Comparative biomechanical evaluation of the U-shaped lumbopelvic stabilization technique in treating unstable sacral fractures.

Introduction: Lumbopelvic fixation is commonly employed to stabilize unstable sacral fractures, particularly U-shaped (US) fractures, which may result in spinopelvic dissociation-leading to significant pain, deformity, and neurological deficits. Due to its superior biomechanical properties, lumbopelvic stabilization (LPS) has become the preferred method for managing such injuries. We aimed to compare the biomechanical stability of US-LPS with conventional LPS and bilateral iliosacral screw (ISS) fixation.

Materials and methods: Six human cadaveric pelvic specimens were subjected to axial (750 N) and torsional (8 Nm) loading using a material testing machine (MTM). Seven configurations of LPS were evaluated. The range of motion (ROM) between three anatomical bony segments-the third lumbar vertebral body (LBV3), the first sacral vertebral body (SVB1), and the Crista Iliaca (CI)-was analyzed using an optical tracking system. Measurements included craniocaudal translation and anterior-posterior tilt under axial loading and internal-external rotation under torsional loading. Stiffness was calculated using force-displacement curves obtained via the MTM's integrated load cells and displacement transducers.

Results: Both LPS and US-LPS configurations demonstrated reduced ROM and increased stiffness compared to ISS fixation under axial and torsional loading. US-LPS exhibited marginally greater stiffness than standard LPS. The use of additional cross-connectors in both LPS groups had minimal to no measurable impact on ROM or overall stability.

Conclusions: US-LPS offers slightly enhanced biomechanical stability over conventional LPS in the fixation of unstable US sacral fractures. In contrast, standalone ISS fixation did not improve stability compared to the unfixed condition in this cadaveric model.