinal dynamic stabilization systems go under the category of “artificial disc,” these need to be separated because they have different indications and potentially different applicable disease states. The first group of devices for the lumbar disc is intended to prevent the collapse of a lumbar disc space after a standard free-fragment disc herniation surgery.6,7,8 These devices are designed to be placed in the center of the disc to halt the secondary changes that would occur over the subsequent years and would hopefully provide stability over many decades, eliminating the need for fusion or rebuilding of the disc space at a later date. The second class of devices is for patients with severe DDD with loss of disc height but normal lordosis, instability of the disc, and little to no significant bony pathology posteriorly. This set of devices requires good facets, posterior ligaments, and muscular structures, as the aim is to replace only the degenerative disc component of the entire lumbar joint. These are currently what will be termed “artificial lumbar discs” and will be the focus of the remainder of this chapter. Four different designs have finished FDA investigational device exemption (IDE) trials (ProDisc, Maverick, FlexiCore, and Kineflex), and two designs have completed IDE trials and received marketing approval (CHARITÉ and ProDisc-L; ▶ Fig. 43.1). It is notable that these devices do not replace the posterior column degenerative changes; neither do they augment them. In fact, a

UNCONSTRAINED CHARITÉ

Fig. 43.1 Artificial lumbar discs that have completed Food and Drug Administration clinical trials separated by unconstrained and semiconstrained (fixed core) designs.

Kineflex

SEMICONSTRAINED FIXED CORE ProDisc

Maverick FlexiCore

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Surgical Techniques contraindication to any of these devices would be spondylolysis or significant spondylosis with facet hypertrophy and potential or ongoing nerve root compression. The third category of devices increases posterior column stiffness,9,10,11 with one currently in an IDE trial and others reported in European surgical series. The fourth class of devices is the total lumbar joint replacement, which would replace both anterior and posterior components. Currently, no such devices are available in any U.S. FDA trials, and none are being implanted elsewhere in the world. In the lumbar spine, in addition to the hard implants, which have metal ends that attach onto the bony end plates, there are also some soft implants made of either all elastic with potential laminations or a sack of fiber filled with some fluid or matrix.12,13,14,15 Currently, none of the soft implants are in FDA trials. There are potential base material problems with all current technology solutions to the bearing surface for the hard lumbar artificial disc replacement designs. Broadly, these fall into three separate classifications: a metal–metal design, a metal–ceramic design, and a metal–plastic design. The metal–metal designs have the potential problem of metal and/or metal ionic debris; with the metal–ceramic designs, there is a risk that the ceramic component may shatter; and with the metal–plastic designs, there is the problem of the plastic wearing out. At first thought, the wear associated with a metal–plastic bearing surface would seem to exclude it from use in the lumbar spine because of excessive long-term wear. This initial opinion is an extrapolation from the well-known fact that the plastic components in the current artificial hips and knees have a 10-year lifetime and then require revision. Because the lumbar artificial disc is made of these same base materials, cobalt-chromium and high-density polyethylene, it might be inferred that the lumbar artificial disc would also require replacement of the plastic cores every 10 years. There are three facts, however, that refute this seemingly common sense idea. First of all, with each step, the hip and the knee move approximately 50 degrees, whereas the lumbar spine will only tilt a few degrees. This greatly decreases the “sandpaper effect” by over an order of magnitude. Next, in the lumbar design the high-density polyethylene is not constrained but is open on the sides. This is in marked contrast to the hips, where the plastic is constrained in a ball-/socket-type joint. In the hip joints, the high-pressure points that arise at the constrained metal–plastic interface greatly accelerate the wearing of the plastic. Because of the nonconstrained nature of the plastic in the lumbar application, there are no wear-accelerated pressure points. Furthermore, there is good experience from Europe that there is no plastic wear in 10 years of implantation, verifying the estimation of the expected lifetime to be far greater than that of the hips and knees. A separate class of dynamic stabilization devices is currently being studied and tested in the cervical spine. These devices, although they are also called “artificial discs,” vary greatly from the lumbar artificial disc. First of all, cervical discs are experiencing much lower loads than lumbar discs, and they have different biomechanical characteristics. But more importantly, in the cervical spine, bony pathology and osteophytes causing radiculopathy and/or myelopathy predominate as causes of intervention rather than pure axial neck pain, as is the case in the lumbar indication (axial back pain) for an artificial disc. The potential patient groups to be studied and the outcome variables are quite different between the cervical and lumbar artificial

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disc studies. Furthermore, the results achieved in the lumbar area are not necessarily directly transferable to the cervical spine. In summary, all artificial discs are not the same. There will be major biomechanical differences between cervical and lumbar implants in the design, the disease treated, and the outcome expected. One needs to consider the pathology that is being treated, whether the disc is of normal disc height, and whether the patient has DDD, osteophytes, and/or facet disease before selecting the best treatment option.

43.3.1 Acroflex Artificial Lumbar Disc The earliest lumbar motion–preserving implant was the Acroflex disc. It was composed of a rubber core vulcanized to two titanium end plates and was pioneered by Dr. A. Steffee in Cleveland. The spinal kinematics, histologic osseointegration, and particulate wear debris after total disc arthroplasty using in vitro and in vivo models were studied.16 The Acroflex disc was also investigated in nonhuman primate model for bony ingrowth to the metal end plates regarding fixation as well as preservation of lumbar motion.17 Three-year follow-up showed that in a small number of patients (n = 6) the results were sufficiently satisfactory to proceed on with a larger study.18 However, larger and longer-term pivotal studies were not done because of detection of mechanical failure of the elastomer on thin-cut CT scans, and examples of osteolysis were also discovered.19,20 Although this design was found to be flawed, it laid the foundation for the modern designs of lumbar total disc replacement (TDR).

43.3.2 ProDisc-L Artificial Lumbar Disc The initial ProDisc-L product was designed in the late 1980s and used by Thierry Marnay, a French orthopedic spine surgeon. From March 1990 to February 1993, Dr. Marnay implanted this artificial disc in 64 patients. In 1999, he went back to examine these patients. He was able to locate 58 of the surviving 61 patients for a 95% follow-up rate at 7 to 10 years after the procedure. At that time, he found that all of the implants were intact and mechanically functioning. There had been no implant removals, revisions, or failures. Furthermore, there was no evidence of subsidence into the bony end plate on follow-up radiographs compared with the perioperative films. There was a highly significant reduction in patient-reported back pain and leg pain, and 92.7% of these patients were either satisfied or extremely satisfied with the results of this procedure. In this study, two-thirds of the patients had single-level implants and one-third had two-level implants. No differences were noted between one- and two-level diseases. Most importantly, at this long-term follow-up there were no device-related safety issues, no untoward effects, no complications, and no adverse events.21,22,23,24 This ProDisc-L was based on spherical articulation and had metal end plates. The current ProDisc-L (Synthes; ▶ Fig. 43.2), which was approved by the FDA in August 2006, consists of two cobalt-chromium end plates and a high-density polyethylene core, and is applied with an inserter no wider than the implant. It has a fin in the midline to help in stabilization and positioning. Because the high-density polyethylene is fixed to the inferior plate, it functions as a fixed pivot design,

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Lumbar Disc Replacement: The Artificial Disc

Fig. 43.2 ProDisc-L artificial lumbar disc. (a) Expanded view showing the two metal end plates and polyethylene core that attach to the lower metal end plate. (b) Assembled ProDisc-L artificial lumbar disc construct. (c–e) Sequence of steps involved in the insertion of the ProDisc-L artificial disc into the L4–L5 disc space. (c–e; reproduced with permission of Synthes Spine Co., LP.) (f,g) L5–S1 one-level ProDisc stabilization. (h,i) L4–L5 and L5–S1 two-level ProDisc-L stabilization.

and the instantaneous axis of rotation is within the lower body rather than in the disc space. The ProDisc-L has been studied in a FDA IDE randomized trial. The initial 2-year results of this trial were published in 200725 and report that the ProDisc-L showed superior results to circumferential fusion by multiple clinical criteria. Zigler and Delamarter26,27,28 and Zigler et al28 published the 5-year follow-up data on this study and reported that the large clinical

improvements that occurred immediately after surgery were maintained throughout the 5-year follow-up period. This data set was also used to report in detail the degenerative changes at the adjacent lumbar level and found that the ProDisc-L case that maintained range of motion (ROM) of the segment was associated with a significantly lower rate of adjacent-level disease compared with the circumferential group.27 The use of two-level ProDisc-L has been shown to lead to improvement in

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Surgical Techniques visual analog scale (VAS) and Oswestry Disability Index scores similar to the one-level ProDisc-L.29

43.3.3 Maverick, FlexiCore, Kineflex, Mobidisc, and Activ-L Artificial Lumbar Discs Four other TDR implants, Maverick,30,31 FlexiCore,32 Kineflex, and Mobidisc, were in FDA IDE trials for which enrollment was initiated about 10 years ago, and have completed planned enrollment and 2-year follow-up (▶ Fig. 43.3). Notably, the data in the Kineflex and the Mobidisc study were so incompletely reported that they were not included at all in a recent review of the TDR literature.33 All four of these prospective studies are incompletely reported in the literature as a result, in large part, of poor reimbursement insurance potential and perceived future FDA regulatory difficulties regarding a potential metal-on-metal bearing problem related to the real metal debris problem in some metal-on-metal hip prostheses. The lack of complete reporting in these studies has left several open questions, which may in fact be answerable by the studies. These questions include the metal-on-metal bearing surface safety in TDR, and long-term safety information on the use of BMP-2 (Infuse) in conjunction with a metal anterior lumbar interbody fusion (ALIF) implant in the Maverick study. Despite the poor reporting of the entire series, some papers on these studies have provided valuable information such as the histological and retrieval findings of Activ-L and Mobidisc TDR in two patients,34 and biomechanics with TDR by examining the mismatched center of rotation on the clinical outcomes and flexion–extension ROM with 5.5-year follow-up.35 A newer lumbar TDR Activ-L (B. Braun; Aesculap, Tuttlingen, Germany) just completed the FDA IDE trial in 2015.36 This new design was a result of wear simulation tests to predict the midand long-term clinical wear behavior for total disc arthroplasty and of biomechanical analysis in human cadaveric spines.37,38 Zander et al39 used a validated finite-element model of the lumbosacral spine to compare the results of total disc arthroplasty influence from different artificial disc (CHARITÉ, ProDisc, Activ-L) kinematics on spine biomechanics. The spinal kinematic alterations due to an artificial disc exceed by far the interimplant differences, while facet joint contact force alterations are strongly implant and load case dependent. Additionally, Wiechert40 commented on the modular design of the Activ-L TDR, which allows for a flexible anchoring concept with either spikes or one or two keels. The advantages of a semiconstrained design that allows for some movement of an ultrahigh-molecular-weight polyethylene (UHMWPE) inlay were also discussed. Lu et al41 reported on the early experience

in China with both a prospective and a retrospective study series42 and found the clinical outcome comparable to other forms of treatment for DDD.

43.3.4 CHARITÉ Artificial Disc The CHARITÉ artificial disc (DePuy Spine, Raynham, MA) was designed to restore disc space height and motion segment flexibility, and to duplicate the kinematics and dynamics of a normal motion segment.43,44 It was designed to restore anatomic lordosis, which will result in normal facet joint motion loading and unloading (▶ Fig. 43.4). The CHARITÉ artificial disc uses two metal alloy end plates of chromium-cobalt and a high-density polyethylene free-floating core. The free-floating core offers the theoretical advantage of allowing the spacer to shift dynamically within the disc space during regular spinal motion, moving posteriorly in flexion and anteriorly in lumbar extension. This not only provides unloading of the posterior facet structures during this normal replication of motion, but also allows forgiveness for slight off-center positioning of the implant. Several clinical studies have been published documenting the European experience with this disc since 1987. Worldwide experience with this unconstrained anatomic disc replacement now exceeds 11,000 cases. Several studies are historically notable. Cinotti et al45 reported on 46 Italian patients in 1996 with 2- to 5-year follow-ups. They noted no implant failures but did report a reoperation rate of 19% for continued pain. Overall satisfaction was 63%. Lemaire,46 who reported on his French series in 1997, followed 105 patients for a mean follow-up period of 51 months with 79% good outcomes and no device failures. Zeegers et al,47 in 1999, reported on 50 patients in a Dutch series, which showed 70% good results with 2-year follow-up. Recently, Lemaire et al48 reported long-term follow-up of clinical and radiologic outcomes for the CHARITÉ artificial disc with a minimum follow-up of 10 years. Of the 107 patients treated with the CHARITÉ artificial disc, 100 were followed for a minimum of 10 years (range 10–13.4 years). A total of 147 prostheses were implanted with 54 one-level procedures, 45 twolevel procedures, and 1 three-level procedure. Clinically, 62% had an excellent outcome, 28% had a good outcome, and 10% had a poor outcome. Of the 95 patients who were eligible to return to work, 88 (91.5%) either returned to the same job they had before surgery or took a different job. Mean flexion–extension motion was 10.3 degrees for all levels (12.0 degrees at L3–L4, 9.6 degrees at L4–L5, and 9.2 degrees at L5–S1). Slight subsidence was observed in two patients, but they did not require further surgery. No subluxation of the prostheses and no cases of spontaneous arthrodesis were identified. There was one case of disc height loss of 1 mm. Five patients required a secondary posterior arthrodesis. A good or excellent clinical outcome rate of 90% and

Fig. 43.3 FlexiCore artificial lumbar disc shown in anteroposterior (a) and lateral (b) views. This is a metal-on-metal device with some contour to the end plate attachment to match the normal anatomy and cleat attachment.

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Lumbar Disc Replacement: The Artificial Disc

Fig. 43.4 CHARITÉ artificial disc. (a) Fully assembled construct and disassembled parts showing the two metal end plates (b) and the ultrahigh-density polyethylene core (c). Note the various-sized footprints that are available. The metal end plates are also available in different angulations.

a

Parallel (0°)

b 25

5°

2 31.5 mm

25

27

2W 35.5 mm

7.5°

3 35.5 mm

27

29

3W 38.5 mm

10°

4 38.5 mm

29

31

5 42.0 mm

4W 42.0 mm

c 7.5 mm

8.5 mm

9.5 mm

10.5 mm

a return-to-work rate of 91.5% compare favorably with results described in the literature for fusion for the treatment of lumbar DDD. Lemaire et al48 concluded that with a minimum follow-up of 10 years, the CHARITÉ artificial disc demonstrated excellent flexion–extension and lateral ROM with no significant complications. The FDA IDE study of the CHARITÉ artificial disc initiated patient enrollment in May 2000, with the Texas Back Institute as the principal institution. Since that time, all patients have been enrolled in the FDA multicenter study with complete 2-year follow-up completed in December 2003. Following the randomized arm of the study, the centers had access to the CHARITÉ artificial disc, on a limited basis, as part of a continuing access study. The FDA granted approval for marketing the CHARITÉ artificial disc in the United States on October 26, 2004. The FDA label states49,50,51,52:

11.5 mm

The CHARITÉ artificial disc is indicated for spinal arthroplasty in skeletally mature patients with DDD at one level from L4 –S1. DDD is defined as discogenic back pain with degeneration of the disc confirmed by patient history and radiographic studies. These patients with DDD should have no more than 3 mm of spondylolisthesis at the involved level. Patients receiving the CHARITÉ artificial disc should have failed at least 6 months of conservative treatment prior to implantation of the CHARITÉ artificial disc. The CHARITÉ artificial disc comes in a variety of base metal sizes as far as the footplate to fit different-sized disc spaces.43 In addition, there are various end plate angles to match the distracted disc space anatomy. The plastic core is inserted between the two metal end plates and also comes in a variety of heights. The sizing of the end plates, angles, and heights is done intraoperatively. The CHARITÉ artificial disc is implanted

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Fig. 43.5 (a) CHARITÉ artificial disc implanted in a model of the spine showing the position of the device and how it transmits forces down the anterior column. (b) Translation of a normal lumbar disc in flexion–extension motion. (c) The translation is available in the sliding core of the CHARITÉ artificial disc to simulate this translation motion.

Fig. 43.6 (a) Flexion–extension views showing the instantaneous axis of rotation and how it changes in a Greek alpha–type pattern during this motion. (b) Pure Y-axis rotation around a fixed point demonstrating how the posterior elements would swing, causing more force on one facet than the other. (Adapted from Bogduk N. Functional anatomy of the disc and lumbar spine. In Buttner-Janz K, Hochschuler SH, McAfee PC, eds. The Artificial Disc. New York, NY: Springer; 2001:19–32.)

with metal end plates of chromium-cobalt on the superior and inferior bony end plates of the disc space and an UHMWPE core between the highly polished insert interfaces. There is a slight difference in the curvature between the polyethylene core and the metal end plates, which allows the core to slide. Spinal forces are transmitted down through the anterior column in a normal manner after the disc is inserted. The core translation allows duplication of anatomic translation (▶ Fig. 43.5, ▶ Fig. 43.6, ▶ Fig. 43.7). Under normal physiologic circumstances, there is a slight translation during the

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flexion–extension motion and lateral bending motion. A normal disc is able to handle this translation. In sagittal rotation (flexion– extension) under normal circumstances, the instantaneous axis of rotation, although generally in the center of the disc, moves in a pattern that duplicates the Greek letter alpha. The CHARITÉ artificial disc duplicates this motion. Coronal motion, likewise, has this slight translation in order to reproduce the normal biomechanics of the intact disc space. Axial rotation also requires a slight coupled rotation–translation to reduce the forces on the posterior facets. Pure axial rotation on a pivot point in the disc

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Lumbar Disc Replacement: The Artificial Disc

Fig. 43.7 Comparison of a fixed inferior component and a sliding intermediate component in the neutral and flexed positions. The fixed inferior component during flexion has more force near the front part of the artificial disc with the potential for jamming of the facets posteriorly. This is in contrast to the sliding intermediate component, which allows translation to release force on both the plastic core and the facets posteriorly.

Translation (average 2.06 mm)

Intact spine

Extension

Fig. 43.8 Coupled flexion–extension and translation for the normal disc and the CHARITÉ artificial disc, both of which have an average translation of approximately 2 mm. Note how the CHARITÉ artificial disc simulates the motion of a normal segment, including the translation.

Flexion

CHARITÉ Artificial Disc

space will result in direct compression of one facet joint while releasing the pressure on the other. If one compares a fixed pivot design to a sliding core design, the facet pressure would be more in a fixed pivot design than in a sliding core design. The exact clinical benefit for those patients who are most helped by the sliding core design will be determined by the outcome of the

Translation (average 1.90 mm)

clinical studies currently underway. It is evident from measurements of the center of intervertebral rotation in cadavers that the CHARITÉ artificial disc preserves normal motion (▶ Fig. 43.8) not only at the repaired disc space, but also at adjacent levels.53 Fusion has been reported to greatly distort the instantaneous axis of rotation at adjacent levels.53

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Surgical Techniques

Fig. 43.9 Typical preoperative radiographs from patient undergoing L5–S1 placement of a CHARITÉ artificial disc during clinical trials. (a) Collapse of the L5–S1 disc space and (b) corresponding T2-weighted MRI showing severe degenerative disc disease at L5–S1 with secondary Modic end plate changes. (c) Discogram showing abnormal L5–S1 disc corresponding to major pain generators. Note egress of contrast out of the disc, whereas it is contained within the L4–L5 disc space.

This mobile sliding core in the CHARITÉ artificial disc works in a similar fashion to the mobile knee bearing in many of the contemporary knee designs. In essence, this could be considered a second-generation device or an advanced-type design over a fixed pivot, much like the mobile core in the knee is considered an advanced design over fixed bearings. In biomechanical studies, this mobile sliding core results in true physiologic restoration of the lumbar segment. The FDA study of the CHARITÉ artificial disc examined onelevel disease only—that is, L4–L5 and L5–S1 (▶ Fig. 43.9). Patients had no radiculopathy, although they could have referred buttock or upper leg pain. Those patients with predominant pain below the knee were excluded from the study. Patients had a positive discogram with concordant pain, and most had MRI scans that showed a collapsed disc space, black disc on T2weighted images indicating decreased water content of the disc, and Modic end plate changes. There were no major social issues. This pivotal study enrolled 304 patients and was randomized between the CHARITÉ artificial disc and a Bagby and Kuslich stand-alone ALIF with autologous iliac crest bone arthrodesis. A typical patient radiograph is shown in ▶ Fig. 43.9a, at L5–S1. The corresponding MRI scan shows the Modic end plate changes in the collapse of L5–S1, as well as some water loss in L4–L5 in this particular patient (▶ Fig. 43.9b). The discogram would have excluded L4–L5 as the significant pain generator (▶ Fig. 43.9c).

43.4 Preoperative Planning Typical lumbar TDR patients have major disc abnormalities imaged at either the L4–L5 or L5–S1 levels with MRI almost always demonstrating loss of height, segmental lordosis, and water on T2 (dark disc) as well as Modic end plate changes in the vertebral bodies adjacent to the DDD, with normal or near-normal imaging at all other lumbar levels. Although initially patients with lumbar radicular pain from nerve root compression were excluded from receiving a lumbar artificial total disc, with the advancement of anterior lumbar surgery many herniated disc fragments can be removed as part of the lumbar TDR surgery. As with fusion procedures, patients should undergo a thorough review of clinical symptoms and radiographic testing along with a prolonged

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nonoperative course before they are considered to be surgical candidates. Provocative discography is recommended by many to aid in localizing the lumbar pain generators. Diagnostic blocks may also be helpful in localizing the exact pain generator site. If the patient has previously had abdominal surgery, examination by the approach surgeon for potential approach-related complications and incision location is highly recommended. As with selection of lumbar fusion patients, preoperative evaluation of the patient and identification of the exact pain generator is the most important part of the entire CHARITÉ artificial disc procedure. It is notable that excellent surgical technique and precise placement of the prosthesis will not overcome poor patient selection to produce a good clinical outcome.

43.5 Surgical Technique 43.5.1 Patient Positioning The placement of the CHARITÉ artificial disc will demonstrate typical TDR placement. All the steps are similar in the various TDR designs although details are implant specific. The patient should be placed in a supine position with the arms across the chest or abducted 90 degrees on a radiolucent table. Care is taken to align the break in the table directly under the affected disc; it may be helpful to adjust the table during the procedure to open up the disc space during the discectomy and implant insertion. Alternatively, a Jackson table, which does not “break” or “hinge” in the middle, can be used and an inflatable lumbar pillow can be placed under the patient’s lumbar spine during positioning to aid in intraoperative patient adjustment. The position of the patient’s arms allows for circumferential C-arm movement over and around the operative level. Although neither a bowel preparation nor a Foley catheter is mandatory, both aid in the retraction of the peritoneal contents and are routinely used by most surgeons.

43.5.2 Surgical Approach Anterior exposure of the spine is an important part of the artificial disc implantation procedure. The anterior approach to the

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Lumbar Disc Replacement: The Artificial Disc L4–L5 and L5–S1 area is performed using standard general surgery techniques to gain access to the retroperitoneal space and dissect the great vessels from the lumbar disc spaces.40 Anterior approaches to the spine may be either transperitoneal or retroperitoneal. The left retroperitoneal approach is preferred because it avoids several complications and allows better visualization. The skin incision may be midline or paramedian. A midline incision is often preferred because it allows a better midline view of the disc space for more accurate midline placement of the prosthesis. The skin incision may also be either transverse or vertical; however, exact placement of a transverse incision is critical, whereas a vertical incision may be extended if placement is not exact. The exact incision depends on the patient’s spinal anatomy and body habitus, and surgeon preference.

Avoiding Surgical Complications Surgical tips for general-access surgeons to help them avoid complications: ●

●

●

●

A retroperitoneal dissection should be performed to avoid injury to the hypogastric plexus and postoperative ileus. Dissection should be done directly over the iliac vein at L5– S1 to avoid injury to the hypogastric plexus as well as to provide access to the plane and to best visualize the presacral branches. The aberrant branch of the iliac vein should be identified and ligated, if necessary, to avoid tearing the iliac vein. The ascending lumbar vein should also be identified, and if there is any tension, it should be ligated to avoid injury to the vena cava.

Technical tips for spine surgeons to help them avoid vascular injuries: ●

●

●

●

●

●

Choose an experienced access surgeon with experience in vascular repairs. Make certain the vascular access surgeon is present during the entire operation. Ensure that the vascular surgeon evaluates the patient preoperatively and postoperatively. Clean side to side; remain in the space; beware of cautery conduction. Always check lateral and superior/inferior clearances before using spreading forceps. Maintain vascular clearance.

The surgeon should be aware that there are several differences between disc exposures of L4–L5 and L5–S1. The exposure of L5–S1 is generally between the bifurcations of the iliac vessels, whereas the exposure of L4–L5 is generally above or to the left of the bifurcation, although patient vessel anatomy can be variable. At L4–L5, the vessels should be retracted to the right. At L5–S1, care should be taken to protect the left and right common iliac vessels on each side of the anterior disc space. Often by flexing the patient’s hips and knees, tension is relieved in the iliac vessel and retraction is easier and requires less force.

Discectomy A complete discectomy is required for implantation of the artificial disc. The disc space has all the cartilaginous end plate and annulus removed. Additionally, the bony end plates are flattened to match the flat surfaces of the metal end plates of the implant. Typically, posterior osteophyte is removed from at least one of the end plates with a chisel, Kerrison punch, or curette. Without this extensive discectomy, the surgeon could force some remaining disc, annulus, or bone into the neural canal during insertion of the implant placement.

Importance of a Complete Discectomy Complete discectomy, including the removal of the posterior lateral recesses of the disc, facilitates the following: ● Parallel distraction, which allows for the restoration of intervertebral height and sufficient opening of the neuroforamen. ● Parallel alignment of the inner surfaces of the end plates, which provides uniform loading of the sliding core, allowing near-normal physiologic motion in flexion–extension. ● Sufficient space for the optimally sized CHARITÉ artificial disc.

Key Maneuvers for Complete Discectomy ● ● ●

Removal of the posterior lateral disc corners. End plate preparation of the L5 lip. Posterior release, and visualization and release, if necessary, of the posterior.

Intraoperative fluoroscopy is an essential part of the procedure, and adequate images are verified before the patient is draped. Both anteroposterior and lateral images are verified. The images are used to identify the midline of the disc space and the implant placement. The initial midline mark estimate should be made with a cautery device adjacent to the disc space. The discectomy is performed by initially incising the anterior longitudinal ligament with a scalpel opened for the width of the disc implant and then a generous discectomy is performed (▶ Fig. 43.10). Although all of the cartilaginous end plates are removed, care should be taken not to disturb the bony end plates because they will support the metal plates of the artificial disc. Removing the bony end plate may lead to subsidence of the prosthesis. The discectomy is enlarged to expose the cortical bone circumferential rim. Deviations from perfectly flat end plates, such as posterior lipping or slight “fish mouthing,” are usually encountered posteriorly. These are removed with a 0.25-inch chisel or a Kerrison punch. Additionally, especially at L5–S1, the anterior longitudinal ligament in the degenerative disease stage can be exceptionally thick (sometimes extending over 1 cm). This needs to be removed to clearly define the anterior bony margin so that when the implant is placed, the surgeon can verify both visually and fluoroscopically that the anterior cleats of the implant are below the anterior cortical margin.

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449

Surgical Techniques

a

b

c

Fig. 43.10 Preparation of the disc space. (a,b) The disc material is removed. (c) A chisel is used to flatten the end plates as necessary.

Fig. 43.11 Central spreader (spreading and insertion forceps) is inserted into the disc space to allow for controlled distraction.

A central spreader (spreading and insertion forceps) is then placed in the disc space to perform parallel distraction (▶ Fig. 43.11). This parallel disc space distraction is accomplished by inserting the T-handled spacers through the spreading and insertion forceps and positioned to the back of the spreader, rotated 90 degrees (▶ Fig. 43.12). The posterior longitudinal ligament is stretched and/or ripped to some extent, increasing the posterior height of the disc space. If the disc space is collapsed, sometimes the surgeon will hear a “pop” when the disc space is opened to the proper tension. Despite the heaviness of the distractor, closing only on the handles will effectively fish mouth the disc space distraction, opening up mostly only the anterior disc with little or no posterior distraction. The force for the parallel distraction is generated by twisting the T-handle between the distractor blades and then just taking up the slack with the distractor handles (▶ Fig. 43.13). Once the disc space has been distracted, additional disc material that was contained within the buckled ligament in the neural canal often moves into the disc space. This is removed with a Kerrison or biopsy punch. The distracted space may also provide a better view of the posterior osteophytes, which should be removed to allow for proper placement of the prosthesis. It is important that the surgeon remove disc material from the

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posterior lateral corner. Any of the following will prevent the surgeon from inserting the prosthesis back far enough: ● Failure to remove enough of the disc from the disc space. ● Failure to remove enough of the disc from the posterior lateral corner. ● Failure to remove a posterior lip from the L5–S1 vertebra. On occasion, either with use of the spreading and insertion forceps or with removal of the posterior disc or the posterior annulus, the epidural veins can bleed in a manner similar to the way they would in a posterior discectomy or posterior lumbar interbody fusion spinal procedure. The bleeding is routinely controlled by packing the area with Avitene and a sponge. During the disc space distraction procedure, in approximately twothirds of the cases, some epidural bleeding or significant bone bleeding along the posterior edge is encountered. This is easily handled with strips of Avitene placed in the disc space and then compressed down against the remaining posterior longitudinal ligament area with a standard 4 × 4 sponge. After allowing this to sit for approximately 2 to 3 minutes, the sponge can be removed, leaving the thin layer of Avitene in place. The hemostatic agent is easier to use during the initial discectomy or after the metal end plates have been inserted than after the core is inserted for the final assembly of the implant.

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Lumbar Disc Replacement: The Artificial Disc

Fig. 43.12 T-handle distraction spacers are inserted into the spreading and insertion forceps. They permit parallel distraction and prevent a “fish mouth.”

Fig. 43.13 Self-retaining retractors in place and the distractor unit in the wound. Note the angled handles of an earlier implantation system.

Footplate Templating After adequate disc space preparation, the CHARITÉ artificial disc can be inserted. The first step for implant insertion is determining the correct footprint size. This is accomplished by using sizing gauges, which correspond to the seven available end plate footprint sizes. The correct size is verified by lateral fluoroscopy (▶ Fig. 43.14). The prosthetic end plates are relatively flat on their metal–bone surface, so in addition to determining the ultimate size that will be used, it is critically important to ensure that there is a flat surface for insertion. If there are sclerotic ridges or irregularities in the bony surface, they must be flattened with curettes or chisels, because the prosthesis needs to sit flush with the bony surface and be “press-fit.” Any irregularity in the posterior lip of the cortical end plate needs to be removed to allow for proper positioning.

Insertion of the Radiolucent Trial with Insertion Guide The radiolucent trials mimic the footprint, angulation, and height of the end plates and sliding core. Correct sizing, placement, and lordotic angle are critical to ensure optimal performance. The Trial Insertion Guide is inserted into the disc space, placing the “marker side” superiorly. Based on the footprint size, as determined by the sizing gauge in the previous step, the surgeon can select the correct lordotic trial and load it onto the Trial Insertion Guide to help in placing the trial guide (▶ Fig. 43.15). The larger lordotic angle is placed inferiorly to reduce shear forces and help protect the prosthesis and posterior elements. The Trial Insertion Guide is removed from the disc space, leaving only the trial.

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451

Surgical Techniques Remove posterior lip to allow for proper posterior positioning

Fig. 43.14 (a,b) Lateral radiographs are obtained to ensure that the posterior lip has been adequately removed to allow for proper posterior positioning of the implant. (c) After removal of the posterior lip, a lateral radiograph confirms that the position of the template extends to the posterior aspect of the vertebral body. Note that the center of the artificial disc implant is approximately 2 mm dorsal to the sagittal midline.

a Position to posterior aspect of vertebral body

Center of rotation 2 mm dorsal to sagittal midline

b

c

a

Fig. 43.15 (a,b) Insertion of Trial Insertion Guide and lordotic trial.

b

Correct Sizing, Placement, and Lordotic Angle ●

●

●

Choose a trial footprint that maximizes the area of vertebral end plate that is covered. Confirm the ability to place the trial as follows: ○ Lateral: center of disc = 2 mm dorsal to midline. ○ Anteroposterior: center of disc = center of disc space. Choose a lordotic angle that restores the desired segmental lordosis; the correct angles have been selected if there is no white line visible between the trial and the vertebral body on lateral fluoroscopy.

midline, as indicated by “ + ”; and (3) there is no lucency between the Trial Insertion Guide and the vertebral end plate, which indicates proper restoration of lordosis (▶ Fig. 43.16b,c). It is mandatory that the C-arm image be positioned directly parallel (colinear) with the end plates. To ensure that the technician aligns the C-arm end plate perfectly parallel, it should be viewed on continuous fluoroscopy. To obtain a lateral view, the bilateral eyelets on the inserter shaft should be aligned to form a circular opening (▶ Fig. 43.17a). Then, the eyelet position can be confirmed at 2 mm posterior to the vertebral body sagittal midline (▶ Fig. 43.17b).

Insertion of the Midline Marker Once the trial guide has been inserted (▶ Fig. 43.16a), an anteroposterior radiograph is obtained to verify that (1) the Trial Insertion Guide is perpendicular to the coronal plane, as indicated by “ + ”; (2) the Trial Insertion Guide is placed on the

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It is important when viewing the radiolucent trial to ensure that the trial is countersunk to the correct depth. The anteroposterior view can indicate whether the prosthesis has the correct width so there will be a good footprint fit. If there are no

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Lumbar Disc Replacement: The Artificial Disc

a

Fig. 43.16 (a) Insertion of the radiolucent trial, placing the “marker side” superiorly. Note the retraction of all vascular structures. Anteroposterior (b) and lateral (c) radiographs confirm that the trial is perpendicular to the coronal plane and is in the midline (+). These radiographs also confirm proper lordosis.

b

Midline

c

Anteroposterior marker Core marker

Align bilateral eyelets on inserter shaft to form a circular opening

a

Fig. 43.17 (a) To obtain a proper lateral image, the eyelet position on the inserter shaft should be aligned bilaterally to obtain a circular opening. (b) The eyelet position is confirmed 2 mm posterior to the vertebral body sagittal midline.

b

gaps above or below, the angulation is good. Once correct placement of the trial is verified, the midline marker is placed in the anteroposterior midline of the superior vertebral body by placing the loaded marker inserter into the grooves of the trial insertion instrument (▶ Fig. 43.18). This marker serves to indicate the correct midline position and assists the surgeon in gaining orientation during insertion of instruments and the implant. The screw is easily visualized on anteroposterior and lateral fluoroscopy (▶ Fig. 43.19).

Insertion of the Pilot Driver The Pilot Driver is used to confirm positioning by matching the footprint geometry and approximating the height of the implanted end plates. The middle tooth of the Pilot Driver and handle must be in line with the midline marker and spinous processes to ensure maintenance of the midline (▶ Fig. 43.20). Note that it is very important to shape any curved vertebral surfaces before Pilot Driver impaction to prevent vertebral body or

end plate fracture during impaction. The center of the Pilot Driver should be 2 mm posterior to the lateral midline. The Pilot Driver must be inserted parallel to the end plates to prevent end plate violation. If resistance is encountered during insertion, a lateral C-arm image should be obtained to confirm that the Pilot Driver is parallel to the end plates to avoid breaking off part of the bone or gouging the end plate.

Confirming Position ● ●

●

The use of the Pilot Driver is critical. The Pilot Drivers match the footprint geometry and closely approximate the height of the two end plates during implantation. If the Pilot Driver can be impacted to the desired location for the prosthesis, successful implantation of the end plates to that same location can be achieved; if this is not possible, additional discectomy or end plate preparation will be required.

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453

Surgical Techniques

a

c

Fig. 43.18 (a) Insertion of the radiolucent trial. (b) Insertion of the midline marker. (c) The midline marker in final position.

b

Fig. 43.19 Screw placed in the inferior portion of the L5 body to serve as a midline marker. The screw was aligned with the handle of the radiolucent trial (▶ Fig. 43.18b).

The next step is to impact the Pilot Driver to make three grooves for the end plates. Notice that the Pilot Drives surfaces are parallel to the adjacent bony endplates. A lateral C-arm image is taken of the Pilot Driver (▶ Fig. 43.21). Note that the end plate holding forceps, sizing templates, and Pilot Drivers all have a midline etch, and the arrows should always point directly to the midline marker during their insertion. The slap hammer is used to safely remove the Pilot Driver from the disc space.

Insertion of the End Plates Next, the metal end plates of the artificial disc are inserted. The end plate insertion tips that correspond to the chosen end plate

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size are attached to the spreading and insertion forceps. Then, the selected end plates are loaded into the end plate insertion tips, placing the more angled of the two end plates inferiorly (▶ Fig. 43.22). When an oblique end plate is used, the surgeon should load the thicker margin into the end plate insertion tip first. The thick margin should be placed anteriorly within the vertebral disc space. The spreading and insertion forceps should be carefully aligned with the anteroposterior midline marker and trajectory. The end plates are slowly advanced into the disc space with multiple impacts and with the assistance of the guided impactor (▶ Fig. 43.23). End plate insertion is carefully monitored with fluoroscopy to accurately control the posterior depth and to verify the appropriate lordotic angle. When the prosthesis has been inserted halfway into the disc space, the break in the table or inflation of the lumbar pillow is removed. Continuous C-arm monitoring is done during final implant positioning, and the implant is positioned to ensure the final position of the center of the end plates is 2 mm posterior to the lateral midline of the vertebral body and centered on the medial–lateral midline.

The Core Trial With the end plates now in place, the next step is to open the disc space. The metal end plates of the implant are impacted into the disc space, positioned posteriorly within the disc space, and then parallel distracted using the spreading and insertion forceps (▶ Fig. 43.24). The distraction spacers and modular Thandle aid in proper distraction and core height selection (▶ Fig. 43.25). During this distraction, it is essential that only the very lateral edges of the implant are touched, because one does not want to scratch the inside of the cups. Scratching the articulating metal cups of the implant would result in a significant increase in the amount of plastic wear. Therefore, a parallel orientation should be maintained between the shaft of the

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Lumbar Disc Replacement: The Artificial Disc

Fig. 43.20 Insertion of the Pilot Driver. (a) The middle tooth and handle of the Pilot Driver must be in alignment with the midline marker and spinous process to ensure maintenance of the midline. The Pilot Driver must be inserted parallel to the end plates to prevent end plate violation. (b) As the Pilot Driver is inserted, the center tooth should be aligned with the midline marker.

Fig. 43.21 (a) Lateral radiograph confirming placement of the Pilot Driver. The handle can be moved caudal or cephalad to stay within the end plates. (b) The operating table must be in the neutral supine position for the final posterior advancement.

spacer and the spreading and insertion forceps. Once the desired distraction is attained, the core size is estimated visually and by means of fluoroscopy. The sliding core height can be confirmed by placing the core trial between the distracted end plates (▶ Fig. 43.26). Slight resistance may be felt as the core trial is passed through the rims of the articulating surfaces of the end plates. Once the core trial is in position, it moves within the articulating surface of the end plates. The core trial should never be impacted. A lateral radiograph is obtained to show the disc height and lordotic angle.

instrument and distraction is removed. To remove the core insertion instrument, the surgeon must remove the end plate insertion tips from the vertebral end plates without changing the position of the prosthesis. The slap hammer is attached to the guided impactor, and the combined instrument is used to safely remove the spreading and insertion forceps; it should be pulled directly out, taking care not to pivot or rotate the instrument during removal.

Core Insertion and Instrument Removal

Points that determine placement accuracy are outlined in the following text box. Anteroposterior and lateral fluoroscopy should be used to help position the device and to provide final verification of placement. One cannot verify proper positioning of the posterior teeth other than by radiographic imaging. The anterior teeth can be seen by direct vision, and it should be ascertained that the implant is recessed below the anterior cortical margin. The final implant position must not allow the anterior teeth to protrude past the vertebral end plates. If necessary, an appropriate-sized grooved driver is used on the sides of the metal end plates of the implant to make minor adjustments and also to impact the anterior cleats within the bony structure (▶ Fig. 43.28a).

Next, the core trial is removed and the implant sliding core inserted. The appropriate core insertion tip is loaded into the core insertion instrument (▶ Fig. 43.27a-c). Then, the sliding core is placed into the core insertion tip by squeezing the handle. The sliding core is positioned between the end plates in the disc space. If resistance is felt, the distraction is slowly increased. Then, the distraction is released on the spreading and insertion forceps, allowing the end plates to close around and engage the sliding core (▶ Fig. 43.27d). Verification that the plastic core is in the correct position to articulate with the cups is made. The core is released by squeezing the handle of the core insertion

Final Positioning

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455

Surgical Techniques to damage the sliding core and the polished surfaces of the end plates. Once the final position has been confirmed, the single end plate impactor may be used to manually engage the anterior fixation teeth of the end plates into the vertebral body, providing additional fixation.

Closure The midline marker is removed before closure, and the wound is closed in a standard manner.

43.5.3 Clinical Case ▶ Fig. 43.30 shows postoperative results from a patient demonstrating motion in angulation and translation in flexion–extension and lateral bending directions.

Largest angle always inferior

Fig. 43.22 The selected end plates are loaded into the end plate insertion tips. The thicker margin should be loaded into the end plate insertion tip first.

Critical Points That Determine Accuracy of Final Placement ● ● ● ●

●

Check final positioning before closure. Check lordotic angles. Verify end plate coverage. Confirm medial and lateral position on an anteroposterior radiograph. Confirm anterior and posterior position on a lateral radiograph.

When repositioning the implant, care must be taken not to damage the sliding core and the polished surfaces of the end plates (▶ Fig. 43.28b,c). ▶ Fig. 43.29 shows good implant positioning, which is confirmed by means of fluoroscopy.

Intraoperative Repositioning If repositioning and adjustment of the device is necessary, it should be performed before insertion of the sliding core to prevent possible bone fracture. If the surgeon notices via radiography or changes in spinal cord monitoring that the prosthesis is positioned too far back or the disc does not appear large enough, the entire device can be removed and reimplanted by carefully distracting the interbody space, removing the sliding core, and then removing each end plate. The goal is to create a working space to remove the prosthesis without damaging the bone and surrounding soft tissue. Care must also be taken not

456

43.5.4 Revision Techniques If the CHARITÉ artificial disc were required to be revised, there would be two approaches. One approach would be to redo the anterior surgery. This would involve dissecting the retroperitoneal area and dealing with the postoperative scarring and hence increased risk of great vessel damage compared to a nonoperated case. This would allow removal of the CHARITÉ artificial disc. The plastic core would be removed first, and then the metal end plates could be separated from the bony end plates by using a chisel between them and levering away from the bone into the disc space. This would allow the placement of another artificial disc in the disc space, as the bony end plates would not be significantly damaged. Alternately, a posterior operation with rod–screw stabilization and posterolateral fusion could be used to fuse the lumbar segment, which would use the CHARITÉ artificial disc as an anterior load share. If the patient has reoccurring or persistent pain, then clinically characterizing the location of the pain generator is more important than the exact surgical technique used. This localization would be determined by a variety of radiologic and provocative studies. Discography at adjacent levels would be helpful, as would epidural facet injections, and potentially even an anesthetic discogram at adjacent levels to see if that would eliminate most of the pain.

43.5.5 Outcomes for CHARITÉ Disc Revision The pivotal study on the CHARITÉ artificial disc was a prospective, randomized, multicenter FDA-regulated IDE clinical trial. The purpose of this study was to compare the safety and effectiveness of lumbar TDR, using the CHARITÉ artificial disc (DePuy Spine), with ALIF, for the treatment of single-level DDD from L4–S1 that is unresponsive to nonoperative treatment. Prior to this, a class I medical evidence study reported results of lumbar TDR that were favorable, but studies have been limited to retrospective case series and/or small sample sizes. A total of 304 patients were enrolled in the study at 14 centers across the United States and randomized in a 2:1 ratio to treatment with the CHARITÉ artificial disc or a control group undergoing instrumented ALIF. Data were collected preoperatively and perioperatively at 6 weeks and at 3, 6, 12, and 24

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Perez-Cruet, An Anatomical Approach to Minimally Invasive Spine Surgery | 01.10.18 - 11:01

Lumbar Disc Replacement: The Artificial Disc

a

c

b

Fig. 43.23 (a) The end plates are carefully inserted into the disc space with the assistance of the guided impactor. (b,c) If necessary, lordosis can be increased to initiate initial implant impaction. (d) The table must be returned to a neutral, supine position when the implant is halfway in the disc space to finalize proper positioning.

d

Fig. 43.24 (a) Metal end plates in place in a posterior position. (b) Parallel distracted end plates. (c) Insertion of the distractor.

months after surgery. The key clinical outcome measures were a VAS assessing back pain, the Oswestry Disability Index questionnaire, and the Short Form-36 Health Survey. Patients in both treatment groups improved significantly after surgery. Patients in the CHARITÉ artificial disc group recovered more quickly than patients in the control group. Patients in the CHARITÉ artificial disc group had lower levels of disability at every time interval from 6 weeks to 24 months,

compared with the control group, with statistically lower pain and disability scores at all times including the 24-month follow-up (p ~ 0.05). At the 24-month follow-up period, a significantly greater percentage of patients in the CHARITÉ artificial disc group expressed satisfaction with their treatment and would have the same treatment again, compared with the fusion group (p < 0.05). The hospital stay was significantly shorter in the CHARITÉ artificial disc group (p < 0.05). The complication

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Fig. 43.25 (a,b) The disc space is distracted to the appropriate disc height with the spacers and modular T-handle.

Fig. 43.26 The core trial is placed between the end plates in the disc space and the distraction is released.

rate was similar in both groups. When the entire patient population in the study is combined (training and randomized) and Wilcoxon/Kruskal–Wallis nonparametric tests are used, the results of the Oswestry Pain Scale and VAS indicated significant improvement in the CHARITÉ group at all time points including the 24-month follow-up time point (▶ Fig. 43.31). This prospective, randomized, multicenter study demonstrated that quantitative clinical outcome measures after lumbar TDR

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with the CHARITÉ artificial disc are at least equivalent to clinical outcomes achieved with ALIF. These results support earlier reports in the literature that TDR with the CHARITÉ artificial disc is a safe and effective alternative to fusion for the surgical treatment of symptomatic disc degeneration in patients with the proper indications. The CHARITÉ artificial disc group demonstrated statistically significant superiority in two major economic areas: a 1day shorter hospitalization and a lower rate of reoperations (5.4 vs. 9.1%). At 24 months, the investigational group had a significantly higher rate of satisfaction (73.7%) than the 53.1% rate of satisfaction in the control group (p = 0.0011). This prospective, randomized, multicenter study also demonstrated an increase in employment of 9.1% in the investigational group and 7.2% in the control group.45,46,47,48 In follow-up radiographic studies, the patients have mobility in both flexion–extension and lateral bending in the level that was dynamically stabilized (▶ Fig. 43.30). Radiographic evidence shows clear movement of the core translation with the flexion–extension movement. The author’s initial impression is that the clinical outcome results are comparable or better than historical fusion results reported in the literature. The biomechanics of the ProDisc-L and the CHARITÉ are quite different, with the ProDisc-L having a fixed pivot point anterior to the normal axis of rotation of the spinal vertebra and the CHARITÉ having a movable central core able to mechanically adapt to both the normal and abnormal axes of rotation of the spinal vertebra. Initially, it was thought that these biomechanical differences would produce a large difference in the clinical outcomes. However, once the 2-year FDA IDE data were published for these two studies, the Oswestry (▶ Fig. 43.32a,b) and VAS (▶ Fig. 43.32c,d) improvement and the maintenance of this improvement were quite similar. In these figures, the VAS improvement with time for the CHARITÉ and ProDisc-L is shown for both the absolute values and the normalized initial values. This set of graphs also demonstrated that all four groups (CHARITÉ TDR, CHARITÉ control group ALIF, ProDisc-L TDR, and ProDisc-L control group 360 fusion) were better than baseline. Additionally, it is noted that the ALIF group of controls had better outcomes than the 360 fusion group and that the CHARITÉ TDR had a numerically better recovery curve in all four graphs.

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Lumbar Disc Replacement: The Artificial Disc

a

b

Fig. 43.27 (a) Insertion of the core. (b) The appropriate core insertion tip is loaded into the core insertion instrument. (c) The core is released by squeezing the core insertion instrument handle. (d) The core is shown in good position. The core and the cups are verified visually.

c d

Fig. 43.28 (a) If minor adjustments are necessary, final positioning of the implant can be done with a grooved driver. (b,c) It is important to note that the anterior profile of the device should not be prominent or close to prominent.

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Fig. 43.29 (a) Completed implant within the disc space. (b,c) Anteroposterior and lateral radiographs of the completed implant.

Fig. 43.30 (a–f) Patient in flexion–extension and lateral bending showing clear motion of the device both in angulation and with translation of the core in both planes of motion.

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Lumbar Disc Replacement: The Artificial Disc OSWESTRY SCALE — ALL CHARITÉ AND CONTROL PATIENTS

60 50 Mean Oswestry Scores

#, p = 0.0016 #, p = 0.0005

40

#, p = 0.0004

*

#, p = 0.019

*

30

*

#, p = 0.026

*

*

12 mos

24 mos

Fig. 43.31 When the entire patient population in the study is combined (training and randomized) and the Wilcoxon/Kruskal–Wallis nonparametric test results are used, the Oswestry Disability Index (a) and visual analog scale (b) scores are significant for improvement in the CHARITÉ group at all time points including the 24-month follow-up time point. TDR, total disc replacement.

20 10 0

Preop

6 wks

All TDR (Non-Randomized + Randomized)

*p < 0.05

a

3 mos 6 mos Follow-up Time Points

Control Group

VISUAL ANALOG SCALE (VAS) — ALL CHARITÉ AND CONTROL PATIENTS

80 70

Mean VAS Scores

60 50

#, p = 0.018 #, p = 0.0010

40

*

30

#, p = 0.0002

#, p = 0.017

#, p = 0.028

*

*

*

*

3 mos

6 mos

12 mos

24 mos

20 10 0

Preop

6 wks

Follow-up Time Points

b

*p < 0.05

All TDR (Non-Randomized + Randomized)

43.6 Conclusion Estimates as to when other devices will be available on the United States market vary greatly. At the time this chapter was initially written, the CHARITÉ artificial disc was the only artificial disc with FDA approval. Furthermore, the FDA trial is the only class I medical evidence currently available comparing any artificial disc technology with spine fusion techniques. Since then, the ProDisc-L was approved and then with the merger of Synthes and DePuy Spine, only the ProDisc-L was marketed by the merged DePuy-Synthes. It is expected that in the coming years, Activ-L will obtain FDA approval. A systematic review of the literature on lumbar TDR surgery in 201049 found the current studies lacking in details of especially long-term follow-ups of 10 to 20 years and recommended further study. This review also found no compelling scientific data to suggest that TDR was superior to lumbar fusion at this time. They also expressed concern about the reoperation and complication

Control Group

rate of the TDR. It is interesting that although these comments are an interpretation of the current state of knowledge for lumbar TDR, the lack of long-term follow-up, complication, and reoperation rate knowledge of the alternative surgical technique, lumbar fusion, was not really discussed in this review article. In conclusion, since lumbar spinal arthroplasty was first reported in clinical settings nearly 30 years ago by Buttner-Janz et al54 and Griffith et al,55 lumbar dynamic stabilization with the CHARITÉ artificial disc is a promising treatment modality for relieving axial lumbar pain and preserving joint mobility in selected patients. The 2-year clinical outcome after single-level discogenic DDD appears superior to historical fusion results. Additional research will be conducted in the coming years to see whether “topping off” a lumbar fusion will help prevent adjacent-level disease and whether this device can be used below a scoliosis when the degenerative changes occur, and whether multilevel disease will have the same good clinical response that single-level disease appears to be having in this clinical study.

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Fig. 43.32 (a,b) Comparison of Oswestry Disability Index in CHARITÉ and ProDisc FDA IDE. Note that all four groups are better than baseline; anterior lumbar interbody fusion has a better outcome than 360 Fusion, and CHARITÉ has a better outcome than ProDisc. (c,d) Comparison of visual analog scale in CHARITÉ and ProDisc FDA IDE. ALIF, anterior lumbar interbody fusion; FDA, Food and Drug Administration; IDE, investigational device exemption; ODI, Oswestry Disability Index; VAS, visual analog scale.

43.7 Author’s Note Portions of the “Surgical Technique” section were adapted from McAfee PC, ed. Lumbar Spine Arthroplasty: The Artificial Disc, Vol. 3. St Louis, MO: Thieme Publishing; 2005.

