
==== Front
Oper Neurosurg (Hagerstown)
Oper Neurosurg (Hagerstown)
ONEUS
ONS
Operative Neurosurgery
2332-4252
2332-4260
Wolters Kluwer Philadelphia, PA

37668987
ONS-D-23-00369
10.1227/ons.0000000000000860
00010
3
Spinal: Lumbar: Posterior Lumbar Approach: Rhizotomy of Lumbosacral Nerve Roots
Stereotactic and Functional
Instrumentation
Stereotactic and Functional
Navigated Radiofrequency Ablation Peripheral Rhizotomy for Lumbosacral Hypertonia in a Nonambulatory Patient With Spinal Fusion: Indications, Surgical Techniques, and Lessons Learned
LoPresti Melissa A. MD, MPH *
Horak V. Jane BA *‡victoria.horak@my.rfums.org

Trierweiler Robin BS, CNIM *§robin.trierweiler@nuvasive.com

Stone Lauren E. MD ‖lauren.stone.nsg@gmail.com

Krater Timothy DO ¶tkrater@sralab.org

https://orcid.org/0000-0002-1865-9888
Raskin Jeffrey S. MS, MD *
* Division of Pediatric Neurosurgery, Department of Neurological Surgery, Ann & Robert H. Lurie Children's Hospital, Northwestern University Feinberg School of Medicine, Chicago, Illinois, USA;
‡ Chicago Medical School, Rosalind Franklin University of Medicine and Science, North Chicago, Illinois, USA;
§ Nuvasive Clinical Services, Columbia, Maryland, USA;
‖ Department of Neurological Surgery, UC San Diego Health, La Jolla, California, USA;
¶ Shriley Ryan AbilityLab, Chicago, Illinois, USA
Correspondence: Jeffrey S. Raskin, MS, MD, Department of Neurological Surgery, Division of Pediatric Neurosurgery, Ann & Robert H. Lurie Children's Hospital, Northwestern University Feinberg School of Medicine, 225 E Chicago Ave, Chicago, IL 60611, USA. Email: jraskin@luriechildrens.org
11 2023
4 9 2023
25 5 461468
08 5 2023
07 6 2023
Copyright © 2023 The Author(s). Published by Wolters Kluwer Health, Inc on behalf of Congress of Neurological Surgeons.
2023
https://creativecommons.org/licenses/by-nc-nd/4.0/ This is an open access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND), where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially without permission from the journal.

BACKGROUND AND OBJECTIVES:

Radiofrequency ablation (RFA) is a destructive therapy which causes target tissue destruction by application of a thermal dose. Neurosurgical applications of RFA are well-described for myriad chronic pain and movement disorder diagnoses. In fact, RFA pallidotomy and thalamotomy are the initial procedures from which the field of neurosurgical management for movement disorders emerged. RFA rhizotomy for post-traumatic spasms was popular in the 1970s and 1980s, although it was largely abandoned after the invention and Food and Drug Administration approval of intrathecal baclofen therapy. RFA has not been described as a primary treatment of hypertonia in nonambulatory children.

METHODS:

We report a case of computer-navigated, nonselective RFA peripheral rhizotomy for a nonambulatory child with a history of severe scoliosis and spinal fusion, where an open rhizotomy was technically impractical.

RESULTS:

Navigation to and ablation of the bilateral L1–L5 peripheral nerves with this approach was successful, and the patient experienced bilateral lower extremity tone improvement.

CONCLUSION:

We use this case to highlight considerations in indications, our applied operative technique, and lessons learned from this novel application of RFA peripheral rhizotomy in children.

KEY WORDS:

RFA
Radiofrequency ablation
Pediatric
Movement disorders
Spasticity
Dystonia
Hypertonia
Rhizotomy
OPEN-ACCESSTRUE
==== Body
pmcABBREVIATIONS:

DRG dorsal root ganglion

EMG electromyography

ITB intrathecal baclofen

RAL right adductor longus

RFA radiofrequency ablation

S EMG spontaneous EMG

T EMG trigger EMG.

