Fig. 6

Radiographic anteversion and inclination of the cup. A Acetabular axis. A’ Projected acetabular axis. ∠RI indicates the radiographic inclination, defined as the angle between the longitudinal axis (Y) and the acetabular axis (norm of cup) projected perpendicular on the coronal plane (A’). ∠RA indicates the radiographic anteversion, defined as the angle between the acetabular axis (A) and the coronal plane. X, Y, and Z represent the coordinate system of the radiostereometric analysis recording