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[4] Hedman TP, Kostuik JP, Fernie GR, Hellier WG. Design of an intervertebral disc prosthesis. Spine. 1991; 16(6) Suppl:S256–S260 [5] Arnold PM, Kirschman DL, Meredith C. Prosthetic vertebral disc replacement. In Vaccaro AR, ed. Principles and Practice of Spine Surgery. Philadelphia, PA: CV Mosby; 2003:379–384 [6] Klara PM, Ray CD. Artificial nucleus replacement: clinical experience. Spine. 2002; 27(12):1374–1377 [7] Wilke HJ, Kavanagh S, Neller S, Claes L. [Effect of artificial disk nucleus implant on mobility and intervertebral disk high of an L4/5 segment after nucleotomy]. Orthopade. 2002; 31(5):434–440 [8] Wilke HJ, Kavanagh S, Neller S, Haid C, Claes LE. Effect of a prosthetic disc nucleus on the mobility and disc height of the L4–5 intervertebral disc postnucleotomy. J Neurosurg. 2001; 95(2) Suppl:208–214 [9] Freudiger S, Dubois G, Lorrain M. Dynamic neutralisation of the lumbar spine confirmed on a new lumbar spine simulator in vitro. Arch Orthop Trauma Surg. 1999; 119(3–4):127–132 [10] Sénégas J. Mechanical supplementation by non-rigid fixation in degenerative intervertebral lumbar segments: the Wallis system. Eur Spine J. 2002; 11 Suppl 2:S164–S169

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[34] Austen S, Punt IM, Cleutjens JP, et al. Clinical, radiological, histological and retrieval findings of Activ-L and Mobidisc total disc replacements: a study of two patients. Eur Spine J. 2012; 21 Suppl 4:S513–S520 [35] Lee CS, Lee DH, Hwang CJ, Kim H, Noh H. The effect of a mismatched center of rotation on the clinical outcomes and flexion-extension range of motion: lumbar total disk replacement using Mobidisc at a 5.5-year follow-up. J Spinal Disord Tech. 2014; 27(3):148–153 [36] Yue JJ, Mo FF. Clinical study to evaluate the safety and effectiveness of the Aesculap Activ-L artificial disc in the treatment of degenerative disc disease. BMC Surg. 2010; 10:14 [37] Grupp TM, Yue JJ, Garcia R, Jr, et al. Biotribological evaluation of artificial disc arthroplasty devices: influence of loading and kinematic patterns during in vitro wear simulation. Eur Spine J. 2009; 18(1):98–108 [38] Ha SK, Kim SH, Kim DH, Park JY, Lim DJ, Lee SK. Biomechanical study of lumbar spinal arthroplasty with a semi-constrained artificial disc (activ L) in the human cadaveric spine. J Korean Neurosurg Soc. 2009; 45(3):169–175 [39] Zander T, Rohlmann A, Bergmann G. Influence of different artificial disc kinematics on spine biomechanics. Clin Biomech (Bristol, Avon). 2009; 24(2):135–142 [40] Wiechert K. Keel-implants: Activ-L. Oper Orthop Traumatol. 2010; 22 (5–6):608–619 [41] Lu S, Kong C, Hai Y, et al. Prospective clinical and radiographic results of active L total disc replacement at 1- to 3-year follow-up. J Spinal Disord Tech. 2015; 28(9):E544–E550 [42] Lu S, Kong C, Hai Y, et al. Retrospective study on effectiveness of activ L total disc replacement: clinical and radiographical results of 1- to 3-year followup. Spine. 2015; 40(7):E411–E417 [43] Link HD, Buttner-Janz K. Link SB CHARITÉ artificial disc: history, design, and biomechanics. In Kaech DL, ed. Spinal Restabilization Procedures. Amsterdam: Elsevier Science BV; 2002:293–316 [44] McAfee PC. Artificial disc prosthesis: the Link SB CHARITÉ III. In Kaech DL, ed. Spinal Restabilization Procedures. Amsterdam: Elsevier Science BV; 2002:299–310 [45] Cinotti G, David T, Postacchini F. Results of disc prosthesis after a minimum follow-up period of 2 years. Spine. 1996; 21(8):995–1000 [46] Lemaire JPSB. SB CHARITÉ III intervertebral disc prosthesis: biomechanical, clinical, and radiological correlations with a series of 100 cases over a followup of more than 10 years. Rachis. 2002; 14:271–285 [47] Zeegers WS, Bohnen LM, Laaper M, Verhaegen MJ. Artificial disc replacement with the modular type SB Charité III: 2-year results in 50 prospectively studied patients. Eur Spine J. 1999; 8(3):210–217 [48] Lemaire JP, Carrier H, Sariali H, Skalli W, Lavaste F. Clinical and radiological outcomes with the Charité artificial disc: a 10-year minimum follow-up. J Spinal Disord Tech. 2005; 18(4):353–359 [49] Geisler FH, Blumenthal SL, Guyer RD, et al. Neurological complications of lumbar artificial disc replacement and comparison of clinical results with those related to lumbar arthrodesis in the literature: results of a multicenter, prospective, randomized investigational device exemption study of Charité intervertebral disc. Invited submission from the Joint Section Meeting on Disorders of the Spine and Peripheral Nerves, March 2004. J Neurosurg Spine. 2004; 1(2):143–154 [50] Geisler FH. Surgical technique of lumbar artificial disc replacement with the Charité artificial disc. Neurosurgery. 2005; 56(1) Suppl:46–57, discussion 46–57 [51] McAfee PC, Cunningham B, Holsapple G, et al. A prospective, randomized, multicenter Food and Drug Administration investigational device exemption study of lumbar total disc replacement with the CHARITE artificial disc versus lumbar fusion: part II: evaluation of radiographic outcomes and correlation of surgical technique accuracy with clinical outcomes. Spine. 2005; 30 (14):1576–1583, discussion E388–E390 [52] Blumenthal S, McAfee PC, Guyer RD, et al. A prospective, randomized, multicenter Food and Drug Administration investigational device exemptions study of lumbar total disc replacement with the CHARITE artificial disc versus lumbar fusion: part I: evaluation of clinical outcomes. Spine. 2005; 30 (14):1565–1575, discussion E387–E391 [53] Cunningham BW, Gordon JD, Dmitriev AE, Hu N, McAfee PC. Biomechanical evaluation of total disc replacement arthroplasty: an in vitro human cadaveric model. Spine. 2003; 28(20):S110–S117 [54] Buttner-Janz K, Hochschuler SH, McAfee PC, eds. The Artificial Disc. New York, NY: Springer; 2001 [55] Griffith JF, Wang YX, Antonio GE, et al. Modified Pfirrmann grading system for lumbar intervertebral disc degeneration. Spine. 2007; 32(24): E708–E712

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44 Minimally Invasive Spine Surgery: Lumbar Case Studies Mick J. Perez-Cruet, Richard G. Fessler, Roman Chornij, and Michael Y. Wang Abstract Minimally invasive surgery has made its greatest advances in the treatment of lumbar pathology due to the prevalence of pathology in the lumbar spine. Mastering these techniques will expand the surgeon’s armamentarium to treat a variety of lumbar spinal disorders. This chapter illustrates the use of a number of techniques and technologies developed to treat a variety of lumbar conditions. Seven unique cases are presented in the chapter. These techniques and technologies offer patients improved outcomes while reducing approach-related morbidity. Keywords: lumbar spine, case studies, minimally invasive spinal surgery, lumbar microendoscopic discectomy, incidental durotomy, transforaminal lumbar interbody fusion, percutaneous screws, decompression, pseudarthrosis, pedicle subtraction osteotomy, spinal realignment, spinal misalignment, fusion/fixation, lateral lumbar interbody fusion, minimally invasive decompression, progressive spondylolisthesis, lumbar stenosis, degenerative dextroscoliosis

44.1 The Evolution of Lumbar Minimally Invasive Spine Surgery Nowhere has minimally invasive spinal surgery (MIS) gained greater adoption than in the lumbar spine. The prevalence of thoracolumbar pathology, the need for better methods of treatment, and the proliferation of technologies have all synergized to allow for rapid advancements in this area of the spinal column over the past decade. Anterior mini-open retroperitoneal, lateral transpsoas, and trans-sacral approaches have been developed. Decompression via tubular, endoscopic, and indirect methods has been innovated to replace a standard open laminectomy. Percutaneous screws, transfacet screws, facet interference constructs, and cortical trajectories have all allowed for less invasive fixation. Today, MIS methods are available for treating a wide spectrum of lumbar spinal pathologies. In addition to degenerative disease, neoplasms, infection, trauma, and deformity are now all accessible through less invasive approaches. Given the continuing advances in osteobiologics, material science, optics, robotics, and miniaturization, innovation in this area will likely continue to evolve the fastest.

44.2.2 Case Selection The patient showed a central disc herniation at L4–L5 (▶ Fig. 44.1).

44.2.3 Preoperative Notes The patient failed 6 weeks of nonoperative therapy including physical therapy (PT) and chiropractic manipulation. He was offered epidural steroid injection (ESI), but he refused.

44.2.4 Instrumentation Notes There is no indication for instrumentation is this case.

44.2.5 Surgical Approach and Technique The patient was induced with general anesthesia and intubated endotracheally. Appropriate arterial and venous access was obtained. The patient was then turned into the prone position on the Wilson frame. Fluoroscopy was placed in the lateral position and the patient’s lumbar spine was shaved, prepped, and draped in the usual sterile fashion. Using lateral fluoroscopy, an appropriate incision to approach the left L4/L5 level was identified and marked 1.5 cm off the midline. This area was infiltrated with 0.5% Marcaine with epinephrine. A no. 10 scalpel was then used to incise the skin over approximately 2 cm. Hemostasis was obtained with bipolar cautery. A Kirschner wire (K-wire) was then placed through the incision and advanced to the L4/L5 facet. This position was confirmed fluoroscopically. A series of

44.2 Case 1: Lumbar Microendoscopic Discectomy 44.2.1 Patient Profile A 38-year-old man with a 2-month history of low back and left lower extremity pain extending from the sacrum to the lateral calf. He can only walk if he leans to the left. Leaning to the right causes severe pain in right lateral calf. The patient is in extreme pain.

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Fig. 44.1 Sagittal T2-weighted MRI demonstrates an extremely large, central disc herniation at the L4–L5 level.

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Minimally Invasive Spine Surgery: Lumbar Case Studies dilators was then placed over the K-wire, and after the first dilator was placed the K-wire was removed. Finally, the working channel was positioned, angled medially, and locked in place. This position was confirmed fluoroscopically. Camera was then introduced into the working channel. Bovie cautery was used to remove a small amount of residual tissue at the bottom of the working channel. An angled curette was then used to define the sublaminar space. Kerrison punch was used to perform a hemilaminotomy and this was extended into a medial facetectomy using the Legend (Sofamor Danek, Memphis, TN) drill with a cutting M8 burr. The traversing nerve root was then retracted slightly medially, and the epidural space explored. The bulging disc was identified and confirmed fluoroscopically. A no. 15 blade scalpel was used to incise the annulus, and a discectomy was performed using a series of curettes and pituitary rongeurs. At the completion of decompression, the exiting and traversing nerve roots were noted to be well decompressed throughout their course. Hemostasis was obtained with bipolar cautery and Gelfoam. The wound was copiously irrigated with antibiotic solution and the retractor was removed. Fascia was closed using 0 Vicryl stitches. The subcutaneous tissue was closed using 2–0 Vicryl stitches. Finally, the skin was closed using Dermabond. The patient was then returned to the supine position and allowed to recover from anesthesia.

44.2.6 Postoperative Care The patient was observed in recovery for 2 hours and was discharged.

and relieved with a recumbent position. Epidural injections were helpful, but only gave transient relief.

44.3.2 Case Selection Radiographic imaging demonstrated a mobile grade I spondylolisthesis at the L3/L4 level due to an old bilateral pars defect (▶ Fig. 44.2a,b).

44.3.3 Preoperative Notes The patient was offered anterior versus posterior versus combined (360-degree) approaches. He elected for a posterior approach, which was more likely to achieve a successful reduction and fixation in a single-stage operation. Additionally, the patient had relatively normal spinal canal diameter at the L3–L4 level and did not require direct decompression to address spinal canal stenosis.

44.3.4 Instrumentation Notes Accomplishing a percutaneous interbody fusion requires the use of expandable cages that can be placed through Kambin’s triangle. As such, all disc preparation and graft placement must be carried out through a maximum of an 8-mm corridor. Percutaneous screws are placed in standard fashion.

44.3.5 Surgical Approach and Technique

Microscope can be used instead of an endoscope. Drilling 2 mm of the medial facet facilitates access to the disc with minimal retraction of the nerve root.

The patient is given sedation with propofol anesthesia but no narcotics. Positioning is prone on a Jackson table. A flank incision is made 12 cm off the midline and access is made into the disc space using the extraforaminal endoscopic approach into Kambin’s triangle. After discectomy and nerve root decompression, disc clearance can be achieved utilizing specialized brushes that do not violate the bony end plate. After disc space preparation, the space is filled with graft material and the interbody expandable cage is inserted. Expansion of the cage allows interbody distraction, spondylolisthesis correction, fusion, and indirect decompression of the contralateral nerve root with disc and foraminal height restoration (▶ Fig. 44.2f). Percutaneous screws are then placed after injecting the screw tracts with long-acting local anesthetic medications.

44.2.9 Postoperative Results

44.3.6 Postoperative Care

Excellent results can be expected in 90 to 95% of patients treated with this technique.

The patient is managed postoperatively with standard pain management and bracing, similar to standard open surgery.

44.3 Case 2: Awake Lumbar Minimally Invasive Transforaminal Lumbar Interbody Fusion

44.3.7 Management of Complications

44.2.7 Management of Complications The most common complication in this procedure is incidental durotomy. This can be handled with a dural sealant and 24 hours of bed rest. Lumbar drain is not necessary. The skin can be closed using a running locking nylon suture to help prevent cerebrospinal fluid (CSF) leakage and allow for healing.

44.2.8 Operative Nuances

44.3.1 Patient Profile A 62-year-old man presented with severe right thigh and back pain. He had failed conservative measures and was only able to walk three blocks before having to stop. The pain was related to mechanical loading, exacerbated with standing and walking,

Routine antibiotic prophylaxis is used to minimize the risk of postoperative infections. Pseudarthrosis can be minimized with proper graft site preparation, use of appropriate graft materials, bracing, external bone stimulation, and the elimination of tobacco use.

44.3.8 Operative Nuances Performing this procedure without a general anesthetic requires careful attention to patient selection, preserving

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Fig. 44.2 (a,b) Sagittal X-ray and MRI views of a patient with a grade I L3/L4 spondylolisthesis. (c,d) Entry and dilation of the intervertebral disc space through Kambin’s triangle. (e) Removal of the disc using a drill with end plate bone preservation. (f) Filling of the disc space with a contrast-filled balloon to ensure adequate disc removal and end plate contact. (g) Intervertebral allograft cage in place and cannulation of pedicles above and below. (h,i) Final fluoroscopic images before disarticulation of the screw and rod extensions.

soft-tissue structures, use of expandable cages, specialized percutaneous screws placed through smaller incisions, and the use of long-acting local anesthetics. In addition, thoughtful coordination with the anesthesiologist is key.

44.3.9 Postoperative Results Patients treated in this manner can be discharged after one night in the hospital and opioid usage is minimal.

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44.4 Case 3: Mini-open Pedicle Subtraction Osteotomy 44.4.1 Patient Profile A 57-year-old woman presented with difficulty standing, walking, and working due to intractable low back pain. She had lost 3 inches of height over the past 4 years. Imaging revealed the patient had a degenerative kyphoscoliosis, consistent with her symptoms (▶ Fig. 44.3a).

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Minimally Invasive Spine Surgery: Lumbar Case Studies

Fig. 44.3 (a) Anteroposterior (AP) and (b) lateral 36-inch standing X-rays showing a degenerative kyphoscoliosis. (c) Intraoperative view showing placement of the four rods through screw extensions and fracture at the mini-pedicle subtraction osteotomy site. Final (d) AP and (e) lateral 36-inch standing X-ray plane films.

44.4.2 Case Selection The goals of spinal realignment and fusion/fixation are central to the proper treatment of this patient. However, the application of standard open deformity surgery carries a significant complication rate. Thus, the patient elected for a less invasive option with the same surgical corrective goals.

44.4.3 Preoperative Notes Careful counseling for the treatment of osteopenia and osteoporosis is common in this patient population. In addition, higher rates of pseudarthrosis and proximal junctional kyphosis are seen when treating adult spinal deformities.

44.4.4 Instrumentation Notes The technique of mini-open pedicle subtraction osteotomy (PSO) necessitates placement of a lordotic rod through a kyphotic spine. Use of four rods (two passed from above and two from below) achieves this objective.

44.4.5 Surgical Approach and Technique After positioning the patient on a Jackson table, a dorsal midline skin incision is made. However, the deeper soft tissues are dissected only at the level of the PSO. Thus, this exposure is similar to an open two-level lumbar fusion. Interbody fusion is performed below the level of the PSO using the MIS transforaminal lumbar interbody fusion (TLIF) technique. The L3 level PSO is performed in standard fashion with spinous process, lamina, and facet removal. This is followed by pedicle removal and a bilateral de-cancellation osteotomy using a series of enlarging curettes to remove two cones of cancellous bone from the vertebral body. Central bone was removed with a curved curette and the de-cancellation is extended superiorly into the L2–L3 disc space. A Leksell rongeur is then used to remove the lateral vertebral body wall bilaterally in a wedge-shaped pattern to match the de-cancellation. Control of the spine to break the osteotomy is then achieved by placing percutaneous pedicle screws at least three levels above and below the PSO site. A total of four rods are bent and passed through each set

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Surgical Techniques of screw heads above and below the PSO. The posterior vertebral body wall and posterior longitudinal ligament are removed, and after ensuring there is no ventral bone or ligament that might impinge on the thecal sac, the osteotomy is closed (▶ Fig. 44.3c). The L3 nerve roots and thecal sac are then inspected to ensure that there is no neural compression, and any bleeding is controlled with powdered collagen matrix. The cranial and caudal rods are connected with offset connectors, and the construct is finally tightened and fusion of the facets above the PSO is achieved through small access sites (▶ Fig. 44.3d,e).

44.4.6 Postoperative Care The patient is managed postoperatively with standard pain management and bracing, similar to standard open surgery.

44.4.7 Management of Complications As with open osteotomies and deformity corrections, these patients are subject to risks associated with bleeding, nerve root compression, pseudoarthrosis, and spinal misalignment.

44.4.8 Operative Nuances Great care must be taken to connect the four rods properly and also to bend them to the proper degree of lordosis.

44.4.9 Postoperative Results In a series of patients treated in this manner, significant reductions in blood loss were made possible by reducing the amount of soft-tissue dissection and subperiosteal exposure.

44.5 Case 4: Minimally Invasive Lateral Lumbar Interbody Fusion 44.5.1 Patient Profile A 56-year-old woman with history of multiple motor vehicle accidents (MVA) and falls presented with 3 years of low back pain, radiating bilaterally to her lateral thighs, calves, and ankles (▶ Fig. 44.4).

44.5.2 Case Selection Two-level spondylolisthesis with back pain equal to or greater than radicular pain suggests that fusion, rather than just decompression, is the better option for this patient. MIS techniques include TLIF or lateral lumbar interbody fusion (LLIF). In this case, LLIF seems to be the less invasive technique, and enables more rapid recovery.

Fig. 44.4 Preoperative (a) lateral, (b) anteroposterior (AP) X-ray, (c) sagittal and (d) axial MRI images showing grade I spondylolisthesis with associated canal compromise at the L3–L4 and L4–L5 levels. Postoperative (e) lateral and (f) AP X-ray plane film images after two-level extreme lateral interbody fusion and posterior percutaneous pedicle screw instrumentation. Note restoration of sagittal alignment, canal, disc, and foraminal height.

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Minimally Invasive Spine Surgery: Lumbar Case Studies

44.5.3 Preoperative Notes The patient failed multiple attempts of PT, which made her stronger but did not relieve her pain. A course of three ESIs provided only temporary relief of her pain.

44.5.4 Instrumentation Notes Although some have argued that stand-alone LLIF is adequate for these cases, the success rate has been shown to be lower than in LLIF with posterior instrumentation.

44.5.5 Surgical Approach and Technique The patient was induced with general anesthesia and intubated endotracheally. Appropriate arterial, venous, and Foley access was obtained. The patient was then turned into the lateral position, with the left side up, on a beanbag, using the Skytron bed. Her upper arm was supported on an arm rest. The table was then “cracked” to maximize exposure of the upper lateral abdomen. When positioning was acceptable, the beanbag was deflated to a stiff, conforming shape. The patient was held in a perfect lateral position and the arm, hip, and upper leg were taped to hold that position. The patient’s lateral lumbar spine was then shaved, prepped, and draped in the usual sterile fashion. Using lateral fluoroscopy the L3–L4 and L4–L5 disc spaces were marked, and the point identifying the disc location onethird posterior to the ventral border was marked at each disc space. An appropriate incision to approach these levels was then marked. This area was infiltrated with 0.5% Marcaine. A no. 10 scalpel was then used to incise the skin over approximately 4 cm. Hemostasis was obtained with bipolar cautery. Using handheld retraction, the subcutaneous tissues were dissected until the fascia of the external oblique muscle was identified. This was cut using a Metz scissors. Blunt dissection was then used to dissect through the external oblique muscle until the fascia of the internal oblique muscle was identified. This was also cut and dissected to identify the transversalis fascia. This was cut with the Metz scissors, exposing the retroperitoneal fat. Blunt dissection of this fat revealed the lateral border of the iliopsoas muscle. The entire length of the iliopsoas muscle was explored under direct vision (a microscope or loupe magnification with headlight can be used) to be certain no neural or visceral structures were in the pathway of the subsequent dissection. When the lateral border was demonstrated to be clear, an electrode was slowly advanced through the muscle toward the L4–L5 disc space under lateral fluoroscopy. Stimulation was then performed to be certain that no neural structures were in the operative bed. When the tip was in appropriate position, and no neural structures were encountered, the tip was then advanced into the disc space. The electrode was then withdrawn from its sheath and a K-wire was advanced through the sheath, into the disc space. A series of dilators were then placed over the K-wire. Finally, the working channel was positioned, expanded, and locked in place. The operative bed over the disc space was then visually inspected. Bovie cautery was used to remove a small amount of residual tissue at the bottom of the working channel. A no. 10 scalpel was then used to incise the annulus. Using a series of curettes and pituitary rongeurs, an

aggressive discectomy was then performed. The end plates were scraped using a series of end plate curettes. Finally, the contralateral annulus was cut using a Cobb dissector. A series of trials then demonstrated that a 12 × 45 mm cage would be the appropriate-sized cage. This cage was selected, packed with hydroxyapatite, and half sponge of bone morphogenetic protein (BMP), and taped gently into place. Position was confirmed with anteroposterior (AP) and lateral fluoroscopy. Hemostasis was obtained with bipolar cautery and Surgifoam. The apparatus was then slowly removed, assuring hemostasis as it was withdrawn. Using exactly the same technique, discectomy and fusion were performed at the L3–L4 level. Percutaneous posterior instrumentation is the same as that described earlier.

44.5.6 Postoperative Care The patient recovered for 2 hours in the recovery room and was transferred to a room on the general neurosurgery floor. She was postoperatively discharged on day 2. She began PT 6 weeks after surgery.

44.5.7 Management of Complications Potential complications include injury to the femoral nerve, genitofemoral nerve, ilioinguinal nerve, great vessels, bowel, and kidney.

44.5.8 Operative Nuances Several steps can minimize complications. Direct observation of the surface of the iliopsoas muscle can avoid injury to the genitofemoral nerve and bowel. Stimulation and direct observation down the retractor tube can avoid injury to the femoral nerve. Care should be taken during the approach and closure to avoid injuring the ilioinguinal nerve running under the external oblique muscle.

44.5.9 Postoperative Results We have observed that recovery from this operation is quite rapid, and return to normal activities faster than MIS TLIF.

44.6 Case 5: Minimally Invasive Decompression and Reduction of Progressive Spondylolisthesis in Redo Operation 44.6.1 Patient Profile A 57-year-old man presented having undergone a previous traditional decompressing laminectomy for grade 1 spondylolisthesis with associated stenosis. Postoperatively, the patient had improvement in symptoms for about 1 year, then began to experience severe back pain with standing and neurogenic claudication symptoms. MRI studies revealed a progression of his spondylolisthesis and return of stenosis with severe bilateral foraminal stenosis secondary to subluxation of the L4–L5 level.

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44.6.2 Case Selection The patient was a candidate for minimally invasive TLIF with the goal to decompress the neural elements directly from a posterior approach and restore sagittal alignment.

44.6.3 Preoperative Notes The patient was informed of treatment options and agreed to proceed with a posterior approach. The patient was informed that he was at higher risk for dural tear and/or nerve root injury because of the prior surgery creating scar tissue and adding to the technical difficulty of the case. A posterior approach was felt optimal to allow for direct decompression of the neural elements as well as reduction of the spondylolisthesis using interbody disc restoration techniques and percutaneous pedicle screw reduction technology.

44.6.4 Instrumentation Notes An interbody system was selected that facilitated the entry into the disc space while minimizing risk of injury to the nerve roots and restoration of disc space height and foraminal diameter. A percutaneous pedicle screw system was selected that allowed for reduction of the spondylolisthesis.

44.6.5 Surgical Approach and Technique The patient was intubated and neuromonitor was placed to measure electromyogram (EMG). The patient was then placed in the prone position with all pressure points adequately padded. The level was then identified with lateral fluoroscopy and a spinal needle and a 25-mm incision was made 3 cm lateral to the midline on the left side overlying the disc space. The One-Step-Dilator (Thompson MIS, Salem, NH) was used to approach the spine in a muscle-splitting fashion. A fascial incision was placed and the dilator was used to approach the spine, opened, and a tubular retractor placed over the dilator through which the procedure was performed.

A minimally invasive decompressive laminectomy was then performed as well as a left ipsilateral facetectomy to approach the disc space. All drilled bone graft material was collected using the Thompson MIS BoneBac to collect autograft used for fusion material. The collapsed disc space was entered with a chisel, followed by serial disc space reamers, curettes, and rongeurs to prepare the disc space for interbody fusion. Adequate disc space preparation is very important to assure interbody fusion. The end plates are prepared to remove the cartilaginous portion. Using AP and lateral fluoroscopy, percutaneous pedicle screws are placed. Pedicles are tapped and percutaneous pedicle screws placed using the Longitude II with Solera Sextant rods (Medtronic, Memphis, TN). K-wires and percutaneous pedicle screws are stimulated once positioned to assure safe placement. Amplitude above the 8-mA threshold is adequate, but we will consider repositioning the K-wire and/or pedicle screw if the amplitude is below 10 mA (▶ Fig. 44.5). Gradual reduction of the spondylolisthesis is performed by tightening the L5 screw bolt onto the rod to secure it in place. Reduction towers are placed on the L4 extender tubes and gradual reduction under fluoroscopic guidance is performed to fully reduce the spondylolisthesis and restore disc and foraminal height as well as canal diameter.

44.6.6 Postoperative Care The patient was transferred to the floor where he made an uneventful recovery. PT worked with the patient to begin ambulation and strengthening exercises. The patient was discharged on postoperative day 3.

44.6.7 Management of Complications Complication avoidance is managed with adequate surgical training in this technique. The interbody device used allows for safer placement into the disc space that limits nerve root retraction as the interbody is 7 mm wide; then it can be rotated 90 degrees to restore disc height once inside the disc space. Monitoring of K-wires and pedicle screws helps assure safe

Fig. 44.5 Using anteroposterior and lateral fluoroscopic images (a), Jamshidi needles are placed through which (b) Kirschner’s wires (K-wires) are applied and the pedicles tapped. (c) Percutaneous pedicle screws are then placed over the K-wires and rods applied.

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Minimally Invasive Spine Surgery: Lumbar Case Studies Fig. 44.6 Four-level spinal stenosis. (a) Preoperative sagittal CT myelogram showing lumbar L1– L2, L2–L3, L3–L4, and L4–L5 lumbar stenosis with corresponding axial CT image (b–e). (Continued)

placement. The patient must be informed of CSF leaks, especially in redo operations where extensive scar tissue is expected. We generally manage these with a small Gelfoam patch and thrombin glue. The fascia is closed in a meticulous fashion and the skin closed with a running locking nylon suture.

44.6.8 Operative Nuances The posterior approach is ideal for direct decompression of the neural elements. Docking the tubular retractor on and exposing the lateral aspect of the facet complex helps orient the surgeon with the location of the thecal sac. Drilling the facet off to approach the disc space avoids the midline scar tissue and potential injury to nerve roots and/or dural tear. The disc space can then be entered safely and interbody preparation done and implant placed.

44.6.9 Postoperative Results This patient made an uneventful recovery with return to work and activities of daily living. We generally have patients wear a lumbosacral orthosis (LSO) brace while ambulating for the first 2 to 3 months. The brace is not necessary while sitting or lying in bed. PT is started in the hospital setting and continued for 4 weeks.

44.7 Case 6: Multilevel Lumbar Stenosis 44.7.1 Patient Profile A 56-year-old man presents with neurogenic claudication symptoms. MRI showed multilevel lumbar stenosis. The patient

had failed to improve with PT and pain management. A CT myelogram was performed to delineate the extent of lumbar stenosis. The CT myelogram showed a four-level stenosis (▶ Fig. 44.6).

44.7.2 Case Selection The patient presents with congenital multilevel lumbar stenosis typically seen in younger males with short pedicle anatomy. A posterior minimally invasive laminectomy with in situ autograft facet fusion allows for a direct decompression of the neural elements while preserving the normal anatomy of the spine.

44.7.3 Preoperative Notes The patient was informed of possible complications such as nerve root injury and/or dural tears. The patient was also informed of the possibility for more extensive instrumented fusion if restenosis occurs. A CT myelogram study is very helpful in delineating the extent of lumbar stenosis as well as the bony anatomy for the surgical approach. A posterolateral facet fusion helps prevent restenosis.

44.7.4 Instrumentation Notes No instrumentation is needed. Using local drilled morselized autograft collected from the surgical site reduces the cost of the procedure and enhances fusion outcomes. A CO2 laser is used to facilitate contralateral ligamentum flavum shrinkage and removal.

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Fig. 44.6 (continued) (f,g) Postoperative CT showing adequate decompression (h,i) L1–L2, (j,k) L2–L3, (l,m) L3–L4, (n) L4–L5, using autograft bone collected with the BoneBac Press to achieve a posterior in situ facet fusion and laminar reconstruction while preserving the spinous process.

44.7.5 Surgical Approach and Technique The patient is intubated and placed in a prone position on a radiolucent Wilson frame. In general, the most severely stenotic level is approached first. An incision is made approximately 1.5 cm lateral to the midline on the more symptomatic side (left in this case). The One-Step-Dilator is used to approach the spine once the dorsal fascia is cut with a Bovie cautery and docked on the facet complex laterally. Tubular retractor is placed and microscope brought into the operative field. The ipsilateral lamina is exposed. An M8 cutting burr is used to perform an ipsilateral laminectomy. Once completed, the patient is tilted 5 degrees away from the surgeon and the tubular retractor repositioned to expose the base of the spinous process. The drill is then used to undercut the base of the spinous process and contralateral lamina. The ligamentum flavum is first removed on the ipsilateral and then the contralateral side. A CO2 laser can then be used to shrink the contralateral ligamentum flavum and then removed with a no. 1 or 2 Kerrison punch. With adequate thecal sac decompression and inspection with a ball-ended probe, the facets are decorticated medially on the contralateral side and laterally on the ipsilateral side. Morselized autograft collected from the surgical site using the BoneBac Press is then placed within the facets to achieve a facet in situ fusion. The tubular retractor is removed and the procedure performed at adjacent levels. Once decompression is completed, a subfascial drain is placed, tunneled under the skin and secured to the skin. The incision is closed in a routine fashion.

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44.7.7 Management of Complications Complications can include dural tear and CSF leak. Prevention of CSF leak can be achieved by maintaining the ligamentum flavum in place while performing bone drilling. Shrinkage of the contralateral ligamentum flavum with a CO2 laser can help make removal safer. Collection of autograft from the surgical bed eliminates graft site morbidity. Postoperative subfascial drain with intravenous (IV) antibiotics helps reduce hematoma formation in the surgical bed. Ambulation postoperatively helps prevent deep vein thrombosis (DVT) formation, constipation, and atelectasis.

44.7.8 Operative Nuances This technique helps maintain normal anatomy and assure faster recovery. In situ autograft fusion helps prevent restenosis. Tilting the patient slightly away from the surgeon and repositioning the tubular retractor allows for undercutting of the spinous process and contralateral lamina.

44.7.9 Postoperative Results The patient was discharged on postoperative day 3. PT was started on an outpatient basis on the 2-week follow-up. The patient returned to work and activities of daily living 4 weeks after surgery.

44.8 Case 7: Degenerative Dextroscoliosis and Severe Stenosis with Associated Spondylolisthesis

44.7.6 Postoperative Care

44.8.1 Patient Profile

The patient is transferred to the floor. Typically, the drain is removed on postoperative day 1. The patient is ambulated with PT on the following day.

An active, healthy 79-year-old female presents with an 8month history of progressive difficulty walking, consistent with a diagnosis of neurogenic claudication. Physical therapy and pain

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Minimally Invasive Spine Surgery: Lumbar Case Studies

Fig. 44.7 Plain X-ray (a) lateral and (b) anteroposterior views show degenerative dextroscoliosis in this elderly female patient. Relative lucency in the vertebrae seen on the lateral image indicates osteoporosis.

Fig. 44.8 (a) Sagittal and (b) axial T2-wieghted MRI images show L4–L5 spondylolisthesis and associated severe canal stenosis with elongation of facet complexes.

management failed to relieve symptoms. Imaging studies revealed a degenerative dextroscoliosis and severe stenosis with associated spondylolisthesis at the L4–L5 level (▶ Fig. 44.7). MRI shows grade I spondylolisthesis, associated central canal stenosis, and elongation of the facet complexes (▶ Fig. 44.8).

44.8.4 Instrumentation Notes The BoneBac TLIF system that allows for the use of the patient’s own morselized autograft harvested for the surgical site and percutaneous pedicle screw system with reduction capabilities was used.

44.8.2 Case Selection Images were reviewed with the patient and treatment options discussed including continuation of nonoperative care. A focused minimally invasive posterior approach, which allowed for decompression along with stabilization, was selected to minimize complications.

44.8.3 Preoperative Notes Many elderly patients found to have degenerative scoliosis are symptomatic from stenosis and not from the scoliotic deformity. Focused decompression and stabilization can result in excellent outcomes without the increased surgical risk that might be associated with correction of the deformity in the elderly, especially women with osteoporosis.

44.8.5 Surgical Approach and Technique The patient was intubated, monitoring placed, including EMG, and positioned in the prone position on a Jackson table. An incision was made 3 cm lateral to the midline on the left side at the L4–L5 level. The One-Step-Dilator was used to approach the spine over which a tubular retractor was placed. The microscope was brought into the surgical field. The ipsilateral lamina was exposed and minimally invasive laminectomy performed, followed by TLIF with percutaneous pedicle screws and reduction towers to reduce the spondylolisthesis (▶ Fig. 44.9). The incision was then closed in a routine fashion.

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44.8.7 Management of Complications Focused operative decompression, instrumentation, and fusion of the symptomatic site in elderly patients with complex degenerative deformity can result in excellent outcomes while helping reduce approach-related morbidity.

44.8.8 Operative Nuances Physical history, examination, and MRI in combination with CT myelogram can help in the diagnosis of the location of symptomatic pathology in the elderly patient with complex spinal deformity. Wanding the fluoroscope in the lateral view will aid in assuring that surgery is performed at the correct level. Careful identification of intraoperative anatomy will assure adequate decompression. When performing percutaneous pedicle screw instrumentation in these patients, each targeted vertebra is optimized in the AP view to visualize the end plate and spinous process properly by placing the fluoroscope in the proper coronal and sagittal plane. Intraoperative monitoring with stimulation of K-wires and percutaneous pedicle screws adds to the safety of the case.

44.8.9 Postoperative Results The patient made an uneventful recovery and was discharged on postoperative day 3. The patient was informed to wear LSO brace while ambulating for 2 to 3 months after surgery. Fig. 44.9 Intraoperative image showing placement of percutaneous pedicle screw instrumentation and reduction towers used to reduce spondylolisthesis from grade I to 0.

44.8.6 Postoperative Care The patient was transferred to the floor and ambulated with PT. A postoperative CT shows restoration of sagittal alignment, adequate canal decompression, and interbody bone graft. She was discharged on postoperative day 3 (▶ Fig. 44.10).

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44.9 Conclusion The chapter reviews a variety of pathology of the lumbar spine treated in a minimally invasive fashion. Mastery of MIS techniques and technology has enabled minimally invasive spine surgeons to treat a myriad of spinal pathology and resulted in improvements in patient outcomes while reducing health care cost. Those surgeons wishing to expand their use of and experience with these techniques should seek out training courses and programs.

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Minimally Invasive Spine Surgery: Lumbar Case Studies

Fig. 44.10 (a) Photo showing small bilateral incisions used to perform the procedure with preservation of spinal anatomy. Postoperative (b) sagittal CT, (c) axial CT with undercutting from the left side of the spinous process and contralateral lamina to allow central canal decompression, and (d) coronal CT with filling of the disc space with device surrounded by the patient’s own morselized autograft collected from the surgical site.

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Part V Minimally Invasive Spine Surgery for Tumors

V

45 Advances in Minimally Invasive Surgery for Spine Tumors

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46 Benign Spinal Tumors

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47 Radiofrequency Tumor Ablation with Vertebroplasty for the Treatment of Spine Metastases

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48 Minimally Invasive Resection of Intradural Spinal Tumors

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Minimally Invasive Spine Surgery for Tumors

45 Advances in Minimally Invasive Surgery for Spine Tumors A. Karim Ahmed, Alp Yurter, Patricia Zadnik Sullivan, Daniel M. Sciubba, and Rory Goodwin Abstract Minimally invasive approaches for metastatic spine disease may reduce the recovery time and morbidity for affected patients. As such, accelerated recovery can facilitate earlier adjuvant therapy and serve as a less invasive option for patients with poor prognosis. Two common minimally invasive spine surgery (MIS) techniques for metastatic spine disease include video-assisted thoracoscopic surgery (VATS) and minimal access spine surgery (MASS). Percutaneous pedicle screw fixation (PPSF) is employed in both techniques. VATS allows for access of the anterior column to treat spinal pathologies located from T1 to L2. MASS, with a greater ease of application, has surpassed VATS in popularity and may be applied from T2–S1. Despite the potential benefits, surgeons should be aware of drawbacks in minimally invasive approaches for spine metastases. MIS techniques have limited utility for circumferential tumors and may increase the risk of postoperative epidural hematoma in highly vascular tumors. Moreover, the benefits, indications, and drawbacks should be taken into consideration on an individual basis to make the best decision in treating patients with metastatic spine disease. Keywords: spine tumor, minimally invasive spine surgery, MIS, metastatic spine disease

45.1 Introduction In the United States alone, approximately 1.7 million new cases of cancer were diagnosed in 2013,1 with over 500,000 deaths resulting from metastatic disease.2 Advances in diagnostics and therapies have extended patient survival, resulting in a greater incidence of long-term complications. Metastatic epidural spinal cord compression (MESCC), one such example, occurs in 5 to 10% of cancer patients and often requires operative management.3 Surgical management of spinal metastasis is increasingly becoming minimally invasive in nature, in order to reduce tissue damage and the incidence of subsequent morbidities associated with open surgery. Fast recovery time is critical for metastatic spine disease patients, as it reduces the period between surgery and a postoperative adjuvant therapy regimen.4,5,6 Moreover, minimally invasive approaches offer patients with poorer health status (i.e., high systemic tumor burden, aggressive tumor pathology, short expected survival [ < 6–12 months], and old age) a less morbid surgical procedure.7,8,9 The two prominent minimally invasive surgery (MIS) techniques used to treat metastatic spine disease are endoscopic video-assisted thoracoscopic surgery (VATS) and mini-open surgery, also known as minimal access spine surgery (MASS).10 These procedures are often used with percutaneous pedicle screw fixation (PPSF) to stabilize the vertebral column.

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This chapter will review the following MIS techniques for spinal metastasis: PPSF, endoscopy VATS, and mini-open decompression/MASS.11,12,13 Preoperative planning, instrumentation, surgical approach and techniques, and patient case examples are discussed.

45.2 Evolution of Techniques 45.2.1 Percutaneous Pedicle Screw Fixation Percutaneous Schanz screws inserted into the pedicles with an external spinal fixation system were first described and popularized by Magerl.14 Since then, image guidance systems (CT and, later, fluoroscopy) have been developed to facilitate percutaneous pedicle screw placement and PPSF has been used to treat numerous spine pathologies, including metastatic spine disease.15

45.2.2 Video-Assisted Thoracoscopic Surgery VATS was developed in order to reduce approach-related morbidity associated with traditional transthoracic approaches.5 While standard thoracotomy provides excellent access to the anterior spine with minimal manipulation of the spinal cord, major surgical complications can ensue, leading to increased length of stay (LOS), mortality, and resource utilization.16,17,18 Moreover, in elderly patients (≥ 65 years) the risk of complications for open thoracotomy exceeds the benefits of operative treatment.19 VATS was adapted from the field of cardiothoracic surgery, in which patients exhibited reduced recovery time, shorter hospital LOS, and decreased morbidity.20,21,22 This technique was first used in 1993 to treat spinal disorders22 (e.g., discectomy for herniated discs, abscess drainage, anterior release for kyphoscoliosis, etc.), but it was not until 1996 that anterior spinal decompression and stabilization was performed via VATS in patients with metastatic spine disease.16 Currently, VATS can approach the spine anteriorly and laterally from either side and treat levels T1–T12 as well as L1–L2.23

45.2.3 Mini-open Decompression/ Minimal Access Spine Surgery MASS was first reported in 1997 as an approach for anterior lumbar fusion in the context of spinal trauma and degeneration.24 Initially, it was used for spinal levels L2–S1, but has since evolved to allow accessibility of T2–S1 using combined mini-open thoracotomy and/or retroperitoneal mini-approach.24,25,26 MASS has surpassed VATS in popularity because of its advantages including ease of application to a wide variety of pathology.

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Advances in Minimally Invasive Surgery for Spine Tumors

45.3 Advantages and Disadvantages of Minimally Invasive Surgery MIS allows for faster recovery time and reduces the period between surgery and a postoperative adjuvant therapy regimen. This is crucial for metastatic cancer patients. In addition, minimally invasive approaches can treat a certain subset of patients with poorer health status who would otherwise be precluded from traditional surgical techniques.7,8,9 For example, VATS approaches reduce lung tissue trauma, and PPSF allows retention of the fascial plane, reducing the likelihood of skin breakdown. Overall analgesic use, pain and discomfort, and hospital LOS are lower with MIS.27 In a 2011 meta-analysis, Molina et al26 found that MIS offered decreased blood loss, shorter operative time, and lower complication rates relative to standard open spine surgery when performed by a trained surgeon with experience in MIS techniques. Current MIS techniques generally have a limited use for circumferential tumors, which are better decompressed with an open approach. Additionally, in the context of highly vascular tumors, MIS decompression techniques can increase the risk of postoperative epidural hematoma, as proper hemostasis may be difficult to achieve in the limited working corridors.11

45.3.1 Percutaneous Pedicle Screw Fixation PPSF provides biomechanical stability in patients with metastatic disease who have particularly high disease burden or do not require operative decompression and/or anterior column restoration.5 PPSF is also used in conjunction with decompression to stabilize the spine after tumor resection. In circumventing the traditional open approach, muscular denervation, increased intramuscular pressure, ischemia, necrosis, and subsequent muscle atrophy and scarring can be significantly minimized if not avoided.28 Thus, modern percutaneous screw instrumentation allows for quick stabilization, minimal soft-tissue exposure, and a reduced soft-tissue healing duration.5 The less invasive exposure decreases the risk of infection.29 Additionally, the benign nature of the procedure allows for subsequent radiosurgery or earlier adjuvant radiation.5 This technique may initially have a steep learning curve, as it requires safe, accurate placement of instrumentation and access to intraoperative fluoroscopy. Moreover, PPSF in the upper thoracic spine can be technically difficult due to the small pedicle sizes. Preoperative CT scans and anteroposterior (AP) radiographs must be carefully examined to determine whether pedicles can be cannulated. Additionally, at the L5/S1 level, percutaneous retraction sleeves may impinge upon each other at the skin level.28 Finally, PPSF is not as secure as standard pedicle screw fixation, and this fact should be accounted for when selecting patients.

45.3.2 Video-Assisted Thoracoscopic Surgery VATS allows for the visualization and magnification of the entire thoracic ventral spine (T1–T12), and permits the decompression,

reconstruction, and stabilization of the spine.10 The magnitude of superficial incisions, muscle dissection, and rib retraction is less than that of open thoracotomy.30 Consequently, this technique provides shorter recovery time and decreased hospital LOS, as well as decreased approach-related and thoracotomy-associated morbidities in comparison to open thoracotomy, while providing comparable exposure for thoracic corpectomy and anterior column stabilization.5,20,21,22,30 In particular, the risk of postoperative pulmonary morbidity, scapular dysfunction, intercostal neuralgia, and hindered chest wall movement is reduced.10 Further, some surgeons find that this technique provides superior access to extreme ends of the thoracic cavity (e.g., T3–T4) as it circumvents the need to mobilize the scapula and transect the rhomboid muscles.30 Finally, VATS allows two surgeons to work in tandem as well as providing visualization to the entire team. However, there are notable drawbacks to VATS: a steep learning curve, the need for specialized training, and expensive equipment.10,26 There is a need for single-lung ventilation for sufficient visualization of anatomical structures. Furthermore, as with open thoracotomy, posterior spinal structures cannot be accessed and the contralateral pedicle can only be exposed in a limited fashion. As such, posterior approaches may be more suitable than VATS for patients who require circumferential decompression or have significant deformity. Finally, the management of intraoperative complications such as hemorrhage and dural tears may be difficult and may require the adoption of an open thoracotomy.30

45.3.3 Mini-open Decompression/ Minimal Access Spine Surgery In comparison to VATS, MASS is easier to learn, involves a more familiar exposure for most spine surgeons, facilitates a faster spinal cord decompression, permits safer mobilization of neurovascular structures, and allows easier reconstruction of the anterior column since spinal elements are visualized in three dimensions.13,26 Due to the high degree of visualization, hemostasis is typically easily achieved and the risk for postoperative hematoma is low.11 Various posterior and anterior approaches to the spine can be undertaken using MASS, making it a versatile technique. Because of these advantages, MASS is the standard means of MIS resection for metastasis.10 However, for MASS techniques, intraoperative fluoroscopy is required to ensure the correct level, and dural closure may be difficult through a tube.31

45.4 Indications and Contraindications Surgery for metastatic spine disease is suited for those with mechanical instability, radioresistant tumors, medically intractable pain, and/or progressive neurological deficits resulting from spinal cord compression, given that they have sufficient life expectancy and health status.32 For open surgeries, literature recommends that patients have an expected survival of at least 3 months, which is determined by a multidisciplinary team of medical and radiation oncologists as well as the surgical teams.33 In general, MIS techniques are indicated for candidates with less favorable characteristics, including high systemic tumor burden,

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Minimally Invasive Spine Surgery for Tumors aggressive tumor type, shorter expected survival (< 6–12 months), and old age.7,8,9 MIS surgical candidates should be unqualified (i.e., have restrictive comorbidities or have failed alternative therapies) for more aggressive treatments.8 MIS approaches are typically contraindicated for circumferential tumors that require an open approach for adequate decompression and highly vascular tumors for which proper hemostasis can only be confidently achieved with an open approach.11 Moreover, because MIS techniques involve partial resection, they have limited applications to solitary metastasis, which may benefit more from en bloc resection.10

45.4.1 Percutaneous Pedicle Screw Fixation Stand-alone PPSF may be appropriate for mechanically unstable patients who are unsuited for cement augmentation procedures (vertebroplasty/kyphoplasty) and who have disease burden that prevents them from undergoing open surgery.5,34 PPSF may be combined with other MIS techniques given that there are no contraindications (see the following discussion). However, patients with major spinal instability (e.g., absence of anterior column support) are contraindicated for stand-alone MIS posterior instrumentation without anterior column augmentation (e.g., cage insertion, methylmethacrylate augmentation, concurrent vertebroplasty/kyphoplasty), as MIS instrumentation is currently not as strong as that used in open surgeries. 11

45.4.2 Video-Assisted Thoracoscopic Surgery VATS is typically indicated in patients who would otherwise undergo open thoracotomy for metastasis, and especially for those who do not have the health status to tolerate the more invasive option. Most spinal lesions requiring surgery using an anterior approach can be treated with VATS.23 However, VATS is unsuitable for patients with the following comorbidities: pleural adhesions (e.g., from prior chest surgery, infection, or trauma) and pulmonary conditions that make single-lung ventilation dangerous (e.g., asthma or chronic obstructive pulmonary disease).30 Moreover, because hemorrhaging is difficult to manage with VATS, surgeons should consider the alternative option in cases of highly vascular tumors; excessive bleeding can hinder visualization and compromise safety. Some surgeons forgo VATS entirely for metastatic spinal malignancies to avoid the risk of tumor dissemination to trocar insertion sites.23

45.4.3 Mini-open Decompression/ Minimal Access Spine Surgery Currently, MASS is the standard minimally invasive surgical technique for decompressing and reconstructing the spine. General indications for this technique are those mentioned at the beginning of this section. However, relative contraindications include tumor involvement at two or more levels, certain hemorrhagic tumors, and morbid obesity because the height of the tube may be too short.31

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45.5 Preoperative Planning In general, patients with MESCC should be started on a corticosteroid regimen.35 Vascular metastatic lesions should be considered for preoperative angiogram and embolization.36 Standard images (MRI, CT, AP radiographs) should be taken to identify the levels of tumor pathology. Patients should undergo standard neurological examination to determine the severity of neurological deficits.

45.5.1 Percutaneous Pedicle Screw Fixation Prior to PPSF, the surgeon should carefully evaluate preoperative CT scans and AP radiographs to determine whether the pedicle can be cannulated. This is particularly relevant for the mid-upper thoracic spine, at which pedicles are small, and T1– T4 levels, at which pedicle angulation changes. Pedicles should be confirmed to have a width of at least 3 to 4 mm to ensure adequate Jamshidi needle navigation.28 If there is an option to choose a specific imaging modality (CT vs. three-dimensional [3D] fluoroscopy vs. standard 2D fluoroscopy), one should weigh the benefits of pedicle screw placement accuracy against the time required to acquire data; while CT navigation has been shown to be more accurate than other modalities, it requires pre- and intraoperative preparatory steps that are not present in fluoroscopic imaging.37,38 Because fluoroscopy avoids time-consuming steps inherent to CT systems without sacrificing too much accuracy, it is the conventional means of navigation.39 For fluoroscopy, two units should be placed to enable lateral and AP views.

45.5.2 Video-Assisted Thoracoscopic Surgery Standard preoperative spine imaging should be supplemented with radiographic assessment of the posteroanterior and lateral chest to determine potential pleural fluid, fibrinous membranes, or pleural adhesions.23 The presence of such conditions significantly increases the need to convert to an open procedure.27 Because VATS requires single-lung ventilation, patients with a history of smoking and chronic obstructive airway disease require preoperative pulmonary function tests, arterial blood gas evaluation, and cessation of smoking prior to surgery.27

45.5.3 Mini-open Decompression/ Minimal Access Spine Surgery Based on the preoperative images, a trajectory should be chosen to access the tumor. There should also be a plan to convert to an open procedure in the event of major intraoperative complications.

45.5.4 Instrumentation Notes Percutaneous Pedicle Screw Fixation Imaging requires equipment for fluoroscopy or CT scanners with stereotactic navigation. Cannulated awls are required for

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Advances in Minimally Invasive Surgery for Spine Tumors pedicle cannulation. Guidewires and cannulated taps assist pedicle screw trajectory. Rods, screws, and screwdrivers/reduction towers are used in the final stages of the procedure to stabilize the spine.11

Video-Assisted Thoracoscopic Surgery VATS requires a video endoscope, C-arm fluoroscopy, and video monitors for visualization. A double-lumen endotracheal tube is necessary to collapse the lung at the side of metastasis. A trocar is needed as a conduit for endoscope insertion.

Mini-open Decompression/Minimal Access Spine Surgery Unique to MASS is the use of a table-mounted retractor system or tubular retractor (either expandable or nonexpendable) for exposure to the site of disease. Additionally, fluoroscopy is used to identify the level of the lesion.

45.6 Surgical Approach 45.6.1 Percutaneous Pedicle Screw Fixation Patients with metastatic spine tumors often have multiple adjacent vertebral bodies affected by disease. In patients undergoing PPSF for local deformity or instability due to metastatic spine disease, the offending level should be identified and bilateral pedicle screw fixation is recommended two to three levels above and below the level of interest to provide multiple sites of fixation.11

45.6.2 Video-Assisted Thoracoscopic Surgery In patients with previous lung surgery, surgical approaches on the affected side may be limited by pleural adhesions.

45.6.3 Mini-open Thoracotomy For tumors of the upper thoracic spine, a right-sided approach is recommended to avoid the thoracic duct. For tumors of the thoracolumbar region, the left-sided approach is recommended to avoid direct trauma to the vena cava.

45.6.4 Surgical Technique Percutaneous Pedicle Screw Fixation The patient is placed prone on the operating table, and biplanar fluoroscopy or an intraoperative CT scanner with navigation is used to localize the level of pathology and any relevant surgical landmarks. Individual paraspinal stab incisions are made for each of the pedicle screw entry sites. Alternatively, a midline incision may be made through the soft tissue to the dorsal interfascial plane. Individual stab incisions off midline may then be made through the interfascial plane for pedicle instrumentation (▶ Fig. 45.1). Preservation of the fascial plane is crucial for expedited wound healing, particularly in metastatic cancer patients who are likely to undergo postoperative radiation therapy or chemotherapy. A cannulated awl and taps are used under the guidance of fluoroscopy or intraoperative navigation to create the trajectory for the pedicle screws. A guidewire is then placed in the cannula and pedicle screws are placed over the guidewires. Guidewires are then removed. An additional stab incision is made for the introduction of the rod and the screws are locked into place. The wound is irrigated and closed using multilayer closure. In order to reduce operating time, when performing multilevel fixation, rod insertion should be carefully planned out. Rod length should be determined, and the length between the retraction sleeves can help in determining this. Whether the rod requires bending or needs an additional incision for insertion, and from which end the rod should be inserted should be determined prior to insertion.28

Fig. 45.1 Example of incisions that could be made in preparation for percutaneous pedicle screw fixation or a posterior mini-open approach.

