These shoulder problems are closely related and often occur in combination, with shoulder tendinitis leading to an impingement syndrome. If the muscles and tendons of the rotator cuff or the bursa of the shoulder are injured, they become inflamed, and swollen. Because there is limited space in the shoulder joint, this swelling caused the muscles and tendons to be squeezed between the bones of the shoulder joint (the head of the upper arm bone (humerus) and the top of the shoulder blade (acromion). Repeated motion involving the arms, or motion over many years may also irritate the tendons, muscles, and surrounding tissue.

Tendinitis is inflammation (redness, soreness, and swelling) of a tendon. In tendinitis of the shoulder the tendons of the rotator cuff or the tendons of the biceps become inflamed and irritated. This is often a result of being pinched by surrounding structures. This injury can be mild or severe. When the rotator cuff tendon becomes inflamed and thickened, it may get trapped under the acromion (the top of the shoulder blade). This squeezing of the rotator cuff muscles is called impingement syndrome.

Bursitis of the shoulder occurs when there is inflammation of the fluid-filled sac called the bursa that lies between a tendon and skin, or between a tendon and bone.

Tendinitis and impingement syndrome are often accompanied by inflammation of the bursa sacs that protect the shoulder. An inflamed bursa is called bursitis. Sports involving overuse of the shoulder and occupations requiring frequent overhead reaching are other potential causes of irritation to the rotator cuff or bursa and may lead to inflammation and impingement.

Signs of these conditions include slow onset of pain in the upper shoulder or upper arm and difficulty sleeping on the shoulder. Tendinitis and bursitis also cause pain when the arm is lifted away from the body or overhead. If tendinitis involves the biceps tendon (the tendon located in front of the shoulder that helps bend the elbow and turn the forearm), pain in the front or side of the shoulder is common and may travel down to the elbow and forearm.

Diagnosis of tendinitis and bursitis includes a physical exam and various tests. Treatment includes rest, ice, and anti-inflammatory medicines. In some cases physical therapy is prescribed. Gentle stretching and strengthening exercises are added. If there is no improvement after 6 to 12 months, arthroscopic surgery may be used to repair damage and relieve pressure on the tendons and bursae.