可吸收镁合金寰枢椎脱位固定系统的生物力学仿真

Biomechanical Simulation on Absorbable Magnesium Alloy Fixation System for Atlantoaxial Dislocation

目的研究可吸收镁合金螺钉应用于寰枢椎脱位固定的可行性。方法选用WE43型镁合金,设计4种不同螺纹形式(三角形、矩形、梯形、锯齿形)镁合金螺钉,对螺钉-聚氨酯试验块模型、寰枢椎固定系统模型进行有限元仿真分析,获得模型上的应力分布和位移分布。结果按照ASTM F543标准对镁合金螺钉进行拔出力仿真分析,三角形、矩形、梯形、锯齿形螺纹螺钉上的应力分别为146.20、185.22、194.98、264.55 MPa,即三角形螺纹螺钉的抗拔出力最大,且应力峰值最小;用三角形螺纹镁合金螺钉进行寰枢椎固定可以满足颈部屈伸、旋转、侧倾所需的强度要求;在三角形螺纹螺钉表面喷涂羟基磷灰石(hydroxyapatite,HA)涂层后,螺钉上应力峰值降低了17.16 MPa,涂层上的应力在涂层与基体的结合强度范围内。结论在相同载荷条件下,三角形螺纹螺钉具有较好的稳定性,抗拔出力性能最佳;使用热处理后的三角形螺纹镁合金螺钉进行寰枢椎固定,螺钉强度满足承载要求;在螺钉表面喷涂HA涂层,可优化螺钉的力学性能,并且涂层与螺钉之间有良好的结合强度。

Objective To investigate the feasibility of absorbable magnesium alloy screws in atlantoaxial dislocation fixation.Methods Four kinds of screws with triangular,rectangular,trapezoidal and zigzag thread were designed with WE43 magnesium alloy.The finite element simulation analyses were performed on the screwpolyurethane model and atlantoaxial fixation system model.The stress and displacement distributions on the models were obtained.Results The pull-out force simulations were carried out on four kinds of magnesium alloy screws according to ASTM F543 standard specification.The stresses of screws with triangular,rectangular,trapezoidal and zigzag thread were 146.20,185.22,194.98,264.55 MPa,respectively.The pull-out strength of the screw with triangular thread was the largest,and the peak stress was the smallest.The magnesium alloy screw with triangular thread used for atlantoaxial fixation could meet the strength requirements of flexion/extension,rotation and bending of the neck.The peak stress of the screw was reduced by 17.16 MPa after adding hydroxyapatite(HA)coating on the surface,and the stress on the screw was within the range of bonding strength between coating and magnesium alloy substrate.Conclusions Under the same loading condition,the screw with triangular thread has good stability and the best pull-out force performance.After heat treatment,the strength of magnesium alloy screw with triangular thread meets the load-bearing requirements for atlantoaxial dislocation fixation.HA coating on screw surface can optimize mechanical properties of the screw,and there exits good bonding strength between the coating and the screw.