Photobiomodulation for the treatment of knee osteoarthritis: therapeutic effects and molecular mechanism

Xia P, Fan T, Huang Y, Zheng H, Ma R, Zhou W, Li Y, Fu SN, et al. · Frontiers in Cell and Developmental Biology

The clinical evidence is tabulated by protocol rather than pooled. Pure low-level laser against placebo — 10 RCTs and 3 systematic reviews, 633-905 nm — is mixed, with many showing pain reduction and some none. Laser acupuncture — 9 RCTs and 1 review — shows consistent short-term pain and function gains. Low-level laser added to exercise — 11 RCTs and 2 reviews — is generally superior to exercise alone, though some reviews disagree. Against other modalities, 6 RCTs found it similar to neuromuscular electrical stimulation and less effective than ozone or pulsed electromagnetic field. High-intensity laser — 12 RCTs and 4 reviews, often 1064 nm — consistently reduces pain and is often superior to low-level laser. LED — 4 RCTs — is mixed, with one study finding no benefit from LED alone and others finding it comparable to low-level laser when combined with exercise. The authors separate the two questions in their conclusion: strong and consistent evidence for immediate and short-term symptomatic relief, and no definitive clinical evidence of joint space widening or structural reversal, with cartilage regeneration in humans described as emerging and partly speculative because it is extrapolated from preclinical histology.

Population

59 human studies of photobiomodulation for knee osteoarthritis, primarily randomized controlled trials and systematic reviews, from a PubMed search covering January 1992 to December 2023, read alongside the preclinical literature

Intervention

Low-level laser therapy alone, as laser acupuncture, and added to exercise; high-intensity laser therapy; and LED

Comparator

Placebo, exercise alone, and other modalities including neuromuscular electrical stimulation, ozone and pulsed electromagnetic field

Limitations

A narrative synthesis, not a meta-analysis: nothing is pooled, and the authors attribute the heterogeneity between trials to the absence of standardised wavelength, energy density and duration. Methodological quality of the included randomised trials was rated on the PEDro scale, scores ranging 5 to 10 with a mean of 6.9, and the authors report that the higher-scoring trials tended to give more consistent short-term results — an appraisal of the trials, not a pooled estimate of effect. The clinical search covered PubMed alone and stopped at December 2023. LED — the cheap, wearable form a reader is most likely to be able to buy — has the thinnest clinical base of the six categories at 4 RCTs with mixed results, and the authors say so. Hong Kong Polytechnic University funding; the authors declare no conflict of interest.