Role of transforaminal epidural injections or selective nerve root blocks in the management of lumbar radicular syndrome - A narrative, evidence-based review

Abstract

Objective: Lumbar radicular Syndrome (LRS) is a common spinal pathology and is attributed to complex interplay of mechanical, inflammatory and immunological processes. Epidural injection of steroids has a significant therapeutic role in mitigating the inflammatory component of LRS. Trans-foraminal approach under image guidance enables a targeted drug delivery. The current narrative review discusses the various aspects related to lumbar trans-foraminal epidural injection of steroid (LTFIS).

Methods: An elaborate search on PubMed, Google and Medline databases was made using keywords "lumbar selective nerve root block", "lumbar trans-foraminal epidural steroid injection", "selective nerve root block in lumbar disc prolapse", "trans-foraminal epidural steroid injection in lumbar prolapse", "selective nerve root block in lumbar radiculopathy", and "trans-foraminal epidural steroid injection in lumbar radiculopathy" The articles were selected based on specific inclusion criteria.

Results: Our search identified 539 articles. All articles discussing alternate procedures, LTFIS in other pathologies, diagnostic roles of LTFIS, not pertaining to concerned questions, in non-English language and duplicate articles were excluded. Review articles, randomised controlled trials or level 1 studies were given preference. Overall, 108 articles were included. Being a focussed narrative review, further screening [Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) or Methodological Index for non-randomized studies (MINORS) criteria] was not performed to select articles. Based on the evidence, LTFIS is an effective and useful treatment modality. It is offered to patients with lumbar disc herniation (LDH) presenting with persistent, unilateral, radiculopathy after a course of conservative measures for around 6 weeks' duration. It has been reported to yield better results than caudal or inter-laminar epidural injections. The anti-inflammatory and nociceptive signal stabilization actions of steroids, as well as mechanical effects of washout of inflammatory mediators and neural lysis contribute to its efficacy. The three different approaches include sub-pedicular, retro-neural and retro-discal. The procedure is performed under image guidance using a water-soluble contrast under fluoroscopy. The four described radiculogram patterns include "arm", "arrow", "linear" and "splash". Computerised tomography, ultrasonography and magnetic resonance imaging are other modalities, which may be helpful in performing LTFIS. The use of particulate versus non-particulate steroids is controversial.

Conclusion: The overall success rate of SNRB is reported to be 76-88%. The majority of benefits are observed during immediate and early post-injection period. Clinical factors including duration and severity of symptoms, and radiological factors like presence of osteophytes, location, size and type of disc prolapse influence outcomes. The radiculogram "splash" pattern is associated with poor outcomes.

Keywords: Lumbosacral radicular syndrome; Radiculogram; Selective nerve root block; Trans-foraminal epidural steroid injection.

Fig. 1

Cross-sectional hand diagram depicting the inter-laminar and transforaminal approaches for epidural injections.

Fig. 2

2Aand 2B – Hand diagrams depicting the three techniques of selective nerve root block administration: sub-pedicle, retro-neural and retro-discal approaches.

Fig. 3

Intra-operative fluoroscopic images showing the four patterns of radiculograms – A. “Arm”, B. “Arrow”, C. “Linear”, D. “Splash”.