Morphology of the acetabulum in hip dislocations caused by cerebral palsy

Twenty-four hip joints in 20 children with spastic cerebral palsy were assessed by standardised three-dimensional reconstructions from computed tomographic scans. All the hip joints showed a channel-like bony deformity of the acetabulum along which the femoral bead had slid out, indicating a unidirectional instability. The channel was oriented along the longitudinal axis of the body within a sector of 25 degrees anteroposteriorly. In relation to the pelvis, the dislocation was directed more dorsally by 20 degrees as a result of a flexion contracture of the hip. The size of the femoral head corresponded with the size of the acetabulum in every case, even in long-standing dislocations.