Fig. 2

Measurement of the parameters used to define acetabular dysplasia. θ3 is the center–edge (CE) angle. c/d is the acetabulum head index (AHI). These parameters were measured on a slice of the hip center in the coronal plane. CE angle was measured as the angle between the line joining the lateral aspect of the weight-bearing zone and the femoral head center and the line perpendicular to the transverse axis of the pelvis. AHI was calculated by dividing the length from the medial margin of the femoral head to the lateral side of the weight-bearing zone by the femoral head width, then multiplying by 100