**2.3. Measurement of radiographs**

All the radiographs were scanned, masked, and coded before being measured by an independent radiologist at the end of the study to avoid measurement bias. The Surgimap software was used for measurement, as it had been found to have good to excellent inter and intraobserver reliability [25].

The coronal Cobb angle, coronal offset, T4-T12 kyphosis, T10-L2 kyphosis, L1-S1 lordosis, sacral slope, pelvic tilt, pelvic incidence [26, 27], and C7-S1 sagittal vertical axis (SVA) [28, 29] were measured (**Figure 1**). The coronal offset, which is the distance from the center of C7 to the vertical line drawn from the center of the sacrum (central sacral line CSL), was also

**Figure 1.** Measurements of the radiographic parameters. (a) "x" stands for the coronal offset. It is the distance between the center of the body of C7 and a perpendicular line from the center of sacrum (CSL). When C7 is situated to the right of CSL, the measurement was designated at "−;" otherwise it was regarded as "+." (b) SVA stands for sagittal vertebral axis. It is the distance between a perpendicular line from the center of the body of C7 to the superoposterior corner of S1. When the line is in front of the superoposterior corner of S1, the measurement was regarded as "+;" otherwise it was regarded as "−." (c) The measurements of other spinopelvic parameters.

determined. When C7 is to the right of CSL, the measurement was designated as negative "-;" otherwise it was regarded as positive "+." The SVA, which was the distance between the perpendicular line from the body of C7 to the superoposterior corner of sacrum, was measured. When the perpendicular dropped in front of the superoposterior corner of the sacrum, the measurement was regarded as positive "+," otherwise it was regarded as negative "-". Measurements of spinopelvic parameters which included the sacral slope, pelvic tilt and pelvic incidence were performed as previously described by Schwab et al. and Glassman et al. [28, 29].
