Corrective Spinal Surgery for Severe Spinal Curvature in People With Ankylosing Spondylitis

To estimate changes in function and sagittal alignment at 12 months after pedicle subtraction osteotomy.

on the 0-10 scale. A negative change indicates improved function.

TPA will be measured on the standing lateral full-spine radiograph as the angle between the line connecting the center of the T1 vertebral body to the bicoxofemoral axis and the line connecting the bicoxofemoral axis to the midpoint of the superior endplate of S1. TPA incorporates both global spinal inclination and pelvic retroversion and provides a global measure of sagittal alignment. A negative change indicates improved function.

Measured on a full-length standing lateral radiograph as the horizontal distance from the C7 plumb line to the posterior-superior corner of the S1 endplate. Unit: millimeters (mm)

Measured as the angle between the C7 plumb line and the sacral endplate line. Unit: degrees (°)

Measured as the angle between the sacral endplate line and the line connecting the femoral head axis to the C7 plumb line. Unit: degrees (°)

Measured as the angle between the line perpendicular to the sacral endplate at its midpoint and the line from that midpoint to the femoral head axis. Unit: degrees (°)

Measured as the angle between the vertical line and the line from the femoral head axis to the sacral endplate midpoint. Unit: degrees (°)

Measured as the angle between the sacral endplate line and the horizontal line. Unit: degrees (°)

Calculated as PI minus LL. Unit: degrees (°)

Measured as the angle between the superior endplate of the upper-most tilted vertebra and the inferior endplate of the lower-most tilted vertebra in the kyphotic segment. Unit: degrees (°)

Measured as the Cobb angle between the superior endplate of T4 and the inferior endplate of T12. Unit: degrees (°)

Measured as the Cobb angle between the superior endplate of T10 and the inferior endplate of L2. Unit: degrees (°)

Measured as the Cobb angle between the superior endplate of L1 and the superior endplate of S1. Unit: degrees (°)

Identified as the vertebra at the apex of the maximal kyphotic curve on the lateral radiograph. Unit: vertebral level (e.g.T8, T9)

Measured as the angle created at the osteotomy site between the superior and inferior endplates of the resected/adjacent vertebrae on intraoperative or postoperative imaging. Unit: degrees (°)

Measured as the Cobb angle between the inferior endplate of C2 and the inferior endplate of C7. Unit: degrees (°)

Measured as the horizontal distance from the C2 plumb line (vertical line from the C2 centroid) to the posterior-superior corner of C7. Unit: millimeters (mm)

Measured as the angle between the superior endplate of T1 and the horizontal line. Unit: degrees (°)

T1 angle measured between the T1 endplate line and the line from the T1 centroid to the C7 centroid. Unit: degrees (°)

Neck tilt measured as the angle between the vertical line and the line from the sternal notch to the T1 centroid

Measured as the Cobb angle between the superior endplate of the upper-end vertebra and the inferior endplate of the lower-end vertebra of the coronal curve. Unit: degrees (°)

Measured as the horizontal distance from the C7 plumb line to the sacral midline (center of S1). Unit: millimeters (mm)

Measured as the angle between the horizontal line and the line connecting the bilateral femoral head centers (or the sacral endplate line) on the AP radiograph. Unit: degrees (°)

Measured as the angle between the inferior endplate of the upper instrumented vertebra (UIV) and the superior endplate of the vertebra two levels above the UIV (UIV+2). Unit: degrees (°)

Defined by the presence of proximal junctional fracture, implant failure, or revision surgery at the proximal junction. Unit: event (yes/no)

Defined as radiographic evidence of screw/rod breakage, loosening, or pullout. Unit: event (yes/no)

Recorded as events (yes/no) or continuous measures during the perioperative and follow-up periods, including but not limited to: intraoperative blood loss (mL), operative time (min), length of hospital stay (d), transfusion rate, surgical site/deep infection rate, neurologic deficit, dural tear, deep vein thrombosis/pulmonary embolism, implant failure, revision surgery rate, readmission rate, and mortality. Units: mL / min / d / event (yes/no) / proportion (%). Lower event incidence, less blood loss, and shorter operative time and hospital stay indicate better safety; the converse indicates worse safety. Serious complications (infection, neurologic deficit, implant failure, revision, death) indicate worse safety.

Composite score calculated from four patient-reported items (back pain, duration of morning stiffness, patient global assessment, peripheral joint pain/swelling) and serum CRP using a weighted formula. Minimum = 0; maximum = no fixed upper limit (typically ~0-6; theoretical minimum 0). Higher scores indicate worse disease activity; lower scores indicate better disease activity. Cut-offs: < 1.3 = inactive disease, < 2.1 = low disease activity, > 2.1 = high disease activity.

Measured in peripheral venous blood as serum CRP concentration. Minimum = 0 (cannot be negative); maximum = no fixed upper limit (assay-dependent). Unit: mg/L (or mg/dL). Higher concentrations indicate greater systemic inflammatory burden (worse); lower concentrations indicate less inflammation (better). Normal reference is typically < 5 mg/L (some laboratories < 3 mg/L).

Measured in peripheral venous blood by the Westergren method as the distance erythrocytes fall at the end of 1 hour. Minimum = 0; maximum = no fixed upper limit (assay-dependent). Unit: mm/h (millimeters per hour). Higher values indicate greater inflammatory activity (worse); lower values indicate better status. Reference ranges are age/sex-specific (e.g., < 15 mm/h in men, < 20 mm/h in women).

Derived from six patient-reported items (fatigue, neck/back/hip pain, peripheral joint pain/swelling, enthesitis, severity of morning stiffness, duration of morning stiffness), each scored on a 0-10 numeric rating/visual analogue scale; total = mean of the six items. Minimum = 0; maximum = 10. Unit: 0-10 score (unitless). Higher scores indicate worse disease activity; lower scores indicate better disease activity. Cut-off: < 4 = low disease activity/well controlled; ≥ 4 = active disease.

Thirty-six patient-reported items yield eight domains (Physical Functioning, Role-Physical, Bodily Pain, General Health, Vitality, Social Functioning, Role-Emotional, Mental Health) and two summary scores (Physical Component Summary [PCS] and Mental Component Summary [MCS]). All domains and summary scores are linearly transformed to a 0-100 scale; minimum = 0, maximum = 100. Unit: 0-100 score (unitless). Higher scores indicate better health-related quality of life; lower scores indicate worse.

The patient marks current status on a 100-mm (or 0-10) horizontal/vertical line; the distance from the "none" anchor to the mark is measured. Minimum = 0; maximum = 100 mm (or 0-10). Unit: mm (or 0-10 score, unitless). In ankylosing spondylitis studies, pain VAS (e.g., back pain over the past week) and patient global assessment VAS (e.g., overall disease status over the past week) are typically measured separately and should be reported as distinct constructs. Higher scores indicate worse pain/overall status; lower scores indicate better status.