Tendinitis is the inflammation of a tendon, a tough rope-like tissue that connects muscle to bone, usually occuring in individuals in middle or old age as a result of overuse over a long period of time. Tendinitis does occur in younger patients as a result of acute overuse. Tendons that commonly become inflamed include those of the hand and of the upper arm that effect the shoulder. Achilles tendon, at the heel of the foot, and the tendon that runs across the top of the foot also may develop tendinitis.

Sudden stretching or repeated overuse causes injury to the connection between the tendon and its bone or muscle. The injury is largely mechanical, but when it appears, the body tries to heal it by initiating inflammation. Inflammation increases the blood supply, bringing nutrients to the damaged tissues along with immunogenic agents to combat infection. The result is swelling...