Radiofrequency ablation (RFA) uses frequency alternating current through a resistive needle with an exposed tip, thus delivering a thermal dose to a focal area of interest. Neuromonitoring can confirm localization, and motor and sensory nerve modalities can be tested before ablation. RFA lesions are created by administering a set temperature for a specific duration, often 90 seconds at 80–90 degrees celsius (°C).1,2

RFA has been used in the neurosurgical armamentarium since the 1970s for hypertonic spasm after spinal cord injury.1-3 In these early applications, the needles were used to target spinal neuroforamen through fluoroscopic guidance.1-3 Although effective for tone control, range of motion remained largely untreated, and the procedure was abandoned after the Food and Drug Administration approval of the intrathecal baclofen (ITB) pump in 1984. Today, RFA is primarily used for pain management, well-described for trigeminal neuralgia,4 dorsal sensory nerves of the zygapophyseal joint in axial back pain, and sympathectomy for hyperhidrosis.5-8

RFA has not been described as a treatment for hypertonia in children with movement disorders. Navigated techniques to the neuroforamen are also not described. We report a case of navigated RFA targeting the bilateral L1-L5 neuroforamen to achieve nonselective peripheral rhizotomy in a child with mixed hypertonia and a spinal fusion for severe scoliosis in which an open rhizotomy was technically impractical. Spinal navigation is underutilized in functional neurosurgery. This case highlights how previous effective surgical techniques can be updated by technology, emphasizes principles of technique, and documents lessons learned and intraoperative considerations to inform surgical decision-making.

CASE METHODS

Procedure Consent and Research Ethics

The participants and any identifiable individuals consented to publication of his/her image. However, for the protection of our patient's identity, we only included deidentified information in this study. Therefore, patient consent for inclusion of identifiable information was specifically waved by our Institutional Review Board because it did not apply in our case. Our Institutional Review Board approved this case report's proposal and found this study to be following the guidelines detailed by the Declaration of Helsinki. Patient data were stored securely, and confidentiality was maintained throughout this process.

Preoperative Evaluation

The patient is a 17-year-old boy with spastic, dystonic quadriplegic cerebral palsy with a gross motor functional classification score of V, epilepsy, neuromuscular scoliosis, and spinal fusion, who was previously treated with oral antispasmodics and ITB. He presented from physiatry to our institution's Complex Movement Disorder Program for consideration of treating lower extremity tone in the context of an unwanted baclofen pump; the family did not think the intrathecal baclofen was effective enough to warrant continued pump filling and maintenance. The consensus recommendation was for ITB wean, explantation, and nonselective rhizotomy.

Given the patient's severe scoliosis and T1-pelvis thoracolumbar spinal fusion with significant heterotopic fusion mass, conventional open rhizotomy with lumbar laminoplasty was deemed impractical (Figures 1 and 2). Therefore, a navigated L1-S1, bilateral RFA for nonselective peripheral rhizotomy was indicated.

FIGURE 1. 3-dimensional computed tomography reconstructions of the lumbosacral spine demonstrating prior spinal fusion, baclofen pump hardware (arrow), and scoliosis with rotational abnormalities and iliac crests at the level of L4-5.

FIGURE 2. Axial bone window computed tomography image through L1 neuroforamen demonstrating rotational anomaly, intraspinal baclofen catheter, and narrow left surgical corridor to the left L1 neuroforamen (arrow). A hyperdense spot in the spinal canal identifies the spinal catheter.

Pump Removal and Navigation Set-Up

The patient underwent general anesthesia, received preoperative antibiosis, and a surgical pause was performed. He was placed supine, and the baclofen pump was accessed through the previous subcostal scar under sterile technique. The side port was aspirated to clear residual baclofen, and the pump and pump segment catheter were removed. The spinal segment was tied off to prevent cerebrospinal fluid egress, and the wound was closed in a typical multilayered fashion. We then turned the patient prone and placed intramuscular needles for electromyography (EMG) recording of the bilateral lumbosacral muscles, including iliopsoas, adductor longus, vastus lateralis, tibialis anterior, biceps femoris, peroneus longus, medial gastrocnemius, adductor hallucis, and external anal sphincter. Spontaneous and trigger EMG were recorded using a 32-Channel Cadwell Cascade Pro through Cascade Surgical Studios. The lumbosacral region was prepped and draped, and a small midline incision was made over the L5 spinous process to place a spinous process patient tracker. A registration scan spanning L1-S1 was performed using the 3-dimensional C-arm fluoroscopy unit. We used the pointer to identify entry points and trajectories to the L1-S1 neuroforamina.

