Triangular Screw Placement to Treat Dysmorphic Sacral Fragility Fractures in Osteoporotic Bone Results in an Equivalent Stability to Cement-Augmented Sacroiliac Screws—A Biomechanical Cadaver Study

<b>Background:</b> Sacroiliac screw fixation in elderly patients with pelvic fractures remains a challenging procedure for stabilization due to impaired bone quality. To improve it, we investigated the biomechanical properties of combined oblique sacroiliac and transiliosacral screw stabilization versus the additional cement augmentation of this construct in a cadaver model of osteoporotic bone, specifically with respect to the maximal force stability and fracture-site motion in the displacement and rotation of fragments. <b>Methods</b><i>:</i> Standardized complete sacral fractures with intact posterior ligaments were created in osteoporotic cadaver pelvises and stabilized with a triangle of two oblique sacroiliac screws from each side with an additional transiliosacral screw in S1 (<i>n</i> = 5) and using the same pelvises with additional cement augmentation (<i>n</i> = 5). A short cyclic loading protocol was applied, increasing the axial force up to 125 N. Sacral fracture-site motion in displacement and rotation of the fragments was measured by optical motion tracking. <b>Results:</b> A maximum force of 65N +/- 12.2 N was achieved using the triangular screw stabilization of the sacrum. Cement augmentation did not provide any significant gain in maximum force (70 N +/- 29.2 N). Only low fragment displacement was observed (2.6 +/- 1.5 mm) and fragment rotation (1.3 +/- 1.2°) without increased stability (3.0 +/- 1.5 mm; <i>p</i> = 0.799; 1.7 +/- 0.4°; <i>p</i> = 0.919) following the cement augmentation. <b>Conclusions:</b> Triangular stabilization using two obliques and an additional transiliosacral screw provides sufficient primary stability of the sacrum. Still, the stability achieved seems very low, considering the forces acting in this area. However, additional cement augmentation did not increase the stability of the sacrum. Given its lack of beneficial abilities, it should be used carefully, due to related complications such as cement leakage or nerve irritation. Improving the surgical methods used to stabilize the posterior pelvic ring will be a topic for future research.