Radiofrequency Ablation Techniques - E-Book: A Volume in the Atlas of Interventional Techniques Series [1 ed.] 9780323870634

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RADIOFREQUENCY ABLATION TECHNIQUES

RADIOFREQUENCY ABLATION TECHNIQUES Atlas of Interventional Pain Management Series Alaa Abd-Elsayed, MD, MPH, CPE, FASA Medical Director, UW Health Pain Services Medical Director, UW Pain Clinic Division Chief, Chronic Pain Management Department of Anesthesiology University of Wisconsin Madison, Wisconsin United States

Elsevier 1600 John F. Kennedy Blvd. Ste 1800 Philadelphia, PA 19103-2899



RADIOFREQUENCY ABLATION TECHNIQUES Atlas of Interventional Pain Management Series Copyright © 2024 by Elsevier LTD. All rights reserved.

ISBN: 978-0-323-87063-4

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Contributors Glossary Alaa Abd-Elsayed, MD, MPH, CPE, FASA Medical Director, UW Health Pain Services Medical Director, UW Pain Clinic Division Chief, Chronic Pain Management Department of Anesthesiology University of Wisconsin Madison, Wisconsin United States Rany T. Abdallah MD, PhD, MBA President Apico Pain Management Bear, DE United States Prashant Angara, MD Anesthesiology New York-Presbyterian/Weill Cornell Medical Center New York, NY United States Evgeny Bulat, MD, MA Anesthesiology NewYork-Presbyterian/Weill Cornell Medical Center New York, NY United States Moorice A. Caparo, MD Assistant Professor Physical Medicine and Rehabilitation Montefiore Medical Center Bronx, NY United States Jay Darji, DO Physical Medicine and Rehabilitation Temple University Hospital/Moss Rehabilitation Philadelphia, PA United States

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Raymon Dhall, MD Montefiore Multidisciplinary Pain Program New York University New York, NY United States Alyson M. Engle, MD Assistant Professor of Anesthesiology & Pain Medicine Northwestern University Feinberg School of Medicine Chicago, IL, United States The Spine and Nerve Center of the Virginias Charleston, WV United States Kenneth J. Fiala, BS Department of Anesthesia University of Wisconsin-Madison School of Medicine and Public Health Madison, WI United States Michael Alan Fishman, MD, MBA Director of Research Center for Interventional Pain & Spine Lancaster, Pennsylvania United States Maria Grabnar, MD Assistant Professor Physical Medicine & Rehabilitation MetroHealth/Case Western Reserve University School of Medicine Cleveland, OH United States

Contributors

Amitabh Gulati, MD, FIPP, CIPS, ASRA-PMUC Director of Chronic Pain Anesthesiology and Critical Care Memorial Sloan Kettering Cancer Center New York, NY United States Behnum Habibi, MD Assistant Professor Chief of Pain Management Department of Physical Medicine and Rehabilitation Lewis Katz School of Medicine at Temple University Philadelphia, PA United States Nasir Hussain, MD, MSc Professor Anesthesiology The Ohio State University, Wexner Medical Center Columbus, OH United States Navdeep Singh Jassal, MD EXCEL Pain and Spine Assistant Clinical Professor Neurology/Pain University of South Florida Tampa, FL United States Hemant Kalia, MD, MPH, FIPP Consultant, Interventional Pain & Cancer Rehabilitation Medicine Managing Director, Greater Rochester Region, InvisionHealth Medical Director, Invision Spine & Pain President & CEO, C.R.I.S.P (Center for Research and Innovation in Spine & Pain) Rochester, NY United States Chong Kim, MD Professor Department of Physical Medicine and Rehabilitation MetroHealth System/Case Western Reserve University School of Medicine Cleveland, Ohio United States

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Paul M. Kitei, MD Physical Medicine & Rehabilitation Rothman Orthopaedic Institute Philadelphia, PA, United States Clinical Assistant Professor Rehabilitation Medicine Sidney Kimmel Medical College of Thomas Jefferson University Philadelphia, PA United States Maher Kodsy, MD, MBA Chairperson Department of Anesthesiology Perioperative Services Surgery University Hospitals Elyria Medical Center Elyria, OH United States President Elyria Anesthesia Services, Inc. Elyria, OH United States Jacob Lambert, BS School of Medicine West Virginia University Morgantown, WV United States Lexi Larson, BS School of Medicine Rocky Vista University College of Osteopathic Medicine Parker, CO United States Tariq Malik, MD Associate Professor Anesthesia and Critical Care University of Chicago Chicago, IL United States

