Fig. 1

Measurement of the parameters used to define acetabular dysplasia. θ1 is the acetabular index. θ2 is the Sharp angle. a/b is the acetabular depth ratio (ADR). These parameters were measured on a slice of the hip center in the coronal plane, orthogonal to the standard axial plane. The acetabular index was measured as the angle between the line joining the medial and lateral aspects of the weight-bearing zone and the line parallel to the transverse axis of the pelvis. Sharp angle was measured as the angle between the line joining the lateral aspect of the weight-bearing zone and the inferior point of teardrop and the line parallel to the transverse axis of the pelvis. ADR was calculated by dividing the depth of the acetabulum by the length between the inferior teardrop point and the lateral weight-bearing zone in the coronal plane of the femoral head center, then multiplying by 1000