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Video-Assisted Thoracoscopic Surgery Prior to surgery, the patient is intubated with a dual-lumen endotracheal tube to allow single-lung ventilation. The patient is prepped and draped in the lateral decubitus position, with the affected side facing superiorly. Within the operating suite, Carm fluoroscopy, video monitors, and endoscopic equipment are organized to optimize the surgeon’s view. When the patient is intubated, the ipsilateral lung to the tumor-involved side is collapsed. The first trocar is then placed over the superior surface of the rib at the fifth or sixth intercostal space. The surgeon then inspects the thoracic cavity and dissects any obvious pleural adhesions. The operating table may then be titled 30 degrees toward the surgeon to displace the mediastinum and increase visualization of the thoracic vertebrae. The tumor mass is then identified, and a second trocar is placed in the midaxillary line cranially or caudally to the first port under direct visualization. The location of the second port depends on the level of the tumor and surgeon’s preference. A third trocar may then be placed ventrally at the ninth or tenth intercostal space. For tumors of the upper thoracic spine, the endoscopic trocar should be introduced at the fourth intercostal space at the anterior border of the latissimus dorsi muscle. Additional ports should be introduced in the third or fourth intercostal space to avoid injury to the axillary arteries and nerves. Tumor resection then proceeds with dissection of the parietal pleura and discectomy above and below the tumor using an endoscopic scalpel. Corpectomy follows using straight and curved osteotomies with resection of the tumor to the posterior longitudinal ligament (PLL), then sectioning of the PLL for spinal cord decompression. Extent of surgical resection may be confirmed using intraoperative fluoroscopy. During tumor removal, the tumor cells may be introduced to the thoracic cavity, and the entire

area should be thoroughly irrigated following complete tumor resection. A cage or plate may then be placed for stabilization. For patients with tumors of the thoracolumbar junction, a combined laparoscopic retroperitoneal approach can be used to visualize the superior and inferior aspects of the diaphragm. This technique involves dual-lumen intubation with collapse of the lung, and placement of the endoscopic port at the seventh intercostal space. The junction of the costal cartilage of the twelfth rib is then dissected to expose retroperitoneal fat. A balloon is then introduced to the retroperitoneal space and filled with 1 L of saline for blunt dissection of the space. The balloon is deflated, followed by insufflation of carbon dioxide for distension of the retroperitoneal space. The diaphragm is then cut under direct visualization from the thoracic endoscopic portal, and surgical instruments from the thoracic ports can then be used for dissection of the lumbar spine. Tumor resection and subsequent stabilization follows. If the diaphragm was sectioned during the procedure, it is reapproximated prior to closure. A chest tube is placed through an existing endoscopic port and secured in the standard fashion. The patient’s collapsed lung is then ventilated under direct visualization. The endoscopic port sites are closed in a multilayer fashion. A postoperative chest X-ray is then performed to confirm chest tube placement and lung inflation.

Mini-open Decompression/Minimal Access Spine Surgery Mini-open Decompression for Posterior Pathologies The patient is placed prone on the operating table, and fluoroscopy should be used to localize the pathology (▶ Fig. 45.2a). Posterior or posterolateral tumors may be resected via a small

Fig. 45.2 Surgical technique for mini-open decompression. (a) Example of a skin markup of anatomical landmarks to treat a lesion at L1 via posterior mini-open decompression and fixation. (b) Possible setup for posterior minimal access spine surgery approach with microendoscopic visualization. (c) Instrument setup of a posterior mini-open decompression. (d) Bird’s-eye view of the lesion site for a posterior mini-open decompression with an inserted screw.

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Advances in Minimally Invasive Surgery for Spine Tumors midline incision at the tumor level, followed by a limited laminectomy to expose the tumor. Intraoperative fluoroscopy may be later used for PPSF (see earlier discussion). To facilitate expanded access to the tumor, portions of the pedicle can also be removed, and angled instruments allow the surgeon a greater range of motion. In contrast to minimally invasive approaches that utilize a cannula or endoscopic port (▶ Fig. 45.2b), miniopen approaches allow greater exposure of the surgical field (▶ Fig. 45.2c,d), facilitating hemostasis and allowing the surgeon to repair any unintended dural tears. The wound is irrigated and closed in a standard fashion.

Bilateral MASS Decompression for Posterior Pathologies MASS, utilizing tubular retractors, can be performed with a bilateral posterior transpedicular approach for large tumors, allowing two surgeons to work in tandem. Similar to posterior mini-open decompression, the patient is placed prone on the operating table and the level of pathology is identified with fluoroscopy. Anatomical landmarks are noted (▶ Fig. 45.3a). The two surgeons eventually decompress the tumor and can visualize the spinal cord (▶ Fig. 45.3b,c). Finally, percutaneous pedicle screws and instrumentation are inserted as previously described (▶ Fig. 45.3d) and proper placement is visually confirmed with imaging (▶ Fig. 45.3e).

Mini-open Thoracotomy Prior to surgery, anesthesiology should be informed of the procedure and the patient intubated with a dual-lumen endotra-

cheal tube for single-lung ventilation. The patient is prepped and draped in the lateral decubitus position, with the tumor-affected side facing superiorly. A lateral radiograph is then used to localize the tumor level. A 5- to 10-cm incision is made over the rib two levels above the affected vertebral body to account for the angulation of the ribs to the vertebral bodies. Dissection proceeds with opening of the parietal pleura, and retraction of the lung. Use of a specialized retractor system was described by Kossman et al25 to eliminate the need for rib resection and lung deflation (▶ Fig. 45.4a). The tumor mass is then identified and resected, and subsequent reconstruction with a cage or plate construct follows (▶ Fig. 45.4b,c). Chest tube placement follows as described earlier. The wound is irrigated and closed in the standard fashion.

45.7 Postoperative Care Patients with metastatic disease often have poor health status due to nutritional deficiencies and immunosuppression from disease and treatments.26 As such, optimum nutrition should be maintained in the postoperative period. Adjuvant therapy regimens should be started as soon as possible.

45.8 Management of Complications Regardless of the surgical procedure, the surgeon should have a plan to convert to an open surgery in the case of a dural tear that cannot be repaired or an uncontrollable hemorrhage.

Fig. 45.3 Surgical technique for minimal access spine surgery decompression. (a) Example of a skin markup of anatomical landmarks to treat a lesion at T3 via minimal access bilateral transpedicular decompression and fixation. (b) Two surgeons working in tandem in a minimal access bilateral transpedicular decompression and fixation procedure. (c) Visualization of the spinal cord in a minimal access bilateral transpedicular decompression and fixation procedure. (d) Insertion of pedicle screws following minimal access bilateral transpedicular decompression. (e) Fluoroscopic confirmation of accurately placed cage and pedicle screws in a minimal access bilateral transpedicular decompression and fixation procedure.

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Fig. 45.4 Surgical technique for mini-open thoracotomy. (a) Setup of SynFrame retractor used in a mini-open thoracotomy. (b) Insertion of screws and plate prior to wound closure for a mini-open thoracotomy. (c) Radiograph confirming successful placement of instrumentation following mini-open thoracotomy.

45.8.1 Percutaneous Pedicle Screw Fixation Screw misalignment is a potential intraoperative complication. For intraoperative correction of a misaligned screw, a Kirschner wire (K-wire) should be inserted, and an undersized tap should force the K-wire in the correct alignment without bending it too much. Once aligned, this K-wire should be replaced with a fresh, straight K-wire. A pedicle screw can then be placed according to this new trajectory.28

45.8.2 Video-Assisted Thoracoscopic Surgery Complications arising in VATS are similar to those of open thoracotomy, but differ in incidence rate. Complications may arise from anesthesia, patient positioning, port placement/access, and manipulation of instruments, resulting in injury to the lung parenchyma and vascular structures in the thoracic cavity.27 With respect to patient positioning, an axillary roll should be placed under the chest to prevent pressure on the brachial plexus in the axilla. Care should be taken not to overabduct the arm on the operated side to avoid traction injuries on the brachial plexus. Additionally, the common peroneal nerve at the fibular head should be padded to prevent postoperative peroneal nerve palsy.27 With respect to port placement and access, care should be taken in the placement of the initial endoscopic port, the only port that is placed blindly. In order to avoid disturbing lung adhesions, which can result in further lung injury and postoperative air leaks, a finger should be passed through the port site and swept circumferentially to release any adhesions prior to port placement. To prevent injury to the diaphragm (and structures beneath it), which can ride up and be punctured during the placement of lower thoracic ports, all ports aside from the initial one should be placed under direct endoscopic vision. When possible, softer ports should be used to reduce the chance of postoperative intercostal neuralgia. Trocars should be carefully placed as well, as they can potentially cause injury to the intercostal nerve, artery, or vein. Following the placement of the initial port, all ports and instruments should be placed under continuous visualization until removal from the chest cavity.27

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Intraoperative complications can be managed depending on severity. Minor bleeding can be controlled with electrocautery. However, if the bleeding is severe, a Foley catheter can be inserted, followed by balloon inflation to create a tamponade. In the event of uncontrollable bleeding, the wound site may need to be expanded to identify the source. A thoracotomy tray should be at hand in the event of unmanageable bleeding.27

45.9 Clinical Cases 45.9.1 Case 1: Tumor Decompression and Stereotactic Radiosurgery The patient is a 50-year-old man who presented to his primary care physician with new-onset abdominal pain and was found to have a 6.5-cm left renal mass. He underwent a left nephrectomy and was found to have clear cell renal carcinoma with positive abdominal lymph nodes. Subsequent positron emission tomography (PET) imaging demonstrated mediastinal involvement and he underwent a left lobe wedge resection. Pathology was significant for a focus of metastatic clear cell renal carcinoma. He later developed worsening back pain and was found to have a lytic lesion at L1 (▶ Fig. 45.5a). On examination, the patient denied focal neurologic deficit and problems with balance or bowel and bladder or sexual function. Due to his past medical history of Crohn’s disease and the insensitivity of clear cell renal carcinoma to standard chemotherapeutics, his medical oncologist expressed concern for beginning medical therapy, and he was referred to radiation oncology and neurosurgery. The treatment team advised preoperative tumor embolization to reduce intraoperative bleeding (▶ Fig. 45.5b), followed by surgical intervention for tumor decompression and stereotactic radiosurgery (SRS). Following successful embolization, the patient underwent an L1 corpectomy via a minimally invasive approach. This was completed using fluoroscopic guidance to map the pedicles of T12–L2. Small incisions were made over the elements of T12–L1 and L1–L2, and the joint capsules at T12–L1 and L1–L2 were resected bilaterally. A small incision was made over the lamina of L1 for a one-level laminectomy and left-sided T12–L2 facetectomy. The tumor was then visualized and the remaining pedicle was removed to facilitate the tumor resection and corpectomy (▶ Fig. 45.5c,d). After tumor

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Advances in Minimally Invasive Surgery for Spine Tumors

Fig. 45.5 (a) Preoperative T2-weighted short tau inversion recovery (STIR) MRI image demonstrating tumor at L1 within the vertebral body extending to the epidural space. (b) Fluoroscopic images taken during preoperative tumor embolization. The vascularity of the tumor is evident on injection of contrast media. Coils can be seen on the left side of the image. (c) Postoperative scout CT image demonstrating construct from T12–L2, with bilateral pedicle screws at T12 and L2 and unilateral pedicle screw placement at L1. Embolization coils can be seen. (d) Postoperative sagittal CT scan demonstrating construct extending T12–L2.

resection, the anterior and right-sided aspects of the L1 vertebral body remained for stability. Pedicle screws were placed using fluoroscopic guidance and rods were fitted to the construct and secured in place. Postoperatively, the patient recovered without complication and received stereotactic radiation of 3,000 cGy 4 weeks after surgery. His disease continued to progress, requiring SRS 5 months after surgery to the T11 vertebral body and 1 year after surgery to T5–T7.

45.9.2 Case 2: Mini-Thoracotomy The patient is a 51-year-old woman with metastatic breast cancer and multiple spinal lesions. She underwent palliative external beam radiation therapy from T10 to L4 and L2 2 years prior to surgery. She developed worsening back pain, with bandlike pain around her ribcage that worsened with breathing. She did not have leg weakness, and denied urinary or bowel complaints. Imaging demonstrated tumor at the T8 vertebral body causing significant spinal cord compression (▶ Fig. 45.6a). Due to the mechanical nature of her back pain and cord compression, surgical intervention was planned with radiation therapy to follow. She underwent a mini-thoracotomy with mini-retropleural thoracic corpectomy. The patient was taken to the operating

room and placed in lateral decubitus for thoracotomy. A minithoracotomy incision was made and a portion of the rib was resected. Extrapleural dissection revealed the T8 vertebral body and fluoroscopic imaging confirmed the proper location. T7–T8 and T8–T9 discectomies followed, and the T8 vertebral body was removed. The PLL was sectioned to reveal the dura, and a distractible cage was then fitted to place and filled with allografted bone. A lateral plate was placed extending from T7 to T9 (▶ Fig. 45.6b). A thoracotomy tube was placed and the incision was closed. The patient had an uncomplicated recovery, with significant improvement in her back pain postoperatively. She underwent SRS to T7–T9 4 weeks after surgery.

45.10 Conclusion MIS for metastatic spine disease consists of PPSF for stabilization and VATS and mini-open decompression/MASS for tumor resection and reconstruction. Within the past decade, MASS has surpassed VATS as the primary means of decompression because of its versatility in tumor approach, easy learning curve, and relatively inexpensive nature. With improvements in systemic therapies and further advances in surgical techniques and technology, operative treatment for metastatic spine disease will, on the whole, continue to become less invasive.

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Fig. 45.6 (a) Preoperative T2-weighted fat-suppressed MRI demonstrating tumor at T8. The tumor originates in the vertebral body and extends to the epidural space, causing significant spinal cord compression. (b) Postoperative CT scan demonstrating a distractible titanium cage replacing the T8 vertebral body as well as a lateral plate extending from T7 to T9.

Clinical Caveats ●

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Minimally invasive approaches for metastatic spine disease may reduce the recovery time and morbidity for affected patients. Faster recovery can facilitate earlier adjuvant therapy and serve as a less invasive option for patients with poor prognosis. Video-assisted thoracoscopic surgery (VATS) and minimal access spine surgery (MASS) are two MIS techniques for minimally invasive approaches for metastatic spine disease. VATS allows for access of the anterior column to treat spinal pathologies located from T1 to L2. MASS allows for access from T2 to S1. Surgeons should be aware of drawbacks in minimally invasive approaches for spine metastases. MIS techniques have limited utility for circumferential tumors and may increase the risk of postoperative epidural hematoma in highly vascular tumors.

References [1] American Cancer Society. Cancer facts & figures 2013. American Cancer Society Web site. Available at: https://www.cancer.org/content/dam/cancer-org/ research/cancer-facts-and-statistics/annual-cancer-facts-and-figures/2013/ cancer-facts-and-figures-2013.pdf Updated 2013 [2] Schiff D. Spinal cord compression. Neurol Clin. 2003; 21(1):67–86, viii [3] Sciubba DM, Gokaslan ZL. Diagnosis and management of metastatic spine disease. Surg Oncol. 2006; 15(3):141–151 [4] Laufer I, Sciubba DM, Madera M, et al. Surgical management of metastatic spinal tumors. Cancer Contr. 2012; 19(2):122–128 [5] Smith ZA, Yang I, Gorgulho A, Raphael D, De Salles AA, Khoo LT. Emerging techniques in the minimally invasive treatment and management of thoracic spine tumors. J Neurooncol. 2012; 107(3):443–455 [6] Smith ZA, Fessler RG. Paradigm changes in spine surgery: evolution of minimally invasive techniques. Nat Rev Neurol. 2012; 8(8):443–450

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[7] Taghva A, Li KW, Liu JC, Gokaslan ZL, Hsieh PC. Minimally invasive circumferential spinal decompression and stabilization for symptomatic metastatic spine tumor: technical case report. Neurosurgery. 2010; 66(3):E620–E622 [8] Kimball J, Kusnezov NA, Pezeshkian P, Lu DC. Minimally invasive surgical decompression for lumbar spinal metastases. Surg Neurol Int. 2013; 4:78 [9] Deutsch H, Boco T, Lobel J. Minimally invasive transpedicular vertebrectomy for metastatic disease to the thoracic spine. J Spinal Disord Tech. 2008; 21 (2):101–105 [10] Ofluoglu O. Minimally invasive management of spinal metastases. Orthop Clin North Am. 2009; 40(1):155–168, viii [11] Rose PS, Clarke MJ, Dekutoski MB. Minimally invasive treatment of spinal metastases: techniques. Int J Surg Oncol. 2011; 2011:494381 [12] Huang TJ, Hsu RW, Liu HP, et al. Video-assisted thoracoscopic surgery to the upper thoracic spine. Surg Endosc. 1999; 13(2):123–126 [13] Huang TJ, Hsu RW, Li YY, Cheng CC. Minimal access spinal surgery (MASS) in treating thoracic spine metastasis. Spine. 2006; 31(16):1860–1863 [14] Magerl F. External spinal skeletal fixation. In: The External Fixator. Berlin: Springer; 1985:289–365 [15] O’Dowd JK. Minimally invasive spinal surgery. Curr Orthop. 2007; 21 (6):442–450 [16] Rosenthal D, Marquardt G, Lorenz R, Nichtweiss M. Anterior decompression and stabilization using a microsurgical endoscopic technique for metastatic tumors of the thoracic spine. J Neurosurg. 1996; 84(4):565–572 [17] Sundaresan N, Shah J, Foley KM, Rosen G. An anterior surgical approach to the upper thoracic vertebrae. J Neurosurg. 1984; 61(4):686–690 [18] Wood K, Buttermann G, Mehbod A, Garvey T, Jhanjee R, Sechriest V. Operative compared with nonoperative treatment of a thoracolumbar burst fracture without neurological deficit. A prospective, randomized study. J Bone Joint Surg Am. 2003; 85-A(5):773–781 [19] Chi JH, Gokaslan Z, McCormick P, Tibbs PA, Kryscio RJ, Patchell RA. Selecting treatment for patients with malignant epidural spinal cord compression-does age matter?: results from a randomized clinical trial. Spine. 2009; 34(5):431–435 [20] Coltharp WH, Arnold JH, Alford WC, Jr, et al. Videothoracoscopy: improved technique and expanded indications. Ann Thorac Surg. 1992; 53(5):776–778, discussion 779 [21] Landreneau RJ, Mack MJ, Hazelrigg SR, et al. Video-assisted thoracic surgery: basic technical concepts and intercostal approach strategies. Ann Thorac Surg. 1992; 54(4):800–807 [22] Mack MJ, Regan JJ, Bobechko WP, Acuff TE. Application of thoracoscopy for diseases of the spine. Ann Thorac Surg. 1993; 56(3):736–738 [23] Assaker R. Minimal access spinal technologies: state-of-the-art, indications, and techniques. Joint Bone Spine. 2004; 71(6):459–469

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Advances in Minimally Invasive Surgery for Spine Tumors [24] Mayer HM. A new microsurgical technique for minimally invasive anterior lumbar interbody fusion. Spine. 1997; 22(6):691–699, discussion 700 [25] Kossmann T, Jacobi D, Trentz O. The use of a retractor system (SynFrame) for open, minimal invasive reconstruction of the anterior column of the thoracic and lumbar spine. Eur Spine J. 2001; 10(5):396–402 [26] Molina CA, Gokaslan ZL, Sciubba DM. A systematic review of the current role of minimally invasive spine surgery in the management of metastatic spine disease. Int J Surg Oncol. 2011; 2011:598148 [27] Perez-Cruet MJ, Fessler RG, Perin NI. Review: complications of minimally invasive spinal surgery. Neurosurgery. 2002; 51(5) Suppl:S26–S36 [28] Mobbs RJ, Sivabalan P, Li J. Technique, challenges and indications for percutaneous pedicle screw fixation. J Clin Neurosci. 2011; 18(6):741–749 [29] O’Toole JE, Eichholz KM, Fessler RG. Surgical site infection rates after minimally invasive spinal surgery. J Neurosurg Spine. 2009; 11(4):471–476 [30] Kan P, Schmidt MH. Minimally invasive thoracoscopic approach for anterior decompression and stabilization of metastatic spine disease. Neurosurg Focus. 2008; 25(2):E8 [31] Nzokou A, Weil AG, Shedid D. Minimally invasive removal of thoracic and lumbar spinal tumors using a nonexpandable tubular retractor. J Neurosurg Spine. 2013; 19(6):708–715

[32] Sciubba DM, Petteys RJ, Dekutoski MB, et al. Diagnosis and management of metastatic spine disease. A review. J Neurosurg Spine. 2010; 13(1):94–108 [33] Fang T, Dong J, Zhou X, McGuire RA, Jr, Li X. Comparison of mini-open anterior corpectomy and posterior total en bloc spondylectomy for solitary metastases of the thoracolumbar spine. J Neurosurg Spine. 2012; 17(4):271–279 [34] Kim CH, Chung CK, Sohn S, Lee S, Park SB. Less invasive palliative surgery for spinal metastases. J Surg Oncol. 2013; 108(7):499–503 [35] Klimo P, Jr, Kestle JR, Schmidt MH. Clinical trials and evidence-based medicine for metastatic spine disease. Neurosurg Clin N Am. 2004; 15(4):549–564 [36] Gottfried ON, Schloesser PE, Schmidt MH, Stevens EA. Embolization of metastatic spinal tumors. Neurosurg Clin N Am. 2004; 15(4):391–399 [37] Liu YJ, Tian W, Liu B, et al. Accuracy of CT-based navigation of pedicle screws implantation in the cervical spine compared with X-ray fluoroscopy technique. Zhonghua Wai Ke Za Zhi. 2005; 43(20):1328–1330 [38] Hardin CA, Nimjee SM, Karikari IO, Agrawal A, Fessler RG, Isaacs RE. Percutaneous pedicle screw placement in the thoracic spine: a cadaveric study. Asian J Neurosurg. 2013; 8(3):153–156 [39] Fu TS, Wong CB, Tsai TT, Liang YC, Chen LH, Chen WJ. Pedicle screw insertion: computed tomography versus fluoroscopic image guidance. Int Orthop. 2008; 32(4):517–521

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Minimally Invasive Spine Surgery for Tumors

46 Benign Spinal Tumors Manish K. Kasliwal, Lee A. Tan, Carter S. Gerard, John E. O’Toole, and Richard G. Fessler Abstract Primary benign tumors of the spinal column are much less common compared to other spinal neoplasms such as metastases, multiple myeloma, or lymphoma. These tumors often affect a younger age group, with back pain being the most common presentation. Considering the ubiquitous nature of back pain and rarity of these benign spinal tumors, the potential for missed diagnosis, if not appropriately suspected, remains high. The differential diagnosis of these lesions is fairly broad and often requires appropriate recognition on initial radiology and subsequent complete workup to formulate the best treatment strategy. There has been significant progress in the treatment options available to treat these tumors that allow safer and more effective treatment with decreased overall morbidity. This chapter provides a brief overview of the presentation, radiology, and management of various benign spinal cord tumors in the light of most recent literature. Keywords: benign, clinical, diagnosis, spine, tumor, neoplasm, radiology, management

46.1 Introduction Primary benign tumors of the spine are much less common lesions compared to other spinal neoplasms such as metastases, multiple myeloma, or lymphoma.1 Hemangioma, enostosis, osteochondroma, osteoid osteoma, osteoblastoma, giant cell tumor, aneurysmal bone cyst (ABC), and eosinophilic granuloma (EG) are the various subtypes of benign spinal tumors. All together, they account for only less than 5% of all spinal neoplasms.2 They tend to occur in younger patients, in contrast to metastases, multiple myeloma, or lymphoma, which usually affect older age groups.1,2,3,4 Some of these benign tumors arise from the posterior elements of the spine, while others mainly originate from the vertebral body.2 Back pain is the most common presenting symptom for patients with benign spinal tumors,5 although sensorimotor deficit can also be present depending on the size and location of the lesion. Many of these lesions have characteristic clinical and radiographic features that can help clinicians to make the correct diagnosis. In contrast to primary malignant lesions that often require en bloc resection for best chance of cure, symptomatic benign primary tumors can often be safely treated with intralesional resection.4 Primary benign spine tumors are classified using the Enneking system (▶ Table 46.1), and generally stage II and III lesions require treatment.

In this chapter, we attempt to provide an overview of current minimally invasive techniques along with general principles of utilizing these minimally invasive surgery (MIS) approaches in treating benign spinal tumors. By having a solid understanding of tumor pathophysiology, local anatomy, and spinal biomechanics, spine surgeons can utilize MIS techniques to successfully treat benign spinal tumors with good clinical outcome. A brief overview of clinical and radiological features of primary benign spinal tumors is presented in the following sections.

46.2 Types of Tumors 46.2.1 Hemangioma Vertebral hemangiomas are vascular malformations consisting of thin-walled blood vessels that usually affect the vertebral body with occasional extension into the posterior elements. They most commonly occur in the thoracic and upper lumbar spine. Classic imaging features include vertical striations on spinal radiographs known as the “corduroy sign,” and “polka-dot” appearance on axial CT images (▶ Fig. 46.1). Vertebral hemangiomas are often asymptomatic and only discovered incidentally. However, those with extension into the posterior elements and with paraspinal involvement are more likely to cause compressive symptoms. Large hemangiomas can also compromise the vertebral body’s ability to bear axial load and can result in vertebral fractures. Treatment options for symptomatic vertebral hemangiomas include sclerotherapy, vertebroplasty, endovascular embolization, and vertebrectomy.6,7,8

Table 46.1 Enneking classification of benign spine tumors

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Stage

Description

1

Latent, asymptomatic, incidentally found

2

Active, symptomatic lesion

3

Aggressive, can metastasize

Fig. 46.1 Hemangioma with “polka-dot” appearance on axial computed tomography.

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Benign Spinal Tumors

Fig. 46.2 Enostosis on radiograph showing a sclerotic lesion in the cervical spine. (a) MRI demonstrating hypointense signals on both T1-weighted (b) and T2-weighted (c) images.

46.2.2 Enostosis Enostosis is a benign hamartomatous lesion consisting of cortical bone with irregular margins within the medullary bone, which is also known as “bone island.”9,10 It typically has a round or oval appearance and is up to 2 cm in size. Imaging features include sclerotic appearance on radiographs, hyperdense on CT, and hypointense on both T1- and T2-weighted MRI images (▶ Fig. 46.2). Enostoses are usually asymptomatic solitary lesions that do not enlarge over time. However, biopsy may be considered if there is an increase in size to rule out other possible osteoblastic lesions.

46.2.3 Osteochondroma Osteochondroma is an abnormal outgrowth of bone capped by hyaline cartilage with its medullary part continuous with the parent bone. It usually affects the appendicular long bones such as the femur, tibia, and humerus, but posterior elements of the spine can also be involved occasionally. It is usually sporadic with a 3:1 gender predilection for males,2 and often discovered during the third and fourth decades of life. Although vertebral osteochondromas can occur anywhere along the spine, they appear to have a predilection for the cervical spine, especially for the C2 vertebrae.2,10 Radiographic features include a “cauliflower-like” mass capped by cartilages with its medullary component in continuity with medullary part of the parent bone on CT (▶ Fig. 46.3). The cartilaginous cap usually appears isointense or hypointense on T1 and hyperintense on T2-weighted MRI. A cartilage cap greater than 1.5 cm may be a red flag for malignant transformation to a chondrosarcoma in adults, which warrants further investigation. Symptoms include pain and neurological deficits, which are due to local mechanical effect or neurovascular compression. Lesions protruding into the spinal canal often present much earlier than those projecting posteriorly, given the limited space available in the spinal canal. Symptomatic lesions can often be cured with excision of the lesion at the point of cortical and marrow junction to the parent bone.

Fig. 46.3 Osteochondroma with a “cauliflower-like” mass capped by cartilages with its medullary component in continuity with medullary part of the vertebral body on CT.

46.2.4 Osteoid Osteoma Osteoid osteoma is a benign bone tumor produced by osteoblasts consisting of osteoid and woven bone frequently surrounded by cortical thickening and bony sclerosis. Although it most commonly involves the posterior elements of the spine, it can rarely involve the vertebral body as well.11 The lumbar spine is the most frequently affected, followed by cervical, thoracic, and sacral segments. It has a slight male predilection and most frequently affects patients in their second or third decades of life. The classic clinical feature is pain that worsens at night or with alcohol consumption, and improves with nonsteroidal anti-inflammatory drugs (NSAIDs). By definition, they are less than 2 cm in size. CT often demonstrates a radiolucent mass with cortical thickening and sclerosis in the posterior elements of the spine (▶ Fig. 46.4).

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Minimally Invasive Spine Surgery for Tumors The nidus can often have central calcification as well. It is usually isointense to hypointense on T1 and isointense to hyperintense on T2-weighted MRI. Radiofrequency ablation often provides symptomatic relief. Surgical excision is curative if the nidus is completely removed.

46.2.5 Osteoblastoma Osteoblastoma is similar to osteoid osteoma histologically, but is greater than 2 cm in size by definition. It is also present in the second and third decades of life with male predilection. Similar to osteoid osteoma, it most frequently originates from the posterior elements but can often extend into the vertebral body. Osteoblastomas tend to have slow growth over time and can rarely have malignant transformation to osteosarcoma. The radiologic appearances are similar to osteoid osteomas, characterized by a radiolucent mass with cortical thickening and sclerosis and surrounding sclerosis with or without central calcifications, but they are by definition greater than 2 cm in diameter (▶ Fig. 46.5). The more aggressive subtype may

demonstrate bony destruction and paravertebral extension; it may also include a component of ABC in a minority of cases.12 Surgical resection is the treatment of choice, with 10 to 15% chance of recurrence.13,14

46.2.6 Aneurysmal Bone Cyst ABC is a benign lesion consisting of blood-filled spaces without endothelial lining within affected bone. About 10 to 30% of ABCs are located in the spine,15 with thoracic spine being the most frequently affected site, followed by lumbar, cervical, and sacral segment. It usually arises from the posterior elements but with frequent expansion into the vertebral body and paravertebral tissue. CT demonstrates an expansile osteolytic mass with a thin rim of sclerosis; MRI demonstrates the characteristic “fluid–fluid level” (▶ Fig. 46.6), which is due to repeated hemorrhage and resultant blood of various ages. Spinal ABCs can be effectively treated with intralesional resection, en bloc resection, or endovascular embolization.15 Preoperative embolization should be considered prior to intralesional resection to limit intraoperative blood loss.

46.2.7 Giant Cell Tumor Giant cell tumors are expansile, lytic lesions consisting of osteoclast-like cells often containing thin-walled vascular channels,

Fig. 46.4 A radiolucent lesion less than 2 cm in size affecting the posterior elements consistent with an osteoid osteoma (arrow).

Fig. 46.5 Osteoid blastoma manifesting as a lytic mass measuring greater than 2 cm affecting the posterior elements (arrow).

Fig. 46.6 (a) Axial and (b) sagittal T2-weighted showing “fluid–fluid” levels in a vertebral aneurysm bone cyst affecting the left lateral aspect of the vertebral body with extension into the posterior elements.

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Benign Spinal Tumors

Fig. 46.8 Classic finding of “vertebra plana” in a patient with eosinophilic granuloma (arrow).

Fig. 46.7 An expansile giant cell tumor destroying adjacent vertebral bodies with extension into the posterior paraspinal tissues (arrow).

which predispose them to hemorrhage. Spinal giant cell tumors often present in the second to fourth decade of life with female predilection. The sacrum is most commonly affected, followed by the thoracic, cervical, and lumbar segments.16 It usually arises from the vertebral body with frequent extension into the posterior elements and paraspinal tissues. Vertebral fracture can often occur. CT demonstrates an expansile lytic lesion (▶ Fig. 46.7); MRI shows isointense to hypointense signals on T1-weighted images and variable appearance on T2-weighted images. Radicle resection with or without adjuvant radiation is usually the preferred treatment.17 New medical treatment with denosumab has been shown to be highly effective and has changed the treatment paradigm for giant cell tumor in recent years.

46.2.8 Eosinophilic Granuloma Eosinophilic granuloma (EG), a form of Langerhans cell histiocytosis, is a benign lesion caused by overproliferation of Langerhans cells. The abnormal cells secrete prostaglandins and lead to bone resorption. The thoracic segments are more commonly affected than the lumbar and cervical segments. The classic radiographic finding is “vertebra plana” (▶ Fig. 46.8), but this finding is only present in about 15% of cases. CT often shows lytic lesions; MRI often demonstrates hypointense signal on

T1-weighted imaging and hyperintense signal on T2-weighted imaging. Symptomatic and progressive lesions can be treated with low-dose radiotherapy, steroid injections, chemotherapy, and surgical curettage.18

46.3 Indications and Contraindications A thorough knowledge of the epidemiology, common presentation, imaging findings, and treatment options for benign bone tumors is essential for successful management of these lesions. The goals of treatment for patients with benign spine tumors are to provide cure if possible, and early return to activity with a stable spinal column and normal or improved neurologic function. Appropriate management of benign tumors may be observational, ablative, or surgical depending on level of pain, instability, neurologic compromise, and natural history of the lesion. Not all patients with benign spine tumors need surgery and some may be amenable to “watchful waiting” to make sure the tumors do not cause pain or dysfunction. Various indications for surgery in patients with benign tumors may be summarized as follows: ● Enneking stage II and III lesions. ● Pathologic fracture or deformity with bony impingement producing neurologic symptoms or pain. ● Tumor progression with development of symptoms. ● Segmental instability with significant pain or impending neurologic injury.

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Minimally Invasive Spine Surgery for Tumors

46.4 Preoperative Planning 46.4.1 Physical Examination Pain and weakness are the most common presenting complaints seen in about 85% and 40% of patients, respectively, at the time of initial presentation. A palpable mass is detectable less often. The characteristics of back pain may be a pointer as when associated with tumors, it tends to be progressive and unrelenting with no close association with activity as has mechanical back pain. Pain at night is particularly worrisome. Pain symptoms may localize to a specific spinal segment or may be radicular in nature, which can mimic a herniated nucleus pulposus, leading to confusion in diagnosis and treatment. Various factors leading to pain are local tumor growth with expansion of the cortex leading to distortion and stretching of the periosteum and subsequent stimulation of pain receptors or a pathologic fracture of the vertebrae with radicular pain resulting from growth of the mass and compression or invasion of the adjacent nerve roots. Spinal deformity may be associated with the onset of pain and usually results from paraspinous muscular spasm. Painful scoliosis is sometimes associated with osteoid osteoma or osteoblastoma, in which case the onset may be rapid. Physical examination would depend on tumor locations and presence or absence of neural compression. There can be presence of local tenderness over the tumor site. Patients with osteoid osteoma may have scoliosis. If cervical spinal cord compression is present, there may be signs of myelopathy, such as a positive Hoffmann sign, spastic weakness as well as hyperreflexia in the upper and lower extremities, Babinski’s signs bilaterally, and gait instability with a sensory or motor level. Patients with lumbosacral tumors with canal compromise may have weakness and/or numbness in one or both extremities, and evidence of perineal numbness and saddle anesthesia. Patients with lumbosacral tumors with severe canal and foraminal involvement may present with low back pain and cauda equina syndrome with perineal numbness, bowel and bladder dysfunction, and/or lower extremity weakness.

46.4.2 Radiographic Workup and Preoperative Imaging Preoperative workup involves various imaging tests that may include radiographs, CT, MRI, positron emission tomography (PET) scans, and CT of the chest, abdomen, and pelvis. Plain roentgenograms are often the first test in any case where a neoplasm is suspected. Anteroposterior (AP) and lateral views of the involved vertebra can provide considerable information about the nature and behavior of the lesion and may be sufficient to identify some characteristic tumor types. Pattern of bone destruction may allude to the presence of benign tumor wherein a geographic pattern of bone destruction is more often seen as compared to malignant tumors, which produce a motheaten appearance. However, because radiographic evidence of bone destruction is not apparent until between 30 and 50% of the trabecular bone has been destroyed, early lesions may be hard to detect. Nevertheless, even though the role of plain radiographs is dwindling with the availability of CT and MRIs, weight-bearing full-spine radiographs are still very helpful and

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may help the surgeon in making a decision regarding overall spinal balance and the need for stabilization. 99mTc bone scans are commonly used to detect neoplastic disease of the musculoskeletal system and are useful in symptomatic patients with negative or equivocal radiographs. The ability to scan the entire body makes bone scans advantageous to determine the extent of dissemination in patients with known systemic disease and to define the most accessible lesion to biopsy in patients, especially in patients with suspected spinal metastasis with an unknown primary malignancy. Bone scintigraphy is almost invariably positive and has been advocated for localizing the vertebral level in patients with clinically suspected osteoid osteoma. However, the main disadvantage of bone scans is their poor specificity because non-neoplastic pathology, most often osteoarthritis, can also cause focal areas of increased uptake. The addition of single photon emission computed tomography (SPECT), a recent technological advancement, however, improves the predictive value of planar scans by better defining the anatomic location of uptake. PET scans are helpful in determining other areas of abnormal radioactive uptake of glucose throughout the body and are often indicated in workup of malignant neoplasms. CT scans are very accurate for evaluating the extent of osseous involvement and the degree of cancellous and cortical bone loss and can be helpful in characterization of the tumor matrix, exact location, extension, and osseous changes. MRI on the other hand is superior for evaluation of the associated soft-tissue mass, bone marrow infiltration, and intraspinal extension, and should be obtained both with and without contrast administration. It can further identify regions of the tumor that may be cystic or necrotic without enhancement, as well as the extension of the tumor burden into surrounding tissues. In addition, MRI is important when identifying tumor burden within the epidural space and the extent of neural element compression or injury, either centrally or foraminally. In the evaluation and management of primary vertebral column tumors, an accurate biopsy is essential in the diagnostic evaluation. Even though various tumors have characteristic radiological appearance permitting a diagnosis following a thorough clinical history and physical examination, an accurate tissue diagnosis through histopathologic examination is very important and is needed to help in determining the aggressiveness and natural history of the spinal tumor as all benign tumors do not behave in a similar fashion. CT-guided biopsy is a fast, economical, and minimally invasive procedure and is typically performed to obtain tissue specimens for histopathologic analysis. In several studies, percutaneous CT-guided biopsy of spinal lesions has been demonstrated to have diagnostic accuracy in more than 90% of cases. In case a primary malignant tumor is in the differential diagnosis, the importance of biopsy incision/track cannot be overemphasized and it should be planned so that it can be excised with the tumor during the definitive procedure, if it turns out to be malignant.

46.4.3 Instrumentation Notes The use of instrumentation in patients with benign spinal tumors varies from case to case and depends on the extent of the lesion and degree of bony destruction. Instrumentation may be indicated either in the presence of preoperative instability or

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Benign Spinal Tumors with anticipated or obvious postoperative instability following resection of the tumor. Nevertheless, apart from the very obvious cases, the diagnosis of overt instability may be challenging and does have significant subjective variation among various spine surgeons. When a reconstruction is necessary following surgical resection of a benign spinal tumor to restore the mechanical stability of the spine, it is prudent to follow some general principles to optimize the overall clinical outcome. First, definitive treatment must restore the anterior weightbearing column especially in cases where a significant amount of the anterior column has been resected either at one level or over many levels to avoid collapse and kyphosis. Second, posterior instrumentation should be applied to restore the posterior tension band after extensive laminectomy, especially in cases where facet joints have been removed. Third, a combined anterior reconstruction with posterior instrumentation may be necessary in cases with significant resection involving both the anterior and posterior columns like subtotal and total spondylectomy at one or multiple levels.

46.5 Surgical Approach and Technique The use of MIS for various pathologies has exploded over the past decade in an attempt to minimize approach-related morbidity.19 These technologies include the use of minimal access portals, needle-based cement vertebral body augmentation, and the placement of percutaneous spinal instrumentation.20,21 While it has gained popularity based on clinical evidence demonstrating its advantages in terms of reduced intraoperative blood loss and decreased pain and hospital stay, patient-related factors have been a key driving force toward the wider acceptance of MIS. As experience has grown with the MIS approaches, various complex pathologies like spinal deformity and vertebrectomies have become amenable to MIS techniques due to improvement in instrumentation and technological advancement notwithstanding several limitations.22,23 Treatment of spinal tumors has been the most recent advancement in the application of MIS with a number of studies in the recent past demonstrating its applicability in treatment of intradural spinal tumors and metastatic spinal neoplasms.24 There is no reason why MIS approaches cannot be applied to surgical management of benign primary spinal tumors. The various retractor systems available for MIS approaches include the tubular fixed or expandable retractors to allow approaching the spine either posteriorly or from the extreme lateral approach. This, along with development of newer systems allowing percutaneous placement of multilevel instrumentation, has paved the way for considering enough experience has been gained in utilizing these approaches for standard degenerative and traumatic cases. These approaches may also be associated with further decrease in postoperative pain and spinal instability through preservation of the musculoligamentous structures and posterior bony elements. With the development of new minimally invasive techniques and the advent of specialized instruments to work within confined tubular corridors, posterior-based thoracic corpectomies can be performed through minimally invasive or mini-open approaches.

Musacchio et al using a dual-tube technique in a cadaveric model demonstrated the feasibility of this approach with recent studies showing the safety and efficacy of such an approach for management of pathologies involving the anterior thoracic spine.22 Similarly, in an attempt to improve upon traditional approaches for anterior lumbar interbody fusion (ALIF), the extreme lateral interbody fusion (XLIF) procedure has been described as an alternative approach to anterior column stabilization and can significantly decrease the morbidity associated with either thoracotomy-based open approaches or large extensile posterior exposures.25 Recent development of percutaneous posterior instrumentation technology, which allows multilevel spinal fixation, has further increased the scope of application of MIS strategies to the management of spinal tumors with minimal soft-tissue exposure and disruption avoiding prolonged periods of soft-tissue healing.26 To determine the appropriate MIS technique, the location and size of the tumor are the critical factors. Any tumor located in the posterior segment of the vertebrae, for instance an osteoid osteoma involving the lamina of the vertebral body, can be safely excised using MIS technique by deploying a fixed tubular tube or an expandable tubular retractor depending on the surgeon’s preference providing access to the spine and the tumor. Similarly, for a tumor located in the vertebral body (in patients with hemangioma/osteoid osteoma/osteoblastoma), an extreme lateral approach can be utilized to dock an expandable dilator system onto the side of the vertebral body in either the thoracic or the lumbar spine. If performed in the lumbar spine, great care needs to be taken to prevent damage to the lumbar plexus and femoral nerve to avoid iatrogenic neural injury. The details of the approach and placement of the retractor system are discussed elsewhere in the book. Once onto the spine, an excision of the tumor can be performed using osteotomes or drills depending on the exact location and size of the tumor. If removal of the tumor leads to possible instability, MIS techniques now allow placement of percutaneous instrumentation and fixation of the spine, which can be done following removal of the tumor. A facet fusion at the instrumented levels can also be performed simultaneously utilizing a tubular dilator that can be docked onto the facet joint, followed by decortication of the joint and placement of osteoinductive material to allow for fusion. Although more useful in patients with vertebral fractures secondary to malignancy, benign tumors such as hemangiomas and osteoid osteoma presenting with pain only may also be amenable to treatment with a minimally invasive approach such as vertebroplasty or kyphoplasty.20

46.6 Postoperative Care Depending on the specific pathology treated and MIS techniques utilized, the postoperative care will vary. An immediate neurological evaluation is performed as soon as the patient is awake and cooperative. Evidence of a new neurological deficit warrants immediate radiographic examination, which may include plain films, a myelogram, a CT scan, and/or a MRI study depending on the type and severity of deficit that may or may not require an operative intervention. Postoperative complete blood count (CBC) and basic metabolic panel (BMP) are routinely ordered to ensure absence of anemia and metabolic derangements. If instrumentation is used, upright radiographs should be obtained to check for placement of instrumentation

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Minimally Invasive Spine Surgery for Tumors as well as to establish baseline spinal alignment. A routine postoperative pain regimen and physical therapy are also indicated as per the institution protocol or surgeon’s preference.

46.7 Management of Complications Depending on the specific pathology and MIS approach, different complications may occur. Careful preoperative planning and meticulous surgical techniques can often avoid these potential complications. Specific management strategies of potential complications are addressed in the techniques section of this book.

46.8 Clinical Case: Aneurysmal Bone Cyst A 23-year-old woman presented with intractable and progressive low back pain for 6 months despite conservative management. Her physical examination was unremarkable. CT and MRI of lumbar spine revealed a large expansile lytic lesion with fluid–fluid levels in the L4 vertebral body consistent with an ABC (▶ Fig. 46.9). CT-guided biopsy confirmed the diagnosis. Given her persistent symptoms and failed course of conservative management, surgical intervention was offered to the patient. A minimally invasive approach with direct lateral corpectomy and posterior instrumentation was utilized to treat this lesion. Preoperative embolization had been performed to reduce the chance of intraoperative bleeding. After induction of general anesthesia, the patient was carefully turned prone in a lateral decubitus position with the left side up.

The operative table was flexed slightly to expose the left. This area was scrubbed, prepped, and draped in the usual sterile fashion. The intraoperative fluoroscopy was used to identify the L4 level. Incision was planned out on the left flank overlying the L4 level. This was injected with local anesthesia and carried out sharply. The subcutaneous fat was divided using monopolar cautery. The fascia of the abdominal wall was identified and divided using sharp scissors. Blunt dissection was then used to divide through the three layers of the abdominal wall musculature including the external oblique, internal oblique, and transversus abdominis muscles. Upon doing so, dissection at this point allowed entry into the retroperitoneal space. The psoas muscle was easily palpated. Tubular dilators were then used to dilate through the abdominal wall musculature and through the psoas muscle onto the L4 vertebral body. Electrophysiological stimulation monitoring was used throughout the dilation to ensure no dilation onto muscles of the lumbar plexus. Following adequate dilatation, a retractor was inserted with 140-mm-length blades over the L4 vertebral body with the whole assembly hooked onto a table-mounted holder. This was locked into place, and then the neurophysiological stimulator was used to stimulate the deep tissues at the base of the retractor, where it was confirmed there were no lumbar plexus nerve roots. The retractor was expanded to encompass the entire L4 level from the base of L3 to the top of L5. Upon expansion, further stimulation was performed and the femoral nerve was identified in the posterior aspect of the exposure and left carefully encapsulated within psoas muscle fibers, so that it would not be violated. The retractor was anchored to the L3 bone via holding pin. The L3–L4 and L4–L5 discs were identified and incised sharply, and partial discectomies were performed using end plate preparatory instruments and pituitary rongeurs. The partial L4 corpectomy

Fig. 46.9 (a,b) Preoperative CT and postoperative radiographs (c,d) of a patient with an aneurysmal bone cyst involving the lumbar spine that was successfully treated with minimally invasive surgery approaches.

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Benign Spinal Tumors was then performed using curettes, a high-speed drill, and pituitary rongeurs. The entire ABC area from this exposure was removed using a curette, pituitary rongeurs, and the high-speed drill. Eventually after removing the entire system from the anterior part of the vertebral body, the end plates of L3 and L5 were prepared for interbody arthrodesis. An appropriately sized intervertebral biomechanical device was selected. This titanium implant was prepared with lordotic end plates and packed with morselized allograft, as well as other osteobiologics. This was inserted into the intervertebral space under AP and lateral fluoroscopy. It was then expanded to appropriately engage the end plates. The images revealed that it sat appropriately in the left half of the vertebral body space consistent with the corpectomy defect. The retractor was then removed and a Hemovac drain was tunneled out percutaneously from the wound and sutured to the skin surface. The wound was closed in layers using interrupted 3–0 Vicryl for the fascia, interrupted inverted 2–0 Vicryl for the subcutaneous layer, and Dermabond for the skin. The drapes were removed and a sterile dressing was applied. The patient was carefully turned prone on the Jackson table and all dependent portions were carefully padded. Lumbar part of the patient’s back was scrubbed, prepped, and draped in the usual sterile fashion. The percutaneous iliac pin was inserted through a stab incision into the left posterior superior iliac spine with a dynamic reference array attached to this. The Oarm was brought onto the field and intraoperative CT scan performed and the images transferred to the navigation system for use of intraoperative image-guided computer-assisted navigation. The navigation wand was used to plan out bilateral paramedian incisions over the L3–L5 levels. These were injected with local anesthesia and carried out sharply. The navigated tactile awl was used to access the pedicles at L3 and L5 bilaterally. This was used to dissect through the pedicles into the vertebral bodies and the navigated tap was used to prepare each pedicle on L3 and L5 bilaterally. The Nitinol K-wires were then placed into the prepared pedicles. The navigated dilating system was then used to dilate the paraspinal muscles, and on the left-hand-side dock an X-tube over the L4 level. A hemilaminectomy, medial facetectomy, and transpedicular approach was carried out on this side with removal of the majority of the transverse process, the entire pedicle, and lateral posterior vertebral body in order to achieve complete curettage and removal of the ABC. This allowed visualization of the anterior cage actually through the defect. The L4 nerve root was completely skeletonized and preserved and in good condition. On the right-hand side, dilation was performed over the L3–L4 and L4– L5 facet joints, which were heavily decorticated using a highspeed drill and then posterolateral arthrodesis was completed by laying down further osteobiologics and morselized allograft. At this point, the retractors were all removed. The cannulated pedicle screws were then placed over the K-wires using the navigator system and fluoroscopy. After seating the screws properly, appropriately sized rods were passed through the extenders on the screws and seated into the heads of the screws and the screws were locked in place with locking caps and finally tightened using the torque driver and countertorque after placing gentle compression across the screws. The extenders were then removed. Final AP and lateral fluoroscopic images were taken to confirm satisfactory implant placement. Hemovac drain was tunneled out

from the left-side wound overlying the transpedicular defect and hooked up to suction drainage. The wounds were closed in layers using interrupted 0 Vicryl in the fascia, interrupted inverted 2–0 Vicryl for the subcutaneous layer, and Dermabond for the skin. There was no change in electromyographic (EMG) or somatosensory evoked potential (SSEP) signals throughout the entire procedure. All pedicle screws were tested using the stimulator and no stimulation of associated nerves could be detected below 20 mA, indicating safe insertion. The patient was turned back supine, awakened from anesthesia, and taken to the recovery room without any complication. She had immediate and dramatic improvement in her back pain postoperatively. Upright radiographs showed proper placement of hardware. The patient remained clinically well at 2-year follow-up with minimal back pain.

46.9 Conclusion With a solid understanding of tumor pathophysiology, local anatomy, spinal biomechanics, and MIS principles, benign spinal tumors can be successfully treated with MIS techniques.

Clinical caveats ● ●

●

Proper patient selection is key to a good clinical outcome. A solid understanding of local anatomy, natural history, and oncological staging is essential for successful treatment of primary benign tumors. Preoperative embolization of vascular lesions may help reduce intraoperative blood loss in lesions such as ABCs and aggressive hemangiomas.

