Objective: To evaluate, through a systematic review of the current literature, the evidence-based outcomes of the use of platelet-rich plasma (PRP) for the treatment of tendon and ligament injuries. Data Sources: A search of English-language articles was per- formed in PubMed and EMBASE using keywords ‘‘PRP,’’ ‘‘platelet plasma,’’ and ‘‘platelet concentrate’’ combined with ‘‘tendon’’ and then ‘‘ligament’’ independently. The search was conducted through September 2010. Study Selection: Search was limited to in vivo studies. Nonhuman studies were excluded. Tissue engineering strategies, which included a combination of PRP with additional cell types (bone marrow), were also excluded. Articles with all levels of evidence were included. Thirteen of 32 retrieved articles respected the inclusion criteria. Data Extraction: The authors reviewed and tabulated data ac- cording to the year of study and journal, study type and level of evidence, patient demographics, method of PRP preparation, site of application, and outcomes. Data Synthesis: The selected studies focused on the application of PRP in the treatment of patellar and elbow tendinosis, Achilles tendon injuries, rotator cuff repair, and anterior cruciate ligament (ACL) reconstruction. Seven studies demonstrated favorable out- comes in tendinopathies in terms of improved pain and functional scores. In 3 studies on the use of PRP in ACL reconstruction, no statistically significant differences were seen with regard to clinical outcomes, tunnel widening, and graft integration. One study exam- ined the systemic effects after the local PRP application for patellar and elbow tendinosis. Conclusions: Presently, PRP use in tendon and ligament injuries has several potential advantages, including faster recovery and, possibly, a reduction in recurrence, with no adverse reactions de- scribed. However, only 3 randomized clinical trials have been con- ducted. INTRODUCTIONInitially introduced in maxillofacial and plastic surgery in 1990s, platelet-rich plasma (PRP) has recently experienced a surge in clinical uses for various sport-related injuries due to potential healing properties on tendons and ligament injuries through the recruitment, proliferation, and differentiation of cells.Sports-related soft tissue injuries represent a significant source of time lost from play for athletes and teams anda significant burden to society in terms of health care resources, personal disability, and activity restriction. In 2002, an estimated 15.8 billion dollars in total health care expenditures were used in the medical management of theseinjuriesDespite the lack of hard evidence through randomized clinical trials, the use of PRP in humans has increasedsignificantly. The increase in recently published pilot studies has prompted our systematic review of the literature, exploring the current knowledge and indications for clinical use. Theoutcomes will be evaluated with emphasis on the effectiveness and safety of the current applications. The processes of PRP production and the various methods of application will be evaluated. Basic SciencePlatelet-rich plasma is a concentrate of platelets and associated growth factors (GFs), obtained through withdrawal and centrifugation of a sample of patient’s own blood. Although the use of PRP varies greatly among studies, the retrieval of PRP from patients is relatively constant. The general protocol for preparing PRP requires the separation of blood components through 1 or 2 centrifugation steps. The first centrifugation step leads to the separation of red and white blood cells from plasma and platelets, and the second produces an increase in the concentration (3-fold to 5-fold) of platelets and GFs. This is followed by the exogenous or endogenous platelet activation (with bovine thrombin or CaCl2) before application to the site of injury. There is little consistency among studies on the time between retrieval and application. Considering the coagulative properties of PRP and plateletsthis timing may have an effect on its activity and reparative potential. It also may be noted that allowing for solidification into a gel may keep the preparation localized but also eliminates its injectability, limiting the use to open surgical procedures.Autologous platelet preparations have demonstrated the potential to modify the natural healing pathway of tendons andligaments in several ways. The action is related to the increasedconcentration of GFs and bioactive proteins released byactivated platelets (Table 1), which seem able to help the regeneration of tissues that otherwise have low healing potential, potentially restoring biomechanical properties similar to normal tendons and ligaments.8 The application of PRP amplifies the surge of chemical mediators to the microenvironment of the injured area, including platelet a-granule–derived factors. The increased concentration of platelets and GFs mimics the initial stage of the inflammatory response, characterized by the migration of neutrophils,monocytes, and macrophages to the site of injury under the guidance of the chemical mediators.These cytokines mediate the initiation of neovasculari-zation, tenocyte proliferation, fibroblast proliferation, and further recruitment of inflammatory cells.6,7 In addition to thestimulatory effects of PRP on reparative cells, there is evidence that PRP may also have an inhibitory effect on certain proinflammatory cytokines that may be detrimental to the early stages of healing, specifically through suppression of IL-1 release from activated macrophages.9 This dual action of enhancing repair and minimizing tissue breakdown may allow local PRP application to accelerate the tissue healing process, leading to a wide range of potential applications and potential advantages for improved outcomes and faster recovery. However, additional studies must be completed to confirm these proposed benefits.
