The shoulder joint has the greatest range of motion of all the bodies’ articulations. The shoulder (Fig.1) is formed by the scapula (shoulder blade), clavicle (collarbone) and the humerus (upper arm). The roof of the scapula is called the acromion. The shoulder is comprised of three main joints:
- The glenohumeral joint (the juncture of the ball of the humerus and the shallow socket of the scapula, glenoid).
- The acromioclavicular (AC) joint (the meeting of the clavicle and the acromion).
- The sternoclavicular (SC) joint (the meeting of the clavicle and sternum).
The shoulder is covered with articular cartilage (Fig.1). This material cushions and provides a smooth surface which permits movement with minimal friction.
Ligaments connect bone to bone. In the shoulder ligaments create a joint capsule (a watertight sac surrounding a joint). The joint capsule (Fig. 2) connects the humerus and the glenoid, maintaining stability and holding the shoulder in place to keep it from dislocating.
The glenoid labrum (Fig.3) is a unique fibrocartilage structure circular in nature. It attaches around the edge of the glenoid and creates a deeper socket for the humerus to sit in. the labrum is also the attachment site of the biceps tendons.
|Muscles and Tendons
Tendons connect muscle to bone. The muscles and tendons of the rotator cuff hold the humeral head in the glenoid socket (Fig.4). The rotator cuff helps to lift and rotate the arm.
The muscles of the rotator cuff are:
- Teres Minor