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. 2024 Jan 6;16(3):724–732. doi: 10.1111/os.13981

Paravertebral Muscular Neurophysiological Function as an Independent Outcome Predictor of Recurring Herniation/Low Back Pain after Radiofrequency Ablation: A Prospective Follow‐Up and Case‐Control Study Based on Surface Electromyography

Jian Li 1,2, Gengyan Xing 2, Pengfei Lu 3,✉, Yi Ding 2,4,✉
PMCID: PMC10925511  PMID: 38183345

Abstract

Objective

Spinal endoscopy radiofrequency is a minimally invasive technique for lumbar disc herniation (LDH) and low back pain (LBP). However, recurring LDH/LBP following spinal endoscopy radiofrequency is a significant problem. Paravertebral musculature plays a crucial role in spine stability and motor function, and the purpose of the present study was to identify whether patients’ baseline lumbar muscular electrophysiological function could be a predictor of recurring LDH/LBP.

Methods

This was a prospective follow‐up and case‐control study focusing on elderly patients with LDH who were treated in our department between January 1, 2018, and October 31, 2021. The end of follow‐up was recurring LBP, recurring LDH, death, missing to follow‐up or 2 years postoperation. The surface electromyography test was performed before the endoscopy C‐arm radiofrequency (ECRF) operation to detect the flexion–relaxation ratio (FRR) of the lumbar multifidus (FRRLM) and the longissimus erector spinae (FRRES), and the other baseline parameters included the general characteristics, the visual analogue scale, the Japanese Orthopaedic Association score, and the Oswestry Disability Index. Intergroup comparisons were performed by independent t‐test and χ2‐test, and further binary logistic regression analysis was performed.

Results

Fifty‐four patients completed the 2‐year follow‐up and were retrospectively divided into a recurring LDH/LBP group (Group R) (n = 21) and a no recurring group (Group N) (n = 33) according to their clinical outcomes. FRRLM and FRRES in Group N were much higher than those in Group R (p < 0.001, p = 0.009). Logistic regression analysis showed that only the FRRLM (odds ratio [OR] = 0.123, p = 0.011) and FRRES (OR = 0.115, p = 0.036) were independent factors associated with the ECRF outcome.

Conclusions

Lumbar disc herniation patients’ baseline FRRLM and FRRES are independent outcome predictors of recurring LDH/LBP after ECRF. For every unit increase in baseline FRRLM, the risk of recurring LDH/LBP is decreased by 87.7%, and for every unit increase in baseline FRRES, the risk of recurring LDH/LBP is decreased by 88.5%.

Keywords: Flexion–Relaxation Ratio, Outcome Predictor, Paravertebral Musculature Function, Spinal Endoscopy Radiofrequency, Surface Electromyography (sEMG)

For every unit increase in baseline FRRLM, the risk of recurring lumbar disc herniation (LDH)/low back pain (LBP) decreases by 87.7%, and for every unit increases in baseline FRRES, the risk of recurring LDH/LBP decreases by 88.5%.

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Introduction

Lumbar disc herniation (LDH) is a common chronic orthopaedic disease closely related to aging and is the most common reason for sciatica and lower back pain (LBP) in the elderly population. 1 , 2 LDH is very common among elderly people from at age of 60 years old. 3 Sciatica and LBP are the main symptoms of LDH, with a lifetime prevalence of 84%. 4 LDH is a typical degenerative process of the lumbar intervertebral disc and is the initial step in spinal degeneration. 5

Spinal endoscopy and C‐arm double‐guided radiofrequency (ECRF) is a newly developing minimally invasive technique of LDH. It can provide both direct visualization and C‐arm guiding during the operation 6 and is suitable for elderly patients. ECRF has superior efficacy for LDH‐caused sciatica. It can reduce the pressure in the intervertebral disc by directly denaturing the protein, deconstructing the molecules of the nucleus pulposus, and shrinking the nucleus pulposus tissue through the thermal effect of molecular resonance caused by radiofrequency (RF). 7 Furthermore, the thermal effect of RF can also destroy the sensory nerve fibers growing into the annulus fibrosus, 7 relieving discogenic LBP in LDH patients.

