ABSTRACT
The hip joint is a ball-and-socket joint. The top of the femur (the long bone in the upper leg) ends in a ball which fits into a socket covering some 60% or so of the ball. This makes the joint very stable. The socket, or acetabulum, is partially formed by the pressure exerted on the pelvis via the femur. This occurs partly from the pressure exerted by the muscles between the pelvis, backbone and femur, but more so by the pressure transmitted up the femur from the baby’s weight, for example, in a baby walker, baby bouncer or when crawling. If the hip is, or becomes, dislocated the acetabulum does not develop, remains shallow and cannot accept the ball, or head, of the femur securely without operation.
