Fig. 1

The radiological parameters are measured pre- and post-operation. Pelvic incidence (PI), sacral slope (SS), thoracic kyphosis (TK), lumbar lordosis (LL), Spinal sacral angles (SSA), T1 slope, C0–C2 angle, C2–C7 angle, External auditory meatus (EAM) tilt, Superior adjacent inter-vertebral angle (SAIV), Inferior adjacent inter-vertebral angle (IAIV). PI is defined as the angle subtended by the line drawn from the hip axis (HA, center of the line connecting the center of each femoral heads) to the center of upper sacral end plate and the line perpendicular to upper sacral end plate. SS is defined as the angle subtended by the horizontal line and upper sacral end plate. TK is defined as the angle subtended by the lines drawn along the superior end plate of T4 and inferior end plate of T12. LL is defined as the angle subtended by line drawn along the superior end plates of L1 and S1. SSA: sacral end plate and the line from the center of C7 vertebral body to the center of upper sacral end plate. T1 slope is defined as the angle between a horizontal line and the superior end plate of T1. C0–C2 angle is defined as the angle between McGregor line and the inferior surface of the axis. C2–C7 angle is defined as the angle subtended by the inferior end plates of C2 and C7. EAM is defined as the angle between the vertical and the line joining the center of C7 and EAM. SAIV is defined as the angle subtended by line drawn along the superior end plate of operation levels and inferior end plate of superior adjacent vertebra. IAIV is defined as the angle subtended by line drawn along the inferior end plate of operation levels and superior end plate of inferior adjacent vertebra