Comparative effectiveness of transforaminal epidural steroid injection: subpedicular versus Kambin’s triangle technique: a single-centre experience

Introduction

Transforaminal epidural steroid injection (TFESI) serves as a cornerstone intervention for managing radicular pain attributed to spinal pathology, including conditions such as lumbar disc herniation (LDH) (1,2). This minimally invasive procedure involves delivering corticosteroids directly into the epidural space adjacent to the affected nerve root, aiming to alleviate inflammation and associated symptoms (2,3). The subpedicular area refers to the space located beneath the pedicle of a vertebra, which this region is often targeted during spinal procedures such as TFESI for the management of radicular leg pain associated with LDH (4). On the other hand, Kambin’s triangle area refers to the anatomical space bordered by the exiting nerve root, the superior border of the caudal pedicle, and the inferior border of the cranial pedicle. This triangle is commonly used as an access point for minimally invasive spinal procedures, allowing direct access to the foraminal space and the affected nerve root (5,6). The subpedicular and Kambin’s triangle areas are significant anatomical landmarks in spinal interventions (Figure 1).

Figure 1 Lumbar spine anatomical model in oblique view. Kambin’s triangle and subpedicular area (left). TFESI of Kambin’s triangle technique and subpedicular technique (right). TFESI, transforaminal epidural steroid injection.

Among the various techniques available for TFESI, the subpedicular and Kambin’s triangle approaches hold prominence. The subpedicular technique involves inserting the needle just below the pedicle of the vertebra, while the Kambin’s triangle technique navigates the needle through the Kambin’s triangle, a safe zone bordered by the exiting nerve root, the superior articular process, and the vertebral body. These techniques offer distinct advantages and challenges, necessitating a comprehensive evaluation of their comparative efficacy and safety profiles to guide clinical decision-making (7,8).

Radicular leg pain, characterized by sharp, shooting sensations radiating along the nerve pathway, often arises from nerve compression or irritation due to conditions such as LDH (4,8,9). LDH involves the displacement of intervertebral disc material, which may impinge on adjacent nerve roots, causing pain, numbness, and weakness in the lower extremities. TFESI serves as a targeted therapeutic modality to address the underlying inflammation and alleviate pain associated with LDH, thereby facilitating functional rehabilitation (9-11). However, selecting the optimal technique for TFESI remains a subject of debate, necessitating empirical evidence to inform clinical practice (12).

This study aims to evaluate and compare the therapeutic effectiveness and safety of two commonly used techniques for TFESI: the subpedicular and Kambin’s triangle approaches. By analyzing pain reduction, functional outcomes, safety profiles, procedure duration, and treatment costs, the study seeks to provide comprehensive evidence to guide clinical decision-making in managing radicular leg pain caused by LDH. We present this article in accordance with the STROBE reporting checklist (available at https://jss.amegroups.com/article/view/10.21037/jss-24-140/rc).

Methods

Study design and methodology

The study design is a retrospective comparative study aimed at evaluating the efficacy and safety of two subpedicular and Kambin’s triangle techniques for TFESI in managing radicular leg pain associated with LDH. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the ethics committee of University of Phayao (No. HREC-UP-HSST 1.1/029/67) and individual consent for this retrospective analysis was waived. The inclusion criteria included as follows: patients included were diagnosed with unilateral radicular leg pain attributed to single-level LDH, the patients underwent TFESI procedure for pain management, and availability of complete medical records, including pre-procedure assessments and follow-up data for at least 8 months. The exclusion criteria include that the patient had a history of previous spinal surgery at the target level to avoid confounding factors such as altered anatomy or scar tissue formation, which could affect the technical feasibility and outcomes of the TFESI procedure, and the patient who had incomplete medical records. Data collection collected demographic information, including age, sex, weight, height, body mass index (BMI), smoking status, and presence of underlying diseases from the medical records of consecutive patients who met the inclusion criteria. Preoperative clinical measures, including the distribution of radicular pain, ratios of right to left unilateral radicular pain, and specific spinal conditions such as LDH and foraminal stenosis, were also documented. We evaluated the outcome measures by the primary outcome measures: pain intensity scores assessed using the numerical rating scale (NRS) and functional improvements measured using the Oswestry Disability Index (ODI). Pain scores and ODI were recorded at baseline, immediate post-procedure, and follow-up intervals. Adverse events related to the procedures were also documented and reported with data visualization using a scatter plot matrix and heatmaps graphical representation. The patient will be scheduled for a follow-up visit in the outpatient clinic to assess response to the injection at 1, 3, 6, and 8 months.

