Surgical Procedures of the Spine for Intraoperative Neurophysiological Monitoring Providers 3031175794, 9783031175794

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Surgical Procedures of the Spine for Intraoperative Neurophysiological Monitoring Providers

Scott Francis Davis Editor

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Surgical Procedures of the Spine for Intraoperative Neurophysiological Monitoring Providers

Scott Francis Davis Editor

Surgical Procedures of the Spine for Intraoperative Neurophysiological Monitoring Providers

Editor Scott Francis Davis Neuromonitoring Associates Las Vegas, NV, USA

ISBN 978-3-031-17579-4    ISBN 978-3-031-17580-0 (eBook) https://doi.org/10.1007/978-3-031-17580-0 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2022 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

Foreword

Neurological monitoring of the spinal cord and nerve roots is a rapidly evolving technology that allows a surgeon, teamed with a neurophysiology specialist, and potentially a neurologist to monitor and protect these important structures. Typically this is seen in spinal surgery to protect the spinal cord, but has evolved into other surgical specialties as well, such as chest surgery and ear, nose, and throat surgery. This technology allows the surgeon to see damage to the spinal cord or nerves early while the damage is still reversible. This can help to prevent paralysis, sensory deficits, and motor deficits in patients during these complex procedures. My personal experience with neuromonitoring began during medical school where I was first exposed, then progressed during residency, and became a normal part of my surgical procedures during my spinal surgery fellowship. When I began my career in private practice, my community had one or two technologists with the University who only monitored complex scoliosis cases. Many advances have occurred during the past 20 years and continue to advance rapidly. No longer are only MEPs monitored, or EMG, or pedicle screw stimulation, or SSEPs, but many more modalities are becoming available. And, these can all be combined and provide even greater information than one of these modalities alone. We are now able to intraoperatively map the local neurological structures using this technology. For example, in a lateral spinal fusion the lumbar plexus is problematic due to its location in the psoas musculature. The lumbar plexus is able to be “visualized” electrically to help in avoiding it, and additionally monitored for ongoing injury if the plexus requires retraction. Surgeons are then able to modify or stop a procedure when necessary to avoid these problems. Many advances have been made in the intraoperative neurophysiology arena, and many more are coming. These advances will allow for safer patient outcomes, limited neurological injury, and limited functional loss when any procedure requires a surgeon to work near a nerve or the spinal cord. This book should be a great starting point for clinicians to understand the use of monitoring and explore the future possibilities for keeping our patients safe. 

Kade Huntsman, MD, FAAOS Chief of Surgery St. Marks Hospital Salt Lake City, UT, USA v

Preface

Surgical Procedures of the Spine for Intraoperative Neurophysiological Monitoring Providers is intended to provide neuromonitoring technologists and neurophysiologists with more in-depth information on commonly monitored spine procedures. As interventionalists, the monitoring team must be familiar with critical stages of each surgical procedure as well as what structures and functions are at risk. Each chapter is written by active practitioners of spine surgery providing up to date figures and references. This book may be successfully used as a supplement in new technologist education programs or as a standalone for those that never received adequate training in monitored surgical procedures. Newer technology such as minimally invasive procedures is well represented in the book and will be of interest to many as the popularity of these techniques continues to grow. Las Vegas, NV, USA

Scott Francis Davis, PhD, CNIM

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Contents

Atlantoaxial Procedures��������������������������������������������������������������������������������������  1 Mark L. Prasarn and Scott Crosby  Anterior Cervical Discectomy and Fusion�������������������������������������������������������� 23 Michael H. Song and Scott Francis Davis Lumbar Spine Surgery���������������������������������������������������������������������������������������� 37 Michael H. Song and Scott Francis Davis  Minimally Invasive Spine Surgery��������������������������������������������������������������������� 55 Kade Huntsman and Scott Francis Davis  Metastatic Disease of the Spine: Operative Considerations���������������������������� 67 Steven Leckie and Craig Methot Index���������������������������������������������������������������������������������������������������������������������� 81

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Contributors

Scott Crosby, BS  Neuromonitoring Associates, Las Vegas, NV, USA Scott  Francis  Davis, Vegas, NV, USA

