The boney elements that make up the shoulder joint include the scapula (shoulder blade), the humerus (upper arm bone), the clavicle (collar bone) and somewhat indirectly, the sternum (breast bone) (Figure 3).

The scapula is a roughly triangular bone on the back of the chest cage that is oriented such that its most pointed edge faces downward toward the feet. The inner surface of the scapula (the side against the back of the chest cage) is generally smooth except at its upper-outer quadrant where a boney protrusion extends forward and hooks toward the shoulder to form the coracoid process (Figure 4). The outer surface of the scapula has a boney ridge that runs diagonally across its surface and ends by curving forward to form a boney knob called the acromion. Nestled between the acromion and coracoid is a shallow hollow called the glenoid fossa, with which only about 33% of surface of the rounded head of the humerus bone fits (see below) to form the glenohumoral joint. This minimal amount of bone-to-bone contact contributes to the great range of motion of the shoulder, but also requires extensive muscular and ligamentous connections at the shoulder to maintain joint structure and function.

The humerus is a tubular bone whose head is composed of a structure approximating 1/3 of a sphere that is angled 30 degrees backward and 45 degrees toward the chest, and forms the "ball" component of the "ball-and-socket" glenohumoral joint between the humerus and scapula (Figure 5). Also of importance, the "bicipital groove" located below the humeral head on the front of the bone allows passage of the long tendon of the biceps muscle to its origin on the genoid labrum. The clavicle is a flattened, double-curved bone that attaches to the scapula (at the acromion via the acromioclavicular joint) on its outside end, and attaches to the sternum at its inside end via the sternoclavicular joint. The sternoclavicular joint, although located some distance from the shoulder, serves an indirect role in maintaining the structure of the shoulder by keeping the far end of the clavicle in a fixed position next to the sternum. The fourth "joint" of the shoulder, the scapulothoracic articulation, is not actually a joint at all, but rather is a muscular attachment of the scapula to the back and side of the chest via musculo-tendinous attachments that insert either onto the ribs or the edges of the spine. This joint allows free "sliding" movement of the scapula over the muscles covering the back of the chest cage, to faciliate movement of the shoulder to the extremes of its range of motion.