It is helpful to understand the basic anatomy of a healthy tendon before examining the pathophysiological changes that occur with tendon injuries. The main structure of a tendon are the numerous collagen bundles that form the many fibers appearing in the tendon. The main cell of the tendon is called the tenocyte which produces collagen and other components of the tendon.  Surrounding the tendon is the epitenon - a very fine connective tissue sheath with blood vessels and nerves that supply the tendon. All tendons have a myotendinous junction, rich in nerves, where the muscle belly transitions to a tendon. The point at which the tendon terminates onto the bone is called the enthesis. The myotendinous junction and the enthesis have limited blood flow which becomes further compromised with aging and significant loading.

Typically the tendon is injured at the myotendinous junction or enthesis area. Because of poor blood flow, it takes time for these structures to heal once injured. However, there is a subsection of the population with tendon injuries that have persistent pain and symptoms, despite rehabilitation and the passage of time. As surgery is rarely considered a treatment option, there is a gap in care between those who have failed rehabilitation, but are not surgical candidates. This is where platelet rich plasma (PRP) can be considered as a viable and safe treatment option for tendinopathies that are not healing.