TFESI technique

The patient was brought to the operating room and placed in the prone position on the fluoroscopy table. The patient was prepped and draped in a sterile fashion. The C-arm fluoroscopy machine was brought into position and operated by technician. The patient’s lumbar spine was palpated to identify the desired vertebral level, which fluoroscopic imaging confirmed. The skin was anaesthetized using 2% lidocaine. A 22-gauge spinal needle was advanced under fluoroscopic guidance towards the target transforaminal space.

Procedure techniques, including TFESI procedures, Kambin’s triangle technique, and subpedicular technique, were demonstrated in Figure 1. Both methods are performed by an interventional single spinal orthopaedic surgeon using either the subpedicular or Kambin’s triangle technique, selected based on clinical judgment and anatomical considerations. The subpedicular approach is typically chosen for targeting the anterior epidural space and the exiting nerve root, particularly in lower lumbar injections. In contrast, Kambin’s triangle technique is used for accessing the epidural space in the posterolateral aspect of the foramen, often preferred for foraminal and far-lateral disc herniations. The choice of technique depends on the specific spinal level, location of pathology, patient anatomy, and the physician’s expertise with each method. The choice between the subarticular and transforaminal (Kambin’s triangle) approaches for TFESI depends on the patient’s pathology, anatomy, and procedural goals. The subarticular approach is preferred for paracentral disc herniations and lateral recess stenosis, offering targeted relief but posing a higher risk of dural puncture. In contrast, the transforaminal approach is ideal for foraminal or extraforaminal disc herniations and stenosis, providing direct access to the exiting nerve root with a lower risk of dural puncture but a potential risk of vascular injury. Patient-specific factors, such as previous surgeries and anatomical variations, also influence the choice. Ultimately, selecting the appropriate approach requires careful evaluation of imaging findings and procedural safety considerations (Table 1).

The subpedicular technique involved inserting the needle just below the pedicle of the vertebra in the anteroposterior (Figure 2A) and oblique views (Figure 2B). Once proper positioning was confirmed, contrast dye (Xenetix^®300, iobitridol 65.81 g (658.1 mg/mL) corresponding to iodine 300 mg/mL solution for injection) diluted with saline to a 1:1 mixed bolus of 1–2 mL was injected to ensure appropriate spread within the epidural space without any evidence of vascular uptake (Figure 2C). Following confirmation of correct needle placement and dye spread by fluoroscopy in anteroposterior, lateral and oblique views, a mixture of corticosteroid (1 mL of 40 mg triamcinolone) and local anaesthetic (1 mL of 0.1% Marcaine) was slowly injected. The spinal needle was then withdrawn (Figure 2D). While Kambin’s triangle technique navigated the needle through the safe zone bordered by the exiting nerve root, the superior articular process, and the vertebral body in the anteroposterior (Figure 2E) and oblique views (Figure 2F). Contrast dye was then injected (Figure 2G), followed by a fluoroscopic check performed as described above (Figure 2H). A sterile dressing was applied to the injection site. The patient was monitored in the recovery area for a brief period before being discharged with post-procedure instructions. All the patients underwent the procedure with a highly experienced single spine surgeon.

Figure 2 Intraoperative C-arm fluoroscopy navigation images in transforaminal epidural steroid injection: subpedicular technique (A-D) and Kambin’s triangle technique (E-H).

Statistical analysis

Descriptive statistics were used to summarize demographic and clinical characteristics. Continuous variables were expressed as mean ± standard deviation, while categorical variables were presented as frequencies and percentages. Comparative analysis between the subpedicular and Kambin’s triangle techniques was performed using independent t-tests for continuous variables and chi-square tests for categorical variables. Statistical significance was P value less than 0.05.

Results

The demographic comparison between patients undergoing TFESI via the subpedicular and Kambin’s triangle techniques (Table 2) demonstrated similar characteristics in age, sex ratio, weight, height, BMI, prevalence of underlying diseases, smoking status, and preoperative clinical measures. No statistically significant differences were observed in these parameters between the two groups. Both groups exhibited comparable distributions of unilateral radicular pain, ratios of right to left unilateral radicular pain, and prevalence of specific spinal conditions such as LDH and foraminal stenosis. Additionally, the mean NRS for pain score and ODI were similar between the two groups.

