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

ABSTRACT: Background:Pelvic ring-comminuted transforaminal sacral fracture injuries are rotationally and vertically unstable and have a high rate of failure. Objective:Our 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. Methods:3D 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). Results:The 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. Conclusion:Inclusion of external fixation improved resistance only to torsional loading. Translational Potential of this Article:Patients with comminuted transforaminal sacral-ipsilateral rami fractures benefit from this fixation.

SUBMITTER: Crist BD

PROVIDER: S-EPMC6350021 | biostudies-other | 2019 Jan

REPOSITORIES: biostudies-other

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

Crist Brett D BD Pfeiffer Ferris M FM Khazzam Michael S MS Kueny Rebecca A RA Della Rocca Gregory J GJ Carson William L WL

Journal of orthopaedic translation 20180710

<h4>Background</h4>Pelvic ring-comminuted transforaminal sacral fracture injuries are rotationally and vertically unstable and have a high rate of failure.<h4>Objective</h4>Our 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.<h4>Methods</h4>3D relative motion across sacral-rami ...[more]

PMID: 30723687

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Project description:BackgroundPedicle screw insertion in osteoporotic patients is challenging. Achieving more screw-cortical bone purchase and invasiveness minimization, the cortical bone trajectory and the midline cortical techniques represent alternatives to traditional pedicle screws. This study compares the fatigue behavior and fixation strength of the cement-augmented traditional trajectory (TT), the cortical bone trajectory (CBT), and the midline cortical (MC).MethodsTen human cadaveric spine specimens (L1 - L5) were examined. The average age was 86.3 ± 7.2 years. CT scans were provided for preoperative planning. CBT and MC were implanted by using the patient-specific 3D-printed placement guide (MySpine®, Medacta International), TT were implanted freehand. All ten cadaveric specimens were randomized to group A (CBT vs. MC) or group B (MC vs. TT). Each screw was loaded for 10,000 cycles. The failure criterion was doubling of the initial screw displacement resulting from the compressive force (60 N) at the first cycle, the stop criterion was a doubling of the initial screw displacement. After dynamic testing, screws were pulled out axially at 5 mm/min to determine their remaining fixation strength.ResultsThe mean pull-out forces did not differ significantly. Concerning the fatigue performance, only one out of ten MC of group A failed prematurely due to loosening after 1500 cycles (L3). Five CBT already loosened during the first 500 cycles. The mean displacement was always lower in the MC. In group B, all TT showed no signs of failure or loosening. Three MC failed already after 26 cycles, 1510 cycles or 2144 cycles. The TT showed always a lower mean displacement. In the subsequent pull-out tests, the remaining mean fixation strength of the MC (449.6 ± 298.9 N) was slightly higher compared to the mean pull-out force of the CBT (401.2 ± 261.4 N). However, MC (714.5 ± 488.0 N) were inferior to TT (990.2 ± 451.9 N).ConclusionThe current study demonstrated that cement-augmented TT have the best fatigue and pull-out characteristics in osteoporotic lumbar vertebrae, followed by the MC and CBT. MC represent a promising alternative in osteoporotic bone if cement augmentation should be avoided. Using the patient-specific placement guide contributes to the improvement of screws' biomechanical properties.

Dataset Information

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

Publications

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

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