ABSTRACT
The human shoulder complex consists of three bones (humerus, scapula, and clavicle) and four joints (glenohumeral, scapulothoracic, acromioclavicular, and sternoclavicular joints; Figure 8.1). Shoulder motion occurs primarily at the glenohumeral and scapulothoracic joints. The glenohumeral joint is sometimes referred to as a ball-and-socket joint, although
the glenoid (i.e., the articulating surface of the scapula) is a particularly shallow socket. The depth of the socket is increased by the labrum, a brous ring of connective tissue located along the perimeter of the glenoid. The glenohumeral joint is passively stabilized by four ligaments-the superior glenohumeral ligament (SGHL), the middle glenohumeral ligament (MGHL), the inferior glenohumeral ligament (IGHL), and the coracohumeral ligament (CHL)—and the joint capsule (Figure 8.1). The ligaments are not distinct structures but rather are continuous with the joint capsule tissue. Glenohumeral joint motion and dynamic stability are provided by the rotator cuff (a group of four muscles originating on the scapula and inserting into the lateral aspect of the humeral head; Figure 8.2), the deltoid muscle group, and the biceps long head. Scapulothoracic motion and dynamic stability are provided primarily by the serratus anterior, trapezius, rhomboids, pectoralis minor, levator scapulae, and subclavius muscles.
