Ball and socket joint

A ball and socket joint, such as the shoulder or hip, allows movement in several directions because a rounded bone end fits into a socket. These joints allow flexion and extension, as well as abduction, movement away from the body’s midline, and adduction, movement towards it. Raising an arm sideways is shoulder abduction; bringing it back towards the body is adduction.

In a ball-and-socket joint, the rounded head of one bone fits into a socket in another. Unlike a hinge, this arrangement allows movement in several directions.