The shoulder complex is one of the most unstable joint structures in the entire body. Some people colourfully describe the shoulder as either a golf ball sitting on a golf tee, or a basketball on a tea saucer. There are only three bones in the shoulder: the clavicle, scapula and humerus. The shoulder complex is actually made up of two separate joints - the glenohumeral and acromioclavicular joints.
The shoulder is often referred to as a “hang down joint” because the arm hangs off the top of the shoulder girdle like the struts from a yoke. The collarbone, above the ribs in the front, is like a girder. It gives the shoulder complex width and reinforcement. It also allows a broad wrap-around for the upper chest, offering shape and form to the upper body. The shoulder girdle is designed to be wide, open and strong. The pectoral muscles and deltoids enfold the shoulder to provide strength and stability all the way to the upper back and neck. There are 30 muscles, 6 ligaments and 3 bones that make up the shoulder complex.