The present study was undertaken to assess the efficacy and safety of the intra-articular injection of PRGF and to obtain useful information about the clinical effects. Since pain is the most pressing problem facing people with OA, a significant improvement in pain would indicate the potential of the proposed treatment. We will also evaluate functionality and quality of life. In addition we will examine changes in novel serum and synovial fluid biomarkers and their correlation with MRI-based parameters in a subgroup of patients.