Fig. 1

Measurement of spino-pelvis parameters. Sagittal vertical axis (SVA) was defined as the horizontal distance from the posterosuperior corner of S1 to the C7 plumb line. Thoracic kyphosis (TK) was measured from the superior endplate of T5 to the inferior endplate of T12. Lumbar lordosis (LL) was measured from the superior endplate of L1 to the superior endplate of S1. Pelvis incidence (PI) was defined as the angle subtended by a line drawn between the center of the femoral head and the sacral endplate and a line drawn perpendicular to the center of the sacral endplate. Pelvis tilt (PT) was defined as the angle subtended by a line drawn from the midpoint of the sacral endplate to the center of the bi-coxo-femoral axis and a vertical plumb line extended from the bi-coxo-femoral axis. Sacral slope (SS) was defined as the angle subtended by a line drawn along the endplate of the sacrum and a horizontal reference line extended from the posterior superior corner of S1