Platelet-rich plasma in orthopedics
Within orthopedics, the use of platelet-rich plasma (PRP) has been increasing in popularity. United States estimates alone suggest that approximately 86,000 athletes are treated with PRP annually. Even though its popularity is rising, its true effectiveness has yet to be fully established.

What is platelet-rich plasma?
The platelets contained within autologous blood play an important role in healing since they secrete several growth factors to the site of injury. Briefly, among other roles, these platelets serve to promote mitogenesis of healing capable cells and angiogenesis in the tissue. Autologous blood, which contains such platelets in higher than normal concentrations, is commonly referred to as platelet-rich plasma (PRP). For instance, the normal platelet count in healthy individuals is around 1.5–4.5 × 105/μL; however, to be considered PRP, the platelet should be 4–5 times above this amount. This relatively recent biotechnology has been reported to enhance the healing process since an increased number of platelets results in an increased number of secreted growth factors, thereby theoretically improving the healing process . Some of the growth factors in PRP include: platelet-derived growth factor (PDGF), transforming growth factor beta (TGF-β), vascular endothelial growth factor (VEGF), and epithelial growth factor (EGF). Thus, unlike recombinant technology which is synthetic, PRP takes advantage of the naturally occurring proteins in the healing process. In addition to these factors, PRP contains adhesion molecules which promote bone formation. These molecules include fibrin, fibronectin, and vitronectin.

PRP Preparation :
A solution of PRP is prepared by first harvesting the patient’s own blood, often from the median cubital vein . This autologous blood is then centrifuged to allow for the separation of the various components based on the relative density. This allows for separation and collection of the platelet-poor plasma from the other components of blood . Further centrifugation allows for the separation and collection of the buffy coat layer that contains PRP and/or leukocytes. The prepared PRP is then re-administered to the site of injury. Whether activated prior to injection or non-activated, it is important to note that 70% of the growth factors are secreted within ten minutes of activation and 100% of growth factors are secreted within one hour of activation .

Mechanism of action :
On a molecular level, for degenerative conditions such as osteoarthritis, in vitro studies have found that the use of PRP stimulates chondrocytes and synoviocytes to produce the cartilage matrix while also downregulating key molecules that are mediators of the inflammatory response, such as IL-1. Additionally, studies have shown that PRP also increases proteoglycan and type II collagen synthesis, two biological molecules which are important for structural organization of the cartilage framework, through increased mRNA gene expression.

 PRP has also been found to have similar effects on damaged tendons to promote accelerated repair. Tendons are known to have low metabolic rates and thus, tend to heal slowly after injury. Studies on severed sheep tendons have shown that PRP promotes the proliferation and secretion of VEGF and hepatocyte growth factor, both of which stimulate angiogenesis and reduce inflammatory fibrosis.PRP has been found to promote both tendon-to-bone healing and remodeling.