However, controversy remains about the clinical outcomes of ECRF. Postoperative recurring LDH/LBP is the main problem limiting its clinical application, which ranges from 5% to 32.5%. 7 , 8 , 9 The relationship between lumbar spinal muscular function and LDH has been receiving increasing attention in the published literature. 10 , 11 , 12 , 13 The lumbar spinal musculature (comprising the paravertebral muscles) plays a crucial role in spine stability and motor function, and it is associated with many spine degenerative diseases, 14 such as LDH and LBP, as well as postoperative complications. 15 , 16 LDH patients have been reported to exhibit imbalanced electrophysiological activity between the agonistic and antagonistic muscles of the lumbar paravertebral musculature. 10 Kong et al. reported that fat infiltration (FI) is a potential risk factor related to recurring LDH after L4–5 percutaneous endoscopic lumbar discectomy. 8 Paravertebral musculature functional parameters, such as electrophysiological parameters, might appear much earlier than the morphological parameters. Hence, we consider whether the baseline lumbar muscular electrophysiological function might be an outcome predictor of ECRF for treating LDH. Identifying ECRF indications preoperation is of great clinical significance to LDH patients.

Surface electromyography (sEMG) is an objective and quantifiable method for assessing musculature electrophysiological and neurophysiological function. 10 , 11 , 12 , 13 We hypothesized that the baseline lumbar muscular dysfunction might be a risk factor affecting the outcomes of ECRF. The aims of the present study include: (i) to explore the outcomes of recurring LDH/LBP at medium‐term follow‐up in elderly LDH patients after an ECRF operation; (ii) to analyze sEMG‐based electrophysiology function in patients with and without recurring LDH/LBP; and (iii) to identify whether the baseline sEMG parameters could be an outcome predictor of ECRF for treating LDH.

Materials and Methods

Patient Involvement

The present study was a prospective follow‐up and case‐control study. The elderly patients included in the study were diagnosed with LDH at our department between January 1, 2018, and October 31, 2021. The inclusion criteria were: (i) age 65–79 years, body mass index (BMI) < 30 kg/m2, and diagnostic sciatica with or without LBP; (ii) L4–L5 or L5–S1 LDH with non‐effective conservative treatment; (iii) unilateral symptoms; (iv) MRI showing a definite segmental LDH corresponding to sciatica or the secondary spinal canal and lateral recess stenosis; (v) positive pain provocation test; and (vi) having undergone ECRF with follow‐up ≥2 years. The exclusion criteria were: (i) LDH combined with a primary osseous‐ligamentous spinal canal/lateral recess stenosis/spondylolisthesis; (ii) MRI showing severe degeneration of the target disc (Pfirrmann grading system: Grade V) 17 ; (iii) calcification of the LDH; (iv) operation history of spine; (v) lower extremity malalignment 18 ; and (vi) LDH combined with systematic diseases, autoimmunity disease, nerve system diseases such as rheumatoid arthritis, ankylosing spondylitis, and Parkinson's disease.

At the end of the follow‐up, patients were retrospectively divided into a recurring LDH/LBP group (Group R) and a no recurring group (Group N) according to their different outcomes. The sample size was pre‐calculated using the following formula: n = (μ α + μ β)2 σ 2/δ 2. α was set at 0.05, β was set at 0.01, and the power was 90% (1 − β). The values of μ α (1.96) and μ β (1.2816) were determined according to the μ table. The values of σ (0.63) and δ (0.52) came from pre‐experiment results (n = 5, FRRLM). The calculated sample size was 15.4 (n = 16) (power: 90%), and it was amplified by 20% (18.5, n = 19). The protocols and procedures for protecting human subjects were approved by the Ethics Committee of our hospital (IRB ethical approval: KY‐2017‐Ob021), and all methods were conducted following the approved guidelines.

