The central third of the patellar tendon is used as a donor site for anterior cruciate ligament (ACL) reconstruction. After months or years the harvest site partially regenerates. The regeneration process is accomplished by biological mechanisms,including cells and proteins known as growth factors. The platelets are natural reservoirs of growth factors, and a platelet concentrate known as Platelet-Rich Plasma (PRP) has a three to five fold increase in growth factors. The hypothesis of the study is that the PRP can improve the regeneration of the patellar tendon.