Figure 1.

A. Right hip: The acetabular index is the angle (β) between the line parallel with pelvic tilt (solid black line which marks the horizontal reference) and the black dashed line from the medial sourcil (sclerotic radiographic density corresponding to the acetabular roof) to the lateral sourcil (where the sourcil meets the lateral acetabular rim). The acetabular angle (ϕ) is the angle made by the solid black line and the white dashed line from the acetabular teardrop to the lateral sourcil. Left hip: The extrusion index is the amount of femoral head uncovered by the acetabulum (distance a) divided by the diameter of the femoral head (distance a + distance b).

B. Right hip: The lateral center edge angle (θ) is formed by a line passing through the center of the femoral head perpendicular to the inferior aspect of obturator foramina (thick black line) and a line from the center of the femoral head to the lateral aspect of the congruent sourcil (medial to calcified labra and up-sloping sourcil and even with the posterior wall). Left hip: Crossover sign is positive on the left, demonstrated by the anterior wall (solid) crossing the posterior wall (dashed). The crossover ratio is the ratio of the distance from the lateral-most acetabular rim to the point of the crossover (distance a) divided by the acetabular diameter (the distance from the lateral acetabular rim to the teardrop, b). The posterior wall distance is the horizontal distance (distance c) measured from the center of the femoral head to the posterior wall. Distances are positive if the posterior wall is lateral to the head center and negative if medial to the head center.