INTRODUCTION
Low back pain is a prevalent issue in modern society, affecting up to 90% of adults at some point in their lives [1,2]. It occurs in more than 80% of the general population.[3] The major cause of this condition is sacroiliac joint (SIJ) pain, accounting for 40% of cases [3-5]. Management of SIJ pain encompasses a range of interventions, including surgical options like fusion surgery, as well as nonsurgical approaches. Nevertheless, a consensus regarding the most effective intervention for achieving optimal therapeutic outcomes remains elusive [5,6].
Radiofrequency ablation (RFA), a nonsurgical procedure, has shown enhanced treatment efficacy in specific studies compared to epidural steroid injections [7,8]. This procedure involves the blockade of the lateral branches that stem from the dorsal rami of L5 to S3, which provide innervation to the SIJ [9]. Various navigation techniques, including fluoroscopy, computed tomography, ultrasound, and endoscopy, have been suggested to improve the accuracy of ablation positioning [10-14]. Yeung and Gore [15] suggested that endoscopically guided visualization could enhance the confirmation of nerve ablation or transection, particularly valuable in identifying the most frequently affected branches of the dorsal ramus during foraminal and dorsal rhizotomy procedures. In 2016, endoscopic RFA was initially employed for treating the SIJ complex [16]. Choi et al. [16] suggest that this novel technique could potentially function as an alternative approach for addressing chronic low back pain (CLBP) associated with the SIJ complex.
Several systematic reviews and meta-analyses have been conducted to date to investigate the efficacy of radiofrequency treatment for low back pain originating from the SIJ and lumbar facet joint [17-20], which respectively account for 40% and 15%–40% of low back pain etiologies [3-5]. The studies systematically gathered and analyzed various approaches to radiofrequency treatment of various joint diseases, with a specific focus on their effectiveness. The precise effectiveness of radiofrequency targeting for SIJ pain using an endoscopic approach has not been extensively examined. This meta-analysis aimed to comprehensively investigate the efficacy of endoscopic RFA for the management of SIJ pain.
MATERIALS AND METHODS
1. General Guidelines
This systematic review was conducted and reported following the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-analyses) statement [21]. The protocol of the study was preregistered on INPLASY (INPLASY202450011). Informed consent and the need for Institutional Review Board approval have been waived by the China Medical University Hospital Institutional Review Board due to the lack of patient-identifying data.
2. Database Searches and the Identification of Eligible Manuscripts
Two authors (BQW and DYC) conducted independent electronic searches in the PubMed, Embase, Cochrane CENTRAL, and Web of Science databases using the following keywords and combinations ("radiofrequency therapy" OR “denervation” OR “nerve block” OR “rhizotomy”) AND (“arthralgia” OR “sacroiliac joint pain” OR “sacroiliac joint” OR “low back pain”) AND (endoscope OR arthroscope). The search encompassed the period from the inception of each database (i.e., the earliest record) to the date of the database search (6 May 2024). The study did not impose any language restrictions.
Initially, the 2 authors (BQW and DYC) responsible for conducting this search screened the identified titles and abstracts for eligibility through a consensus process. In cases where agreement could not be reached between the 2 authors (BQW and DYC), they sought consultation with a third author involved in the study (CT).
3. Inclusion and Exclusion Criteria
The inclusion and exclusion criteria are determined according to the PICO (population, intervention, comparison, outcome) framework.
The PICO of this study was as follows: P: human participants experienced low back pain and were diagnosed as SIJ pain origin, I: endoscopically visualized RFA, C: placebo treatment or baseline clinical status, O: change in pain symptom scores and functional outcomes.
The following inclusion criteria were used: (1) studies investigating the quantitative evaluation of pain symptoms and consequential disability or impairment in functional outcomes, and (2) studies with available data of pre- and postintervention assessments of pain symptom scores and functional outcomes. This study also encompassed open-label design trials, as open-label placebos demonstrated similar efficacy to double-blind placebos [22,23].
The exclusion criteria of this study were as follows: (1) animal studies, (2) studies lacking assessments of pain symptom scores and functional outcomes, (3) studies without pre- and postintervention assessments, or lacking data of change between pre- and postintervention. (4) studies of whom pain symptom scores and functional outcomes were not the main outcome measures of interest, and (5) studies do not adequately describe the criteria used to select patients for undergoing endoscopically visualized radiofrequency treatment.
4. Data Extraction and Quality Appraisal
Two independent authors (BQW and DYC) extracted data from the evaluated studies. Each included study provided the following data: first author, publication year, country, study design, number of treated patients and their gender distribution, follow-up period, metrics for clinical outcomes, levels of operation, baseline clinical status, and postoperative adverse events. To avoid misinterpretation, the 2 evaluators (BQW and DYC) paid special attention to the effect direction of the scale used in each study. If the 2 evaluators (BQW and DYC) were unable to reach an agreement, they would seek consultation from a third author (CT) who was part of this study.
