1. Bridge vs. Tension Band Construct for Spinal Fractures Fixation: A Biomechanical Analysis C. Richards, J. Ouellet, M. Fouse, N. Noiseux, P. Jarzem, R. Reindl, D. Giannitsios, T. Steffan ORTHOPAEDIC RESEARCH LABORATORY Division of Orthopaedic Surgery, McGill University

2. Problem Traditional pedicle screw instrumentation:  Parallel to endplate  Kyphotic collapse is a known complication  Risk of posterior pullout if not supported anteriorly

3. Hypothesis For spinal fracture fixation  bridge-type fixation = divergent screws vs.  tension-band = parallel screws  Significantly stiffer  Better resistance to failure in kyphosis  Better resistance to screw pull-out

4. Hypothesis >

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6. Purpose Bridge vs. Tension Band Constructs  Construct stiffness  Ultimate failure load Stiffness Ultimate Failure Load

7. Materials and Methods 1. Finite Element Analysis of ASTM Polyethylene Constructs

8. Methods and Materials 1. Finite Element Analysis of ASTM Polyethylene Constructs 2. Mechanical testing of ASTM Polyethylene Construct

9. Methods and Materials 1. Finite Element Analysis of ASTM Polyethylene Constructs 2. Mechanical testing of ASTM Polyethylene Construct 3. Mechanical testing of Cadaveric Constructs

10. ASTM Corpectomy Model UHMWPE blocks Worst case scenario for vertebral body fracture Followed precisely for T-B Constructs  Pedicle screws inserted parallel to horizontal plane

11. ASTM Corpectomy Model Altered for Bridge Constructs  Change in pedicle screw orientation w.r.t. horizontal plane 16.5º superiorly 26.4º inferiorly

12. Finite Element Analysis Linear FEA  3-D models of ASTM constructs  Mechanical properties of polyethylene and titanium

13. Finite Element Analysis Models loaded at 100N, 300N, & 600N Displacement data generated for each load

14. Polyethylene Construct 6 constructs built  3 TB  3 Bridge Constructs loaded using MTS Load and displacement data generated

15. Cadaveric Constructs 6 male cadavers dissected  3 Matched pairs based on Vertebral body size and BMD  instrumented @ T11-L1 3 – TB Construct 3 – Bridge Construct #2 Osteotome

16. Cadaveric Constructs Potted in PMMA  Anterosuperior endplate of superior vertebra free  Anteroinferior endplate of inferior vertebra free

17. Cadaveric Constructs Loaded using MTS Load and displacement data generated

18. Results – Stiffness (N/mm) 34.1 21.6 17.3 20.6 15.2 18.4 FEA PolyethyleneCadavers p=0.015p=0.012

19. Results – Ultimate Failure Load 419 622 p=0.076

20. Results All specimens were evaluated for accuracy and safety of schanz screw insertion  Maximum angles as determined by the anatomic study were achieved  No breech of pedicle wall

21. Results Pattern of Failure  Tension Band Construct All 3 constructs failed into kyphosis Screw pullout at the pedicle-body junction

22. Results Pattern of Failure  Bridge Construct 2/3 constructs failed 1. Screw pullout at the pedicle-body junction 2. Screw pullout through superior endplate

23. Discussion Increased stiffness  Better protection of anterior column Allows better potential for healing Decrease risk of kyphotic failure

24. Conclusions Bridge Construct is significantly stiffer than the Tension Band Construct Ultimate failure load was 50% greater for the Bridge Construct Further Cadaveric testing is required and is ongoing >

25. Thank You C. Richards, J. Ouellet, M. Fouse, N. Noiseux, P. Jarzem, R. Reindl, D. Giannitsios, T. Steffan ORTHOPAEDIC RESEARCH LABORATORY Division of Orthopaedic Surgery, McGill University