References [1] Flemming DJ, Murphey MD, Carmichael BB, Bernard SA. Primary tumors of the spine. Semin Musculoskelet Radiol. 2000; 4(3):299–320 [2] Orguc S, Arkun R. Primary tumors of the spine. Semin Musculoskelet Radiol. 2014; 18(3):280–299 [3] Cugati G, Singh M, Pande A, et al. Primary spinal epidural lymphomas. J Craniovertebr Junction Spine. 2011; 2(1):3–11 [4] Kaloostian PE, Zadnik PL, Etame AB, Vrionis FD, Gokaslan ZL, Sciubba DM. Surgical management of primary and metastatic spinal tumors. Cancer Contr. 2014; 21(2):133–139 [5] Smith J, Wixon D, Watson RC. Giant-cell tumor of the sacrum. Clinical and radiologic features in 13 patients. J Can Assoc Radiol. 1979; 30(1):34–39 [6] Acosta FL, Jr, Dowd CF, Chin C, Tihan T, Ames CP, Weinstein PR. Current treatment strategies and outcomes in the management of symptomatic vertebral hemangiomas. Neurosurgery. 2006; 58(2):287–295, discussion 287–295 [7] Acosta FL, Jr, Sanai N, Cloyd J, Deviren V, Chou D, Ames CP. Treatment of Enneking stage 3 aggressive vertebral hemangiomas with intralesional spondylectomy: report of 10 cases and review of the literature. J Spinal Disord Tech. 2011; 24(4):268–275 [8] Jiang L, Liu XG, Yuan HS, et al. Diagnosis and treatment of vertebral hemangiomas with neurologic deficit: a report of 29 cases and literature review. Spine J. 2014; 14(6):944–954 [9] Greenspan A. Bone island (enostosis): current concept—a review. Skeletal Radiol. 1995; 24(2):111–115 [10] Murphey MD, Andrews CL, Flemming DJ, Temple HT, Smith WS, Smirniotopoulos JG. From the archives of the AFIP. Primary tumors of the spine: radiologic pathologic correlation. Radiographics. 1996; 16(5):1131–1158 [11] Azouz EM, Kozlowski K, Marton D, Sprague P, Zerhouni A, Asselah F. Osteoid osteoma and osteoblastoma of the spine in children. Report of 22 cases with brief literature review. Pediatr Radiol. 1986; 16(1):25–31

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Minimally Invasive Spine Surgery for Tumors [12] McLeod RA, Dahlin DC, Beabout JW. The spectrum of osteoblastoma. AJR Am J Roentgenol. 1976; 126(2):321–325 [13] Kroon HM, Schurmans J. Osteoblastoma: clinical and radiologic findings in 98 new cases. Radiology. 1990; 175(3):783–790 [14] Lucas DR, Unni KK, McLeod RA, O’Connor MI, Sim FH. Osteoblastoma: clinicopathologic study of 306 cases. Hum Pathol. 1994; 25(2):117–134 [15] Boriani S, Lo SF, Puvanesarajah V, et al. AOSpine Knowledge Forum Tumor. Aneurysmal bone cysts of the spine: treatment options and considerations. J Neurooncol. 2014; 120(1):171–178 [16] Bidwell JK, Young JW, Khalluff E. Giant cell tumor of the spine: computed tomography appearance and review of the literature. J Comput Tomogr. 1987; 11(3):307–311 [17] Li G, Fu D, Chen K, et al. Surgical strategy for the management of sacral giant cell tumors: a 32-case series. Spine J. 2012; 12(6):484–491 [18] Brown CW, Jarvis JG, Letts M, Carpenter B. Treatment and outcome of vertebral Langerhans cell histiocytosis at the Children’s Hospital of Eastern Ontario. Can J Surg. 2005; 48(3):230–236 [19] Smith ZA, Fessler RG. Paradigm changes in spine surgery: evolution of minimally invasive techniques. Nat Rev Neurol. 2012; 8(8):443–450 [20] Gerszten PC. The role of minimally invasive techniques in the management of spine tumors: percutaneous bone cement augmentation, radiosurgery, and

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microendoscopic approaches. Orthop Clin North Am. 2007; 38(3):441–450, abstract viii Smith ZA, Yang I, Gorgulho A, Raphael D, De Salles AA, Khoo LT. Emerging techniques in the minimally invasive treatment and management of thoracic spine tumors. J Neurooncol. 2012; 107(3):443–455 Musacchio M, Patel N, Bagan B, Deutsch H, Vaccaro AR, Ratliff J. Minimally invasive thoracolumbar costotransversectomy and corpectomy via a dualtube technique: evaluation in a cadaver model. Surg Technol Int. 2007; 16:221–225 Deutsch H, Boco T, Lobel J. Minimally invasive transpedicular vertebrectomy for metastatic disease to the thoracic spine. J Spinal Disord Tech. 2008; 21(2):101–105 Nzokou A, Weil AG, Shedid D. Minimally invasive removal of thoracic and lumbar spinal tumors using a nonexpandable tubular retractor. J Neurosurg Spine. 2013; 19(6):708–715 Ozgur BM, Aryan HE, Pimenta L, Taylor WR. Extreme Lateral Interbody Fusion (XLIF): a novel surgical technique for anterior lumbar interbody fusion. Spine J. 2006; 6(4):435–443 Hansen-Algenstaedt N, Schäfer C, Beyerlein J, Wiesner L, Knight R. Percutaneous multilevel reconstruction in revision surgery. Eur Spine J. 2012; 21 (6):1220–1222

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Radiofrequency Tumor Ablation with Vertebroplasty for the Treatment of Spine Metastases

47 Radiofrequency Tumor Ablation with Vertebroplasty for the Treatment of Spine Metastases Anthony A. Turk and Daniel K. Fahim Abstract Radiofrequency tumor ablation, combined with vertebroplasty, is a relatively new tool in the minimally invasive treatment of metastatic disease involving the thoracic and lumbar spine. This percutaneous, outpatient procedure can contribute to local oncological control and provide nearly instantaneous and dramatic pain relief of painful pathological fractures involving the spine secondary to metastatic disease. Keywords: radiofrequency ablation, metastatic disease, pathological fracture, vertebroplasty

47.1 Introduction to Spine Metastases The skeleton is the third most common site of tumor metastasis after lung and liver, with the spine most frequently involved. There have been progressively more diagnoses of spine metastases in recent years, primarily due to the development of newer imaging modalities, as well as improvements in systemic treatments. As medical techniques have advanced and patient survival periods have increased, postmortem studies indicate that, depending on the primary cancer, 30 to 90% of patients with terminal cancer have metastatic spinal tumors.1,2,3 Metastatic tumors are estimated to be 20 times more frequent than primary spine tumors.4 Although metastatic disease to the spine can occur at any age, it is most common between the ages of 40 and 70. In addition, men are more afflicted by spine metastases5,6; however, this may be attributed to the higher incidence of prostate cancer relative to breast cancer (both of which commonly metastasize to the spine). Spine metastases arise in the thoracic region 70% of the time, followed by the lumbar and then cervical spine.7,8 Spinal metastases from a tumor can spread via the arterial system, Batson’s venous plexus, cerebrospinal fluid, or direct extension from paraspinous disease. The posterior vertebral body is the initial site of involvement in two-thirds of cases, with the posterior elements being involved typically later and seldom in isolation. Spinal metastases are extradural in 94 to 98% of patients, predominantly arising in the vertebral column and secondarily extending into the epidural space. Intradural metastases are exceedingly rare with only 0.5% occurring in the intradural/intramedullary compartment.9,10 The most common presentation of metastatic spine tumors is back pain. The pain associated with spine metastases is due to either direct tumor progression and subsequent destruction or biomechanical weakness from bone loss.11 Tumor-related pain is predominantly nocturnal or early morning pain and generally improves with activity throughout the day. It may be caused by inflammatory mediators or tumor stretching the periosteum of the vertebral body.12 Mechanical pain results from a structural abnormality of the spine, such as a

pathologic vertebral compression fracture (VCF) resulting in instability. This pain is movement-related and may be exacerbated by sitting or standing, which increases the axial load on the spine. The incidence of VCF is estimated to be 24, 14, 6, and 8% among patients with multiple myeloma and breast, prostate, and lung cancers, respectively.13,14 Additionally, most untreated metastatic spine tumors eventually cause neurological deficits at the terminal stage. It must be understood that VCFs secondary to cancer are much different than osteoporotic fractures. Osteoporotic VCF is a relatively benign condition with spontaneous healing occurring in approximately 33% of patients.14 The probability of selfhealing is less likely in cancer patients because of the increased rate of bone loss from tumor osteolysis, chemotherapy, steroid treatment, and poor nutrition. It is clear spinal metastases are a significant source of morbidity for an increasingly large number of patients. Early diagnosis and aggressive intervention of spinal metastases are essential to minimize the consequences and maximize patient quality of life.

47.2 Current Treatment Options for Spine Metastases Current treatment options of spinal metastases are typically palliative rather than curative, with the following goals: ● Relieving pain. ● Preventing development of pathological fractures. ● Retaining mobility. ● Preserving neurological function. These options include radiotherapy, surgery, chemotherapy, and radiosurgery. The decision-making paradigm for treatment of patients with spine metastases is beyond the scope of this chapter. It is important to note that, thus far, there has been minimal use of percutaneous procedures to treat the actual neoplastic disease, but rather only consequences of the tumor such as utilization of vertebroplasty or kyphoplasty for the treatment of VCFs. Radiation therapy (RT) is extremely effective in alleviating tumor-associated pain. It is generally the first line of treatment. This is appropriate when the patient has multiple metastatic lesions in the spine, no compromise of the structural integrity of the spine, and no neurological deficits. Mechanical instability pain involving the spine does not respond well to radiation treatment. Radiculopathic pain associated with nerve root compression secondary to a metastatic tumor responds to radiation treatment only if the tumor is radiosensitive and decreases in size in response to radiotherapy. Approximately 90% of patients experience at least minimal relief of tumor-related pain, with 54 to 66% obtaining complete relief.11,15 The mechanism of pain relief by RT is still unclear, although it is thought to be related to tumor shrinkage or to depressed cytokine production by inflammatory cells surrounding the tumor cell.16,17

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Minimally Invasive Spine Surgery for Tumors Unfortunately, the benefits of pain relief and tumor control provided by RT are not able to control mechanical pain associated with a fracture. In fact, RT has been shown to increase the risk of developing VCF in some studies.14 High doses of radiation can damage collagen, which compromises the integrity of bone.18 At high doses, degradation of the collagen matrix might occur via the breaking of peptide bonds in the collagen backbone.19 Ultimately, exposure to radiation progressively degrades the strength, ductility, and durability of bone tissue.20 The risk of vertebral body fractures has become even more evident with the increasing use of stereotactic radiosurgery for the treatment of patients with solitary or oligometastatic disease involving the spine.21,22,23,24,25 Because pain relief by RT may take weeks and restabilization months, if it occurs at all, less invasive techniques such as kyphoplasty or vertebroplasty are important adjuncts for the treatment of patients with spine metastases who may be experiencing mechanical back pain or have associated VCFs. Percutaneous kyphoplasty is a fluoroscopically guided procedure that, unlike vertebroplasty, involves percutaneous insertion of a balloon that creates a cavity, followed by intravertebral infusion of polymethyl methacrylate (PMMA). An advantage of kyphoplasty and vertebroplasty is they can be used to treat both benign and metastatic lesions. Furthermore, these vertebral augmentation procedures (VAPs) are associated with short surgical times and low morbidity while also providing spine stabilization and immediate pain reduction.26,27 Despite the variety of treatment options available, approximately one-third of patients remain inadequately relieved. Even analgesic medications may be insufficient or cause adverse reactions.28 In light of this evidence, it is clear there is great need for a superior treatment option. Spinal metastases must be recognized as a complex condition requiring integrated multistep and multidisciplinary care. Therefore, successful cancer treatment should consist of a combination of surgery, chemotherapy, and irradiation. Thermoablative procedures such as radiofrequency ablation (RFA), laser-induced thermotherapy, and cryoablation are established treatment options for soft-tissue tumors. In particular, RFA has received increased attention

as an effective, minimally invasive treatment for various benign and malignant tumors. Recent technological advances have allowed this technology to be applied to the spine.29,30,31

47.2.1 Radiofrequency Ablation RFA uses thermal energy generated from a high-frequency alternating current to destroy tissue surrounding an electrode, resulting in coagulative necrosis of tissue from high temperatures. This typically involves a percutaneous transpedicular approach to access the affected vertebral body (▶ Fig. 47.1). Optimal tissue destruction occurs between 50 and 90 °C.32 The radius of the ablation zone is dependent on the tissue temperature and time the tissue is maintained at that temperature. Accurate temperature measurements are vital to ensure proper tumor ablation and also to minimize unintended tissue damage. Thermal destruction of pain-sensitive nerve fibers ceases transmission of pain signals. Tumor cell necrosis has also been implicated in decreasing the cytokine-mediated pain pathways involving interleukins and tumor necrosis factor.33 RFA also delays tumor progression to the sensitive periosteum.34,35 The combination of these mechanisms leads to rapid decrease in pain that can provide long-lasting relief. RFA is a relatively new method for the treatment of spine tumors. It was initially introduced for the treatment of osteoid osteoma29 and then became an important tool in the treatment of metastatic liver, renal, and lung tumors.30,36,37,38 RFA is now approved by the U.S. Food and Drug Administration for the treatment of spinal metastases, which often include unresectable spinal tumors unresponsive to chemotherapy and RT. It has the advantage of being able to destroy a tumor without requiring its removal and can be used in patients who are otherwise poor surgical candidates. RFA can be performed under conscious sedation and local anesthesia and has the advantage of allowing the operator to control the size of the ablation using image guidance.39 Up to 80% of patients reported a decrease in their analgesic medication use at some time during their follow-up period after treatment of painful osteolytic metastases.40,41

Fig. 47.1 Artist’s depiction of the radiofrequency ablation process. (a) After gaining access into the vertebral body through the pedicle (in this case the left pedicle), the radiofrequency ablation probe is targeted into the vertebral body lesion. (b) Depiction of the ablation beginning (shows as a darker region within the vertebral body lesion). (c) Completion of the ablation to involve the entire metastatic lesion and withdrawal of the radiofrequency probe. (Reproduced with permission from Merit Medical.)

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Radiofrequency Tumor Ablation with Vertebroplasty for the Treatment of Spine Metastases Data show that a clinically and statistically significant reduction in spinal pain is usually achieved within 6 weeks following RFA, which decreases further at 6 months and is maintained at that level for an extended period of time.42 RFA is not only effective, but also highly predictable and therefore a feasible technique for destroying tumors adjacent to vulnerable structures. The use of multiple temperature measuring centers allows for real-time measuring of spinal canal temperatures and consequently a more precise ablation zone.43 The use of two active thermocouples is known as bipolar RFA (▶ Fig. 47.2). In summary, RFA may prevent or delay tumor progression and the risk for fracture, thereby delaying or preventing the effects of metastases to the spine. Several studies have confirmed it is feasible, safe, and effective for treating neoplastic disease. However, RFA alone does not address the issue of mechanical instability due to bone loss, and therefore should be coupled with a cement augmentation procedure such as vertebroplasty.

47.2.2 Vertebroplasty Vertebroplasty consists of a radiologically guided percutaneous injection of PMMA (“surgical cement”) into a vertebral body to provide mechanical stability. It can be used to treat benign lesions such as osteoporotic fractures or malignancies such as spine metastases.44,45 It is particularly useful to treat VCFs secondary to spine metastases because it provides mechanical stability where bone weakness is a source of severe back pain. Unlike kyphoplasty, vertebroplasty does not use an expandable balloon to create a cavity and restore vertebral height prior to injection of PMMA. However, recent studies found no correlation between restoration of vertebral height and pain relief.46

Nonetheless, vertebroplasty has been effective for reducing mechanical pain in the spine. Vertebroplasty is a particularly attractive option for patients with metastatic disease who are poor surgical candidates, have limited survival, or have recurrent disease and have received maximal spinal RT. One study reported 94% of patients experienced improvement in pain after undergoing the procedure.45 The improvement was stable in 73% of patients at 6 months and 65% at 1 year.45 Other studies showed that 97% of patients with osteolytic metastases or myeloma had partial or complete pain control within 6 to 72 hours.47 The benefits of vertebroplasty include a minimally invasive approach, outpatient care, immediate pain relief, opportunity for biopsy, and possible antitumor effects.14 Patients can also resume anticoagulation therapy, chemotherapy, and RT on the first postoperative day. The physiological mechanisms of this analgesic effect are not perfectly understood, possibly due to the stabilization of microfractures by the PMMA or destruction of pain fibers on contact with the cement, through the exothermic reaction generated during its polymerization.48 One study contends the mechanical effect takes precedence over the thermal effect since no histological lesions of intraosseous nerve fibers were seen on contact with PMMA injected into the vertebrae of rabbits.49 In agreement, another report found identical analgesic efficacy in three groups of patients treated with cements with very different peak polymerization temperatures.50 Vertebroplasty is well documented to be a safe, feasible, and effective method for pain reduction due to bone instability, but it is neither a curative therapy nor an anticancer treatment when used as a sole intervention. In order to achieve optimal

Fig. 47.2 (a) A 10-gauge articulated bipolar electrode. (b) Thermocouples allow for real-time monitoring of temperature 10 and 15 mm from the center of the ablation zone. (c) The generator display during radiofrequency ablation allows for precise, timed delivery and continuous temperature monitoring. Note the temperatures measured at the Proximal TC (the thermocouple at 10 mm) and the Distal TC (the thermocouple at 15 cc). (Reproduced with permission from Merit Medical.)

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Minimally Invasive Spine Surgery for Tumors outcomes in patients with spinal metastases, vertebroplasty is coupled with RFA. RFA treats the neoplastic disease and vertebroplasty provides stabilization while preventing progression to fracture. This is also a suitable combination because the transpedicular approach of RFA allows for easier access to the vertebral body during cement augmentation.

47.2.3 Benefits of Combining Radiofrequency Ablation and Vertebroplasty The aim of combining RFA and vertebroplasty (RFAV) is listed in the following text box.

Goals for Combining RFE and RFAV ●

●

●

Pain reduction. Thermal energy from RFA can cease transmission of pain through sensory nerve fibers in the periosteum and thereby reduce tumor-associated pain.51 In addition, injection of PMMA by vertebroplasty provides spinal stability in areas of bone weakness, reducing mechanical pain. Destroying neoplastic tissue. RFA has a strong catabolic effect on tumor cells that are producing nerve-stimulating cytokines such as tumor necrosis factor alpha (TNF-α) and interleukins (IL-1 and IL-6), resulting in inhibition of osteoclast activity.38 PMMA has a direct toxic effect on the neoplastic cells due to its chemical and thermal properties.52,53,54 Prevention of neurological impairment secondary to vertebral collapse. The combined effects of RFAV have been shown to reduce development of VCF and enhance quality of life in early studies.38,41 In addition, RFA, which causes vascular necrosis and thrombosis in highly vascularized metastatic tumors, might reduce the risk of symptomatic vascular leakage during the cement augmentation.38

Indeed, combining vertebroplasty with RFA has the benefit of thrombosing the paravertebral and intravertebral venous plexus, thereby minimizing the procedure-related complications of vertebroplasty.55 Although RFA alone does not lead to improved stability of the spine,56 by destroying the tumor it may improve the cement distribution in the vertebral lesion and increase the duration of stability provided by the vertebroplasty.55 This will increase the success rate of vertebroplasty and reduce complications. In conclusion, there is potential for RFAV to be the superior treatment option for spinal metastases because it is a minimally invasive outpatient procedure that treats the cancer as well as the associated symptoms (e.g., VCF). It is also important to note RFAV is an outpatient procedure that does not disrupt chemotherapy or radiotherapy regimens.

47.3 Indications and Contraindications The indications to treat spinal metastases with RFAV include the following: patient can receive intravenous sedation, patient

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can be placed in the prone position, a platelet count greater than 100,000/µL of blood, discontinuation of anticoagulation medication, and no severe neutropenia.

47.4 Management of Complications There exist two major potential complications associated with RFAV: ● Thermal injury to the spinal cord and nerve roots by RFA. ● Cement extravasation into the spinal canal or neural foramen during vertebroplasty. Other much less likely complications include hematoma within the spinal canal or wound infection. Minor complications include hematoma at the puncture site and transient hyperthermia. In order to destroy the spine tumor adequately, the entire lesion must be subject to cytotoxic temperatures. This often means a wide margin of apparently healthy tissue adjacent to the tumor must be treated due to the uncertainty regarding the precise location of actual tumor margins and to eliminate microscopic foci of disease.3 This is the main challenge of RFA when treating spine metastases, despite the guidelines put forth by several studies.57,58 The temperature of soft tissue surrounding RFA depends on the thickness of the cortical bone, the distance relative to the periosteum, and the duration of the radiofrequency treatment.28,59 To avoid causing irreversible nerve damage, maintaining a safety distance of 10 mm is recommended between the periosteum and the nearest nerve structure when the thickness of cortical bone between the electrode and the periosteum is less than 5 mm.28,60 In the spinal vertebra, a margin of safety exists if there is cancellous or cortical bone between the tumor and the spinal cord or nerve roots, as the cortical bone acts as an insulator and the cancellous bone has decreased heat transmission compared with soft tissues.30,41 It is suggested that the ablation zone be planned to encompass the entire tumor without entering the spinal canal and without placing the radiofrequency electrode directly against the posterior cortex.41,61 However, with spine metastases, the cortical bone is often pathological and therefore limited in its insulating properties, which increases the risk of the ablation zone extending into periosseous regions. A thermocouple can be placed in contact with the adjacent vulnerable structure to monitor the temperature in real time during the procedure and ensure precise thermal ablation. Fortunately, bipolar RFA provides multiple temperaturemeasuring centers, making it much easier to assess the boundaries of the ablation zone at different temperatures. The temperature within the tumor can reach nearly 100 °C during the delivery of RFA.62,63 Nerve damage occurs when the spinal canal temperature reaches 45 °C.30,64 Spinal tumors that have invaded the posterior cortex of the vertebrae and are located within 1 cm of the spinal cord have been considered to be unsuitable for RFA by some studies.65,66 Placing the probe in the center of the vertebral body with the shortest distance from the spinal cord as 10 mm is a safe way to minimize unintended thermal injury. Cement leakage beyond the confines of the vertebral body can lead to severe sequelae such as symptomatic pulmonary cement

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Radiofrequency Tumor Ablation with Vertebroplasty for the Treatment of Spine Metastases embolism or even paraplegia; however, the overall risk is relatively low.24,67 Another possible complication is substantial radicular pain if the cement extravasates into the neural foramen or spinal cord compression if the cement extravasates into the spinal canal and compromises the spinal cord.24 In summary, thermal injury to adjacent vulnerable structures is a complication that can be prevented by built-in safety measures of the RFA instrumentation, such as the use of multiple thermocouples. Risk of cement extravasation from vertebroplasty is thought to be decreased when coupled with RFA because the destruction of tumor tissue allows for better distribution of the cement. Although these complications have potentially significant consequences, the likelihood remains low.

47.4.1 Clinical Case: Metastatic Disease Secondary to Breast Cancer Hoffman et al68 treated 22 patients with 28 lesions located in the thoracic and lumbar spine, sacrum, pelvis, acetabulum, femur, and tibia. Fluoroscopically guided RFA was performed under moderate sedation, followed by cement injection. Pain relief was evaluated by the visual analog scale (VAS). Technical success and pain relief was achieved in all patients. Pain ratings decreased from a mean of 8.5 to 5.5 after 24 hours (p < 0.1), and then to 3.5 after 3 months (p < 0.1).68 The amount or strength of analgesics was reduced in 15 patients. They concluded RFA and osteoplasty are both feasible and effective to treat bone metastases. Munk et al69 performed a retrospective analysis of 19 patients who received RFA, followed by injection of PMMA. Patients ranged in age from 42 to 82 years (mean: 58.9 years) and

included 5 women and 14 men. Eleven vertebrae (8 lumbar and 3 thoracic), 9 acetabula, 3 sacra, 1 pubis, and 1 humerus were treated. A total of 25 combined RFA and cementoplasties were performed in the 19 patients. The technical success rate was 100%. There were seven minor complications: six limited cement extravasations and a transient thermal nerve injury. The mean radiofrequency time was 9.1 minutes (range: 6–12 minutes). The mean cement volume injected was 6.1 mL (range: 0.8–16 mL). The mean pretreatment pain (as measured with a VAS) was 7.9 (range: 7.0–9.0) and the mean posttreatment pain was 4.2 (range: 0–6); the difference was statistically significant (mean score: 4.08; 95% confidence interval: 3.92, 4.87; p < 0.0001) using a paired t-test.69 They concluded that combined RFAV is safe and effective in the treatment of painful neoplastic lesions of bone. A 36-year-old woman with a history of breast cancer several years earlier presented with progressive lumbar spine pain. MRI of the lumbar spine revealed lesions at L2 and L5 concerning for metastatic disease. CT of the chest/abdomen/pelvis and MRIs of the brain and the remainder of the spine revealed no other apparent lesions. Several different treatment options were offered to the patient, and she ultimately elected to undergo percutaneous transpedicular biopsy (to confirm diagnosis of metastatic disease) with concomitant radiofrequency tumor ablation and vertebroplasty, followed by stereotactic radiosurgery to both the L2 and L5 lesions. Some of her intraoperative images are shown in ▶ Fig. 47.3a–f. She tolerated her outpatient percutaneous procedure well and had radiosurgery at L2 1 week post-op and radiosurgery to L5 3 days later. The MRI that was obtained prior to her radiosurgery is shown along with her pre-op MRI in ▶ Fig. 47.3g–t.

Fig. 47.3 (a,b) Intraoperative anteroposterior (AP) and lateral fluoroscopic images showing Jamshidi needles being used to access the L2 pedicle from a left-sided approach. Note that great care is taken to not transgress the medial border of the pedicle before the tip of the probe has crossed the threshold of the posterior border of the vertebral body. (c,d) Intraoperative AP and lateral fluoroscopic images show excellent positioning of the Jamshidi needle within the affected vertebral body. It is at this point in the procedure that a biopsy is obtained to confirm the suspected diagnosis of metastatic cancer. (e,f) Intraoperative AP and lateral fluoroscopic images show the radiofrequency ablation probe in position to deliver treatment. (g,h) After completing the radiofrequency tumor ablation, cement augmentation of the vertebral body is undertaken, as seen in these sequential AP and lateral fluoroscopic images revealing increasing amounts of polymethyl methacrylate within the vertebral bodies. (Continued)

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Fig. 47.3 (continued) (i–p) Intraoperative AP and lateral fluoroscopic views of the radiofrequency ablation probe in the L5 vertebral body.

Fig. 47.3 (continued) Axial MRI images of the L2 vertebral body preoperatively (q) and postoperatively (r) revealing the excellent overlap between the patient’s tumor within the vertebral body (q) correlating with the cement (r), which is always dark on the T1-weighted sequences. Sagittal MRIs preoperatively (s) and postoperatively (t) of the L5 vertebral body lesion (s) and the correlating placement of the cement (t).

The cement can be seen to closely conform to the apparent lesion on the preoperative MRI, highlighting this technology’s unique targeting capabilities.

47.5 Conclusion Approximately one in four deaths in the United States is due to cancer.70 Bone is the third most common site of metastasis, with the spine most frequently involved. In addition to the rise of cancer, as diagnostic tools and screening methods have become more advanced, the identification of spinal metastases has also increased. Most of these patients present with severe

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back pain that is never permanently alleviated. This is clearly a rapidly growing issue with no adequate response. Many current treatment options are palliative with no direct effect on the cancer itself, such as VAPs, decompression and stabilization techniques, and radiotherapy. Surgery is the standard intervention to treat the neoplastic tissue; however, it is usually highly invasive and excludes a large number of patients due to the demanding medical fitness requirement. This is precisely why the combination of RFAV shows such promise. Thus far, there has been minimal use of the combination of RFAV to treat spine metastases. Further research is warranted in this area to discover its true potential.

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Radiofrequency Tumor Ablation with Vertebroplasty for the Treatment of Spine Metastases

Clinical Caveats ●

●

●

●

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RFAV is a minimally invasive, outpatient procedure that destroys neoplastic tissue as well as offers spine stabilization. As a result, the tumor-associated pain and mechanical pain are both reduced. RFAV does not disrupt chemotherapy or radiotherapy treatment plans, allowing multiple regimens to be followed concurrently. RFA may also complement vertebroplasty by allowing for better cement distribution in the vertebral body. The major complications of RFAV are thermal injury to neurological structures and cement extravasation. The risks are relatively low, and can be prevented with the use of built-in safety measures such as using multiple thermocouples. RFAV is a safe, effective, and feasible therapeutic option for spinal metastases. It provides immediate pain relief, destroys cancerous tissue, and prevents progression to vertebral compression fracture.

References [1] Cobb CA, III, Leavens ME, Eckles N. Indications for nonoperative treatment of spinal cord compression due to breast cancer. J Neurosurg. 1977; 47(5):653–658 [2] Wong DA, Fornasier VL, MacNab I. Spinal metastases: the obvious, the occult, and the impostors. Spine (Phila Pa 1976). 1990(15):1–4 [3] You NK, Lee HY, Shin DA, et al. Radiofrequency ablation of spine: an experimental study in an ex vivo bovine and in vivo swine model for feasibility in spine tumor. Spine. 2013; 38(18):E1121–E1127 [4] Perrin RG, Laxton AW. Metastatic spine disease: epidemiology, pathophysiology, and evaluation of patients. Neurosurg Clin N Am. 2004; 15(4):365–373 [5] Constans JP, de Divitiis E, Donzelli R, Spaziante R, Meder JF, Haye C. Spinal metastases with neurological manifestations. Review of 600 cases. J Neurosurg. 1983; 59(1):111–118 [6] Gilbert RW, Kim JH, Posner JB. Epidural spinal cord compression from metastatic tumor: diagnosis and treatment. Ann Neurol. 1978; 3(1):40–51 [7] Camins MB, Jenkins AL, Singhal A, Perrin RG. Tumors of the vertebral axis: benign, primary malignant, and metastatic tumors. In: Winn RH, ed. Youmans Neurologic Surgery. 5th ed. Philadelphia, PA: W.B. Saunders Company; 2004:4835–4868 [8] Steinmetz MP, Mekhail A, Benzel EC. Management of metastatic tumors of the spine: strategies and operative indications. Neurosurg Focus. 2001; 11(6):e2 [9] Schick U, Marquardt G, Lorenz R. Intradural and extradural spinal metastases. Neurosurg Rev. 2001; 24(1):1–5, discussion 6–7 [10] Harel R, Angelov L. Spine metastases: current treatments and future directions. Eur J Cancer. 2010; 46(15):2696–2707 [11] Aaron AD. The management of cancer metastatic to bone. JAMA. 1994; 272 (15):1206–1209 [12] Bilsky MH, Lis E, Raizer J, Lee H, Boland P. The diagnosis and treatment of metastatic spinal tumor. Oncologist. 1999; 4(6):459–469 [13] Saad F, Lipton A, Cook R, Chen YM, Smith M, Coleman R. Pathologic fractures correlate with reduced survival in patients with malignant bone disease. Cancer. 2007; 110(8):1860–1867 [14] Aghayev K, Papanastassiou ID, Vrionis F. Role of vertebral augmentation procedures in the management of vertebral compression fractures in cancer patients. Curr Opin Support Palliat Care. 2011; 5(3):222–226 [15] Schocker JD, Brady LW. Radiation therapy for bone metastasis. Clin Orthop Relat Res. 1982(169):38–43 [16] Choong PF. The molecular basis of skeletal metastases. Clin Orthop Relat Res. 2003(415) Suppl:S19–S31 [17] Matsumura A, Hoshi M, Takami M, Tashiro T, Nakamura H. Radiation therapy without surgery for spinal metastases: clinical outcome and prognostic factors analysis for pain control. Global Spine J. 2012; 2(3):137–142 [18] Currey JD, Foreman J, Laketić I, Mitchell J, Pegg DE, Reilly GC. Effects of ionizing radiation on the mechanical properties of human bone. J Orthop Res. 1997; 15(1):111–117

[19] Barth HD, Zimmermann EA, Schaible E, Tang SY, Alliston T, Ritchie RO. Characterization of the effects of X-ray irradiation on the hierarchical structure and mechanical properties of human cortical bone. Biomaterials. 2011; 32 (34):8892–8904 [20] Sahgal A, Whyne CM, Ma L, Larson DA, Fehlings MG. Vertebral compression fracture after stereotactic body radiotherapy for spinal metastases. Lancet Oncol. 2013; 14(8):e310–e320 [21] Al-Omair A, Smith R, Kiehl TR, et al. Radiation-induced vertebral compression fracture following spine stereotactic radiosurgery: clinicopathological correlation. J Neurosurg Spine. 2013; 18(5):430–435 [22] Boehling NS, Grosshans DR, Allen PK, et al. Vertebral compression fracture risk after stereotactic body radiotherapy for spinal metastases. J Neurosurg Spine. 2012; 16(4):379–386 [23] Cunha MV, Al-Omair A, Atenafu EG, et al. Vertebral compression fracture (VCF) after spine stereotactic body radiation therapy (SBRT): analysis of predictive factors. Int J Radiat Oncol Biol Phys. 2012; 84(3):e343–e349 [24] Sahgal A, Atenafu EG, Chao S, et al. Vertebral compression fracture after spine stereotactic body radiotherapy: a multi-institutional analysis with a focus on radiation dose and the spinal instability neoplastic score. J Clin Oncol. 2013; 31(27):3426–3431 [25] Sung SH, Chang UK. Evaluation of risk factors for vertebral compression fracture after stereotactic radiosurgery in spinal tumor patients. Korean J Spine. 2014; 11(3):103–108 [26] Dalbayrak S, Onen MR, Yilmaz M, Naderi S. Clinical and radiographic results of balloon kyphoplasty for treatment of vertebral body metastases and multiple myelomas. J Clin Neurosci. 2010; 17(2):219–224 [27] Schmidt R, Wenz F, Reis T, Janik K, Bludau F, Obertacke U. Kyphoplasty and intra-operative radiotherapy, combination of kyphoplasty and intra-operative radiation for spinal metastases: technical feasibility of a novel approach. Int Orthop. 2012; 36(6):1255–1260 [28] Palussière J, Pellerin-Guignard A, Descat E, Cornélis F, Dixmérias F. Radiofrequency ablation of bone tumours. Diagn Interv Imaging. 2012; 93 (9):660–664 [29] Rosenthal DI, Alexander A, Rosenberg AE, Springfield D. Ablation of osteoid osteomas with a percutaneously placed electrode: a new procedure. Radiology. 1992; 183(1):29–33 [30] Dupuy DE, Hong R, Oliver B, Goldberg SN. Radiofrequency ablation of spinal tumors: temperature distribution in the spinal canal. AJR Am J Roentgenol. 2000; 175(5):1263–1266 [31] Hadjipavlou AG, Lander PH, Marchesi D, Katonis PG, Gaitanis IN. Minimally invasive surgery for ablation of osteoid osteoma of the spine. Spine. 2003; 28 (22):E472–E477 [32] Brace CL. Radiofrequency and microwave ablation of the liver, lung, kidney, and bone: what are the differences? Curr Probl Diagn Radiol. 2009; 38 (3):135–143 [33] Anchala PR, Irving WD, Hillen TJ, et al. Treatment of metastatic spinal lesions with a navigational bipolar radiofrequency ablation device: a multicenter retrospective study. Pain Physician. 2014; 17(4):317–327 [34] Mannion RJ, Woolf CJ. Pain mechanisms and management: a central perspective. Clin J Pain. 2000; 16(3) Suppl:S144–S156 [35] Cleeland CS, Gonin R, Hatfield AK, et al. Pain and its treatment in outpatients with metastatic cancer. N Engl J Med. 1994; 330(9):592–596 [36] Goldberg SN, Grassi CJ, Cardella JF, et al. Society of Interventional Radiology Technology Assessment Committee. Image-guided tumor ablation: standardization of terminology and reporting criteria. J Vasc Interv Radiol. 2005; 16 (6):765–778 [37] Jansen MC, van Duijnhoven FH, van Hillegersberg R, et al. Adverse effects of radiofrequency ablation of liver tumours in the Netherlands. Br J Surg. 2005; 92(10):1248–1254 [38] Katonis P, Pasku D, Alpantaki K, Bano A, Tzanakakis G, Karantanas A. Treatment of pathologic spinal fractures with combined radiofrequency ablation and balloon kyphoplasty. World J Surg Oncol. 2009; 7:90 [39] Schaefer O, Lohrmann C, Herling M, Uhrmeister P, Langer M. Combined radiofrequency thermal ablation and percutaneous cementoplasty treatment of a pathologic fracture. J Vasc Interv Radiol. 2002; 13(10):1047–1050 [40] Callstrom MR, Charboneau JW, Goetz MP, et al. Painful metastases involving bone: feasibility of percutaneous CT- and US-guided radio-frequency ablation. Radiology. 2002; 224(1):87–97 [41] Halpin RJ, Bendok BR, Sato KT, Liu JC, Patel JD, Rosen ST. Combination treatment of vertebral metastases using image-guided percutaneous radiofrequency ablation and vertebroplasty: a case report. Surg Neurol. 2005; 63 (5):469–474, discussion 474–475

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Minimally Invasive Spine Surgery for Tumors [42] Gevargez A, Groenemeyer DH. Image-guided radiofrequency ablation (RFA) of spinal tumors. Eur J Radiol. 2008; 65(2):246–252 [43] Nakatsuka A, Yamakado K, Takaki H, et al. Percutaneous radiofrequency ablation of painful spinal tumors adjacent to the spinal cord with real-time monitoring of spinal canal temperature: a prospective study. Cardiovasc Intervent Radiol. 2009; 32(1):70–75 [44] Cortet B, Cotten A, Boutry N, et al. Percutaneous vertebroplasty in patients with osteolytic metastases or multiple myeloma. Rev Rhum Engl Ed. 1997; 64 (3):177–183 [45] Weill A, Chiras J, Simon JM, Rose M, Sola-Martinez T, Enkaoua E. Spinal metastases: indications for and results of percutaneous injection of acrylic surgical cement. Radiology. 1996; 199(1):241–247 [46] Röllinghoff M, Zarghooni K, Zeh A, Wohlrab D, Delank KS. Is there a stable vertebral height restoration with the new radiofrequency kyphoplasty? A clinical and radiological study. Eur J Orthop Surg Traumatol. 2013; 23(5):507–513 [47] Cotten A, Dewatre F, Cortet B, et al. Percutaneous vertebroplasty for osteolytic metastases and myeloma: effects of the percentage of lesion filling and the leakage of methyl methacrylate at clinical follow-up. Radiology. 1996; 200 (2):525–530 [48] Deschamps F, de Baere T. Cementoplasty of bone metastases. Diagn Interv Imaging. 2012; 93(9):685–689 [49] Urrutia J, Bono CM, Mery P, Rojas C. Early histologic changes following PMMA injection (vertebroplasty) in rabbit lumbar vertebrae. Spine. 2008; 33(8):877–882 [50] Anselmetti GC, Manca A, Kanika K, et al. Temperature measurement during polymerization of bone cement in percutaneous vertebroplasty: an in vivo study in humans. Cardiovasc Intervent Radiol. 2009; 32(3):491–498 [51] Mannion RJ, Woolf CJ. Pain mechanisms and management: a central perspective. Clin J Pain. 2000; 16(3) Suppl:S144–S156 [52] Khanna AJ, Neubauer P, Togawa D, Kay Reinhardt M, Lieberman IH. Kyphoplasty and vertebroplasty for the treatment of spinal metastases. Support Cancer Ther. 2005; 3(1):21–25 [53] Gaitanis IN, Hadjipavlou AG, Katonis PG, Tzermiadianos MN, Pasku DS, Patwardhan AG. Balloon kyphoplasty for the treatment of pathological vertebral compressive fractures. Eur Spine J. 2005; 14(3):250–260 [54] Thanos L, Mylona S, Galani P, et al. Radiofrequency ablation of osseous metastases for the palliation of pain. Skeletal Radiol. 2008; 37(3):189–194 [55] Schaefer O, Lohrmann C, Markmiller M, Uhrmeister P, Langer M. Technical innovation. Combined treatment of a spinal metastasis with radiofrequency heat ablation and vertebroplasty. AJR Am J Roentgenol. 2003; 180(4):1075–1077 [56] Orgera G, Krokidis M, Matteoli M, et al. Percutaneous vertebroplasty for pain management in patients with multiple myeloma: is radiofrequency ablation necessary? Cardiovasc Intervent Radiol. 2014; 37(1):203–210

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[57] Ko HK, Kim HB, Kang CM, et al. Newly designed flexible electrode for laparoscopic radiofrequency ablation: ex vivo and in vivo comparative studies with needle electrode in a porcine liver as technical study. J Surg Res. 2011; 168(1):88–96 [58] Cha J, Kim YS, Rhim H, Lim HK, Choi D, Lee MW. Radiofrequency ablation using a new type of internally cooled electrode with an adjustable active tip: an experimental study in ex vivo bovine and in vivo porcine livers. Eur J Radiol. 2011; 77(3):516–521 [59] Rachbauer F, Mangat J, Bodner G, Eichberger P, Krismer M. Heat distribution and heat transport in bone during radiofrequency catheter ablation. Arch Orthop Trauma Surg. 2003; 123(2–3):86–90 [60] Bitsch RG, Rupp R, Bernd L, Ludwig K. Osteoid osteoma in an ex vivo animal model: temperature changes in surrounding soft tissue during CT-guided radiofrequency ablation. Radiology. 2006; 238(1):107–112 [61] Nour SG, Aschoff AJ, Mitchell IC, Emancipator SN, Duerk JL, Lewin JS. MR imaging-guided radio-frequency thermal ablation of the lumbar vertebrae in porcine models. Radiology. 2002; 224(2):452–462 [62] Rhim H, Goldberg SN, Dodd GD, III, et al. Essential techniques for successful radio-frequency thermal ablation of malignant hepatic tumors. Radiographics. 2001; 21(Spec No):S17–S35, discussion S36–S39 [63] Varghese T, Zagzebski JA, Chen Q, et al. Ultrasound monitoring of temperature change during radiofrequency ablation: preliminary in-vivo results. Ultrasound Med Biol. 2002; 28(3):321–329 [64] Diehn FE, Neeman Z, Hvizda JL, Wood BJ. Remote thermometry to avoid complications in radiofrequency ablation. J Vasc Interv Radiol. 2003; 14 (12):1569–1576 [65] Goetz MP, Callstrom MR, Charboneau JW, et al. Percutaneous image-guided radiofrequency ablation of painful metastases involving bone: a multicenter study. J Clin Oncol. 2004; 22(2):300–306 [66] Toyota N, Naito A, Kakizawa H, et al. Radiofrequency ablation therapy combined with cementoplasty for painful bone metastases: initial experience. Cardiovasc Intervent Radiol. 2005; 28(5):578–583 [67] Mendel E, Bourekas E, Gerszten P, Golan JD. Percutaneous techniques in the treatment of spine tumors: what are the diagnostic and therapeutic indications and outcomes? Spine. 2009; 34(22) Suppl:S93–S100 [68] Hoffman RT, Jakobs TF, Trumm C, Weber C, Helmberger TK, Reiser MF. RFA in combination with osteoplasty in the treatment of painful metastatic bone disease. J Vasc Interv Radiol. 2008; 19:419–425 [69] Munk PL, Rashid F, Heran MK, et al. Combined cementoplasty and radiofrequency ablation in the treatment of painful neoplastic lesions of bone. J Vasc Interv Radiol. 2009; 20(7):903–911 [70] Siegel R, Ma J, Zou Z, Jemal A. Cancer statistics, 2014. CA Cancer J Clin. 2014; 64(1):9–29

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Minimally Invasive Resection of Intradural Spinal Tumors

48 Minimally Invasive Resection of Intradural Spinal Tumors Trent L. Tredway and Mick J. Perez-Cruet Abstract Increasingly surgeons are performing more complicated cases using minimally invasive spine (MIS) techniques. This chapter discusses resection of intradural tumors using MIS techniques. Critical to the safe and effective resection of these tumors using MIS techniques is patient selection. Not all intradural tumors can be safely resected using MIS techniques and it is up to the surgeon to carefully select which patient is an appropriate candidate. This chapter reviews commonly seen intradural tumors including meningiomas, ependymomas, and schwannoma. Keywords: extradural, intradural extramedullary, intramedullary, dural closure, minimally invasive, meningioma, schwannoma

48.1 Introduction Primary tumors of the spinal cord represent 2 to 4% of all primary tumors of the central nervous system (CNS). It is estimated that there are 850 to 1,700 new adult cases of primary spinal cord tumors diagnosed each year in the United States.1 The majority of primary spinal cord tumors are classified as low grade (grades I and II) according to the World Health Organization (WHO) pathology classification.

48.2 Types of Spinal Cord Tumors Primary spinal cord tumors are divided into three categories based on anatomic location2: ● Extradural. ● Intradural extramedullary. ● Intramedullary.

are quite aggressive and there is an increased incidence in patients with neurofibromatosis type II (NF2). Adolescents and young adults with NF2 often have multiple schwannomas and have a higher risk for malignant transformation. The anatomic location of the tumor is helpful for surgical planning and in determining if a minimally invasive approach is feasible (▶ Fig. 48.1). Patients with schwannomas may be asymptomatic. However, most patients present with mild sensory symptoms, radicular pain, or paresthesias. If asymptomatic, schwannomas may be followed with serial imaging given their usual benign behavior. Symptomatic or radiographically enlarging tumors should undergo maximal safe resection. Surgery has minimal morbidity, improves symptoms, and may be curative. Incompletely resected tumors should be followed given the benign growth of the majority of these tumors. Malignant schwannomas (MPNST) should be treated with postoperative radiotherapy, even if total resection was achieved. Neurofibromas are benign tumors that arise from peripheral sensory nerves. Solitary neurofibromas are discretely localized, globular, or fusiform nodules. Plexiform neurofibromas consist of nerve fiber bundles and tumor tissue intermixed in a disorganized pattern that extends over multiple nerve roots. Neurofibromas encase nerve roots rather than displacing them as is typical of schwannomas. Spontaneous pain and dysesthesias are the most common presenting symptoms. Patients with neurofibromatosis type 1 (NF1) may have multiple spinal cord neurofibromas that often increase in number with age. Patients

48.2.1 Extradural Spinal Cord Tumors Most extradural spinal cord tumors in adults are a consequence of systemic metastases originating from lung, breast, or prostate cancer, or lymphoma, and clinically result in epidural spinal cord compression.3,4,5 Extradural primary tumors of the spine can be separated into benign and malignant types. Benign tumors include osteoid osteoma, osteoblastoma, osteochondroma, hemangioma, aneurysmal bone cyst, giant cell tumor, and eosinophilic granuloma. Malignant tumors include chordoma, multiple myeloma, osteosarcoma, chondrosarcoma, Ewing’s sarcoma, lymphoma, soft-tissue sarcomas, and plasmacytoma.

48.2.2 Intradural Extramedullary Spinal Cord Tumors Schwannomas, neurofibromas, and meningiomas are the most common intradural extramedullary spinal cord tumors. Schwannomas are nerve sheath tumors that arise from the dorsal nerve root. They are benign tumors in the vast majority, although malignant peripheral nerve sheath tumors (MPNST)

Fig. 48.1 Axial image of midthoracic intradural extramedullary meningioma with marked spinal cord compression. This particular tumor was approached via a conventional open multilevel thoracic laminectomy.

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Minimally Invasive Spine Surgery for Tumors with NF1 should be followed closely with serial imaging studies as there is a higher incidence of malignant transformation. On imaging, neurofibromas appear as rounded or fusiform tumors that are isointense on T1-weighted (T1W) images, hyperintense on T2-weighted (T2W)/fluid-attenuated inversion recovery (FLAIR) images, and intensely enhanced postcontrast. Since there are no imaging characteristics that differentiate malignant transformation of neurofibromas, a high index of suspicion is required, such as rapidity of tumor growth. Patients with symptomatic or enlarging solitary neurofibromas should undergo surgical resection. Complete resection with minimal morbidity is usually achieved and minimally invasive techniques may be employed in many cases.6,7,8 The clinical results following resection of a plexiform neurofibroma associated with NF1 are poor because complete resection is rarely achieved. Furthermore, plexiform neurofibromas may undergo malignant transformation. Meningiomas are dural-based tumors that arise from arachnoid cap cells and are found throughout the CNS. Approximately 25% of all primary spinal cord tumors are meningiomas (▶ Fig. 48.1). Most are slow-growing low-grade tumors (WHO grade 1). Genetic predisposition (NF2) and prior exposure to ionizing radiation are the only definite risk factors. Common presenting symptoms include back pain, motor weakness, sensory disturbance, and incontinence. Meningiomas appear as solid, well-circumscribed lesions with an attachment to the dura on MRI. The tumor is iso- to hypointense on T1 W MRI and slightly hyperintense on T2 W/ FLAIR images. Meningiomas display intense, homogenous contrast enhancement, and the majority of all spinal cord meningiomas are intradural extramedullary, while few are extradural. Asymptomatic patients with spinal cord meningioma can be followed clinically with serial imaging studies. If treatment is indicated, surgery is the primary modality and can be curative with complete resection. Conventional external beam–fractionated radiotherapy or stereotactic radiosurgery is utilized for patients with incomplete resection or recurrence.

48.2.3 Intramedullary Spinal Cord Tumors Intramedullary spinal cord tumors (IMSCT) constitute 8 to 10% of all primary spinal cord tumors with the majority comprising gliomas (80–90%), of which 60 to 70% are ependymomas and 30 to 40% are astrocytomas.9 The third most common IMSCT is hemangioblastoma, representing approximately 3 to 8% of all IMSCT, of which 15 to 25% are associated with von Hippel–Lindau (VHL) syndrome.10,11,12 The clinical presentation of primary spinal cord tumors is determined in part by the location of the tumor and in nearly all clinical instances pain is the predominant presenting symptom. In a recent series of IMSCT, pain was the most common presenting symptom (72%) and may manifest as back pain (27%), radicular pain (25%), or central pain (20%). Motor disturbance was the next most common presenting symptom (55%), followed by sensory loss (39%).13 Diagnosis of a primary spinal cord tumor requires a high index of suspicion based on clinical signs and symptoms as well as spine-directed MRI. Astrocytomas and ependymomas represent the most common intramedullary neoplasms. It is estimated that the

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intracranial-to-spinal ratios for astrocytomas and ependymomas are 10:1 and 3:1 to 20:1 (depending on the histological variant), respectively.14 The clinical presentation of an intramedullary tumor is variable, but pain and a mixed sensorimotor tract disturbance are usually present. On MRI, an intramedullary tumor is radiographically recognized by focal, and sometimes holocord, spinal cord expansion with associated T2 W and FLAIR image hyperintensity, T1 W hypo- or isointensity, variable contrast enhancement, and occasional tumor-associated syrinx.3 Ependymomas are the most frequent IMSCT in adults.1,15 Histologically, there are two distinct pathological types: cellular (WHO grades 2 and 3) and myxopapillary (WHO grade 1). Cellular (classic) ependymoma arises from the intraspinal canal of the cervical and thoracic cord. Myxopapillary ependymomas arise from the filum terminale and occur almost exclusively at the conus medullaris. The treatment prognosis for spinal cord ependymomas is often excellent as these tumors may be resected completely and in such instances manifest a low recurrence risk.13,16,17 Ependymomas appear as a focal enlargement of the cord and hyperintense on T2 W and FLAIR images and hypo- or isointense to normal spinal cord on T1 W images with heterogeneous contrast enhancement.3 These tumors may also be associated with cystic changes, hemosiderin suggestive of previous hemorrhage, and syrinx. Ependymomas most often are low grade with a benign indolent course, although malignant histological subtypes (anaplastic ependymoma; WHO grade 3) rarely occur. Surgery is the most effective treatment, with complete surgical resection yielding reported local control rates of 90 to 100%, although gross total resection is not achieved in the majority of patients.17,18,19 Intraoperative monitoring of motor evoked potentials (MEPs) and somatosensory evoked potentials (SSEPs) is often utilized to assist in achieving a more safe and complete resection.20,21,22 Approximately 40% of IMSCT are astrocytomas.15,23 The majority (75%) are low-grade (WHO grade 2) fibrillary astrocytomas with 5-year survivorship exceeding 70%.13,15,24 Histology is the most important prognostic variable.25,26,27 Juvenile pilocytic astrocytoma, or JPA, is a low-grade (WHO grade I) variant that more commonly presents in younger patients. High-grade spinal cord gliomas (WHO grades 3 and 4, 25%) are less common and associated with a poor survival. Regardless of WHO grade, spinal cord astrocytomas are infiltrative and associated with poorly characterized boundaries and consequently are typically biopsied only. Astrocytomas appear on MRI as fusiform expansion of the cord with indistinct and occasionally a cystic component.3 Associated edema or syrinx (seen in 40%) may be present. The tumor is hypo- to isointense on T1 W images, and hyperintense on T2 W and FLAIR images, with variable contrast enhancement. In general, the distinction between astrocytomas and ependymomas by MRI is not always possible. Initial treatment consists of maximal safe surgical resection or biopsy, followed by observation or external beam radiotherapy. Because spinal cord gliomas are infiltrative, gross total resection is rarely accomplished (in ~12% of WHO grade 2 and 0% of grade 3 or 4 astrocytomas).13 The optimal extent of surgical resection and need for postoperative radiotherapy is controversial.

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Minimally Invasive Resection of Intradural Spinal Tumors Tumor histology, extent of resection, and functional status at time of presentation appear to be the primary determinants of outcome.10,13 Nonetheless, radiotherapy is indicated for patients with high-grade histology, tumors in which a substantial resection cannot be performed, biopsied-only tumors, and those with progressive disease. Though rare in adults, the majority of spinal cord juvenile pilocytic astrocytomas can occasionally be completely resected (up to 80%).13 Hemangioblastomas, the third most common IMSCT, are rare vascular tumors that occur as a solitary tumor or as part of VHL syndrome.4,5,6,7 Approximately 10 to 30% of patients with hemangioblastoma of the spinal cord have VHL syndrome, an autosomal-dominant disorder caused by a deletion on chromosome 3p. Other tumors associated with VHL include retinal hemangiomas, renal and pancreatic cysts, pheochromocytomas, and renal cell carcinomas. Whether hemangioblastoma occurs as part of the VHL syndrome or solitarily, the clinical and histopathologic characteristics are identical. There is a male predominance, and presentation is usually in the fourth decade.11,28 Hemangioblastomas have unique imaging characteristics of enhancing nodules in association with nonenhancing cysts (▶ Fig. 48.2). The majority of hemangioblastomas arise from the dorsal or dorsolateral portion of the spinal cord.9,11,28 As such, presenting symptoms are usually sensory, especially slowly progressive proprioception deficits. There may also be other long tract signs and radicular symptoms. Rarely, patients present with subarachnoid or intramedullary hemorrhage.29,30,31,32,33 On MRI, the hemangioblastomas appear as a homogenously enhancing hypervascular nodule with associated cyst or syrinx and peritumoral edema.11 Spinal angiography demonstrates enlarged feeding arteries, intense nodular stains, and early-draining veins.3 Hemangioblastoma can be differentiated from ependymoma by the vascular abnormalities on MRI and angiography if performed. Hemangioblastoma is differentiated from a spinal cord vascular malformation by associated syrinx and tumor enhancement on MRI. Surgical resection is the primary treatment for spinal hemangioblastomas. There are often well-defined margins allowing for a complete resection. Excessive intraoperative

bleeding, obscuring the operative field, is the limiting factor for subtotal resection.11 In contrast to posterior fossa hemangioblastomas, preoperative embolization is usually not performed as complications have been reported.34,35,36,37 Serial MRI should be obtained, as de novo lesions can appear in patients with VHL. Stereotactic radiosurgery is an option for patients with recurrent or unresectable tumors.38 Other rare primary IMSCT include primary CNS lymphoma, germinoma, melanoma, primitive neuroectodermal tumor (PNET), paraganglioma, teratoma, dermoid cyst, epidermoid cyst, lipoma, and hamartoma. Treatment following diagnosis is similar to that of intracranial counterparts and in most instances (except for lymphoma, germinoma, and PNET) surgery suffices as primary therapy.

48.3 Surgical Treatment of Intramedullary Tumors The treatment of IMSCT has been largely based on open surgical biopsy or resection if possible. Successful surgical resections with good clinical outcomes have been reported in the literature with traditional open surgery.39,40,41,42,43 However, surgical morbidity should also be considered when resecting these lesions. Open surgical intervention requires adequate exposure with removal of the posterior spinal elements. These structures are also important in maintaining alignment of the spinal column. Extensive removal of the posterior elements can be associated with increased pain and increased blood loss, and can lead to worsening kyphotic deformities of the spine.44 This is more pronounced in the cervical spine, but can also occur in the thoracic spine. It has been reported in the literature that there has been an increased risk of kyphosis in the pediatric population after patients underwent surgeries that required greater than three levels of laminectomy for the intradural tumor resection.44 Therefore, some neurosurgeons perform laminoplasties in the pediatric population in order to decrease the risk of postsurgical kyphotic deformity as the patient ages.

Fig. 48.2 (a) Pre- and (b) post–contrast-enhanced sagittal T1-weighted MRI demonstrating imaging characteristics of a cervical hemangioblastoma that is located intradural intramedullary (note: contrast-enhanced nodule in association with noncontrast enhancing cyst; yellow arrow).

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Minimally Invasive Spine Surgery for Tumors

48.3.1 Evolution of Minimally Invasive Rationale and Technique

48.3.2 Indications and Contraindications

Advantages and Disadvantages

Patients identified as having symptomatic intradural lesions are evaluated for surgical resection. The majority of intradural extramedullary tumors can be resected through minimally invasive techniques. However, complex meningiomas spanning multiple levels (> 2 vertebral body levels) and causing severe cord compression are contraindications for minimally invasive resection. These tumors are best approached through a traditional open procedure as separation of the dentate ligament bilaterally may be required for complete resection of the tumor. Furthermore, the spinal cord is typically compromised in these patients and the slightest manipulation of the cord is not well tolerated. The surgeon may encounter extremely large schwannomas and neurofibromas that will require an open procedure. In regard to large intrathoracic schwannomas, the author prefers to perform a posterior minimally invasive approach with ligation and resection of the involved exiting nerve root in a lateral position prior to performing a thoracotomy and resection of the lesion using an en bloc technique. It is important to remember that the goal of the surgery is complete resection with limited neurologic injury. Patients with lesions that are well circumscribed, smaller, and are close to the dorsal surface of the spinal cord are better candidates for a minimally invasive procedure (▶ Fig. 48.3).

