Background: Many patients who undergo spinal decompressive surgery experience persistent postdecompression numbness for 1–2 years or longer, even in the absence of nerve root compression. This
study assessed the effi cacy of pulsed radiofrequency (PRF) when being applied to the dorsal root ganglion
(DRG) during lumbar decompression surgery.
Methods: This prospective study collected clinical data pertaining to neurological examinations,
comorbidities, and related medication history among patients who underwent dorsal root ganglion
radiofrequency (DRG-RF) stimulation during spinal surgery. Intra-operative bipolar PRF was performed
under direct visualization, and follow-up assessments were conducted at 2 weeks, 1 month, and 3 months
post-decompression surgery.
Results: Among the 25 patients enrolled in this study, only 2 cases of post-surgery pain and numbness
were observed. Roughly 92% of the patients reported immediate positive effects resulting in an average
decrease in pain of 80% (range: 50%–90%). All or nearly all patients reported satisfaction with the
procedure at 2 weeks (n = 25), 1 month (n = 23), and 3 months (n = 23) post-DRG-RF therapy. Numeric
rating scores at these time points were minimal, with median scores of 2 (range: 1–6), 2 (range: 0–5), and
1 (range: 0–5), respectively. DRG-RF therapy was also shown to reduce reliance on painkillers at 2 weeks
(n = 12), 1 month (n = 16), and 3 months (n = 16) after decompression surgery.
Conclusion: This study recommends the implementation of bipolar pulse radiofrequency during lumbar
decompression surgery to reduce recovery time and enhance the quality of life of patients.

Keywords: decompression surgery, pain, paresthesia, radiofrequency, spinal, thermocoagulation

Lumbar radicular pain is the most common form of neuropathic pain, affecting up to 25% of the general population [1]. Individuals suffering from lumbar radicular pain must live with declines in functional ability and quality of life [2]. This condition is a form of neuralgia resulting from irritation or damage to the roots of sensory nerves in the lumbar spine [3]. Radicular pain in the lower extremity can be traced back to the ectopic fi ring of action potentials in the lumbar nerve roots or other neuropathic mechanisms [4]. The resulting sharp stabbing pain radiates through the area innervated by the affected nerve. The most common causes include the stimulation of inflammatory processes, mechanical compression by a herniated intervertebral disc (HIVD) in the lumbar spine, or peripheral foraminal stenosis [5]. Roughly 75% of patients with acute lumbar radicular pain enjoy full recovery within a few months [6]; however, some patients require decompression or even reconstructive surgery.

Pulsed radiofrequency (PRF) stimulation is commonly used to treat the pain of sciatica following HIVD or foraminal stenosis. This treatment was first presented by Sluijter in 1997 as a safe and minimally invasive approach to alleviating pain via the delivery of an electrical field and heat bursts to targeted nerves or tissue without damaging these structures [7-9]. PRF delivers a brief electrical stimulation followed by a long resting phase to prevent the buildup of potentially damaging thermal energy. Several studies have reported that PRF stimulation of the dorsal root ganglion (DRG) is an effective approach to controlling lumbar radicular pain [10-13].

In the current study, we developed a hybrid procedure involving the application of bipolar PRF stimulation to the DRG during lumbar decompression surgery to reduce post-decompression numbness and pain. Our objectives were to evaluate the effects of intraoperative bipolar PRF stimulation at the patient level and to assess the cost-effectiveness of this treatment strategy.

Between January and December 2019, a total of 25 patients underwent intra-operative bipolar DRGPRF stimulation for the treatment of lumbar radicular numbness or pain at our institution. We prospectively collected clinical data including medical history, medication history, and comorbidities. All patients underwent thorough pre-surgical evaluations prior to lumbar surgery, including X-rays (antero-posterior and lateral views), dynamic X-rays, and magnetic resonance imaging (MRI). Bipolar PRF stimulation was used to prevent the numbness that commonly occurs after decompression surgery. Follow-up assessments were performed at 2 weeks, 1 month, and 3 months after the operation (Figure 1).

