Fig. 3

Measurement of the parameters used to define acetabular dysplasia. θ4 and θ5 are the anterior acetabular sector angle (AASA) and posterior acetabular sector angle (PASA), respectively. These parameters were measured on a slice of the hip center in the axial plane. AASA was measured as the angle between the horizontal line joining the bilateral femoral head center and the line joining the anterior margin of the acetabulum and the femoral head center. PASA was measured as the angle between the horizontal line combing the bilateral femoral head center, and the line joining the posterior margin of the acetabulum and femoral head center