Tendons are ropes of fibrous tissue that connect muscles to bones. It is this connection that permits joint motion. When muscles contract, they pull on the tendons which cause the bones to move. In order for tendons to glide they move inside a lubricated sheath of tissue that is lined with synovial tissue. This synovial tissue is the same type of tissue that lines the inside of joints. Tendonitis refers to a condition where the sheath through which a tendon glides becomes inflamed. This leads to severe pain. The pain usually gets worse with use of the affected joint. However, when tendonitis becomes severe, there may be pain at rest.

Since muscles and tendons surround most joints, tendonitis is rather common. The diagnosis of tendonitis is relatively simple for the experienced clinician. Genrally, the diagnosis is made by history and physical examination. In difficult diagnostic cases, magnetic resonance imaging is helpful in confirming the diagnosis.

Some of the more common types of tendonitis are:

Shoulder tendonitis. The tendons in the shoulder that are most often affected are the rotator cuff and the biceps tendon. The rotator cuff consists of four tendons that sit on top of the upper arm bone. The location of these tendons and the muscles they attach to are what give the shoulder such an expansive range of motion. Rotator cuff tendonitis may occur as a result of repetitive activity or tendon degeneration. Pain is felt with most movements and is located on the outside part of the shoulder. The biceps tendon allows the arm to be flexed at the elbow. Biceps tendonitis also occurs due to repetitive activity and pain is felt in the front of the shoulder. Shoulder tendonitis can be treated successfully with anti-inflammatory medication, physical therapy, and occasionally glucocorticoid injection.

Tendonitis in the elbow is usually located either on the outside and is called lateral epicondylitis or tennis elbow. It may also occur along the inside part of the elbow- medial epicondylitis. This is called golfer