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Contributors

Joshua M. Martens, BS School of Medicine University of Wisconsin–Madison School of Medicine Cottage Grove, WI United States

David Rosenblum, MD Director of Pain Management Department of Anesthesiology Maimonides Medical Center Brooklyn, NY United States

Nicholas Mata, MD Pain Medicine All Star Pain Management Annapolis, MD United States

Gary S. Schwartz, MD Director of Acute Pain Management Department of Anesthesiology Maimonides Medical Center Brooklyn, NY United States

Neel Mehta, MD Medical Director Anesthesiology New York-Presbyterian/Weill Cornell Medical Center New York, NY United States Marlena Rose Mueller, DO Physical Medicine & Rehabilitation MetroHealth/Case Western Reserve University School of Medicine Cleveland, OH United States Kailash Pendem, MD Department of Physical Medicine & Rehabilitation University of Florida College of Medicine Gainesville, Florida United States Neal Rakesh, MD, MSE Department of Anesthesia and Critical Care Memorial Sloan Kettering Cancer Center New York, NY United States Douglas K. Rausch, DO Anesthesiology Jackson Health System Miami, FL United States

Herman Sehmbi MD, EDRA, EDAIC, MSc Assistant Professor, Department of Anesthesiology & Perioperative Medicine Western University, London Canada Peter Shehata, DO, MA Department of Anesthesiology Cleveland Clinic Foundation Cleveland, OH United States John Silva, MD Acute Pain and Regional A ­ nesthesiology Department of Anesthesiology University of Wisconsin Madison, WI United States Vladimir Suric, MD Pain Division Department of Physical Medicine and Rehabilitation Department of Anesthesia, Division of Pain Medicine Medical College of Wisconsin Wisconsin, United States Marianne Tanios, MD, MPH Outcomes Research The Cleveland Clinic Cleveland, OH United States

Contributors

Caroline Tybout MD Department of Anesthesiology The Ohio State University Wexner Medical Center Columbus, OH United States

Steven Zhou, MD Anesthesiology The Ohio State University Wexner Medical Center Columbus, Ohio United States

Shashank Vodapally, DO Department of Physical Medicine and Rehabilitation Michigan State University East Lansing, MI United States

Xiaoying Zhu, MD, PhD Associate Professor Anesthesiology University of Virginia Charlottesville, VA United States

Sayed Emal Wahezi, MD Program Director Montefiore Medical Center Professor of Physical Medicine and Rehabilitation Professor of Anesthesiology Professor of Orthopedic Surgery New ­Rochelle, NY United States

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Preface Radiofrequency ablation (RFA) and pulsed radiofrequency (PRF) represent stalwart procedures that have witnessed significant advancements in the past decade. Procedural advancements have resulted from improvements in technology (generators, needles, and probes), techniques, indications, and stimulation parameters. RFA and PRF were implemented as treatment modalities for spine and joint pain but have recently been deployed for a variety of painful indications including headache, peripheral nerve related pain, and sympathetic-mediated pain. The implementation of RF technology is an art that requires an understanding of appropriate temperature/ duration requirements, the need for motor and/or sensory testing, and the location of vulnerable structures in proximity to the target nerve. The wide variety of indications and approaches to RFA and PRF mandates

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considerable thoughtfulness when creating an individualized treatment plan. This atlas contains an exhaustive review of RFA and PRF treatment considerations and indications. The liberal utilization of figures and fluoroscopic/ ultrasound images provides the most detailed resource for performance of RFA and PRF procedures. I would like to thank all my colleagues who contributed to this work. Their dedication is evident in the top-quality chapters and excellent images that they have provided. I would like to also thank the publisher for sponsoring this work and facilitating the publication of the most comprehensive and up-to-date RFA and PRF review. Alaa Abd-Elsayed, MD, MPH, CPE, FASA

Contents

1 History of Radiofrequency Ablation (RFA) 1

 

Maria Grabnar, Marlena Rose Mueller, and Chong Kim



2 Mechanism of Action 4

12 Shoulder Joint 88



 

Douglas K. Rausch, and Rany T. Abdallah

13 Radiofrequency Ablation and Pulsed



Radiofrequency of the Upper Extremities 97

 



