Lithograph of the Rotator Cuff group from Gray's Anatomy.

The Rotator Cuff is a group of four muscles that attach to the humerus and scapula to support the shoulder joint. The Glenohumeral joint (where the scapula and humerus meet, a.k.a. the shoulder) is a ball and socket style joint and due to the small surface area of each bone where they connect, it is the most moveable joint in the entire body. The Rotator Cuff along with deltoid, teres major and the coracobrachialis make up the 7 muscles responsible for the movement and stability in the shoulder.

The four muscles of the Rotator Cuff include the supraspinatus, the subscapularis, infraspinatus and teres minor all of which have their attachment and/or insertion points on the scapula bone and/or the humerus (the large bone connecting the shoulder to the elbow). The most commonly damaged muscles in the group are the supraspinatus and the infraspinatus.

A sudden, powerful movement of the shoulder joint can cause an acute tear. Bowlers, tennis players, boxers, and pitchers often suffer an acute tear. A chronic tear is caused by repetitive motion wearing down the muscle on or near the tendon. Chronic tears can lead to Impingement Syndrome; the condition where the inflammed muscles are squished under the acromial arch before they attach to the Humerus. Chronic tears occur most often in people over 40 years old.

Rotator Cuff tears have a 40-90% treatment success rate.