Does preoperative anterior osteophyte/bridging ossification at the disc proximal to the upper instrumented vertebra affect early proximal junctional disease after adult spinal deformity surgery?

Proximal junctional disease (PJD) remains a formidable challenge in adult spinal deformity (ASD) surgery. While disc degeneration is a recognized risk factor, the specific impact of preoperative anterior osteophyte formation and bridging ossification on junctional stability has not been fully elucidated. This study aims to evaluate the association between these morphological patterns and early postoperative PJD. We retrospectively reviewed 33 ASD patients undergoing posterior fusion (minimum 6-month follow-up). Anterior bridging ossification at the disc proximal to the upper instrumented vertebra (UIV) was graded via preoperative CT as Low-grade (Grades 0–1; ≤50% bridging) or High-grade (Grades 2–3; >50% to complete bridging). Given the small cohort and low event rates, Firth’s penalized logistic regression was employed. PJD occurred in 27% ( n = 9) of patients. High-grade bridging ossification was associated with a significantly lower frequency of PJD ( p = 0.005). While Firth’s penalized logistic regression analysis indicated that high-grade ossification was linked to significantly decreased odds of PJD (OR: 0.045, 95% CI: 0.00033–0.423, p = 0.003), these findings must be interpreted with caution due to the complete separation of events in the high-grade cohort. Additionally, higher postoperative SVA ( p = 0.034) and prophylactic vertebroplasty at the UIV + 1 level ( p = 0.034) were associated with PJD rates. Our findings suggest that the grade of anterior bridging ossification at the disc proximal to the UIV may be an important factor to consider in the risk assessment for PJD. Although this morphological pattern potentially serves as a ‘natural stabilization’ zone, the observed complete separation of events and the limited sample size categorize this study as hypothesis-generating. Further, prospective multi-center validation is required before these findings can be integrated into clinical UIV selection protocols. Retrospective cohort study (Level of evidence: III).