Surface Electromyography‐Based Lumbar Spinal Musculature Function

All the included LDH patients performed the sEMG test preoperatively. The sEMG‐based flexion–relaxation ratio (FRR) is a validated reliable neurophysiological parameter for assessing the flexion–relaxation phenomenon (FRP) of the spine musculature. 18 , 19 The FRP represents a normal muscular function and refers to extensors’ normal electrical activity silence during the relaxation phase. 18 , 19

The muscle electrical activity of the lumbar multifidus (LM) and longissimus erector spinae (ES) during the flexion and re‐extension task were measured by sEMG (FlexComp Infiniti System, T7550, Thought Technology, Canada). MF and longissimus ES are the main paravertebral muscles at L4–L5 (Figure 1A,B) and L5–S1 segments (Figure 1A,C). The Ag/AgCl electrodes (diameter 2 cm, CH55RD, Cathay Manufacturing Group, Shanghai, China) for LM were located 1 cm from the spinous process at the L5 level. 14 Electrodes for ES were located 5 cm from the spinous process at the L5 level (Figure 1D).

FIGURE 1.

FIGURE 1

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The surface electromyography (sEMG) test of the lumbar multifidus (LM) and longissimus erector spinae (ES) in patients with L4/5 or L5/S1 lumbar disc herniation (LDH). (A) The blue line shows LDH at the L4/5 segment, and the yellow line shows LDH at the L5/S1 segment. (B) The axial MRI at the L4/5 segment; the blue zone is LM, and the yellow zone is longissimus ES. (C) The axial MRI at the L5/S1 segment; the blue zone is LM, and the yellow zone is longissimus ES. (D) The sEMG locating LM and ES; the blue circle is the LM location, and the yellow circle is the longissimus ES location.

The lumbar flexion and re‐extension task comprised four phases of movement 10 : the neutral position (first phase, standing upright), lumbar flexion (second phase, bending forward), relaxation (third phase, maintaining the bending position), and lumbar re‐extension (fourth phase, standing upright to the neutral position), and each movement phase lasted 3 s. 18 , 19 An audio signal was provided to signify each movement. Sufficient practice was needed to familiarize patients with the movement phases and speeds. The sEMG signal was 1000 Hz and was band‐pass filtered between 20 and 450 Hz. Muscle electrical activities were recorded during the task and the root mean square (RMS) values were calculated automatically by the system. Finally, the FRR of LM (FRRLM) and ES (FRRES) were calculated. FRR = maximal activity during the re‐extension phase/mean activity during the relaxation phase. 18 , 19 A lower FRR indicates muscle dysfunction. 18 , 19 We performed three trials for each patient, and bilateral LM and ES were detected at the same time per trial. Finally, the averaged FRR (three results from the symptomatic side and three results from the other side) were presented and analyzed.

Spinal Endoscopy and C‐Arm Double‐Guided Radiofrequency Operation for Lumbar Disc Herniation

LDH patients were under local anesthesia, and the spinal endoscopic RF annuloplasty was performed using the posterior–lateral transforaminal approach reported by Yeung and Tsou. 20 Under C‐arm guidance, an 8‐mm incision was made approximately 6–10 cm from the midline of the targeted segment (Figure 2A,B), and then a working cannula was placed. An RF electrode was connected to the RF instrument (Beijing Bei Qi Technology Medical Company, Beijing, China) and placed. The electrical impedance (200–400 Ω), sensory‐evoked impedance (100 Hz, 0.5–1.0 mA), and motion‐evoked impedance (3 Hz, 1.0–2.0 mA) were measured. The LDH was explored (Figure 2C) to make sure the electrode was distant enough from the nerve root (and did not induce pain in the lower limb muscle during contraction). 7

FIGURE 2.

FIGURE 2

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The spinal endoscopy and C‐arm double‐guided radiofrequency (ECRF) annuloplasty operation for lumbar disc herniation (LDH). (A, B) Intraoperative C‐arm guidance of the L4–L5 LDH. (C) Spinal endoscopy showing the LDH. (D) Spinal endoscopy showing total remission after the radiofrequency annuloplasty.

