Shoulder Anatomy
The shoulder has the greatest range of motion of any joint in the body. A complex assemblage of bones, muscles and tendons work together to allow you to reach, lift and throw and to position the arm and hand.
This large range of motion is possible, in part, because the shoulder's function relies more on the function of muscles and tendons than other major joints.
The bones of the shoulder are the humerus (upper arm bone), scapula (shoulder blade) and clavicle (collar bone), which come together at four joints. The main shoulder joint is the ball-and-socket joint where the ball of the humerus fits into a shallow socket on the scapula called the glenoid.
Particularly important to shoulder function is the rotator cuff, a group of muscles and tendons around the head of the humerus that help stabilize the shoulder joint by holding the humeral head in the glenoid socket. The outer layer of muscle on the shoulder is the large triangle-shaped deltoid muscle.