Dear Drs Andia and Maffulli:
Thank you for your insightful comments regarding our manuscript. In vitro modeling of the clinical situation is indeed very difficult. In the culture system utilized in our study, we optimized the system to include naturally diseased osteoarthritic tissues, including articular cartilage and synovial membrane, to mirror the arthritic environment within the knee joint. As you point out in your review article, there are many effects of platelet-rich plasma (PRP) that might account for its mechanism of action in addition to those that we measured in the present study, emphasizing the need for further basic science investigations into PRP alone or a a combination therapy. In a subsequent clinical study, we compared PRP to hyaluronic acid with 5 synovial fluid aspirates used to analyze several anabolic and catabolic cytokines. This study, when completed, should provide evidence for mechanisms of action of PRP in osteoarthritic joints.