The healthy hip is a ball-and-socket joint. The ball (femoral head) is at the top of the thighbone (femur), and the socket (acetabulum) is in the hipbone (pelvis). The connection allows the leg to move in a variety of positions.
The ball and socket are each covered with cartilage that lubricates and cushions the bones during movement. Cartilage acts as a natural shock absorber, preventing both bone on bone contact and provides a smooth, pain-free surface for the bones to glide against.