Knee Osteoarthritis and Thermal Spa Treatment

Inclusion Criteria: * Knee osteoarthritis with Kellgren and Lawrence stage 2 to 4 evidenced by a knee X-ray examination in the past 3 years. * 100-normalized score of the WOMAC physical function subscale greater than or equal to 30. * Signed inform consent. * With health insurance affiliation. Exclusion Criteria: * Presented with balneotherapy contraindication or to certain adjuvant treatment techniques (balneation, hydrotherapy jets, massage): chronic infectious pathology, active cancer, decompensated cardiac, hepatic or renal insufficiency, "open" leg ulcer, immune deficiency, phlebitis, erysipelas or history of erysipelas, active thrombosis, behavioral disorders, etc. * Presented with chronic pain for reasons other than osteoarthritis: chronic inflammatory rheumatism (rheumatoid arthritis, ankylosing spondylitis, lupus, psoriatic arthritis) or fibromyalgia. * Patient scheduled for knee osteoarthrosis-related surgery within the next 7 months. * Having had spa treatment in the past 6 months whatever the indication or intra-articular corticosteroid injection within the previous 90 days or hyaluronic acid infiltration or other viscosupplementation or platelet-rich plasma (PRP) injection within the previous 6 months. * Having planned a spa treatment in another indication between inclusion and final visit. * Residing more than 30 kilometers from Enghien-les-Bains at the time of spa treatment. * Women of childbearing potential who are not using effective contraception (estrogen/progestin or progestin-only oral, vaginal, transdermal, injectable or subcutaneous) or who plan to discontinue contraception within the next 7 months. * Likely to be unable to comply with protocol or to attend visits, particularly in view of the duration of the research, or unable to read or understand French. * Regulatory reason (guardianship or already enrolled in a clinical trial). * Already included in a clinical trial or in the exclusion period of a clinical trial.