The anterior pelvic plane (APP) was the plane formed by both anterior superior iliac spines and the pubic symphysis. APPA was defined as the angle between the line connecting the midpoint of both anterior superior iliac spines to the pubic symphysis and the vertical line of the lateral radiograph of the pelvis in the standing position. Pelvic incidence (PI) is the angle formed by the line connecting the midpoint of the bilateral femoral head center point to the center point of the sacral endplate and the line perpendicular to the sacral endplate. Pelvic tilt (PT) is the angle between the line connecting the midpoint of the bilateral femoral head center point to the center point of the sacral endplate and the vertical line; the sacral slope (SS) is the angle between the superior plate of S1 and the horizontal line.