The scatter plot matrix graphical representation for comparing the NRS pain score is shown in Figure 3A. Heatmap graphical representation compares the NRS pain score, which is shown in Figure 3B. The scatter plot matrix graphical representation for comparing the level of disability by ODI is shown in Figure 3C. Heatmap graphical representation of the level of disability by ODI, which is shown in Figure 3D. The comparison between the subpedicular and Kambin’s triangle techniques of TFESI in terms of NRS pain scores and ODI is summarized in Tables 3,4. At baseline, intermediate post-op, and all follow-up time points (1, 3, 6, and 8 months), no statistically significant differences were observed for NRS pain scores between the two techniques. Similarly, no significant differences were observed for ODI at baseline, intermediate post-op, and all follow-up time points between the subpedicular and Kambin’s triangle techniques. Table 5 showed the effectiveness comparison between the two groups by analyzing the NRS pain scores and ODI at baseline and final follow-up. The results indicate notable improvements in pain scores and disability indices for both techniques from baseline to final follow-up. Importantly, no statistically significant discrepancy emerged between the two methodologies in terms of efficacy, with both demonstrating comparable reductions in NRS pain scores and ODI scores over the duration of the study.

Figure 3 Scatter plot matrix graphical (A,C) and heatmap graphical representation (B,D). NRS, numerical rating scale; ODI, Oswestry Disability Index.

Comparison of the two groups’ operation time and treatment cost showed in Table 6. The mean operation time was 25.55±2.01 min for the subpedicular technique and 24.16±3.56 min for the Kambin’s triangle technique. Analysis revealed a non-significant difference between the two techniques. Similarly, the mean treatment cost was 214±5.32 USD for the subpedicular technique and 211±4.36 USD for the Kambin’s triangle technique, with no statistically significant variation observed (P=0.43).

Discussion

Low back pain and radiculopathy are widespread, affecting people of all ages, with LDH being a significant factor. LDH, which can cause back and leg pain, contributes to socioeconomic strains like increased sickness absenteeism (13). Its prevalence, with a lifetime occurrence of 40% (14). Despite this, interventions like TFESI are effective in managing LDH-related leg pain (6,15,16). An epidural injection is indicated for patients with LDH who have persistent back and leg pain that has not responded adequately to non-operative treatments (6). It can provide temporary relief by delivering anti-inflammatory medication directly to the affected area around the spinal nerves, allowing patients to engage in rehabilitative activities. However, it may not be suitable for everyone, and contraindications include patients with systemic infections, bleeding disorders, or allergies to the medications used in the injection (17,18). Galley et al. demonstrated that the infraneural approach to TFESI is as effective as the supraneural approach for treating lumbosacral radicular pain while offering greater safety by avoiding arterial injury risks. Their randomized trial supports the infraneural method as a safer alternative for clinical use (19). Recently, Agarawal et al. reported on both subpedicular and Kambin’s triangle techniques offer comparable relief and functional improvement, emphasizing the importance of tailoring treatment approaches to individual patient needs and procedural expertise for optimal outcomes in LDH management (6). However, they were not reported on cost-effectiveness and procedural safety was not mentioned, and a longer follow-up period is needed.

This study reported the comparative effectiveness of the subpedicular and Kambin’s triangle techniques for TFESI in managing radicular leg pain associated with LDH. The study findings demonstrate that both techniques exhibit comparable efficacy in alleviating pain and improving functional outcomes over the short to medium term (20). This suggests that both approaches are viable options for clinicians when selecting a TFESI technique for patients with unilateral radicular leg pain due to LDH. The absence of significant differences in pain scores, disability indices, and adverse event rates between the two techniques underscores their equivalence in providing symptomatic relief and functional improvement. Despite the comparable efficacy demonstrated by both the subpedicular and Kambin’s triangle techniques for TFESI in managing radicular leg pain associated with LDH, certain patient-specific factors, anatomical considerations, and clinician experience may influence the selection of the appropriate technique and subsequent treatment outcomes. Although the current guidelines from the International Pain & Spine Injection Society recommend the use of nonparticulate steroids for TFESI given the risk of catastrophic neurologic events with particulate steroids such as triamcinolone, a test dose of anesthetic (2% lidocaine) should always be given before the steroid, NOT mixed with the steroid to evaluate for possible neurologic compromise. Marcaine is not recommended for use in the epidural space and should not be used during TFESI, or Omni 300 equivalent contrast media should not be diluted for use with fluoroscopy to maximize the chance of detection of unintended arterial access; our technique showed no complication, which was all injected in the safe zone and was confirmed by fluoroscopic check.

