Functional Outcomes of Therapeutic Selective Nerve Root Block for Single-Segment Lumbar Spinal Stenosis: A Retrospective Study

Introduction

Lumbar spinal stenosis (LSS) is a common syndrome induced by cauda equina nerve or nerve root compression of the spinal canal, neural tube, or intervertebral foramen. Clinically, LSS is characterized by lumbosacral radicular pain, intermittent claudication, numbness along with gait disturbance, and even urinary dysfunction, which greatly influence the patients’ daily activities and quality of life [1]. However, LSS symptoms and signs are often inconsistent with the imaging examination, which can be asymptomatic in some patients. The lumbar spine degenerative process is reported to be the main pathogenesis of LSS [2]. It is estimated that the prevalence of LSS is 47.2% and increases with age [3]. With the escalation of the aging population in China, the incidence of LSS is increasing. To date, current guidelines were developed on the basis of limited evidences, resulting in unclear treatment pathways and negative impact on clinical nursing and the prognosis of patients [4]. The therapeutic methods for LSS can be classified into surgical and non-surgical treatment. Although the effectiveness of surgery for LSS has been credited for years and surgical techniques are becoming increasingly mature, an increasing number of patients with LSS are prone to choose non-surgical treatment due to concerns about perioperative complications. Non-surgical treatment has been also recommended as the first-line treatment for LSS, such as muscle relaxants, rest, non-steroidal anti-inflammatory drugs, and physiotherapy [5]. However, the clinical management of LSS is still challenging [6]. Meanwhile, not all patients with ineffective conservative management are fit for surgical treatment, making it essential to explore an alternative treatment, such as therapeutic selective nerve root block (SNRB).

Since its first use in lower leg radicular pain treatment in 1971, SNRB was reported to be used as a diagnostic and therapeutic method for radicular pain in studies. SNRB has been playing a critical role in accurately determining the responsible segment, especially when encountering inconsistent clinical and radiographic findings [7]. SNRB can be used in multiple sites, such as the lumbar and cervical spine. SNRB might be indicated if no response occurred in other conservative treatments. However, the evidences of its therapeutic effects are still limited. The correlation between symptomatic improvement before and after therapeutic SNRB has been rarely reported. Thus, more studies are needed to explore the efficiency of therapeutic SNRB. To better assess functional outcome improvement, this study included a total of 117 patients with single-segment LSS, who all received a single therapeutic SNRB. Functional outcomes were evaluated using the Oswestry Disability Index (ODI) and Japanese Orthopaedic Association (JOA) scoring systems. The duration of SNRB reducing pain symptoms in sub-populations with LSS were assessed. Correlation between the patients’ characteristics and functional scores were explored. Our study is intended to provide a reference for the selection of LSS treatment.

Material and Methods

PATIENTS:

This study retrospectively collected patients with single-segment LSS who underwent a single therapeutic SNRB between January 2019 and December 2021. All patients with LSS were confirmed by clinical symptoms of lumbosacral radicular pain and obvious magnetic resonance imaging (MRI) manifestations of LSS. Ethics approval was obtained from the Medical Ethics Committee of our hospital (No. 2023IRB064).

Eligible patients must have met the following criteria. The inclusion criteria were as follows: (1) patients with single-segment LSS of lateral stenosis type; (2) patients who received conservative management ineffective for more than 6 months; (3) clinical symptoms of lower limb root pain or intermittent claudication; and (4) patients were accessible in daily communication, and able to accurately express their own feelings. The exclusion criteria were as follows: (1) patients with malignant tumors; severe cardiovascular, cerebrovascular, liver, and kidney diseases; coagulation dysfunction; and systemic infection or skin infection at the puncture point who received more than 1 treatment; (2) patients who had once undergone intervertebral decompression or endoscopic surgery; (3) patients with multi-segment stenosis; (4) patients who got pregnant during the study duration; and (5) LSS with a central or mixed type.

