The Shoulder
The shoulder is made up of three bones - the collarbone, the shoulder blade, and the upper arm bone - as well as associated muscles, ligaments and tendons. The spaces between the bones of the shoulder make up the shoulder joints.
The shoulder must be flexible for the wide range of motion required in the arms and hands and also strong enough to allow for actions such as lifting, pushing and pulling. The compromise between these two functions results in a large number of shoulder problems such as shoulder dislocation, shoulder subluxation, shoulder separation, and frozen shoulder. Some conditions will resolve with minimal treatment and others will require shoulder surgery.
The shoulder is the most movable joint in the body. However, it is an unstable joint because of its broad range of motion. It injures easily because the ball of the upper arm is larger than the shoulder socket that holds it. To remain stable, the shoulder is tethered by muscles, tendons, and ligaments. Some shoulder problems are caused by disruption of these soft tissues from shoulder injuries or from overuse or underuse of the shoulder. Other problems are caused by tissue degeneration.
Shoulder pain may be localized or radiate to areas around the shoulder and down the arm. Diseases that involve the gallbladder, liver, heart, or cervical spine also may generate pain that travels along nerves to the shoulder. Pain in the region of the shoulder blade nearly always has its origin in the neck.