The benefit of using platelet rich plasma (PRP) in cartilage injuries, and specifically in degenerative ones, has not been assessed yet. Current studies on the PRP healing or repairing effect on knee cartilage degenerative injuries are not conclusive to establish a standard of behavior, although PRP has shown to improve joint functionality and reduce pain.

Hypothesis: PRP intra-articular injections in osteoarthritic knees reduces pain and leads to a more effective and lasting functional recovering than corticosteroid intra-articular injections.

Inclusion Criteria:

• Degenerative osteoarthritis of the knee confirmed radiologically
• Degenerative osteoarthritis of the knee replacement candidate
• Walking ability in patients with or without external support
• Baseline in pain VAS greater than 60

Exclusion Criteria:

• Neoplastic disease
• Immunosuppressive States
• Patients who received intra-articular injections of steroids, anesthetic and / or hyaluronic acid in the last 3 months.
• Patients who have undergone arthroscopic surgery on the last 3 months
• Patients with involvement of bone metabolism except osteoporosis (Paget's disease, renal osteodystrophy, osteomalacia)
• Fibromyalgia or chronic fatigue syndrome
• Liver disease
• Deficit coagulation (blood dyscrasia)
• Thrombocytopenia
• Anticoagulant treatment