Radiofrequency coagulation was performed, and the initial working parameter was set at 70°C/60 s, followed by 80°C/60 s, 85°C/60 s, and 90°C/60 s. The RF coagulation was continued for two cycles, and the endoscopy was used to check the result of the annuloplasty between each cycle. When the endoscopy showed a reduction of the LDH compression (Figure 2D) or the patient's sciatica/LBP disappeared, the operation was ended with a drainage placement, and the patient was permitted to walk 2 h later.

Postoperative Rehabilitation

Standard postoperative rehabilitation was performed for all LDH patients. The patient was asked to wear a brace to perform full weight‐bearing motion from 48 h to 1 month after surgery. Lumbar muscle exercises (arch bridge and backward walk training) began from 1 week to 6 months after surgery. Lumbar weight motions and strenuous exercise were avoided for 6 months after surgery.

Follow‐Up

The missing to follow‐up was started when the ECRF operation was completed. The end was recurring LBP, recurring LDH, death, missing or 2 years postoperation, whichever occurred first. General characteristics included age (years), gender, BMI, disease history of LDH, LDH‐related symptoms, and follow‐up time. All of the data above was extracted from the medical record system.

Perioperative complications consisted of nonsurgical‐related complications and surgical‐related complications. Nonsurgical‐related complications included transient fever, transient LBP, urinary retention, urinary system infection, pneumonia, deep vein thrombosis, pulmonary embolism, and pressure ulcers. Surgical‐related complications included surgical site infection, deep infection, nerve injury, and cerebrospinal fluid leakage.

Outcome of Recurring Lumbar Disc Herniation/Low Back Pain

Patients with recurring LDH/LBP were recorded during follow‐up. Recurring LBP was defined as simple LBP (without sciatica) that recurred postoperation, with a pain‐free interval greater than 6 months. Recurring LDH was defined as disc herniation at the same level by MRI, regardless of ipsilateral or contralateral herniation, with a pain‐free interval greater than 6 months. 9 The preoperative MRIs were only performed in symptomatic patients with LBP or sciatica at the end of follow‐up.

Subjective Functional Assessments

The visual analogue scale (VAS), the Japanese Orthopaedic Association (JOA) score, and the Oswestry Disability Index (ODI) were used as clinical functional parameters. All of the LDH patients were assessed with VAS and JOA at the baseline and at the end of the follow‐up.

The pain of LBP was assessed by VAS, which rates the pain severity with a score from 0 to 10. LDH‐related symptoms were assessed by JOA score, including sciatica, sensory disturbance, and dyskinesia, 21 and the total score was 29 22 : nine points for the subjective symptoms, including LBP, leg pain/tingling, and gait difficulties; six points for the clinical symptoms, including straight leg raising test, dyskinesia, and sensory disturbance; and 14 points for the daily activity limitation, including supine turning, standing, washing, forward flexion, sitting, lifting, and walking. ODI comprises 10 items, including lifting, walking, standing, pain intensity, sleeping, sex life, social life, personal care, sitting, and traveling, and each question has six options with a score from 0 to 5 points. The total actual ODI score is 50 points. ODI = the actual score/50 × 100%. 23 Higher ODI scores indicated severer lumbar dysfunction, while lower ODI scores indicated better quality of life and better outcomes.

Statistical Analysis

The continuous data were expressed as mean ± SD, and the count data were expressed as number (n) and rate (/). The comparisons of continuous data were performed using independent t‐tests and Levene variance homogeneity tests, while the comparisons of the count data were performed using the χ2‐test or Fisher's exact test. Binary logistic regression analysis was performed to determine the independent affecting factors of the outcome of recurring LDH/LBP. The level of significance was set at 0.05 (two‐sided test). The statistical analysis was performed using SPSS 20.0 (SPSS, 2009, Chicago, IL, USA).

