Platelet Therapy for Musculoskeletal Disease

Introduction:
In the search of new biological treatments for musculoskeletal injuries and conditions, the use of platelet-rich plasma (PRP) has gained popularity over the past decade. Platelets contain -granules, which are a large reservoir of growth factors and cytokines known to aid tissue healing. This, together with the fact that is PRP is a patient-side autologous treatment with minimum risk of adverse events, has made it an accepted treatment approach worldwide. It is important to acknowledge, however, that both the human and veterinary fields are lacking data to show which type of PRP preparation is optimal for which condition, and how the PRP should be administered.

Platelet concentration and activation:
PRP is often simply defined as plasma with a concentration of platelets greater than that amount found in the peripheral blood. There are several systems for the preparation of canine PRP that produce different platelet concentrations as well as different amounts of red and white blood cells (WBCs). Although there is some controversy in the field, the current recommendation for the use of PRP in the treatment of tendon injuries is to use a preparation that is low in WBCs, and in particular, neutrophils, as the neutrophils release pro-inflammatory cytokines including IL-1 and TNF-. In the literature, these preparations are termed leukocyte-poor PRP or leukocyte-reduced PRP and are typically generated using soft spin centrifugation techniques or less commonly with filters that remove the WBCs.

If different systems provide different platelet concentration, which is the best concentration? Currently, the answer is unknown. A high concentration of platelets appears to be not as beneficial as expected. Based on a porcine study researches feel that a good concentration is three to fivefold increase in platelets, however, lower concentrations have shown to induce cell proliferation of osteoblast and fibroblast. Based on this, it looks that the total number of platelets in the PRP is not the critical parameter and other characteristics of the PRP should be considered for definition of the optimal PRP, like number of red and white cells, activation protocol, condition to be treated, etc.  [...]