Fixation of Zone 2 Sacral Fractures Utilizing a Novel Compressive Bolt - A Biomechanical Comparison.

OBJECTIVES

To compare a novel bicortical compression bolt to standard partially threaded transiliac-transsacral cannulated screws for fixation of Denis zone 2 sacral fractures in a biomechanical model. The hypothesis was that the compression bolt would demonstrate greater resistance to deforming forces, with less rotational displacement and reduced fracture gap formation.

METHODS

Twelve standardized Sawbones pelvic models with zone 2 sacral fractures and ipsilateral superior and inferior pubic ramus fractures were randomized to cannulated screw (n=6) or compression bolt (n=6) fixation at S1 and S2. Both transiliac-transsacral constructs were placed with washers and tightened to a target of 1.13 N-m. Custom 3D-printed cutting jigs ensured identical fracture creation and implant placement across specimens. Models underwent cyclic loading to 250 N in a single-leg stance configuration for 10,000 cycles. Infrared optical tracking quantified rotational displacement in three planes and fracture gap formation. Construct completion rates, sacral fracture gap formation, rotational displacement in the sagittal, transverse, and coronal planes, and variance heterogeneity were compared between groups.

RESULTS

Five of six cannulated screw constructs completed testing versus all six compression bolt constructs; the single screw failure resulted from S1 implant backout with synthetic-bone fracture at 6,277 cycles. At 10,000 cycles, the cannulated screw group demonstrated significantly greater sacral gap widening (3.5 mm vs. 0.6 mm, p=0.008) and rotational displacement in the sagittal (15.9° vs. 3.6°, p=0.002) and coronal planes (2.1° vs. 0.3°, p=0.018). The compression bolt group exhibited 51-fold less variance in fracture gap formation (95% CI: 4.3-382.1, p<0.001).

CONCLUSION

In this synthetic biomechanical model of Denis zone 2 sacral fractures, compression bolts demonstrated greater resistance to sagittal and coronal deforming forces compared to cannulated screws, with significantly less fracture gap formation and greater fixation reliability. Bicortical fixation with adjustable compression represents an alternative approach for zone 2 sacral fracture stabilization.