RFA

The planned entry site was infiltrated with 0.5% lidocaine 1:200 000 epinephrine, and a small skin incision was opened with a 15-blade scalpel. We used a 14-gauge bone marrow needle, affixed with a navigation star, to navigate into the neuroforamen. The inner stylet was then removed. Next, a 15-cm, 18-gauge angled RFA needle with a 10-mm exposed tip was placed through the navigated bone marrow biopsy needle and advanced an additional 12 mm to target, distally exposing the RFA tip.

Once positioned, we stimulated at 50 Hertz (Hz), beginning at 0.05 V and escalating until we identified EMG activity in the appropriate myotome. We interpreted very low stimulation thresholds (ie, 0.05 V) to indicate our nerve root level and proximity to the nerve. We then injected 1 cc normal saline through the side port of the RFA needle to promote a homogenous aqueous environment for heat transfer and then ablated to a thermal dose of 90°C for 90 seconds using the G4™ RF Cosman Generator (Boston Scientific). Once RFA was complete, we injected 1 mL of 0.5% lidocaine before removing both needles. This step was conducted at each neural foramen from L1 to L5, bilaterally. Notably, the S1 foramen was inaccessible with our set-up because of the prominence of the iliac crest and may have been targetable using longer access and RFA needles. After RFA, we removed the patient tracker and closed each incision with absorbable suture. The total surgery length, including pump explant, was 4 hours 22 minutes, with the navigated RFA peripheral rhizotomy lasting 1 hour 34 minutes (Video).

VIDEO. A picture-in-picture video displaying the RFA-navigated rhizotomy described in our report. This video was collaboratively produced by Jesse Arseneau and Jeffrey S. Raskin.

1_93ggl3ff Kaltura

Postoperative Course

The patient experienced immediate and significant amelioration of bilateral lower extremity tone. Formal clinical evaluation of muscle tone using the Modified Ashworth Scale performed by an expert physiatrist revealed preoperative hip extension 2, hip abduction 2, knee extension 3, and ankle dorsiflexion 2. Postoperative evaluation by the same examiner demonstrated improvement to Modified Ashworth Scale hip extension 0, hip abduction 0, knee extension 2, and ankle dorsiflexion 2. Similarly, his mother noted that he could easily be positioned without preoperative hip flexion, hip adduction, and knee flexion posturing episodes. He was discharged to his facility in stable condition on postoperative day 2. At the 2-week follow-up, his incisions were healing as expected, and his tone improved significantly. He has begun weaning oral baclofen and started gabapentin for what is interpreted as mild pain.

DISCUSSION

We present a pediatric patient with bilateral lower extremity hypertonia and severe scoliosis with instrumented spinal fusion who underwent a navigated RFA for nonselective peripheral rhizotomy. We successfully navigated to and ablated the bilateral L1-L5 peripheral nerves with this approach. We highlight this case to detail our operative technique and lessons learned.

Considerations for RFA Peripheral Rhizotomy in Pediatric Patients

Movement disorders in children most commonly manifest as hypertonia from pathologies such as cerebral palsy, congenital abnormalities, and metabolic conditions. Treatment is multimodal including bracing, therapies, medical management with antispasmodics, and ITB and rhizotomy evaluation. Unfortunately, the nonambulatory population of gross motor functional classification score IV and V patients do not benefit from selective rhizotomy; the surgical approaches to these patients are termed nonselective, palliative, or partial and sometimes include the addition of ventral root sectioning.

Dorsal afferent pathways are implicated in the pathophysiology of hypertonia from spasticity,9,10 and the interruption of this pathway produces the desired improvement. Therefore, there are many modifications to the surgical access and technique of dorsal rhizotomy, first described in the 1960s11 and further pioneered by Drs. Peacock and Park,12,13 with exposure ranging from multilevel laminectomy for access to each nerve root as it exits the spinal canal or focally over the conus, respectively.

