Biomechanical Comparison of Trans-Sacral and Triangular Osteosynthesis in a Vertically Unstable Pelvic Fracture Model

Vertically unstable fractures of the pelvis are uncommon high-energy injuries. There exist various methods of fixation for posterior pelvic ring injuries such as anterior plating, tension band-plating, trans-iliac bars, spinopelvic fixation, and iliosacral (IS) screws. Recent literature supports that triangular osteosynthesis (spinopelvic fixation) provides superior fixation strength compared to traditionally placed IS screw fixation. The theoretical advantage of triangular osteosynthesis fixation is that this technique combines unilateral spinopelvic distraction osteosynthesis for vertical stabilization with ipsilateral iliosacral screw fixation for horizontal stabilization, thereby providing biplanar stability. While spinopelvic fixation provides biplanar biomechanical stability there are inherent risks of spinal instrumentation, including neurologic injury from malpositioned pedicle screws, hardware loosening or breakage, local infection, wound dehiscence, hardware prominence requiring removal, and predisposition of spinal arthritis. Iliosacral screws are thought to be advantageous in that they can be applied percutaneously or as an open procedure, potentially limit soft tissue dissection, and minimize blood loss. However, IS screw fixation alone has been associated with fixation failure in unstable vertical shear pelvic fractures. There exists a vertical shear repair technique that has been used in revisional and non-union cases, which utilizes trans-sacral screws to stabilize vertical shear fractures. This trans-sacral technique provides biplanar stability and can be implemented without spinal instrumentation. The purpose of this study was to compare the structural integrity of trans-sacral (TS) versus triangular osteosynthesis (TO) in an unstable sacral fracture model.