Rotator Cuff Injuries: The rotator cuff muscles (the teres minor, infraspinatus, supraspinatus and subscapularis muscles) all originate on the scapula and extend to the humerus, forming a nearly circumferential tendonous attachment composed of short, broad attachments that attach to the humerus just below humeral head. Working in concert with one another, the muscles of the rotator cuff contribute to both the motion and stability of the glenohumeral joint by balancing the upward pull of the deltoid muscle and contributing to both internal and external rotation of the humerus.

Injuries to the rotator cuff commonly occur at the insertion of the supraspinatus muscle, (Figure 13) and were usually thought to result from traumatic injury to this area. More recently, however, injury due to over-use and/or repetitive small traumas to the area has been implicated as the most common cause of these injuries. When the arm is held high overhead and a throwing motion is made, the tendon of the supraspinatus muscle can become transiently compressed between the greater tuberosity of the humeral head on the underside of the acromion. When this occurs repeatedly, as with a baseball pitcher who always delivers the ball overhand, the repeated injury to the supraspinatus tendon can result in damage to it as well as the biceps tendon with which it is intimately associated. A common physical sign of rotator cuff pathology is pain on abduction (lifting the arm away from the body to extend directly out to the side) of the shoulder between 60 and 120 degress of arc, with inability to complete the arc and raise the arm above the head. The severity of injuriy to the rotator cuff can vary across a broad range, from mild local inflammation that resolves with rest, all the way to complete tearing of the supraspinatus tendon which requires surgical repair for recovery.