The rotator cuff is an integral musculotendinous component of the human shoulder complex. Although it serves a variety of functions, its most important one perhaps is to control the head of the humerus. The two major subgroups of rotator cuff injuries, impingement injuries and avulsive tears, result from compressive and tensile forces, respectively. In addition, either of these two conditions may be seen in association with calcifying tendonitis. The treatment of rotator cuff lesions typically emphasizes conservative measures. These may often consist merely of active rest and specific strengthening exercises. For patients who remain refractory to such therapy, however, arthroscopy or other surgical interventions may be necessary.
The fundamental principle that "structure dictates function" applies to most anatomic and physiologic considerations. Accordingly, any description of rotator cuff injuries must include a comprehensive depiction of the context in which they occur. The human shoulder is one of the least stable joint complexes of the human body (12:16). This instability, however, is compatible with its main purpose: i.e., the positioning of the hand in space. In fact, the shoulder's range of motion is so great, that it exceeds what is required for most daily activities (10:1).
The term, "shoulder complex" refers to three bones, the humerus, clavicle, and scapula, as well as their surrounding soft tissues (10:15). Precise movements of the arm depend on the coordinated functioning of the entire complex. This occurs according to the relative motion of four joints: the glenohumeral, acromioclavicular, and sternoclavicular joints, and the scapulothoracic gliding mechanism. Each of these joints has little bony stability. For example, the shallowness of the glenoid fossa as well as the lack of congruency between the articular surfaces renders the glenohumeral joint inherently unstable.
While instabilit...