Spino cranial angle (SCA): the angle is defined between the C7 slope and the straight line joining the middle of the C7 endplate and the middle of the sella turcica; T1 slope (T1s): the angle between a horizontal line and the superior endplate of T1; C2–C7 lordosis (CL): the angle created by a line parallel to the inferior aspect of the C2 body and a line parallel to that of the C7 body; C2–C7 sagittal vertical axis (cSVA): horizontal distance between the center of C2 and the posterior edge of the upper endplate of C7