Fig. 3

PT (green line) is defined as the angle between the vertical reference line and the line connecting the femoral head to the midpoint of the sacral plate. PI (red line) is defined by the angle between the line perpendicular to the sacral plate midpoint and another line connecting the sacral plate midpoint to the femoral head. SS (purple line) is the angle formed between the sacral endplate and the horizontal reference line [5]