Relationship between Preoperative Global Sagittal Alignment and Changes in Cervical Alignment Following Lumbar Pedicle Subtraction Osteotomy

Retrospective cohort study. The objectives are to assess changes in cervical sagittal alignment after lumbar pedicle subtraction osteotomy (PSO) surgery and examine their association with preoperative global sagittal alignment (GSA) parameters. Changes in cervical alignment after lumbar PSO have been reported, yet the progression over time and predictors of long-term decompensation are poorly understood. Patients who underwent lumbar PSO between 2016 and 2021 were included. Cervical alignment was assessed preoperatively and at five postoperative time points: 1-30 days (PO1), 31-90 days (PO2), 91-180 days (PO3), 181 days-1 year (PO4), and 1-2 years (PO5). Cervical alignment parameters included cervical lordosis, C2-7 sagittal vertical axis (cSVA), C0-2 angle, T1 slope, C7 slope, C2 slope, T1 slope minus cervical lordosis (TS-CL), cervical tilt, neck tilt, thoracic inlet angle (TIA), cranial slope, cranial tilt, and cranial incidence. Preoperative GSA parameters included pelvic tilt (PT), global SVA and pelvic incidence-lumbar lordosis mismatch (PI-LL). A total of 99 patients were included. Immediate postoperative changes (preoperative to PO1) demonstrated consistent reductions in cSVA, cervical lordosis, T1 slope, C7 slope, cervical tilt, and neck tilt. In the longer-term analysis (PO1 to PO5), progressive increases were observed in cSVA, T1 slope, C2 slope, and cranial slope. Higher preoperative SVA was associated with greater immediate reductions in cSVA, C7 slope, and T1 slope. Higher BMI and older age were associated with reductions in distinct parameters. Longer-term analysis showed that greater preoperative PT was associated with increased TS-CL, neck tilt, cranial tilt, and T1 slope, while greater PI-LL mismatch was linked to smaller increases in these parameters. Our findings suggest that preoperative GSA parameters may influence cervical alignment in a phase-specific manner: Higher preoperative SVA was associated with immediate cervical adaptation, whereas pelvic parameters appear more related to long-term compensatory responses.