 

Behnum Habibi, Jay Darji, and Chong Kim



3 Patient Selection, Indications, and

Contraindications 10  



Radiofrequency of the Lower Extremities 140  

John Silva, Peter Shehata, Herman Sehmbi, and Alaa Abd-Elsayed

4 Perioperative Management 14  



Evgeny Bulat, Prashant Angara, and Neel Mehta



14 Radiofrequency Ablation and Pulsed

David Rosenblum, and Gary S. Schwartz

John Silva, Herman Sehmbi, Kenneth J. Fiala, Peter Shehata, and Alaa Abd-Elsayed

5 Cervical Medial Branches 18

15 Radiofrequency Ablation for Headache 169

 



Caroline Tybout, Steven Zhou, Nasir Hussain, and Alaa Abd-Elsayed

 

Moorice A. Caparo, Paul M. Kitei, and Sayed E. Wahezi



6 Thoracic Medial Branches 28

 

16 Radiofrequency Ablation and Pulsed



Radiofrequency Ablation for the Sympathetic Nervous System 186

Tariq Malik



7 Lumbar Medial Branches 35

 

Joshua M. Martens, Kenneth J. Fiala, Hemant Kalia, and Alaa Abd-Elsayed

 

Navdeep Singh Jassal, Raymon S. Dhall, and Kailash Pendem



8 Radiofrequency Ablation Involving the Sacroiliac

17 Radiofrequency Ablation of the Medial Branch in



the Presence of Other Devices 202



Joint

45

 

Jacob Lambert, and Alyson M. Engle

 

Shashank Vodapally, Neal Rakesh, and Amitabh Gulati

9 Radiofrequency Ablation of Hip Joint Articular

18 Radiofrequency Ablation Complications and



Management



Nerves

 

60

Xiaoying Zhu

19 Measuring Outcomes 209

10 Knee Joint 67





 



Alaa Abd-Elsayed, Michael Alan Fishman, and Lexi Larson

 

Vladimir Suric, Nicholas Mata, and Chong Kim

11 Ankle Joint Articular Nerves 78



206

 

Jacob Lambert, and Alyson M. Engle

Index, 213



 

 

Alaa Abd-Elsayed, Marianne Tanios, and Maher Kodsy

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Chapter 1

History of Radiofrequency Ablation (RFA) Maria Grabnar, Marlena Rose Mueller, and Chong Kim

History The first known use of thermocoagulation for the treatment of chronic pain was in 1931, with successful ablation of the gasserian ganglion for trigeminal neuralgia by Martin Kirschner. A direct current of 350 mA was delivered through a 10-mm uninsulated tip, which produced a lesion of unpredictable size.1 However, the use of thermal energy for the destruction of tissue may be traced back to even earlier, in the mid-1800s, when direct current was used to create a lesion in an animal brain. This is when preliminary thoughts of quantifying lesion size based on current and time came about.2 The use of high-frequency electric current was found to produce lesions of predictable size and was named “radiofrequency” current because the same frequencies of 300 to 500 kHz were also used in radio transmitters.3 In the late 1950s, the first commercial radiofrequency (RF) lesion generator was developed by Cosman and Aronow.4,5 During stereotactic brain surgery in 1960, using the refined RF lesioning, Mundlinger et al. studied controlled dosages of RF and found that temperature monitoring was the most important factor in obtaining a standardized lesion size.6 The first use of RF lesioning for pain management occurred in 1965, when Rosomoff performed a percutaneous lateral cordotomy for unilateral pain in cancer patients.7 In 1968, Letcher and Goldring demonstrated that RF lesions block the action potentials of small nociceptive fibers in cats, preferentially sparing motor and proprioceptive fibers, which denoted the initial understanding of nerve fiber selectivity by thermocoagulation and ultimately introduced the concept of RF lesioning for therapeutic purposes.8 In 1974, Sweet and Wepsic noted that touch was preserved in some or all of a zone

