How Does the Shoulder Work?

The shoulder is made up of three bones: the upper arm bone (humerus), the shoulder blade (scapula), and the collarbone (clavicle). It is a ball-and-socket joint that allows for a wide range of motion.

The head of the upper arm bone (humerus) is the ball, and a circular depression (glenoid) in the shoulder bone (scapula) is the socket. The head of the upper arm bone is coated with a smooth, durable covering called cartilage that protects the bones and enables them to move easily. The rotator cuff is the collective set of surrounding muscles and tendons that provide stability, support, and work together with the deltoid muscle to move the shoulder.