Fig. 1

Measurements of spinal parameters. The SVA was defined as the distance between the vertical line from the center of the seventh vertebral body and the posterior edge of the first sacral vertebra. TK was defined as the angle between the parallel lines drawn along the twelfth inferior thoracic vertebra and the fourth superior thoracic vertebra. LL was defined as the angle between the parallel lines drawn along the first superior lumbar and sacral vertebrae. SS was defined as the angle between the horizontal line and first superior sacral vertebra. PT was defined as the angle between the vertical line and the line connecting the centers of the bilateral femoral heads. PI was defined as the angle between the vertical line from the superior first sacral vertebra and the line connecting the centers of the bilateral femoral heads. SVA sagittal vertical axis, TK thoracic kyphosis, LL lumbar lordosis, SS sacral slope, PT pelvic tilt, PI pelvic incidence