Results

General Characteristics

Finally, 54 patients completed the 2‐year follow‐up and were retrospectively divided into the recurring LDH/LBP group (Group R) and the no recurring group (Group N) according to their clinical outcomes. Twenty‐one patients were included in Group R (n = 21), consisting of seven cases with recurring LDH (ranging from 4 to 14 months postoperation), 12 cases with recurring LBP (ranging from 4 to 18 months postoperation), and two cases with recurring LBP and LDH (ranging from 3 to 11 months postoperation). The medium time of recurring LDH/LBP was 8 months postoperation (Q1/4: 5 months, Q3/4: 13 months). The other 33 patients without recurring LDH/LBP were included in Group N (n = 33).

Three patients in Group N and two patients in Group R had a transient fever (37.6–37.8°C), but all of those complications disappeared spontaneously within 1–2 days postoperatively. One patient in Group N had urinary retention, and two patients had urinary system infection in Group R postoperation (Table 1). We did not face any severe perioperative complications such as deep infection, nerve injury, cerebrospinal fluid leakage, deep venous thrombosis, or pulmonary infection.

TABLE 1.

General characteristics of the lumbar disc herniation (LDH) patients in Groups N and R

Characteristics Group N (n = 33) Group R (n = 21) p‐value
Age (years) 69.21 ± 4.57 68.38 ± 3.43

t = 1.174

p = 0.244
Gender (n) Male: 27 Male: 19 χ 2 = 0.231
Female: 6 Female: 2 p = 0.631
BMI (kg/m2) 24.92 ± 2.05 24.35 ± 1.48

t = 0.372

p = 0.711
LDH‐related symptoms (n)

Sciatica with LBP: 6

Without LBP: 27

Sciatica with LBP: 4

Without LBP: 17

χ 2 = 0.006

p = 0.936
Pfirrmann grade (n) Grade II: 22 Grade II: 15

χ 2 = 1.510

p = 0.470
Grade III: 4 Grade III: 4
Grade IV: 7 Grade IV: 2
Disease history (n) <5 years: 8 <5 years: 8

χ 2 = 1.496

p = 0.473
5–10 years: 14 5–10 years: 6
>10 years: 11 >10 years: 7
Follow‐up (months) 24.02 ± 0.86 23.73 ± 0.81

t = 1.035

p = 0.304
Perioperative complication (n) With: 4 With: 4 χ 2 = 0.093
Without: 29 Without: 17 p = 0.760
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The general characteristics including age, age distribution, gender, BMI, as well as LDH‐related symptoms, intervertebral disc degeneration degree (Pfirrmann grade), disease history, follow‐up time, and rate of perioperative complication were not significantly different between Group N (n = 33) and Group R (n = 31) (Table 1).

The Surface Electromyography‐Based Muscular Function of Lumbar Multifidus and Erector Spinae

Preoperative sEMG showed that the FRP of LM was relatively normal in Group N (Figure 3A), but the FRP of ES was mildly impaired (Figure 3B), while the FRP of LM and ES were both severally impaired in Group R (Figure 3C,D). The inter‐group comparison revealed that the FRRLM and FRRES in Group N were 33.8% and 23.6% higher than those in Group R (Table 2).

FIGURE 3.

FIGURE 3

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Surface electromyography (sEMG)‐based flexion–relaxation phenomenon (FRP) was detected on the lumbar multifidus (LM) and erector spinae (ES). (A) relatively normal FRP of LM in Group N: there was an electrical activity silence during the relaxation (third) phase. (B) The FRP of ES in Group N was mildly impaired: there was no typical electrical activity silence during the third phase, but the sEMG value of the third phase was lower than the re‐extension (fourth) phase. (C) The FRP of the LM in Group R was severally impaired: there was no typical electrical activity silence during the third phase, and the sEMG value of the third phase was even higher than the re‐extension (fourth) phase. (D) The FRP of the ES in Group R was severally impaired.

TABLE 2.

Comparisons of the preoperative clinical parameters between Group N and Group R.

