Platelets are blood cells made in bone marrow. They are made up of protein packets that are responsible both for wound healing and clotting.
After platelets have been released from the marrow into the bloodstream, their circulating lifespan is approximately 7-10 days. Platelets can accumulate at the site of acute injury. The formation of a blood clot, followed by the release of growth factors, is a sequence of events. These growth factors draw other blood cells to the region. These growth factors and other cells aid in healing. To stimulate growth factors' release, many people have used calcium chloride and humanthrombin (Recothromb). Bovine thrombin can also be used but there have been some reports of hypersensitivity reactions among a few patients.
A concentrate of whole blood that has at least 1,000,000 platelets per 6 cm's is called platelet-rich plasma (PRP). Platelet concentrations between 3-5 million and 5-6 million are ideal, as higher platelet counts can lead to faster healing and more growth factors.
Where has PRP been used? Mishra & Pavelko published one of the earliest papers on the use of PRP in 2006 in the American Journal of Sports Medicine. The authors presented a non-randomized study on 20 patients suffering from chronic lateral epicondylitis (tennis knee) and presented the results. Eight weeks later, the patients were evaluated and found that there was a 60% improvement in PRP treatment compared to the 16% in the control group.
This treatment was also used to treat Achilles tendon issues. These results were mixed. In a Dutch study, 54 patients were compared in a 2010 Journal of the American Medical Association. There was no statistical difference in the PRP-treated group versus the exercise and saline groups Platelet Rich Plasma in Washington DC
There have been some criticisms about the study design and there have been positive studies that report PRP with Achilles tendonitis.
Another condition for which PRP can be used is patellar tendonitis ("jumper’s knee") and rotator cuff tendonitis (shoulder), plantar fasciitis, gluteus medius tendonitis in the hip, osteoarthritis, and plantar fasciitis.
The procedure that administers PRP involves a needle tenotomy, which is a procedure in which a small needle is introduced to the area of tendon injury using ultrasound guidance. To create an acute injury, the needle is used to puncture small areas of diseased tendon. This is what triggers an acute inflammatory response that causes platelets to release growth and healing factors.
There are several contraindications to PRP use, including active infection, bleeding disorders and the use strong anticoagulant drugs ("blood thinners")
The use of human growth hormone with PRP is a concern. This is sometimes combined with PRP. Unfortunately, we don't have long-term data about the safety of this combination. This approach can also be problematic when it comes to athletes and regulations of the World Anti-Doping Agency.