The superior parallel line (SPL); a straight line parallel to the inferior plateau of the superior healthy vertebrae. The inferior parallel line (IPL); straight line parallel to the superior plateau of the inferior healthy vertebrae. The distances between the sternal notch to the SPL and IPL on the axis of the sternum were measured. * : sternal notch, empty arrow head : point of the SPL meets with sternum, filled arrow head : point of the IPL meets with the sternum.