Finite element analysis of sacral fixation strategies for fragility fractures of the pelvis.

This study aimed to evaluate the biomechanical performance of different sacroiliac screw fixation strategies for posterior pelvic ring injuries in older adults with fragility fractures of the pelvis. A finite element model was created using the pelvis of an older woman with combined anterior and posterior ring injuries, simulating a unilateral pubic rami fracture and a Denis zone I sacral fracture. A subcutaneous internal fixator (INFIX) system was used to support the anterior pelvic ring. Percutaneous sacroiliac screws of different lengths and fixation levels were used to create six posterior fixation configurations. The peak von Mises stress within the INFIX system remained below 4 MPa across all configurations, whereas the maximum displacement at the pubic fracture site was < 0.04 mm. Among posterior constructs, the dual-segment long screw configuration showed the lowest sacral fracture displacement (0.02 mm) and the highest screw stress (28.66 MPa). Compared with single-level fixation, constructs with both S1 and S2 fixation demonstrated less fracture displacement and superior load distribution patterns. Furthermore, compared with short screws, long screws exhibited distinct load-sharing features, suggesting improved stress transfer through the posterior pelvic ring. In conclusion, dual-segment sacroiliac screw fixation—particularly using long trans-iliac–trans-sacral screws spanning both S1 and S2 levels—provided improved fracture stability and more advantageous load-sharing behavior in this simulation setting, both in the osteoporotic finite element model and under static, symmetric loading conditions.