Fig. 1

Measurement of the sagittal spinopelvic parameters. a Lumbar lordosis is measured from the superior endplate of L1 to the superior endplate of S1, and thoracic kyphosis is measured from the superior endplate of T4 to the inferior endplate of T12. b Sagittal vertical axis is the horizontal offset from the posterosuperior edge of S1 to the body of C7. c Sacral slope is the angle between the horizontal and the superior sacral endplate. d Pelvic tilt is the angle between the vertical axis and the line running from the midpoint of the sacral plate to the centre of the femoral head axis. (e) Pelvic incidence is the angle between a line perpendicular to the superior sacral endplate at its midpoint and the line connecting this point to the centre of the femoral head axis