Table 2.

Definitions of the investigated radiographic hip parameters (see Fig. 3 for schematic illustration)

Parameter	Definition
Lateral center-edge angle [24]	Angle formed by a line parallel to the longitudinal pelvic axis and a line connecting the center of the femoral head with the lateral edge of the acetabulum
Acetabular index [23]	Angle formed by a horizontal line and a line through the most medial point of the sclerotic zone of the acetabular roof and the lateral edge of the acetabulum
Extrusion index [12]	Percentage of uncovered femoral head (A) in comparison to the total horizontal head diameter (A + B)
ACM angle [6]	Angle constructed by the following points: (A) lateral edge of the acetabulum, (M) midpoint of a line connecting the lateral and the inferior acetabular edge, (C) point of the bony acetabulum intersecting the perpendicular line relative to line AM through point M
Anterior coverage	The percentage of femoral head covered by the anterior acetabular rim in AP direction
Posterior coverage	The percentage of femoral head covered by the posterior acetabular rim in the AP direction
Craniocaudal coverage	The percentage of femoral head covered by the acetabulum in the craniocaudal direction
Sharp angle	Angled formed by a horizontal line and a line through the caudal tip of the teardrop and the lateral edge of the acetabulum
Crossover sign [14]	Positive if the projected anterior wall crosses the posterior wall
Retroversion index [21]	Ratio of length of retroverted acetabular opening (E) to the entire length of the lateral acetabular opening (E + F)
Posterior wall sign [14]	Positive if the posterior acetabular rim is projected medial of the center of the hip