Exploratory Biomechanical Comparison of Three Posterior Pelvic Ring Fixation Strategies in a Standardized Tile C1.2...

Background: Tile C1.2 pelvic ring injuries are characterized by combined rotational and vertical instability and require reliable posterior stabilization. The aim of this exploratory biomechanical study was to compare the construct-level mechanical behavior of three posterior pelvic ring fixation strategies in a standardized Tile C1.2 injury model while maintaining identical anterior symphyseal fixation in all specimens. Methods: Nine fourth-generation composite pelvic specimens with a simulated Tile C1.2 injury pattern were allocated to three groups (n = 3 per group) according to posterior fixation method: anterior sacroiliac plating, sacroiliac screw fixation, and ilioiliac plate fixation. All specimens received the same anterior symphyseal plate. Mechanical testing was performed under monotonic axial compression using a universal testing machine and a custom acetabular support designed to ensure reproducible load transmission. A preload of 50 N was applied before data acquisition, after which displacement was zeroed. Loading was then continued up to a predefined maximum load of 1.9 kN. Axial displacement was obtained from actuator travel, and apparent axial secant stiffness was evaluated at predefined load levels. Results: Across the tested loading range, sacroiliac screw fixation demonstrated the lowest axial displacement and the highest apparent axial secant stiffness, whereas ilioiliac plate fixation showed the greatest displacement and the lowest stiffness values. Anterior sacroiliac plate fixation showed intermediate mechanical behavior. No structural failure occurred within the tested load range. Conclusions: Within the limits of this small synthetic biomechanical study, the investigated posterior fixation strategies showed different construct-level displacement and stiffness profiles under monotonic axial compression when anterior fixation was kept constant. Among the tested posterior constructs, sacroiliac screw fixation was associated with lower displacement and higher apparent stiffness within this experimental model.