Efficacy of Adjunctive Photobiomodulation in Patellofemoral Pain Syndrome: A Systematic Review and Meta-Analysis

OBJECTIVE: To evaluate the effectiveness and safety of adjunctive photobiomodulation (PBM) or low-level laser therapy (LLLT) combined with exercise-based rehabilitation in reducing pain and improving function in individuals with patellofemoral pain syndrome (PFPS). DATA SOURCES: PubMed, Scopus, Embase, Web of Science, PEDro, the Cochrane Library, and China National Knowledge Infrastructure were searched from inception to October 2025. STUDY SELECTION: Randomized controlled trials (RCTs) were included if they examined PBM/LLLT with clearly reported parameters compared with placebo, sham, or no-intervention controls in individuals with PFPS. Studies with mixed knee pathologies or nonrandomized designs were excluded. DATA EXTRACTION: Two reviewers independently extracted data on participant features, PBM parameters, interventions, comparators, outcomes, and adverse events. Risk of bias was assessed using the Cochrane tool, with disagreements resolved by consensus. DATA SYNTHESIS: Four RCTs (n=162) were eligible. Meta-analysis using a random-effects model showed a statistically nonsignificant trend favoring PBM for pain reduction (effect size=-1.520; 95% confidence interval: -3.542 to 0.502; P=.097), with substantial heterogeneity (I2=91.1%) and a wide 95% prediction interval (-5.880 to 2.840). Importantly, the 4 included trials used distinct PBM delivery approaches, including laser acupuncture, PBM combined with trigger point therapy, classic PBM, and monochromatic infrared energy. This diversity may limit the validity of pooling these heterogeneous interventions within a single meta-analysis. Individually, PBM produced greater short-term pain reduction and some functional improvements in certain trials. No adverse events were reported. CONCLUSIONS: PBM/LLLT may provide short-term pain relief and modest functional benefits for young adults with PFPS and appears to be safe. However, the considerable variability among PBM modalities, including acupuncture-based laser stimulation, PBM combined with trigger point therapy, conventional PBM, and monochromatic infrared energy, introduces important methodological heterogeneity and raises concerns regarding the appropriateness of aggregating these interventions. In addition, the limited sample sizes and heterogeneous PBM protocols reduce confidence in these findings. Larger, standardized RCTs are needed.