Hip dysplasia, subluxation, and dislocation in cerebral palsy: an arthrographic analysis

Fifty-nine hip arthrographic roentgenograms were performed on 31 children with cerebral palsy (CP) and plain radiographic evidence of hip deformity. Five levels of hip instability were defined by the arthrographic migration index (MI). The incidence of femoral head deformation increased with an increase in MI. A new measurement, defined by the intersection of Hilgenreiner's line with a tangent drawn from the lateral cartilaginous acetabular anlage, decreased proportionally with the increase in the MI. These findings indicate that progressive deformation of the cartilaginous acetabulum and femoral head occurs during (and, in some cases, before) evolution of hip instability in patients with CP.