Efficacy of low-level laser therapy for subacromial impingement syndrome: a meta-analysis of randomized controlled trials

To systematically explore the therapeutic effects of low-level laser therapy (LLLT) on pain, shoulder range of motion (ROM), and functional disability in patients with subacromial impingement syndrome (SIS). Eight databases were systematically searched. We assessed study quality with the Cochrane Risk of Bias tool, and evidence quality was evaluated using the GRADE approach. Seventeen studies and twenty-one RCTs were included, with 1118 patients enrolled. Relative to the control group, LLLT markedly reduced pain (MD = -0.54, 95% CI: -1.05 to -0.02, P = 0.04). LLLT also significantly improved shoulder flexion (MD = 4.35, 95% CI: 1.13 to 7.58, P = 0.008), abduction (MD = 3.72, 95% CI: 0.79 to 6.64, P = 0.01), and external rotation (MD = 1.96, 95% CI: 0.51 to 3.42, P = 0.008). However, no significant improvement was found in shoulder extension (MD = 0.79, 95% CI: -0.47 to 2.06, P = 0.22), internal rotation (MD = 1.14, 95% CI: -1.51 to 3.78, P = 0.40), and functional disability (MD = -3.61, 95% CI: -9.49 to 2.26, P = 0.23). Low-quality evidence suggests that LLLT effectively alleviates pain in patients with SIS and enhances shoulder flexion, abduction, and external rotation ROM. Very low-quality evidence indicates that LLLT exerts no significant effect on shoulder functional disability, extension, and internal rotation ROM. Additionally, we suggest that clinicians reassess the need for continued treatment when the number of sessions approaches 12, rather than routinely adopting extended protocols. Owing to the high heterogeneity among the included studies, the above conclusions are regarded as exploratory findings.