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

Knee osteoarthritis (KOA) is a common chronic and degenerative disease, particularly prevalent in the ageing population. The pathological features of KOA include articular cartilage degeneration, osteophyte formation, subchondral bone changes, and synovial hyperplasia. Photobiomodulation (PBM) involves the application of non-ionizing light sources including laser and light-emitting diodes (LED) and broadband light in the visible and near-infrared spectrum to produce stimulatory effect on healing and modulate the inflammatory process in different tissues, including synovium and cartilage of KOA. However, the therapeutic effectiveness and the molecular mechanism of PBM are not fully understood. The results of clinical studies regarding the effects of PBM on KOA are controversial due to differences in study design and execution among these studies. In addition, the lack of unified standards for the optimal treatment strategies, parameters and courses, which has hampered the application of PBM in KOA. In this review, we synthesized clinical and preclinical evidence to evaluate PBM's efficacy. Our analysis indicates that PBM offers robust symptomatic relief (pain and inflammation) for KOA. However, while preclinical models suggest disease-modifying potential (e.g., cartilage protection), its clinical efficacy in structural regeneration remains speculative and requires further validation through long-term imaging studies.