Shoulder tendonitis or tenosynovitis is a degenerative condition of any of the tendons and bursa surrounding the shoulder joint. This predominantly occurs in the rotator cuff tendons, although it may also occur in the Biceps Brachii and Deltoid muscles. Impingement refers to mechanical compression and/or wear of the rotator cuff tendons or inflammation of the bursa. This occurs when the space between the acromion (the bony process on the scapula) and rotator cuff narrows. The acromion can rub against, or impinge, the tendon and bursa causing irritation and pain.