Evaluation of the Evolution of Biological and Imaging Markers of Bone and Cartilage Degradation in Patients With Knee Osteoarthritis Receiving Intra-articular Injections of a Hyaluronan Derivative HYMOVIS®

Inclusion Criteria: * Male or female between the age of 40 and 80 with BMI ≤ 40 * Monolateral (unless contralateral knee is grade I and asymptomatic) femorotibial knee OA associated or not with femoropatellar knee OA * Responding to clinical and radiological criteria of the American College of Rheumatology (ACR) (Appendix 1) * Symptomatic for more than 6 months in the most painful knee * Radiological Kellgren \& Lawrence (K\&L) II or III in radiographs from less than 12 months (Appendix 2) * Mean knee pain score at rest over the last 24 hours evaluated on VAS (0-100) ≥ 40 (Appendix 3) with a washout period for Paracetamol and oral NSAIDs depending on the half-life of the drug (Appendix 4). The most painful knee is considered. * Able to follow the instructions of the study * Having signed an ICF Exclusion Criteria: Related to the OA pathology * Bilateral (except asymptomatic and grade I) OA of the knee * Radiological K\&L grade I or IV (Appendix 2) * Chondromatosis or villonodular synovitis of the knee * Recent trauma (\< 1 month) of the knee responsible of the symptomatic knee * Acute inflammatory OA (KOFUS (Knee Osteoarthritis Flare Up Scale) score ≥ 7, Appendix 5) * Articular disease resulting from articular dysplasia, aseptic osteonecrosis, acromegaly, Paget's disease, hemophilia, hemochromatosis…. * Inflammatory disease i.e. rheumatoid arthritis, gout, infectious arthritis, acute calcium pyrophosphate arthritis * Pathologies interfering with the evaluation of OA (radiculalgia in the lower limbs, arteritis…..) * Presence of another joint (other than the target knee) affected by OA (confirmed in radiographs and symptomatic) Related to treatments * Corticosteroids injection in the target knee in the last month before first injection * Hyaluronan injection in the target knee in the last 6 months before first injection * Arthroscopy and surgery in the target knee in the last 6 months before first injection * Oral corticotherapy ≥ 5mg/day (in Prednisone equivalent) in the last 3 months before first injection * OA treatments based on curcuma extract (e.g. FLEXOFYTOL) in the last 3 months before first injection * Change in the dosage of SYSAD i.e. chondroitin, glucosamine, diacerein or avocado-soy unsaponifiables in the last 3 months before first injection * Paracetamol and oral NSAIDs before inclusion and follow-up visits (washout period depending on the half-life of the drug, Appendix 4). * Osteoporosis-related treatments based on strontium ranelate, selective estrogen-receptor modulator (SERM) and parathormone (PTH) in the last 12 months before first injection * An anticipated need for any forbidden OA treatments during the trial * Contraindications to HYMOVIS®: hypersensitivity to the product components and infections or skin diseases in the area of the injection site. * Non-pharmacologic therapy (including physical therapy) for the lower extremities initiated in the month before first injection * Anticoagulant (coumarinic compound) and heparin Related to associated diseases * Severe diseases (liver or renal failure, lung/heart disease, tumor, HIV….) * Allergy or contra-indication to hyaluronan * Severe alteration of mobility enabling functional evaluation * High risk of hemorrhage and risk of infection at the site of injection * Anticipated need for any surgical or other invasive procedure during the trial including prosthesis in the target knee Related to patients * Participation to a therapeutic clinical trial in the last 3 months before first injection * Under guardianship or judicial protection * Pregnancy, breastfeeding, planned conception, premenopausal women without contraception, tubal ligation or hysterectomy Related to MRI counter-indication * Patient with a pacemaker, an implantable defibrillator, neurosurgical clips, a neurostimulator, cochlear implant, a stent from less than 3 weeks, an insulin pump * Patient with a ferromagnetic splinter in the body, or having wire sutures * Serious mobility problem (Parkinson, tremors), * Claustrophobia