Figure 1. Flowchart for This Clinical Study
NPRS, numerical pain rating scale; PRF, pulsed radiofrequency.

Inclusion criteria were as follows:

1. History of segmental pain of lumbar or sacral origin radiating from the back to the leg over a period of at least 6 months.

2. Age between 20 and 79 years.

3. Unsatisfactory response to conservative treatment involving medication and rehabilitation, as evidenced by self-reported radicular pain of at least 5 on the numeric rating scale (NRS) radiating into the leg.

4. Imaging findings (MRI and/or computed tomography) of HIVD or lumbar stenosis (lateral recess or foraminal stenosis) compatible with pain symptoms.

5. No previous history of spinal surgery, such as lumbar fusion or laminectomy. Exclusion criteria were as follows:

1. Neurological symptoms involving more than 1 level dermatome.

2. Myelopathy.

3. Infection of the spine.

4. Coagulation disorders.

The Institutional Review Board of our hospital approved this study, and all patients provided signed informed consent.

In this cohort of 25 patients, when facet instability is present, we opt for a fusion procedure to address and treat the pain originating from the facet or sacroiliac joint. Conversely, if there is no instability, our choice is to perform discectomy or laminectomy alone.

PRF therapy was performed using a 20 G isolated needle targeting the DRG. Following root decompression, the location of the indwelling needle tip was confirmed via microscope observation. Sensory and motor tests were not performed due to anesthetic status. PRF therapy involved 4-min 65 V PRF treatment cycles to maintain the temperature of the lesion between 40°C and 42°C.

In this study, the symptom level and laterality corresponding to the patient’s symptoms align with the levels of PRF stimulation. As per the definition, the DRG is located at the base of the nerve root, as illustrated in our Figure 2B. We positioned two electrodes on the upper and lower sides of the nerve root base, with the distance between the two electrodes being equal to the diameter of the nerve root, which varies depending on the size of the patient’s nerves. While the diameter differs for each individual, the PRF protocol remains consistent.

Figure 2. Bipolar Radiofrequency Treatment
(A) Bipolar radiofrequency treatment during laminectomy (X-ray); (B) Bipolar radiofrequency treatment during
laminectomy (direct vision); (C) Bipolar radiofrequency treatment during foraminotomy (X-ray); (D) Bipolar
radiofrequency treatment during foraminotomy (direct vision).

All patients were evaluated for at least 3 months after surgery/RF treatment. Follow-ups were conducted at 2 weeks, 1 month, and 3 months after the procedure. The clinical condition of the patients was evaluated pre-RF and post-RF using a questionnaire probing the severity of lower leg hypoesthesia and weakness, the patterns of low back pain, the time interval between treatment and pain relief, the need for pain medication, and the degree of lower leg hypoesthesia and weakness. To avoid selection bias, the questionnaires were administered by a nurse from our hospital who was not involved in the selection or management of patients.

Pain outcomes were scored using the NRS, which is an 11-point scale ranging from “0” indicating “no pain” to “10” indicating “pain as bad as you can imagine” or “the worst pain imaginable.” The patients were asked to make three pain ratings corresponding to the current, least, and greatest pain experienced over the previous 24 hours. The average of the three ratings was used to represent the level of pain experienced by the patient over the previous 24 hours.

Data are presented as median (range) or mean (± standard deviation) for continuous variables and as frequencies and percentages for categorical variables. Logistic regression analysis was employed to assess the influence of various clinical factors on treatment outcomes. Statistical significance was evaluated using the Wilcoxon rank sum and Kruskal-Wallis tests for continuous data as well as Pearson chi-square and Fisher exact tests for categorical data using SPSS software (Version 17.0; SPSS Inc, Chicago, IL, USA).

