Table 2.

Definitions of the investigated radiographic hip parameters (see Fig. 2 for schematic illustration)

Parameter	Definition
Lateral center-edge (LCE) angle	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 acetabular sourcil
Medial center-edge (MCE) angle	Angle formed by a line parallel to the longitudinal pelvic axis and a line connecting the center of the femoral head with the medial edge of the acetabular sourcil
Acetabular arc	Angle formed by two lines connecting the center of the femoral head with the medial and the lateral edge of the acetabular sourcil (sum of the LCE and the MCE angle)
Extrusion index	Percentage of uncovered femoral head (A) in comparison to the total horizontal head diameter (A + B)
Acetabular index	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
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	Positive if the projected anterior wall crosses the posterior wall
Posterior wall sign	Positive if the posterior acetabular rim is projected medial of the center of the hip
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 posteroanterior direction
Craniocaudal coverage	The percentage of femoral head covered by the acetabulum in craniocaudal direction