Fig. (1) The 3D calculation of the femoral offset is schematically shown in a 3D-reconstruction of the pelvic bone and the proximal femur produced by the Amira 4.1.1 (Amira®, San Diego, California, USA) software package. Ellipses have been fitted automatically into the medullary canal (shown here for the right side). The femoral axis was calculated by the best line of fit through the ellipse-center points. A virtual plane was created containing the femoral axis and the center of the femoral head. The femoral offset was calculated as the distance between the femoral axis and the femoral head center perpendicular to the femoral axis.