Parameters Group N (n = 33) Group R (n = 21) p‐value
FRRLM 1.82 ± 0.57 1.36 ± 0.29 t = 3.880
p < 0.001**
FRRES 1.36 ± 0.34 1.10 ± 0.35 t = 2.717
p = 0.009**
VAS 7.06 ± 0.80 6.97 ± 0.75 t = 0.448
p = 0.656
JOA 9.67 ± 0.78 9.38 ± 0.67 t = 1.388
p = 0.171
ODI (%) 49.94 ± 8.48 53.43 ± 11.45 t = 1.202
p = 0.238
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Abbreviations: FRR, flexion–relaxation ratio; JOA, Japanese Orthopaedic Association; ODI, Oswestry Disability Index; VAS, visual analogue scale.

**

p < 0.01.

Preoperative Subjective Functional Parameters

Inter‐group comparisons showed that the preoperative VAS, JOA, and ODI did not have a significant difference between the two groups (Table 2).

Logistic Regression Analysis

Binary logistic regression analysis was performed to determine the independent factors affecting the clinical outcome of ECRF (whether LDH/LBP recurred or not), and the baseline characteristics, including age, gender, BMI, disease history of LDH, LDH‐related symptoms, intervertebral disc degeneration degree (Pfirrmann grade), and the complication rate, as well as the preoperative assessment parameters, including FRRLM, FRRES, VAS, JOA, and ODI, were all considered in the analysis.

Logistic regression analysis showed that only the FRRLM and FRRES were independent factors associated with ECRF outcome for elderly patients with LDH (Omnibus tests of model coefficients, p < 0.001; Hosmer and Lemeshow test, p = 0.264), for every one‐unit increases in baseline FRRLM, the risk of recurring LDH/LBP decreases by 87.7%, and for every unit increases in baseline FRRES, the risk of recurring LDH/LBP decreases by 88.5% (Table 3).

TABLE 3.

Logistic regression analysis for the predictor of spinal endoscopy and C‐arm double‐guided radiofrequency outcome (recurring lumbar disc herniation/low back pain or not).

Independent affectors B SEM p‐value OR value 95% CI
FRRLM −2.093 0.822 0.011* 0.123 0.025–0.618
FRRES −2.162 1.032 0.036* 0.115 0.015–0.869
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Abbreviations: CI, confidence interval; FRR, flexion–relaxation ratio; SEM, standard error of mean.

*

p < 0.05.

Discussion

Argument on Recurring Lumbar Disc Herniation/Low Back Pain of Spinal Endoscopy and C‐Arm Double‐Guided Radiofrequency

The present study found that the recurring rate of LDH/LBP after ECRF was 38.9% (21/54) for treating elderly patients with LDH at 2‐year follow‐up, which indicated that more than one‐third of elderly patients with LDH had recurring LDH/LBP in the medium term. Recurring LDH/LBP after ECRF is the main problem that needs to be addressed. It has been reported in many clinical studies to range from 5% to 32.5%. 7 , 8 , 9 Kim et al. reported the rate of recurring LDH after ECRF as 5%–12%. 9 A 10‐year retrospective study of ECRF combined with collagenase chemonucleolysis for treating LDH found that only 65.08% of patients (82/126) experienced no pain, 3.17% of patients (4/126) experienced both LBP and sciatica, 2.38% of patients (3/126) experienced sciatica alone, and 29.37% of patients (37/126) experienced residual LBP. 7 The rate of recurring LDH was 8.73% (11/126), and the rate of recurring LBP was approximately 32.5%. 7

The present study found that the recurring rate of LDH/LBP after ECRF (38.9%) was slightly higher than in the reported data, probably because of the difference in subjects’ age attribution. To explore the relationship between the baseline paravertebral musculature function and the outcomes of ECRF, we selected elderly patients as the objects, as we considered that elderly patients were prone to have a notable paravertebral musculature dysfunction compared to middle‐aged and young patients. Elderly LDH patients usually have a longer disease history, and the spinal degeneration in those patients can be much more severe than in middle‐aged patients. Brinjikji et al. (2015) reported that LDH and the related facet arthropathy are present in nearly 90% of elderly people over the age of 60. 24 Further, spinal musculature is less functional in elderly LDH. For example, age‐related sarcopenia is associated with a worse outcome after degenerative lumbar spine surgery. 25

