Study Design: Retrospective cohort comparative study. Objective: To investigate whether specific upper instrumented vertebra (UIV) pedicle screw characteristics—particularly screw slope (UIV SS), tip-to-endplate distance (TED), and tip-to-anterior cortex distance (TAD)—are associated with the development of upper instrumented vertebra fracture (UIVF) following adult spinal deformity (ASD) surgery.

Methods: This retrospective study included 132 patients (mean age: 68.4 years) who underwent corrective surgery from 2013 to 2022, with a minimum follow-up of two years. The radiographic parameters and UIV screw characteristics (TED, TAD, and SS) were analyzed. Patients were categorized into UIVF and non-UIVF groups. Logistic regression and Receiver Operating Characteristic (ROC) curve analyses were used to identify the risk factors and cutoff values.

Results: UIVF occurred in 28.8% (38/132) of the patients. Post-thoracic kyphosis (Post-TK) and TED of the upper UIV screw (Post-TEDupper) were independently associated with UIVF. Cutoff values predictive of UIVF were post-TK > 36.5° and Post-TEDupper < 6.5 mm. Patients with a TEDupper < 6.5 mm had a significantly higher incidence of UIVF (HR = 2.417, p = 0.010). Kaplan–Meier analysis showed that UIVF commonly occurred within three months postoperatively. Progressive reduction in TED was observed over time, particularly in the UIVF group.

Conclusion: Post- TK > 36.5° and Post-TEDupper < 6.5 mm are significant predictors of UIVF. To mitigate the risk of UIVF, surgeons should aim for a TED ≧ 6.5 mm when placing pedicle screws at the UIV. Intraoperative navigation may help optimize screw placement to achieve this target and prevent endplate violation.