Photobiomodulation therapy combined with a static magnetic field for chronic non-specific knee pain: protocol for a multicentre, randomised, triple-blind, placebo-controlled trial.

introductionChronic non-specific knee pain represents a prevalent and disabling musculoskeletal condition that often lacks a clearly identifiable structural cause and evidence-based management strategies. Photobiomodulation therapy combined with a static magnetic field (PBMT-sMF) has been proposed as a non-invasive approach capable of modulating inflammation, reducing oxidative stress and promoting tissue repair. However, high-quality clinical evidence regarding its effectiveness in this population remains scarce. This trial aims to investigate the effects of PBMT-sMF on pain intensity, biochemical and functional outcomes and patient satisfaction in individuals with chronic non-specific knee pain. METHODS AND ANALYSIS: This superiority, multicentre, randomised, placebo-controlled, triple-blind clinical trial will include 86 adults (aged 18-50 years) with chronic, unilateral, non-specific knee pain. Participants will be randomly allocated (1:1) to receive either active or placebo PBMT-sMF, applied three times per week for four consecutive weeks (12 sessions in total). The active intervention will be delivered using a Multi Radiance Medical Super Pulsed Laser device (905 nm laser, 850 nm infrared LEDs [light-emitting diodes], 640 nm red LEDs and an sMF), while the placebo device will be identical in appearance but emit biologically inactive energy. The primary outcome will be pain intensity measured by a 100 mm Visual Analogue Scale at the end of treatment. Secondary outcomes will include prostaglandin E₂ (PGE₂) concentrations, subjective knee function (International Knee Documentation Committee), patient satisfaction and safety (adverse events and co-interventions), all assessed at the end of treatment and reassessed 1 week postintervention. Pain intensity will also be measured at the 1-week follow-up. Statistical analyses will follow the intention-to-treat principle, with significance set at p<0.05. ETHICS AND DISSEMINATION: This study was approved by the Research Ethics Committee of Irmandade da Santa Casa de Misericórdia de Porto Alegre and prospectively registered on ClinicalTrials.gov (NCT05830344). The findings will be disseminated through publication in peer-reviewed journals and presentations at national and international conferences. TRIAL REGISTRATION NUMBER: NCT05830344.