Table 1 Definitions and functions of the modified centre-edge, Norberg, acetabular slope, and inclination angles, and the width and area indices of the dorsal acetabular femoral head (AFH) coverage

Modified centre-edge (CE) angle

The angle between two lines originating from the femoral head center, a line tangential to the lateral acetabular rim and a second line parallel to the long axis of the body of the corresponding ilium (iliac axis).

Evaluates the degree of lateral acetabular femoral head (AFH) coverage.

Norberg angle (NA)

The angle between a line connecting the centers of the femoral heads and a line connecting the center of the femoral head to the corresponding lateral edge of the cranial acetabular rim.

Evaluates the degree of lateral acetabular femoral head (AFH) coverage.

Acetabular slope (AS) angle

The angle between a line connecting the lateral and medial extents of the sclerotic cranial acetabular edge and a horizontal line perpendicular to the corresponding iliac axis.

Quantifies the steepness of the cranial acetabular edge (acetabular “sourcil” slope).

Inclination angle (IA) (Method B)

The angle formed between a line bisecting the shaft of the femur and the second line bisecting the femoral head/ neck.

Evaluates the proximodistal alignment of the femoral head and neck relative to the corresponding femoral axis.

Dorsal AFH coverage width index

The width of the dorsal AFH coverage divided by the diameter of the corresponding femoral head.

Determine the extent of dorsal AFH coverage.

Dorsal AFH coverage area index

The area of the dorsal AFH coverage divided by the overall area of the corresponding femoral head.