This study enrolled 15 male and 10 female participants with a median age of 62 years (range: 18–82 years), the characteristics of which are listed in Tables 1 and 2. The median duration of postoperative symptoms was three months (range: 0.5–240.0 months). Among the subjects, 20% (n = 5) had spinal stenosis, 32% (n = 8) had spondylolisthesis, 24% (n = 6) had HIVD, 12% (n = 3) had a ruptured disc, 8% (n = 2)had a fracture, and 4% (n = 1) had HIVD in combination with spinal stenosis. Among the subjects, 52% (n = 13) suffered unilateral symptoms, while 48% (n = 12) suffered bilateral symptoms. Additionally, 60% of the individuals (n = 15) reported experiencing numbness, while 52% (n = 13) reported sensory abnormalities. The median baseline NRS score was 8.0 (range: 5–9). Prior to initiating the DRG-PRF procedure, all patients (n = 25) received opioid-based pain control. Among the subjects, 92% (n = 23) received PRF at one spinal level, whereas 8% received PRF at two spinal levels.

As shown in Table 3, 92% of the patients treated with DRG-RF (n = 23/25) reported positive treatment effects immediately after the operation, with an average pain relief of 80% (range: 50%–90%). All of the patients expressed satisfaction with DRG-PRF therapy at 2 weeks (n = 25/25), and most patients expressed lasting satisfaction at 1 month (n = 23/25) and 3 months (n = 23/25). The NRS scores were as follows: 2 weeks (2; range: 1–9), 1 month (2; range: 1–9), and 3 months (1; range: 1–9). This treatment was shown to reduce reliance on painkillers: 2 weeks (n = 12/25), 1 month (n = 16/25), and 3 months (n = 16/25). Regarding opioid use, it was observed that 14 out of 25 patients (56%) were able to discontinue the use of opioids by the 2-week mark. Additionally, throughout the three-month follow-up period, 16 out of 25 patients (64%) did not require any opioids. Note that a successful outcome was defined by self-reported patient satisfaction and a reduction in the reported pain index (i.e., NRS). Logistic regression analysis was used to identify the clinical factors associated with success in the treatment of pain. Overall, treatment success did not vary with age, gender, duration of symptoms, previous decompression surgery, the number of pain levels treated, baseline NRS, or the treatment group to which patients were assigned. In other words, this was a negative finding.

Modern approaches to decompression surgery (i.e., total laminectomy or foraminolaminectomy) make it possible to stimulate the nerve root directly under visual guidance to eliminate the need for repeated punctures in localizing the root or DRG.Decompression of pain generators in the disc or foramen generally leads to an immediate cessation of pain; however, radicular numbness can persist for an extended duration. In the current study, we sought to eliminate persistent radicular numbness and pain through the use of a hybrid surgical procedure in which decompression is implemented in conjunction with bipolar PRF stimulation of the DRG (see Figure 2A to 2D).

In the current study, bipolar PRF was shown to reduce numbness and/or pain in a remarkable 92% of subjects. Note that this surgical procedure was made possible by specially designed cannulas (straight or curved) in conjunction with an RF probe (Cosman Medical, Inc. MA, USA). The visualization of foraminal nerve roots ensured the reliable implementation of the PRF procedure with a high degree of accuracy.

Intra-operative PRF is not a novel procedure. In 2005, researchers performed a non-randomized pilot study involving 50 patients undergoing endoscope-visualized rhizotomy of the dorsal ramus in conjunction with PRF for the relief of chronic low back pain resulting from lumbar spondylosis or facet arthrosis. Note that the study cohort was limited to patients who experienced pain relief of at least 50%–70% via medial branch blocks. Since that time, roughly 1,000 patients have undergone endoscopic visualized dorsal rhizotomy [14,15], and in 2016, Yeung and Teoh [14] employed PRF stimulation during endoscopic decompression.

The primary mechanisms underlying PRF-induced pain relief include thermocoagulation and the generation of an electromagnetic field within ganglion nerves. In 1968, an electrophysiology experiment conducted on felines by Letcher and Goldring [16] revealed that the heat generated by PRF selectively blocked delta and C waves. This suggests that alpha and beta waves persist even at temperatures at which delta waves and C waves are no longer present. This study was predicated on the supposition that if PRF allowed the selective targeting of pain nerve fibers while preserving other fibers, then intra-operative bipolar PRF would be an ideal approach to dealing with post-decompression radiculopathic numbness. It also appears that the nerve depression induced by thermocoagulation and electromagnetic effects within the ganglion contribute to long-term post-operative pain Case control [17,18].