SNRB PROCEDURE:

Before therapeutic SNRB, affected nerve roots were correctly judged by MRI (Discovery MR750, GE Healthcare, USA) and clinical symptoms. Similar to previous studies [8,9], therapeutic SNRB was conducted under local anesthesia (1% lidocaine) by the same doctor, with more than 10 years of experience. The patient receiving therapeutic SNRB was asked to lie in a prone position. A digital subtraction angiography (DSA) machine (INNOVA2100, GE Healthcare, USA) was used to fluoroscopically locate the affected segment, and the direction of the needle insertion on the body surface was then marked (anteriorposterior view: lower vertebral upper endplate, lateral view: joint process line). After routine surgical disinfection and local anesthesia, a PA18/20 puncture biopsy needle was inserted approximately 3 to 4 cm, to touch the transverse process. At an angle of 25° to 30° to the coronal plane, the needle was further inserted about 1 to 1.5 cm along the lower edge of the transverse process, that is, to reach the corresponding intervertebral foramens. The anteriorposterior view showed that the needle tip was placed approximately 0.5 cm below the pedicle of the vertebral arch. The lateral view showed that the puncture needle tip was located below the pedicle of the vertebral arch and posterior one-third of the intervertebral foramen. When the needle tip touched the nerve root, radiating pain along the nerve occurred in the ipsilateral buttocks or lower limbs, which was basically consistent with the clinical symptoms. Then, 2 mL of Iodoxamer was injected into the nerve root sheath. The target nerve root was visualized and confirmed by the DSA fluoroscopy (INNOVA2100, GE Healthcare, USA). A mixture of solution containing 1 mL of compound betamethasone, 0.5 mL of sodium chloride and 0.5 mL of lidocaine was injected. After therapeutic SNRB, the patient was asked to continue walking in order to fully absorb the medication. Follow-up was performed at 3 days, 3 months, 6 months, and 12 months after therapeutic SNRB.

DATA COLLECTION:

Baseline data including age, sex, body mass index (BMI), sedentary time, hypertension, diabetes, affected side, pathology level, intervertebral disk were collected. Functional outcomes after therapeutic SNRB were assessed using the ODI and JOA scoring systems. The ODI and JOA scores were collected preoperatively and at 3 days, 3 months, 6 months, and 12 months after therapeutic SNRB. ODI scores were mainly used to assess the functional improvement to daily life, which included pain intensity, personal food management, weight lifting, walking, standing, sitting, sleep status, sexual activity, social life, and the ability to travel [10]. ODI scores ranged from 0 (the lowest score) to 100 (the highest score). The higher the score, the more severe the condition and dysfunction. JOA scores were mainly used to assess patients’ subjective symptoms, clinical signs, daily activities, and bladder function [11]. Subjective symptoms included pain, numbness, and gait, among others. Clinical signs included the active straight leg raise test and sensory and muscle strength abnormalities, among others. Daily activities mainly included abnormal behaviors, such as while standing, lying, sitting, and walking. Bladder function mainly assessed whether nerve injury caused dysuria, urinary incontinence, or urine retention. JOA scores ranged from 0 (the lowest score) to 29 (the highest score). The lower the score, the more severe the condition and dysfunction.

STATISTICAL ANALYSIS:

Analysis was performed using SPSS software (version 21.0; SPSS Inc, IBM Corp, Armonk, NY, USA). Normal distribution was assessed by the time series plot, P-P plot, or Q-Q plot. Measurement data were expressed as mean±standard deviation. Enumeration data were expressed as n (%). Stratified analysis of ODI and JOA scores was respectively performed according to age, sex, BMI, sedentary time, hypertension, diabetes, affected side, pathology level, and intervertebral disk. The ODI and JOA scores preoperatively and at 3 days, 3 months, 6 months, and 12 months after therapeutic SNRB were analyzed by using one-way ANOVA. The correlation between the ODI and JOA scores at 12 months after therapeutic SNRB was analyzed using univariate linear regression analysis. A P value <0.05 was considered statistically significant.

