Route or reach? Caudal epidural versus nerve-root-targeted injection for lumbar radiculopathy: a systematic review of randomized controlled trials.

Abstract

Epidural steroid injections remain a cornerstone in the nonoperative management of lumbar radiculopathy, yet the optimal route of delivery remains debated. Caudal epidural injection (CEI) offers broad epidural spread and technical simplicity, whereas nerve-root-targeted techniques provide focused perineural drug delivery and diagnostic value. Despite widespread use of both approaches, their comparative clinical effectiveness remains uncertain. A PRISMA-compliant search of MEDLINE, Embase, CENTRAL, Scopus, and PubMed identified randomized controlled trials comparing CEI with nerve-root-targeted injections in adults with lumbar radiculopathy. Primary outcome was pain intensity (VAS or NRS); secondary outcomes included functional improvement (Oswestry Disability Index) and adverse events. Pooled analyses were performed using standardized mean differences (Hedges' g) with random-effects models. Five randomized controlled trials encompassing 310 patients met inclusion criteria. At approximately 1 month, CEI demonstrated a small-to-moderate advantage in pain reduction compared with nerve-root-targeted injections (Hedges g = 0.41, 95% CI 0.08-0.74). However, the absolute between-group differences reported in individual studies were modest, and the clinical importance of this early effect is therefore uncertain. Eventually this difference was not sustained. By 3 months, pain outcomes converged, with no significant difference between techniques (Hedges g = 0.07, 95% CI - 0.25 to 0.39). Functional outcomes followed a similar pattern, with no meaningful between-group differences at intermediate follow-up. Trials employing balanced injection frequency showed clinical equivalence, whereas apparent long-term advantages of CEI were confined to studies permitting repeated caudal injections, suggesting confounding by cumulative steroid exposure rather than injection route. When treatment intensity was equal, targeted transforaminal delivery showed signals of greater durability in longer-term follow-up. Adverse events were infrequent and mild across both approaches. Caudal epidural and nerve-root-targeted injections provide comparable short- and intermediate-term pain relief and functional improvement for lumbar radiculopathy. Early differences favoring CEI are small and transient, while longer-term outcomes appear more dependent on treatment intensity, anatomical level, and injectate distribution than on injection route alone. Given equivalent efficacy, procedural selection should be individualized based on anatomical considerations, diagnostic needs, safety profile, and clinician expertise rather than expectations of superior clinical outcomes from a specific technique.