Ventral-dorsal rhizotomy is an adaptation of dorsal rhizotomy to include sectioning of the ventral nerve roots. It is a tone control surgery for nonambulatory children, and not a gain-of-function surgery, with ventral rhizotomy performed in addition to the dorsal root sectioning when dystonia is present to further facilitate muscle relaxation.14,15 This surgical intervention may involve inclusion of the dorsal root ganglion (DRG) in the ablation field. The DRG is not the target of the RFA because injury to the DRG has been linked to allodynia.16 Here, we present the application of percutaneous RFA to achieve a nonselective ventral-dorsal rhizotomy, further expanding on modifications and techniques used to reduce hypertonia.

LESSONS LEARNED

Patient Selection

Nonambulatory patients with severe lower extremity hypertonia who might be considered for a lumbosacral rhizotomy but have significant open surgical access difficulty (eg, spinal fusion) are indicated for an RFA peripheral rhizotomy. The main limitations of RFA peripheral rhizotomy are the lack of direct visualization of the nerve root target and the limited ability to confirm the extent of ablation intraoperatively. We could not access the S1 nerve roots based on the length of the 15 cm RFA needle, and we had to take a very angled trajectory to L5 by entering through our L3 skin incision. Severe lordosis will worsen this access issue.

Our navigated technique relies on surgical adjuncts. We used the inferior pedicle as our target guide, aiming parallel and superior to access the peripheral nerve in the foramen. We have found that navigation improves OR efficiency over fluoroscopy and optimizes the successful targeting of the neuroforamina, especially in this child with a severe scoliotic deformity with a rotational component. The benefit of navigation was most evident when planning trajectories to the L5 nerve root, allowing us to avoid the iliac crest.

Severe spinal deformity with prior spinal fusion and heterotopic bone mass makes any attempt at open rhizotomy unlikely. The close approximation of rods, depth of heterotopic bone, and dural scarring make the risk profile of a conventional open approach very high, thus favoring this safe and effective minimal access technique. In addition, this technique decreases pathologic tone in the available range of motion; these patients often have comorbid contractures which any tone surgery will not treat.

Electrophysiology

EMG facilitates successful open rhizotomy by providing real-time confirmation of nerve root level, guidance for separating ventral and dorsal rootlets, and assessment of root excitability.17 For our patients, we also used EMG to localize our position within the neuroforamen and estimate distance from the nerve based on the stimulation threshold. Despite artifact presence, apparent EMG spike-train activity was present at low voltages, suggesting proximity to the ventral nerve root.17 Any positive EMG responses obstructed by an artifact in the spontaneous recording could be more clearly seen using a triggered EMG recording (Figure 3).

FIGURE 3. Positive spontaneous EMG (S EMG) and trigger EMG (T EMG) response to stimulation of right L3 nerve root at 50 Hz and 0.06 V. Spike-train EMG seen from right adductor longus (RAL) and right vastus lateralis (RVL). EMG, electromyography; RAL, right adductor longus; S EMG, spontaneous EMG; T EMG, trigger EMG.

For this patient's right L2, the initial EMG response before ablation required 0.5 V, which we found to be much higher than other targets (Table). With later restimulation, we were unable to elicit the prior EMG response. It was, therefore, unclear whether the lack of stimulation was due to a negative response from ablation or confounded due to lidocaine.

TABLE. Stimulation Voltages and Frequency

Nerve root	Stimulation parameters	
Left	Right	
V	Hz	V	Hz	
L1	0.3	50	0.05–0.2	a	
L2	0.4	50	0.5	50b	
L3	0.5	50	0.06	50	
L4	0.17	50	0.19	50	
L5	0.5	50	0.15	50	
a EMG masked by stim artifact.

b Stimulated later in procedure with no response.

L1–5 signifies corresponding nerve root level in the lumbar spine. The stimulation voltages are measured in volts (V), and the frequencies are measured in hertz (Hz).

