The incidence of cartilage pathology has grown due to the ageing population, and the increase in sports participation and its associated trauma. The aim of the treatment of symptomatic osteoarthritis consists in reducing pain and improving the knee function in order to limit the sport, professional and social negative impact in the youngest patients.

The symptomatic treatment of knee osteoarthritis associates painkillers and non steroid anti inflammatory drugs (nsad). In case of ineffectiveness of the oral drugs intra articular injections are proposed.

Intra articular injections of hyaluronic acid are recommended by the American College of Rheumatology and the European League against Rheumatism for the treatment of knee osteoarthritis. Nevertheless their efficacy remain non predictable in patients so as the duration of clinical improvement which does not exceed 6 months.

The articular cartilage has a limited capacity for self-repair due to the low mitotic activity of chondrocytes and its avascularity.

Platelet-rich plasma is a natural concentrate of growth factors: PDGF, TGF b, IGF-1, FGF and the cytokines, liberated by platelet degranulation. The influence of these growth factors in the cartilage repair is being widely investigated in vivo and in vitro. These factors could stimulate the chondral reparation via a neovascularization, a collagen synthesis and an activation of the chondrocytes.

The hypothesis is that the intra articular injection of PRP, with its capacity to enhance articular cartilage repair, could be a therapeutic alternative to hyaluronic acid in the treatment of knee osteoarthritis resisting the oral drugs.

Material and methods: We intend to conduct a comparative, monocentric prospective randomized, double-blind study on 80 patients with symptomatic knee osteoarthritis to compare the results of 2 intra articular treatment: platelet-rich plasma and hyaluronic acid.

Inclusion Criteria:

• 1. Males and females between 20 to 75 years of age 2. Symptomatic knee arthritis 3. Axial deformity of the lower limb equal or lower than 5° 4. BMI between 20 to 30 5. Written informed consent, signed by patient or legal representative (if patient unable to sign).

  6. HB > 10g/dl 7. Negative pregnancy test

Exclusion Criteria:

1. Axial deformity of the lower limb over 5°
2. Knee instability
3. BMI < 20 or > 30
4. Thrombocytopenia < 150 G/L
5. Thrombopathy
6. Anaemia: HB < 10g/dl
7. Positive serology VIH1 and 2, Agp24, Ac HCV, Ag HbS, AcHbc, Ac HTLV I and II, TPHA
8. Chronic treatment by corticosteroid per os or treatment completed more than 2 weeks before inclusion
9. Intra articular knee injection of corticosteroid or completed more than 8 weeks before inclusion
10. Intra articular knee injection of hyaluronic or completed more than 24 weeks before inclusion
11. NSAI treatment completed more than 2 weeks before inclusion
12. Fever or recent disease
13. Auto immune disease
14. Inflammatory Arthritis
15. Immune deficit
16. Infectious disease
17. Pregnancy
18. Patient under guardianship.
19. Participation in another investigational trial within this trial