The term minimally invasive surgery has been credited to a British urologist, JEA Wickham, who, in his 1987 article describing the new surgery, proclaimed: “This means that surgeons will need to be trained as microendoscopists and bioengineers rather than as butchers and carpenters.”45 Over the past few decades, neurosurgeons have been utilizing advances in surgical instrumentation, surgical optics, and endoscopy in order to perform spinal surgery with less morbidity and faster and less painful recovery, as well as maintaining excellent patient outcomes. The technological advancements combined with the ingenuity of surgeons have allowed us to treat a wide variety of spinal disorders utilizing minimally invasive concepts and techniques. Disc herniations, lumbar stenosis, spondylolisthesis, and extradural and intradural extramedullary tumors, as well as traumatic fractures, spinal column metastases, tethered cords, and syringomyelia can all be treated with minimally invasive techniques.8,46,47,48,49,50,51,52,53,54,55 These advancements have also allowed us to treat selected patients harboring intramedullary pathology including tumors as was first reported by Ogden and Fessler.56

Patient Selection

Fig. 48.3 (a) Preoperative T2- and (b) T1-weighted contrast-enhanced axial MRI showing paraspinal schwannoma. Intraoperative photos showing (c) resection of posterior component using a minimally invasive spine posterior approach with tubular retractor and (d) removal of thoracic component of schwannoma using the da Vinci Robot.

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Minimally Invasive Resection of Intradural Spinal Tumors

48.3.3 Preoperative Planning Physical Examination, Radiographic Workup, and Preoperative Imaging Patients presenting with signs/symptoms consistent with an intradural extramedullary or intramedullary tumor should be evaluated with an MRI with and without contrast to determine the imaging characteristics of the lesion including the size and location as well as associated factors including edema, presence/absence of a cyst, and the presence of a well-delineated lesion versus a diffuse lesion without well-defined borders. This will enable the surgeon to determine the feasibility of resection of the lesion versus obtaining a biopsy for histological confirmation. It is also important to obtain anteroposterior (AP), lateral, and flexion/extension radiographs to determine if there is any preoperative instability or kyphosis that may worsen with the surgical removal of the posterior elements. This may help determine if surgical stabilization is required at the time of the tumor resection. After obtaining the information, the surgeon can then weigh the risks and benefits of removing the tumor through a minimally invasive approach.

Instrumentation Notes Special instrumentation is required for minimally invasive surgical resection of intradural tumors. Namely, a series of dilators and a tubular retraction system are necessary in order to gain access to the lesion. Bayoneted instruments are required if the surgeon elects to utilize an operative microscope. Nonbayoneted instruments are the choice for surgeons adept at using endoscopy as their mode of visualization. Moreover, a few modifications to common instruments may be helpful during the surgical procedures. Longer microdissectors, angled microscissors, endoscopic knot pushers, and sutures with small needles can facilitate minimally invasive surgery immensely.

48.3.4 Surgical Technique Preparation All patients undergoing a minimally invasive resection of an intramedullary tumor should be consented for surgical resection as well as for intraoperative monitoring including the use of MEPs as well as SSEPs. This will enable the surgeon to have some real-time feedback when resecting the lesion. The author prefers to initiate a methylprednisolone protocol consisting of an initial load of 30 mg/kg over 15 minutes, followed by a maintenance dose of 5.4 mg/kg/h during the surgical procedure and continues it for 24 hours in the postoperative period. Patients are also started on a proton pump inhibitor medication to reduce the risk of gastric ulceration. All patients are also given preoperative antibiotics and a discussion with our anesthesia colleagues is initiated with a goal of keeping the mean arterial blood pressure (MAP) above 60 to 70 mm Hg. Adequate perfusion of the spinal cord is necessary during surgical resection and inadvertent spinal cord manipulation.

Patient Positioning Patients with tumors in the cervical spinal cord or upper thoracic (T1–T3) are placed in a prone position using cranial fixation

tongs with the neck placed in a neutral position. Patients who have thoracic lesions below T4 are placed on a chest frame, with the arms in a “superman” position so that anesthesiologists have access to the intravenous (IV) sites and arterial lines. This position also allows for easier fluoroscopic confirmation of the correct levels undergoing surgical intervention. All bony prominences are well protected with gel barriers, and an effort to keep the patient’s eyes from pressure-related incidents is paramount during the prone operative procedures. Finally, intraoperative monitoring needles are placed and baseline MEP and SSEP responses are recorded prior to incision.

Incision After verification of the correct surgical level with lateral fluoroscopy, a paramedian incision is made in the skin, subcutaneous tissue, and fascia to allow for entry of the tubular retractor system. In the cervical spine, the incision is made approximately 2 cm off midline; however, in the thoracic and lumbar spine, the incision is made approximately 2.5 to 3 cm off midline.

Operative Technique Once the incision is completed, serial dilators are utilized in order to dock overlying the lamina where the intradural tumor is located. The soft tissue is removed with a monopolar electrocautery and a hemilaminectomy with undercutting of the spinous process is performed using a combination of a high-speed drill and Kerrison rongeurs. This will allow the surgeon to perform a midline durotomy. The dura is incised with a dural knife and the edges are tacked back using a 4–0 braided nylon suture to expose the spinal cord. If the lesion is extramedullary, the tumor should be easily visualized after dissection of the arachnoid and release of cerebrospinal fluid (CSF). If the lesion is intramedullary, care is taken to identify the midline and enter the cord between the dorsal columns so as to reduce the risk of postoperative dorsal column dysfunction. If the lesion is present on the surface, then the tumor can be accessed through the shortest, most direct route, thus limiting damage to the spinal cord. Laterally based lesions can be accessed through the dorsal root entry zone (DREZ) with minimal damage to the cord. The lesion is identified and a surgical plane is developed between the lesion and the spinal cord proper. The author prefers to not use pial sutures as this may lead to decreased perfusion of the spinal cord secondary to traction. Once the lesion is gently dissected from the spinal cord proper, it can be removed using an en bloc technique if possible, or it can be resected in a piecemeal fashion using an ultrasonic aspirator. Ultrasonography can be helpful in identifying the lesion prior to removal as well as documenting the complete resection after surgery. Intraoperative MRI can also be helpful if the operative suite has the capability.

Closure Once the tumor is resected, the dura is closed either with a running 4–0 braided nylon suture or with dural clips as has been reported in the literature.57 The suture line is reinforced with a small piece of synthetic dural substitute and reinforced with a fibrin sealant to decrease the risk of a postoperative pseudomeningocele. The tubular retractor and endoscope/microscope are removed, the fascia and muscle are reapproximated with a 2–0

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Minimally Invasive Spine Surgery for Tumors resorbable suture, and the subdermal region is reapproximated with a 3–0 resorbable suture. The skin is closed with a 4–0 resorbable suture using a subcuticular closure and the skin is covered with a 2-octyl cyanoacrylate sealant.

48.3.5 Postoperative Care Patients undergoing a minimally invasive resection of an intramedullary tumor are observed in the intensive care unit (ICU) for the first 24 hours with close attention to their neurologic examination, blood pressure with goals of an MAP > 60 mm Hg, and their blood glucose response to the high-dose steroid therapy. An MRI with and without contrast is performed to determine the extent of resection as well as to obtain a baseline imaging study for possible future adjunct therapy if necessary. In contrast, patients that undergo resection of an intradural extramedullary tumor are often discharged within 24 hours and rarely require ICU observation.

Rehabilitation and Recovery After transfer from the ICU to the ward, the patient is evaluated by physical therapists and occupational therapists to determine the need for inpatient versus outpatient rehabilitation. Important factors in determining their clinical disposition include ambulatory status, hand function, bowel/bladder function, ability to perform transfers if needed, and the amount of assistance required for their activities of daily living.

48.4 Management of Complications Invariably, surgical complications can occur even if the preoperative plan is followed. Complications can be limited if a methodical plan is adhered to during the procedure. Wrong-level surgery has been well documented, especially in regard to pathology located in the thoracic region. Diligent and judicious use of fluoroscopy can help alleviate this medicolegal nightmare. Furthermore, the use of intraoperative ultrasound can help document the correct level prior to performing the durotomy. Neurologic complications resulting from direct surgical trauma

to the spinal cord and/or secondary to vascular injury to the anterior spinal artery can lead to devastating postoperative dysfunction. As stated previously, intraoperative electrophysiologic monitoring can help guide the surgeon in some lesions where a surgical plane is difficult to obtain. However, it should be noted that once a significant change is noted, the monitoring will only support the fact that a neurologic injury has occurred and there is little that one can do if the injury is from direct trauma to the cord. Increasing the MAP may provide recovery in patients suffering from ischemia to the cord. Meticulous closure of the dura, fascia, muscle, and dermis is vital in reducing postoperative pseudomeningocele formation and the sequelae that can occur with a CSF leak, namely meningitis. If a pseudomeningocele accumulates or the patient develops symptoms from an active CSF leak, then lumbar drainage versus reoperation with the goal of reinforcing the layered closure should be considered. This complication can also delay the start of rehabilitation and discharge.

48.5 Clinical Cases 48.5.1 Case 1: Resection of the Intradural Extramedullary Lesion A 45-year-old man with a 1-month history of foot drop presented to the neurosurgical clinic for evaluation. On examination, the patient was neurologically intact with the exception of weakness in the right extensor hallucis longus (EHL) and dorsiflexion (DF). The patient was also noted to have some decreased sensation in the right L5 distribution. MRI of the lumbar spine demonstrated a heterogeneously enhancing lesion near the conus compromising the cauda equina (▶ Fig. 48.4a). After discussion regarding the risks and benefits of the surgery, the patient elected to undergo a minimally invasive resection of the intradural extramedullary lesion. The patient was taken to the operating room and placed in a prone position as described previously. An incision approximately 2.5 cm in length and 2.5 cm to the right of midline was utilized. An expandable retractor was used to dock overlying the tumor and a hemilaminectomy was performed. A midline dural incision allowed for excellent visualization and resection

Fig. 48.4 (a) Preoperative sagittal T1-weighted MRI with gadolinium demonstrating imaging characteristics of a patient with a lumbar schwannoma. (b) Intraoperative view of completely resected intradural schwannoma. (c) Postoperative sagittal T1-weighted MRI with gadolinium demonstrating complete resection of schwannoma.

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Minimally Invasive Resection of Intradural Spinal Tumors

Fig. 48.5 (a) Intraoperative view of incision after midline durotomy demonstrating an intradural extramedullary clear cell meningioma. (b) Intraoperative view of nerve roots after minimally invasive resection of clear cell meningioma. (c) Intraoperative view of dural closure following complete resection of intradural clear cell meningioma.

Fig. 48.6 (a) Intraoperative view of resection of intramedullary ependymoma using microdissection technique. (b) Intraoperative view of dural closure utilizing a 4–0 braided nylon suture and bayoneted instruments.

of the tumor ensued. A complete resection of the tumor was performed and the dura was closed with a running, locking suture prior to closure of the fascia, muscle, and dermis (▶ Fig. 48.4b). A gross total resection of a schwannoma was verified on the postoperative MRI (▶ Fig. 48.4c).

48.5.2 Case 2: Invasive Resection of Intradural Tumors A 51-year-old woman presented to the neurosurgical clinic with low back pain, radiculopathy, and numbness in the lower extremity. The patient underwent imaging studies including an MRI of the lumbar spine that revealed two intradural, extramedullary lesions (▶ Fig. 48.5a). The patient elected to undergo a minimally invasive resection of the intradural tumors. The patient was positioned and an incision was performed overlying the lesion. With the use of a tubular retractor and microscope, the lesions were removed en bloc from the spinal nerve roots (▶ Fig. 48.5b,c). Postoperatively, the histology of the tumors proved to be clear cell meningioma. A gross total resection was obtained and the patient has undergone routine serial images on an annual basis.

48.5.3 Case 3: Multiple Intracranial Meningiomas A 27-year-old woman with a history of NF2 and multiple intracranial meningiomas presented to the clinic for evaluation of mid and lower thoracic back pain. Imaging studies revealed an intradural extramedullary lesion consistent with schwannoma as well as an intramedullary lesion (▶ Fig. 48.6). Due to the

small size of the tumors, a minimally invasive approach was recommended and the patient consented. The patient was placed in a prone position and the thoracic spine was imaged and the operative level was verified with fluoroscopy. A right paramedian incision approximately 2.5 cm off midline was utilized to gain access to the laminae through a minimally invasive approach. An expandable tube was utilized and again, a hemilaminectomy was performed to allow for access to the midline of the dura. A midline durotomy was performed and the intradural extramedullary lesion was readily visualized and resected in an en bloc fashion. The intraoperative histological examination revealed features consistent with a schwannoma. The tumor indented the spinal cord proper and upon further inspection, a grayish tumor was noted. The lesion was intramedullary in nature and a surgical plane was identified and the lesion was removed in an en bloc fashion (▶ Fig. 48.6a,b). Intraoperative histological evaluation was thought to be consistent with a juvenile pilocytic astrocytoma; however, the final pathology revealed features consistent with an ependymoma.

48.6 Conclusion Although there have been reports of minimally invasive treatment of intradural extramedullary tumors with good clinical outcomes, there are few reports in the literature regarding the minimally invasive treatment of intramedullary tumors.8,58,59 Minimally invasive resection of intramedullary tumors is relatively new to the neurosurgeon’s armamentarium, and thus clinical outcome measures are sparse in the literature to date. Ogden and Fessler reported on the resection of an intramedullary ependymoma with good clinical outcome.56 With more

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Minimally Invasive Spine Surgery for Tumors neurosurgeons training in minimally invasive techniques, hopefully, there will be more reports and outcome studies regarding this exciting new neurosurgical arena. The mainstay for treatment of intradural tumors is surgical resection. Open surgical resection of tumors has been performed with good clinical outcome. However, recent advances in surgical instrumentation, optics, endoscopy, and minimally invasive approaches have allowed neurosurgeons to resect intradural (extramedullary and intramedullary) tumors safely and efficaciously using these less-invasive techniques. With reduction of damage to the surrounding soft tissue and bony structures, these techniques may reduce the amount of hospitalization and postoperative pain, and may eliminate the need for larger surgical interventions and stabilization procedures. The minimally invasive approaches offer an alternative option to traditional open procedures.

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Primary spinal cord tumors are often described based on their anatomical location: extradural, intradural extramedullary, intramedullary. The most common extradural spinal cord tumors arise from metastases. Schwannomas, neurofibromas, and meningiomas are the most common intradural extramedullary tumors. Intramedullary spinal cord tumors (IMSCT) are predominantly of glial origin, with ependymomas and astrocytomas representing the most common tumors encountered. Patients with spinal cord tumors often present with pain, paresthesias, motor weakness, or sensory deficits. Surgical intervention is the treatment modality of choice for most spinal cord tumors. Although traditional open procedures have been utilized to treat these lesions, recent advances in technology have allowed many of these tumors to be treated through minimally invasive procedures. The minimally invasive resection of the spinal cord tumors requires special instrumentation including a tubular retractor and special bayoneted instruments. The minimally invasive technique may also be performed using endoscopic visualization. Minimally invasive surgical resection of spinal cord tumors can be performed safely and with excellent patient outcomes. Reduction in damage to surrounding tissue, hospital stay, and postoperative pain makes minimally invasive resection of spinal cord tumors an alternative to traditional open procedures.

References [1] Campello C, Le Floch A, Parker F. Neuroepithelial intramedullary spinal cord tumors in adults: study of 70 cases. Paper presented at: American Academy of Neurology Annual Meeting; Seattle, WA; 2009 [2] Elsberg CA. Some aspects of the diagnosis and surgical treatment of tumors of the spinal cord: with a study of the end results in a series of 119 operations. Ann Surg. 1925; 81(6):1057–1073 [3] Abul-Kasim K, Thurnher MM, McKeever P, Sundgren PC. Intradural spinal tumors: current classification and MRI features. Neuroradiology. 2008; 50 (4):301–314

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[4] Connolly ES, Jr, Winfree CJ, McCormick PC, Cruz M, Stein BM. Intramedullary spinal cord metastasis: report of three cases and review of the literature. Surg Neurol. 1996; 46(4):329–337, discussion 337–338 [5] Loblaw DA, Perry J, Chambers A, Laperriere NJ. Systematic review of the diagnosis and management of malignant extradural spinal cord compression: the Cancer Care Ontario Practice Guidelines Initiative’s Neuro-Oncology Disease Site Group. J Clin Oncol. 2005; 23(9):2028–2037 [6] Jinnai T, Koyama T. Clinical characteristics of spinal nerve sheath tumors: analysis of 149 cases. Neurosurgery. 2005; 56(3):510–515, discussion 510–515 [7] Conti P, Pansini G, Mouchaty H, Capuano C, Conti R. Spinal neurinomas: retrospective analysis and long-term outcome of 179 consecutively operated cases and review of the literature. Surg Neurol. 2004; 61(1):34–43, discussion 44 [8] Tredway TL, Santiago P, Hrubes MR, Song JK, Christie SD, Fessler RG. Minimally invasive resection of intradural-extramedullary spinal neoplasms. Neurosurgery. 2006; 58(1) Suppl:ONS52–ONS58, discussion ONS52–ONS58 [9] Miller DJ, McCutcheon IE. Hemangioblastomas and other uncommon intramedullary tumors. J Neurooncol. 2000; 47(3):253–270 [10] Browne TR, Adams RD, Roberson GH. Hemangioblastoma of the spinal cord. Review and report of five cases. Arch Neurol. 1976; 33(6):435–441 [11] Lee DK, Choe WJ, Chung CK, Kim HJ. Spinal cord hemangioblastoma: surgical strategy and clinical outcome. J Neurooncol. 2003; 61(1):27–34 [12] Lonser RR, Weil RJ, Wanebo JE, DeVroom HL, Oldfield EH. Surgical management of spinal cord hemangioblastomas in patients with von Hippel-Lindau disease. J Neurosurg. 2003; 98(1):106–116 [13] Raco A, Esposito V, Lenzi J, Piccirilli M, Delfini R, Cantore G. Long-term followup of intramedullary spinal cord tumors: a series of 202 cases. Neurosurgery. 2005; 56(5):972–981, discussion 972–981 [14] Parsa AT, Miller JI, Eggers AE, Ogden AT, III, Anderson RC, Bruce JN. Autologous adjuvant linked fibroblasts induce anti-glioma immunity: implications for development of a glioma vaccine. J Neurooncol. 2003; 64(1–2):77–87 [15] Helseth A, Mørk SJ. Primary intraspinal neoplasms in Norway, 1955 to 1986. A population-based survey of 467 patients. J Neurosurg. 1989; 71(6):842–845 [16] Jallo GI, Freed D, Epstein FJ. Spinal cord gangliogliomas: a review of 56 patients. J Neurooncol. 2004; 68(1):71–77 [17] McCormick PC, Torres R, Post KD, Stein BM. Intramedullary ependymoma of the spinal cord. J Neurosurg. 1990; 72(4):523–532 [18] Cooper PR, Epstein F. Radical resection of intramedullary spinal cord tumors in adults. Recent experience in 29 patients. J Neurosurg. 1985; 63(4):492–499 [19] Volpp PB, Han K, Kagan AR, Tome M. Outcomes in treatment for intradural spinal cord ependymomas. Int J Radiat Oncol Biol Phys. 2007; 69 (4):1199–1204 [20] Yanni DS, Ulkatan S, Deletis V, Barrenechea IJ, Sen C, Perin NI. Utility of neurophysiological monitoring using dorsal column mapping in intramedullary spinal cord surgery. J Neurosurg Spine. 2010; 12(6):623–628 [21] Sala F, Palandri G, Basso E, et al. Motor evoked potential monitoring improves outcome after surgery for intramedullary spinal cord tumors: a historical control study. Neurosurgery. 2006; 58(6):1129–1143, discussion 1129–1143 [22] Quinones-Hinojosa A, Gulati M, Lyon R, Gupta N, Yingling C. Spinal cord mapping as an adjunct for resection of intramedullary tumors: surgical technique with case illustrations. Neurosurgery. 2002; 51(5):1199–1206, discussion 1206–1207 [23] Guidetti B. Intramedullary tumours of the spinal cord. Acta Neurochir (Wien). 1967; 17(1):7–23 [24] Rodrigues GB, Waldron JN, Wong CS, Laperriere NJ. A retrospective analysis of 52 cases of spinal cord glioma managed with radiation therapy. Int J Radiat Oncol Biol Phys. 2000; 48(3):837–842 [25] Minehan KJ, Brown PD, Scheithauer BW, Krauss WE, Wright MP. Prognosis and treatment of spinal cord astrocytoma. Int J Radiat Oncol Biol Phys. 2009; 73(3):727–733 [26] Kim MS, Chung CK, Choe G, Kim IH, Kim HJ. Intramedullary spinal cord astrocytoma in adults: postoperative outcome. J Neurooncol. 2001; 52(1):85–94 [27] Innocenzi G, Salvati M, Cervoni L, Delfini R, Cantore G. Prognostic factors in intramedullary astrocytomas. Clin Neurol Neurosurg. 1997; 99(1):1–5 [28] Murota T, Symon L. Surgical management of hemangioblastoma of the spinal cord: a report of 18 cases. Neurosurgery. 1989; 25(5):699–707, discussion 708 [29] Cerejo A, Vaz R, Feyo PB, Cruz C. Spinal cord hemangioblastoma with subarachnoid hemorrhage. Neurosurgery. 1990; 27(6):991–993 [30] Dijindjian M, Djindjian R, Houdart R, Hurth M. Subarachnoid hemorrhage due to intraspinal tumors. Surg Neurol. 1978; 9(4):223–229 [31] Kormos RL, Tucker WS, Bilbao JM, Gladstone RM, Bass AG. Subarachnoid hemorrhage due to a spinal cord hemangioblastoma: case report. Neurosurgery. 1980; 6(6):657–660

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Minimally Invasive Resection of Intradural Spinal Tumors [32] Minami M, Hanakita J, Suwa H, Suzui H, Fujita K, Nakamura T. Cervical hemangioblastoma with a past history of subarachnoid hemorrhage. Surg Neurol. 1998; 49(3):278–281 [33] Yu JS, Short MP, Schumacher J, Chapman PH, Harsh GR, IV. Intramedullary hemorrhage in spinal cord hemangioblastoma. Report of two cases. J Neurosurg. 1994; 81(6):937–940 [34] Eskridge JM, McAuliffe W, Harris B, Kim DK, Scott J, Winn HR. Preoperative endovascular embolization of craniospinal hemangioblastomas. AJNR Am J Neuroradiol. 1996; 17(3):525–531 [35] Standard SC, Ahuja A, Livingston K, Guterman LR, Hopkins LN. Endovascular embolization and surgical excision for the treatment of cerebellar and brain stem hemangioblastomas. Surg Neurol. 1994; 41(5):405–410 [36] Tampieri D, Leblanc R, TerBrugge K. Preoperative embolization of brain and spinal hemangioblastomas. Neurosurgery. 1993; 33(3):502–505, discussion 505 [37] Vázquez-Añón V, Botella C, Beltrán A, Solera M, Piquer J. Preoperative embolization of solid cervicomedullary junction hemangioblastomas: report of two cases. Neuroradiology. 1997; 39(2):86–89 [38] Ryu SI, Kim DH, Chang SD. Stereotactic radiosurgery for hemangiomas and ependymomas of the spinal cord. Neurosurg Focus. 2003; 15(5):E10 [39] Epstein F, Epstein N. Surgical treatment of spinal cord astrocytomas of childhood. A series of 19 patients. J Neurosurg. 1982; 57(5):685–689 [40] Epstein FJ, Farmer JP. Pediatric spinal cord tumor surgery. Neurosurg Clin N Am. 1990; 1(3):569–590 [41] Epstein FJ, Farmer JP, Freed D. Adult intramedullary spinal cord ependymomas: the result of surgery in 38 patients. J Neurosurg. 1993; 79(2):204–209 [42] Constantini S, Miller DC, Allen JC, Rorke LB, Freed D, Epstein FJ. Radical excision of intramedullary spinal cord tumors: surgical morbidity and long-term follow-up evaluation in 164 children and young adults. J Neurosurg. 2000; 93 (2) Suppl:183–193 [43] Jallo GI, Kothbauer KF, Epstein FJ. Intrinsic spinal cord tumor resection. Neurosurgery. 2001; 49(5):1124–1128 [44] Sciubba DM, Chaichana KL, Woodworth GF, McGirt MJ, Gokaslan ZL, Jallo GI. Factors associated with cervical instability requiring fusion after cervical laminectomy for intradural tumor resection. J Neurosurg Spine. 2008; 8(5):413–419 [45] Wickham JE. The new surgery. Br Med J (Clin Res Ed). 1987; 295 (6613):1581–1582

[46] Foley KT, Smith MM, Rampersaud YR. Microendoscopic approach to far-lateral lumbar disc herniation. Neurosurg Focus. 1999; 7(5):e5 [47] Perez-Cruet MJ, Foley KT, Isaacs RE, et al. Microendoscopic lumbar discectomy: technical note. Neurosurgery. 2002; 51(5) Suppl:S129–S136 [48] Khoo LT, Fessler RG. Microendoscopic decompressive laminotomy for the treatment of lumbar stenosis. Neurosurgery. 2002; 51(5) Suppl:S146–S154 [49] Khoo LT, Palmer S, Laich DT, Fessler RG. Minimally invasive percutaneous posterior lumbar interbody fusion. Neurosurgery. 2002; 51(5) Suppl:S166–S181 [50] Khoo LT, Beisse R, Potulski M. Thoracoscopic-assisted treatment of thoracic and lumbar fractures: a series of 371 consecutive cases. Neurosurgery. 2002; 51(5) Suppl:S104–S117 [51] Isaacs RE, Podichetty V, Fessler RG. Microendoscopic discectomy for recurrent disc herniations. Neurosurg Focus. 2003; 15(3):E11 [52] Isaacs RE, Podichetty VK, Santiago P, et al. Minimally invasive microendoscopy-assisted transforaminal lumbar interbody fusion with instrumentation. J Neurosurg Spine. 2005; 3(2):98–105 [53] Tredway TL, Musleh W, Christie SD, Khavkin Y, Fessler RG, Curry DJ. A novel minimally invasive technique for spinal cord untethering. Neurosurgery. 2007; 60(2) Suppl 1:ONS70–ONS74, discussion ONS74 [54] O’Toole JE, Eichholz KM, Fessler RG. Minimally invasive insertion of syringosubarachnoid shunt for posttraumatic syringomyelia: technical case report. Neurosurgery. 2007; 61(5) Suppl 2:E331–E332, discussion E332 [55] Deutsch H, Boco T, Lobel J. Minimally invasive transpedicular vertebrectomy for metastatic disease to the thoracic spine. J Spinal Disord Tech. 2008; 21 (2):101–105 [56] Ogden AT, Fessler RG. Minimally invasive resection of intramedullary ependymoma: case report. Neurosurgery. 2009; 65(6):E1203–E1204, discussion E1204 [57] Park P, Leveque JC, La Marca F, Sullivan SE. Dural closure using the U-clip in minimally invasive spinal tumor resection. J Spinal Disord Tech. 2010; 23 (7):486–489 [58] Pompili A, Caroli F, Telera S, Occhipinti E. Minimally invasive resection of intradural-extramedullary spinal neoplasms. Neurosurgery. 2006; 59(5):E1152 [59] Haji FA, Cenic A, Crevier L, Murty N, Reddy K. Minimally invasive approach for the resection of spinal neoplasm. Spine. 2011; 36(15):E1018–E1026

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Part VI Complications and Outcome Analysis

VI

49 Clinical Outcome Analyses

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50 Avoiding Complications in Minimally Invasive Spine Procedures

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Complications and Outcome Analysis

49 Clinical Outcome Analyses Dino Samartzis, Devanand A. Dominique, Mick J. Perez-Cruet, Michael G. Fehlings, and David R. Nerenz Abstract Increasingly attention has been focused on the tenets of evidence-based medicine in an effort to improve health care delivery and patient management by evaluating the best evidence along with the different parameters that may affect present-day management of spine disorders. A variety of outcome measures have been developed over the years to evaluate the effectiveness of treatments. These outcome measures will be discussed in this chapter as well as levels of evidence, and types of clinical research and methodology. More specifically, and as stated by Sackett et al, “Evidence-based medicine is the conscientious, explicit, and judicious use of current best evidence in making decisions about the care of individual patients. The practice of evidence-based medicine means integrating individual clinical expertise with the best available external clinical evidence from systematic research.” Keywords: patient outcome measures, Oswestry, SF-36, research design, methodology, clinical evidence, levels of evidence

49.1 Introduction The principal objectives of spine surgery include the following: relief and stabilization of pain, appropriate decompression, and restoration of function. To that end, spine surgery has undergone a tremendous evolution over the past 30 years in terms of the development and use of instrumentation, refined or newly designed surgical techniques, use of different graft substrates and biologic agents, implementation of surgical adjuncts, and the application of tissue engineering and gene therapy. Such advances in spine biotechnology have been fueled by the urgent need to improve patient outcomes. However, costs associated with patient management continue to increase and are a growing concern directly affecting physicians’ practices, insurance rates, and hospital expenses. As a result, clinical outcomes have become even more significant in terms of monitoring and evaluating various clinical practices within the discipline of spine surgery and their correlation with the quality of health care delivery. Therefore, much attention has been focused on the tenets of evidence-based medicine in an effort to improve health care and patient management by evaluating the best evidence along with the different parameters that may affect presentday management of spine disorders. More specifically, and as stated by Sackett et al,1 “Evidence-based medicine is the conscientious, explicit, and judicious use of current best evidence in making decisions about the care of individual patients. The practice of evidence-based medicine means integrating individual clinical expertise with the best available external clinical evidence from systematic research.” To determine the best evidence with respect to treatment efficacy in improving a patient’s health status, outcomes research is an integral component in the decision-making armamentarium of the spine surgeon. In essence, outcomes research is research

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that strives to compare the effects of one or more treatment regimens among various groups. In spine surgery, physical examination and radiographic analysis have been instrumental in evaluating various outcome parameters. However, the past decade has seen the development of a variety of outcome assessment tools addressing a wide range of factors that are indicative of a patient’s condition as well as the preoperative and postoperative course. These outcome measurement tools may have the potential to affect outcomes and provide a foundation for developing the best treatment strategy for each patient.

49.2 Criteria for Standardized Outcomes Assessment The past decade has been witness to a paradigm shift away from an emphasis on disease to a focus on the patient’s health, ability to function, and sense of well-being.2 Incorporating health-related quality-of-life (HRQL) assessments into practice enables the clinician, hospital, and patient to devise and adopt optimal management strategies. The primary focus of HRQL assessments is to address the effects of the patient’s physical, emotional, and social well-being on his or her medical condition and treatment. More specifically, and according to Patrick and Deyo,3 HRQL measurements define the scope of the following: impairment, functional status, health perceptions, social interaction, and duration of life. To properly address clinical outcomes or progression of a medical condition and the effects of treatment, various aspects of assessment should be considered. It has been recommended that the following five measures be incorporated into any treatment plan: the patient’s physical condition or health status, the effect of the condition on the patient’s quality of life, general assessments of health status (not specifically linked to the patient’s condition), patient expectations and satisfaction with treatment, and covariates needed to identify subgroups of patients who might respond differently to treatment.4 Because of the multitude of factors that may affect outcome, a proper measurement tool should be employed. However, the breadth of coverage of the selected outcomes instrument must be balanced with an appropriate length of time needed for completion as well as an ability to measure the outcome of interest.

49.3 Classification of Health Status Instruments Implementation of instruments for proper assessment of health status and clinical outcomes is key, and there are a variety of appropriate measurement tools from which to choose (▶ Table 49.1). We will limit our discussion to the generic or disease-specific instruments that are commonly used in spine surgery. 5 Generic instruments are more comprehensive in

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Clinical Outcome Analyses Table 49.1 Types of outcome measures

Table 49.2 Various conditions and outcome measurement tools

Type of measure

Description

Category

Type of measurement

Dimension specific

Focus is on a particular aspect of health (e.g., Beck’s depression inventory54)

Pain scales

Verbal Rating Scale

Disease/ population specific

Measures several health domains and focuses on aspects of health that are relevant to particular health problems

Numerical Rating Scale

Generic

Measures outcomes across diseases and different patient populations

Memorial Pain Questionnaire

Individualized

Measures the importance of certain aspects of the respondent’s life and assigns weights to produce a single score (e.g., patient-generated index scores55)

Role specific

A more specific generic tool that captures aspects of working life (e.g., Occupational Role Questionnaire19)

Utility

Developed for economic evaluation; entails preferences for health states and yields a single index (e.g., EuroQol EQ-5D56)

scope and address the overall impact of an illness or intervention on conditions across a wide variety of populations. However, generic instruments lack specificity because they fail to isolate variables of interest, and thus certain aspects of treatment and additional health-related dimensions affected by a particular condition may be overlooked. Alternatively, diseasespecific instruments strive to identify the various domains associated with a condition and intervention. Such an outcome measurement tool is either clinical in scope (i.e., focuses on signs, symptoms, and direct sequelae) or experimental in design (i.e., addresses the impact of an illness or problem).5 A plethora of tools for assessing outcomes have been designed to address spine-related pathology. However, development of such instruments has been a daunting task because of the wide variability in therapeutic interventions and the challenge of properly quantifying and assessing the aspects of pain and the functional disabilities of a given condition. A number of assessment instruments do exist including method of measuring pain, back-specific disability scales, neck pain and disability scales, and instruments for evaluating general functional status (▶ Table 49.2). The strength of a particular outcome-measuring tool is based on its specificity with regard to a given condition or population, sensitivity to various factors stemming from the patient’s condition, reproducibility, validity, responsiveness, and interpretability (▶ Table 49.3). In recent years, such tools have been specifically designed not only to address localized manifestations stemming from the spinal pathology, but also to include assessment of patient-specific factors that may affect health status and treatment outcomes including the following: level of education, employment history and job satisfaction, psychological considerations, worker’s compensation and third-party claims, expectations, and level of satisfaction (see ▶ Table 49.2). Whatever the case, the practitioner and the researcher should both be aware of the many factors that may adversely affect clinical outcomes and select the health status assessment tool that best addresses the pathology in question and its associated domains. Several examples of outcome measurement tools that are common in spine surgery are discussed in this chapter.

Visual Analog Scale

Wisconsin Brief Pain Questionnaire

McGill Pain Questionnaire Patient Outcome Questionnaire Medical Outcomes Study Descriptor Differential Scale Integrated Pain Scale Pain Perception Profile West Haven-Yale Multidimensional Pain Inventory Brief Pain Inventory Unmet Analgesic Needs Questionnaire City of Hope Mayday Pain Resource Center Pain Audit Tools City of Hope Mayday Pain Resource Center Patient Pain Questionnaire Dallas Pain Questionnaire Northwick Park Neck Pain Questionnaire Neck Pain and Disability Scale Disability: lower back questionnaires

Modified Oswestry Low Back Pain Disability Questionnaire Million Disability Questionnaire Roland–Morris Disability Questionnaire Waddell Disability Index Low Back Pain Type Specifications

Disability: cervical Neck Disability Index questionnaires Neck Pain and Disability Scale Headache Disability Index Psychometric questionnaires

Illness Behavior Questionnaire Psychosocial Pain Inventory Waddell Nonorganic Low Back Pain Signs Modified Somatic Perception Questionnaire Somatic Amplification Rating Scale Modified Self-Rating Zung Depression Scale Minnesota Multiphasic Personality Inventory Health Status Questionnaire Fear Avoidance Beliefs Questionnaire

Patient satisfaction

Patient Satisfaction Questionnaire

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Complications and Outcome Analysis Table 49.2 continued Category

Type of measurement

questionnaires

Low Back Pain Patient Satisfaction Group Health Association of America Consumer Satisfaction Survey

Table 49.3 Critical analyses models for review of outcome tools Type

Criteria

Conceptual and measurement

Does the scale measure a single or distinct domain? Is the variability of the scale reported?

Chiropractic Satisfaction Questionnaire Combined assess- Edmonton Symptom Assessment System ment scales Symptom Distress Scale

Determine intended level of measurement (categorical, ordinal, interval, or rational) Reliability

Did the instrument address reproducibility?

Memorial Symptoms Assessment Scale Symptom Scale Voices

Validity

Did the instrument address content- and construct-related factors as well as criterion validity?

Responsiveness

Was the scale used as an outcome measure before and in what populations?

Interpretability

Who is the population being tested?

Rotterdam Symptom Checklist Support Team Assessment Schedule National Hospice Study COOP Charts Hospice Quality of Life Index McGill Quality of Life Index Quality of Well-Being Scale EORTC QOL-30 VITAS Quality of Life Index SF-36, SF-12 Health Status Questionnaire RAND 36-Item Health Survey Sickness Impact Profile Nottingham Health Profile Scoliosis Follow-Up Questionnaire Cervical Spine Outcomes Questionnaire North American Spine Society Lumbar Spine Outcome Assessment Instrument

49.4 Outcome Assessment Instruments 49.4.1 Short Form-36 The Short Form-36 (SF-36) is a 36-item questionnaire that was developed to evaluate how the health care system affects patient health.6 The SF-36 was initially formulated to address a variety of psychometric standards for group comparisons and stemmed from concepts proposed by the Medical Outcomes Study (MOS) of the late 1980s.7 Relying on various health assessment instruments of the 1970s and 1980s, such as the Health Insurance Experiment,8 the Health Perceptions Questionnaire,9 the General Psychological Well-Being Inventory,10 the Functioning and WellBeing Profile,11 and other physical and functioning measures, the SF-36 health survey has been a widely used, comprehensive, generic outcome assessment tool that quantitatively measures physical and psychological dimensions. The SF-36 survey has

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Did the instrument address internal consistency?

Can the score be translated to a relevant clinical event? Is the score predictive of outcome events?

been the subject of numerous investigations and has been translated into different languages in more than 40 countries as part of the International Quality of Life Assessment (IQOLA) Project.12 Based on the standard SF-36 survey, which was introduced in the early 1990s,6 a second version of the IQOLA questionnaire now includes the following components: physical functioning, limitations due to physical or emotional problems, bodily pain, social interaction, general mental health (psychological distress and well-being), vitality (energy/fatigue), and general health perceptions. In essence, the SF-36 is a reliable and valid tool that is commonly used because of its brevity, psychometric assessment, and applicability to patients with a variety of medical conditions and demographics.13,14,15,16 Moreover, the SF-36 questionnaire is self-administered, is sensitive to differences in disease severity, and distinguishes between sick and healthy populations.7 In addition, to further improve efficiency and decrease the costs associated with administering the SF-36, a shorter version of the questionnaire was created in the mid1990s and aptly named the SF-12. This shorter questionnaire continues to use the same eight-scale profile as the SF-36, but with fewer levels and less precise scoring in comparison to its more in-depth counterpart.17

49.4.2 Sickness Impact Profile Another generic assessment tool, the Sickness Impact Profile (SIP), was also developed to evaluate the functional consequences of health care.18 The SIP is a behavior-based measurement tool that presents a set of items, in a “yes/no” dichotomous format, that relate to the type of work chronically ill patients will perform to accommodate limitations with respect to their illnesses and also addresses how these individuals will respond in their working environments as a result of their medical conditions. Although the SIP attempts to elicit a descriptive profile of the changes in patients’ behaviors resulting from their illnesses, it fails to capture the potential dynamics between a person’s health and his or her occupation. This is likely due to

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Clinical Outcome Analyses the inadequate depiction of a general set of work activities as well as the potential categorical limitations that the form presents because of the yes/no response format, which weakens the sensitivity of such a tool. However, the SIP and certain other measurement tools, such as the Occupational Role Questionnaire (ORQ),19 the Work Limitations Questionnaire (WLQ),20,21 and the Work Limitation Questionnaire (WL-26)22 have become the foundation as well as the impetus for more precise role-specific assessments as they relate to a patient’s working life.

49.4.3 North American Spine Society Lumbar Spine Outcome Assessment Instrument The North American Spine Society Lumbar Spine Outcome Assessment Instrument is a self-administered tool that is designed to measure disabilities and neurogenic symptoms related to back pain.23 This instrument is region specific and assesses five broad categories: demographics; medical history; pain, neurogenic symptoms, and function; employment history; and treatment outcomes. Although the questionnaire strives to address influential outcome factors, such as sociodemographics and work-related issues, it fails to examine the impact of the disability and does not address health-related concerns inherent in the pediatric population with spine pathology.23,24

49.4.4 McGill Pain Questionnaire Considered a benchmark for standardization in the evaluation of pain, the McGill Pain Questionnaire (MPQ) is a reliable, valid, and sensitive tool in the assessment of pain relief and treatment.25 The MPQ relies on descriptors to measure subjective pain experiences. Four major groups, each consisting of five items, represent these descriptors and entail the following: sensory, affective, evaluative, and miscellaneous. Each descriptor contains a rank value, which is based on its position in the word set. The sum of the rank values results in the pain rating index. A pain rating intensity is also implemented and is based on a scale of 1 to 5. In addition, a short form of the MPQ (SF-MPQ) has been developed that entails 15 questions; 11 of these address sensory dimensions and 4 are related to affective dimensions. The intensity scale in the SF-MPQ has been reduced to 4 points, and the pain rating index is incorporated as a visual analog scale.

49.4.5 Oswestry Disability Index One of the first disease-specific instruments, the Oswestry Disability Index (ODI), is a self-administered tool that measures disability due to low back pain.26 The development of this tool was initiated in 1976 by Dr. John O’Brien. At that time, the questionnaire was administered by an orthopedic surgeon and an occupational therapist. The questionnaire was eventually published in 198026 and after the 1981 annual meeting of the International Society for the Study of the Lumbar Spine, this instrument gained widespread attention. Since then, this assessment tool has undergone revisions.27,28,29 In general, the

ODI is divided into the following 10 sections: pain intensity, personal care, lifting, walking, sitting, standing, sleeping, social life, traveling, and changing degree of pain. Each section comprises six statements that describe a greater degree of disability in that particular activity. The results are scored as percentages of the level of function and provide some type of insight into how conditions of the low back affect everyday function. However, this questionnaire fails to address aspects of occupation and psychometric properties that may affect outcome. Nonetheless, this instrument is a reliable and reproducible tool for the assessment of disability due to low back pain.26,30

49.4.6 Neck Pain and Disability Scale The Neck Pain and Disability Scale (NPDS) is a comprehensive tool that is used to measure neck pain and associated functional status.31 This instrument is an extension of the Neck Disability Index (NDI), developed by Vernon and Mior32 in 1991, which consisted of 10 sections of distinct activity with increasing severity addressing that activity. The NPDS consists of 10 items in the same vein as the NDI, but with the exception of an ordinal scale to measure neck pain. Nonetheless, the NPDS addresses the severity of pain and its interference with vocational, recreational, social, and functional aspects of living. However, this tool fails to address psychological factors, patient satisfaction, and the secondary economic gain that may affect patient outcome and interpretation.

49.4.7 Prolo Anatomic–Economic– Functional Rating System Regarded as a simple outcome measure that provides a semiquantitative method for denoting the patient’s progress and outcome, the Prolo Anatomic–Economic–Functional Rating System is a useful measure that addresses economic and functional status before and after treatment.33 Based on this assessment, an economic grade is determined that aids in establishing the patient’s capacity for employment or ability to participate in other types of activities. This rating system also helps determine the effect of pain on daily activities but overall evaluates five criteria before and after treatment. Responses to these criteria are based on scores ranging from 2 to 10, where 2 is defined as incapacitating and 10 as perfect. As a result, the following four main grades are possible: excellent (10, 9), good (8, 7), fair (6, 5), and poor (4–2).

49.4.8 Cervical Spine Outcomes Questionnaire Although various generic and disease-specific outcome health assessment tools exist to evaluate conditions in the neck, a comprehensive tool for evaluating the cervical spine did not exist until the Cervical Spine Outcomes Questionnaire (CSOQ) was developed by BenDebba et al.34 The CSOQ has its roots in past instruments, such as the NDI, the NPDI, the ODI, and the North American Spine Society Cervical Spine Outcome Assessment tool, and covers a range of factors organized in a 57-item format. The CSOQ was designed not only to address levels of pain

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Complications and Outcome Analysis severity, functional disability, physical symptoms, health care utilization, and patient satisfaction but also to encompass psychometric parameters that are deemed essential in the architecture of a proper health care strategy and outcome assessment.35,36

49.4.9 American Spinal Injury Association Impairment Scale A grading system for classifying spinal cord injuries was developed in the early 1990s by the American Spinal Injury Association (ASIA) and the International Society of Paraplegia. It is known as the American Spinal Injury Association Impairment Scale.37 This scale is, in essence, a modified form of Frankel’s classification denoting various levels of functional disability and has been universally accepted for classification of spinal cord injury.38 The scale is composed of four categories or grades. Grade A represents a complete injury where no sensory or motor function is preserved in the lowest sacral level. Grade B denotes an incomplete injury where sensory, but not motor, function is preserved below the level of injury. Based on preservation of motor function below the neurologic level, grades C and D represent incomplete spinal cord injuries with muscle grades less than 3 and greater than 3, respectively. Alternatively, grade E represents normal sensory and motor functions.

49.4.10 Modified Japanese Orthopedic Association Scale In recent years, the modified Japanese Orthopedic Association (mJOA) scale has been applied and validated to assess outcomes in patients undergoing surgical treatment for various forms of degenerative cervical myelopathy (DCM), including cervical spondylotic myelopathy and ossification of the posterior longitudinal ligament. The mJOA is a scale that rates patients’ function on a 0 to 18 point scale that assesses function on the domains of hand and upper extremity function, sensation, gait, and bladder function. Patients’ level of impairment is classified into mild (mJOA 15–17), moderate (12–14), and severe (0–11). The minimal clinically important difference (MCID) of the mJOA has also been established and varies according to the level of baseline impairment (1 point for mild dilated cardiomyopathy [DCM], 2 points for moderate DCM, and 3 points for severe DCM).39,40

49.5 Methodological Issues Relevant to Outcomes Research The basic premise of outcomes research lies in understanding that medical practitioners need to know when recommending management the likely outcomes of different treatments and what matters to patients. Moreover, outcomes research can further elaborate on how patients value alternative outcomes that can have a direct effect on or guide policy decisions and practice guidelines. However, lack of good-quality data or access to

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data, small sample sizes, self-serving manipulation of data, inappropriate and inadequate statistical analyses, biases, and confounding variables may impede proper analysis and the quality of outcomes research. Various study designs can address such concerns, to some extent; however, meta-analysis and, to a greater extent, systematic reviews are considered studies associated with the highest level of evidence.41 Systematic reviews focus on a clinical question encompassing a comprehensive and explicit search strategy with a uniformly applied criterionbased selection that undergoes rigorous critical appraisal and is synthesized with formal rules (that may include meta-analysis), the inferences of which are evidence based and can be replicated.41 Moreover, systematic reviews evaluate the “quality” of the study design, methodology, and analyses, thereby endeavoring to integrate valid and reliable information to establish or facilitate rational decision making. A hierarchy of evidence for grading research has been recommended as part of the initiative by the Canadian Task Force on Preventive Health Examination from the late 1970s.42 The levels of evidence (▶ Table 49.4) and associated grading (▶ Table 49.5) contemplated by this group were further refined by Sackett et al at McMaster University, and at the University of Oxford in the ensuing years.1,43,44,45,46,47 Based on such levels and grades of evidence, evaluation of the reported peer-reviewed literature by Freedman et al48 examined 500 published research papers in two highly regarded orthopedic journals and noted only 33 randomized controlled trials (▶ Fig. 49.1). Table 49.4 Levels of evidence Level

Sources of evidence

I

Meta-analysis of multiple well-designed, controlled studies; randomized trials with low false-positive and low falsenegative errors (high power)

II

At least one well-designed experimental study; randomized trials with high false-positive or high false-negative errors or both (low power)

III

Well-designed, quasi-experimental studies, such as nonrandomized, controlled, single-group, preoperative/postoperative comparison, cohort, time, or matched case/control series

IV

Well-designed, nonexperimental studies, such as comparative and correlational descriptive and case studies

V

Case series, case reports, and clinical examples

Table 49.5 Grade of recommendations of levels of evidence Grade

Grade of recommendation

A

Evidence of type I or consistent findings from multiple studies of type II, III, or IV

B

Evidence of type II, III, or IV and generally consistent findings

C

Evidence of type II, III, or IV, but inconsistent findings

D

Little or no systematic empiric evidence

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Clinical Outcome Analyses

Case series Case-control

Fig. 49.1 Distribution of study designs from evaluation of 1 year’s volumes of the American and British Journals of Bone and Joint Surgery and Clinical Orthopaedics and Related Research. (Adapted from Freedman et al.48)

Retrospective cohort Prospective cohort Randomized controlled trial Case reports

49.6 Types of Research Various methods and types of research are available to address the question of interest or the clinical dilemma. Two main fields of research exist and encompass quantitative or qualitative methods and, at times, a combination of the two. Quantitative research is initiated with an idea, followed by a measurement, data generation, and deductive reasoning to reach a conclusion. Alternatively, qualitative research begins with an intention to explore a certain area, gathers data by observation or interviews to identify certain themes based on individual experiences or behavior, and through inductive reasoning generates ideas and hypotheses. Moreover, the strength of qualitative research is found in its validity based on its methods of data collection, whereas quantitative research relies on the reproducibility of measurements used to assess outcomes and treatment effects. Various research designs and their respective methodologies are discussed below.

49.7 Quantitative Research Designs and Methodologies To address specific quantitative studies, each of these designs can adequately facilitate a scientific inquiry; however, each is unique in its methodology, comparability of study groups, measurement issues, and statistical analyses. Although various research approaches exist, observational studies are common in outcome analyses and are either retrospective or prospective in nature. Conversely, experimental studies, such as randomized controlled trials, are prospective and the intervention each participant receives is controlled or manipulated by the investigator via allocation in hopes of minimizing confounding variables. In a retrospective design, the phenomenon has occurred before the study has taken place and various potential confounding variables may exist that are difficult to account for or control. In contrast, in prospective studies the participants are either randomly assigned to groups or nonrandomized or followed for a specific duration to monitor an effect based on an intervention. In such cases, extraneous variables may be accounted for and a temporal sequencing of events may be controlled.5 Conversely, such an ap-

proach may be time-consuming and costly, and may require a sample size that may not be possible to attain. In addition, various advantages and disadvantages exist with each research design and methodology, and these need to be considered when designing the appropriate protocol (▶ Table 49.6).

49.7.1 Randomized Controlled Study If well constructed, a randomized controlled trial quite possibly has the greatest impact with regard to research. Randomized controlled trials are prospective studies that evaluate outcomes in two groups; these studies can be either short or long term. Both groups are randomly selected and patients are properly allocated to treatment groups, ensuring equal distribution of any preexisting confounding variables that can affect the outcome of interest. Typically, the treatment groups will be the same before the trial starts, and differences observed between the two groups at the end of the trial are likely to be attributed to the treatment given. Design issues are numerous, but proper blinding techniques, randomization and allocation methods, exclusion/inclusion criteria, and measures to minimize attrition are paramount.49 Two types of randomized controlled trials have been described: the crossover design and the parallel design. The latter entails two independent groups: a control group and an intervention group; these groups receive two different treatments and are then followed for a specific duration and their outcomes observed. A crossover design represents two paired groups that receive the same treatment at one point or another, but at alternating times. In the crossover design, the main interest is to measure the treatment effect and determine the existence of a sequential or period effect. Also, concern rests with any residual or carryover effect that the previous treatment had on participants. If such a factor is an issue, a washout or adaptation period may be incorporated to minimize the effects of prior treatment. However, a proper design is constructed so that each treatment is administered the same number of times. In such a design, comparisons are within each subject, whereas in a parallel design comparisons are between groups. Also, proper power analysis in randomized controlled trials can be conducted beforehand to determine the size of the sample groups,

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Complications and Outcome Analysis Table 49.6 Main types of quantitative research designs and their associated advantages and disadvantages Type of study design

Advantages

Randomized controlled trial (parallel design)

●

● ● ●

In a well-constructed study, unbiased distribution of confounding variables Blindness of assessment Can provide temporal sequence of events Statistical analysis is facilitated by randomization

Disadvantages ●

● ●

●

●

●

Randomized controlled trial (crossover design)

●

●

●

Cohort study

●

●

●

●

●

Case–control study

●

●

All subjects receive treatment and serve as their own controls Error variance reduced and sample size needed is reduced Blinding may exist

●

Determines the incidence of developing the disease in both groups Confounding variables can be evaluated and their influence on outcome determined Can evaluate various outcomes, can detect associations and analyze time relationships, can monitor changes over time and assess rare and unique exposures Can establish correlation between antecedent events and outcomes Compared to randomized controlled trial, less expensive and easier to administer

●

Beneficial in studying rare diseases or diseases with long duration to develop outcome Retrospective and thus inexpensive and quick studies to conduct if time is an issue

●

● ●

● ● ● ●

●

●

● ●

●

●

●

●

Cross-sectional survey

● ● ●

Case series and case reports

●

●

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Inexpensive Simple Ethically sound May provide insightful information into an area for further investigation Provides insight for very rare diseases and their management

Ethical issue of who receives a specific treatment and if that treatment can possibly do more harm than good Designs are costly and time-consuming Compliance issues or participants lost to follow-up may occur, which affects validity Randomization techniques may be faulty; however, proper methods are established that could account for proper randomization of patients Through time, contamination between groups may occur and should be accounted for Biases (preallocation, selection, performance, detection, exclusion, publication) All subjects receive placebo or alternative treatment at some point Unknown or lengthy washout period Not applicable in treatments associated with permanent effects Can be time-consuming (if prospective in nature, but retrospective cohort designs may reduce time and subsequent costs) Difficult to follow original sample group through time Blinding is difficult and randomization not present Poor sample sizes and short follow-up for rare diseases Various hidden confounding variables may affect outcome

Obtaining an adequate representative control group may be difficult Sampling bias may exist where defining a homogeneous disease group as well as a control group could be problematic and contain confounding variables Demographics of groups in question may prevent generalizing results and increasing external validity How subjects are recruited may be questionable Obtaining data to determine exposure may be difficult and prove challenging/time-consuming Due to the retrospective nature of the study, establishing a timeline when events occurred that may have contributed to the outcome is difficult; thus, obtaining consistent values of timing of events for both groups may not be probable Control subjects for study are selected by the investigator and can entail sampling bias; thus, they are not representative of the population as a whole and risk ratios cannot be analyzed Recall bias by the participants may be present and dilute the validity of the results Hidden confounding variables

●

Does not establish causality, but possible association Potential for recall bias Confounding variables unequally distributed Unequal group sizes

●

Multiple and nonexistence of comparison group

● ● ●

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Clinical Outcome Analyses but an ideal sample size may not always be feasible because of ethical considerations and the placebo exposure, which some participants may find disturbing. In addition, randomized controlled trials possess strong internal validity based on the comparability of the two groups, but the ability to generalize or the strength of external validity in such designs is severely limited if the trial was based on a homogeneous group, which prevents replication in real-life situations.5

49.7.2 Cohort Study A cohort study is an observational study in which a population is selected on the basis of its exposure to a potential cause of a particular disease. The participants are then divided into groups (exposed vs. nonexposed) and followed over time to evaluate their outcomes. Such a design can be a short follow-up or longterm study; however, retrospective follow-up evaluations can be performed. A cohort study attempts to determine the chances of developing the disease in both groups. Confounding variables can be evaluated and their influence on the outcome determined. Such a study can evaluate various outcomes, detect associations, analyze time relationships, monitor changes over time, and assess rare and unique exposures. The particular strength of such a design lies in establishing the relationship between antecedent events and outcomes. Because the groups are followed over time, a timeline is established for when these events occurred. Cohort designs are further categorized as single group (identify all subjects who meet a specific criterion and follow them over time to assess outcomes) or multigroup (two or more groups are identified at the initial assessment and followed over time to evaluate outcomes of interest).