deemed analgesic while performing percutaneous retrogasserian thermal rhizotomy, concluding that large, heavily myelinated fibers were more resistant to heating than small nerve fibers.9 In 1975, Shealy et al. performed the first RF lesioning for spinal pain. The medial branches of the facet joints were ablated using a 14-gauge electrode inserted through a 12-gauge guide needle, which is fairly large compared to the 18- or 20-gauge cannula with a 10 mm active tip used presently. It was thought that mechanical lesions along with thermal lesions were produced due to the large size.10 Some of the most common procedures performed today by pain management specialists are medial branch blocks and RF ablation (RFA). Another use for RF lesioning for spinal pain was introduced by Uemetsu, who first performed the procedure for dorsal root ganglion (DRG) lesioning, using the same electrode that was used by Shealy for medial branch lesioning.11 However, combining the tip temperature of 75°C with the large electrode diameter produced sizeable lesions that resulted in deafferentation pain when used for spinal pain, and the utility for RF lesioning became limited to percutaneous cordotomy and gasserian ganglion ablation.12 In addition, contradictory findings were shown after the work of Sweet and Wepsic in 1974. In 1977, histologic studies of the sciatic nerve in cats showed indiscriminate destruction of Aδ and C fibers, along with motor and proprioceptive nerves.11 This was supported by Smith et al. in 1981, who demonstrated lack of specificity at RF lesioning temperatures of 45°C, 55°C, 65°C, and 75°C in dogs.13 Due to these findings, RF lesioning fell out of favor for the time being. It wasn’t until the 1980s that the use of RFA for spinal pain was reintroduced due to crucial modifications made to the electrode. The electrode was made to be significantly smaller and capable of temperature 1

2

Radiofrequency Ablation Techniques

monitoring, which eliminated the pan-destructive mechanical and thermal lesioning created by largerdiameter electrodes that were previously used.14 The Sluijter Mehta Kit (SMK) system consisted of a 22-gauge disposable cannula with a thermo-coupled probe included for temperature measurement, resulting in less risk and discomfort during procedures. Due to this novel electrode system, RFA for medial branches and adjacent to the dorsal root ganglion became a therapeutic option in the field of pain management. With the combination of small-diameter RF needles and the use of enhanced imaging under fluoroscopy for precise placement of needles, a current passed through the electrode could reliably reproduce the patient’s concordant pain, and a thermal lesion could then target specific neural structures. After extensive studies were performed to investigate the optimal time and temperature needed for neurolysis, the standard of generating a lesion at 80°C for 60 to 90 seconds was established.15 In the 1980s and 1990s, more evidence became available regarding sympathetically mediated or maintained pain syndromes, which became an area of interest regarding RF lesioning. In 1984, Wilkinson developed an effective treatment for central hyperhidrosis using RF thoracic sympathectomy at the T2–3 and, at times, T4 levels,16 followed by the development of the percutaneous RF lumbar sympathectomy.17 Sluijter developed the cervicothoracic RF sympatholysis for treatment of sympathetically mediated or maintained pain syndromes of the face, head, neck, shoulder, and upper extremity.18 The use of RF lesioning to produce dorsal root entry zone (DREZ) lesions for treatment of deafferentation pain such as brachial plexus and conus medullaris avulsions, phantom pain syndromes, and postherpetic neuralgias was also introduced during this time frame.19 Neuroanatomic studies have demonstrated that the intervertebral disk is highly innervated, motivating Sluijter to introduce RF lesioning for the treatment of discogenic pain in 1996.20 It is thought that annular tears induce discogenic pain, and nociceptive fibers in the posterior annulus (thought to be derived from the sinuvertebral and sympathetic nerves) could be effectively ablated through intradiscal RF lesioning. Over the years, the simplicity of using heat to disrupt nociceptive transmission was questioned. This

