Comparison of sacroiliac screw techniques for unstable sacroiliac joint disruptions: a finite element model analysis

Vertically unstable pelvic injuries associated with sacroiliac disruption are challenging. Although percutaneous iliosacral fixation using two screws at S1 vertebral body has been shown beneficial, the use of two transiliac screws at S1 has been proposed to increase the fixation strength of the construct. In the herein study, the finite element method (FEM) was performed to analyse the biomechanical behaviour of five different constructions using iliosacral screws only, transiliac screws only, and combining an iliosacral and a transiliac screw. A vertically unstable AO 61C1.2 type pelvic injury was produced for the evaluation of the posterior pelvic displacement and implant stress, and the anterior implant stress using FEM. The symphysis pubis was fixed with a 3.5-mm reconstruction plate in all cases. The model was axially loaded with 800N applied in the centre of S1 body, perpendicular to the ground (Y-axis), simulating the bipodal stance moment. There was a statistically significant reduction in both posterior displacement and implant stresses in the groups fixed with at least one transiliac screw compared to the groups fixed with iliosacral screws. In our FEM study, the construct using two transiliac screws in S1 is biomechanically superior for stabilizing the sacroiliac joint in vertically unstable pelvic ring injuries compared to the other configurations. Lateral displacement, posterior displacement, and von Mises stress were reduced with this construct. A good option can be the use of one iliosacral screw and one transiliac screw in S1.