Tendons are sturdy structures consisting of compact collagen fibers with little to no elasticity; there is little vascularization and it is derived exclusively from the tissue that lines them, such as the loose connective tissue of the peritenon or synovial sheath.
Tendons connect muscle structures to the bones and are part of the muscle-tendon unit; they have the function of transmitting muscle force to the bones allowing joint movements. The cause leading to tendinopathy is mainly due to repeated mechanical stresses that result in focal injuries and alterations in tendon structure. Along with strenuous work activities, the sports activities that cause the most stress to the Achilles tendon are running and, for the patellar tendon, jumping, in explosive sports such as basketball, volleyball, and rugby.
Ultrasound study well visualizes the tendon structure and is able to highlight even small focal lesions and initial degenerative aspects leading to tendinopathy.