I am also considering PRP for knee OA and trying to learn more about it.
Thus far, there does not appear to be any medical studies that conclusively prove its effectiveness, which is probably why it is not covered by insurance.
Given that PRP injections have been commonly used for at least the past several years, I would have expected a verdict by now...
Although some studies such has the one below, indicate that it has potential, but again, nothing definitive.
Feb. 12, 2013 — A study by researchers from Hospital for Special Surgery has shown that platelet-rich plasma (PRP) holds great promise for treating patients with knee osteoarthritis. The treatment improved pain and function, and in up to 73% of patients, appeared to delay the progression of osteoarthritis, which is a progressive disease. The study appears online, ahead of print, in the Clinical Journal of Sports Medicine