Background: Injection with anaesthetics and/or steroids is one of the treatment modalities used in patients with chronic low back pain which needs evaluation with respect to the effectiveness on short and long term pain relief.
Objectives: To evaluate the effectiveness of injection therapy in patients with low back pain lasting longer than one month. We distinguished between three injection sites: facet joint, epidural or local injections.
Search strategy: We searched the Medline and Embase databases up to 1996 and other search methods as advocated by the Back Review Group search strategy. Abstracts and unpublished studies were not included.
Selection criteria: Randomized controlled trials of injection therapy for pain relief (although additional treatments were allowed) in patients with benign low back pain lasting longer than one month and not originating from cancer.
Data collection and analysis: Two authors independently assessed the trials for methodological quality. Subgroup analyses were made between trials with different control groups (placebo and active injections), with different injection site (facet joint, epidural and local injection), and timing of outcome measurement (short and long term). Within the resulting 12 subcategories of studies (2*3*2), the overall relative risks and corresponding 95% confidence intervals were estimated, using a random effects model (DerSimonian and Laird). In the case of trials in which control groups were active injections, we refrained from pooling the results.
Main results: Twenty-one randomized trials were included in this review. All studies involved patients with low back pain lasting longer than one month. Only 11 studies compared injection therapy with placebo injections (explanatory trials). The methodologic quality of many studies was low: only 8 studies had a methodologic score of 50 or more points. There were only three well designed explanatory clinical trials: one on injections into the facet joints with a short-term RR of 0.89 (95% CI: 0.65-1.21) and a long-term RR of 0.90 (95% CI: 0.69-1.17); one on epidural injections with a short-term RR of 0.94 (95% CI: 0.76-1.15) and a long-term RR of 1.00 (95% CI: 0.71-1.41); and one on local injections with a long-term RR of 0.79 (95% CI: 0.65-0.96). Within the 6 subcategories of explanatory studies the pooled RRs with 95% confidence intervals were: facet joint, short-term: RR=0.89 (0.65-1.21); facet joint, long-term: RR=0.90 (0.69-1.17); epidural, short-term: RR=0.93 (0.79-1.09); epidural, long-term: RR=0.92 (0.76-1.11); local, short-term: RR=0.80 (0.40-1.59); local, long-term: RR=0.79 (0.65-0.96).
Authors' conclusions: Convincing evidence is lacking on the effects of injection therapies for low back pain. There is a need for more, well designed explanatory trials in this field.