When considering which approach to use, clinicians should consider various factors such as spinal anatomy, comorbidities, and procedural preferences. For instance, the subpedicular approach may be preferable in cases where the herniated disc is located centrally or posterolaterally, as this technique allows for precise targeting of the affected nerve root while minimizing the risk of nerve injury (21). On the other hand, the Kambin’s triangle approach may be more suitable when the disc herniation is located laterally within the intervertebral foramen, as it provides better access to the foraminal space and facilitates direct delivery of the steroid medication to the affected nerve root (5).

Tailoring treatment based on patient-specific factors and procedural expertise is vital in optimizing outcomes for patients with LDH and radicular leg pain (2,22). The decision between the subpedicular and Kambin’s triangle techniques for TFESI hinges on anatomical considerations, such as the location of the herniated disc, patient-specific factors like medical history and the clinician’s expertise (6,22,23). The subpedicular approach may be preferred for centrally or posterolaterally located disc herniations, offering precise nerve root targeting with minimized risk, while the Kambin’s triangle approach may be more suitable for laterally located disc herniations, providing better access to the foraminal space. Ultimately, a tailored approach based on these considerations ensures personalized care and optimal outcomes for patients suffering from radicular leg pain associated with LDH (22,24).

Furthermore, the study findings contribute to the existing body of evidence supporting the role of TFESI as a valuable therapeutic option for patients with radicular leg pain secondary to LDH. The favorable outcomes observed in both treatment groups highlight the importance of TFESI in the multimodal management of this debilitating condition. TFESI offers a minimally invasive, targeted approach to pain relief, allowing patients to achieve meaningful improvements in pain severity, functional status, and quality of life while minimizing the need for surgical intervention and opioid analgesics (7).

The study has several limitations. First, this study was conducted at a single-center, and the approach varies by each patient’s underlying pathology which were central disc or far lateral lesions may limit the generalizability. The sample size, while adequate for preliminary analysis, but may lack the statistical power. Furthermore, patient-reported outcomes were the primary measures of effectiveness, which may introduce subjective bias. Future research should focus on larger and multi-center prospective studies with objective functional outcomes and long-term follow-up to confirm these findings and further inform clinical guidelines to provide robust evidence. Exploring patient-specific factors could identify predictors of treatment response, guiding personalized approaches. Additionally, investigating TFESI in combination with adjunctive therapies and conducting health economic evaluations would offer insights into optimizing treatment strategies and resource allocation. These efforts can refine clinical guidelines, improve patient outcomes, and enhance care for radicular leg pain associated with LDH.

Conclusions

This study suggests the comparable effectiveness of the subpedicular and Kambin’s triangle techniques for TFESI in alleviating radicular leg pain from LDH. Both approaches demonstrated similar pain reduction and functional improvement, highlighting their significance in treatment. Moreover, the study revealed notable improvements in pain scores and disability indices for both techniques from baseline to final follow-up. Further research is needed to refine clinical practice and enhance patient care in interventional pain management.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://jss.amegroups.com/article/view/10.21037/jss-24-140/rc

Data Sharing Statement: Available at https://jss.amegroups.com/article/view/10.21037/jss-24-140/dss

Peer Review File: Available at https://jss.amegroups.com/article/view/10.21037/jss-24-140/prf

Funding: The study was supported by Thailand Science Research and Innovation Fund (Fundamental Fund 2025) (grant No. 5025/2567) and School of Medicine, University of Phayao, Thailand.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jss.amegroups.com/article/view/10.21037/jss-24-140/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the ethics committee of University of Phayao (No. HREC-UP-HSST 1.1/029/67) and individual consent for this retrospective analysis was waived.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

