Comparison of mechanical stability of modified pedicle screw fixator and unilateral lumbopelvic fixation for treating sacroiliac joint disruption: A finite element analysis study.

Objective: This study aimed to investigate the mechanical stability of a modified pedicle screw fixator and compare it with unilateral lumbopelvic fixation for treating sacroiliac joint disruption using finite element simulation technology.

Methods: The digital model of a normal spine-pelvis-femur containing the main pelvic and lumbar ligaments was established based on computed tomography images. A sacroiliac joint disruption model was built and validated, which was stabilized with the models of a modified pedicle screw fixator or unilateral lumbopelvic fixation. A 400 N follower loading was applied to the lumbar vertebrae for the 2 fixation models to analyze displacement and stress distribution. In addition, the construct stiffness was calculated.

Results: The peak amounts of sacral vertical displacement, horizontal displacement, posterior displacement, and overall displacement were 0.70 mm, 0.17 mm, 0.73 mm, and 0.88 mm, respectively, in the modified pedicle screw fixator model, which were less than those in the unilateral lumbopelvic fixation model (1.17 mm, 0.31 mm, 2.21 mm, and 2.29 mm, respectively). Compared with unilateral lumbopelvic fixation, the percentage decreases of the modified pedicle screw fixators were 40.2%, 45.2%, 67.0%, and 61.6%, respectively. The peak stress of the internal fixation and pelvis in the modified pedicle screw fixator model was 351.23 MPa and 39.91 MPa, which has 15.5% and 70.4% lower than in the unilateral lumbopelvic fixation model. The construct stiffness of the modified pedicle screw fixator (571 N/ mm) was 67% better than that of unilateral lumbopelvic fixation (342 N/mm).

Conclusion: The finite element simulation results showed that the modified pedicle screw fixator model demonstrated smaller sacral displacement, fewer stresses on the internal fixation and bone, and higher construct stiffness compared with the unilateral lumbopelvic fixation model. Thus, the modified pedicle screw fixator may provide biomechanical advantages over unilateral lumbopelvic fixation in the treatment of sacroiliac joint disruption.