Results

BASIC CHARACTERISTICS OF PATIENTS WITH SINGLE-SEGMENT LSS:

A total of 117 patients with single-segment LSS of lateral stenosis type were finally selected in this study, including 66 male and 51 female patients (Table 1). The lesions were located on the left side in 57 cases and right side in 60 cases, with the L3–4 level in 37 cases, L4–5 level in 39 cases, and L5-S1 level in 41 cases. LSS in all patients were induced by intervertebral disk protrusion (including 36% protrusion, 34% herniation, 30% prolapse). The overall average age was 57.21±15.75 (range: 16–88) years old, and patients aged >50 years old accounted for 74% (86/117). A total of 46 patients (39%) had a BMI >25, and 41 patients (35%) had a sedentary time >8 h. A total of 56 patients (48%) had hypertension, and 48 patients (41%) had diabetes.

ANALYSIS OF FUNCTION IMPROVEMENT IN PATIENTS WITH SINGLE-SEGMENT LSS BEFORE AND AFTER THERAPEUTIC SNRB:

Functional outcomes after therapeutic SNRB were assessed using the ODI and JOA scores. First, analysis of ODI and JOA score changes before and after therapeutic SNRB in all patients revealed significant differences (Table 2, F=420.140, P<0.05; F=361.900, P<0.05, respectively). The ODI scores at 6 months were the lowest, and the JOA scores were the highest. Next, stratified analysis of ODI and JOA scores according to age, sex, BMI, sedentary time, hypertension, diabetes, affected side, pathology level, and intervertebral disk was respectively performed (Tables 3, 4). As expected, ODI scores showed an opposite tendency from the JOA scores in each subgroup within 6 months after therapeutic SNRB. The ODI scores were gradually decreased and the JOA scores were gradually increased (P<0.05). Most subgroup analysis revealed that the significantly increased ODI scores and the significantly decreased JOA scores were observed at 12 months after therapeutic SNRB, compared with those at 6 months after therapeutic SNRB (P<0.05). Interestingly, there was no significant differences in ODI scores and JOA scores in patients with BMI ≤25 (P>0.05). Moreover, no significant differences were even observed in ODI scores and JOA scores, whether in patients with BMI >25 or patients with sedentary time >8 h (P>0.05). The results suggested most patients with single-segment LSS could return to the optimal state at 6 months after a single therapeutic SNRB, and the effectiveness of SNRB could be maintained for 1 year, or even longer in patients with BMI <25.

CORRELATION BETWEEN ODI/JOA SCORES AND BMI/SEDENTARY TIME BY UNIVARIATE LINEAR REGRESSION ANALYSIS:

Further, univariate linear regression analysis was performed to explore the correlation between ODI/JOA scores and BMI/sedentary time (Table 5). The result revealed that ODI/JOA scores were closely correlated with BMI (β=0.818, t=9.426, P=0.000; β=−0.908, t=−14.402, P=0.000) and sedentary time (β=0.747, t=7.021, P=0.000; β=−0.808, t=−8.576 P=0.000), respectively. The results suggested the long-term effectiveness of SNRB could be significantly affected by BMI and sedentary time.

TYPICAL CASE:

One female patient with left lateral recess stenosis, aged 47 years old, presented with persistent pain and numbness of the left waist and leg for half a year. Therapeutic SNRB was performed after the failure of conservative management (Figure 1). MRI indicated the left lateral recess stenosis and compressed nerve root was caused by the posterior protrusion of the left side at the L4–5 level (Figure 1A, 1B, arrow). After injection of contrast agent, the anteroposterior and lateral views revealed under DSA fluoroscopy that the tip of the puncture needle was passing through the foramen of the exiting L4 nerve root (Figure 1C, 1D, arrow).

Discussion

Here, we explored the efficacy of therapeutic SNRB in 117 patients with single-segment LSS who underwent a single therapeutic SNRB. Our findings demonstrated that 1 therapeutic SNRB was an effective treatment option for LSS to alleviate lumbosacral radicular pain for more than 6 months. At 12 months after therapeutic SNRB, the clinical symptoms of LSS returned to some extent. Especially, the ODI and JOA scores at 12 months after therapeutic SNRB showed a notably significant correlation with BMI/sedentary time, which returned to the preoperative level in patients with BMI >25 or sedentary time >8 h.

