Comparative Effectiveness of Botulinum Toxin Injection for Chronic Shoulder Pain: A Meta-Analysis of Randomized Controlled Trials

Botulinum toxin (BoNT) injection is regarded as a promising treatment for musculoskeletal pain. However, its efficacy for treating chronic shoulder pain remains unclear. We investigated the effectiveness of BoNT injections for chronic shoulder pain by conducting a systematic search of electronic databases up to March 2020 for randomized control trials (RCTs) that used BoNT injections for chronic shoulder pain treatment. The primary outcome was the between-group comparison of pain reduction, quantified by the standardized mean difference (SMD). Nine RCTs comprising 666 patients were included and divided into two groups: one group with shoulder joint pain (n = 182) and the other group with shoulder myofascial pain (n = 484). Regarding shoulder joint pain, the efficacy of BoNT injections was similar to that of the reference treatment (SMD: −0.605, 95% confidence level [CI]: −1.242 to 0.032 versus saline; SMD: −0.180, 95% CI: −0.514 to 0.153 versus corticosteroids) at one month post-intervention, and was superior (SMD: −0.648, 95% CI: −0.1071 to −0.225 versus corticosteroids) between one and three months. Likewise, in terms of shoulder myofascial pain, the effectiveness of BoNT injections did not differ from the reference treatment (SMD: −0.212, 95% CI: −0.551 to 0.127 versus saline; SMD: 0.665, 95% CI: −0.260 to 1.590 versus dry needling and SMD: 1.093; 95% CI: 0.128 to 2.058 versus lidocaine) at one month post- intervention, and appeared superior (SMD: −0.314, 95% CI: −0.516 to −0.111 versus saline) between one and three months. Our meta-analysis revealed that BoNT injections could be a safe and effective alternative for patients with chronic shoulder pain.