disorder of unknown cause in which the head of the thighbone ( femur) is displaced from its socket in the pelvic girdle. It is generally recognized at birth but in some cases can escape notice for a number of months, until the child places stress on its hips (hip). The disorder is familial, occurs seven times more often in females than in males, and varies markedly in frequency in different populations. If untreated, a false socket develops, and the individual later walks with a severe limp. Treatment consists in reduction of the dislocation and the use of splints to keep the femur in the socket until the joint ligaments (ligament) adapt to the new position.