IV, retrospective study.

Level IV, retrospective study.

IntroductionChronic patellar tendinopathy (PT) remains a challenging problem for both orthopedic surgeons and sport medicine practitioners. It is often caused by overuse of the knee extensors in activities such jumping, running and kicking. Clinically, this tendinopathy is characterized by anterior knee pain and focal tenderness at the distal border of the patella. It affects athletes in numerous sports, at all levels of participation and can severely limit performance 1 . The precise etiology of this tendinopathy is not clear. Several histopathological studies have shown a degenerative process with tendon thickening, disturbed collagen distribution, neovascularization and increased cellularity with incompletely healed tendon micro-ruptures 2-5 . There is currently no consensus on its optimal treatment. Conservative management is the first line treatment including eccentric physical therapy, icing, activity modification, and non-steroidal anti-inflammatory drugs (NSAIDs) 6,7 . Despite conservative treatment, patellar tendinopathy may remain resistant to therapy and can often lead to a prolonged clinical course. Autologous PRP intra-lesional injection is being used increasingly in the treatment of many soft tissue injuries. Recently, there has been great interest in using PRP for sports related injuries, particularly patellar tendinopathy 8 , although the rationale for use PRP is still unclear 9 . It is hypothesized that the growth factors and other bioactive molecules released by the alpha granules in platelets present in PRP have the potential to enhance cellular migration, proliferation, angiogenesis, and matrix deposition in tendon healing [10][11][12][13] . To date, the ideal protocol of PRP application concerning the volume, number and timing of injections has not been established 14