The aim of this clinical trial is to assess the efficacy of the 18-day balneotherapy program (therapeutic indication: Rheumatology) in terms of functional incapacity and the disorders (pain, joint stiffness) induced by osteoarthritis of the knee, and thus improves patients\' quality of life, in patients presented with knee osteoarthritis. The French National Academy of Medicine encourages the re-use of RCT data when available. In this context, the current study is designed as a single-arm prospective study with external comparison using the propensity score. The Control group consists of the patients which were allocated to the Control group of reference randomized clinical trial (RCT) ANGELLO Study (NCT05819437). These patients received standard care for knee osteoarthritis, i.e., pain management and exercise recommendations. All patients enrolled in the current study benefit of 18-day balneotherapy program (therapeutic indication: Rheumatology) with Mineral Water of Santenay (Burgundy, France), and examination with a practitioner at enrollment and 6 months after the beginning of spa treatment.