Platelet rich plasma in tendinopathies: how to explain the failure

Tendinopathies are very common in athletes and in people practicing sport activities. The experimental evidence that Growth Factors (GFs), present in platelets, enhance the recruitment, proliferation and differentiation of cells involved in tissue regeneration, has prompted the use of Platelet Rich Plasma (PRP) preparations in the treatment of these diseases. However, at present, a sound demonstration of the clinical efficacy of PRP is still lacking. Several theoretical and practical reasons can explain the failure of the treatment: a) animal experiments have been carried out on normal tendons submitted to surgical lesions, and it is questionable whether these models may best mimic human pathology; b) the pathway of chronic tendinopathies is very complex, involving, besides GFs, many other pathogenetic factors, which operate at different stages of the disease; c) several methods have been used to produce PRP, which can result in a large variation in GF content, and in kinetics of release. Therefore, further research is desirable. As a preliminary step, it is necessary to standardize PRP preparation, and to establish the modalities of its activation and administration. Secondly, prospective, randomized, double-blind studies are needed, selecting subjects with homogenous forms of tendinopathies: load-bearing and non-load-bearing tendons, midportion and insertional tendinopathies, with or without neovascularization. Finally, new strategies in PRP use should be exploited: among them, the association of PRP with autologous stem cells or the administration of selective GFs (fibroblast growth factor, vascular endothelial growth factor, or anti-angiogenic factors), which could be better options in specific situations.