49.7.3 Case–Control Study In contrast to cohort designs, case–control studies begin with the outcome of interest that has occurred, and the exposure is then measured or multiple causes relating to one event are evaluated. In such a design, a group is selected that has the disease, which is usually rare in nature, and this group is compared to a control group that is disease free. In the event that the number of cases is very small, the power of the study may be increased by increasing the number of control subjects matched to each case, thereby producing a matched case–control study. Case–control designs are retrospective in nature and can be carried out quickly in comparison to other research designs.

49.7.4 Cross-Sectional Surveys, Case Series, and Case Reports Various other study designs exist, but the level of evidence is not as strong as for the previously described designs. For example, a cross-sectional survey is used to obtain information on a population at a particular point in time. It attempts to draw a correlation between two factors of interest, and this is usually accomplished with the use of questionnaires. Furthermore, case series and case reports are often used to describe or report on the effects of a particular treatment in a small group of patients. Unlike the many alternative study designs previously described, such accounts provide little with respect to generalizations

about specific treatments and their associated outcomes. However, such designs may prove useful in providing anecdotal information that is suggestive of potential avenues for investigation.50

49.7.5 Statistical Considerations It is important to note that various statistical analyses exist to properly evaluate, interpret, and extrapolate relevant data. Implementing statistical methods to determine appropriate sample sizes and power is always ideal, but it is usually unrealistic, from a practical standpoint, to expect to accomplish in various aspects of spine surgery. Descriptive and frequency statistics are essential for any study. Distinguishing between ordinal, interval, ratio, and categorical data sets is imperative to guide proper analyses. Evaluation between noncontinuous and continuous data and the existence of normal distribution with respect to certain factors is also extremely important to determine the appropriate statistical test. Various designs are also associated with distinct measures of interest. For example, randomized controlled trials are commonly reported with relative risk and its associated confidence intervals, attributable risk, number needed to treat, intention to treat analyses, and use of a CONSORT statement. Alternatively, cohort designs may entail measures of disease frequency as well as assessments of relative risk and confidence intervals, whereas case–control studies routinely implement odds ratios to measure the odds of exposure in patients relative to the odds of exposure in control subjects. Furthermore, various hypothetical tests exist and these can entail any study and are dependent on parametricity, group design, and various stratifications and weighted principles to minimize confounding variables.

49.8 Qualitative Methods to Address 49.8.1 The Clinical Problem Applying qualitative methods to address a question or parameter of interest could provide critical insight into a clinical problem that cannot be resolved in a quantitative manner. Such avenues would encompass predetermined variables and would avoid the more telling human-based experiences and perceptions that need attention and consideration. Qualitative methods attempt to interpret phenomena as to the meaning that individuals bring to them and as such employ various research methods to address the question of interest51,52 (▶ Table 49.7). In addition, this type of research may raise preliminary questions that might provide the foundation for various quantitative studies, such as outcomes research, and at times both may be used depending on the study design and outcome of interest. Nonetheless, various qualitative approaches exist and are briefly highlighted below.

49.8.2 Phenomenology The phenomenology approach seeks to explore the real-life experiences of an individual and focuses on the meaning of that experience to the individual. Such a method does not have to

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Complications and Outcome Analysis Table 49.7 Examples of qualitative research methods Method

Description

Documents such as Study of documentary accounts of events meetings Passive observation Systematic watching of behavior and talk in naturally occurring settings Participant observation

In addition to observing, researcher also occupies a role or part in the setting

In-depth interviews Face-to-face conversation for the purpose of exploring issues or topics in detail; does not use preset questions but is shaped by a defined set of topics Focus groups

Method of group interview that explicitly includes and uses group interaction to generate data

Source: Greenhalgh T, Taylor R. How to read a paper: papers that go beyond numbers (qualitative research). BMJ 1997;315:740–743.

entail a large number of people; the purpose is to obtain an individual’s point of view. Such an approach does not predict behavior, but describes an experience. Also, this approach implements data collection via interviews and written accounts, which the researcher then brackets as various ideas or recurring themes in those experiences. This approach is unilateral and would only target the patient, and avoids the role of the health care professional in influencing or contributing to the patient’s behavior.

49.8.3 Ethnography Ethnography attempts to look at various persons in a particular cultural setting. The sample is generally large and is not intended to predict behavior but describe the environment. The study population is observed in its natural environment, and attempts are made to understand behavior within that group.

49.8.4 Action Research This method entails attempting to initiate change stemming from identification of a specific problem that would be useful to the practitioner’s practice and everyday work. This research relies heavily on the relationship between the researcher and the study participants, the development of theory, and changes in practice. Qualitative methods as well as quantitative avenues are used in this approach.

49.8.5 Grounded Theory Grounded theory attempts to investigate the symbiotic interactions people have with their surrounding conditions and others. Such a method evaluates situations the individuals are in, actions taken as a result of their conditions, and the consequence of those actions. By implementing a questionnaire along with tools for obtaining data, such as interviews, focus groups, and various methods of observation, grounded theory can address the question from a multifaceted perspective and how that influences people’s behavior; thus, this method attempts to explain and predict behavior.

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49.9 Interpretation of the Evidence Although a hierarchy of evidence has been suggested (see ▶ Table 49.4 and ▶ Table 49.5), grading of the quality of evidence goes beyond such classifications. The appropriate type of research to consider is ultimately based on the type of clinical question. Several disadvantages do exist with such a hierarchy of evidence and its associated grading principles. Such drawbacks consist of the failure to draw attention to novel or hybrid research designs, such as crossover designs, that are not incorporated into this hierarchy. Also, limitations exist purely on the premature assumption that a study has enormous strength if it is a systematic review. However, systematic reviews do exist that entail a few small, poor-quality, randomized controlled trials and yet are graded as a level I source of evidence, whereas one large, multicenter, well-conducted randomized controlled trial may be regarded as a level II source. The ranking of evidence may have potential problems resulting from the collapse of many dimensions that give structure and direction to a design turning it into a single grade. For example, if the many dimensions encompassing a randomized controlled trial are not properly conducted, such as proper blinding, randomization techniques, follow-up assessment, patients lost to follow-up, and so forth, the objective of reducing confounding variables due to proper randomization techniques in a controlled setting has failed.53 In addition, randomized controlled trials can provide insightful information concerning the effectiveness of treatment but provide little information regarding prognosis where a tailored cohort design might prove more beneficial. Moreover, if the question at hand were to address the phenomena or underlying behavior that may affect outcome, a qualitative approach may be more appropriate. Thus, the best evidence is dependent on the type of question, and the best structured design properly addresses the question and all of its facets therein (▶ Table 49.8).

49.10 Ethical Considerations The role of the medical practitioner has undergone many changes over time. Although at one time medical doctors were thought to be infallible, medical doctors now often assume the role of consultant, helping patients make their own decisions rather than making decisions for them. With the pressing concerns of medical expenditures that directly affect the economic foundations of hospitals and health insurance providers, as well as the ongoing threat of malpractice lawsuits and the shift to managed care, the role of the physician has been diminished from a champion solely devoted to providing the penultimate care for patients to a mere “puppet” with conflicting loyalties between organizations and patients. Because health care carries the burden of such concerns as well as the ever-increasing costs for providing care, appropriate health care decisions need to be addressed that consider the many facets of the medical community without sacrificing the quality of the care offered to patients. The dilemma of providing a balance between patients and other “bodies” holding interest within medical care has caused concern as to the implications on medical ethics and their role in research and treatment strategies.

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Clinical Outcome Analyses Table 49.8 Levels of evidence for primary research questions Therapeutic studies: investigating the results of treatment Level I

●

●

Level II

●

●

●

Prognostic studies: investigating the effect of a patient characteristic on the outcome of disease

High-quality randomized controlled trial with statistically significant difference or no statistically significant difference but narrow confidence intervals Systematic review of level I randomized controlled trials (studies were homogeneous)

●

Lesser-quality randomized controlled trial (e.g., 80% follow-up, no blinding, or improper randomization) Prospective comparative study Systematic review of level II studies or level I studies with inconsistent results

●

●

●

●

●

Level III

● ●

●

Level IV Level V

●

●

Case–control study Retrospective comparative study Systematic review of level III studies

●

Case series

●

Expert opinion

Diagnostic studies: investigating a diagnostic test

High-quality prospective study (all patients were enrolled at the same point in their disease with 80% follow-up of enrolled patients) Systematic review of level I studies

●

Retrospective study Untreated controls from a randomized controlled trial Lesser-quality prospective study (e.g., patients enrolled at different points in their disease or 80% follow-up) Systematic review of level II studies

●

Case–control study

●

Testing of previously developed diagnostic criteria in series of consecutive patients (with universally applied reference “gold” standard) Systematic review of level I studies

●

Development of diagnostic criteria on basis of consecutive patients (with universally applied reference “gold” standard) Systematic review of level II studies

●

Study of nonconsecutive patients (without consistently applied reference “gold” standard) Systematic review of level III studies

●

Poor reference standard Case–control study

●

No sensitivity analyses

● ●

Expert opinion

●

Expert opinion

●

●

●

●

Case series

●

Expert opinion

Economic and decision analyses: developing an economic or decision model

●

●

●

Sensible costs and alternatives; values obtained from many studies; multiway sensitivity analyses Systematic review of level I studies

Sensible costs and alternatives; values obtained from limited studies; multiway sensitivity analyses Systematic review of level II studies

Analyses based on limited alternatives and costs; poor estimates Systematic review of level III studies

Source: Adapted from OCEBM Levels of Evidence Working Group. The Oxford 2011 Levels of Evidence. Oxford Centre for Evidence-Based Medicine. Available at: http://www.cebm.net/index.aspx?o=5653.

In consideration of the changing role of the physician, escalating medical costs, the evolution of medical technology, and society-based altered perceptions of health care, consideration of medical ethics has taken center stage. Such concern has brought renewed attention to the ethical tenets and principles of the Hippocratic Oath and prompted us to revisit such philosophical frameworks as utilitarianism and deontology. The former is based on the concept of “the greatest good for the greatest number” with the intent to produce just actions for the overall good consequences. Conversely, deontology is duty based with the notion that the “end could never justify the means” and the act itself should be considered independent of the consequences. From the deontological framework, several principles are stressed and include the following: nonmalfeasance, beneficence, autonomy, and justice. Based on such principles, the drive for proper medical conduct and ethical considerations has garnered considerable attention and has guided the belief system of many medical doctors. In any event, the struggle to secure proper medical ethics has been an ongoing concern and has warranted the establishment of governing bodies such as the Declaration of Helsinki, the Protection of

Human Subjects Act, the new Health Insurance Portability and Accountability Act (HIPAA) guidelines, and other agencies to properly monitor and secure patients’ rights. As such, ethical considerations in research, primarily pertaining to certain study design and outcome analyses, are of grave importance and patients’ rights should always take center stage.

49.11 Standards, Guidelines, and Options Health care expenditures represent more than 10% of the U.S. economy. As a result, local and federal governing bodies have concluded that health care policy is directly related to cost containment. As such, advocacy of efficient health care policies is an ongoing battle to lower and maintain costs as well as prevent medicolegal issues. However, adoption of various treatment strategies is dependent on numerous directives for recommending a particular clinical action. On such a premise, informed opinion is based on nonsystematic and subjective assessment of available medical literature coupled with clinical experience. Another form

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Complications and Outcome Analysis is a group consensus by an expert panel representing initiatives posed by the National Institutes of Health. However, improper data collection and panel composition contribute to biases with such an approach in adopting clinical policy. Therefore, an evidence-based approach has gained tremendous momentum in the past decade in developing clinical policy based on its systematic approach of the quality of evidence.54 Clinical policy should clearly be based on methods of gathering evidence and synthesizing information and should represent what is known about a condition or its treatment to recommend sound patient management. Three levels of certainty exist for clinical policies. The first relies on accepted standards that reflect a high degree of clinical certainty and are based largely on level I evidence and possibly strong level II evidence (see ▶ Table 49.4). Nonetheless, to develop a standard, both clinical and economic effectiveness must be established, and a consensus between the health care practitioner and the patient must be reached with respect to the desirability of the outcome. Clinical guidelines reflect a moderate degree of clinical certainty illustrating a particular strategy that is flexible, with known outcomes, supporting evidence, and preferred outcome between patient and provider.5 Guidelines can be tailored to fit individual needs and are largely based on level II evidence and a preponderance of level III evidence.55 Third, clinical options are a practice policy where clinical certainty is unclear because of the insufficient existence of high levels of evidence and the lack of known outcomes.55 Another approach, which has been termed “syntegration,” has recently attracted some attention. This approach relies on the union between the synthesis process heralded by evidencebased medicine and the integration process that stems from physicians’ integration of critical resources and personal experiences. This approach attempts to address the inadequacy of assessment tools that are not known by health care professionals, but who otherwise conduct evidence-based research or are avid readers and supporters of such endeavors.56

49.12 Conclusion A tremendous variety of research designs and methodologies exist to address clinical outcomes assessment. Selection of the appropriate design is based on the type of question of interest. Health care policy making and clinical treatment strategies rely heavily on the best evidence available to guide the decisionmaking process. If carefully constructed and employed, clinical policy standards, guidelines, options, and even novel synthesis of evidence integration may potentially contain costs, improve patient care, medical education, and clinical research, and achieve optimal clinical outcomes.

References [1] Sackett DL, Rosenberg WM, Gray JA, Haynes RB, Richardson WS. Evidence based medicine: what it is and what it isn’t. BMJ. 1996; 312(7023):71–72 [2] Sousa KH. Description of a health-related quality of life conceptual model. Outcomes Manag Nurs Pract. 1999; 3(2):78–82 [3] Patrick DL, Deyo RA. Generic and disease-specific measures in assessing health status and quality of life. Med Care. 1989; 27(3) Suppl:S217–S232 [4] Keller RB, Rudicel SA, Liang MH. Outcomes research in orthopaedics. Instr Course Lect. 1994; 43:599–611

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[5] Mark BA, Salyer J. Methodological issues in treatment effectiveness and outcomes research. Outcomes Manag Nurs Pract. 1999; 3(1):12–18, quiz 18–19 [6] Ware JE, Jr, Sherbourne CD. The MOS 36-item short-form health survey (SF-36). I. Conceptual framework and item selection. Med Care. 1992; 30(6):473–483 [7] Stewart AL, Hays RD, Ware JE, Jr. The MOS short-form general health survey. Reliability and validity in a patient population. Med Care. 1988; 26(7):724–735 [8] Brook RH, Ware JE, Jr, Davies-Avery A, et al. Overview of adult health measures fielded in Rand’s health insurance study. Med Care. 1979; 17(7) Suppl: iii–x, 1–131 [9] Ware JE, Jr, Brook RH, Davies AR, Lohr KN. Choosing measures of health status for individuals in general populations. Am J Public Health. 1981; 71(6):620–625 [10] Dupuy HJ. The Psychological General Well-Being (PGWB) index. In: Wenger NK, Mattson ME, Furberg CD, et al, eds. Assessment of Quality of Life in Clinical Trials of Cardiovascular Disease. New York, NY: Le Jacq Publishing; 1984:170–183 [11] Stewart AL, Greenfield S, Hays RD, et al. Functional status and well-being of patients with chronic conditions. Results from the Medical Outcomes Study. JAMA. 1989; 262(7):907–913 [12] Aaronson NK, Acquadro C, Alonso J, et al. International Quality of Life Assessment (IQOLA) Project. Qual Life Res. 1992; 1(5):349–351 [13] King JT, Jr, Roberts MS. Validity and reliability of the Short Form-36 in cervical spondylotic myelopathy. J Neurosurg. 2002; 97(2) Suppl:180–185 [14] Gatchel RJ, Mayer T, Dersh J, Robinson R, Polatin P. The association of the SF36 health status survey with 1-year socioeconomic outcomes in a chronically disabled spinal disorder population. Spine. 1999; 24(20):2162–2170 [15] Jenkinson C, Wright L, Coulter A. Criterion validity and reliability of the SF-36 in a population sample. Qual Life Res. 1994; 3(1):7–12 [16] Lyons RA, Perry HM, Littlepage BN. Evidence for the validity of the Short-form 36 Questionnaire (SF-36) in an elderly population. Age Ageing. 1994; 23(3):182–184 [17] Ware J, Jr, Kosinski M, Keller SDA. A 12-Item Short-Form Health Survey: construction of scales and preliminary tests of reliability and validity. Med Care. 1996; 34(3):220–233 [18] Bergner M, Bobbitt RA, Pollard WE, Martin DP, Gilson BS, The Sickness Impact Profile. The sickness impact profile: validation of a health status measure. Med Care. 1976; 14(1):57–67 [19] Kopec JA, Esdaile JM. Occupational role performance in persons with back pain. Disabil Rehabil. 1998; 20(10):373–379 [20] Lerner D, Amick BC, III, Rogers WH, Malspeis S, Bungay K, Cynn D. The Work Limitations Questionnaire. Med Care. 2001; 39(1):72–85 [21] Lerner D, Reed JI, Massarotti E, Wester LM, Burke TA. The Work Limitations Questionnaire’s validity and reliability among patients with osteoarthritis. J Clin Epidemiol. 2002; 55(2):197–208 [22] Amick BC, III, Lerner D, Rogers WH, Rooney T, Katz JN. A review of health-related work outcome measures and their uses, and recommended measures. Spine. 2000; 25(24):3152–3160 [23] Daltroy LH, Cats-Baril WL, Katz JN, Fossel AH, Liang MH. The North American spine society lumbar spine outcome assessment Instrument: reliability and validity tests. Spine. 1996; 21(6):741–749 [24] Gerszten PC. Outcomes research: a review. Neurosurgery. 1998; 43 (5):1146–1156 [25] Melzack R. The McGill Pain Questionnaire: major properties and scoring methods. Pain. 1975; 1(3):277–299 [26] Fairbank JCT, Couper J, Davies JB, O’Brien JP. The Oswestry low back pain disability questionnaire. Physiotherapy. 1980; 66(8):271–273 [27] Fairbank J. Revised Oswestry Disability questionnaire. Spine. 2000; 25(19):2552 [28] Page SJ, Shawaryn MA, Cernich AN, Linacre JM. Scaling of the revised Oswestry low back pain questionnaire. Arch Phys Med Rehabil. 2002; 83(11):1579–1584 [29] Peterson CK, Bolton JE, Wood AR. A cross-sectional study correlating lumbar spine degeneration with disability and pain. Spine. 2000; 25(2):218–223 [30] Fairbank JCT, Pynsent PB. The Oswestry Disability Index. Spine. 2000; 25 (22):2940–2952, discussion 2952 [31] Wheeler AH, Goolkasian P, Baird AC, Darden BV, II. Development of the Neck Pain and Disability Scale. Item analysis, face, and criterion-related validity. Spine. 1999; 24(13):1290–1294 [32] Vernon H, Mior S. The Neck Disability Index: a study of reliability and validity. J Manipulative Physiol Ther. 1991; 14(7):409–415 [33] Prolo DJ, Oklund SA, Butcher M. Toward uniformity in evaluating results of lumbar spine operations. A paradigm applied to posterior lumbar interbody fusions. Spine. 1986; 11(6):601–606 [34] BenDebba M, Heller J, Ducker TB, Eisinger JM. Cervical spine outcomes questionnaire: its development and psychometric properties. Spine. 2002; 27 (19):2116–2123, discussion 2124

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Clinical Outcome Analyses [35] Deyo RA, Andersson G, Bombardier C, et al. Outcome measures for studying patients with low back pain. Spine. 1994; 19(18) Suppl:2032S–2036S [36] Deyo RA, Battie M, Beurskens AJ, et al. Outcome measures for low back pain research. A proposal for standardized use. Spine. 1998; 23(18):2003–2013 [37] American Spinal Injury Association; International Medical Society of Paraplegia. International Standards for Neurological and Functional Classification of Spinal Cord Injury. Chicago, IL: ASIA/IMSOP; 1992 [38] Tator CH. Spinal cord syndromes with physiological and anatomic correlations. In: Menezes AH, Sonntag VKH, eds. Principles of Spinal Surgery. New York, NY: McGraw-Hill; 1995:785–799 [39] Tetreault L, Kopjar B, Nouri A, et al. The modified Japanese Orthopaedic Association scale: establishing criteria for mild, moderate and severe impairment in patients with degenerative cervical myelopathy. Eur Spine J. 2017; 26 (1):78–84 [40] Tetreault L, Wilson JR, Kotter MR, et al. Predicting the minimum clinically important difference in patients undergoing surgery for the treatment of degenerative cervical myelopathy. Neurosurg Focus. 2016; 40(6):E14 [41] Centre for Evidence Based Medicine. Levels of evidence and grades of recommendations. Available at: www.cebm.net/levels_of_evidence.asp. Accessed July 10, 2004 [42] Canadian Task Force on the Periodic Health Examination. The periodic health examination. Can Med Assoc J. 1979; 121(9):1193–1254 [43] Cohen L. McMaster’s pioneer in evidence-based medicine now spreading his message in England. CMAJ. 1996; 154(3):388–390 [44] Cook DJ, Guyatt GH, Laupacis A, Sackett DL. Rules of evidence and clinical recommendations on the use of antithrombotic agents. Chest. 1992; 102(4) Suppl:305S–311S

[45] Sackett DL. Rules of evidence and clinical recommendations for the management of patients. Can J Cardiol. 1993; 9(6):487–489 [46] Sackett DL. Rules of evidence and clinical recommendations on the use of antithrombotic agents. Chest. 1986; 89(2) Suppl:2S–3S [47] Sackett DL. Rules of evidence and clinical recommendations on the use of antithrombotic agents. Chest. 1989; 95(2) Suppl:2S–4S [48] Freedman KB, Back S, Bernstein J. Sample size and statistical power of randomised, controlled trials in orthopaedics. J Bone Joint Surg Br. 2001; 83 (3):397–402 [49] Wall EM, Susman J, Hagen MD, LeFevre M. An overview of clinical policies with implications for clinical practice, medical education, and research. Fam Med. 1994; 26(5):314–318 [50] Vandenbroucke JP. In defense of case reports and case series. Ann Intern Med. 2001; 134(4):330–334 [51] Silverman D. Interpreting Qualitative Data. Methods for Analysing Talk, Text, and Interaction. London: Sage Publications Ltd; 2001 [52] Greenhalgh T, Taylor R. Papers that go beyond numbers (qualitative research). BMJ. 1997; 315(7110):740–743 [53] Glasziou P, Vandenbroucke JP, Chalmers I. Assessing the quality of research. BMJ. 2004; 328(7430):39–41 [54] Eddy DM. Clinical decision making: from theory to practice. Practice policies: guidelines for methods. JAMA. 1990; 263(13):1839–1841 [55] Eddy DM. Clinical decision making: from theory to practice. Designing a practice policy. Standards, guidelines, and options. JAMA. 1990; 263(22):3077– 3081, 3084 [56] Errico TJ. Syntegration: a knowledge-based approach to the practice of medicine. SpineLine. 2004; 5:8–11

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Complications and Outcome Analysis

50 Avoiding Complications in Minimally Invasive Spine Procedures Gabriel A. Smith and David J. Hart Abstract This chapter is a review of many of the most frequently utilized minimally invasive spine surgery procedures, presented from the perspective of complication avoidance with a particular emphasis on avoiding complications through awareness and anticipation of these complications. Thus, prevention is emphasized as the best means of managing complications whenever possible. Cervical, thoracic, and lumbar procedures are reviewed, with both common pitfalls and rare but potentially devastating complications discussed. Anterior, lateral, posterolateral, and posterior procedures are included. Tubular access, endoscopic, and percutaneous approaches are discussed. Anatomic and technical considerations are evaluated with a goal of understanding the potential risks of each procedure, and complication management is discussed for cases when prevention fails. Keywords: minimally invasive spine surgery, complications, minimal access spine surgery, percutaneous, complication avoidance

50.1 Introduction The use of minimally invasive spine (MIS) procedures is rapidly increasing. This is partly due to patient demand, improvements in techniques, and the physician’s desire to provide less invasive treatment options. These techniques can also result in improved patient outcomes and a reduction in costs. The less invasive nature of these techniques reduces approach-related morbidity by preserving normal anatomic muscular, ligamentous, and bony structures of the spine. These procedures attempt to focus the operative dissection on the pathologic condition being treated. Currently effective minimally invasive approaches have been proven efficacious and safe for pathology in the cervical,1,2,3,4 thoracic,5,6,7,8,9,10 and lumbar spine.11,12,13,14,15,16 However, long-term outcomes are still under investigation in most instances. Whether the surgeon is operating through a tubular retractor, with an endoscope, or under a microscope, a mastery of the anatomy and pitfalls must be understood to avoid complications. Comfort with these techniques starts with understanding the equipment used in each particular procedure. Using tubular retractors makes orientation difficult, but concurrent use of an operating microscope or loupe magnification permits better visualization and can help facilitate these procedures. To help guide the surgeon, fluoroscopy or image guidance technology can be used. In some cases, complications can be higher, such as the incidence of dural tears, particularly in early case series, until the operator becomes more proficient with the technique.17 Training in live animal and cadaver surgeries, as well as working closely with a surgeon experienced in MIS, can lead to mastery of these techniques. Fellowships, training courses, and instructional material are increasingly becoming available to facilitate the mastering of MIS procedures and reducing patient risks.

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50.2 Cervical Complications 50.2.1 Minimally Invasive Posterior Cervical Laminoforaminotomy Recently microsurgical techniques have been applied to perform decompression for foraminal stenosis causing cervical radiculopathy using the microendoscopic discectomy (MED) technique and instrumentation.1,3,18 This muscle-splitting approach is effective in limiting postoperative pain and muscle spasms while maintaining the integrity of midline posterior muscular and ligamentous attachments to the spine. This technique can be performed in the semisitting position (▶ Fig. 50.1) or prone. Under fluoroscopic guidance a Kirschner wire (K-wire) or small dilator should be docked directly over the facet joint of interest (▶ Fig. 50.2). If the surgeon is not careful, the initial K-wire or smaller dilators can be inadvertently pushed between the cervical laminae, leading to potential serious spinal cord or nerve root injury during the approach. Additionally, lateral displacement of the K-wire or dilators can result in nerve root or vertebral artery injury, or brisk venous bleeding from the venous plexus surrounding the vertebral artery. Once the final dilator and tubular retractor are placed over the facet complex, the surgeon can continue with the facetectomy and foraminotomy. A dural tear is the most commonly encountered complication. Adamson1 retrospectively reviewed 100 cases of patients undergoing posterior cervical microendoscopic laminoforaminotomy (MEF) and reported complications in three patients; two cases of dural puncture required no intervention other than Gelfoam, and in one case a superficial wound infection was reported. Khoo et al4 reported three complications in 25 patients that were attributable to surgical technique. These included two small cerebrospinal fluid (CSF) leaks and one case of partial-thickness dural violation. After 2 to 3 days of routine lumbar drainage for patients with CSF leaks, none of these patients went on to have long-term clinical sequelae. Primary repair or tamponade with a small piece of Gelfoam or DuraGen followed by fibrin glue application are other options for repair. Patients should be well advised of this potential complication, but also counseled that with appropriate management it generally results in no long-term complications.19

50.2.2 Anterior Cervical Foraminotomy An anterior cervical foraminotomy is effective for unilateral radicular symptoms, but has not been readily adopted due to technical difficulties and risk of vertebral artery injury.2,18 The primary risk of the procedure is inadvertent injury to the vertebral artery during drilling of the uncovertebral joint. Jho2,18 identified three potential sites of vertebral artery injury: at the C6–C7 level, lateral to the uncinate process, and at the transverse foramen. The C6–C7 site has a high risk of injury to the vertebral artery because it courses between the transverse process of

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Avoiding Complications in Minimally Invasive Spine Procedures

Fig. 50.1 Patient placed in the semisitting position for posterior cervical microendoscopic laminoforaminotomy/discectomy.

Fig. 50.2 (a-c) Intraoperative lateral fluoroscopic images showing sequential dilator placement after skin and fascia incision during a posterior cervical microscopic laminoforaminotomy/discectomy. Of note, the first dilator is sufficient to approach the spine. Not using a K-wire can potentially avoid inadvertent injury during K-wire placement. The patient underwent a right C5-6 laminoforaminotomy/discectomy.

C7 and the longus colli muscle. To avoid vertebral artery injury, Jho recommended incising the longus colli muscle at the level of the C6 transverse process. The muscle stump is then reflected toward the C7 transverse process to expose the vertebral artery, which lies under the longus colli muscle. At the uncinate process, vertebral artery injury can also be avoided by leaving a thin layer of cortical bone during drilling of the uncovertebral joint.2,3,18 This bone is then removed with a curette after drilling is completed. However, the transverse foramen should not be entered during drilling to avoid vertebral artery injury, and brisk venous bleeding is a warning the venous plexus that surrounds the vertebral artery in the foramen has been encountered.

Injury to the vertebral artery could be lethal and difficult to repair.20,21,22 Packing with Gelfoam, muscle, and/or bone wax, followed by angiography, should be performed if primary repair cannot be performed. Direct exposure of the vessel in the foramen is exceptionally challenging, even in the most skilled surgeon’s hands.20,21,22 The sympathetic chain is another structure that can be injured because it lies just anterior to the longus colli muscle. Injury results in Horner’s syndrome. Efforts to adequately retract the longus colli muscle laterally and restricting muscle dissection to the most medial aspect can reduce the risk of sympathetic chain injury.

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Complications and Outcome Analysis Failure to adequately decompress the nerve root by leaving residual disc or osteophyte due to unfamiliarity with the surgical approach can be avoided by performing a cadaveric anterior cervical foraminotomy study before performing this procedure. Additional complications can be related to poor patient selection. Those patients with mechanical neck pain do poorly with simple nerve root decompression. Performing this procedure at junctional levels (i.e., cervicothoracic junction and levels adjacent to previous fusions) may result in mechanical neck pain after partial removal of the uncovertebral joint because of preexisting poor biomechanics. Similarly, patients with asymptomatic contralateral foraminal narrowing at the same level may develop new radicular symptoms contralateral to the anterior cervical foraminotomy, likely because of hypermobility after the procedure.23

50.2.3 Microendoscopic Anterior Cervical Discectomy and Fusion Microendoscopic anterior cervical discectomy and fusion has recently been performed using a tubular retractor and endoscopic visualization to perform the procedure. The muscle dilators and tubular retractor are placed only after the cervical vertebral bodies are approached and identified through a standard fascial approach medial to the sternocleidomastoid muscle. Dilators should never be placed blindly, because significant potential for injury to the anterior neck structures exists (e.g., carotid artery, esophagus, and trachea). The tube through which the procedure is performed simply acts as a retractor. Difficulties encountered with this technique include the limited working space and inability to distract the disc space. The potential benefits of this approach may include reduced postoperative dysphagia. A recent clinical study did find the tubular retractor technique useful for anterior odontoid screw fixation in repairing type II odontoid fractures.24 The primary risks associated with anterior odontoid screw fixation are related to exposure and relatively blind passage of the screw during placement.25 The tubular retractor technique appears to facilitate safe screw placement by maximizing intraoperative visualization and rigid fixation of the retractor to the table.24

50.3 Thoracic Complications 50.3.1 Thoracoscopic-Assisted Decompression Techniques The potential complications associated with thoracoscopic procedures are similar to those associated with open thoracotomy, although the incidence varies. There is a reduced incidence of post-thoracotomy pain, intercostal neuralgia, pulmonary dysfunction, and scapular dysfunction associated with a thoracoscopic compared to an open approach.26,27,28,29,30,31 Complications may arise from patient positioning, port placement and access, and manipulation of instruments with injury to the lung parenchyma or thoracic vascular structures.28 Expertise in performing an open thoracotomy does not necessarily translate to expertise in thoracoscopic procedures, and additional training to master this technique is required.32,33,34 Many surgeons elect to have a thoracic surgeon assist with the opening to avoid or minimize these risks.

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Patient selection is important to avoiding complications. Extensive lung adhesions, prior thoracic procedures resulting in extensive scar formation, severe scoliosis, and advanced thoracic vascular disease such as an aortic aneurysm often make the approach perilous. Single lung ventilation is required for access, and patients with a history of smoking and chronic obstructive airway disease are often difficult to adequately ventilate, which can lead to serious intraoperative hypoxia and acidosis from CO2 retention. These patients need to undergo preoperative testing of pulmonary function prior to elective surgery and urgent cases must be performed with caution. Complications resulting from prolonged nonventilation of one lung may lead to the accumulation of excessive secretions in the airways.35,36 Therefore, in prolonged operative procedures, an aggressive postoperative pulmonary toileting can prevent significant “down-lung” atelectasis and pneumonia. Additionally, intraoperative positive endexpiratory pressure (PEEP) on the ventilated lung and continuous positive airway pressure (CPAP) on the nonventilated lung can significantly reduce these complications. Patients undergoing thoracoscopic procedures are placed in the lateral decubitus position; therefore, adequate padding by placing an axillary roll under the chest to prevent pressure on the brachial plexus in the axilla is critical.5,6 Traction injuries to the brachial plexus by abducting the arm on the operated side must be prevented. Other pressure points, particularly the common peroneal nerve at the fibular head, should also be adequately padded to avoid postoperative peroneal nerve palsy. The initial port is commonly placed at the sixth or seventh intercostal space for mid- and lower thoracic spine pathology and in the fourth or fifth intercostal space for upper spine pathology. The initial endoscopic port is the only port that is placed blindly and can result in injury to the lung parenchyma and other vascular structures in the chest. Therefore, lung adhesions, which cause the lung to adhere to the chest wall, can result in lung injury during port placement and postoperative pneumothorax. To prevent this complication, a finger is passed through the port site and swept circumferentially within the chest cavity to release any adhesions before placement of the port. With the lung collapsed, the diaphragm can ride up and be perforated during placement of lower thoracic ports, with possible injury to structures under the diaphragm. To overcome this problem, all ports after the initial port should be placed under direct endoscopic vision. Injury to the intercostal nerve, artery, or vein is also possible during trocar placement. Damage to the nerve can result in severe postoperative pain and dysesthesia.6,37 It is imperative that all ports, after the initial endoscopic port, be placed under continuous endoscopic vision and that all instruments be visualized from entry to exit from the chest cavity. Bleeding from port sites can be more a nuisance than a complication and can be controlled with bipolar coagulation. If the bleeding at the port site is severe, a Foley catheter can be inserted and the balloon inflated to tamponade the bleeding. If the bleeding cannot be stopped by the aforementioned techniques, the wound may need to be enlarged to identify and control the bleeding. Injury to large intrathoracic vessels rarely occurs, but a thoracotomy tray must be in the room ready to be opened in the event of uncontrollable bleeding. Pneumothorax requiring a chest tube is common and many surgeons leave a

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Avoiding Complications in Minimally Invasive Spine Procedures pigtail catheter or chest tube in place for a few days after the procedure.6,36,37,38,39,40,41

50.3.2 Thoracoscopic Microdiscectomy Thoracic disc herniation is a relatively common disorder identified by magnetic resonance imaging as 14.5% of all disc herniations.42 The vast majority of these herniations are asymptomatic and do not require surgical intervention. Surgery is reserved for those patients with long-tract signs of myelopathy and with thoracic radicular pain corresponding to the herniated disc level who have failed conservative management. With improvements in operative instrumentation, the treatment of this condition using thoracoscopic techniques has evolved.10,37,43,44,45,46,47 Nevertheless, the steep learning curve, instrumentation setup cost, and infrequency of symptomatic thoracic disc herniations have limited the widespread use of thoracoscopic discectomy. Complication rates vary per series, but the types of complications are similar to those seen in open thoracotomy procedures. Reports cite a lower incidence of costovertebral neuralgia, postoperative respiratory complications, and chest pain using thoracoscopic techniques compared to the more traditional open procedure.6,36,37,38 In one series, the incidence of complications of disabling intercostal neuralgia (50% open vs. 16% thoracoscopic) and postoperative atelectasis and pulmonary dysfunction (33% open vs. 7% thoracoscopic) clearly showed less postoperative discomfort.47

50.3.3 Minimally Invasive Costotransversectomy Approach Recent developments have been made in the application of a minimally invasive costotransversectomy technique to treat thoracic disc herniations and neoplasms. The advantage of this technique is that the approach is via a posterior muscle-splitting technique and avoids entering the thoracic cavity. Complication avoidance relies on adequate fluoroscopic visualization and level localization along with proper docking of the K-wire, muscle dilators, and tubular retractor in a paramedian fashion. Calcified disc herniations should be approached by more conventional means, namely, thoracotomy or MIS thoracoscopic approaches. The lateral approach taken, generally 3 to 5 cm off the midline depending on patient size, as well as the angled visualization used in this technique, reduces the risk of thoracic spinal cord manipulation over a traditional posterior approach. Obvious complications that should be reviewed with the patient include the risk of spinal cord injury, pneumothorax, and dural tear with CSF leak. Fluoroscopy, in both the anteroposterior (AP) and lateral views, is helpful in orienting the surgeon during the surgical approach. Although recently introduced, this procedure has been successful in treating patients with acceptably low complication rates.48,49,50

50.3.4 Vertebroplasty and Kyphoplasty Vertebroplasty has become an effective treatment modality for painful debilitating osteoporotic vertebral body compression fractures.51,52 Methylmethacrylate is currently the most widely used vertebral cement filling product. Further applications

beyond the treatment of osteoporotic compression fractures have included spine fractures caused by spinal metastasis and myeloma.53,54 The reported incidence of complications with vertebroplasty is less than 10% with most coming from cement leakage outside the vertebral body.52,54,55,56,57 There is a reported higher incidence of cement leakage leading to radiculopathy or spinal cord compression in those patients undergoing vertebroplasty for metastasis or myeloma compared to those treated for osteoporotic compression fracture.51 The reported incidence of radiculopathy and cord compression from cement migration was 4% and less than 0.5%, respectively, in those patients treated for osteoporotic compression fractures.56,58,59 To reduce the incidence of complications related to cement migration, more recent reports suggest that partial filling of vertebral bodies (< 30% by volume of the vertebral body) can result in successful clinical outcomes (reduced pain, adequate strengthening, and stabilization of fractured vertebrae).51 One recent study by Liebschner et al suggests that only approximately 15% volume fraction is needed to restore stiffness to predamaged levels and that greater filling may result in a substantial increase beyond an intact level.60 Another study has shown vertebral body strength restoration and favorable clinical outcomes with as little as 2 mL of cement injected.54,56 Smaller filling volumes could conversely reduce the risk of cement extravasation outside the vertebral body and reduce loadbearing forces on adjacent vertebral bodies. The kyphoplasty procedure was developed to help restore vertebral body height as well. The vertebroplasty technique requires that methylmethacrylate cement be injected directly into the vertebral body compression fracture under relatively high pressure, which could result in cement extravasation. Conversely, the kyphoplasty technique insufflates a balloon within the compression fracture, restoring the vertebral body height. The cement is then injected into the cavity made by the balloon under low pressure, thus reducing the incidence of cement extravasation. Preliminary data suggest that kyphoplasty is a safe procedure associated with a lower risk of cement extravasation than vertebroplasty, and it can restore vertebral body height.55,56,61,62

50.4 Lumbar Complications 50.4.1 Minimally Invasive Microdiscectomy Tubular retractor systems combined with a microscopic or endoscopic technique allow spine surgeons to reliably decompress a symptomatic lumbar nerve root via a minimally invasive approach with limited morbidity.16,63 These systems offer the surgeon a direct working corridor to the nerve root while minimizing tissue trauma, yielding less postoperative pain, a smaller incision size, and lower hospital lengths of stay. Using fluoroscopic guidance to localize the level of interest, a 2-cm incision is made roughly 1 cm off the midline on the symptomatic side. A K-wire is used to dock onto the facet joint and tubular dilators are then used to spread the muscle apart prior to placement of the retractor system. A serious technical complication can occur with improper K-wire placement. Most surgeons recommend using fluoroscopy and ensuring that the

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Complications and Outcome Analysis K-wire is docked onto the medial aspect of the facet prior to proceeding with tubular dilation. Thecal sac penetration or nerve root injury can occur if the K-wire is not docked carefully. The most common technical complication is a dural tear, estimated to occur at an incidence of 5%, but clinical series have shown low morbidity.63 In a series of 100 consecutive patients, complications included 3 patients with dural tears that were all repaired intraoperatively and 1 patient with a delayed pseudomeningocele formation.64 A prospective multicenter clinical study has shown the efficacy of this system in treating lumbar disc disease.14,63,65

50.4.2 Automated Percutaneous Lumbar Discectomy Automated percutaneous discectomy is reserved for a small number of highly selected patients with an isolated herniated disc, excluding those patients with sequestered disc fragments, synovial cyst, or bony compression as a cause of radicular symptoms.14,64,66,67,68 However, it is estimated that only 3 to 4% of disc patients treated surgically actually meet the criteria for percutaneous nucleotomy.69,70 The primary morbidity of the procedure is discitis, which may result from scraping of the end plates by the automated Nucleotome during disc removal. Only two cases of cauda equina injury have been reported; these occurred in heavily sedated or anesthetized patients.71

50.4.3 Percutaneous Thoracolumbar Pedicle Screw Instrumentation Innovations in the application of thoracolumbar spine instrumentation have resulted in systems that can now be applied in a less invasive manner.72,73,74 Percutaneous pedicle screw placement is commonplace now, but pitfalls do exist that can lead to serious complications. Inaccurate image guidance or poor visualization on fluoroscopy can lead to poor screw placement. Medial breach of the pedicle can cause injury to the neural elements and must be avoided.75 After accessing the pedicle, careful manipulation of the K-wires must be taken as these can bend or fracture if the surgeon is not careful. Rod placement can oftentimes be difficult if screws are poorly aligned, scoliosis is present, or long-segment fixation is being performed. The first mistake is often trying to pass the rod above the fascia. A lateral X-ray can prevent this by visualizing the rod at the level of the screw heads. Next, as the rod is passed through each screw head in succession, the surgeon should confirm this is going through the tower by manual manipulation of the rod and attempting to rotate the screw extensions—if the rod has been passed successfully, they will not rotate. Recently a variation in this technique has been developed that employs the use of a specially designed device that sits on top of the superior facet complex to act as a guide for K-wire placement through the pedicle (P-C Pedicle Access Device; Spinal Concepts, Austin, TX). Once an AP view of the pedicle is achieved, the K-wire can be passed through the pedicle in a “bull’s-eye” fashion (▶ Fig. 50.3). Although the K-wire and subsequent tap and pedicle screw are placed directly down the middle of the pedicle, a less medial trajectory reduces the potential

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risks of violating the medial wall of the pedicle. In a series of 100 consecutive percutaneous pedicle screws placed in 25 patients by means of this technique and evaluated with postoperative computed tomography, 96% of pedicle screws were found to be directly within the pedicle (▶ Fig. 50.4), 3% had slight medial screw thread violation not requiring repositioning, and 1% had slight lateral screw thread violation not requiring repositioning.74,76 Therefore, this technique for percutaneous pedicle screw placement can add a margin of safety to preventing medial wall violation and neural injury. Robotic percutaneous screw placement is also being investigated as a possible means to reduce screw malpositioning.77,78

50.4.4 Minimally Invasive Posterolateral and/or Transforaminal Lumbar Interbody Fusion Posterior minimally invasive techniques for lumbar fusion are one of the hallmarks in MIS. Two- to three-level open lumbar fusions can be exceptionally morbid procedures with high rates of postoperative pain, long lengths of stay in the hospital, and dissatisfied patients from large incisions. Using a minimally invasive tubular retractor system, a paramedian approach can be taken. Similar techniques to percutaneous pedicle screw placement can be performed, but the addition of a tubular retractor can allow posterolateral arthrodesis and fusion or the placement of a transforaminal interbody device into the disc space to aid in fusion.12,15 Identification of the transverse processes laterally and decortication can be performed prior to placement of pedicle screws on the contralateral side to where the interbody will be placed. After placement of screws on the contralateral side, if a spondylolisthesis is present, a reduction can be attempted. Risks to performing a reduction include nerve root injury, or screw failure with pullout or fracture.79 A tubular retractor can then be used to visualize the facet joint on the interbody side of the procedure. After removal of the facet joint and identification of the nerve root, the disc space can be accessed and an arthrodesis can be performed for placement of an interbody graft to promote fusion. Nerve root injuries from traction or direct damage can occur during placement of an interbody cage or from instruments used to prepare the disc space for fusion. Wong et al80 published a retrospective series of 513 patients undergoing MIS transforaminal lumbar interbody fusion (TLIF) to evaluate complication rates. Their overall complication incidence was 15.6% (80/513), broken down into durotomies (5%, 26/513), urinary retention (1.4%, 7/513), Kwire fracture (1.2%, 6/513), pulmonary embolism (1.0%, 5/513), cage migration (1.0%, 5/513), nerve root injury (0.8%, 4/513), ileus (0.8%, 4/513), hematoma (0.8%, 4/513), and others (0.4%, 2/513).80 The incidence of complications was comparable to open TLIF in the literature and suggests MIS TLIF is safe and efficacious.

50.4.5 Lateral Retroperitoneal Transpsoas Interbody Fusion Lateral minimally invasive techniques for lumbar decompression are becoming mainstream in modern spine surgery. A lateral retroperitoneal transpsoas approach allows the surgeon

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Avoiding Complications in Minimally Invasive Spine Procedures

a

b

c

d

Fig. 50.3 Percutaneous pedicle screw targeting using the “bull’s eye” approach. The Kirschner wire (K-wire) is initially placed under fluoroscopic guidance. (a) “Bull’s eye” targeting of the pedicle in the anteroposterior fluoroscopic trajectory. (b) Illustration of the initial trajectory. (c) Lateral fluoroscopic view as the K-wire is driven into the vertebral body. (d) Trajectory of the K-wire.

Jamshidi needle stops on facet

Fig. 50.4 Plain radiograph (a) and CT (b) views after percutaneous pedicle screw placement using this technique.

access to midlumbar pathology with ease, and allows for indirect and direct decompression for pathologies ranging from neoplasm to deformity. Careful patient selection is paramount as the transpsoas approach is perilous and can result in serious complications. Prior infections or retroperitoneal procedures could cause significant scarring of the retroperitoneum, making the dissection dangerous to large vessels or the lumbar plexus coursing through the psoas muscle.76,81,82,83,84,85,86 High-grade spondylolisthesis will also cause displacement of the lumbar plexus and should not be considered for this procedure. Above L2, the surgeon must take into account the 12th rib and crural attachments of the diaphragm. Below the L4–L5 disc space, the

iliac crest may prevent docking, and nerve root injury through a transpsoas approach has been shown to be more common at L4–L5 compared to more cephalad levels due to the posteriorly located lumbar plexus.87,88 Placement of the patient in the lateral decubitus position must be performed with an axillary roll to prevent brachial plexus injury. Skin incision and dissection should only be carried out once true AP and lateral position is confirmed with imaging.88,89,90 Electrocautery can be used until the external oblique fascia is identified, but blunt dissection should be performed through the external oblique, internal oblique, and transverse abdominis muscles until retroperitoneal fat is seen. Sharp dissection can lead to breach of the peritoneum leading to

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Complications and Outcome Analysis significant morbidity. After palpating the transverse process, the quadratus lumborum, and the psoas muscle, some surgeons opt at this point to place their retractor superficial to the psoas muscle prior to dilation.88,89,90,91 Continuous neuromonitoring is recommended during transpsoas dilation at all levels as nerve root injury rates have been estimated between 3 and 10% persisting up to 18 months after surgery.92 An extremely important point is to ensure that chemical neuromuscular blockade is worn off prior to proceeding. Once the initial probe reaches the annulus of the disc or vertebral body, the probe should be docked into the disc space to prevent migration during dilation, which has led to great vessel injury.82,91 During preparation of the disc space or corpectomy site, caution must be taken not to fracture the end plates or plunge laterally out the contralateral side, potentially resulting in contralateral muscle, vascular, and/or plexus injury. The latter complication is of particular concern when transecting the contralateral annulus fibrosis as part of the anterior release of the disc. Reoperation rates from subsidence, pseudoarthrosis, or persistent symptoms after lateral interbody fusion have been estimated at 10%.93

50.4.6 Laparoscopic Anterior Lumbar Interbody Fusion Complications that can occur during laparoscopic anterior lumbar interbody fusion (ALIF) are similar to those encountered for an open ALIF approach and include ventral hernia, injury to abdominal viscera, injury to great vessels, venous or arterial thrombosis, ureteral injury, retrograde ejaculation, and device misplacement or migration.94,95,96,97,98 Although not a laparoscopic approach, open mini-ALIF paramedian muscle-sparing and muscle-splitting approaches can reduce postoperative pain and discomfort.11,94,99 Laparoscopic techniques are effective for performing ALIF procedures while minimizing tissue damage. Conversion to an open procedure should not be interpreted as a complication but rather as “safe” surgical practice if there is bleeding from presacral veins, difficulties in mobilizing great vessels, or inability to adequately insufflate the abdominal cavity. Injury to the great vessels in the retroperitoneal space can occur during the initial exposure.97,100,101,102,103 The common iliac arteries and veins have to be dissected and retracted to facilitate placement of the cages and dowels in the disc spaces. Injury to these vessels, especially the common iliac veins, can occur during the initial dissection or during the placement of the interbody graft. Continuous monitoring and retraction of the vessels during the placement of the guide tubes for discectomy and placement of the cages is critical to prevent injury. Retrograde ejaculation is reported to occur in 0.42 to 8% of cases after retroperitoneal lower lumbar interbody fusion and is caused by manipulation and/or damage of the superior hypogastric nerve plexus that overlies the ventral lower lumbar segments.99,104,105 Although the majority of these patients recover within 6 to 12 months, approximately 3 to 5% have permanent difficulties. The use of the harmonic scalpel (ultrasonic dissector) or gentle retraction of soft tissues and avoidance of electrocautery around the disc spaces have reduced this complication.99,104 The possibility of retrograde ejaculation has resulted in some hesitancy in using the ventral approach in young sexually active males who intend to have families.

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Studies have compared the incidence of complications between open and laparoscopic ALIF.103 Zdeblick and David103 noted the approach to the L5–S1 level is routine, but the L4–L5 level can pose significant technical difficulties because of the overlying vascular anatomy, and found complication rates were significantly higher in the laparoscopic group (20% laparoscopic vs. 4% open). These investigators concluded that there were no significant advantages to performing laparoscopic ALIF at the L4–L5 level.103 The incidence of complications in laparoscopic ALIF (19.1%) is similar to an open ALIF (14.1%) in experienced hands.106 A study comparing major intraoperative complications between two large series of patients, those undergoing open (N = 305 patients) and laparoscopic (N = 215 patients) ALIF, revealed an incidence of implant migration, great vessel damage, and pulmonary embolism of 1.0, 0.7, and 0.3%, respectively, in the open ALIF group compared to 0% for all three in the laparoscopic group.106

50.5 Conclusion MIS procedures can be performed effectively in the cervical, thoracic, and lumbar spine to treat a variety of spinal disorders. However, these techniques can only be applied safely after a thorough understanding of the anatomy, mastery of the technique, and an appreciation of potential complications. Patients should be advised of possible complications that may require additional treatment. Although these procedures are minimally invasive, they nonetheless carry similar risks to open procedures. Many of these procedures have steep learning curves and require additional training to master including fellowship training, cadaveric workshops, and animal laboratory study. However, once mastered, these techniques can result in a significant reduction in postoperative pain and discomfort, and allow patients to return to their activities of daily living sooner than standard open, more conventional procedures.

Clinical Caveats ●

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Fluoroscopic and stereotactic navigation can act as guidance for the surgeon operating through a complex—and at times disorienting—working corridor. Tubular retractor usage in the cervical spine is best performed for odontoid screw placement and keyhole foraminotomies, both of which require mastery of the local anatomy to avoid complications. In a thoracoscopic or mini-open thoracic discectomy or corpectomy, patient selection is critical as extensive lung adhesions or scars, severe scoliosis, and advanced thoracic vascular disease such as an aortic aneurysm make the approach perilous. The lateral transpsoas approach requires continuous neuromonitoring to avoid plexus injury during docking and tubular dilation. Minimally invasive transforaminal lumbar interbody fusion complication rates are similar to open techniques in skilled hands. Performing an ALIF laparoscopically at L4–L5 can be perilous due to the close proximity of the great vessels. A vascular or general surgery trained co-surgeon may be considered for these complex approaches.

