At rest, they lie in the normal position against the floor of the acetabulum. Subluxated hips, lie in a position away from the floor of the acetabulum. They also slide within the acetabulum. Dislocated hips rest in the dislocated position, the femoral head rests outside of the acetabulum. The ability to reduce the hip depends on the age and length of time that the hip has been dislocated.
Dysplasia also means abnormal formation of tissue, including the femur, acetabulum, or soft tissues.
Incidence varies with race. There is an increased incidence in native American populations, and a decrease incidence in the black, Korean, and Chinese populations. Associated birth factors include breech presentation, torticollis, talipes equinovarus, metatarsus adductus, and being first born. These factors are believed to be packaging issues . There is a familial predisposition that is believed to be multifactorial.