Level V Evidence
Platelet-Rich Plasma: The PAW Classification System

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Abstract

Platelet-rich plasma (PRP) has been the subject of hundreds of publications in recent years. Reports of its effects in tissue, both positive and negative, have generated great interest in the orthopaedic community. Protocols for PRP preparation vary widely between authors and are often not well documented in the literature, making results difficult to compare or replicate. A classification system is needed to more accurately compare protocols and results and effectively group studies together for meta-analysis. Although some classification systems have been proposed, no single system takes into account the multitude of variables that determine the efficacy of PRP. In this article we propose a simple method for organizing and comparing results in the literature. The PAW classification system is based on 3 components: (1) the absolute number of Platelets, (2) the manner in which platelet Activation occurs, and (3) the presence or absence of White cells. By analyzing these 3 variables, we are able to accurately compare publications.

Section snippets

Identifying Content of PRP

Several essential factors exist that need to be identified to adequately determine the effects of PRP treatment.

  • The most essential factor is to ensure accurate and definitive concentration measurements of platelets. Without precise quantification of the cellular components, validation and accurate comparison of studies will remain extremely difficult, ultimately impeding discovery of optimum dosing. Many studies published in the recent literature lack this most basic requirement.

  • The presence

Understanding PRP Methods and Systems

PRP can be manufactured in 2 basic formats: plasma-based and buffy-coat preparations. Both begin with whole blood but differ in the centrifugation process, which isolates and concentrates different blood-cell components.12

Plasma-based methods work to isolate only plasma and platelet components and remove WBCs. Protocols for these preparations leave some platelets behind and focus on intentionally excluding leukocytes, which are thought to be detrimental to the healing process.2, 3, 4, 5, 6, 7, 8

Platelet Concentration

Few studies have compared the healing effects of different PRP platelet concentrations for the same indication.14, 41 This may prove to be the most significant aspect in identifying the true effectiveness of PRP and in choosing the proper protocol.

Activation Methods

Platelets can be activated endogenously or through the addition of an exogenous clotting factor to any commercially available system. Each type of activator may produce varying effects and significantly influence growth factor kinetics. Accurately documenting the delivery method and activation scheme used is another key to a successful classification system.

PAW Classification System

With all of the previous information being taken into consideration, the PAW classification system of PRP is based on 3 components: (1) the absolute number of Platelets, (2) the manner in which platelet Activation occurs, and (3) the presence or absence of White cells. By analyzing these 3 variables, we are able to accurately compare publications (Table 3, Table 4).

Conclusions

PRP continues to occupy both orthopaedic literature and the lay press, and more funding is being dedicated to unraveling its mysteries; a simple method for comparing published data based on the content of PRP needs to be established. Our system offers a simple, effective method for quickly documenting the cellular components and activation method used. The acronym PAW serves as a pneumonic for Platelets, Activation, and White cells, and the subcategories are thoughtfully organized to enhance

Acknowledgment

The following individuals are acknowledged for their substantial contribution in the development of the classification system: Bryan T. Hanypsiak, M.D., David O. Shepard, M.B.A., C.T.B.S., and Brandon L. Roller, M.D. All are employees of Arthrex, Naples, Florida.

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    The authors report the following conflict of interest in relation to this article: A.D.M. received research support and is a consultant for Arthrex, Inc., Naples, Florida.

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