SCA is considered as the angle between the C7 slope and the straight line connecting the middle of the Sella turcica and the middle of the C7 endplate. cSVA is regarded as the distance between the C7 posterior superior corner and the plumbline from the center of C2 body. T1s is defined as the angle between the T1 superior endplate and a horizontal line. Disc height is calculated as the mean value of the anterior (a) and posterior (b) disc height. Interfacet distance is regarded as the interfacet distance at the most severely degenerated level