References

1. Liu JH, Soo CW, Lin YC, et al. An alternative approach for lumbar transforaminal epidural steroid injection-Far lateral approach. Pain Pract 2021;21:978-83. [Crossref] [PubMed]
2. Davis N, Hourigan P, Clarke A. Transforaminal epidural steroid injection in lumbar spinal stenosis: an observational study with two-year follow-up. Br J Neurosurg 2017;31:205-8. [Crossref] [PubMed]
3. Ozturk EC, Sacaklidir R, Sencan S, et al. Caudal epidural steroid injection versus transforaminal ESI for unilateral S1 radiculopathy: a prospective, randomized trial. Pain Med 2023;24:957-62. [Crossref] [PubMed]
4. Kwon JW, Moon SH, Park SY, et al. Lumbar Spinal Stenosis: Review Update 2022. Asian Spine J 2022;16:789-98. [Crossref] [PubMed]
5. Kambin P, Brager MD. Percutaneous posterolateral discectomy. Anatomy and mechanism. Clin Orthop Relat Res 1987;145-54. [PubMed]
6. Agarawal S, Ramachandraiah MK. Traditional Safe Triangle Approach Versus Kambin's Triangle Approach: Does Approach Really Matter in Transforaminal Epidural Steroid Injection (TFESI) for Lumbar Disc Herniation? Cureus 2023;15:e48701. [Crossref] [PubMed]
7. Patel HA, Cheppalli NS, Bhandarkar AW, et al. Lumbar Spinal Steroid Injections and Infection Risk after Spinal Surgery: A Systematic Review and Meta-Analysis. Asian Spine J 2022;16:947-57. [Crossref] [PubMed]
8. Hong JY, Song KS, Cho JH, et al. An Updated Overview of Low Back Pain Management. Asian Spine J 2022;16:968-82. [Crossref] [PubMed]
9. Schmid AB, Tampin B, Baron R, et al. Recommendations for terminology and the identification of neuropathic pain in people with spine-related leg pain. Outcomes from the NeuPSIG working group. Pain 2023;164:1693-704. [Crossref] [PubMed]
10. Liawrungrueang W, Kim P, Kotheeranurak V, et al. Automatic Detection, Classification, and Grading of Lumbar Intervertebral Disc Degeneration Using an Artificial Neural Network Model. Diagnostics (Basel) 2023;13:663. [Crossref] [PubMed]
11. Motiei-Langroudi R, Sadeghian H, Ekanem UO, et al. Predicting the Need for Surgery in Patients with Lumbar Disc Herniation: A New Internally Validated Scoring System. Asian Spine J 2023;17:1059-65. [Crossref] [PubMed]
12. Soni P, Punj J. Ultrasound-Guided Lumbar Transforaminal Epidural Injection: A Narrative Review. Asian Spine J 2021;15:261-70. [Crossref] [PubMed]
13. Manchikanti L, Singh V, Falco FJ, et al. Epidemiology of low back pain in adults. Neuromodulation 2014;17:3-10. [Crossref] [PubMed]
14. Frymoyer JW, Pope MH, Clements JH, et al. Risk factors in low-back pain. An epidemiological survey. J Bone Joint Surg Am 1983;65:213-8. [Crossref] [PubMed]
15. Koes BW, van Tulder MW, Peul WC. Diagnosis and treatment of sciatica. BMJ 2007;334:1313-7. [Crossref] [PubMed]
16. Jensen RK, Kongsted A, Kjaer P, et al. Diagnosis and treatment of sciatica. BMJ 2019;367:l6273. [Crossref] [PubMed]
17. Cohen SP, Bicket MC, Jamison D, et al. Epidural steroids: a comprehensive, evidence-based review. Reg Anesth Pain Med 2013;38:175-200. [Crossref] [PubMed]
18. Botwin KP, Gruber RD, Bouchlas CG, et al. Complications of fluoroscopically guided caudal epidural injections. Am J Phys Med Rehabil 2001;80:416-24. [Crossref] [PubMed]
19. Galley HF, Adam R, Columb MO, et al. Supraneural versus Infraneural Approach to transforaMinal Epidural StEroid injection for unilateral lumbosacral radicular pain (SIAMESE): a study protocol for a randomised non-inferiority trial. BJA Open 2023;5:100126. [Crossref] [PubMed]
20. Gopireddy R, Rangasamy K, Goni VG, et al. Can High-Sensitivity C-Reactive Protein Levels Predict Functional Outcome Following Epidural Steroid Injection in Patients with Lumbar Disc Disease? Asian Spine J 2021;15:753-60. [Crossref] [PubMed]
21. Botwin KP, Gruber RD, Bouchlas CG, et al. Fluoroscopically guided lumbar transformational epidural steroid injections in degenerative lumbar stenosis: an outcome study. Am J Phys Med Rehabil 2002;81:898-905. [Crossref] [PubMed]
22. Jain A, Agarwal A, Jain S, et al. Comparison Between a Single Subpedicular Transforaminal Epidural Steroid Injection and Lateral Recess Steroid Injection in Reducing Paracentral Disc Herniation-Related Chronic Neuropathic Leg Pain: A Retrospective Study. World Neurosurg 2021;149:e392-9. [Crossref] [PubMed]
23. Gellhorn AC, Chan L, Martin B, et al. Management patterns in acute low back pain: the role of physical therapy. Spine (Phila Pa 1976) 2012;37:775-82. [Crossref] [PubMed]
24. Kim C, Moon CJ, Choi HE, et al. Retrodiscal approach of lumbar epidural block. Ann Rehabil Med 2011;35:418-26. [Crossref] [PubMed]