Fig. 1.

Measurement of Spino-pelvic sagittal parameters. Lumbar lordosis (LL) was measured using the Cobb angle between the superior endplate of the L1 and S1. The pelvic tilt angle (PT) was defined as the angle between a straight line connecting the midpoint of the bilateral femoral head centre to the midpoint of the sacral plate and the plumb line. The pelvic incidence angle (PI) was defined as the angle between the perpendicular line of the sacral plate and the line of the midpoint of the superior endplate of S1 joining with the center of the hip axis. The sacral slope (SS) was defined as the angle formed by the upper endplate of S1 and the horizontal plane