Biomechanical evaluation of location and mode of failure in three screw fixations for a comminuted transforaminal sacral fracture model

Abstract

BackgroundPelvic ring–comminuted transforaminal sacral fracture injuries are rotationally and vertically unstable and have a high rate of failure.ObjectiveOur study purpose was to use three-dimensional (3D) optical tracking to detect onset location of bone–implant interface failure and measure the distances and angles between screws and line of applied force for correlation to strength of pelvic fracture fixation techniques.Methods3D relative motion across sacral–rami fractures and screws relative to bone was measured with an optical tracking system. Synthetic pelves were used. Comminuted transforaminal sacral–rami fractures were modelled. Each pelvis was stabilised by either (1) two iliosacral screws in S1, (2) one transsacral screw in S1 and one iliosacral screw in S1 and (3) one trans-alar screw in S1 and one iliosacral screw in S1; groups 4–6 consisted of fixation groups with addition of anterior inferior iliac pelvic external fixator. Eighteen-instrumented pelvic models with right ilium fixed simulate single-leg stance. Load was applied to centre of S1 superior endplate. Five cycles of torque was initially applied, sequentially increased until permanent deformation occurred. Five cycles of axial load compression was next applied, sequentially increased until permanent deformation occurred, followed by axial loading to catastrophic failure. A Student t test was used to determine significance (p < 0.05).ResultsThe model, protocol and 3D optical system have the ability to locate how sub-catastrophic failures initiate. Our results indicate failure of all screw-based constructs is due to localised bone failure (screw pull-in push-out at the ipsilateral ilium–screw interface, not in sacrum); thus, no difference was observed when not supplemented with external fixation.ConclusionInclusion of external fixation improved resistance only to torsional loading.Translational Potential of this ArticlePatients with comminuted transforaminal sacral–ipsilateral rami fractures benefit from this fixation.

Stabilization of Traumatic Iliosacral Instability Using Innovative Implants: A Biomechanical Comparison

“…The TriFix screw is equivalent to a reinforced fixation anchor in the iliac bone. Therefore, failures such as the washer penetration described are virtually impossible [ 26 ].…”

Percutaneous screw fixation of the pubic symphysis versus plate osteosynthesis: a biomechanical study

“…[18] Synthetic bone models have been used in numerous recent biomechanical studies of the pelvis. [14,15,19,22] They allow for consistent comparisons by eliminating the variability seen among cadaver specimens because of disease, diet, age, sex, and a host of other factors. Simonian et al [25][26][27] in their comparison of multiple plate fixation methods found significant reduction in motion with all plate constructs but supraphysiological motion in all but a "box plate" construct.…”

“…We created a single-leg stance model similar to previously described models, [14,[19][20][21][22] with elements used from other biomechanical models. [19,20,23,24] Each pelvis was securely attached to the material testing system (Bionix 858, MTS, Eden Prairie, MN).…”

“…We created a single-leg stance model similar to previously described models, [14,19–22] with elements used from other biomechanical models. [19,20,23,24] Each pelvis was securely attached to the material testing system (Bionix 858, MTS, Eden Prairie, MN). Hip abductor muscle function was represented by maintaining a level pelvis by adjusting the tension on the ilium using a turnbuckle.…”

Pelvic antropometric measurement in 3D CT for placement of two unilateral iliosacral S1 - 7.3 mm screws

“…Biomechanical investigations showed that two unilateral screws in S1 generate less cut-out and allow more load cycles in the finite-element model [15,29] and have less risk of neurological injury compared to screws in S2 [25,[30][31][32][33][34].…”