Apparently not all PRP is made equal

Orthobiologics have become increasingly popular in recent years. OrthoInfo defines orthobiologics as “therapies developed from biologic (natural) substances that can be used by orthopaedic specialists to relieve pain […], enhance the body’s ability to heal from a repetitive use injury […] and in some cases, improve healing after orthopaedic surgery.”

One of the most popular therapies is platelet-rich plasma (PRP). It is autologous since it is made from the patient´s blood by centrifuging. PRP supposedly includes many growth factors which should work as chondroprotective agents in vivo, as mentioned above. Numerous randomized trials have been performed in recent years comparing PRP with a placebo injection. Quite surprisingly, all these well-planned and well-conducted trials have not been able to show that PRP would have any clinical benefit. A most recent study was published in the American Journal of Sports Medicine. Paget et al. concluded, “For patients with ankle osteoarthritis, PRP injections did not improve ankle symptoms and function over 52 weeks compared with placebo injections”.

This study was quite heavily criticised on Twitter. Opponents said this study and all other negative PRP studies have not included a true PRP. Apparently, some platelet-rich plasma injections are not platelet-“rich” enough. One of the proponents of PRP referred me to this video:

This video was a thorough presentation about PRP and included a critical review of the published trials. Many trials have used a PRP system which produces a substance with a platelet count “only” twice as high in the blood. The main statement made by the PRP proponents is that true PRP should have a platelet count at least 3-4 times that measured in the blood. Sure. The presenter in the above video have this slide:

The dose-response relationship is, of course very important and fundamental in medicine. My only concern is that there needs to be evidence that PRP has this response curve. This kind of curve is very reasonable if you believe in PRP. Many trials mentioned above have indeed had a platelet dose of 2, but evidence supporting this curve is fragile. Firstly, everything correlates with everything, so “no help” is not a feasible statement in medicine. Nature does not dichotomise. Secondly, even if this curve were true, sure, some of these trials would show some benefit as SOMETIMES, even a small dose can show an effect when several trials are done.

I will continue on this topic in following posts.

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