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Avoiding Complications in Minimally Invasive Spine Procedures

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[81] Ahmadian A, Verma S, Mundis GM, Jr, Oskouian RJ, Jr, Smith DA, Uribe JS. Minimally invasive lateral retroperitoneal transpsoas interbody fusion for L4–5 spondylolisthesis: clinical outcomes. J Neurosurg Spine. 2013; 19(3):314–320 [82] Aichmair A, Fantini GA, Garvin S, Beckman J, Girardi FP. Aortic perforation during lateral lumbar interbody fusion. J Spinal Disord Tech. 2015; 28(2):71–75 [83] Arnold PM, Anderson KK, McGuire RA, Jr. The lateral transpsoas approach to the lumbar and thoracic spine: a review. Surg Neurol Int. 2012; 3 Suppl 3: S198–S215 [84] Berjano P, Lamartina C. Minimally invasive lateral transpsoas approach with advanced neurophysiologic monitoring for lumbar interbody fusion. Eur Spine J. 2011; 20(9):1584–1586 [85] Caputo AM, Michael KW, Chapman TM, et al. Extreme lateral interbody fusion for the treatment of adult degenerative scoliosis. J Clin Neurosci. 2013; 20(11):1558–1563 [86] Castellvi AE, Nienke TW, Marulanda GA, Murtagh RD, Santoni BG. Indirect decompression of lumbar stenosis with transpsoas interbody cages and percutaneous posterior instrumentation. Clin Orthop Relat Res. 2014; 472(6):1784–1791 [87] Dahdaleh NS, Smith ZA, Snyder LA, Graham RB, Fessler RG, Koski TR. Lateral transpsoas lumbar interbody fusion: outcomes and deformity correction. Neurosurg Clin N Am. 2014; 25(2):353–360 [88] Graham RB, Wong AP, Liu JC. Minimally invasive lateral transpsoas approach to the lumbar spine: pitfalls and complication avoidance. Neurosurg Clin N Am. 2014; 25(2):219–231 [89] Formica M, Berjano P, Cavagnaro L, Zanirato A, Piazzolla A, Formica C. Extreme lateral approach to the spine in degenerative and post traumatic lumbar diseases: selection process, results and complications. Eur Spine J. 2014; 23 Suppl 6:684–692 [90] Gates TA, Vasudevan RR, Miller KJ, Stamatopoulou V, Mindea SA. A novel computer algorithm allows for volumetric and cross-sectional area analysis of indirect decompression following transpsoas lumbar arthrodesis despite variations in MRI technique. J Clin Neurosci. 2014; 21(3):499–502 [91] Assina R, Majmundar NJ, Herschman Y, Heary RF. First report of major vascular injury due to lateral transpsoas approach leading to fatality. J Neurosurg Spine. 2014; 21(5):794–798 [92] Lykissas MG, Aichmair A, Hughes AP, et al. Nerve injury after lateral lumbar interbody fusion: a review of 919 treated levels with identification of risk factors. Spine J. 2014; 14(5):749–758 [93] Nemani VM, Aichmair A, Taher F, et al. Rate of revision surgery after standalone lateral lumbar interbody fusion for lumbar spinal stenosis. Spine. 2014; 39(5):E326–E331 [94] Baker JK, Reardon PR, Reardon MJ, Heggeness MH. Vascular injury in anterior lumbar surgery. Spine. 1993; 18(15):2227–2230 [95] McAfee PC, Cunningham BW, Lee GA, et al. Revision strategies for salvaging or improving failed cylindrical cages. Spine. 1999; 24(20):2147–2153 [96] Regan JJ, McAfee PC, Guyer RD, Aronoff RJ. Laparoscopic fusion of the lumbar spine in a multicenter series of the first 34 consecutive patients. Surg Laparosc Endosc. 1996; 6(6):459–468 [97] Regan JJ, Yuan H, McAfee PC. Laparoscopic fusion of the lumbar spine: minimally invasive spine surgery. A prospective multicenter study evaluating open and laparoscopic lumbar fusion. Spine. 1999; 24(4):402–411 [98] Zucherman JF, Zdeblick TA, Bailey SA, Mahvi D, Hsu KY, Kohrs D. Instrumented laparoscopic spinal fusion. Preliminary results. Spine. 1995; 20 (18):2029–2034, discussion 2034–2035 [99] Flynn JC, Price CT. Sexual complications of anterior fusion of the lumbar spine. Spine. 1984; 9(5):489–492 [100] Hannon JK, Faircloth WB, Lane DR, et al. Comparison of insufflation vs. retractional technique for laparoscopic-assisted intervertebral fusion of the lumbar spine. Surg Endosc. 2000; 14:300–304 [101] Lieberman IH, Willsher PC, Litwin DE, Salo PT, Kraetschmer BG. Transperitoneal laparoscopic exposure for lumbar interbody fusion. Spine. 2000; 25 (4):509–514, discussion 515 [102] O’Dowd JK. Laparoscopic lumbar spine surgery. Eur Spine J. 2000; 9 Suppl 1:S3–S7 [103] Zdeblick TA, David SM. A prospective comparison of surgical approach for anterior L4-L5 fusion: laparoscopic versus mini anterior lumbar interbody fusion. Spine. 2000; 25(20):2682–2687 [104] Christensen FB, Bünger CE. Retrograde ejaculation after retroperitoneal lower lumbar interbody fusion. Int Orthop. 1997; 21(3):176–180 [105] Tiusanen H, Seitsalo S, Osterman K, Soini J. Retrograde ejaculation after anterior interbody lumbar fusion. Eur Spine J. 1995; 4(6):339–342 [106] Regan JJ, Aronoff RJ, Ohnmeiss DD, Sengupta DK. Laparoscopic approach to L4-L5 for interbody fusion using BAK cages: experience in the first 58 cases. Spine. 1999; 24(20):2171–2174

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Part VII

51 Stem Cell–Based Intervertebral Disc Restoration

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51 Stem Cell–Based Intervertebral Disc Restoration Mengqiao Alan Xi and Mick J. Perez-Cruet Abstract Biologic restoration of the degenerative intervertebral disc is the goal for restoring the natural integrity of the intervertebral disc. This chapter discusses the latest developments in science and technology to achieve this goal. A review of the current literature as well as the latest science on stem cell–based intervertebral disc restoration and possible future medical technology is conducted. It is hoped that the future may offer patients a biologic treatment that restores the normal anatomical function of the intervertebral disc for those suffering from debilitating spinal conditions. Keywords: biologic intervertebral disc regeneration, stem cells, annular traction, disc degeneration, chronic back pain

51.1 Introduction Strides in basic science research continue to shape the way health care is delivered. Stem cell technology has gained significant ground in the past few decades with the promise to restore the anatomical and physiological properties of the spine. Studies on intervertebral disc (IVD) restoration, in particular, have witnessed great success in both in vitro and in vivo settings, with some of the pilot projects beginning to explore the first human-subject stem cell implants. This chapter reviews pertinent spine studies that demonstrate the potential of stem cell– based IVD regeneration.

51.2 Fundamentals of Stem Cell Biology Stem cells are known for their ability to proliferate indefinitely and to differentiate down different lineages. For this reason, many researchers have proposed various models to investigate the possibility of using stem cells to replace or regenerate damaged human tissue including components of the IVD. The fate of a stem cell is a result of the chemical and environmental milieu it is exposed to during development. Although much unknown remains, many of these lineage-determining factors have been elucidated so that a variety of targeted cell types can be procured by manipulating the growth environment.1 The IVD consists of two distinct structures. The outer annulus fibrosus (AF) contains abundant collagen fibers. The nucleus pulposus (NP) contains glycosaminoglycans that act like a sponge to maintain intradiscal fluid pressure. Age-related deterioration of IVD occurs slowly but eventually results in dysfunction and apoptosis of NP cells, which are associated with reduced extracellular matrix (ECM) maintenance and loss of structural integrity.2 This pathologic process is referred to as degenerative disc disease (DDD). Humans are born with notochordal cells, which are gradually replaced by NP cells during development (▶ Fig. 51.1). Adult NP cells resemble chondrocytes morphologically and functionally. For this reason, the primary aim of IVD restoration is to regenerate chondrocyte-like cells from stem cells to replenish the senescent or depleted NP

Fig. 51.1 As humans age, the notochordal cell population (a) disappears and is replaced by sparse chondrocyte-like cell populations (b). (c,d) Apoptosis with aging and degeneration. (c) Disc at 13 years of age and (d) disc at 26 years of age.

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Stem Cell–Based Intervertebral Disc Restoration Table 51.1 Notochordal cell retention in various mammalian species4

Table 51.2 Pros and cons for use of stem cells

Animal

Age at skeletal maturity

Age at loss of notochordal cells

Age at onset of disc degeneration

Embryonic stem cells

Induced pluripotent stem cells

Adult stem cells

Rat

2 mo

12 mo

12 mo

Isolated from embryo at blastocyst stage

Rabbit

6 mo

6 mo

NA

Generated by ectopic expressions of pluripotent genes in primary cells

Isolated from various niches such as bone marrow

Horse

5y

Birth

NA

Cat

2y

18 y

Rare

Human

20 y

10 y

30–50 y

cell pool in DDD.3 Hunter et al4 showed that notochordal cell retention in various mammalian species is lost with age, after which degeneration of the IVD can occur (▶ Table 51.1). A few viable sources of stem cell have been investigated for this purpose, among which mesenchymal stem cells (MSCs) and embryonic stem cells (ESCs) are the most frequently studied (▶ Table 51.2). MSCs are multipotent adult cells derived from bone marrow (called bone marrow stromal cells or BMSCs), adipose tissue (called adipose-derived stem cells or ADSCs), peripheral blood, and the umbilical cord.1 BMSCs and ADSCs are most commonly used for disc restoration. They share many common characteristics in gene expression, developmental pattern, and cell surface profile.5 It remains controversial which of the two is more chondrogenic. ADSCs are more abundant and accessible than BMSCs, but at the same time require a larger sample to yield the same quantity of cells. In contrast with MSCs, ESCs are primitive, pluripotent cells derived from the blastocyst during early development. ▶ Fig. 51.2 illustrates the various fates of an ESC when subjected to patterned biochemical environments. Our group is designing methods to develop chondroprogenitor stem cell lines that can restore the functional capability of the IVD. Our preliminary results show the ability of stem cells to differentiate into a chondrocyte cell line. The immune-modulatory function of MSCs affords another avenue to combat disc degeneration. It is known that DDD is characterized by a cytokine-mediated response that involves classical proinflammatory factors such as interleukin-1 (IL-1), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α).6,7 MSCs are capable of mitigating inflammation by virtue of three mechanisms.8 First, they secrete IL-1 receptor antagonists that directly inhibit the IL-1 signaling cascade. Second, they serve as a relay mediator of a negative feedback loop where MSCs produce antiphagocyte molecules in response to inflammation. These molecules cause macrophages to either deactivate or produce the immunosuppressive interleukin-10 (IL-10). Third, MSCs reduce the generation of reactive oxygen species (ROS), which are critical for inflammation and apoptosis.

51.2.1 In Vitro Studies The harsh IVD microenvironment poses a challenge for cell survival. These unyielding conditions are further accentuated in DDD.2 Due to its avascular structure that provides limited blood supply, the NP is bathed in a hypoxic and low-glucose niche that promotes anaerobic respiration and low pH formation.9 Although NP cells are surprisingly well adapted to living in such

Unlimited self-renewal Unlimited self-renewal Limited self-renewal and differentiation po- but limited differenbut limited differentential into all somatic tiation potential tiation potential cell types Potential to form teratoma

Little or no therapeutic potential due to viral vectors and changes in DNA

Alternative source for tissue engineering and cell therapy

conditions, MSCs demonstrate variable response to different chemical factors. For instance, IVD-like low glucose and hypoxia positively regulate cell viability and ECM deposition in BMSC and ADSC, while high osmolarity and low pH are negative regulators.10,11,12 Therefore, it is believed that predifferentiation of MSC into NP-like cells prior to implantation may be necessary to increase in vivo viability of cell grafts. Despite the difficulty in culturing chondrocyte-like NP cells, they have been successfully differentiated from MSCs with two mainstream methods, growth factors and cell–cell interaction.13 The most commonly used exogenous growth factors in vitro include transforming growth factor-beta (TGF-β), insulinlike growth factor-1 (IGF-1), fibroblast growth factor-2 (FGF-2), platelet-derived growth factor-BB (PDGF-BB), and bone morphogenetic protein-2 (BMP-2).14,15 Other factors such as cis-retinoic acid and ascorbic acid are also used. In addition, growth and differentiation factor-5 (GDF-5) may be more specific for promoting differentiation toward NP cell–like lines.16 Notochordal cell-conditioned medium has been shown to induce MSC differentiation toward a phenotype that is characteristic of earlier NP development stages, including elevated expression of type III collagen (compared with type II collagen in mature NP cells) and sulfated glycosaminoglycans.17 This finding is likely mediated by secreted soluble growth factors yet to be characterized. Differentiation of MSC can also be achieved via cell–cell interactions. When co-cultured with degenerate NP cells, both BMSCs and ADSCs differentiate to acquire NP cell–like traits.18,19 Interestingly, this interaction is reciprocal in that MSCs also enhance self-repair in dysfunctional NP cells via transfer of membrane components, resulting in increased ECM production.20 Via direct cell-to-cell contact, autologous BMSCs can also activate degenerate NP cells from human patients to induce DNA replication, proteoglycan synthesis, and cell proliferation.21

51.2.2 In Vivo Animal Studies A number of animal species have been used in preclinical studies on the effect of stem cell implantation to regenerate IVD tissue. These include rabbits, rats, dogs, sheep, goats, pigs, and mice. Several models of DDD have been proposed using either physical trauma (e.g., needle puncture22) or biochemical lesion (e.g., injection of bromodeoxyuridine23 or protease24). In most of these studies, parametric analysis of disc degeneration was

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Fig. 51.2 The differential potential of stem cells and their therapeutic applications including intervertebral disc regeneration.

based on four factors: disc height index, MRI T2 signal intensity (which reflects water content), production of NP-related products such as type II collagen, and histological disc degeneration grades. Most animal research on stem cell–based disc regeneration focused on BMSCs and only some on ADSCs. The relatively immunoprivileged IVD provides a suitable platform for xenographic implants. In rats, human BMSCs can survive and differentiate into collagen-producing, chondrocyte-like cells.25 Similarly, human ADSC implant following iatrogenic injury to rat IVDs is associated with less pronounced disc degeneration and elevated ECM production compared with injured discs without implantation.26 These findings are reproduced in rabbits and other mammalian species, as well as with use of ESCs.27,28,29 The degeneration-protective effect is accentuated when the cells are injected via a three-dimensional carrier compared with simple suspensory media.30 On the other hand, stem cell grafts have been used as a vehicle to introduce transfected genes into the IVD.31 This raises the possibility of weaving targeted gene therapy into stem cell technology to produce implants with a greater regenerative potential. Recent animal experiments have invoked a more conscientious, minimally invasive approach in eliciting artificial injury in order to recapitulate the slow, progressive disc degeneration in humans.32 In a representative study conducted by our group,28 a novel in vivo percutaneous animal model of disc degeneration was developed by performing needle punctures on healthy, intact

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discs of New Zealand white rabbits (▶ Fig. 51.3). This model reproduced the degenerative disc process that occurs in the human lumbar spine (▶ Fig. 51.4). Interestingly, degenerated discs in humans are seen in the setting of annular tears as illustrated with lumbar discography, making one speculate whether annular tears are responsible for initiating the cascade of disc degeneration (▶ Fig. 51.5). MRIs were obtained preoperatively and at 2, 4, and 8 weeks postoperatively. Before implantation, ESCs were cultured with cis-retinoic acid, TGF-β, ascorbic acid, and insulin growth factor to induce differentiation into a chondrocyte lineage. After MRI was used to confirm the level of disc degeneration, the discs were injected with murine ESCs that were labeled with a mutant green fluorescent protein (GFP). Alcian blue staining and other histologic analyses confirmed that viable chondrogenic progenitor cells existed before implantation. At 8 weeks postimplantation, IVDs were harvested and analyzed by hematoxylin and eosin (H&E) staining, confocal fluorescent microscopy, and immunohistochemical analysis. Three intervertebral test groups were analyzed: group A consisted of control animals with nonpunctured discs; group B consisted of control animals with experimentally punctured discs; and group C consisted of animals with experimentally punctured discs that were subsequently implanted with ESC. MRI confirmed reproducible IVD degeneration after needle punctures of disc segments, starting approximately 2 weeks postoperatively (▶ Fig. 51.3). Postmortem H&E histologic analysis of group A IVDs showed chondrocytes but no notochordal cells.

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Stem Cell–Based Intervertebral Disc Restoration

Fig. 51.3 (a) An in vivo rabbit model was developed for creating intervertebral disc degeneration using a novel, lateral fluoroscopicguided needle percutaneous technique to access the disc space through Kambin’s triangle. (b) Lateral view. (c,d) Anteroposterior views.27

Fig. 51.4 Comparative MRIs seen in (a) human sagittal MRI with L5–S1 degenerative disc with posterior annular tear and (b) sagittal rabbit MRI showing two-level disc degeneration (yellow lines). Axial MRIs showing induced degeneration (“dark disc”) in a (c) rabbit induced by disc needle puncture compared with (d) degenerated human disc having an annular tear (blue arrow).

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Fig. 51.5 (a) CT after lumbar discography of L3– L4, L4–L5, and L5–S1 disc levels showing intact L3–L4 disc. Annular tears with posterior egress of dye are seen in the (b) L4–L5 and (c) L5–S1 disc consistent with disc degeneration.

Group B discs displayed intact AF and generalized disorganized fibrous tissue of the NP. Group C discs showed new notochordal cell growth. Fluorescent microscopic analysis was negative for groups A and B, but positive for group C tissue. These results confirmed the viability of implanted GFP-labeled ESCs within the injected IVD. In addition, the notochordal cells in group C– implanted NP stained positive for cytokeratin and vimentin, giving further evidence of their chondrocytic origin. Notably, cell-mediated immune response was not observed in group C animals. Our study revealed a novel, reproducible model for the study of disc degeneration.28 New notochordal cell populations were seen in ESC-injected degenerated discs. The lack of an immune response to xenograft-implanted mouse stem cells in an immune-competent rabbit suggested an immunoprivileged site within the IVD space. Although preliminary, this study highlighted the possible use of stem cells to promote IVD regeneration. Further ongoing studies are probing the genetic processes that occur during ESC differentiation of chondrogenic cell lines that may be useful for new disc formation.

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Conclusions Reached Based on Stem Cell Study28 ●

●

●

●

●

●

A DDD model was established in a rabbit using a novel percutaneous technique that preserves the integrity of the nucleus pulposus. This model can be used to investigate both the underlying pathophysiology of DDD and various disc regenerative strategies. MRI and histological studies demonstrated that murine embryonic–derived chondrogenic progenitor cells can integrate and remain viable in degenerated discs. Implanted chondrogenic progenitor stem cells can form into new disc material in the degenerated rabbit discs. The lack of an immune response to the xenograft suggests that the intervertebral disc space is an immunologically privileged site and could serve as a place for xenograft transplantation. The result of this study points to the future of biologic treatment of DDD for restoration of intervertebral disc function.

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Stem Cell–Based Intervertebral Disc Restoration

Fig. 51.6 In vitro differentiation of mesenchymal stem cells into nucleus pulposus cells. (a–f) Morphological analysis by phase contrast microscopy. Nucleus pulposus (diabetes mellitus) induced cells expressed higher levels of extracellular matrix proteins (glycosaminoglycans [GAGs]. and proteoglycans) and chondrogenic (nucleus pulposus genes).

Umbilical cord blood (UCB) was initially recognized for its therapeutic potential over 30 years ago. In 1980, UCB stem cells were used to treat a child with Fanconi’s anemia in France. Since then, UCB stem cells have been investigated for other clinical uses. Our interest is to investigate their efficacy in the application to IVD regeneration. We have also recognized that UCB stem cells can be further differentiated toward a chondroprogenitor cell line and that these cells may ultimately be the best candidates for disc regenerative therapies (see text box below and ▶ Fig. 51.6). Our investigation involves UCB chondroprogenitor cells injected into the degenerative disc of rabbits13,33,34,35 (▶ Fig. 51.7).

Umbilical Cord Blood as a Source of Stem Cells for Therapeutic Use13,33,34,35 Umbilical cord blood was initially recognized for its therapeutic potential more than 30 years ago: ● UCB stem cells were used to treat a child in France with Fanconi’s anemia in 1980. ● Today, cord blood is used for the treatment of more than 80 life-threatening diseases, including a wide range of cancers, genetic disease, immune system deficiencies, and blood disorders.

Sagittal T2-weighted MRI images before and 8 weeks after implantation of umbilical cord chondroprogenitor cells show preservation of NP in stem cell–implanted disc compared to

continued disc degeneration seen in the punctured nonimplanted disc, thus validating the potential of these cells to restore the integrity of the NP (▶ Fig. 51.8). Further histologic analysis was conducted using H&E-stained sections of harvested rabbit disc showing control disc, punctured disc, and punctured disc implanted with either mesenchymal UCB stem cells or differentiated chondroprogenitor cells. The most improved cellularity and extracellular matrix were observed in punctured disc implanted with UCB chondroprogenitor cells (▶ Fig. 51.9). Several theoretical limitations exist for animal studies. First, the non-weight-bearing spine of quadrupeds functions under much lower mechanical strain than that of upright humans. The high-pressure IVD system in humans, particularly the lumbar segment where IVD degeneration tends to occur, can present very different findings with in vivo implantation of stem cells. Second, there exists a large disparity in the developmental profiles of different mammalian species. For instance, loss of notochordal cells occurs before skeletal maturity in humans, whereas the opposite is true for rats, and both occur at the same age for rabbits.36 It is unclear how this difference affects chondrogenicity. Finally, Wang et al29 noted the high heterogeneity across previous animal studies, suggesting significant risk of bias. These issues must be carefully evaluated before data from animal studies can be applied to clinical trials. Notwithstanding the difficulty of benchside-to-bedside translation, a few pilot clinical studies on human patients have taken place and are discussed in the following sections.

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Fig. 51.7 In vivo rabbit animal model of disc degeneration used to test the capability of umbilical cord stem cells to regenerate intervertebral disc.44

Fig. 51.8 Sagittal T2-weighted MRI images of (a) preoperative rabbit, (b) 2 weeks after disc puncture and preimplantation of umbilical cord stem cells, and (c) 6 weeks after chondroprogenitor cell (i.e., nucleus pulposus cells) showing regeneration of the nucleus pulposus in stem cell–implanted disc (green arrow) compared to disc degeneration seen in the punctured nonimplanted disc (red arrow).

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Stem Cell–Based Intervertebral Disc Restoration

Fig. 51.9 Hematoxylin- and eosin-stained sections of harvested rabbit disc showing (a) control disc, (b) punctured disc, (c) mesenchymal umbilical cord stem cell–injected disc with relative cellular preservation, and (d) chondroprogenitor (i.e., nucleus pulposus) injected cells showing improved cellularity and extracellular matrix.44

51.2.3 Human-Subject Studies While stem cell research aimed at restoring the IVD garners generally favorable outcomes from animal models, only a few clinical trials have been carried out to date in human patients. These intriguing clinical studies have yielded conflicting but promising results. The first report was published in 2006.37 It was based on 10 patients who voluntarily opted for stem cell therapy after discectomy had failed. Autologous bone marrow aspirate was directly injected into the symptomatic disc levels as identified by discography. The patients were then placed under movement restriction and hyperbaric oxygen in an attempt to overcome the hypoxic environment. Visual analog scale (VAS) scores for pain measurement at 1-year postoperative follow-up revealed no pain improvement in any patient (0%). Due to poor outcomes, the majority of these patients eventually underwent fusion or artificial disc replacement surgeries. It is noteworthy that this study used raw bone marrow material instead of cultured cells. Also, the effect of hyperbaric oxygen may have been counterproductive as hypoxia has been shown to induce chondrogenic differentiation of MSC.10,11 Four years later, a Japanese team performed a stem cell implant into two patients diagnosed radiographically and clinically with

DDD.38 In this case, iliac bone marrow aspirate was centrifuged with the aim to isolate BMSCs, which were then incubated in a controlled setting. The culture was not passaged or expanded. After 2 to 4 weeks of growth, cells were delivered via collagen sponge carriers through a small incision. Flexible corsets and physical rehabilitation were used after surgery with no oxygen support. VAS scores showed marked decrease from original values, and both symptomatic and functional improvements were seen at least 2 years postoperatively. An increased IVD water content was found on T2-weighted MRI. The authors reported improvement of the vacuum phenomenon that had been observed in both patients before surgery. Disc height was not evaluated. In 2011, a Spanish group reported a 10-patient series treated with autologous BMSC injection.39 These patients had reportedly undergone conservative treatments for DDD without avail. Stem cells were cultured from bone marrow aspirates and expanded by passaging three times. Undifferentiated BMSCs were confirmed by flow cytometry and morphology prior to implantation. Both VAS and Oswestry Disability Index (ODI) scores decreased rapidly and significantly in the initial 3 months and remained low after 12 months. Short Form-36 Physical Component Score (SF-36 PCS) also improved significantly, although the Mental Component Score (SF-36 MCS) showed a slight decrease.

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Future Considerations IVD water content increased postsurgically despite unchanged disc height. Taken together, these studies demonstrate potential for clinical application of the aforementioned animal experiments. Yoshikawa et al38 and Orozco et al39 successfully correlated radiographic findings with clinical outcome. Culture expansion of harvested stem cells with subsequent delivery through organic carriers is perhaps the optimal consideration for future trials. However, with postoperative follow-ups of no more than 2 years, the long-term benefit and safety of this method are yet to be tested.

51.3 Disc Distraction and Stem Cell Implant The concept of disc distraction is based on the observation that many physical parameters such as intradiscal pressure and load distribution are altered along with biologic changes in DDD. Animal studies show that distraction alone restores these parameters, resulting in ECM production, disc rehydration, and apoptosis inhibition.40,41 The only study to date using a combination of mechanical distraction and BMSC implantation was performed on a small number of rabbits.42 The results showed similar benefits compared with control, although the combination method was not convincingly different from the distraction-only group or the BMSC-only group. Nevertheless, preclinical research in orthopaedic and plastic surgery has demonstrated success in enhancing bone formation histochemically and biomechanically using distraction osteogenesis with stem cell supplementation.43,44 The similarities between bone and the cartilaginous IVD render it reasonable to generalize these results. Even though no data are presently available pertaining to IVD regeneration, future research is warranted to determine the efficacy of mechanical restoration of disc height in conjunction with stem cell graft.

51.3.1 The Annulo Concept New devices such as the Annulo system (MI4Spine LLC, Bloomfield, MI) are in place for translation of nonhuman research into clinical trials. Using the concept of distractive force to restore

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long bone length and integrity developed by Ilizarov, the Annulo system was developed45 (▶ Fig. 51.10 and ▶ Fig. 51.11). The Annulo device is a pedicle screw–based disc distractive device that causes distraction between two or more opposing vertebrae. Over time, the degenerated collapsed disc height is restored. Once the disc height is restored, stem cell–based chondroprogenitor (i.e., NP) cells can be injected into the NP, thus regenerating the NP. The intent of Annulo technology is to restore the biologic integrity of degenerated disc. This proprietary technology is currently in development and will require clinical studies to validate its efficacy33 (▶ Fig. 51.12, ▶ Fig. 51.13).

51.4 Conclusion The vast regenerative potential of stem cells originates in its physiological role in a natural setting. Harnessing this unique ability by artificial means represents a crucial step toward a biologic approach to treating diseases of the degenerate IVD. A great deal of basic science research has paved the way to understanding the behavior of stem cell grafts both in vitro and in vivo. Current evidence converges on the consensus that stem cells are capable of restoring the biochemical, biomechanical, histological, and functional properties of the IVD. Notably, a few human clinical trials have also been undertaken with preliminary but promising results. The safety of this approach is yet to be determined through randomized controlled trials. Nonetheless, the medical world is prepared to welcome an exciting array of future endeavors into the utility of stem cell–based treatment for IVD disorders.

Clinical Caveats ●

Biological intervertebral disc regeneration remains a laudable goal to achieve long-term treatment for a variety of degenerative disc conditions. In order for it to become a reality, advances in basic science will need to be tested and validated in the clinical setting. Nevertheless, this is an exciting forefront in the development of advanced stem cell–based treatments for spinal disorders.

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Stem Cell–Based Intervertebral Disc Restoration

Fig. 51.10 (a) Ilizarov device with (b) X-ray image showing placement and (c) distraction can lead to long bone elongation by applying distractive force to bone over time. This technique is used to restore the length of injured long bones.

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Future Considerations

Fig. 51.11 (a,b) Annulo device (MI4Spine LLC) was developed to apply pedicle screw–based gradual, length-limited distraction to the intervertebral disc space.

Fig. 51.12 Annulo device used to apply gradual distractive forces to the degenerative disc. (a) The device. (b) Chondroprogenitor cells postimplantation. (c) Stem cell cultivation. (d) Device postexpansion. (Reproduced with permission from Sheikh H, Zakharian K, Perez De La Toree R, et al. In vivo intervertebral disc regeneration using stem cell-derived chondroprogenitors. J of Neurosurgery (Spine). 2009;10:265-272.)

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Stem Cell–Based Intervertebral Disc Restoration

Fig. 51.13 (a–c) Once disc height is restored, chondroprogenitor cells can be injected to restore the integrity of the degenerated nucleus pulposus. It is hypothesized that this technique could potentially lead to intervertebral disc regeneration as illustrated in (d) sagittal MRI showing marked degenerated disc to (e) restored disc integrity.

References [1] Gilbert HT, Hoyland JA, Richardson SM. Stem cell regeneration of degenerated intervertebral discs: current status (update). Curr Pain Headache Rep. 2013; 17(12):377 [2] Singh K, Masuda K, Thonar EJ, An HS, Cs-Szabo G. Age-related changes in the extracellular matrix of nucleus pulposus and anulus fibrosus of human intervertebral disc. Spine. 2009; 34(1):10–16 [3] Gou S, Oxentenko SC, Eldrige JS, et al. Stem cell therapy for intervertebral disk regeneration. Am J Phys Med Rehabil. 2014; 93(11) Suppl 3:S122–S131 [4] Hunter CJ, Matyas JR, Duncan NA. Cytomorphology of notochordal and chondrocytic cells from the nucleus pulposus: a species comparison. J Anat. 2004; 205(5):357–362 [5] Rada T, Reis RL, Gomes ME. Adipose tissue-derived stem cells and their application in bone and cartilage tissue engineering. Tissue Eng Part B Rev. 2009; 15(2):113–125 [6] Bachmeier BE, Nerlich AG, Weiler C, Paesold G, Jochum M, Boos N. Analysis of tissue distribution of TNF-alpha, TNF-alpha-receptors, and the activating TNF-alpha-converting enzyme suggests activation of the TNF-alpha system in the aging intervertebral disc. Ann N Y Acad Sci. 2007; 1096:44–54 [7] Le Maitre CL, Hoyland JA, Freemont AJ. Catabolic cytokine expression in degenerate and herniated human intervertebral discs: IL-1beta and TNFalpha expression profile. Arthritis Res Ther. 2007; 9(4):R77 [8] Prockop DJ, Oh JY. Mesenchymal stem/stromal cells (MSCs): role as guardians of inflammation. Mol Ther. 2012; 20(1):14–20 [9] Shoukry M, Li J, Pei M. Reconstruction of an in vitro niche for the transition from intervertebral disc development to nucleus pulposus regeneration. Stem Cells Dev. 2013; 22(8):1162–1176 [10] Felka T, Schäfer R, Schewe B, Benz K, Aicher WK. Hypoxia reduces the inhibitory effect of IL-1beta on chondrogenic differentiation of FCS-free expanded MSC. Osteoarthritis Cartilage. 2009; 17(10):1368–1376 [11] Wuertz K, Godburn K, Neidlinger-Wilke C, Urban J, Iatridis JC. Behavior of mesenchymal stem cells in the chemical microenvironment of the intervertebral disc. Spine. 2008; 33(17):1843–1849 [12] Liang C, Li H, Tao Y, et al. Responses of human adipose-derived mesenchymal stem cells to chemical microenvironment of the intervertebral disc. J Transl Med. 2012; 10:49 [13] Beeravolu N, Brougham J, Khan I, McKee C, Perez-Cruet M, Chaudhry GR. Human umbilical cord derivatives regenerate intervertebral disc. J Tissue Eng Regen Med. 2018; 12(1):e579–e591 [14] Ehlicke F, Freimark D, Heil B, Dorresteijn A, Czermak P. Intervertebral disc regeneration: influence of growth factors on differentiation of human mesenchymal stem cells (hMSC). Int J Artif Organs. 2010; 33(4):244–252

[15] Shen B, Wei A, Tao H, Diwan AD, Ma DD. BMP-2 enhances TGF-beta3-mediated chondrogenic differentiation of human bone marrow multipotent mesenchymal stromal cells in alginate bead culture. Tissue Eng Part A. 2009; 15 (6):1311–1320 [16] Stoyanov JV, Gantenbein-Ritter B, Bertolo A, et al. Role of hypoxia and growth and differentiation factor-5 on differentiation of human mesenchymal stem cells towards intervertebral nucleus pulposus-like cells. Eur Cell Mater. 2011; 21:533–547 [17] Korecki CL, Taboas JM, Tuan RS, Iatridis JC. Notochordal cell conditioned medium stimulates mesenchymal stem cell differentiation toward a young nucleus pulposus phenotype. Stem Cell Res Ther. 2010; 1(2):18 [18] Strassburg S, Richardson SM, Freemont AJ, Hoyland JA. Co-culture induces mesenchymal stem cell differentiation and modulation of the degenerate human nucleus pulposus cell phenotype. Regen Med. 2010; 5(5):701–711 [19] Sun Z, Liu ZH, Zhao XH, et al. Impact of direct cell co-cultures on human adipose-derived stromal cells and nucleus pulposus cells. J Orthop Res. 2013; 31 (11):1804–1813 [20] Strassburg S, Hodson NW, Hill PI, Richardson SM, Hoyland JA. Bi-directional exchange of membrane components occurs during co-culture of mesenchymal stem cells and nucleus pulposus cells. PLoS One. 2012; 7 (3):e33739 [21] Watanabe T, Sakai D, Yamamoto Y, et al. Human nucleus pulposus cells significantly enhanced biological properties in a coculture system with direct cellto-cell contact with autologous mesenchymal stem cells. J Orthop Res. 2010; 28(5):623–630 [22] Sobajima S, Kompel JF, Kim JS, et al. A slowly progressive and reproducible animal model of intervertebral disc degeneration characterized by MRI, Xray, and histology. Spine. 2005; 30(1):15–24 [23] Zhou H, Hou S, Shang W, et al. A new in vivo animal model to create intervertebral disc degeneration characterized by MRI, radiography, CT/discogram, biochemistry, and histology. Spine. 2007; 32(8):864–872 [24] Hoogendoorn RJ, Wuisman PI, Smit TH, Everts VE, Helder MN. Experimental intervertebral disc degeneration induced by chondroitinase ABC in the goat. Spine. 2007; 32(17):1816–1825 [25] Wei A, Tao H, Chung SA, Brisby H, Ma DD, Diwan AD. The fate of transplanted xenogeneic bone marrow-derived stem cells in rat intervertebral discs. J Orthop Res. 2009; 27(3):374–379 [26] Jeong JH, Lee JH, Jin ES, Min JK, Jeon SR, Choi KH. Regeneration of intervertebral discs in a rat disc degeneration model by implanted adipose-tissue-derived stromal cells. Acta Neurochir (Wien). 2010; 152(10):1771–1777 [27] Cai F, Wu XT, Xie XH, et al. Evaluation of intervertebral disc regeneration with implantation of bone marrow mesenchymal stem cells (BMSCs) using quantitative T2 mapping: a study in rabbits. Int Orthop. 2015; 39(1):149–159

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Future Considerations [28] Sheikh H, Zakharian K, De La Torre RP, et al. In vivo intervertebral disc regeneration using stem cell-derived chondroprogenitors. J Neurosurg Spine. 2009; 10(3):265–272 [29] Wang Z, Perez-Terzic CM, Smith J, et al. Efficacy of intervertebral disc regeneration with stem cells - a systematic review and meta-analysis of animal controlled trials. Gene. 2015; 564(1):1–8 [30] Henriksson HB, Svanvik T, Jonsson M, et al. Transplantation of human mesenchymal stems cells into intervertebral discs in a xenogeneic porcine model. Spine. 2009; 34(2):141–148 [31] Sobajima S, Vadala G, Shimer A, Kim JS, Gilbertson LG, Kang JD. Feasibility of a stem cell therapy for intervertebral disc degeneration. Spine J. 2008; 8 (6):888–896 [32] Subhan RA, Puvanan K, Murali MR, et al. Fluoroscopy assisted minimally invasive transplantation of allogenic mesenchymal stromal cells embedded in HyStem reduces the progression of nucleus pulposus degeneration in the damaged intervertebral [corrected] disc: a preliminary study in rabbits. Sci World J. 2014; 2014:818502 [33] Beeravolu N, McKee C, Alamri A, et al. Isolation and characterization of mesenchymal stromal cells from human umbilical cord and fetal placenta. J Vis Exp. 2017; 3(122) [34] Beeravolu N, Khan I, McKee C, et al. Isolation and comparative analysis of potential stem/progenitor cells from different regions of human umbilical cord. Stem Cell Res (Amst). 2016; 16(3):696–711 [35] McKee C, Perez-Cruet M, Chavez F, Chaudhry GR. Simplified three-dimensional culture system for long-term expansion of embryonic stem cells. World J Stem Cells. 2015; 7(7):1064–1077 [36] Hunter CJ, Matyas JR, Duncan NA. The notochordal cell in the nucleus pulposus: a review in the context of tissue engineering. Tissue Eng. 2003; 9(4):667–677

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[37] Haufe SM, Mork AR. Intradiscal injection of hematopoietic stem cells in an attempt to rejuvenate the intervertebral discs. Stem Cells Dev. 2006; 15 (1):136–137 [38] Yoshikawa T, Ueda Y, Miyazaki K, Koizumi M, Takakura Y. Disc regeneration therapy using marrow mesenchymal cell transplantation: a report of two case studies. Spine. 2010; 35(11):E475–E480 [39] Orozco L, Soler R, Morera C, Alberca M, Sánchez A, García-Sancho J. Intervertebral disc repair by autologous mesenchymal bone marrow cells: a pilot study. Transplantation. 2011; 92(7):822–828 [40] Kroeber M, Unglaub F, Guehring T, et al. Effects of controlled dynamic disc distraction on degenerated intervertebral discs: an in vivo study on the rabbit lumbar spine model. Spine. 2005; 30(2):181–187 [41] Guehring T, Omlor GW, Lorenz H, et al. Disc distraction shows evidence of regenerative potential in degenerated intervertebral discs as evaluated by protein expression, magnetic resonance imaging, and messenger ribonucleic acid expression analysis. Spine. 2006; 31(15):1658–1665 [42] Hee HT, Ismail HD, Lim CT, Goh JC, Wong HK. Effects of implantation of bone marrow mesenchymal stem cells, disc distraction and combined therapy on reversing degeneration of the intervertebral disc. J Bone Joint Surg Br. 2010; 92(5):726–736 [43] Earley M, Butts SC. Update on mandibular distraction osteogenesis. Curr Opin Otolaryngol Head Neck Surg. 2014; 22(4):276–283 [44] Ma D, Ren L, Yao H, et al. Locally injection of cell sheet fragments enhances new bone formation in mandibular distraction osteogenesis: a rabbit model. J Orthop Res. 2013; 31(7):1082–1088 [45] Ilizarov GA, Deviatov AA. Surgical elongation of the leg. Ortop Travmatol Protez. 1971; 32(8):20–25

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Index Note: Page numbers set bold or italic indicate headings or figures, respectively.

A abdominal wall 388, 389–390 ACDF, see anterior cervical discectomy and fusion (ACDF) Acroflex artificial lumbar disc 442 action research 524 Activ-L artificial lumbar disk 444 adult spinal deformity (ASD) correction, minimally invasive 266 – ASD definition 266 – clinical case 272, 273 – clinical caveats 273 – closure 272 – indications and contraindications 266 – introduction 266 – management of complications 272 – percutaneous pedicle screw and rod placement 271 –– See also percutaneous pedicle screw fixation (PPSF) –– patient positioning 271 –– step-by-step surgical technique 271, 271, 272 – postoperative care 272 – preoperative planning 266 –– instrumentation 268 –– physical examination 266 –– preexisting fusion between spinal segments 267, 268 –– radiographic workup and preoperative imaging 266, 267 – surgical approach and algorithm 268 –– stage 1 268, 269 –– stage 2 268 – surgical technique 268 – transpsoas discectomy and fusion 268 –– closure 271 –– incision 270, 270 –– patient positioning 268, 269 –– step-by-step surgical technique 270 advertising, targeted 110 aggrecan 43 airway obstruction, in transoral approach to CCJ 187 alar ligaments 18, 33 ALIF, see anterior lumbar interbody fusion (ALIF) ALL, see anterior longitudinal ligament (ALL) ambulatory spine surgery centers 93 – ambulatory procedures performed in U.S. 94, 94 – benchmarks of success 94 – evolution of 93 – features and design 106 – financial projections 111 –– competition affecting 111 –– risks for stakeholders 111 – introduction 93 – keys to success 98 –– benchmarks and statistics 102

–– communication systems 104 –– personnel recruitment and management 102 –– philosophy of care 98 –– staffing 101, 101 – marketing, see marketing of outpatient spine surgery services – medical procedures 107 – minimally invasive surgery suite, furnishing 95 – patient benefits 97, 99–100 – payment relationships with insurance companies 107 –– bundled fees 97, 108 –– competitive pricing 94, 108 –– payment methodologies 108 –– preapproval of surgical procedures 108 – physician benefits 97 –– part-time office space 98, 106 –– simplification of paperwork 97 –– standardized pre- and postoperative order forms 97, 98 –– surgeon’s expectations 97 – procedures suitable for 93 – prototype facilities 111 – regulatory considerations 108 –– Certificate of Need requirements 108 –– licensure and certification 109 –– relationships among health care service providers 109 –– Safe Harbor requirements 109, 114 –– Stark Regulations on referrals for designated health services 110, 115 – services of 107 – staff testing of equipment and layout 96 – trend toward outpatient surgery 96 American Spinal Injury Association Impairment Scale 520 anatomy of spine 12 – See also specific spinal structures – components 12 – considerations for minimally invasive surgery 26 – curvatures 12, 28 – embryonic development 12 – facet joints 31, 31 – intervertebral discs 17 – introduction 12 – ligaments 17, 31 – mechanical properties 30 – muscles 19 – normal structure 12 – osseous structures 30 – vertebrae and surrounding structures 13, 30 ancillary services 113 – Anti-Kickback Statute 113 – introduction 113 – physician-owned distributorships 117 – regulatory considerations 117 – Safe Harbor regulations affecting 114 – Stark Laws exceptions for in-office services 115 – types of 113 anesthetics and anesthesia

– intraoperative neuromonitoring and 146–147 –– EMG/MMG requirements 146 –– physiologic monitoring 147 –– successful management of 147 –– train-of-four twitch test 146 – pharmacology, local anesthetics 152, 152 aneurysmal bone cyst 490, 490, 494, 494 anisotropy 30 ankylosing spondylitis 214 annular tears, posterior 312 Annulo system 546, 547–549 annulotomy 208, 210, 327, 330 annulus fibrosis 17, 39, 40, 538 anterior cervical discectomy and fusion (ACDF) – annulotomy in 208, 210 – autograft in 207, 211–212 – avoiding complications 209, 530 – clinical cases 209 – clinical caveats 211 – closure 208 – comparison with cervical arthroplasty 213 – complications 213 – endoscopy-assisted 57 – indications for 207 – interbody implants 208, 210 – introduction 207 – osteophyte removal 208, 210 – preoperative planning 207 – surgical instrumentation 207, 208 – surgical technique 207, 209–210 anterior cervical discectomy with arthroplasty (ACDA) – clinical case 219 –– examination 219 –– imaging 219, 219, 220 –– presentation 219 –– treatment and outcome 221, 221 – clinical caveats 221 – comparison with ACDF 213 – contraindications 213 – evolution of technique 213 – indications 213 – instrumentation 214 – introduction 213 – management of complications 219 – postoperative care 218 – preoperative planning 214 – surgical technique 214 –– closure 218 –– decompression 217, 218 –– device implantation 217, 217, 218– 219 –– discectomy and endplate preparation 215, 216–217 –– exposure 214, 215–216 –– positioning 214 anterior longitudinal ligament (ALL) 15, 17, 19, 31 anterior lumbar interbody fusion (ALIF) 362 – advantages of 362, 362 – avoiding complications 534 – clinical case 367, 367 – clinical caveats 368

– comparison with other interbody fusion techniques 363 – contraindications 363 – development of 6 – disadvantages 363 – indications 363 – instrumentation 365 – internal fixation with 366 – introduction 362 – management of complications 366 –– retrograde ejaculation 363, 366, 534 –– vascular injuries 366, 534 – postoperative care 366 – preoperative planning 363 – presacral approach vs. 407 – surgical approach 364 –– laparoscopic 364 –– mini-open retroperitoneal 364 – surgical technique 364, 364, 365 anterior thoracoscopic sympathectomy, see thoracoscopic sympathectomy, anterior anterior triangle of neck 22 Anti-Kickback Statute (Medicare and Medicaid) 113 – civil and criminal penalties 114 – prohibiting payments for referrals 113 – provisions of 113 – Safe Harbor regulations 114 APD (automated percutaneous discectomy) 6, 532 apical ligament 18 artificial lumbar discs 440 – advantages vs. lumbar fusion 440 – design 441, 442 –– See also names of individual devices –– base material problems 442 –– biomechanical requirements 441 –– categories of 441 –– devices completing FDA IDE trials 441 –– discs completing FDA clinical trials 441 –– dynamic stabilization devices 442 –– types of 441 ASD, see adult spinal deformity (ASD) correction, minimally invasive astrocytoma 506 – incidence 506 – treatment 506 – types of 506 atlanto-occipital membrane 181 atlas (craniocervical junction) 181 automated percutaneous discectomy (APD) 6, 532 axial (transverse) plane 27, 28 axial lumbar interbody fusion (AxiaLIF) 6, 406, 406, 407 axis (craniocervical junction) 181 axis of rotation, Instantaneous (IAR) 27

B back pain, see low back pain – anatomy of nociceptors 49, 51 – benign spinal tumors and 488 – clinical caveats 52 – deep somatic pain 52

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Index – descending pathways, central nervous system 51 – discogenic back pain 39 –– introduction 39 –– pathophysiology 43 –– surgical treatment 44 – introduction 49 – nerve root/dorsal root ganglion compression 52, 53 – pathophysiology 49 – peripheral pain mechanisms 49 – physiology 52 – radicular pain 52, 54–55 – spinal cord and supraspinal structures 50 Bagby basket 362 benchmarks – clinical 103 – growth 104 – operational 102 – revenue cycle 103 benign spinal tumors, see spinal tumors, benign bicycle test (claudication) 341 biomechanics of spine 27 – Cartesian coordinate system 27, 27 – coronal and sagittal balance 27 – functional spine unit 27 – instantaneous axis of rotation (IAR) 27 – intervertebral discs 36 – introduction 27 – ligamentous structures 31 – lumbosacral angle 17, 28, 29 – motion, types of 27, 28 – muscular structures 33 – normal curvature of spine 28 – osseous structures 30 – pelvic tilting 28, 29 – principles of 27 – rib cage and 35 – sagittal balance 29, 29 – spinal mobility 36 – spinal stability schemes 34 biopsy 492 bone cyst, aneurysmal 490, 490, 494, 494 bone morphogenetic proteins (BMPs) 7 bone scans 492 bone scintigraphy 492 BoneBac Press – for lumbar microdiscectomy 325, 325 – in transforaminal lumbar interbody fusion 382, 383, 383 bundled fees 97, 108 bupivacaine 152, 152

C cadaveric training 71, 72 Cancer Patient Fracture Evaluation (CAFE) study 66 carotid triangle 23 Cartesian coordinate system (biomechanics) 27, 27–28 case reports (research method) 523 case series (research method) 523 case-control study 523 caudal epidural injections 155, 156 CCJ, see craniocervical junction (CCJ) central nervous system (CNS) 51

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central stenosis 340 cerebrospinal fluid leaks 236 Certificate of Need programs 108 – as ambulatory spine surgery center risk factor 111 – competition affecting 111 cervical arthroplasty 93, 213 – See also anterior cervical discectomy with arthroplasty (ACDA) cervical disc herniation (case study) 226 cervical foraminotomy, minimally invasive – anterior –– avoiding complications 528 –– development of 4 – case study 223 –– case selection 223 –– complications 224 –– operative nuances 224 –– patient profile 223, 223 –– preoperative notes 223 –– surgical approach and technique 223 – clinical outcome 58 – posterior, see posterior cervical microforaminotomy and discectomy (MF/D) cervical spine – anatomy and pathophysiology 198 – lordotic curvature 199 – spinal artery 198 – spinal cord diameter 198 Cervical Spine Outcomes Questionnaire (CSOQ) 519 cervical spine surgery – advancements in 3 –– anterior cervical foraminotomy 4 –– artificial disk and motion preservation 4 –– internal fixation devices 3–4 –– minimally invasive procedures 4 – anterior discectomy and fusion 207 –– See also anterior cervical discectomy and fusion (ACDF) – arthroplasties, see anterior cervical discectomy with arthroplasty (ACDA), cervical arthroplasty – avoiding complications –– anterior cervical discectomy and fusion 530 –– anterior cervical foraminotomy 528 –– minimally invasive posterior cervical laminoforaminotomy 528, 529 – computer navigational guidance 133, 134 –– anterior insertion of odontoid screw 134 –– anterior vertebrectomies 134 – minimally invasive approaches 57 –– anterior 57 –– case studies 223 –– evolution of 223 –– posterior 58, 197 –– posterior microforaminotomy and discectomy (MF/D) 191 – surgical approach, choice of 199 cervical spondylosis – differential diagnosis 197, 198 – incidence and manifestations 197, 197 – treatment options 198 cervical vertebrae 13

– angulation of facet joints 13, 14 – atlas (C1) 13, 13 – facets, C1-C2 13 – morphology 13 – pedicles 13 – subaxial 13, 14 – transverse processes 14, 14–15 Chamberlain’s line 182, 183 CHARITÉ artificial disc 444, 445 – base metal sizes and endplate angles 446–447 – biomechanics 458, 462 – clinical studies 444 – FDA approval for marketing 441, 445 – FDA study limited to one-level disease 448, 448 – long-term follow-up and patient outcomes 444 – outcomes for disc revision 456 – preservation of normal motion 447, 447 – revision techniques 456 CHARITÉ artificial disc, outcomes for disc revision 461 checklist for clinical instability (Whie and Panjabi) 35 chemonucleolysis 6 chlorhexidine gluconate 153 chymopapain 71 clinical benchmarks 103 clinical guidelines 526 clinical options, as practice policy 526 clinical outcome analyses 516 – criteria for standardized outcomes assessment 516 – ethical considerations 524 – health status instruments, classification of 516 –– conditions and outcome measurement tools 517, 517 –– critical analyses models 517, 518 –– types of outcome measures 516, 517 – interpretation of evidence 524 – introduction 516 – levels of evidence 519, 520, 525 – methodological issues 520 – outcome assessment instruments 518 – qualitative research methods 523 – quantitative research designs 521, 522 – standards, guidelines, and options 525 – types of research 520, 520 clinical policies and levels of certainty 526 clinical target volume (CTV) 171 Cobb angle – in spinal deformity algorithm 74 – lumbar spine deformity 30 – minimally invasive ASD correction and 266, 266, 267 coccyx 17 cohort study 523 collagen 43 compression (translational motion) 27 computer navigation in spine surgery 128 – advantages 129, 135 – clinical caveats 136 – image acquisition 130 – introduction 128

– limitations 136 – navigational applications 133 –– cervical spine 133, 134 –– lumbar spine 135 –– thoracic spine 134, 135 – navigational concepts 128 – navigational space 128 – reference points 129 – surgical procedure 130 –– imaging procedure 129, 131, 132 –– patient position 132 –– pedicle screw placement 132, 132, 133 –– preoperative preparation 130 –– system placement 129, 131, 131 – visualizing surgical space in realtime environment 130 computer-assisted patient education 90 concentric contractions 33 concordant pain 44, 44 congenital stenosis, definition 340 constipation management, postoperative 91 contrast agents 153 coronal (frontal) plane 27, 28 corpectomy 65, 208 corticosteroids 152 costotransverse joints 36 costotransversectomy 531 costovertebral joints 36 costs and cost analysis, minimally invasive surgery 94 coupled motions 37, 37 craniocervical junction (CCJ) – anatomy 181, 181 –– C1-C2 182 –– occipital-C1 181 –– relative, in approach to 182, 183 – approaches to 181 – clinical caveats 189 – pathology 182, 183 – transnasal approach 187, 187 –– complications 188 –– preoperative planning 187 –– technique 187, 188 – transoral approach 184, 184 –– anatomy 184 –– clinical case 188, 189 –– complications 187 –– extended transoral exposure 185 –– retractor of tongue and mandible 184 –– technique 184, 184, 185–186 cremaster muscle 390 cross-sectional surveys 523 crossover design, randomized controlled trials 521 cruciform ligament 18, 33

D da Vinci robotic surgical system 290, 290 – See also robotic-assisted thoracic spine surgery, minimally invasive (MARSS) – anterior approach to spinal tumors 294, 295 – contraindications 290 – for schwannoma resection 292 – technical advantages 296 – training for 295

