Hip displacement is the second most common deformity after equinus. These children have normal hips at birth but the hip displaces under the influence of abnormal muscle balance and tone. It is thought that increased tone in the hip flexors and adductors overcomes the relatively weaker extensors and abductors resulting in transfer of the center of hip rotation from the center of the femoral head to the lesser trochanter. The abnormal forces prevent the normal development of the acetabulum and proximal femoral geometry. In unaffected children the acetabulum normally deepens around a concentrically located femoral head during the first 6 years of life resulting in an acetabular index (Al) of less than 300. In cerebral palsy the Al is commonly found to be higher than this. Multi-planar CT-3D reconstruction has also shown that both anterior and posterior acetabular cover is reduced in people with cerebral palsy (124). Chung et al. The effects of abnormal tone on the proximal femur are equally detrimental. The neonate usually has a neck-shaft angle (NSA) of 1400 that reduces to a mean of 120° in the adult. At birth femoral neck anteversion is about 40°and gradually reduced to about 12-15° at skeletal maturity. These changes may not occur in cerebral palsy and a persistent femoral anteversion of greater than 30° and NSA of 140-150° is often found.