concept suggests that the thermal lesion must be made in between the nociceptive stimulus and the central nervous system, but RF lesioning can be successfully utilized in other situations. In the treatment of acute radiculitis due to disc herniation, the electrode is placed distally to the nociceptive focus,21 and lesioning adjacent to the DRG induces only transient sensory loss that is heat related, but the pain relief may be of much longer duration.22 Pulsed-dose RF lesioning, developed in 1996,23 was intended to be a minimally invasive pain relief modality that did not cause neurodestruction. The mechanism of neuromodulation remains to be fully elucidated, but it is thought that high current in the electromagnetic field may reversibly disrupt the sodium or calcium pump in the dorsal root ganglion, rendering small nociceptive fibers less capable of pain transmission while sparing larger fibers that are protected by their myelin sheath. In addition, maintaining the electrode temperature at 42°C ensures that neural structures are not damaged.24 Pulsed-dose RF lesioning is not used for neurotomy of the medial branches of the dorsal rami, as the technique has not been shown to provide a consistent lesion.13 Two of the potential side effects of conventional RFA are painful cutaneous dysesthesias and increased pain due to neuritis,25 which may be mitigated by pulsed RF lesioning. Cooled RF lesioning was developed around the same time as pulsed RF lesioning. When traditional RF electrodes are not placed properly in parallel to the medial branch nerve, there is a risk of not capturing the nerve within the radius of the thermal lesion. Cooled RF technology creates a spherical, forwardprojecting lesion,26,27 which provides a theoretical technical advantage in capturing a target medial branch nerve, as the RF probe can be positioned at a range of possible angles and still capture the target neural structure. Cooled RF has shown effectiveness for sacroiliac joint pain,28 knee pain due to osteoarthritis (OA),29,30 and facet-mediated pain.31 The start of the 21st century brought about additional uses for RFA. Lateral branch blocks and sensory stimulation-guided neurotomy were developed for the treatment of sacroiliac joint pain.32,33 Radiofrequency ablation of the geniculate nerves for knee osteoarthritis was introduced in 201034 and remains a commonly performed procedure today.

1  History of Radiofrequency Ablation (RFA)

Radiofrequency lesioning for the treatment of persistent spinal and peripheral joint pain has increased substantially over the past few decades, due to its minimal invasiveness and effectiveness in properly selected patients when used along with a multidisciplinary approach for the treatment of chronic pain. REFERENCES 1. Kirschner M. Zur Elektrochirurgie. Arch Klin Chir. 1931;147:761. 2. Wenger CC. Radiofrequency lesions in the treatment of spinal pain. Pain Dig. 1998;8:1-16. 3. Hunsperger RW, Wyss OA. Quantitative elimination of the nervous tissues by high-frequency coagulation. Helv Physiol Pharmacol Acta. 1953;11(3):283-304. 4. Aronow S. The use of radio-frequency power in making lesions in the brain. J Neurosurg. 1960;17:431-438. 5. Cosman ER. Radiofrequency lesions. In: Textbook of Stereotactic and Functional Neurosurgery. New York, NY: McGraw-Hill; 1998. 6. Mundinger F, Riechert T, Gabriel E. Studies on the physical and technical bases of high-frequency coagulation with controlled dosage in stereotactic brain surgery. Zentralbl Chir. 1960;85: 1051-1063. 7. Rosomoff HL, Brown CJ, Sheptak P. Percutaneous radiofrequency cervical cordotomy: technique. J Neurosurg. 1965;23(6): 639-644. 8. Letcher FS, Goldring S. The effect of radiofrequency current and heat on peripheral nerve action potential in the cat. J Neurosurg. 1968;29(1):42-47. 9. Sweet WH, Wepsic JG. Controlled thermocoagulation of trigeminal ganglion and rootlets for differential destruction of pain fibers. 1. Trigeminal neuralgia. J Neurosurg. 1974;40(2):143-156. 10. Shealy CN. Percutaneous radiofrequency denervation of spinal facets. Treatment for chronic back pain and sciatica. J Neurosurg. 1975;43(4):448-451. 11. Uemetsu S. Percutaneous electrothermocoagulation of spinal nerve trunk, ganglion, and rootlets. In: Current Techniques in Operative Neurosurgery. New York, NY: Grune and Stratton; 1977. 12. Sluijter ME. Radiofrequency Part I. Meggen, Switzerland: Flivopress; 2001. 13. Smith HP, McWhorter JM, Challa VR. Radiofrequency neurolysis in a clinical model. Neuropathological correlation. J Neurosurg. 1981;55(2):246-253. 14. Sluijter ME. Treatment of chronic back and neck pain by percutaneous thermal lesions. In: Persistent Pain: Modern Methods of Treatment. Vol 3. London, England: Academic Press; 1981. 15. Bogduk N. International Spinal Injection Society guidelines for the performance of spinal injection procedures. Part 1: Zygapophysial joint blocks. Clin J Pain. 1997;13(4):285-302. 16. Wilkinson HA. Percutaneous radiofrequency upper thoracic sympathectomy: a new technique. Neurosurgery. 1984;15:811-814. 17. K. Sri Kantha. Radiofrequency percutaneous lumbar sympathectomy: technique and review of indications. In: Racz GB, ed. Techniques of Neurolysis. Boston: Kluwer Academic Publishers; 1989.

