腰椎峡部裂机翼型记忆合金固定装置的有限元分析

The finite element analysis of Aerofoil shape memory alloy fixation instrument for surgically treating spondylolysis

目的以正常人体CT影像数据为基础,建立腰椎峡部裂弹性固定有限元模型,分析内固定器受力并对其进行改进。方法采用分辨率0.625 mm薄层CT扫描数据,导入Mimics10.0软件建立三维几何面网格模型,通过Geomagic studio12.0、HyperMesh 10.0前处理,最终导入Abaqus10.1软件生成腰椎峡部裂记忆合金固定模型,并在椎体上表面施加500N压力和7.5 Nm力矩,模拟前屈、后伸、侧屈和旋转四种生理载荷,观察并比较不同载荷下固定装置的应力分布。结果机翼型记忆合金固定装置应力集中于侧翼,尤其是侧翼和底座的接合部位,后伸和旋转时最大,容易导致疲劳性断裂。结论提高镍钛合金材料质量和工艺水准,术后延长腰围保护时间,以避免机翼型记忆合金固定装置断裂的风险。

Objective To establish the three-dimensional finite element model （FEM） with the bilateral pars defect and reconstruct by AEROFOIL fixation. Methods According to spiral CT scan images of 0.625 mm thickness,finite element model of lumbosacral vertebrae was established using Mimics10.01, Geomagic studio12.0, HyperMesh 10.0 and Abaqus10.1 software. Moreover, it＇s validity had been verified and then imported the AEROFOIL fixation. The reconstructed model was analyzed under 500N pressure loading on the upper surface of L1, and 7.5Nm torque loading for simulating axial compression and flexion, extension, lateral bending and rotation. The Von mises stress of fixation were recorded and analyzed. Results It showed that high stress concentrated at the bottom part of the swings, especially at the junction of the swings and the U-shape base. Extension and axial rotation motion resulted in breakage of the AEROFOIL fixation. Conclusions Improving Nitinol material quality and process standards and suitably prolonging the need for external bracing are necessary for reducing the higher risk of fracture on fixation devices.