We began trials with platelet rich plasma in 1997. While conceptually, PRP makes sense and there was a great deal of excitement over the ease of harvest and delivery, PRP still struggles to find it’s ideal clinical role. All PRP is not created equal and the final product for delivery depends on the skill and experience of the provider and the clinic.
PRP is a reasonable adjunct to other procedures when tissue biology is poor and signaling cell concentrates are not available. Its role in the chronic setting is controversial outside of an indication for arthritic joint pain. Soluble anti-inflammatory proteins found in the plasma including alpha-2-macroglobulin (A2M) and Interleukin one receptor antagonist protein (IRAP) have been shown to be responsible for this effect. Separate kits to capture A2M have been specifically developed and proven valuable in this setting.
PRP is harvested by drawing approximately 60 mL of peripheral blood from a routine venipuncture like when you’re giving blood. The peripheral blood is then separated by density gradient using a centrifuge (isopycnic separation). Three layers are left after centrifugation (Image 1):
Platelet Poor Plasma (PPP)
Buffy Coat (Platelets and few cells).
Red blood cells (RBC)-discarded.
Platelet Poor Plasma
After centrifugation, the quality of the PRP product you get from your doctor depends on a critical ultrafiltration step performed using a polyethersulfone filter (PES) that has pores of specific molecular weight cut-off (MWCO). These nanopores enable selective ultrafiltration and removal of pro-inflammatory biochemicals naturally present in the blood plasma while retaining anti-inflammatory proteins (Table 1).
The vast majority of processors or ‘kits’ do not contain a PES filter and the vast majority of clinics do not include this filtration step because it is more costly. It makes sense that immediate clinical results and more lasting patient satisfaction improve remarkably in the setting of arthritic knee pain when PES kits are used.
The buffy coat contains platelets that house the growth factors granules necessary for healing. PRP typically concentrates platelets and presumably the growth factor count 3-8 times that found in normal plasma. The growth factors in platelets must be activated by a second step by adding calcium chloride or calcium gluconate. Without this step, the growth factors are not released unless the platelets are activated by exposed collagen upon administration, which may not have any value in the chronic setting. Most clinics do not include this activation step or a final step to activate the fibrinogen present in the soluble fraction (PPP) that turns the injectate into a very controllable jelly-like substance that is more likely to adhere to local tissues after injection.
Summary and Conclusion
PRP can be valuable for the relief of arthritic knee pain mediated by immunomodulatory and anti-inflammatory effects from the concentrated soluble cell signaling proteins and growth factors from activated platelets if an ultrafiltration step is taken to eliminate pro-infammatory signaling proteins before administration.
PRP has a controversial role when used alone for the treatment of medial (golf elbow) or lateral (tennis elbow) epicondylitis and efficacy is similar or better than corticosteroid. While reports claim efficacy comparable to corticosteroid injection and none of the detrimental catabolic effects from the steroid, the treatment is largely dependent on the surgical skill of the provider when needle bevel debridement of the epicondyle is performd during the procedure. Meaning that if the provider is not aggressive enough with the degenerate tissue to prompt a natural healing response, then neither treatment is likely to be as effective. No randomized, controlled clinical trial or scientific study has been able to demonstrate a meaningful improvement in healing capability with clinical administration of PRP.
PRP should be thought of as a possible alternative to hyaluronic injections (“rooster” or “chicken shots”) and corticosteroid with similar efficacy when used for a pain indication.