Knee osteoarthritis is a frequent disease with important consequences for quality of life of patients. In France, prevalence was estimated at 7.6% among subjects between 40-75 years old. The management of knee osteoarthritis is essentially based on lifestyle and dietary measures and the use of analgesic treatment. Spa treatments are also part of the overall management of this pathology.~In this context, the spa town Saint-Lary Soulan requests the approval of the  Rheumatology  therapeutic orientation for its new borehole water (SL5), which requires a study (Larytherm) conducted according to the criteria of the French Academy of Medicine.~Secondary objectives are to evaluate 6 months after spa therapy in Saint-Lary Soulan, the evolution of:~Body Mass Index (BMI),~knee pain due to knee osteoarthritis,~functional impact,~fatigue,~physical activity,~quality of life,~consumption of analgesic treatments,~the occurrence of episodes of joint effusion requiring puncture/infiltration,~the occurrence of adverse events.~The patients will be identified by local physicians or through a local public communication campaign. The patients with criteria of eligibility will complete a self-reported questionnaire before the beginning of spa therapy, after the spa therapy and 6 months after the end of spa therapy, and the physicians practising at the spa center will complete a medical questionnaire at inclusion and after the spa therapy.
The hypothesis is that the use of spa therapy in Saint-Lary Soulan for knee osteoarthritis treatment would have a therapeutic effect on this pathology.~The main objective of this external comparison study is to evaluate the comparative effectiveness at 6 months of spa therapy in the Saint-Lary Soulan spa center on functional disability and pain (MCII: Minimal Clinical Important Improvement) in knee osteoarthritis compared to the control group of the Thermarthrose multicenter randomized clinical trial, receiving standard cares.~The patients included in the Larytherm cohort will undergo a three-week spa therapy in Saint-Lary Soulan with a follow-up of 6 months after the end of spa therapy.