Background: Knee pain is a common complaint among middle-aged and older adults, often leading to reduced mobility and diminished quality of life. Synovitis is a major underlying cause, present in up to 80% of individuals with moderate knee pain. While light therapy has shown anti-inflammatory and analgesic effects in preclinical studies, our prior animal experiments revealed that light therapy at 810 nm significantly alleviated inflammation and pain-like behaviors. These findings suggest a potential wavelength-specific therapeutic effects. However, it remains unclear whether such effects can be replicated in humans. This study aims to evaluate the efficacy of 810 nm light therapy, compared to sham treatment, in reducing knee pain and synovitis in patients with chronic knee pain and knee synovitis.

Methods/design:

This is a randomized, placebo-controlled clinical trial involving 90 participants with chronic knee pain and ultrasound-detected synovitis. Participants will be randomized into two groups to receive 810 nm light therapy, or sham therapy, delivered twice weekly over five weeks. Primary outcomes include knee pain assessed by the Visual Analogue Scale (VAS) and synovitis assessed by ultrasound. Secondary outcomes include the Knee injury and Osteoarthritis Outcome Score (KOOS), the 30-second chair stand test, and the 40-meter fast-paced walk test. Outcome assessments will be performed at baseline, post-intervention (week 5), and at 1 month and 6 months after treatment completion. Linear mixed-effects models will be used to compare outcome changes between groups.

Discussion:

This trial will assess whether 810 nm light therapy provides clinically meaningful benefits for reducing knee pain and synovitis in humans, building on promising preclinical findings. Results from this study may support the use of near-infrared light as a safe, non-invasive, and effective intervention for synovitis-related knee pain.

Inclusion Criteria:

• Participants aged between 40 and 80 years
• Able to provide written informed consent
• Have experienced knee pain that persists or recurs for more than 3 months
• A knee pain score of at least 30 mm on the 100-mm Visual Analogue Scale (VAS) during the past week
• Ultrasound-measured knee synovitis ≥1
• Presence of knee OA according to criteria established by the American College of Rheumatology

Exclusion Criteria:

• Anticipated need for knee surgery within the next one year
• Previous or planned knee replacement within the next one year
• Knee surgery or other physical therapy in the previous 3 months
• Use of intra-articular, intra-muscular, or oral corticosteroids in previous 4 weeks
• Malignant tumors or other life-threatening diseases
• Severe mental disorders, including but not limited to schizophrenia, bipolar disorder, or major depressive disorder, that may interfere with the participant's ability to comply with the study protocol or provide informed consent

Individual participant data (IPD) that underlie the results reported in this article, after de-identification, will be shared. Data will be available upon reasonable request from qualified researchers, subject to ethics approval and data use agreement. The data will become available after the publication of the main results and will be accessible for a period of 5 years.

De-identified individual participant data and supporting documents will be available beginning 6 months after publication of the primary results, and will be available for 5 years thereafter.

Data will be available to qualified researchers whose proposed use of the data has been approved by an independent review committee. Access will be provided after signing a data access agreement. Interested researchers should contact the Principal Investigator by email.

Allocation will be not revealed to the participants and ultrasound assessors until the completion of the final data analyses.