Internal fixation of S1-S3 iliosacral screws and pubic screw as the best configuration for unstable pelvic fracture with unilateral vertical sacral fracture (AO type C1.3): A biomechanical study

Background: Although internal fixation is the definitive treatment in unstable pelvic fractures with disruption of the anterior arch and a vertical fracture of the sacrum (AO type C1.3), there have been no agreement of the best technique of internal fixation yet. We aimed to derive comparable objective data on stiffness and load to failure in this type of fracture fixations. Methods: Synbone was modified into AO type C1.3 fracture model, while treatments were divided into six internal fixation treatment groups using tension band plate (TBP), symphysis pubis plate (SP) with iliosacral screw at S1 and S2 (IS S1-S2), pubic screw (PS) with iliosacral TBP, PS and IS S1-S2, SP and IS S1-S3, PS and S1-S3 and finally PS and IS S1-S3. Sensor was applied to detect the shifting and rotation of fracture fragments. Mechanical strength test conducted with the application of axial force on the sacrum vertebra (S1). Results: The highest translational stiffness was observed in the group IS S1-S3 + PS (830.36 N/mm, p = 0.031) and there was no difference on the rigidity of the rotation between the groups posterior fixation using IS S1-S2 and IS S1-S3 (p = 0.51). Meanwhile the highest load to failure was found in group IS S1-S3 + PS (1522.20 N). PS provided advantages compared to the use of plate. Conclusions: Group of PS and S1-S3 IS is the configuration of internal fixation with best translational and rotational stiffness and the largest load to failure compared to other techniques in AO type C1.3 fracture.