Injection therapy for subacute and chronic benign low back pain

The Medline and Embase databases containing randomized controlled trials of injection therapy published to 1998 were systematically reviewed.

To evaluate the effectiveness of injection therapy with anesthetics, steroids, or both in patients with low back pain persisting longer than 1 month.

Two reviewers independently assessed the trials for the quality of their methods. The primary outcome measure was pain relief. Subgroup analyses were performed between trials with different control groups (placebo and active injections), with different injection sites (facet-joint, epidural, and local injections), and with timing of outcome measurement (short- and long-term). Within the resulting 12 (2 x 3 x 2) subcategories of studies, the overall relative risks and corresponding 95% confidence intervals were estimated, using the random effects model of DerSimonian and Laird. In the case of trials using active injections as a control, the results were not pooled.

This review included 21 randomized trials. All the studies involved patients with low back pain persisting longer than 1 month. Only 11 studies compared injection therapy with placebo injections (explanatory trials). The methodologic quality of many studies was low: Only eight studies had a methodologic score of 50 points or more. There were only three well-designed explanatory clinical trials: one on injections into the facet joints with a short-term relative risk of 0.89 (95% confidence interval = 0.65-1.21) and a long-term relative risk of 0.90 (95% confidence interval = 0.69-1.17), one on epidural injections with a short-term relative risk of of 0.94 (95% confidence interval = 0.76-1.15) and a long-term relative risk of 1.00 (95% confidence interval = 0.71-1.41), and one on local injections with a long-term relative risk of 0.79 (95% confidence interval = 0.65-0.96). Within the six subcategories of explanatory studies, the pooled relative risks were as follows: facet joint, short-term: relative risk = 0.89 (95% confidence interval = 0.65-1.21); facet joint, long-term: relative risk = 0.90 (95% confidence interval = 0.69-1.17); epidural, short-term: relative risk = 0.93 (95% confidence interval = 0.79-1.09); epidural, long-term: relative risk = 0.92 (95% confidence interval = 0.76-1.11); local, short-term: relative risk = 0.80 (95% confidence interval = 0.40-1.59); and local, long-term: relative risk = 0.79 (95% confidence interval = 0.65-0.96).

Convincing evidence is lacking regarding the effects of injection therapy on low back pain. Additional well-designed explanatory trials in this field are needed.