枢椎有限元模型建立及齿突骨折的有限元分析

目的 建立并验证枢椎三维有限元模型,并应用该模型探讨齿突垂直和水平方向不同角度载荷下的损伤机制和骨折类型.方法 对健康成年男性颈部进行CT扫描,层厚0.6mm,无间隔.将DICOM图像数据导入Mimics软件中,生成网格化的枢椎表面三维图像,再经ANSYS ICEM CFD处理,生成包括皮质骨和松质骨的实体模型.模拟体外生物力学试验验证模型.模型验证后,通过对齿突前部垂直和水平方向上施加不同角度的载荷,分析各种条件下齿突的应力分布并探讨相应的骨折类型.结果 (1)模型验证结果与体外生物力学试验的数据基本一致,后伸载荷下产生Ⅲ型齿突骨折,最大应力为123 Mpa;倾斜45°载荷下产生Ⅱ型齿突骨折,最大应力为121 Mpa,与皮质骨的屈服应力(138 Mpa)分别相差11%和12%.(2)齿突前部垂直和水平方向不同角度外力加载的应力分布图显示,应力集中区域可发生转变,预示骨折类型可能由Ⅲ型转变为Ⅱ型,且最大应力值逐渐增大.皮质骨承受主要应力.结论 我们建立的枢椎有限元模型经过验证可以很好地模拟枢椎的生物力学特性,其中包括皮质骨和松质骨结构.两种力学加载模式的应力分布图显示随着作用力角度的变化,会出现齿突骨折类型的转变,预示外力作用的方向是决定齿突骨折类型的关键因素.

The establishment of a finite element model of axis to analyze the mechanism of odontoid fracture in different loads

Objective A finite element model of axis is established and validated,and the injury mechanisms and fracture patterns of odontoid under anterior load in different orientation on the vertical and horizontal plane is analyzed.Methods The raw data obtained from a healthy adult man.His cervical spine was scanned by the Siemens Somatom Sensation 64 with 0.6 mm thinkness without any interval.Then the CT datas were inputed to the Materialise Mimics and produced a meshed 3D surface image of axis.The 3D image was inputed to the ANSYS ICEM CFD 10.0 and produced a 3D entity, which contained cortical bone and cancellous bone.For validation, the FE model was constrained and loaded to simulate that used in previous biomechanical studies.The validated model was loaded in different orientation on the vertical and horizontal plane.The fracture patterns based on the Von Mises stress patterns in different load patterns were discussed.Results 1) The result of present finite element model of axis closely correlate with the biomechanical testing of results obtained in previous biomechanical testing.Pure extension loading produced a type Ⅲ stress pattern with maximum stress of 123 MPa.Loading at 45°produced a type Ⅱ stress distribution with a maximum stress of 121 MPa.These stresses are within 11% and 12%, respectively, of the reported yield stress of cortical bone (138 MPa).2)The Von Mises stress patterns were predicted that a transition from a type Ⅲ to a type Ⅱ pattern occurred with different orientation of load on the vertical and horizontal plane.Conclusion The current finite element model of axis can properly simulate the characteristic of axis in biomechanics testing.The Von Mises stress patterns of two load cases demonstrate that a transition from a type Ⅲ to a type Ⅱ pattern happened with different orientation of load on both vertical and horizontal plane.