Finite Element Analysis Of Screw Stress After Oblique Insertion Angle Change Of Short Segment Schanz Screw In Lumbar 1 Fracture

Objective:We established a finite element model of short-segment Schanz pedicle screw(T₁₂2 and L₂)oblique downward fixation for the treatment of L₁ severe burst fractures?LSC?7?and evaluated its biomechanical properties,and its safety.Methods:A healthy volunteers data was used to simulate the finite element model.According to the oblique downward angle?0°,5°,10°and15°?,we established four instrumentation models with T₁₂ and L₂ schanz pedicle screw fixed oblique downward in treating L₁ severe fracture?LSC?7?.350N vertical load and torque of 7.5N·m during vertical,extension,bending,rotation and were applied to the upper surface of the T₁₂vertebral body,respectively,and the screw stress and the displacement/micro-motion of L₁ vertebra of each group were analysed by the finite element software.Results:The validity of the model was validated.The maximum stress of the screw was located at the root of the superior screw,The maximum stress values were not significantly different and were all lower than the threshold of screw fatigue.The maximum stresses of screw in the 0°,5°,10°and 15°groups were respectively:?vertical?:230.1861MPa,217.8517MPa,232.8764MPa,220.0251MPa;?flexion?:230.3132MPa,217.9787MPa,233.0026MPa,220.1519MPa;?extension?:230.0590MPa,217.7247MPa,233.0026MPa,220.1519MPa;?L-bending?:230.1612MPa,217.7936MPa,232.8186MPa,219.9670MPa;?R-bending?:230.2109MPa,217.9098MPa,232.9342MPa,220.0382MPa;?L-rotation?:230.1049MPa,217.8656MPa,232.8902MPa,220.0382MPa;?R-rotation?:230.2672MPa?217.8380MPa?232.8626MPa?220.0119MPa.The maximum axial displacement of the injured Vertebra was at the anterior edge of the upper part of the vertebral body.And the displacement/micro-motion of L₁ vertebra of each group respectively were:?vertical?:3.1992mm,3.1992mm,3.2877mm,3.0861mm;?flexion?:3.2013mm,3.0604mm,3.2897mm,3.0881mm;?extension?:3.1972mm,3.0563mm,3.2857mm,3.0841mm;?L-bending?:3.1991mm,3.0582mm,3.2876mm,3.0862mm;?R-bending?:3.1904mm,3.0585mm,3.2878mm,3.0863mm;?L-rotation?:3.1993mm,3.0584mm,3.2878mm,3.0862mm;?R-rotation?:3.1992mm,3.0583mm,3.2877mm,3.0861mm.Conclusion:Compared to the parallel instrumentation,short segment schanz pedicle screw oblique downward fixation did not change the maximum stress of the screw with low risk for break.The compression displacement/micro-motion of bony defect during flexion may lead to the postoperative re-collapse of injured vertebrae.