It is reported that approximately 103 million patients with LSS (especially older patients) worldwide are bearing back pain, leg pain, and difficult walking [12]. Among multi-factors, lumbar disc herniation is the main cause for LSS [13–15]. The degenerative changes in the fibrous ring of the nucleus pulposus and the cartilage plate can rupture under external forces, leading to lumbar disc herniation, protrusion, and prolapse, and further resulting in LSS [13,14]. In the present study, all of the 117 patients with LSS also had lumbar disc herniation, suggesting that lumbar disc herniation was the main cause of LSS. The patients with intervertebral disk protrusion, herniation, and prolapse accounted for 36%, 34%, and 30%, respectively. Consistent with previous studies, the age of patients with LSS in our study ranged from 16 to 88 years old, with 74% patients >50 years old. The nonspecific inflammation caused by the exudation of inflammatory factors in the patient’s own nucleus pulposus could result in injury-related excitation of nerve receptors, which further directly leads to nerve damage, intermittent claudication, or radicular pain [6]. Therefore, nerve root pain can be achieved only by eliminating nerve root edema and surrounding inflammation.

As a minimally invasive procedure, SNRB has been used as a tool for diagnosis of the affected segment, which also revealed great therapeutic value, especially for patients unsuitable for surgery. Before intervertebral decompression and endoscopic surgery, SNRB could effectively reduce the scope of subsequent surgery and provide a basis for a precise surgery protocol [16]. To accurately evaluate the effectiveness of therapeutic SNRB in LSS treatment, we selected only patients with single-segment lateral stenosis. The patients who had LSS with central and mixed types, multi-segment LSS, or had undergone intervertebral decompression/endoscopic surgery were excluded. In our clinical practice, LSS is usually classified into central, lateral, and mixed types [17]. If there are LSS patients with a central or mixed type, it means that the stenosis is already severe, and a surgical treatment or minimally invasive surgery is still necessary. In the present study, the effectiveness of therapeutic SNRB was evaluated by using ODI and JOA scores before and after therapeutic SNRB. The results revealed that all the patients presented with improved function, with the gradually decreased ODI scores and increased JOA scores within 6 months after therapeutic SNRB. The functional recovery reached the best state at 6 months after therapeutic SNRB. Most patients self-reported they could get out of bed and walk immediately after therapeutic SNRB, with the lumbosacral radicular pain significantly eased, and the quality of life significantly improved. Functional outcomes at 12 months after therapeutic SNRB were also better than those at admission, even in each subgroup stratified by the variables age, sex, BMI ≤25, sedentary time ≤8 h, hypertension, diabetes, affected side, pathology level, and intervertebral disk. The principle of therapeutic SNRB is to inject anesthetics (lidocaine) and glucocorticoids (compound betamethasone) directly into the local area of the diseased nerve root and the edema site of the nerve lesion, which provides assurance for longer control of LSS symptoms [18]. Lidocaine can block the transmission pathway of pain sensation, achieving analgesic effects, and dilate blood vessels and improve local blood circulation at a high concentration [19]. Compound betamethasone is an aqueous solution injection composed of a mixture of betamethasone dipropionate and betamethasone phosphate sodium, which effectively suppresses immune responses, reduces inflammatory factors, reduces nerve stimulation and congestion and edema of nerve roots, and indirectly reduces pressure [20,21]. After injection of compound betamethasone into the nerve root, soluble betamethasone phosphate sodium was quickly absorbed and took effect, while low solubility betamethasone dipropionate was stored and slowly absorbed to maintain a therapeutic effect. Our finding demonstrated that therapeutic SNRB was effective in treating nerve root pain caused by LSS, and that most patients maintained more than 1 year of therapeutic effect. Similarly, Kanaan et al demonstrated that a single therapeutic SNRB could effectively alleviate pain, with lowered VAS scores for at least 6 months in 29% of patients, and avoid surgery in 54% patients with lumbar radiculopathy [22]. Kim et al revealed that therapeutic SNRB effectively improved radiating pain in patients with single-segment LSS and disc herniation [23]. Martin et al found that 87% of patients had rapid pain relief within 4 days, and that 60% of patients experienced permanent pain relief [24]. Pfirmmann et al found that therapeutic SNRB was effective in sciatica, with 75% patients experiencing pain relief 15 min after the procedure, and 86% reporting a benefit after 2 weeks [7]. Even though these previous studies mainly focused on the effect of therapeutic SNRB on pain relief, their conclusions supported our findings. There are different experiences of the effect of therapeutic SNRB. In the early case series by Anderberg et al, the use of therapeutic SNRB was proved effective only in 20% of cases (3/15), suggesting its challenge in a patient population with traumatically induced spondylotic radicular pain [25]. Arun-Kumar et al reported that therapeutic SNRB gained a valuable interval period with reduced pain before severe disease developed where surgery is well indicated, especially in patients with inconclusive radiological indication for surgery. Overall, our findings expanded the evidences of therapeutic SNRB in the treatment of LSS. It is recommended for patients for whom conservative treatment is ineffective and for those who are not suitable for surgical treatment.

