Fig. 1

Sagittal spinopelvic parameters for radiologic measurements. The angle between the sacral endplate and the horizontal was defined as sacral slope (SS), the angle between the line joining the center of the sacral endplate and hip axis and the vertical axis was defined as pelvic tilt (PT), and the angle between a line perpendicular to the sacral endplate and a line joining the center of the sacral plate and hip axis was defined as pelvic incidence (PI). The following three measures were evaluated using Cobb’s method: global kyphosis (GK) was measured as the angle between the upper endplate of the T1 vertebra and the lower endplate of the T12 vertebra; thoracolumbar kyphosis (TLK) was measured as the angle between the upper endplate of the T10 vertebra and the lower endplate of the L2 vertebra; and lumbar lordosis (LL) was measured as the angle between the upper endplate of the L1 vertebra and the lower endplate of the L5 vertebra. The horizontal distance of a C7 plumb line dropped from the C7 body center to the posterosuperior corner of the S1 body was defined as sagittal vertical axis (SVA). Anterior displacement of the sagittal plumb line was considered as positive. The angle between the line from the femoral head axis to T1 body center and the line from the femoral head axis to the center of the S1 superior endplate was defined as T1 pelvic angle (TPA)