PhD,

CNIM  Neuromonitoring

Associates,

Las

Kade Huntsman, MD  Salt Lake Orthopedic Clinic, St Mark’s Hospital, Salt Lake City, UT, USA Steven Leckie, MD  Plymouth Bay Orthopedic Associates, Beth Israel Deaconess Hospital Plymouth, Plymouth, MA, USA Craig Methot, MS  Drexel University College of Medicine, Philadelphia, PA, USA Mark  L.  Prasarn  Department of Orthopaedic Surgery, University of Texas Houston, Houston, TX, USA Michael H Song, MD  Advanced Neurosurgery, Reno, NV, USA

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Atlantoaxial Procedures Mark L. Prasarn and Scott Crosby

Posterior C1-C2 Instrumentation and Fusion Techniques Introduction The atlas and axis comprise the first and second cervical vertebrae, respectively (Fig. 1). The articulations in the atlantoaxial complex allow for significant rotation, flexion, extension and lateral bending of the upper cervical spine. Destabilization of the bony or ligamentous structures that comprise this complex can lead to pathologic atlantoaxial movement and potential neurologic compromise of the upper spinal cord. Posterior atlantoaxial instrumentation and fusion addresses instability of the upper cervical spine that can be caused by trauma, inflammation, congenital defects, neoplasm or iatrogenic sources. Traumatic injury to the atlantoaxial complex commonly manifests as C1 burst (Jefferson) or odontoid fractures. Jefferson fractures with compromise of the transverse atlantal ligament are indicated for surgery based on displacement indicating instability. Certain odontoid fractures can also compromise inherent atlantoaxial stability. Both injuries have multiple treatment options, including posterior atlantoaxial instrumentation and fusion. More rarely, isolated ligamentous compromise has also been described in the literature. Rupture of essential ligaments necessitates stabilization to protect the spinal cord and brainstem (Fig. 1).

M. L. Prasarn Department of Orthopaedic Surgery, University of Texas - Houston, Houston, TX, USA S. Crosby (*) Neuromonitoring Associates, Las Vegas, NV, USA e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2022 S. F. Davis (ed.), Surgical Procedures of the Spine for Intraoperative Neurophysiological Monitoring Providers, https://doi.org/10.1007/978-3-031-17580-0_1

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M. L. Prasarn and S. Crosby

Articular facet for dens of axis Dens Transverse ligament Atlas (C1) Axis (C2)

Fig. 1  Articulation of the atlas and axis

Autoimmune mediated inflammation of the atlantoaxial articulation can occur in patients with rheumatoid arthritis. This chronic systemic disorder can also advance to basilar invagination and subaxial subluxation. Degeneration can lead to progressive instability of the upper cervical spine. This instability with the formation of pannus can lead to spinal cord compression and necessitate surgical decompression and stabilization, most commonly at C1-C2. Congenital malformation of the dens leads to effective dissociation between the atlas and axis. There are multiple theories as to the exact cause of malformation, as both developmental and traumatic causes have been described. During development, failure of secondary ossification and migration of the dens could both attribute to the secondary abnormal anatomy. Os odontoideum is the condition associated with failure of connection between the odontoid and base of the axis. Similarly, hypoplasia of the odontoid can lead to situations requiring surgical fusion. Techniques for posterior instrumentation and fusion of the atlantoaxial joint are numerous and have developed over the past century. Beginning with Mixter and Osgood, the first descriptions of posterior stabilization included wiring the posterior elements of the axis and atlas (Mixter and Osgood). Outcomes with early wiring techniques are associated with required post-operative external immobilization with a halo and significant fusion failure rates. Today, most common stabilizations are performed with transarticular screw fixations (TAS) or atlantoaxial screws and rods constructs (SRC) with bone grafting.

