Biomechanical optimization of iliolumbar fixation strategies for unilateral vertical sacral fractures: Prioritizing stability-mobility balance via finite element analysis

OBJECTIVE: This study aims to optimize iliolumbar fixation strategies for unilateral vertical sacral fractures via finite element analysis, by comparing stability, implant stress, and lumbar mobility to identify the optimal clinical option. METHODS: A finite element model of the pelvis and L3-L5 lumbar spine was constructed to simulate four fixation models (L4L5IS, L5S1IS, L5IS, S1IS) under a 600 N vertical load. Sacral vertical displacement, implant stress, and fracture line separation were analyzed. RESULTS: Double-segment fixation (L4 + L5 + iliac screw and L5 + S1 + iliac screw) demonstrated superior sacral stability compared to single-segment fixation (L5 + iliac screw and S1 + iliac screw). The L5 + S1 + iliac screw configuration achieved the best balance of stability and lumbar mobility. Stress concentrations were primarily observed at iliac screw connectors, but all models remained within safe mechanical limits. CONCLUSIONS: Double-segment fixation, particularly the L5 + S1 + iliac screw model, is recommended for optimal sacral stability. For cases with compromised S1 pedicles, L4 + L5 + iliac screw fixation is a reliable alternative. Short-segment fixation is viable when prioritizing lumbar mobility.