Notably, subgroup analyses in our study demonstrated that the ODI and JOA scores at 12 months after therapeutic SNRB returned to the levels at admission in sub-populations with BMI >25 or sedentary time >8 h. The possible explanation was that the patients with a BMI >25 or sedentary time >8 h usually had excessive body weight and poor lifestyle, which exposed the intervertebral disc under a long-term pressure, making it more prone to water loss, fibrosis, and loss of elasticity. The nucleus pulposus inside the cartilage ring breaks through the fibrous ring outward, compressing the nerve roots and causing symptoms of low back and leg pain. Consistently, Hirano et al demonstrated that BMI might be one of the most relevant risk factors for LSS, which was significantly positively correlated with thoracic and lumbar kyphosis angles and spinal inclination angle, and negatively correlated with lumbar and total spinal range of motions and sacral slope angle [26]. Norden et al demonstrated that patients with symptomatic LSS were extremely sedentary and were encouraged to reduce sedentary time and increase time in physical activity [27]. Our findings suggested that controlling BMI within a normal range and maintaining a healthy lifestyle (controlling sedentary time and having appropriate physical exercise) are crucial for prolonging the efficacy of SNRB.

There are several limitations that should be acknowledged in our study. First, this was a retrospective study, which can result in some bias to patient selection and results. Second, each participator was given only 1 single therapeutic SNRB. It is unknown whether a repeated therapeutic SNRB be performed within a year to prolong the lasting effective time, with low relapse rate. Third, it is unknown whether the effective time can be extended by optimizing the dosage or changing the ratio of blockers. Fourth, the follow-up time was 1 year, and a longer follow-up result should be considered in future research. In clinical practice, patients with multi-segment stenosis who have undergone intervertebral decompression or endoscopic surgery are common. To facilitate the scoring of the ODI and JOA, only patients with single-segment lateral stenosis were selected in our study. Thus, more studies are needed in the future.

Conclusions

Therapeutic SNRB was an effective treatment option for LSS. The best therapeutic efficiency was achieved at 6 months after a single therapeutic SNRB in most patients with single-segment LSS. Results could be maintained for more than 1 year, with patients showing no symptoms of lumbosacral radicular pain and having a normal quality of life. In patients with BMI >25 or sedentary time >8 h, both BMI and sedentary time were positively correlated with the ODI and JOA scores at 12 months after therapeutic SNRB, which showed no significant differences than those before therapeutic SNRB, respectively. Changing sedentary habits with appropriate exercise, and controlling weight with a healthy diet can contribute to the improved effectiveness of SNRB, especially for patients with LSS for whom conservative treatment is ineffective and for those not suitable for surgical treatment.