The primary focus of the study was on pain symptom scores and functional outcomes at 2 specific time points: 6 months and 12 months following the endoscopic RFA.
The strength of evidence in the studies was evaluated utilizing the Joanna Briggs Institute Critical Appraisal Tool [24].
5. Statistical Analyses
This meta-analysis was conducted with a random-effects model [25] using the Comprehensive Meta-Analysis software (Version 4, Biostat, Englewood, NJ, USA). A 2-tailed p-value less than 0.05 was defined as statistically significant.
The effect size measurement was defined as the mean difference (MD), calculated as the postoperative assessment minus the preoperative assessment. A negative effect size value signifies a favorable outcome from endoscopic RFA relative to the baseline. Heterogeneity was quantified using I2 and Cochran Q test. A p-value below 0.05 in Cochran Q test suggests statistically significant variances among the related studies. I2 values of 25%, 50%, and 75% were classified as low, moderate, and high heterogeneity, respectively [26].
Subgroup analyses were performed based on 2 postoperative time points, specifically at 6 months and 12 months. The distinction between the 2 subgroups was measured utilizing Cochran Q test. A p-value lower than 0.05 in Cochran Q test indicates statistically significant differences among the related subgroups.
Guidelines from the Cochrane Handbook for Systematic Reviews of Interventions were used to evaluate for potential publication bias [24]. Funnel plots were generated and visually inspected for symmetry. Egger regression tests were conducted when 10 or more datasets were available.
RESULTS
1. Study Identification and Selection
Initially, 338 studies were identified through the electronic search. After eliminating duplicate and retracted articles, excluding those deemed irrelevant based on their titles and abstracts, and removing articles that did not satisfy the selection criteria, 4 articles were ultimately incorporated into the study (Figure 1).
2. Methodological Quality of the Included Studies
In terms of the methodological quality of the included articles, all studies received positive assessments on every item of the checklists, with the exception of question 2. This inquiry pertains to the assessment of whether a consistent and dependable method was utilized to measure all participants in the case series. In the examined studies, pain intensity was assessed utilizing the visual analogue scale (VAS), which is a self-reported measurement method. Disability levels were evaluated using the Oswestry Disability Index (ODI), which was administered to participants through a questionnaire. Therefore, a significant proportion of respondents documented subjective encounters throughout the evaluation, prompting apprehensions regarding the dependability of this inquiry. Table 1 presents a summary of the appraisal results of the included studies.
3. Characteristics of The Included Studies
Table 2 displays the characteristics of the studies that were included [10,14,16,27]. VAS and ODI were employed to assess the levels of pain intensity and disability across all the studies included. Three of the studies were case series [14,16,27], and one was a retrospective cohort study [10]. Neither a randomized controlled trial nor an open-label study was identified. The percentage of female participants varied between 64% and 94%. The shortest follow-up time points involved immediate preoperative and postoperative outcome assessments, whereas the longest follow-up was 24 months postsurgery. Except the research conducted by Ibrahim et al. [27], which involved surgical procedures at levels L4–S1, the operation levels in the remaining studies were performed at levels L5–S3 [10,14,16]. Baseline pain symptom scores ranged from 6.7 to 7.25, while baseline functional outcome measurements varied from 20.8 to 44.85. No postoperative adverse events were documented throughout the follow-up period in any of the studies.
Table 3 provides comprehensive details, encompassing patient selection criteria, baseline conditions, ablation target areas, surgical levels, the endoscopic system utilized, and postoperative outcomes at different follow-up time points.
Choi et al. [16] included 17 patients into their study. All patients underwent 2 distinct diagnostic intra-articular and multisite lateral sacral branch blocks of the SIJ complex. The single-port endoscopic RFA targeted the following areas: (1) perforating branches that innervate the posterior capsule of the SIJ, (2) long posterior SI ligament, and (3) lateral edges of the foramen at the levels of S1, S2, and S3. The nerve targets selected for ablation included the lateral branches of S1, S2, S3, and the dorsal ramus of L5. For pain symptom outcomes, the mean VAS scores for back pain decreased from 6.7±1.41 preoperatively to 3.6±1.28, 3.2±1.06, 2.8±1.14, and 3.1±1.78 immediately postoperatively, and at 1-, 3-, and 6-month follow-up visits, respectively. For functional outcomes, the mean preoperative ODI score was 22.2±3.36. This score decreased to 14.1±3.35, 13.1±4.05, 12.9±4.32, and 12.0±4.69 immediately postoperation and at the 3, 6, and 12-month follow-up visits, respectively. The average patient satisfaction rate was 86.6% (70%–100%).
