This monocentric protocol is designed to evaluate the efficacy of therapeutic management of symptomatic knee osteoarthritis (resistant to medical first-line treatment) by intra-articular injection of autologous PRP prepared in the same procedure and using a dedicated CE marked medical device and a validated and reproducible method of preparation

The main objective is to get a 50% proportion of responders defined by answers "absent" or "light" in the KOOS questionnaire on questions about pain and difficulty walking on flat ground.

Secondary objectives include the safety validation of the use of PRP (prepared standardized manner by means of a given medical device) as second-line standard of care for osteoarthritis by the introduction of a systematic monitoring; and the feasibility of the health care system dedicated to the treatment of knee osteoarthritis by autologous PRP.

Furthermore, the secondary objectives are to monitor and follow the evolution of pain (VAS) and the knee function (KOOS score) at 1 month, 3 months, 6 months. Evaluation of MRI will be performed within 15 days prior (inclusion visit) injection and 6 months to assess the cartilage thickness and visualize a regenerative effect.

Inclusion Criteria:

• Men and women 20 to 80 years
• Gonarthrosis diagnostic objectified by the criteria of the American College of Rheumatology
• Joint pain for more than 6 months
• Answer "moderate" to the question about pain walking on flat ground
• Answer "moderate" to the question about trouble walking on flat ground
• Osteoarthritis stage 2 or 3 on the scale of Kellgren Lawrence (objectified radiography) within 6 months previous inclusion
• Axial deformation of less than or equal to 5 ° lower limbs
• Informed consent signed by the patient
• HB> 10g / dl
• Beta-HCG negative at baseline
• Ability to perform the procedures in the follow-up (50 not walk on a flat surface and up / down stairs).
• Being affiliated to a system of health insurance

Exclusion criteria:

• Axial deformation > 5 °
• Ligamentous instability
• Significant injuries or target knee or knee surgery contralateral side in 12 months previous the inclusion visit
• Ligament reconstruction in the 12 months précédants the inclusion visit
• Need a cane or assistance to move
• BMI> 35
• Thrombocytopenia <150 G / L
• Thrombocytosis> 450 G / L
• Known thrombopathy
• Anemia HB <10g / dl
• Active infections to HIV 1 and 2, Agp24, HCV Ab, Ag and HbS AcHbc, Ac HTLV I and II, TPHA
• Chronic treatment with corticosteroids per os or older than 2 weeks
• Injection intra-articular corticosteroid of less than 2 months
• Intra-articular injection of hyaluronic acid of less than 6 months
• NSAIDs or antiplatelet agent of less than 15 days
• Inability to stop NSAIDs (including aspirin) 15 days before the injection and the week following the injection
• Fever or recent illness
• Autoimmune diseases
• Inflammatory arthritis
• Immune deficiency
• Infectious diseases
• Pregnant women
• Adults legally protected (under guardianship and trusteeship)
• People simultaneously participating in other biomedical research16. Inability

study for knee osteoarthritis patients treated in the center