Differential Risk Factors for Proximal Junctional Kyphosis Between T8-T10 and T11-L1 Upper Instrumented Vertebrae in Adult Spinal Deformity.

Abstract

Proximal junctional kyphosis (PJK) remains a persistent mechanical complication after adult spinal deformity surgery. While lower thoracic upper instrumented vertebrae (UIV; T8-L1) are frequently selected, some studies have treated them as a single group, potentially obscuring sublevel-specific risk profiles. Therefore, this study aims to compare risk factors for PJK between patients undergoing lower thoracic fusion with UIV at T8-T10 and those with UIV at T11-L1. A retrospective review was performed of 334 adult spinal deformity patients (mean age, 69.6 years; 88.3% female) who underwent corrective fusion from T8-L1 to the sacrum/pelvis between 2014 and 2022 with a 2-year follow-up. Based on UIV, patients were categorized into group I (T11-L1, N = 157) and group II (T8-T10, N = 177). Demographic, surgical, and radiographic variables were compared between groups. Univariate and stepwise multivariate logistic regression analyses identified independent PJK predictors. Receiver operating characteristic analyses determined optimal cutoff values. PJK developed in 99 patients (29.7%), more frequently in group I than group II (35.7% vs 24.3%; P = .023). Preoperative proximal junctional angle was a significant predictor in both groups, with optimal cutoffs near 0° (1.0° in group I; -0.8° in group II). In group I, additional independent predictors included osteoporosis (odds ratio [OR], 6.435) and postoperative change in lumbar lordosis ≥28.7° (OR, 1.056). In group II, advanced age ≥72 years (OR, 1.138) and postoperative age-adjusted pelvic incidence minus lumbar lordosis overcorrection (OR, 2.745) were significant risk factors. While preoperative proximal junctional angle is a universal predictor, surgeons should consider avoiding the thoracolumbar junction for osteoporotic patients or for those requiring large lordosis corrections, and in T8-T10 fusions, particular attention should be paid to age-adjusted alignment targets and patient age. These findings may guide UIV-level-specific surgical planning to mitigate PJK risk.