The joint formed by the head of the thigh bone and the deep, cup-shaped hollow on the side of the pelvis which receives it (acetabulum). The joint is of the ball-and-socket variety, is dislocated only by very great violence, and is correspondingly difficult to reduce to its natural state after dislocation. The joint is enclosed by a capsule of fibrous tissue, strengthened by several bands, of which the principal is the ilio-femoral or Y-shaped ligament placed in front of the joint. A round ligament also unites the head of the thigh bone to the margin of the acetabulum.

For hip-joint disease, see under JOINTS, DISEASES OF.