Pathology The atlantoaxial complex provides the connection between the skull base and the cervical spine. The atlas is an osseous ring structure that articulates with the base of the occiput above and the atlas below it. The axis has a central projection, referred to as the dens, that articulates with the anterior arch of the atlas. This articulation provides approximately 50% of the rotation in the cervical spine and is stabilized by important ligamentous structures (Fig.  2). The transverse ligament is the most important stabilizer, as it connects the anterior arch of the atlas to the dens. Cranial

Atlantoaxial Procedures

3 Dens

Dens

Facets for attachment of alar ligaments

Superior view

Posterior view

Apical ligament of dens

Tectorial membrane (upper part of posterior longitudinal ligament)

Atlas (C1 vertebra) and axis (C2 vertebra) and base of skull

Transverse ligament of atlas

Alar ligaments

Inferior longitudinal band of cruciform ligament

Posterior longitudinal ligament

Posterosuperior view

Fig. 2  Posterosuperior view of the atlantoaxial complex with a focus on the ligamentous structures necessary for stabilization of the articulation

to the transverse ligament lie the alar and apical ligaments, connecting the dens to the occiput. Along the posterior aspect of the vertebral bodies lies the posterior longitudinal ligament, with its most cranial extension becoming the tectorial membrane as it inserts into the base of the skull (Fig. 2). Compromise of normal osseous or ligamentous anatomy from trauma, inflammation, congenital defects, neoplasm or iatrogenic sources can cause significant instability requiring surgical intervention.

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M. L. Prasarn and S. Crosby

Lateral or direct compression forces to the atlas result in fractures of the ring, with potential secondary injury to the transverse ligament. Stability of atlas fractures in isolation is dependent upon the integrity of this ligament, which is determined by radiographs or advanced imaging. Imaging studies that suggest disruption indicate the patient for operative stabilization. Forceful hyperflexion or extension moments to the upper cervical spine typically result in odontoid fractures. Anderson and D’Alonzo classified these fractures based on their anatomic location, which has helped dictate treatment options (Anderson and D’Alonzo). Type II fractures, those that occur at the base of the odontoid, are associated with significant nonunion rates and management is controversial (Hsu and Anderson 2010). Of the treatment modalities that are available, posterior atlantoaxial fusion is one option based on patient factors and surgeon preference. Atlantoaxial instability can also result from isolated transverse ligament injury. This is less commonly described but is managed in a similar way as atlas fractures with imaging studies and stabilization if indicated. Rheumatoid arthritis commonly affects the cervical spine, as early as within 2 years of initial diagnosis (Kim and Hilibrand 2005). The numerous joints of the upper cervical spine can weaken secondary to synovitis and pannus formation. This eventually leads to transverse, alar and apical ligament attenuation and compromise. Bony erosion of the odontoid may also occur leading to instability. Chronic inflammation eventually leads to anterior subluxation of the atlas on the axis and could lead to spinal cord compression (Fig. 3). As the space available for the spinal cord decreases secondary to progressive degeneration, 14  mm or less of the posterior atlantodental interval has been described as the cut-off indicating operative stabilization (Kim and Hilibrand 2005). Os odontoideum has been described as a congenital malformation with an independent ossicle separate from a hypoplastic dens (Arvin et al. 2010). Two alternative etiologies have been proposed, one describing initial failure of fusion with development and the other with antecedent trauma and subsequent nonunion. Symptomatic cases with instability and compression of the upper spinal cord can be managed with decompression and atlantoaxial fusion (Jacobson et al. 2012). Neoplasm and iatrogenic sources of instability to the atlantoaxial complex are usually multifactorial. Compromise of the structural integrity of bony and ligamentous structures require operative stabilization following similar principles in patients with traumatic, inflammatory, iatrogenic or congenital causes.

Monitoring Plan The primary structures at risk with either TAS or SRC procedures are the vertebral arteries and the upper cervical cord secondary to screw malposition. More rarely, there have been reports of hypoglossal nerve paresis, suboccipital paresthesias and dural tears (Jacobson et al. 2012). The standard monitoring plan would include sensory and motor evoked potentials (SSEPs and MEPs). Spontaneous electromyography (sEMG) is commonly employed in procedures of the cervical spine involving lower levels of the c-spine in order to monitor for manipulation to the spinal nerve