RFA Technique

We selected the 15-cm, 18-gauge curved RFA needle with a 10-mm exposed tip from the catalog based on its expected ablation dimensions of 12.6 mm long by 7.6 mm wide.18 Our monopolar technique using 90°C for 90 seconds is within the recommended parameters. We found that the curved needle had to be slightly bent back to straight to fit through the bone marrow aspiration needle. Extending the RFA needle beyond the bone marrow needle is critical to focus the current at the RFA needle tip (Figure 4). The integrity of the insulation should be frequently checked because the insulation is thin and can be denuded easily by movement through the bone marrow needle. If this occurs, or the RFA needle is within the bone marrow needle, the current will instead become diffused over the length of the bone marrow needle, manifesting as increased impedance, and resulting in a failure to achieve the thermal dose.

FIGURE 4. The left L2 trajectory is depicted. A and B, The right rip hump and left pelvic tilt. C, A spinous process clamp patient reference array at the level of D, the baclofen pump anchor. E, The trajectory of the navigated bone marrow needle biopsy through which F, the radiofrequency ablation needle electrode protrudes 12 mm past the tip of the G Steri-Strip.

The RFA machine tracks temperature, resistance, current, power, and voltage. We identified 2 limitations to achieving the thermal dose (Figures 5, 6, 7, and 8). First, 1 milliliter (mL) of irrigation was injected through the bone marrow needle to facilitate a homogenous heat spread at the target; more than 1 mL of irrigation led to abnormal fluctuation about the target temperature set point (left L1). Similarly, a failure to achieve the thermal dose occurred when the RFA needle was placed to target but lodged in bone; this was corrected by slightly retracting the RFA needle (left L5).

FIGURE 5. Radiofrequency ablation lesion curve over time for all nerve roots. Left L1 (green) demonstrates oscillation around the temperature target set point due to excessive irrigation. Left L5 (dark blue) demonstrates inability to achieve the temperature set point until it was repositioned.

FIGURE 6. RFA lesion curve over time demonstrating voltage ramp-up curves for RFA (left L2) vs abnormal ramp-up curves until the left L5 RFA needle was retracted from bone. RFA, radiofrequency ablation.

FIGURE 7. RFA lesion curve over time demonstrating current ramp-up curves for RFA (left L2) vs abnormal ramp-up curves until the left L5 RFA needle was retracted from bone. RFA, radiofrequency ablation.

FIGURE 8. RFA lesion curve over time demonstrating impedance ramp-up curves for RFA (left L2) vs abnormal ramp-up curves until the left L5 RFA needle was retracted from bone. RFA, radiofrequency ablation.

Limitations

While we review a novel case highlighting the application of RFA for peripheral rhizotomy in children and considerations regarding planning and execution, our findings are limited in that this case study does not include a large sample size from which statistically significant conclusions can be drawn. Furthermore, this technique successfully reached L1-L5, but we could not reach the S1 nerve roots. We used several methodologies to target the mixed spinal nerve, including computer navigation, neuromonitoring with EMG, and a parallel trajectory to maximize potential contact of the nerve to the RFA volume; however, there is no intraoperative or postoperative radiographic evidence of a lesional effect. Alternative strategies to prove this surgical technique could include a lateral contrast durogram to define the dural root sleeve further and maximize RFA needle placement and postoperative MRI to show a nerve root lesion. The durability of this treatment is unproven.

CONCLUSION

We report a case of nonselective RFA peripheral rhizotomy in a child with a history of severe scoliosis and prior spinal fusion, where an open rhizotomy was technically not feasible. Instead, we improved tone using a minimally invasive approach that did not require extensive dissection of the patient's previously instrumented spinal fusion. When applying this technique, we learned many salient lessons which we highlight here, underscoring the importance of surgical adjuncts such as navigation and neuromonitoring, as well as nuances regarding RFA workflow and interpretation.

Funding

This study did not receive any funding or financial support.

Disclosures

Jeffrey S. Raskin received educational honoraria from Medtronic. The other authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article.

COMMENTS

Chronic intrathecal baclofen (ITB) therapy can be effective in treating spasticity of multiple etiologies but requires lifelong maintenance and carries the risk of acute withdrawal upon device malfunction/end of life. The authors report a patient with an implanted ITB system and a spinal fusion, with suboptimal response from ITB, who underwent an image-guided radiofrequency ablation peripheral rhizotomy with improved clinical outcome. Assuming the appropriate navigation equipment is available, this technique may be useful in patients who have failed ITB therapy due to lack of clinical efficacy or device-related complications.

