A Short Distance Between Pedicle Screw Tip and Upper Endplate as a Risk Factor for Upper Instrumented Vertebra Fracture Following Adult Spinal Deformity Surgery.

Study DesignRetrospective cohort comparative study.ObjectiveTo 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.MethodsThis retrospective study included 132 patients (mean age: 68.4 years) who underwent corrective surgery from 2013 to 2022, with a minimum follow-up of 2 years. The radiographic parameters and UIV screw characteristics 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.ResultsUIVF 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 3 months postoperatively. Progressive reduction in TED was observed over time, particularly in the UIVF group.ConclusionPost- TK > 36.5° and Post-TEDupper < 6.5 mm are significant predictors of UIVF. Based on the study findings, a postoperative TED of ≥ 6.5 mm may be associated with a reduced risk, and could be considered as a potential target in surgical planning, while acknowledging the limitations of the retrospective design and the model's moderate predictive accuracy.