Ball-and-socket joint


The ball and socket joint is a type of synovial joint in which the ball-shaped surface of one rounded bone fits into the cup-like depression of another bone. The distal bone is capable of motion around an indefinite number of axes, which have one common center. This enables the joint to move in many directions.
An enarthrosis is a special kind of spheroidal joint in which the socket covers the sphere beyond its equator.

Examples

Examples of this form of articulation are found in the hip, where the round head of the femur rests in the cup-like acetabulum of the pelvis; and in the shoulder joint, where the rounded upper extremity of the humerus rests in the cup-like glenoid fossa of the shoulder blade.