Osteoarthritis (OA) is one of the main causes of chronic pain and physical disability, which directly impacts the quality of life of patients. The prevalence of OA among adults over 60 years of age is approximately 13% in women and 10% in men. Knee OA (gonarthrosis) has as main risk factors, in addition to age, female gender and obesity. Pharmacological treatment of gonarthrosis is based on approaches to reduce symptoms and/or pain, with joint replacement (arthroplasty) being reserved for more advanced forms of the disease. In general, currently available treatments have only moderate effects and low satisfaction rates among patients. Photobiomodulation Therapy (TFBM) has been used for at least 50 years by health professionals to treat a variety of clinical conditions, especially those associated with chronic pain. TFBM is a treatment using a non-ionizing light source such as Low Intensity Laser (LBI) or Light Emitting Diodes (LED), with near-infrared wavelengths. The aim of this study is to evaluate the intensity of knee pain in the short and medium term after photobiomodulation therapy in patients with gonarthrosis. In this multicenter, randomized, placebo-controlled, double-blind clinical trial, 238 volunteers with gonarthrosis grades II and III according to the Kellgren-Lawrence classification will be recruited to be administered adjuvant treatment with TFBM. The TFBM will be performed in the knee region, twice a week, for five weeks, totaling 10 sessions. Volunteers will be allocated in the intervention group (n=119) or in the placebo group, which will be treated with 10 sessions of inert light (n=119). The hypothesis is that the photobiomodulation therapy will have a positive impact, in the short and medium term, on improving pain, functionality and quality of life of patients with symptomatic gonarthrosis.

Osteoarthritis (OA) is one of the main causes of chronic pain and physical disability, which directly impacts the quality of life of patients. The prevalence of OA among adults over 60 years of age is approximately 13% in women and 10% in men. Knee OA (gonarthrosis) has as main risk factors, in addition to age, female gender and obesity. It can involve all three compartments of the knee and is clinically characterized by pain and progressive impairment of cartilage, bone, synovial membrane and ligaments. Pharmacological treatment of gonarthrosis is based on approaches to reduce symptoms and/or pain, with joint replacement (arthroplasty) being reserved for more advanced forms of the disease. In general, currently available treatments have only moderate effects and low satisfaction rates among patients. Photobiomodulation Therapy (TFBM) has been used for at least 50 years by health professionals to treat a variety of clinical conditions, especially those associated with chronic pain. TFBM is a treatment using a non-ionizing light source such as Low Intensity Laser (LBI) or Light Emitting Diodes (LED), with near-infrared wavelengths. The technique does not emit heat, is painless and non-invasive and does not have significant side effects, and can be used as an adjuvant therapy to control pain associated with gonarthrosis. The aim of this study is to evaluate the intensity of knee pain in the short and medium term after photobiomodulation therapy in patients with gonarthrosis. In this multicenter, randomized, placebo-controlled, double-blind clinical trial, 238 volunteers with gonarthrosis grades II and III according to the Kellgren-Lawrence classification will be recruited to be administered adjuvant treatment with TFBM. The TFBM will be performed in the knee region, twice a week, for five weeks, totaling 10 sessions. Volunteers will be allocated in the intervention group (n=119) or in the placebo group, which will be treated with 10 sessions of inert light (n=119). The evaluations will be made before and after TFBM or placebo and will consist of (i) measurement of pain intensity through the application of questionnaires; (ii) verify the functional mobility of the knee joint and the muscle strength of the lower limb through physical tests; (iii) evaluate the quality of life and levels of anxiety and depression through the application of questionnaires; and (iv) record the consumption of medication for analgesic purposes and the frequency of physical therapy during the trial period. The hypothesis is that the photobiomodulation therapy will have a positive impact, in the short and medium term, on improving pain, functionality and quality of life of patients with symptomatic gonarthrosis. It is also expected to observe a reduction in pain on the Visual Analog Scale of more than 20% after 10 treatment sessions.

Inclusion Criteria:

• Patients of both sexes, aged between 50 and 75 years;
• Uni or bilateral symptomatic gonarthrosis grades II or III according to the Kellgren-Lawrence classification confirmed on radiographs with weight bearing in anteroposterior, lateral and axial patella. When the disease is bilateral, the knee indicated by the patient as being the most symptomatic will be included;
• Complaint of knee pain ≥4 on the Visual Analogue Scale at the time of inclusion in the study;
• Able to walk independently, with or without walking aids;
• Cognitive ability to answer questionnaires and perform physical tests;
• Agreement to participate in the study by signing the Free and Informed Consent Form (TCLE).

Exclusion Criteria:

• Diagnosis of active malignancy except basal cell carcinoma (BCC);
• Diseases or neurological conditions that compromise the ability to perform the physical tests;
• Epilepsy;
• Skin lesions on the lower limb, close to the TFBM application site;
• Tattoos on the lower limb, close to the TFBM application site;
• Unicompartmental or total knee arthroplasty in the knee included in the study;
• History of direct trauma to the knee included in the study within the last six months;
• Active systemic inflammatory disease;
• Rheumatological diseases;
• Any previous procedure with an intra-articular approach to the knee in the last six months;
• Anticipation of adopting another form of treatment during the study period, including arthroplasty;
• Patients undergoing knee shock wave treatment in the knee included in the study;
• Absence, inability or refusal to sign the informed consent form.