Shoulder Anatomy

The bones that make up the shoulder girdle include the clavicle, scapula and humerus. The scapula or shoulder blade glides over the chest wall in an envelope of muscle. It has a bony spine that curves up and over top of the head of the humerus to form a roof for the shoulder called the acromion. Another bony prominence, the coracoid process, curves around in front of the joint to provide attachments for important ligaments and tendons.

The acromioclavicular joint joins the clavicle to the shoulder blade. It is frequently injured in falls on the point of the shoulder. When the AC joint is disrupted it is called a shoulder separation. The joint between the shoulder blade and the humerus is called the glenohumeral joint. The joint is lined by smooth articular cartilage on both sides.

The glenoid side is deepened by a rim of fibrous tissue called the labrum. The GH joint is held together by rather flimsy capsular ligaments. With shoulder instability or dislocations these structures can be torn or stretched. Repeated dislocations of the shoulder often require surgery to prevent recurrence.

The rotator cuff is a series of muscles that come from the shoulder blade and attach to and move the humerus. They are powerful rotators of the arm. They can be injured by either sudden injuries, or repetitive stresses such as in throwers and swimmers. (see FAQ on rotator cuff)