Low-volume versus high-volume caudal epidural steroid injection for lumbar radiculopathy: A randomised superiority trial

The optimal injectate volume for caudal epidural steroid injections (CESI) in lumbar degenerative disc disease (LDDD) remains debated. This randomised superiority trial compared low-volume (5 mL) versus high-volume (12 mL) CESI for LDDD-related radiculopathy. A single-centre, open-label trial with blinded outcome assessment was conducted. Eligible adults (n=154, aged 25–50) with MRI-confirmed L4–S1 radiculopathy were randomised 1:1 to receive 80 mg triamcinolone in either 5 mL or 12 mL saline. Primary outcome was pain reduction (Visual Analogue Scale, VAS); secondary outcomes included functional improvement (Oswestry Disability Index, ODI) and complication rates. Assessments occurred at 3 weeks, 6 weeks, 3 months, and 6 months. The low-volume group demonstrated superior pain relief at all follow-ups (mean VAS at 6 months: 1.49 vs. 2.07, *p*<0.001) and greater functional improvement (mean ODI: 15.8 vs. 20.9, *p*<0.001). Adverse events were significantly lower with low-volume CESI (5.2% vs. 15.6% post-injection discomfort, *p*=0.03). Effect sizes were large (VAS η 2 =0.47; ODI η 2 =0.43), confirming clinical superiority. Low-volume CESI (5 mL) provides sustained, superior analgesia and functional recovery with fewer complications compared to high-volume (12 mL) injections. These findings support adopting low-volume protocols as a safer, more effective standard for LDDD-related radiculopathy. CTRI/REF/2023/01/062213 • Low-volume (5 mL) CESI provides superior and sustained pain relief compared to high-volume (12 mL) injection, with a significantly lower mean VAS score at 6 months (1.49 vs. 2.07, p<0.001). • Functional improvement is significantly greater with the low-volume protocol , demonstrated by a lower mean Oswestry Disability Index at 6 months (15.8 vs. 20.9, p<0.001) and a greater increase in claudication distance. • The safety profile of low-volume CESI is markedly better , with a significantly lower incidence of post-injection discomfort (5.2% vs. 15.6%, p=0.03) and fewer vasovagal reactions. • Large effect sizes (VAS η 2 =0.47; ODI η 2 =0.43) confirm that injectate volume is a major determinant of clinical outcomes, not just a minor factor. • This evidence challenges the conventional practice of using high volumes , supporting a shift towards low-volume CESI as a safer, more effective, and resource-efficient standard of care for single-level radiculopathy.