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18. Sluijter ME. Radiofrequency Lesions in the Treatment of Cervical Pain Syndromes. Burlington, VT: Radionics; 1990. 19. Nashold Jr BS. Modification of DREZ lesion technique. J Neurosurg. 1981;55(6):1012. 20. Sluijter ME. Percutaneous intradiscal radio-frequency thermocoagulation. Spine (Phila Pa 1976). 1996;21(4):528-529. 21. Teixeira A, Grandinson M, Sluijter ME. Pulsed radiofrequency for radicular pain due to a herniated intervertebral disc—an initial report. Pain Pract. 2005;5(2):111-115. 22. van Kleef M, Spaans F, Dingemans W, et al. Effects and side effects of a percutaneous thermal lesion of the dorsal root ganglion in patients with cervical pain syndrome. Pain. 1993;52(1): 49-53. 23. Cosman ER. A comment on the history of the pulsed radiofrequency technique for pain therapy. Anesthesiology. 2005;103(6):1312; author reply 1313-1314. 24. Mikeladze G, Espinal R, Finnegan R, et al. Pulsed radiofrequency application in treatment of chronic zygapophyseal joint pain. Spine J. 2003;3(5):360-362. 25. Michael Hammer, Meneese W. Principles and practice of radiofrequency neurolysis. Curr Rev Pain. 1998;(2):267-278. 26. Lorentzen T. A cooled needle electrode for radiofrequency tissue ablation: thermodynamic aspects of improved performance compared with conventional needle design. Acad Radiol. 1996;3(7): 556-563. 27. Watanabe I, Masaki R, Min N, et al. Cooled-tip ablation results in increased radiofrequency power delivery and lesion size in the canine heart: importance of catheter-tip temperature monitoring for prevention of popping and impedance rise. J Interv Card Electrophysiol. 2002;6(1):9-16. 28. Cohen SP, Hurley RW, Buckenmaier CC III, et al. Randomized placebo-controlled study evaluating lateral branch radiofrequency denervation for sacroiliac joint pain. Anesthesiology. 2008;109(2):279-288. 29. Davis T, Loudermilk E, DePalma M, et al. Prospective, multicenter, randomized, crossover clinical trial comparing the safety and effectiveness of cooled radiofrequency ablation with corticosteroid injection in the management of knee pain from osteoarthritis. Reg Anesth Pain Med. 2018;43(1):84-91. 30. McCormick ZL, Reddy R, Korn M, et al. A prospective randomized trial of prognostic genicular nerve blocks to determine the predictive value for the outcome of cooled radiofrequency ablation for chronic knee pain due to osteoarthritis. Pain Med. 2018;19(8):1628-1638. 31. McCormick ZL, Choi H, Reddy R, et al. Randomized prospective trial of cooled versus traditional radiofrequency ablation of the medial branch nerves for the treatment of lumbar facet joint pain. Reg Anesth Pain Med. 2019;44(3):389-397. 32. Cohen SP, Abdi S. Lateral branch blocks as a treatment for sacroiliac joint pain: a pilot study. Reg Anesth Pain Med. 2003;28(2):113-119. 33. Yin W, Willard F, Carreiro J, et al. Sensory stimulation-guided sacroiliac joint radiofrequency neurotomy: technique based on neuroanatomy of the dorsal sacral plexus. Spine (Phila Pa 1976). 2003;28(20):2419-2425. 34. Choi WJ, Hwang SJ, Song JG, et al. Radiofrequency treatment relieves chronic knee osteoarthritis pain: a double-blind randomized controlled trial. Pain. 2011;152(3):481-487.

