Proximal femoral geometry in cerebral palsy: a population-based cross-sectional study.

There is much debate about the nature and extent of deformities in the proximal femur in children with cerebral palsy. Most authorities accept that increased femoral anteversion is common, but its incidence, severity and clinical significance are less clear. Coxa valga is more controversial and many authorities state that it is a radiological artefact rather than a true deformity. We measured femoral anteversion clinically and the neck-shaft angle radiologically in 292 children with cerebral palsy. This represented 78% of a large, population-based cohort of children with cerebral palsy which included all motor types, topographical distributions and functional levels as determined by the gross motor function classification system. The mean femoral neck anteversion was 36.5 degrees (11 degrees to 67.5 degrees) and the mean neck-shaft angle 147.5 degrees (130 degrees to 178 degrees). These were both increased compared with values in normally developing children. The mean femoral neck anteversion was 30.4 degrees (11 degrees to 50 degrees) at gross motor function classification system level I, 35.5 degrees (8 degrees to 65 degrees ) at level II and then plateaued at approximately 40.0 degrees (25 degrees to 67.5 degrees) at levels III, IV and V. The mean neck-shaft angle increased in a step-wise manner from 135.9 degrees (130 degrees to 145 degrees) at gross motor function classification system level I to 163.0 degrees (151 degrees to 178 degrees) at level V. The migration percentage increased in a similar pattern and was closely related to femoral deformity. Based on these findings we believe that displacement of the hip in patients with cerebral palsy can be explained mainly by the abnormal shape of the proximal femur, as a result of delayed walking, limited walking or inability to walk. This has clinical implications for the management of hip displacement in children with cerebral palsy.