Data Collection

Demographic and radiographic parameters were collected and measured by 2 individual surgeons, including patients’ age, TPA (the angle between the line from the femoral head axis to the centroid of T1 and the line from the femoral head axis to the middle of the S1 endplate), thoracic kyphosis,¹⁰ lumbar lordosis,¹⁰ thoracolumbar kyphosis (TL),¹⁰ sacral slope (SS),¹¹ pelvic incidence (PI),¹² pelvic tilt (PT),¹¹ T1 spinopelvic inclination (T1SPI, the angle between the vertical plumbline and the line drawn from the vertebral body center of T1 and the center of the bicoxofemoral axis), and SVA (sagittal vertical axis).¹⁰ The parameters were measured twice at a 1-week interval for intraclass correlation coefficient (ICC) analysis. Numeric rating scales (NRS, 0–10) were used to assess the unspecific low back pain.¹³ ICC analysis was performed to assess the inter- and intraobserver reliability of TPA, and the correlation coefficient between TPA and other sagittal parameters was explored. The severe deformity threshold for TPA was 20° as proposed in Ryan et al,⁵ based on which the patients were divided into the well-aligned group (Group A, TPA ≤ 20°) and poorly aligned group (Group B, TPA > 20°). Then, demographic and sagittal parameters were compared between the 2 groups.