Ibrahim et al. [27] included 30 patients into their study. All participants successfully underwent 3 distinct intra-articular SI joint injections and multisite medial branch blocks targeting the lower facet joints (L4–S1). A single-port endoscopic RFA targeted the following areas: (1) perforating branches innervating the posterior capsule of the SIJ, (2) long posterior SI ligament, and (3) lateral edges of the S1, S2, and S3 foramen. The nerve targets for ablation were: (1) lateral branches of S1, S2, and S3, and (2) medial marginal nerve branches of L4, L5, and S1. For pain symptom outcomes, the VAS score decreased from 7.23±1.55 at baseline to 2.82±1.33 at 24 months (61% reduction). For functional outcomes, ODI was improved from 44.85±21.73 at baseline to 22.24±19.09 at 24 months (50% reduction). The study did not report patient satisfaction after the ablation.
Chen et al. [10] included 36 patients with CLBP who underwent full-endoscopic rhizotomy for SIJ pain into their study. Following identical inclusion and exclusion criteria, age-matched controls who received cooled RFA were also incorporated. A single-port endoscopic RFA targeted the following areas: (1) perforating branches innervating the posterior capsule of the SIJ, (2) long posterior SI ligament, and (3) lateral edges of the S1, S2, and S3 foramen. The nerve targets for ablation were the lateral branches of S1, S2, S3, and the dorsal ramus of L5. The improvement of SIJ pain and functional disability persisted in both surgical groups for up to one year postoperatively. The endoscopic ablation group was superior to the cooled RFA group in terms of reducing VAS amplitude. An increasing trend was observed in VAS and ODI in the cooled RFA group during the 1-year follow-up period. The endoscope group demonstrated a 97% rate, whereas the cooled RFA group exhibited a 67% rate of patients who reported feeling "excellent" or "good" on the self-report questionnaire.
Tseng et al. [14] incorporated 16 patients in their study. All patients underwent diagnostic intra-articular and multisite lateral sacral branch blocks of the SIJ complex. A bi-portal endoscopic RFA targeted the following areas: (1) lateral edges of the S1, S2, and S3 foramen and (2) medial border of the SIJ. The nerve targets selected for ablation included the lateral branches of S1, S2, S3, and the dorsal ramus of L5. Regarding pain symptom outcomes, the median VAS score demonstrated improvement from 7 (6–8) to 1 (0–3) at 12 months. In terms of functional outcomes, there was a significant improvement in the median ODI score from 33 (25–48) to 10 (5–22) at the 12-month follow-up. The overall patient satisfaction score, measured at the 6-month mark, was 89.1%.
4. The Efficacy of Endoscopic RFA
The endoscopic RFA resulted in a significant reduction in both VAS and ODI scores during the 6- and 12-postoperative follow-up assessments. In terms of the VAS reduction, the MD between preoperative and 6-month postoperative assessments was -5.60 (95% confidence interval [CI], -6.33 to -4.87); the MD between preoperative and 12-month postoperative assessments was -5.96 (95% CI, -6.79 to -5.13) (Figure 2). In terms of the ODI reduction, the MD between preoperative and 6-month postoperative assessments was -21.03 (95% CI, -28.37 to -13.69); the MD between preoperative and 12-month postoperative assessments was -23.67 (95% CI, -32.22 to -15.11) (Figure 3).
High heterogeneity was noted in VAS and ODI reduction during their respective follow-up intervals, except for the VAS reduction at the 12-month postoperative time point. The heterogeneity in VAS reduction at the 6-month postoperative time point was 92.39%. In contrast, there was 0% heterogeneity observed at the 12-month postoperative time point. The heterogeneity of ODI reduction at the 6-month postoperative time point was 96.89%, while the heterogeneity at the 12-month postoperative time point was 94.93%.
The Cochran Q test p-value for the 6-month and 12-month postoperative time points in VAS reduction was 0.52, while the p-value for the same comparison time points in ODI reduction was 0.65 (Table 4).
DISCUSSION
1. Novel Findings
Despite its promotion in 2016, there is insufficient evidence available to assess the effectiveness of endoscopic RFA. This meta-analysis represents the initial study to assess the efficacy of treatment in relatively large sample sizes using current real-world data. The study demonstrated that endoscopic RFA leads to a significant reduction in both pain intensity and disability levels. There was no significant difference in the degree of improvement between the 6-month and 12-month follow-up periods. The current evidence does not conclusively establish the long-term efficacy of endoscopic RFA.