Chapter 2

Mechanism of Action Behnum Habibi, Jay Darji, and Chong Kim

Introduction Radiofrequency ablation (RFA) is a unique modality used to treat many different conditions in a variety of clinical scenarios. The principles of RFA were first described in 1891 by French physician and physicist Jacques-Arsene D’Arsonval (1851–1940). His research included work on alternating currents and their physiological effects. He demonstrated, among other things, that alternating currents with a frequency greater than 5000 Hz do not cause muscular contractions or nerve stimulation, unlike other electric shocks applied to neuromuscular tissues.1 This constituted the beginning of the field of electrotherapy and later the development of therapeutic diathermy. By the early 1900s, applications of radiofrequency (RF) waves included treatment of bladder neoplasms using cauterization through a cystoscope and the use of oscillatory desiccation in the treatment of malignant tumors accessible for minor surgical procedures.2,3 Perhaps the most well-known application of RF from the early 20th century is the Bovie knife, which was introduced in 1928 by William T. Bovie (1882–1958) and Harvey Cushing (1869–1939). Bovie was an American scientist and inventor, and Cushing is frequently cited as the father of modern neurosurgery.4 The first-generation Bovie knife was a monopolar electrode similar to modern electrodes used for percutaneous RF techniques.4 The device produces an alternating current from a small knife-like electrode and a large grounding pad. Continuous current produces the cutting effect of the Bovie knife, while cauterization is an effect of a pulsed or damped current. In 1931, a German surgeon, Martin Kirschner (1879–1942), was investigating a novel treatment for

4

trigeminal neuralgia utilizing a head frame and thermocoagulation of the gasserian ganglion.5 This is perhaps the first application of RFA for the treatment of chronic pain as well as the first stereotactic surgery performed in humans. Kirschner’s body of work was expanded upon by B.J. Cosman, S. Aronow, and O.A. Wyss in the 1950s and 1960s, eventually leading to the first commercial availability of RFA machines.6

Mechanism of Action Radiofrequency waves are part of the electromagnetic (EM) spectrum and range in frequencies from 3 Hz to 300 GHz, with further subdivisions ranging from extremely low frequency to extremely high frequency. RF waves in the human body can generate heat. The amount of heat generated by RF waves depends on the duration of the radiation, the frequencies used (which correspond to energy of the waves), the shape of the RF emitting device, and the constitution of the surrounding tissue. For example, the small size of typical modern RF probes creates a high degree of energy flux at the site of the probe. Conversely, the grounding pad used in modern RF procedures has a large surface area exposed to tissue, leading to a small amount of energy flux across the adjacent tissue, and thus there is typically no burning at the site of the grounding pad. This circuit (Fig. 2.1), from probe tip to grounding pad, is essential to a functional RFA. In general all RFA systems are designed to impart a necrotic effect on the local tissue at the site of the probe. This process begins with the molecules, predominantly water, directly adjacent to the

 

2

5

Mechanism of Action

Probe Pads

Generator

Grounding

Fig. 2.1 Schematic diagram of the RF circuit. Note the difference in flux, or line density, at the needle tip compared to the grounding pad. (From: Hong K, Georgiades C. Radiofrequency ablation: Mechanism of action and devices. J Vasc Interv Radiol. 2010;21(suppl 8). doi:10.1016/j.jvir.2010.04.008)  



probe. The EM field, with a focal point at the tip of the probe, causes nearby water molecules to orient in the direction of the field. As the field’s orientation is flipped rapidly, the molecules vibrate. Friction between adjacent vibrating molecules results in heat and ultimately an increase in local temperature. An important point is that the probe itself does not become hot or generate heat. As the temperature approaches 50˚C, human tissue burns rapidly. Tissue death in mammals occurs in 2 seconds at 55˚C, whereas at 100˚C tissue death is instantaneous and results in charring of tissue adjacent to the electrode tip.7 The longer the duration of the RF ablation, the larger the volume of the burnt tissue. As demonstrated in Figs. 2.2 and 2.3, both temperature and duration of the ablation are important considerations when performing an RFA procedure. Time to cell death

Modern continuous RF devices apply energy at a frequency of 0.1–1 MHz to produce an RF heat lesion. Sensory stimulation at 50 Hz at less than 0.5 V is utilized to produce pain or paresthesia in the area involved. Motor stimulation, usually at 2 Hz, is utilized to ensure proper placement and to avoid lesioning of motor nerves.8 The RFA lesion is then maintained at a temperature of 60–90˚C for 60–90 seconds.8 One of the limitations of traditional RFA is the radius of the ablation. Larger ablations using traditional RFA require either longer duration of applied RF energy or higher amounts of energy, both of which cause increasing impedance in the core of the ablation, thereby limiting their feasibility. Larger ablations are possible using probes perfused with liquid that circulates to cool the tissue at the core of the ablation (Fig. 2.4). This is termed cooled RFA. For example, in one 2017 study of ex vivo bovine livers, the mean 15 min 20 secs 2 secs