Figure 1

Pelvic Incidence (PI): The PI was determined on sagittal CT planes of the pelvis. A line was drawn along the axis of the superior end plate of S1 (left image). Then, originating at the center of this axis, an orthogonal line was drawn (left image). Secondly, the middle of the femoral head was determined by the intersecting point of a vertical and horizontal line within the femoral head (middle and right image). Finally, a line was drawn from the middle of the each femoral head to the center of the superior end plate axis and the angle was measured in regard to the orthogonal line originating at this point (middle and right image). The red box indicates the PI. The blacked out numbers were disregarded because they were created automatically by our software and contained irrelevant information. In order to acquire the superposition of the two femoral heads, left and right, the PI was measured for both sides and the mean was stated.