Alon Y. Mogilner

New York, New York, USA
==== Refs
REFERENCES

1. Turnbull IM . Percutaneous lumbar rhizotomy for spasms in paraplegia. Spinal Cord. 1983;21 (2 ):131-136.
2. Kasdon DL Lathi ES . A prospective study of radiofrequency rhizotomy in the treatment of posttraumatic spasticity. Neurosurgery. 1984;15 (4 ):526-529.6493461
3. Coleman P . The problem of spasticity in the management of the spinal cord-injured patient and its treatment with special reference to percutaneous radiofrequency thermal selective sensory rhizotomy. J Neurosci Nurs. 1976;8 (2 ):97-104.
4. Wasim MH Saleem SA Naqvi SA Hasan MN Durrani NA Zubair M . Recurrence rate of trigeminal neuralgia with the use of percutaneous stereotactic continuous radiofrequency ablation at 80°C for 90 seconds: a single-center study. Cureus. 2022;14 (1 ):e21453.35223237
5. Reyad RM Hakim SM Abbas DN Ghobrial HZ Mansour E . A novel technique of saddle rhizotomy using thermal radiofrequency for intractable perineal pain in pelvic malignancy: a pilot study. Pain Physician. 2018;21 (6 ):e651-e660.30508996
6. Palea O Andar HM Lugo R Granville M Jacobson RE . Direct posterior bipolar cervical facet radiofrequency rhizotomy: a simpler and safer approach to denervate the facet capsule. Cureus. 2018;10 (3 ):e2322.29765790
7. Leon JF Ortiz JG Fonseca EO Martinez CR Cuellar GO . Radiofrequency neurolysis for lumbar pain using a variation of the original technique. Pain Physician. 2016;19 (3 ):155-161.27008289
8. Garcia Franco CE Perez-Cajaraville J Guillen-Grima F Espana A . Prospective study of percutaneous radiofrequency sympathicolysis in severe hyperhidrosis and facial blushing: efficacy and safety findings. Eur J Cardiothorac Surg. 2011;40 (4 ):e146-e151.21683609
9. Enslin JMN Langerak NG Fieggen AG . The evolution of selective dorsal rhizotomy for the management of spasticity. Neurotherapeutics. 2019;16 (1 ):3-8.30460456
10. Sherrington CS . Nervous rhythm arising from rivalry of antagonistic reflexes: reflex stepping as outcome of double reciprocal innervation. Proc R Soc Lond B. 1913(86 ):233-261.
11. Gros C Ouaknine G Vlahovitch B Frerebeau P . La radicotomie selective posterieure dans le traitement neuro-chirurgical de lhypertonie pyramidale. Neurochirurgie. 1967;13 (4 ):505-518.6049136
12. Peacock WJ Staudt LA . Selective posterior rhizotomy: evolution of theory and practice. Pediatr Neurosurg. 1991;17 (3 ):128-134.1819326
13. Park TS Gaffney PE Kaufman BA Molleston MC . Selective lumbosacral dorsal rhizotomy immediately caudal to the conus medullaris for cerebral palsy spasticity. Neurosurgery. 1993;33 (5 ):929-934; discussion 933-4.8264897
14. Ahluwalia R Bass P Flynn L Conus-level combined dorsal and ventral lumbar rhizotomy for treatment of mixed hypertonia: technical note and complications. J Neurosurg Pediatr. 2021;27 (1 ):102-107.
15. Albright AL Tyler-Kabara EC . Combined ventral and dorsal rhizotomies for dystonic and spastic extremities. Report of six cases. J Neurosurg Pediatr. 2007;107 (4 ):324-327.
16. Nakamura SI Myers RR . Injury to dorsal root ganglia alters innervation of spinal cord dorsal horn lamina involved in nociception. Spine. 2000;25 (5 ):537-542.10749628
17. Rose RD . Selective posterior rhizotomy: a guide for intraoperative neurophysiography. Am J Electroneurodiagnostic Technol. 1997;37 (1 ):27-50.
18. Cosman ER Jr. Dolensky JR Hoffman RA . Factors that affect radiofrequency heat lesion size. Pain Med. 2014;15 (12 ):2020-2036.25312825
