Sacral Dysmorphism as an Independent Risk Factor for Cortical Breach During Percutaneous S1 Iliosacral Screw Fixation

Background/Objectives: Sacral dysmorphism is a common anatomical variant that may significantly affect the safety of percutaneous iliosacral screw fixation. Although its morphological characteristics are well described, its impact on clinically relevant outcomes-particularly cortical breach during S1 screw placement-remains insufficiently defined. This study aimed to evaluate whether sacral dysmorphism is an independent risk factor for cortical breach during percutaneous S1 iliosacral screw fixation. Methods: This retrospective cohort study included 112 adult patients with sacral fractures treated with percutaneous S1 iliosacral screw fixation between January 2018 and December 2024. Sacral dysmorphism was defined on preoperative CT scans using qualitative features, with ≥2 criteria required for classification as dysmorphic. Quantitative morphometric parameters, including S1 osseous corridor width and screw anteversion angle, were also measured. The primary outcome was the presence of cortical breach on postoperative CT imaging. Multivariate logistic regression analysis was performed to evaluate the independent association between sacral dysmorphism and cortical breach. Results: Sacral dysmorphism was identified in 32 patients (28.6%). Cortical breach occurred in 19 patients (17.0%) and was significantly more frequent in the dysmorphic group compared with the non-dysmorphic group (34.4% vs. 10.0%; p = 0.002). Sacral dysmorphism was independently associated with cortical breach (adjusted OR: 4.38; 95% CI: 1.42-13.50; p = 0.010). Dysmorphic sacra demonstrated significantly narrower S1 osseous corridors (16 mm vs. 25 mm; p < 0.001) and greater screw anteversion angles (28° vs. 9°; p < 0.001). Breach severity was also significantly greater in dysmorphic patients (p = 0.003). Conclusions: Sacral dysmorphism is an independent risk factor for cortical breach during percutaneous S1 iliosacral screw fixation. The geometric constraints of dysmorphic sacra, including corridor narrowing and increased anteversion requirements, significantly compromise screw placement safety. Careful CT-based evaluation and individualized trajectory planning are essential to optimize fixation outcomes in this high-risk anatomical subgroup.