2. Insight From Current Fields
Clinical outcome assessments indicated no statistically significant variances at the 6-month and 12-month postoperative intervals in this meta-analysis. In the study conducted by Chen et al., it was observed that both pain levels and functional disability exhibited a gradual relapse during the period between 6 and 12 months following the surgical procedure [10]. Although not subjected to statistical analysis in their study, Ibrahim et al. [27] noted a comparable trend in both the VAS and ODI assessments, showing increments starting at 9 months after the surgery. Several factors could potentially account for these findings. The baseline ODI in the Ibrahim study was notably higher compared to other studies (Table 2). This indicates that individuals experiencing severe SIJ pain might derive more benefits from surgical intervention rather than ablation therapy. Another aspect to consider is that the existing measurements for assessing pain intensity and disability levels may lack the necessary sensitivity to detect the alterations induced by RFA therapy, indicating a need for more sensitive evaluation methods. Following the ablation procedure, this meta-analysis suggests that clinicians should establish a comprehensive long-term outpatient follow-up protocol to ensure the enduring effectiveness of the treatment.
High heterogeneity may come from several aspects. Firstly, the studies incorporated in this meta-analysis displayed a diverse range of gender distributions and ages, potentially impacting the outcomes. Secondly, the lack of a standardized ablation protocol poses a challenge to the practicality of utilizing meta-regression in this therapy. Thirdly, the VAS and ODI assessments incorporate a considerable amount of subjective feedback, potentially influencing the precision and impartiality of efficacy assessments, as indicated in the section on methodological quality.
3. Recommended Algorithm of Diagnosis for SIJ Pain
The typical presentations of SIJ pain include sharp pain located inferolaterally to the SIJ, which exacerbates upon changing positions or during rotational pelvic motions. Other etiologies can cause similar symptoms, including excessive axial loading and joint stress, degenerative changes, traumatic events, pregnancy, and inflammatory arthropathies [28,29]. Therefore, additional stress tests, such as the FABER (Flexion, ABduction, External Rotation) test, distraction, thigh thrust, sacral compression, Gaenslen test, and sacral thrust, should be conducted to ascertain the structural origin of the pain. Consequently, endoscopic RFA is recommended as a nonsurgical management approach (Figure 5). The significance of precise patient selection and diagnosis is underscored by the incorporation of diagnostic intra-articular and multisite lateral sacral branch blocks prior to RFA in all the studies. While there is no universally accepted standard, diagnostic SIJ block has demonstrated utility as a confirmatory tool for evaluating pain attributed to the SIJ [30]. This diagnostic approach ensures that the treatment is accurately tailored to patients experiencing pain originating from the SIJ, thereby potentially increasing the success rate of the intervention.
4. Comparison With Other Modalities
Choi et al. [16] and Tseng et al. [14] reported rapid improvements in pain management and functional abilities that were sustained throughout their respective follow-up periods. The sustained pain relief and functional improvement observed across these studies underscore the potential efficacy of endoscopic RFA as a treatment option for SIJ pain, aligning with existing literature that supports the use of RFA for chronic pain management.
Chen et al.'s [10] comparison of endoscopic ablation to cooled RFA provides valuable insights into the relative effectiveness of different RFA technologies. The superior performance of endoscopic RFA in terms of VAS reduction highlights its potential as a more effective treatment method for SIJ pain compared to cooled RFA. This finding suggests that the precision and reach of endoscopic RFA may better target the nerve structures that contribute to SIJ pain.
5. Limitations and Future Research Directions
While the results exhibit promise, the discussion should acknowledge specific limitations, such as small sample sizes, the lack of control groups in some studies, and variations in follow-up durations. The aforementioned factors may influence the generalizability of the findings. Furthermore, the studies predominantly focus on short- to medium-term outcomes, highlighting the need for additional research on the long-term efficacy and safety of endoscopic RFA for SIJ pain, which presents an avenue for further exploration.
Future studies should strive to address these limitations by conducting larger randomized controlled trials with extended follow-up durations. Moreover, comparing endoscopic RFA directly with other minimally invasive procedures and conservative treatments could provide deeper insights into its relative effectiveness and position in the treatment hierarchy for SIJ pain. Exploring patient-reported outcomes beyond pain alleviation and enhanced functionality, such as quality of life and psychological well-being, could provide additional insights into the holistic advantages of endoscopic RFA for SIJ pain.
CONCLUSION
Endoscopic RFA has shown effectiveness and potential as a therapeutic approach for SIJ pain. The need to investigate the long-term effects arises from the lack of sufficient evidence in current research areas. By acknowledging the limitations and promoting further research, the discourse can improve a nuanced understanding of the role of endoscopic RFA among the various treatments for SIJ pain and chronic lower back pain.
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