Atlantoaxial Procedures

5

Skull

C1 C2 Odontoid process

Cord

C1 - C2 instability

Subaxial instability

Proximal migration

Fig. 3  The effect of rheumatoid arthritis on atlantoaxial stability and resulting compression of the spinal cord

roots, however the nerve roots above C3 do not involve a motor component and thus are not monitored by sEMG. MEPs provide protection against insult to the vascular territory of the vertebrobasilar system. The left and right vertebral arteries join in the midline to form the basilar artery. The vertebrobasilar complex supplies the ventral brainstem and gives rise to the superior cerebellar artery and posterior cerebral artery. MEPs are sensitive to ischemia and, since they are not averaged, can

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provide instant feedback on the integrity of the pyramidal tracts which run through the ventral brainstem and spinal cord and thereby offer inferred protection from brainstem ischemia. Compression of the spinal cord resulting from spinal instability can be detected through MEP monitoring. MEP baselines should be obtained prior to placing the patient in the prone position and repeated immediately after positioning. Loss of MEPs during positioning should prompt the surgeon to position the patient back into the supine position and ascertain whether MEPs have recovered. The instability of the spine may make the patient intolerant of prone positioning and another surgical approach would have to be considered. SSEP monitoring will provide complementary information on the posterior circulation when the thalamic N18 potential is monitored. Additionally, brainstem auditory evoked potentials (BAEPs) may be used when there is pre-existing neural dysfunction or basilar invagination. BAEPs are highly sensitive to brainstem ischemia and can be a reliable adjunct to SSEP and MEP monitoring. The hypoglossal nerve runs adjacent to the vertebral artery and is at risk for injury during the procedure. sEMG from the tongue will provide information on potential stretch or compression injury to the nerve. sEMG, however, is not sensitive to ischemia and will not protect the nerve from hemodynamic insult. Anesthesia is a confounding factor in neuromonitoring interpretation, especially during positioning. The optimal regimen for the use of MEPs is total intravenous anesthesia (TIVA) using propofol, dexmedetomidine, or etomidate supplemented with an opioid anesthetic such as remifentanil. Dexmedetomidine is also a good choice in opioid-tolerant patients, however it must be titrated to an infusion level that achieves the desired anesthetic effects without suppressing MEP recordings, much like propofol (Mahmoud et al. 2010). Infusion of lidocaine in a TIVA protocol has been shown to reduce the amount of propofol and opioids necessary for adequate anesthesia (Sloan et al. 2014). The agents listed above are compatible with monitoring when used alone, but not in combination. If TIVA is not possible, then halogenated agents may be used in combination with intravenous propofol administration provided the inhalant is maintained at no more than 0.5 MAC and the propofol less than 200 mcg/kg/min. Propofol infusion rates of 120–180 mcg/kg/min are usually effective for providing suppression of movement without attenuating the MEP recordings, however dose response curves vary from patient to patient. The administration of higher amounts of inhalant or a bolus of propofol should be avoided if MEP integrity is to be maintained. The use of neuromuscular blockers can prevent the recording of MEPs and EMG. While no neuromuscular blockade is certainly preferred, MEPs and EMG have been demonstrated to be recordable when the second twitch is reduced to no more than 50% of the first twitch (T2:T1 50–66% of the facets are preserved during surgery and the disc space is not violated(maintains integrity of anterior and middle column” (Greenberg and Abel 2010, p. 483). A retrospective study of 500 patients who underwent 1 to 3 level laminectomies found, “Following lumbar laminectomy, patients experienced statistically significant improvement in back pain, neurogenic claudication, radiculopathy, weakness, and sensory deficits. The rate of intraoperative durotomy was 10.00%; however, 1.60% experienced a postoperative cerebrospinal fluid leak. The risk of experiencing at least one postoperative complication with a lumbar laminectomy was 5.60%. Seventy-two patients (14.40%) required reoperations for progression of degenerative disease over a mean of 3.40 years. The most common symptoms prior to reoperation included back pain (54.17%), radiculopathy (47.22%), weakness (18.06%), sensory deficit (15.28%),

Lumbar Spine Surgery

41

and neurogenic claudication (19.44%). The relative risk of reoperation for patients with postoperative back pain was 6.14 times higher than those without postoperative back pain (P