Chen L. et al. - Photobiomodulation and Subacromial Impingement: A Meta-Analysis of Randomized Trials

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In this meta-analysis of 21 randomized trials, low-intensity laser therapy was associated with less pain and improved shoulder flexion, abduction, and external rotation in subacromial impingement. However, no significant improvement was observed in functional impairment, extension, or internal rotation, and the authors consider these findings to be exploratory.

What this study measured

This is a meta-analysis of randomized trials. Eight databases were searched to evaluate low-intensity laser therapy, or photobiomodulation, in people with subacromial impingement.

A total of 17 studies and 21 randomized trials were included, involving 1,118 patients. The outcomes analyzed were pain, range of motion of the shoulder, and functional impairment. The risk of bias was assessed using the Cochrane tool, and the quality of the evidence was assessed using the GRADE approach.

Key Findings

Compared with the control group, laser therapy was associated with less pain and improved range of motion in three movements, with no significant effect on the others. Key figures, expressed as mean differences (MD) with 95% confidence intervals.

Pain: DM = -0.54 (95% CI -1.05 to -0.02; p = 0.04)
Shoulder flexion: OR = 4.35 (95% CI 1.13–7.58; p = 0.008)
Abduction: DM = 3.72 (95% CI 0.79 to 6.64; p = 0.01)
External rotation: DM = 1.96 (95% CI 0.51–3.42; p = 0.008)
Extension: DM = 0.79 (95% CI -0.47 to 2.06; p = 0.22), not significant
Internal rotation: DM = 1.14 (95% CI: -1.51 to 3.78; p = 0.40), not significant
Functional disability: DM = -3.61 (95% CI -9.49 to 2.26; p = 0.23), not significant

For pain, the upper limit of the confidence interval is very close to zero, which calls for caution. The authors suggest reassessing whether to continue treatment when the number of sessions approaches 12.

How photobiomodulation works for this indication

This meta-analysis did not measure any biological mechanisms. The following explanations remain hypotheses.

Red and near-infrared light is thought to be absorbed by components of the mitochondria, which could alter cellular energy production. A modulation of local inflammation and tissue circulation has also been suggested. These hypotheses are plausible, but this study does not provide evidence to confirm them.

Limits You Should Know

The evidence is of low quality for pain, flexion, abduction, and external rotation, and of very low quality for functional disability, extension, and internal rotation. There is high heterogeneity among the studies, leading to exploratory conclusions.

The negative results are significant: no significant improvement in functional impairment, extension, or internal rotation, and an effect on pain with a confidence interval close to zero. The abstract does not specify the light parameters, the duration of follow-up, or any adverse effects.

What This Means in Practice

These findings suggest that this treatment may provide some relief for pain and certain shoulder movements. They do not show any effect on functional impairment and do not establish a specific treatment protocol.

Persistent shoulder pain warrants an evaluation by a healthcare professional. Photobiomodulation is not a substitute for this evaluation or for prescribed treatment.

Frequently Asked Questions

Does low-intensity laser therapy reduce shoulder pain in subacromial impingement?

It is associated with less pain than in the control groups (SM = -0.54; 95% CI -1.05 to -0.02), but the interval is close to zero and the evidence is of low quality.

Does it improve shoulder mobility?

Partially. The authors report an increase in flexion, abduction, and external rotation, but no significant improvement in extension or internal rotation.

How many sessions should I plan for?

The abstract does not specify a precise protocol. The authors merely suggest reassessing the need to continue when the number of sessions approaches 12.

Reference

Chen L, Wang Y. Efficacy of low-level laser therapy for subacromial impingement syndrome: a meta-analysis of randomized controlled trials. Lasers Med Sci, 2026. PMID 42733098. DOI 10.1007/s10103-026-05028-7. https://pubmed.ncbi.nlm.nih.gov/42733098/

This summary is provided for informational purposes only and does not constitute medical advice. Photobiomodulation is not a substitute for prescribed treatment. Consult a healthcare professional.