Recent research has indicated that parallel RF cannulas are superior to monopolar PRF in terms of pain reduction. Cosman et al. [19] reported that the lesions induced by parallel-tip bipolar RF were larger than those induced by monopolar RF. Kapural et al. [20] reported that bipolar intradiscal RF allows the targeting of broader areas than is possible using monopolar RF. In an imaging study, Shen et al. [21] compared monopolar and bipolar RF in terms of lesion size: monopolar RF using a 20-gauge cannula with a 10-mm exposed tip (7.8 × 12.8 mm2 ) and bipolar RF with parallel cannulas spaced 10 mm apart (15.5 × 11.8 mm2 ). Considering the average mean length of the L5 DRG in a normal human lumbar (11.58 mm × 6.40 mm), it appears that bipolar RF but not monopolar RF could cover the entire DRG. In a 2017 study of 50 patients with chronic lumbosacral radicular pain, Chang et al. [22] determined that bipolar PRF was more effective than monopolar PRF in reducing chronic lumbosacral radicular pain. Furthermore, several studies have suggested that bipolar PRF may possess the potential to ameliorate pain in patients with prior exposure to transforaminal epidural steroid injection and monopolar PRF [23-25]. Beyond the theoretical mechanisms, this observation may provide additional clinical perspective on the potential superiority of bipolar PRF over monopolar PRF. Note however that no previous studies have assessed the therapeutic efficacy of bippolar PRF stimulation during decompression surgery.

Nonetheless, it is important to consider the degree to which variations in treatment mechanisms and underlying etiologies can affect clinical outcomes. Modern RF machines allow the adjustment of multiple parameters, including stimulation voltage, frequency, and pulse width. Further advances in this technology will require a comprehensive understanding of RF techniques and the establishment of standardized protocols for intra-operative RF procedures.Despite the widespread clinical use of RF, determining the optimal parameters for PRF remains a challenge. Cosman and Cosman [26] emphasized the need to elucidate the effects of electrical and thermal fields on neurons. They posited that the overall response of neurons to this treatment varies as a function of electrical dose, which in turn is determined by the duration of exposure. Nonetheless, there is currently no consensus among researchers as to the recommended duration for PRF stimulation. The typical duration is 120 s; however, a number of researchers have reported successful outcomes using durations ranging from 4 to 10 mins [27,28]. Some researchers have also explored the use of analgesics and steroids as an adjunct at the conclusion of PRF treatment [29].

The proposed intra-operative PRF stimulation scheme is easily implemented with direct visualization, and the placement of RF cannulas close to the root during disc decompression (i.e., in the shoulder and axilla regions) makes it possible to identify nerve branches in the foramen and safely work on small nerves (< 1 mm). Distal pushing makes it possible to prevent air exposure and achieve temperatures reaching 45°C. Unlike percutaneous PRF procedures, the proposed method ensures the transfer of RF energy to the root ganglion, even when a patient is under anesthesia.

The results obtained in the current study indicate that many patients with severe deformities or degenerative scoliosis (i.e., those at high-risk for post-decompression radicular numbness and pain) could safely undergo the proposed hybrid procedure. Future research should aim for level 1 evidence to support the efficacy and safety of intra-operative bipolar PRF stimulation; however, implementing blinded assessments will likely impose challenges. Nonetheless, the favorable clinical outcomes reported in this study provide a solid basis for continued research on this approach to dealing with the pain/numbness associated with decompression surgery.

This study could be criticized for including patients with a variety of pathologies pertaining to chronic lumbar pain; however, it should be noted that in terms of treatment response rates, previous largescale case series have revealed no differences between disc-related cases and other causes of pain [26]. The fact is that most patients present a combination of degenerative spinal diseases involving lateral recess stenosis, disc changes, facet arthropathy, and foraminal or spondylolisthesis. Narrowing the inclusion criteria to only one of these conditions would greatly limit recruitment opportunities.

None.