Fig. 1

(A) Parameters used to measure acetabular dysplasia and lateral subluxation. θ1 is the lateral CE angle (LCEA). a/b is the acetabular depth ratio (ADR). c/d is the acetabulum head index (AHI). These parameters were measured on the AP radiograph. CE angle was measured as the angle between the line joining lateral aspect of the weight-bearing zone and the femoral head center and the line running vertically along the longitudinal axis of the pelvis. ADR was calculated by dividing the depth of the acetabulum by the length between the inferior teardrop point and the aspect of the weight-bearing zone, then multiplying by 100. AHI was calculated by dividing the length from the medial margin of the femoral head to the lateral rim of the acetabulum by the femoral head width, then multiplying by 100. (B) Parameters used to measure acetabular dysplasia and lateral subluxation. θ2 is the Sharp angle. θ3 is the acetabular roof obliquity angle of Tönnis (TA). e/(f*1/2) is the head lateralization index (HLI) described by Ninomiya S. These parameters were measured on the AP radiograph. 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 joining bilateral inferior points of teardrop. Acetabular roof obliquity angle of Tönnis was measured as the angle between the line joining the lateral aspect of the weight-bearing zone and the medial aspect of the weight-bearing zone and the line joining bilateral medial aspects of the weight bearing zone. HLI was calculated by dividing the length from the medial margin of the teardrop and the femoral head center by half of the length between bilateral medial margins of the teardrop