Lumbar Spinal Musculature Function and Spinal Endoscopy and C‐Arm Double‐Guided Radiofrequency Outcome

Our study found that the patients who did not have recurring LDH/LBP after ECRF (Group N) had a higher baseline FRRLM and FRRES than those who had recurring LDH/LBP (Group R) at 2‐year follow‐up. The FRRLM and FRRES were the only baseline parameters that had inter‐group difference before the operation, suggesting that lumbar spinal musculature function was associated with the outcome of ECRF for treating elderly patients with LDH. Musculature is the strongest stabilizer for the spine 18 , 19 and plays an even more important role than the osseous‐ligamentous system. 26 , 27 It has been reported that spinal muscular dysfunction can cause spinal instability, 26 , 28 which might contribute to intervertebral disc herniation. 29 MF and longissimus ES are the main paravertebral muscles at L4–L5 and L5–S1 segments. 2 MF accounts for two‐thirds of lower lumbar segmental stability, 30 and there is evidence to suggest that MF dysfunction is closely related to LDH. 31 Muscular FRR is an important function parameter. It has great reproducibility in the diagnosis and detection of muscular disorders and dysfunctional diseases, such as neck tension, and non‐specific muscular pain. 18 , 19 Lower FRR reveals FRP loss and muscle dysfunction, as the extensor muscles still maintain the tension during the relaxation phase. 18 , 19 Our results indicated that the elderly LDH patients who obtained a good outcome without recurring LDH/LBP after ECRF had relatively normal functional LM and ES at baseline, while patients who ended up with recurring LDH/LBP had dysfunctional LM and ES.

Baseline FRRLM and FRRES Are Outcome Predictors of Spinal Endoscopy and C‐Arm Double‐Guided Radiofrequency

Further logistic regression analysis showed that the FRRLM (OR = 0.123, p = 0.011) and FRRES (OR = 0.115, p = 0.036) were the only baseline independent factors affecting the ECRF outcome. For every unit increase in baseline FRRLM, the risk of recurring LDH/LBP is decreased by 87.7%, and for every unit increase in baseline FRRES, the risk of recurring LDH/LBP will be decreased by 88.5%. As lumbar spondylolisthesis and spinal stenosis have been reported as inducing factors of LDH, 32 we have excluded patients with a simple L4/5 or L5/S1 LDH. Our results showed that the other baseline characteristics, including age, gender, BMI, disease history of LDH, LDH‐related symptoms, and the perioperative complication rate, as well as the preoperative VAS, JOA, and ODI, were not outcome predictors of ECRF.

Although many studies have reported an association between paravertebral musculature and clinical outcomes, most have focused on the morphology changes based on CT or MRI, such as the FI ratio and cross‐sectional area (CSA). However, the prediction value of those morphology parameters for LDH radiofrequency ablation is not satisfactory. In the present study, we used sEMG to analyze the electrophysiology function in patients. sEMG‐based FRR is a functional parameter of paravertebral musculature, which has better sensitivity and specificity than morphological parameters because paravertebral muscular dysfunction can occur much earlier than CSA 33 or FI 34 variations.

Our results indicate that the outcome of ECRF for treating elderly LDH patients can be predicted by the baseline FRRLM and FRRES preoperation. A patient with relatively higher FRRLM and FRRES can obtain a good outcome without recurring LDH/LBP, while a patient with relatively lower FRRLM and FRRES might end up with recurring LDH/LBP. The paravertebral muscular function is of great significance to the pathological process, operative efficacy, and postoperative outcomes of LDH and LBP. 14 , 15 , 16 Paravertebral musculature is the strongest stabilizer for the spine, 18 , 19 playing an even more important role than the osseous‐ligamentous system. 26 , 27 It has been reported that spinal muscular dysfunction can cause spinal instability, 26 , 28 which might contribute to intervertebral disc herniation. 29 The relatively normal function of LM and ES at baseline might help to maintain the lumbar spinal stability after ECRF, prohibiting the recurring LDH/LBP postoperation, which might explain the potential mechanism of the predictors of FRRLM and FRRES.