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Index DDD, see degenerative disc disease (DDD) decompression, anterior, and expandable cage reconstruction (case study) – case selection 227 – instrumentation notes 227 – management of complications 228 – operative nuances 228 – patient profile 227, 228 – postoperative care 228 – preoperative notes 227, 228 – surgical approach and technique 228 decompression, cervical (case study) 224 – case selection 224 – operative nuances 225 – patient profile 224, 224 – postoperative results 225 – preoperative notes 224 – surgical approach and technique 224 decompression, posterior cervical spine 58, 58 degenerative disc disease (DDD) – animal model 42 – anterior lumbar interbody fusion for 363 – L4–S1, trans-sacral approach to lumbar fusion (clinical case), 412, 414 – stem cell therapy 538 –– Annulo concept 546, 547–549 –– disc distraction and stem cell implant 546 –– human-subject studies 545 –– in vitro studies 539 –– in vivo animal studies 539, 541– 544 –– umbilical cord blood in 542, 543, 544 – two-level presacral fusion with spondylolisthesis (clinical case) 413, 414 depth perception, lack of 76 desiccation 43 dexamethasone sodium 152 dextroscoliosis, degenerative, with stenosis and spondylolisthesis (case study) 472 – case selection 473 – management of complications 475 – operative nuances 475 – patient profile 472, 473 – postoperative care 474, 475 – postoperative results 475 – preoperative notes 473 – surgical approach and technique 473 diffuse idiopathic skeletal hyperostosis 214 discitis, endoscopic spine techniques for 313 discogenic back pain 39 – introduction 39 – pathophysiology 43 – surgical treatment 44 distraction (motion) 27 dorsal lateral pontine tegmentum (DLPT) 51 dose-related toxicity (radiosurgery) 170 dosimetric planning 172

dural tears, postoperative management 77 durotomy 337

E EBRT (external beam radiation therapy) 170 eccentric contractions 33 elderly patients 63–64 electromyography (EMG) – electrode placement 142 – in neuromonitoring 138 – limitations of 144 – spontaneous 142 – stimulus-evoked, for intraoperative monitoring 142 –– ball-tipped feeler probe 142 –– for nerve mapping 143 –– placement of pedicle screws 142, 143 –– variability in magnitude of response 143 electronic medical records (EMR) 104 – as communication system 104–105 – benefits of 105 – consolidation of information from multiple providers 105 – customized patient education materials 106 – implementation of 105, 105 – patient summary display 105, 106 – quality improvement process and 106 – sharing of information 106 – work flow process 105 electrophysiologic monitoring 83, 86, 96 embryology, spinal 12 embryonic stem cells (ESC) 539, 539 EMG, see electromyography (EMG) EMR, see electronic medical records (EMR) endoscopic spine techniques 311 – clinical case 321 – clinical caveats 322 – contraindications 313 – indications for 312 –– discitis 313 –– herniations 312 –– interbody fusion 313 – inside-out vs. outside-in approach 315 – instrumentation –– basic instrument set 314 –– evolution of 311 –– Yeung Endoscopic Spine Surgery System (YESS) 313 – introduction 302 – management of complications 321 – postoperative care 320 – preoperative planning 313 – step-by-step surgical technique 317, 318–319 –– evocative chromo-discography 318 –– instrument placement 319 –– needle placement 318 –– performing discectomy 319, 320 –– wound closure 141 – surgical approach 315, 315 –– optimal needle placement protocol 316 –– setup and exposure 316, 317

–– surgical technique 316, 316 endoscopy, evolution of 2 enostosis 489, 489 eosinophilic granuloma 491, 491 ependymomas – pathological types 506 – radiologic presentation 506 – surgical resection 506 epidural injections 155 – caudal 155, 156 – intralaminar 156, 157 – transforaminal 156 erector spinae muscle 24 ethics, medical 524 ethnography (research method) 524 evidence-based medicine, see clinical outcome analyses – health policy and 526 – interpretation of evidence 524 – levels of evidence 519, 520, 525 – tenets of 516 extension 27 external beam radiation therapy (EBRT) 170 extradural spinal cord tumors 505 eXtreme lumbar interbody fusion (XLIF) 397 – advantages and disadvantages 398 – applications of 362 – clinical cases 403, 403 – clinical caveats 404 – evolution of technique 6, 398 – for adult degenerative scoliosis 64 – indications and contraindications 398 – management of complications 403 – patient profiles 398 – patient selection 398 – postoperative care 402 – preoperative planning 398 –– instrumentation notes 399 –– physical examination 398 –– radiographic workup and preoperative imaging 399 – surgical technique 399 –– closure 402 –– device implantation 402, 402 –– patient positioning 400 –– patient preparation 399, 399 –– skin incisions and retroperitoneal dissection 400, 400, 401 – utilization of 398

F facet joint injections 160 – cervical 160–161 – lumbar 160, 160 – thoracic 161, 161 facet joints – cervical, angulation of 13, 14 – mechanical properties 31, 31, 37 – pain referral patterns 159, 160 – spinal mobility and 36 far-lateral herniations (FLLDHs) – disk fragments in foraminal space 333, 333 – surgical management of 333 far-lateral microdiscectomy 333 – clinical case 337, 338 – clinical caveats 338 – indications and contraindications 334

– introduction 333 – management of complications 337 – patient positioning 334 – postoperative care 337 – pre-operative planning 334 – surgical technique 334, 335–337 FDA 510 (k) process 119, 123 femoral nerve – anatomy 390, 391 – surgical injuries 394 filum terminale 19 flat-back syndrome 28 flexibility, biomechanics and 34 FlexiCore artificial lumbar disk 444, 444 flexion 27 fluoroscopy – radiation dose in 129 – radiation exposure, minimizing 83, 153 – spine injections 153 foraminal stenosis – as indication for anterior cervical discectomy 207 – endoscopic spine techniques for 312 foraminoplasty, endoscopic 313 fracture stabilization, thoracolumbar spine 60 Fraud and Abuse Law Safe Harbor Rules 109 Freedom to Practice Opinion (patents) 120 functional spine unit 27

G genitofemoral nerve – anatomy 388, 390, 390 – surgical injuries 394 giant cell tumor 490, 491 glucocorticoids 152 glycosaminoglycan 40 gross tumor volume (GTV) 171 grounded theory 524 growth benchmarks 104

H hanging drop technique (intralaminar epidural) 156 health policy and cost containment 525 health-related quality-of-life (HRQL) 516 hemangioblastoma 507 – association with VHL syndrome 506–507 – radiologic presentation 507 – surgical resection 507 hemangioma 484, 488 hemisacralization 17 hemorrhage, postoperative 78 herniations, see cervical disk herniation, lumbar disk herniation, thoracic disk herniation (TDH) – endoscopic spine techniques for 312 hyperhidrosis – anterior thoracoscopic sympathectomy for 240 – compensatory 245–246, 246 – nonsurgical treatments 241 – pathophysiology 240, 240

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553

Index – physical examination 241

I iliacus muscle 25 iliohypogastric nerve 389, 389 ilioinguinal nerve 389 iliolumbar ligaments 19, 33 image acquisition 130 image guidance, in minimally invasive spine surgery 3 image-guided radiotherapy (IGRT) 170 implants, valuation and reimbursement codes 120 incision, see under specific procedures – minimally invasive spine surgery vs. traditional surgery 75, 75 injection-based spine procedures, see spine injections instantaneous axis of rotation (IAR) 27 instrumentation, preoperative planning for 74 instruments, for minimally invasive procedures 95, 96 intensity-modulated radiation therapy (IMRT) 170 interbody fusion, see lumbar interbody fusion internal fixation devices, development of 4 International Quality of Life Assessment (IQOLA) Project 518 interosseous ligaments 19 interspinous ligament 32 intertransverse ligaments 32 intervertebral discs (IVD), see degenerative disc disease (DDD) – abnormalities –– artificial disc advantages for 440 –– procedures addressing 440 – aging and degeneration of 41, 41, 538, 538–539 – anatomy 17, 538 – animal model of degeneration 41, 42 – back pain and, see discogenic back pain – physiology 39, 39, 40–41 – spinal mobility and 36, 36 – stem cell regeneration of 538 –– See also stem cells and stem cell therapy – structure and physiology of components 43 intervertebral joints 36 intradiscal electrothermal therapy (IDET) 6 intradural extramedullary spinal cord tumors 505 – case study 303 – minimally invasive techniques vs. open procedures for 508 – resection of (clinical cases) 510, 510–511 intradural spinal cord tumors, minimally invasive resection 66, 505 – clinical caveats 512 – indications and contraindications 508 – management of complications 510 – patient selection 508, 508 – preoperative planning 509 –– instrumentation notes 509

554

–– physical examination, radiographic workup, and preoperative imaging 509 – rationale and technique, evolution of 508 – rehabilitation and recovery 510 – surgical technique 509 –– closure 509 –– incision 509 –– operative technique 509 –– patient positioning 509 –– preparation 509 – treatment outcome 511 intralaminar epidural injections 156, 157 – cervical, fluoroscopy with 156 – hanging drop technique 156 – loss of resistance technique 156 intramedullary spinal cord tumors 506 – clinical presentation 506 – management of complications 510 – rare primary tumors 507 – surgical treatment 507 –– indications and contraindications 508 –– minimally invasive rationale and technique 508 –– open vs. minimally invasive procedures 507 –– postoperative care 510 –– preoperative planning 509 –– surgical technique 509 – types of 506 intraoperative neuromonitoring, see specific techniques – anesthesia for 146–147 – clinical caveats 148 – electromyography –– spontaneous 142, 142 –– stimulus-evoked 142 – historical review 137 – introduction 137 – mechanomyography 144 – motor evoked potentials 140 – recommendations for 147, 147 – somatosensory evoked potentials 138 – variation in interpretation of signals 138 iohexol (Omnipaque) 153 iopamidol (Isovue) 153 IQOLA (International Quality of Life Assessment) Project 518 isodose line 172 isometric contractions 33 isopropyl alcohol 153

J Jackson table 80, 82 Japanese Orthopedic Association scale, modified (mJOA) 520

K K-wire placement, postoperative complications 77 Kineflex artificial lumbar disk 441, 444 kyphoplasty 286 – avoiding complications 531 – clinical case 288, 288 – defined 286

– for spine metastasis pain relief 498 – indications for 286 kyphoscoliosis, degenerative 468 kyphosis – physiologic 12, 28 – postoperative, management of 202 – progressive, with spinal cord compression (case study) 209, 211 – thoracic kyphosis (TK) 267

L laminectomy – facet anatomy and surgical approach 342, 346–350 – hemilaminectomy 341 – ipsilateral 199, 200, 201 – minimally invasive, for lumbar stenosis 340 –– clinical caveats 360 –– evolution of techniques 340 –– indications and contraindications 341 –– introduction 340 –– operative microscope 342, 346 –– operative setup and instrumentation 342, 345 –– patient selection 341 –– preoperative planning 341 –– radiographic workup 341, 341, 342–344 – minimally invasive, with in situ posterior fusion (MIL-ISF) 344 –– avoiding complications 348 –– closure 348 –– effectiveness of 345 –– incision 345, 345, 353 –– laminectomy technique 346, 351– 352, 354–357 –– methods 344, 351 –– patient positioning and operative preparation 345 –– postoperative care 348 –– results 344 –– surgical technique 345 – open laminectomy 340, 340 – skipping for muscle attachment preservation 204 – unilateral approach 341 – with fusion and instrumentation 203 laminoplasty 204 laminotomy defect, posterior 312 laparoscopic equipment 95 lateral arcuate ligaments 19 lateral femoral cutaneous nerve (LFCN). 389 lateral lumbocostal arches of Henle 19 lateral transpsoas procedures, patient positioning for 80, 84 latissimus dorsi 24 levator veli palatini 182 licensed practical nurses 102 licensure and certification, ambulatory spine surgery centers 109 lidocaine 152, 152 ligamentous capsules 18 ligaments – alar ligaments 18, 33 – anatomy of 17 – anterior longitudinal 17, 31 – biomechanics 31 – cruciform 18, 33

– iliolumbar 19, 33 – interspinous 32 – intertransverse 32 – ligamentous capsules 18 – ligamentum flavum 18, 18, 31, 32 – ligamentum nuchae 18 – lumbar 18, 19 – moment arm 31, 32 – odontoid 18 – posterior longitudinal 17, 32 – sacral and coccygeal 19 – supraspinous 32 – thoracic 15, 18 local anesthetics (pharmacology) 152, 152 lordosis 12, 28 loss of resistance technique (intralaminar epidural) 156 low back pain – about 416 – definition 49, 50, 398 – etiologies 416 – incidence 362 lumbar arthroplasty, advancements in 6, 440 lumbar disc herniations – endoscopic spine techniques for 312 – far-lateral (FLLDHs) –– disk fragments in foraminal space 333, 333 –– microdiscectomy for 333 –– surgical management of 333 – microdiscectomy for 61, 323 – muscle-preserving technologies 61, 61, 323 –– See also lumbar microdiscectomy, muscle preserving – open discectomy vs. minimally invasive techniques 61 lumbar discogram 165 – diagnostic use 164 – double-needle technique 164, 165 – provocative 164 lumbar interbody fusion – anterior, see anterior lumbar interbody fusion (ALIF) – as alternative to posterolateral fusion 362 – axial lumbar interbody fusion (AxiaLIF) 406, 406 – benefits for discogenic back pain 44, 44, 45–47 – endoscopic techniques 313 – extreme, see eXtreme lumbar interbody fusion (XLIF) – history of 362 – lateral (case study) –– case selection 468 –– instrumentation notes 469 –– management of complications 469 –– operative nuances 469 –– patient profile 468, 468 –– postoperative care 469 –– postoperative results 469 –– preoperative notes 469 –– surgical approach and technique 469 – lateral retroperitoneal transpsoas, avoiding complications 532 – mini-open pedicle subtraction osteotomy (case study) 466 – posterior, see posterior lumbar interbody fusion

Perez-Cruet et al, An Anatomic Approach to Minimally Invasive Spine Surgery, 2nd Ed. (ISBN 978-1-62623-643-1), copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.

Index – postoperative outcomes 44 – trans-sacral approach, see trans-sacral approach, lumbar interbody fusion – transforaminal, see transforaminal lumbar interbody fusion (TLIF) lumbar ligaments 18, 19 lumbar lordosis (LL) 28–29, 267 lumbar microdiscectomy, muscle preserving 323 – See also microendoscopic discectomy, lumbar – avoiding complications 328, 531 – clinical cases 331 – clinical caveats 331 – far-lateral herniation 333 –– See also far-lateral microdiscectomy – introduction 323 – management of complications 328 – patient positioning and operating room setup 82, 323, 325 – postoperative care 328 – surgical approach 323 – surgical technique 324, 326 –– discectomy and closure 327, 330 –– laminar and interlaminar space identification 325, 328–329 –– ligamentum flavum removal 326, 329 –– nerve root exploration and retraction 327, 329–330 –– soft-tissue removal and laminar identification 324 lumbar plexus – anatomy 390 – femoral nerve 390, 391 – genitofemoral nerve 388, 390, 390 – obturator nerve 390 – sympathetic trunk 391 lumbar spinal pain 49, 50 lumbar spine surgery, see lumbar interbody fusion – advancements in 5, 362 –– automated percutaneous discectomy (APD) 6, 532 –– chemonucleolysis 6 –– intradiscal electrothermal therapy (IDET) 6 –– lumbar arthroplasty 6 –– microendoscopic discectomy 5 – avoiding complications 531 – computer navigational guidance 135 – minimally invasive approaches 61 –– case studies 464 –– clinical caveats 534 –– decompression vs. open laminectomy 62 –– evolution of 464 –– laminectomy for lumbar stenosis 340 –– lateral transpsoas 387 –– microdiscectomy 61, 323, 531 –– open discectomy vs. 61 lumbar stenosis – incidence 340 – minimally invasive decompression vs. open laminectomy 62 – minimally invasive laminectomy 340 – multilevel (case study) 471 –– case selection 471 –– instrumentation notes 471 –– management of complications 472

operative nuances 472 patient profile 471, 471 postoperative care 472 postoperative results 472 preoperative notes 471 surgical approach and technique 472 lumbar total disc replacement 440 – See also artificial lumbar discs – avoiding surgical complications 449 – clinical case 456, 460 – discectomy technique 449 –– importance of complete discectomy 449 –– initial incision and preparation of disc space 449–450, 450 –– intraoperative fluoroscopy 449 –– key maneuvers 449 –– parallel distraction 450, 450–451 – introduction 440 – preoperative planning 448 – revision techniques 456 – surgical technique 448 –– closure 456 –– core insertion and instrument removal 455, 459 –– core trial 454, 457–458 –– end plates insertion 454, 456–457 –– final positioning 455–456, 459–460 –– footplate templating 451, 452 –– incision 449 –– intraoperative repositioning 456 –– midline marker insertion 454 –– patient positioning 448 –– Pilot Driver insertion 453, 453, 455 –– radiolucent trial with insertion guide, insertion of 451, 452, 452, 453 –– surgical approach 448 lumbar transforaminal epidural steroid injections 156, 158 lumbarization 17 lumbosacral angle 17, 28, 29 –– –– –– –– –– ––

M magnetic resonance imaging (MRI), for benign spine tumor workup 492 managed care and cost containment 94, 108 manubriosternal joints 36 marketing of outpatient spine surgery centers, as centers of excellence for niche services 94 marketing of outpatient spine surgery services 96, 110 – budget 110 – contract negotiation 110 – market sizing 96 – marketing and promotion activities 110 – positive patient experience 110, 110 – targeted advertising 110 – trend toward outpatient services 96 MARSS, see robotic-assisted thoracic spine surgery, minimally invasive (MARSS) MASS, see minimal access spinal surgery (MASS) Maverick artificial lumbar disc 441, 444 MaXcess Retractor System 398 McGill Pain Questionnaire (MPQ) 519

McGregor’s line 182, 183 mechanomyography (MMG) – application of sensor patches 144, 145 – clinical applications 144 – for intraoperative neuromonitoring 144 – for nerve mapping 143–144 – indications for 145 – pedicle screw placement 145, 145– 146 – smart sensor systems 138 – technique 144 – use during dissection 145 medial arcuate ligaments 18 medial branch nerve blocks 162 – cervical 163 – lumbar 162, 162 – radiofrequency neurotomy (rhizotomy) 163, 163 – thoracic 162 medial lumbocostal arches 19 medical and nursing assistants 102 medical devices – bringing to marketplace 119 –– introduction 119 –– key points 124 –– product development process 126 –– steps in 125 – design and development 122 –– costs for device approval 123 –– FDA 510 (k) process 119, 123 –– identifying user requirements/specifications 122 –– interrelatedness of commercialization process 122 –– quality assurance and regulatory affairs 122 –– traceability matrix 123 – development options 120 –– contract negotiations 121 –– due diligence in choice of partners 121, 122 –– funding 121 –– going it alone 121 –– partnering with others 120 – distribution and marketing 123, 124 – FDA product registration and regulations 121 – first steps in marketing –– determining value proposition 119 –– improvements in patient outcomes 119 –– legal considerations 120 –– patents and patent applications 120, 121 – managing expectations 120 – manufacturing of device 123, 123 – nondisclosure agreements 120 Medicare and Medicaid, Anti-Kickback Statute and 113 Medtronic O-Arm and StealthSystem 131, 131 meningiomas – multiple intracranial, minimally invasive resection of (clinical case) 511, 511 – pathophysiology 506 – radiologic presentation 505, 506 MEPs, see motor evoked potentials (MEPs) mesenchymal stem cells (MSC) – in vitro studies 539

– in vivo animal studies 539 – therapeutic potential of 539, 539 methylprednisolone acetate (Depo-Medrol) 152 METRx System (Medtronic Sofamor Danek) 2, 5, 323 microendoscopic discectomy, lumbar – case study 464 –– management of complications 465 –– operative nuances 465 –– patient profile and case selection 464, 464 –– preoperative notes 464 –– surgical approach and technique 464 – history of 2, 5 – instrumentation –– METRx Microdiscectomy System 2, 5, 323 –– microendoscopic discectomy (MED) system 323, 324 –– One-Step Dilator 324, 326–328 microforaminotomy, cervical 57–58 microneurosurgery, history of 2 microscope, operating 2 minimal access spinal surgery (MASS) – advantages and disadvantages 479 – evolution of technique 478 – indications and contraindications 480 – instrumentation notes 481 – outcomes vs. standard thoracotomy 65 – preoperative planning 480 – surgical techniques 482 –– bilateral decompression for posterior pathologies 483, 483 –– mini-open decompression for posterior pathologies 482, 482 –– mini-open thoracotomy 481, 483, 484 minimally invasive robotic-assisted spine surgery, see robotic-assisted thoracic spine surgery, minimally invasive (MARSS) minimally invasive spine surgery (MISS) – advancements in –– cervical surgical spine techniques 3 –– general advancements 2 –– lumbar surgical spine techniques 5 –– percutaneous vertebroplasty 7 –– spine tumor surgery 478 –– thoracic surgical spine techniques 4 – advantages of 56 – approaches to –– adult spinal deformity 64, 266 –– cervical spine 57 –– decompression/laminectomy 62 –– lumbar spine 61 –– minimal access spinal surgery vs. standard thoracotomy 65 –– resection of intradural lesions 66 –– robotic-assisted thoracic spine surgery 290 –– spinal malignancies/extradural tumors 65 –– thoracic and thoracolumbar idiopathic scoliosis 275 –– thoracic spine 58 –– transpsoas anatomical approach to lumbar spine 387 – avoiding complications in 528

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555

Index –– See also specific procedures –– cervical complications 528 –– introduction 528 –– lumbar complications 531 –– thoracic complications 530 – evolution of 70 – expansion of applications 56 – goals and benefits 56, 57 – history 2 – intraoperative neuromonitoring recommendations 147, 147 – introduction 2, 56 – mastering surgical techniques, see training for minimally invasive spine surgery – neurological injury risk in 137 – patient selection 72 – preoperative planning for 74 – rationale for 56 Mobidisc artificial lumbar disk 444 modified Japanese Orthopedic Association scale (mJOA) 520 moment arm 31, 32 motion segment (functional spine unit) 27 motion, types of 27, 28 motor evoked potentials (MEPs) 140 – anesthesia effects on 146 – in neuromonitoring 138 – indications for neuromonitoring 141 – limitations in neuromonitoring 141 – technique 141 –– alarm criteria 141 –– electrode placement 139, 141 –– threshold level approach to TcMEPs 141 – transcranially triggered (TcMEPs) 140 muscles 19 – biomechanics 33 –– contractions, types of 33 –– endurance 33, 34 –– flexibility 34 –– strength 33 – cervical spine 19 –– deep intrinsic 20 –– intermediate intrinsic 20 –– platysma, sternocleidomastoid, and trapezius 20 –– posterior cervical/intrinsic 20 –– prevertebral 20, 21 –– suboccipital 22 –– superficial intrinsic 20 – iliacus 25 – muscular triangles of neck 22, 22 – posterior abdominal wall 25, 25 – psoas group 25 – quadratus lumborum 26 – thoracic spine 21, 24 muscular triangle 23 myelopathy, radiation-induced 173

N navigational reference points 129 – producing 3-D images for computer guidance 129–130, 131 – radiofrequency-emitting devices as 129 – reference frame 129, 129 navigational space 129 navigational space, computer-related 128

556

NDAs (nondisclosure agreements) 120 Neck Disability Index (NDI) 519 neck muscles 20 neck pain 214 Neck Pain and Disability Scale (NPDS) 519 nerve mapping 143 neurofibroma 505 neurofibromatosis 505 neurogenic claudication 341 neuromonitoring, postoperative 395 nociceptors 49, 49, 51 nondisclosure agreements (NDAs) 120 North American Spine Society Lumbar Spine Outcome Assessment Instrument 519 notochordal cells 539, 539 nucleus pulposus 17, 39, 41, 41, 538 nucleus raphe magnus (NRM) 51 nurse practitioners 101 nutrition, postoperative 91

O obesity – minimally invasive decompression/ laminectomy 63 – morbid, and minimally invasive surgery 72 – presacral fusion technique vs. ALIF and TLIF 407 – transforaminal lumbar interbody fusion in 63 obturator nerve 390 occipital bone 181 occipital triangle 23 Occupational Role Questionnaire (ORQ) 519 ODI (Oswestry Disability Index) 418, 418, 519 odontoid ligaments 18 Office of the Inspector General (OIG) – Safe Harbor regulations 109, 114, 114 – Special Fraud Alert for physicianowned device companies 117 office suites 98, 106 One-Step Dilator – for lumbar microdiscectomy 324, 326–328 – for transforaminal lumbar interbody fusion 380 operating room setup 80, 106 – electrophysiologic monitoring 83, 86 – equipment 80 –– essential equipment 80 –– operating instruments and retractors 83, 86 –– placement of 80, 81 –– surgical microscope position 80, 82 –– typical equipment needs 83 – introduction 80 – patient positioning 80, 84 – radiation safety 81, 85 operational benchmarks 102 operative training, see training for minimally invasive spine surgery operative view 76, 77 organs at risk (OARs) 171 OsiriX MD (software) 419, 419–421 osteoblastoma 490, 490 osteochondroma 489, 489

osteoid osteoma 489, 490 osteoporosis 30, 72, 214 osteotomy, mini-open pedicle subtraction (case study) 468 Oswestry Disability Index (ODI) 418, 418, 519 outcome assessment instruments 518 – American Spinal Injury Association Impairment Scale 520 – Cervical Spine Outcomes Questionnaire 519 – modified Japanese Orthopedic Association (mJOA) scale 520 – Neck Pain and Disability Scale 519 – North American Spine Society Lumbar Spine Outcome Assessment Instrument 519 – Oswestry Disability Index 519 – Prolo Anatomic–Economic–Functional Rating System 519 – Short Form-36 health survey 518 – Sickness Impact Profile 518 outcomes research, see clinical outcome analyses outpatient surgery centers, see ambulatory spine surgery centers

P pain management 91, 164 palate muscles 182 parallel design, randomized controlled trials 521 patents and patent applications 121, 123 – Freedom to Practice Opinion 120 – U.S. Patent and Trademark Office website 120 patient education 90 – computer-assisted 90 – introduction 90 – introductory education 91 – methodology 90 – pain management 91 – postoperative education 91 – preoperative education class 91 –– effectiveness of 92 –– impact on length of stay 92, 92 – traditional approach 90 patient flow, unidirectional 106 patient positioning, see under specific procedures – anatomic alignment 74 – preoperative planning 74 patient selection 72 – See also under specific procedures pedicle subtraction osteotomy, miniopen (case study) – case selection 467 – instrumentation notes 467 – management of complications 468 – operative nuances 468 – patient profile 466, 467 – postoperative results 468 – preoperative notes 467 – surgical approach and technique 467, 467 pelvic incidence (PI) 219, 267 pelvic incidence-lumbar lordosis (PILL) 267 pelvic tilt (PT) 28, 29, 30, 267 percutaneous discectomy, automated (APD) 6, 532

percutaneous pedicle screw fixation (PPSF) 370 – advantages and disadvantages 479 – avoiding complications 532, 533 – clinical caveats 375 – evolution of technique 478 – foraminal stenosis and mobile spondylolisthesis (clinical case) 374, 375 – indications and contraindications 371, 480 – instrumentation notes 371, 480 – introduction 370 – management of complications 484 – open techniques vs. 370 – postoperative care 374 – preoperative planning 371, 480 – radiation exposure in 370, 370 – Sextant system 370 – surgical approach 481 – surgical technique 371, 371, 481, 481 –– pedicle access using oblique images (owl’s eye) 372, 372 –– pedicle access using posterior view 372, 373 –– rod insertion 481 –– screw placement 373, 373, 374, 481 percutaneous vertebral augmentation (PVA) 66 percutaneous vertebroplasty 7 periaqueduct gray (PAG) 50–51 phenomenology (research method) 523 philosophy of care – algorithm 100 – ambulatory spine surgery center success and 98 – leadership and 98 – principles 98 physician assistants 101 physician-owned distributorships (POD) – Anti-Kickback Statute considerations for 117 – OIG Special Fraud alert regarding 117 – ownership investment decisionmaking 117 planning target volume (PTV) 171 platysma muscle 20 polymethylmethacrylate (PMMA) bone cement 7 pontomedullary junction 181 posterior approach to cervical spine 197 – clinical caveats 205 – introduction 197 – postoperative kyphosis, management of 202 – surgical techniques 199 –– cadaveric studies 199, 200 –– clinical experience 201, 202 –– ipsilateral laminectomy 199, 200, 201 –– laminectomy with fusion and instrumentation 200, 203 –– laminoplasty 204 –– skip laminectomy for muscle attachment preservation 204 –– soft tissue dissection 201, 202–203 posterior cervical microforaminotomy and discectomy (MF/D) 191

Perez-Cruet et al, An Anatomic Approach to Minimally Invasive Spine Surgery, 2nd Ed. (ISBN 978-1-62623-643-1), copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.

Index – advantages for cervical tradiculopathy 195 – clinical case 195, 195 – clinical caveats 196 – complications 194 – contraindications 191 – indications 191 – introduction 191 – laminoforaminotomy, avoiding complications 528, 529 – microendoscopic foraminotomy (CMEF) 58 – postoperative care 194 – preoperative evaluation 191, 192 – surgical technique and instrumentation 191 –– dilators 193 –– step-by-step technique 192, 194– 195 –– tubular retractor and endoscopic setup 192, 193 posterior column instability 214 posterior longitudinal ligament (PLL) 15, 17, 32, 213 posterior lumbar interbody fusion (PLIF) – avoiding complications 532 – development of 6 – patient profile 398 posterior triangle 23 posterolateral fusion (PLF) 362 postoperative care, minimally invasive vs. traditional surgery 77 postoperative complications, see under specific procedures – dural tears 77 – hemorrhage 78 – management of, MISS vs. traditional surgery 77 postoperative education of patients 91 postoperative instructions 100 povidone-iodine 153 preapproval of surgical procedures 108 preoperative education class 91 preoperative instructions 99 preoperative planning 74 presacral approach, see trans-sacral approach, lumbar interbody fusion prevertebral muscles 20, 21 ProDisc-L artificial lumbar disk 441, 442, 443 – biomechanics 458, 462 – FDA approval for marketing 441 – FDA IDE randomized trial results 443 – patient satisfaction with 442 Prolo Anatomic–Economic–Functional Rating System 519 provisional patents 120 psoas muscles 25, 388–389, 390, 391

Q quadratus lumborum 25, 26 qualitative research methods 523 – action research 524 – application for clinical problems 523 – ethnography 524 – examples of 524 – grounded theory 524 – phenomenology 523 quality assurance and regulatory affairs (QA/RA) 122

quality-of-life, health-related (HRQL) 516 quantitative research designs and methodologies 521, 522 – case series and case reports 523 – case-control study 523 – cohort study 523 – cross-sectional surveys 523 – randomized controlled trials 521

R radiation safety – fluoroscopy and 83, 153 – operating room setup and 81, 85 radiation therapy, for tumor-associated pain 497 radiation toxicities 173 radiation-induced myelopathy (RIM) 173 radicular pain – physiology 52, 54–55 – posterior cervical microforaminotomy and discectomy for 191, 195 radiofrequency ablation (RFA) 498 – spinal pain reduction following 499, 499 – therapeutic process 498, 498 – with vertebroplasty, for spine metastasis treatment –– benefits of 500 –– clinical caveats 503 –– goals of 500 –– indications for 500 –– metastatic disease secondary to breast cancer (clinical case) 501, 501 radiofrequency neurotomy (rhizotomy), medial branch 163, 163 radiolucent bed (frame) 80, 82, 95, 95 radiotherapy, image-guided (IGRT) 170 randomized controlled trials 521, 521 Raynaud’s disease, thoracoscopic sympathectomy for 241 registered nurses 101 retrograde ejaculation, as ALIF complication 363, 366 retroperitoneal cavity 390 revenue cycle benchmarks 103 RFA, see radiofrequency ablation (RFA) rib cage 35, 36 robotic-assisted thoracic spine surgery, minimally invasive (MARSS) – clinical caveats 296 – indications and contraindications 290 – introduction 290 – management of complications 295 – postoperative care 294 – preoperative planning 290, 291 – schwannoma (clinical case) 292 –– outcome 293 –– preoperative planning 290 – surgical technique 290, 292 –– autograft collection 290, 293 –– port placement 291, 295 –– tumor resection 290, 294, 296 – tumor of right T2-T3 neural foramen (clinical case) 293, 297 –– anterior approach 294, 298 –– posterior approach 293, 297 Roland-Morris Disability Questionnaire (RDQ) 66

rostral ventromedial medulla (RVM) 50 rotational motions 27, 28

S sacral slope (SS) 219, 266 sacral spinal pain 49 sacrococcygeal joint 19 sacroiliac joint fusion, minimally invasive 416 – clinical caveats 438 – indications and contraindications 416 – literature reviews 417 – management of complications 437, 438 – postoperative care 148 – preoperative planning 419 –– instrumentation notes 421 –– operating room setup 420 –– OsiriX MD software for 419, 419– 421 –– patient positioning and draping 421, 422–423 – surgical technique 421, 424 –– drilling, broaching, and placing implants 423–425, 428–432, 434–435 –– hemostasis and closure 426, 437 –– incision 422, 425 –– marking of inlet and outlet views 422, 424 –– placement of Steinmann pins 422, 424, 426–427, 433 –– steps in 421 – systematic review 417 –– operative parameters 418 –– Oswestry Disability Index 418, 418 –– pain severity 418, 418 –– patient characteristics 417, 417 –– types of implants 418 sacroiliac joint pain – arthrodesis vs. lumbar decompression for 416 – etiologies 416 – injections for 164, 164 – nonsurgical treatment for 416 sacroiliac ligaments 19 sacrospinous ligament 19 sacrum (sacra vertebrae) 16 sagittal balance, assessment of 29, 29 sagittal plane 27, 28 sagittal vertical axis (SVA) 267 schwannoma – clinical presentation 505 – MARSS for (clinical case) 292, 292, 293–295 –– outcome 293 –– preoperative planning 290 – pathophysiology 505 scoliosis surgery, minimally invasive – for adult spinal deformity 64 – posterior spinal fusion vs. 283–284 – thoracic and thoracolumbar idiopathic scoliosis 275 –– advantages of 284 –– comparison of thoracolumbar scoliosis treatments 284 –– compression 280, 281 –– discussion 283 –– exposure and discectomy 276, 276, 277 –– graft harvest 277, 278

–– indications, contraindications, and preoperative planning 275 –– introduction 275 –– management of complications 281, 283 –– minimally invasive outcomes 284 –– patient positioning and port placement 275, 276 –– screw placement 277, 278–281 –– surgical technique 275 –– thoracic clinical cases 281, 282 –– thoracolumbar clinical cases 283 –– video-assisted thoracoscopy vs. open thoracotomy for 283 Short Form-12 (SF-12) survey 518 Short Form-36 (SF-36) health survey 518 Sickness Impact Profile (SIP) 518 single photon emission computed tomography (SPECT) 492 skeletal hyperostosis, diffuse idiopathic 214 skin preparation, spine injections and 153 sodium bicarbonate 152 somatosensory evoked potentials (SSEPs) 138 – anesthesia effects on 146 – as alternative to wake-up test 137 – assessing dorsal column function 138 – indications for monitoring 140 – limitations for neuromonitoring 137–138, 140 – technique 138 –– alarm criteria 139 –– anesthesia and loss of signals 139 –– electrode placement 139 –– intraoperative baseline 139 –– physiologic variables affecting 140 –– positioning effects on 140 SPECT (single photon emission computed tomography) 492 spinal anatomy, see anatomy of spine, biomechanics of spine, specific spinal structures spinal cord and supraspinal structures, in back pain transmission 50 spinal cord compression – anterior cervical discectomy and fusion for (case study) 211, 212 – progressive kyphosis with (case study) 209, 211 – thoracic spine, neurologic deficits from 256 spinal cord tumors – extradural 505 – incidence 505 – intradural, see intradural spinal cord tumors – intradural extramedullary 505 – intramedullary, see intramedullary spinal cord tumors – types of 505 spinal deformity in adults – minimally invasive spine surgery 64 – patient selection for minimally invasive spine surgery 74 – treatment in elderly patients 305 spinal infection 214 spinal kinematics 27 spinal mobility 36, 36 spinal stability schemes 34

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557

Index – checklist for clinical instability (Whie and Panjabi) 35 – instability categorization scheme (Benzel) 35 – three-column spine concept (Denis) 34 spinal stenosis, definitions 340 spine injections 152 – bent tip –– advancing needle with 155 –– bending needle tip 154, 155 –– needle trajectory and 154 – clinical caveats 166 – commonly used needles 154, 155 – complications 166 – epidural 155 –– See also epidural injections – facet joints 160 –– See also facet joint injections – fluoroscopic guidance 153 – fundamentals 152 – joint injections, needle considerations 154 – lumbar discogram 164, 165 – medial branch nerve blocks 162 – needle control techniques 153 –– advancing needle tip in one direction 153 –– bevel tip effects on needle direction 153 – pharmacology 152 –– contrast agents 153 –– corticosteroids 152 –– local anesthetics 152, 152 – pre- and postprocedure care 153 – sacroiliac joint 164, 164 – skin preparation 153 spine metastases – current treatment options 497 – incidence and presentation 497 – introduction 497 – metastatic disease secondary to breast cancer (clinical case) 501, 501 – minimally invasive surgery 478 – radiofrequency ablation with vertebroplasty for 497 – tumor-related back pain 497 – vertebral compression fractures secondary to 497 spine surgery – evolution of 56, 56 – objectives of 516 spine tumor surgery, see spine tumors, benign – clinical cases 484 –– mini-thoracotomy 485, 486 –– tumor decompression and stereotactic radiosurgery 485 – evolution of techniques 478 – intradural lesions, minimally invasive resection 65 – mini-open decompression/minimal access, see minimal access spinal surgery (MASS) – minimally invasive 478 –– advantages and disadvantages 479 –– clinical cases 484 –– clinical caveats 486 –– for spinal metastases 478 ––– See also spine metastases –– indications and contraindications 479 –– instrumentation notes 480

558

–– introduction 478 –– management of complications 483 –– preoperative planning 480 –– surgical approach 481 –– surgical techniques 481 – percutaneous pedicle screw fixation, see percutaneous pedicle screw fixation (PPSF) – stereotactic radiosurgery potential for 170 – video-assisted, see video-assisted thorascopic surgery (VATS) spine tumors, benign 488 – aneurysmal bone cyst (clinical case) 494, 494 – classification 488 – incidence 488 – introduction 488 – minimally invasive surgery for –– clinical caveats 495 –– indications and contraindications 491 –– instrumentation notes 492 –– management of complications 493 –– physical examination 492 –– postoperative care 493 –– preoperative planning 492 –– radiographic workup and preoperative imaging 492 –– surgical approach and technique 493 – types of 488 –– See also specific histologic type – watchful waiting 491 spinous process fixation device 130 spondylitis, ankylosing 214 spondylolisthesis – contraindications in trans-sacral approach to lumbar interbody fusion 409, 409 – degenerative dextroscoliosis and stenosis with (case study) 472, 473– 474 – lateral lumbar interbody fusion (case study) 468 – nerve root/dorsal root ganglion compression in back pain 52, 53 – progressive, TLIF decompression and reduction in redo operation (case study) 469 – trans-sacral approach to lumbar interbody fusion (clinical case) 412, 413 – two-level presacral fusion with degenerative disc disease (clinical case) 413, 414 spondylolysis 441 spondylosis, cervical, see cervical spondylosis SSEPs, see somatosensory evoked potentials (SSEPs) Stagnara wake-up test 137 Stark Laws – exceptions for in-office ancillary services 115 – regulations on referrals for designated health services 110, 115 statistical analysis 523 stem cells and stem cell therapy – clinical caveats 546 – disc distraction and stem cell implant 546 –– Annulo concept 546, 547–549

– for intervertebral disc regeneration 538 – human-subject studies 545 – in vitro studies 539 – in vivo animal studies 539, 541 – therapeutic potentials 539, 539 – types and sources of 539 – umbilical cord blood in 542, 543, 544 stereotactic radiosurgery for spinal tumors 169 – challenges of 170 – clinical cases 174, 175 – clinical caveats 175 – complications 173 –– dose-related toxicity 170 –– radiation-induced myelopathy 173 –– treatment-related toxicity 173 –– vertebral compression fractures 173 – introduction 170 – outcomes 174 – pain relief following 174 – patient immobilization and imaging 171, 171 – potential for 170 – technique 170 – treatment delivery 172 – treatment planning 171 –– critical organ definition 171 –– dose selection 172 –– dosimetric planning 172 –– target volumes 171, 172 stereotaxis, frameless 170 sternocleidomastoid muscle 20 subclavicular triangle 23 subcostal nerve 388, 388 subluxation 27 submandibular triangle 23 submental triangle of neck 22 suboccipital muscles 22 suboccipital triangle 23, 24 supraspinous ligament 32 surgeon-driving neuromonitoring systems 138, 138 surgical endoscope, evolution of 311 sympathectomy, see thoracoscopic sympathectomy, anterior sympathetic trunk 391 syntegration and health standards 526

T target volumes, stereotactic radiosurgery 171, 172 thoracic disc herniation (TDH) – incidence 231, 249 – lateral extracavitary approach 237 – minimally invasive approaches 58, 231 –– anterior approaches 59, 59 –– costotransversectomy, avoiding complications 531 –– mini-open lateral approach 59, 60 –– posterior approaches 58 –– posterolateral approach 237 –– thoracoscopic discectomy 236 – preoperative assessment 249 – radiographic evaluation 232 – surgical approaches to 231, 249 – transthoracic approaches to 236 – with spinal cord compression (case study) 306

–– case selection 306 –– instrumentation notes 306, 307– 308 –– management of complications 307 –– operative nuances 307 –– patient profile 306 –– postoperative care 306–307 –– postoperative results 310 –– preoperative notes 306, 306 –– surgical approach and technique 307, 307, 308 thoracic discectomy, retropleural (case study) 299 – case selection 299 – instrumentation notes 299 – management of complications 299 – operative nuances 299 – patient profile 299, 300 – postoperative care 299 – postoperative results 300 – preoperative notes 299 – surgical approach and technique 299, 300–301 thoracic discectomy, trans-facet (case study) 302 – management of complications 303 – operative nuances 303 – patient profile 302, 303 – postoperative care 303 – postoperative results 303 – preoperative notes 302 – surgical approach and technique 302 thoracic fixation, percutaneous (case study) 300 – case selection 300, 302 – instrumentation notes 300 – operative nuances 301 – postoperative care 301 – postoperative results 301 – preoperative notes 300 – surgical approach and technique 301, 302 thoracic kyphosis (TK) 267 thoracic levo-dextroscoliosis, rotatory (case study) 304 – case selection and preoperative planning 305 – management of complications 305 – operative nuances 305 – patient profile 304, 305 – postoperative care 305 – surgical approach and technique 305, 306 thoracic ligaments 15, 18 thoracic microdiscectomy, posterior 231 – clinical case 236, 237 – clinical caveats 238 – indications and contraindications 231 – instrumentation for 232 – introduction 231 – management of complications 236 – patient positioning and incision 232, 233 – postoperative care 236 – preoperative planning 232 – radiographic evaluation 232 – surgical approach and technique 232, 234 –– transfacet pedicle-sparing approach 232, 234–236

Perez-Cruet et al, An Anatomic Approach to Minimally Invasive Spine Surgery, 2nd Ed. (ISBN 978-1-62623-643-1), copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.

Index –– transpedicular approach 234 thoracic spine – muscles 21, 24 – rib cage and spinal stability 35 thoracic spine pain, defined 49, 50 thoracic spine surgery – advancements in 4 – avoiding complications 530 –– minimally invasive costotransversectomy 531 –– thoracoscopic microdiscectomy 531 –– thoracoscopic-assisted decompression techniques 530 –– vertebroplasty and kyphoplasty 531 – computer navigational guidance 134 –– anterior approach 135 –– pedicle screw insertion 134, 135 – minimally invasive techniques 5, 58 –– case studies 299 –– evolution of 299 –– intradural/extramedullary tumor 302 –– posterior thoracic microdiscectomy 231 –– robotic-assisted surgery 290 –– rotatory thoracic levo-dextroscoliosis 304 –– thoracic and thoracolumbar idiopathic scoliosis 275 –– thoracic disc herniation 58 –– thoracic disc herniation with spinal cord compression 306 –– thoracolumbar spine fracture stabilization 60 thoracic transforaminal epidural steroid injections 159 thoracic vertebrae 14, 14, 15–16 thoracolumbar spine fracture stabilization 60 thoracoscopic discectomy 249 – anesthesia considerations 250 – as alternative to thoracotomy 254 – bone fusion and 253 – drilling of vertebral bodies/decompression of spinal cord 252 – introduction 249 – microdiscectomy, avoiding complications 531 – postoperative care 254 – preoperative assessment 249 – surgical technique 249 –– exposure and preparation of surgical field 251 –– identification of disc space 251 –– patient position 250 –– resection of rib 251, 253 –– thoracoscopic port placement 250, 251 – thoracoscopy-assisted retractorguided discectomy 252, 254 – tubular retractor-guided 254 – wound closure 253 thoracoscopic equipment 95 thoracoscopic surgery, anterior 256 – analgesia, postoperative 263 – clinical case 263, 264 – clinical caveats 264 – indications for 256 – instrumentation 257 – introduction 256 – management of complications 263

– postoperative care 263 – preoperative planning 257 – surgical approach and technique 257 –– anesthesia and patient positioning 257, 257, 258 –– Kirschner wire-guided screw insertion and wire placement 260, 260 –– orientation 260, 261 –– port placement 258, 258, 259 –– prevertebral dissection and access to thoracolumbar junction 259, 259, 260 –– thoracoscopic corpectomy and discectomy 260, 261 – vertebral reconstruction with bone grafting and cage placement 260, 262 –– assembly of insertion instrument 262 –– centralizer attachment 262 –– closure 260, 263 –– decortication instrumentation 261, 262 –– distraction maneuvers 261, 262 –– final fixation 261, 262 –– insertion instrument removal 262 –– insertion of anterior and locking screws 261, 263 –– Kirchner wire removal 262 –– plate and rod placement 262 –– rod insertion 262 –– screw insertion 261, 262 –– tightening of polyaxial screws 261, 263 thoracoscopic surgery, learning curve for 249 thoracoscopic sympathectomy, anterior 240 – advantages and disadvantages 240 – biportal approach to 247 – clinical cases 245 – clinical caveats 247 – evolution of technique 240 – indications and contraindications 241, 241 – instrumentation 241 – patient profiles 241 – patient selection 241 – preoperative planning 241 –– physical examination 241 –– radiographic work-up and imaging 241 – success rate for procedures 247 – surgical approach and technique 241 –– closure 244, 244 –– incision 242 –– management of complications 245, 247 –– patient positioning 241, 242 –– postoperative care 245 –– step-by-step surgical technique 243, 243 thoracoscopy, biportal microsurgical 240 – See also thoracoscopic sympathectomy, anterior thoracotomy, mini-open 481, 483, 484 three-column spine concept (Denis) 34 torque, defined 33, 34 total disc replacements (TDRs) 93 traceability matrix 123

train-of-four twitch test 146 training for minimally invasive spine surgery 70 – cadaveric training 71, 72 – challenges and benefits of MISS 78 – clinical caveats 78 – evolution of minimally invasive techniques 70 – indications and contraindications 71 – intraoperative imaging advances 70, 71 – introduction 70 – operative training 71, 73 – preoperative planning 74 – surgical approach, MISS vs. traditional surgery 74 –– incision 75, 75 –– management of complications 77 –– operative technique 74 –– operative view 76, 77 –– postoperative care 77 –– working channel 75, 76 trans-sacral approach, lumbar interbody fusion 406 – advantages 407 – AxiaLIF device 406, 406 – bowel perforations, management of 412 – clinical cases –– degenerative disc disease L4–S1 with long-term follow-up 412, 414 –– spondylolisthesis, L5–S1 412, 413 –– two-level presacral fusion for spondylolisthesis and degenerative disc disease 413, 414 – clinical caveats 415 – disadvantages 407 – evolution of technique 406, 407 – indications and contraindications 409 – instrumentation notes 408, 410 – interspace preparation 406, 407 – introduction 406 – management of complications 412 – postoperative care 412 – preoperative planning 409 –– evaluation of bowel integrity 408 –– patient profiles 409 –– patient selection 409 –– physical examination 409 –– radiographic workup and preoperative imaging 409, 410 –– spondylolisthesis as contraindication 409, 409 – presacral access kit 408, 408 – presacral space as anatomic corridor 406 – protection of rectum 407 – suitability for obese patients 407 – surgical technique 410 –– accessing and preparing disc space 411, 411 –– closure 411 –– fluoroscopy setup 410, 410 –– measuring and placing interbody device 411, 411 –– two-level presacral approach 412 – unique features as barrier to adoption of 406 transfacet screw fixation (case study) 226 – case selection 226 – instrumentation notes 226

management of complications 226 operative nuances 226 patient profile 226, 227 preoperative notes 226 surgical approach and technique 226 transforaminal epidural injections 156 – cervical steroid injections 157 – lumbar steroid injections 156, 158 – thoracic steroid injections 159 transforaminal lumbar interbody fusion (TLIF) 63, 362, 377 – case study 465 –– instrumentation notes 465 –– management of complications 465 –– operative nuances 465 –– patient profile and case selection 465, 466 –– postoperative care 465 –– postoperative results 466 –– preoperative notes 465 –– surgical approach and technique 465, 466 – clinical caveats 386 – contraindications 378 – decompression alone vs. decompression with TLIF 379, 379 – decompression and reduction of progressive spondylolisthesis (case study) 469, 470 – degenerative dextroscoliosis and stenosis with spondylolisthesis (case study) 472, 473–474 – efficacy of 377, 378 – indications 378, 378 – introduction 378 – long-term results 384, 386 – management of complications 385 – mini-open pedicle subtraction osteotomy (case study) 468 – patient profile 398 – postoperative care 384 – preoperative planning 379 – surgical technique 380 –– incision 380 –– interbody fusion 381–383, 383 –– lumbar exposure and decompression 380, 383 –– patient positioning 82, 380 –– percutaneous pedicle screw fixation 383, 384 –– spinal approach 380 – with decompression and spondylolisthesis reduction (clinical case) 385, 385 translational motions 27, 28 transpsoas approach to lumbar spine 387 – benefits of 388 – clinical caveats 395 – introduction 388 – relevant anatomy 388 –– abdominal wall 388 –– lumbar plexus 390 –– psoas muscle 388–389, 390, 391 –– retroperitoneal cavity 390 –– spinal 391 – surgical technique 391 –– avoiding complications 394 –– interbody graft placement 393, 393 –– monitoring of lumbar plexus 392 –– opening psoas 392, 393 –– patient positioning 392, 392 – – – – –

Perez-Cruet et al, An Anatomic Approach to Minimally Invasive Spine Surgery, 2nd Ed. (ISBN 978-1-62623-643-1), copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.

559

Index –– shallow docking 393–394 –– surgical approach 392 transpsoas discectomy and fusion 268 – closure 271 – incision 270, 270 – lateral retroperitoneal interbody fusion, avoiding complications 532 – patient positioning 268, 269 – step-by-step surgical technique 270 transversospinal muscles 24 trapezius muscle 20, 24 treatment plans, outcome measures 516 triamcinolone acetonide (Kenalog) 152 triangular zone 311, 311 tubular access for instrumented fusion (case study) – case selection 225 – instrumentation notes 226 – management of complications 226 – operative nuances 226 – patient profile 225, 225 – postoperative care 226 – postoperative results 226 – preoperative notes 226 – surgical approach and technique 226 tubular retractors 80, 82

U U.S. Patent and Trademark Office (USPTO) 120 umbilical cord blood and stem cell therapy 542, 543, 544 user requirements and specifications 122

560

V value proposition, determining 119 vascular claudication 341 vascular injuries, as surgical complication 394 VATS, see video-assisted thorascopic surgery (VATS) velopharyngeal insufficiency 187 velopharynx 182 vertebrae and surrounding structures 13 – cervical vertebrae 13, 198 – coccyx 17 – intervertebral discs 17 – lumbar vertebrae 16, 16 – mechanical properties 30 – sacrum 16 – thoracic vertebrae 14, 15 – vertebral arch 30 – vertebral body 30, 30 vertebral augmentation procedures (VAP) 286 – See also kyphoplasty, vertebroplasty – clinical case 288 – clinical caveats 284 – contraindications 287 – for spine metastasis pain relief 498 – indications for 286 – management of complications 288 – patient positioning 287 – postoperative care 287 – procedure 287 – surgical technique 287 vertebral compression fractures – following stereotactic radiosurgery 173

– incidence 286 – kyphoplasty and vertebroplasty for 286 vertebral compression fractures (VCF), secondary to spine metastases 497 vertebropelvic ligaments 19 vertebroplasty 286 – avoiding complications 531 – defined 286 – for spine metastasis pain relief 498, 499 – history of 286 – indications for 286 – percutaneous 7 – physiologic mechanisms 499 – radiofrequency ablation with, for spine metastasis treatment –– benefits of 500 –– clinical caveats 503 –– goals of 500 –– indications for 500 –– metastatic disease secondary to breast cancer (clinical case) 501, 501 video imaging equipment 95, 95 video-assisted thorascopic surgery (VATS) – advantages and disadvantages 479 – discectomy 249 – indications and contraindications 480 – instrumentation notes 481 – open thoracotomy vs., for scoliosis 272 – preoperative planning 480 – surgical approach 481 – surgical technique 482

viscoelasticity 30 volumetric modulated arc therapy (VMAT) 170 von Hippel-Lindau (VHL) syndrome 506–507

W waiting areas 106 wake-up test 137 Wilson frame 80, 84 Work Limitations Questionnaire (WLQ) 519 working channel – minimally invasive spine surgery vs. traditional surgery 75, 76 – narrowness in minimally invasive spine surgery 76

X xiphisternal joints 36 XLIF, see eXtreme lumbar interbody fusion (XLIF)

Y Yeung Endoscopic Spine Surgery System (YESS) 313

Z zygapophyseal joints, see facet joints

Perez-Cruet et al, An Anatomic Approach to Minimally Invasive Spine Surgery, 2nd Ed. (ISBN 978-1-62623-643-1), copyright © 2019 Thieme Medical Publishers. All rights reserved. Usage subject to terms and conditions of license.