The capitulum is a round anatomical feature at the distal end of the humerus that mates with a shallow concave depression on the head of the radius. This creates a shallow ball-and-socket joint that primarily moves through sagittal-plane flexion and extension and allows pivoting around the long axis of the forearm. The surface of both the capitulum and the radial head are covered by articular cartilage. This is the other joint in the elbow.
