Influence of lumbar epidural injection volume on pain relief for radicular leg pain and/or low back pain.

Background Context: Epidural injections are commonly used to treat low back disorders. It has been proposed that in addition to the anti-inflammatory effects, injected material displaces the dura forward and inward, producing a stretch of the nerve roots that leads to lysis of neural adhesions. Despite this, there are no controlled trials investigating the effect of volume injected with pain as an independent outcome.

Purpose: Review the existing literature to assess the effect of epidural injection volume on relief of radicular leg and low back pain.

Study Design: A systematic review of published clinical trials to assess the correlation between volume of epidural injection and relief of radicular leg and low back pain.

Methods: We searched MEDLINE (1966 to January 2009), EMBASE (1980 to January 2009), The Cochrane Library, and the reference lists of retrieved articles. The literature search was limited to English and Human subjects. Studies were included if they involved the following: 1) a controlled clinical trial; 2) epidural injections in treatment groups compared with control injections; 3) the same approach to epidural space in both groups; and 4) pain relief as an independent outcome. Trials that measured pain relief for radicular leg and low back pain, before and after epidural injections were included. Using the Cochrane Back Review Group recommendations, pain relief data were extracted independently by two reviewers into four categories: immediate (6 weeks-3 months); intermediate (>or=3 months-1 year); and long-term (>or=1 year). Common effect sizes were calculated for each data point. Quality of the trials was assessed (two independent authors) using the 11-item criteria list recommended in the method guidelines for systematic reviews for the Cochrane Back Review Group. The data were analyzed by calculating the following: correlations between volume difference and effect size at each data point; and comparing the average effect sizes in the studies with same volume in both groups to ones with different volumes.

Results: Fifteen studies fulfilled the inclusion/exclusion criteria. The correlation between volume difference and pain relief was 0.8027 (p=.002) for the immediate category, 0.5019 (p=.168) for the short-term category, and 0.9470 (p=.014) for the intermediate category. Insufficient data were available to calculate the correlation coefficient in the long-term category. There was a statistically significant difference when comparing the mean effect size where the volume injected was the same between the two groups (mean, standard deviation [SD]: 0.07, -0.26) with those where the volumes were different between comparison groups (mean, SD: 0.81, -0.6), irrespective of the medications injected.

Conclusions: These preliminary results suggest a positive correlation between larger volumes of fluid injected in the epidural space and greater relief of radicular leg pain and/or low back pain. Clinicians should not change their practice, until further high-quality clinical studies confirm these findings.