Potential Influence of the Present Study

Although ECRF is very suitable for elderly LDH patients, with the advantages of good perioperative safety, being less invasive, and faster rehabilitation, postoperative recurring LDH/LBP remains a significant problem that limits its application. The present study found that the patients’ baseline FRRLM and FRRES are independent outcome predictors of the recurring LDH/LBP after ECRF. Elderly LDH patients with relatively higher FRRLM and FRRES can obtain a good outcome without recurring LDH/LBP, while patients with relatively lower FRRLM and FRRES might end up with recurring LDH/LBP. The predictability of FRRLM and FRRES for recurring LDH/LBP at baseline might help to select the appropriate patients for ECRF, and it is useful for therapeutic decision‐making (ECRF indication).

Strengths and Limitations

Our study had two key strengths. First, the present study used sEMG‐based FRR as a functional parameter to analyze the electrophysiology function of lumbar paravertebral musculature in LDH patients, which has better sensitivity and specificity than the traditional morphological parameters. Second, the present study used binary logistic regression analysis to determine the independent factors affecting recurring LDH/LBP following ECRF. The baseline characteristics were included as much as possible, consisting of the general characteristics, Pfirrmann grade, FRRLM, FRRES, VAS, JOA, and ODI.

Our study had several limitations. First, it was a pilot study, and the sample size was relatively small, which might cause bias. To control bias as much as possible, logistic regression analysis was performed using all the baseline parameters and clinical parameters to determine the independent factors affecting recurring LDH/LBP. Although the present study was a pilot study with a small sample size, we consider the results to be relatively reliable. Second, we only detected the static function parameters of the lumbar spinal musculature based on sEMG. It should be noted that spinal muscular functional parameters are likely more complex during motion and daily life (e.g., walking and exercising). Gait analysis would be useful to detect dynamic changes in lumbar spinal musculature function, and we plan to incorporate this in future research. Third, we did not analyze the cut‐off value of FRRLM and FRRES for predicting the outcome of ECRF for treating elderly patients with LDH. Further longitudinal studies with more samples and muscular functional parameters are needed to determine the cut‐off value of FRRLM and FRRES that can predict the outcome of ECRF.

Conclusions

The present study found that patients’ baseline FRRLM and FRRES are independent outcome predictors of the recurring LDH/LBP after ECRF. For every unit increase in baseline FRRLM, the risk of recurring LDH/LBP decreases by 87.7%, and for every unit increase in baseline FRRES, the risk of recurring LDH/LBP decreases by 88.5%.

Conflict of Interest Statement

The authors have no conflicts of interest to declare.

Author Contributions

Conceptualization: Jian Li, Yi Ding. Data curation: Jian Li, Gengyan Xing, Yi Ding. Formal analysis: Pengfei Lu, Yi Ding. Investigation: Jian Li, Gengyan Xing, Yi Ding. Writing – original draft: Jian Li, Yi Ding. Writing – review and editing: Pengfei Lu, Yi Ding.

Funding Information

The study was funded by the National Natural Science Foundation of China (Grant No. 8187071706) (Gengyan Xing, Jian Li).

Ethics Statement

Ethical approval was obtained prior to the study (IRB ethical approval: KY‐2017‐Ob021) for the protection of human subjects.

Acknowledgments

The authors would like to thank Professor Liyuan Tao and Professor Hua Zhang from the Research Center of Clinical Epidemiology at Peking University Third Hospital for the statistics support.

Yi Ding, Pengfei Lu have contributed equally to this work.

Contributor Information

Pengfei Lu, Email: lpf3000@163.com.

Yi Ding, Email: dl_dingyi@126.com.

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