Ball-and-socket joint

The ball-and-socket joint (or spheroid 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 of this form of articulation are found in the hip, where the round head of the femur (ball) rests in the cup-like acetabulum (socket) of the pelvis; and in the shoulder joint, where the rounded upper extremity of the humerus (ball) rests in the cup-like glenoid fossa (socket) of the shoulder blade. (The shoulder also includes a sternoclavicular joint.)

• 
  Hip
• 
  Shoulder
• 
  Details of hip joint.

  1. Femur
  2. Femoral Neck
  3. Femoral Head
  4. Acetabulum
  5. Acetabular labrum
  6. Pelvis

This article incorporates text in the public domain from page 287 of the 20th edition of Gray's Anatomy (1918)

• Media related to Spherical joints at Wikimedia Commons
• The dictionary definition of ball-and-socket joint at Wiktionary