Comparison of radiographic parameters for analysis of normal and dysplastic hips in the adult

Radiographic quantitation of the dysplastic hip in adults is difficult. This study compares the values for commonly used indices, the acetabular angle (AA), the center edge angle (CEA), and femoral head coverage, and the X-Y coordinate system on the anteroposterior pelvic radiograph in 30 adult patients with 60 normal hips, and 20 adult patients with 27 dysplastic hips. Dysplastic hips demonstrated significantly higher values for the AA and the X-Y coordinates, and significantly lower values for the CEA and femoral head coverage compared to normal hips. Femoral head coverage in dysplastic hips correlated best (negatively) with the Y coordinate, i.e., poorer coverage was associated with greater superior migration of the femoral head. The AA describes the slope of the acetabular roof, but does not take into account the relative position of the femoral head. The CEA measures the position of the femoral head in relation to the lateral lip of the acetabulum, but does not necessarily use the true acetabulum. The X-Y coordinate system relates the center of the femoral head to an identifiable acetabular landmark, the teardrop shadow. These coordinates are easily determined and can serve as an adjunct to other radiographic indices that quantitate the amount of subluxation in dysplastic hips in adults.