桡骨远端FrykmanⅧ型骨折钢板固定有限元模型的建立及力学分析

Establishment and mechanical analysis of the finite element model of the type Frykman Ⅷ fracture of the distal radius with steel plate fixation

背景:临床中对于桡骨远端骨折或是关节脱位的治疗普遍比较重视,但却很少关注尺骨茎突骨折,而且对尺骨茎突骨折是否需要固定存在争议。骨科生物力学研究中,选用尸体实验可能会遇到尸体模型选择标准不一以及力学测量手段不同等问题。目的:选用有限元分析方法,基于Mimics软件构建桡骨远端FrykmanⅧ型骨折钢板螺钉固定的有限元仿真模型,并设定工况与载荷进行力学分析,希望给此类骨折修复方案的选择提供参考。方法:基于1例健康志愿者的前臂及手部CT图像建立正常腕关节三维有限元基础模型,调试后通过轴向加载100 N应力得出桡骨远端的应力分布云图,与文献中尸体实验数据对比来验证模型的有效性。通过有限元相关软件分网、切割造模建立桡骨远端FrykmanⅧ型骨折合并尺骨茎突Ⅰ型和Ⅱ型骨折的2种有限元模型,并完成桡骨远端钢板螺钉固定模型的组装。在旋转工况下设定载荷,分析2个模型中钢板内植物单元的应力分布、下尺桡关节的相对位移及尺骨茎突骨折端位移的变化情况。结果与结论:①建立并验证了正常腕关节的三维有限元模型,以此为基础延伸建立出桡骨远端FrykmanⅧ型骨折合并尺骨茎突Ⅰ型和Ⅱ型骨折桡骨远端钢板螺钉固定的2种有限元模型;②在设定相同旋转载荷条件下,桡骨远端FrykmanⅧ型骨折合并尺骨茎突Ⅰ型骨折的钢板固定模型中钢板单元承受的应力及应力分布范围均小于合并尺骨茎突Ⅱ型骨折钢板固定的骨折模型,下尺桡关节的相对位移值及尺骨茎突骨折端位移值也小于后者;③提示构建的腕关节三维有限元模型可用于腕部骨折的力学机制分析;通过有限元分析研究显示,桡骨远端FrykmanⅧ型骨折中尺骨茎突骨折会影响下尺桡关节的稳定性,其中合并有尺骨茎突Ⅱ型骨折时较为明显,可以给此类骨折修复方案的选择提供一定的临床参考。

BACKGROUND: Generally, the treatment of distal radius fractures or joint dislocations is generally valued in clinical practice, but little attention is paid to the ulnar styloid fracture, and whether the ulnar styloid fracture needs to be fixed is controversial. In the study of orthopedic biomechanics, the selection of cadaver model may encounter some problems, such as different selection criteria of cadaver model and different mechanical measurement methods. OBJECTIVE: Based on Mimics software, the finite element simulation model of type Frykman Ⅷ fracture of the distal radius fixed by plate and screw was constructed using finite element analysis. The working condition and load were set for mechanical analysis. It is hoped to provide a reference for the choice of the repair plan of this kind of fracture. METHODS: A three-dimensional finite element model of normal wrist joint was established based on the forearm and wrist CT images of a healthy volunteer. After debugging the model, Von Mises stress of the distal radius was obtained by loading the 100 N stress in the axial direction, and the validity of the model was verified by comparing with the experimental data in the literature. Two kinds of finite element models of Frykman Ⅷ fracture with ulnar styloid type I and type II fractures were established by using finite element software to divide the mesh, cut and mold, and the model of plate and screw fixation of distal radius was assembled. Setting load under rotating working conditions, we analyzed the changes of the stress distribution of the steel plate unit in two models, and the relative displacement of the distal radioulnar joint as well as the ulnar styloid fracture broken end. RESULTS AND CONCLUSION:(1) A three-dimensional finite element model of normal wrist joint was established and validated, and the other two models of type Frykman Ⅷ fracture of the distal radius with ulnar styloid type I and type II fractures fixed by plate and screw were established based on this model.(2) Under the same rotating load, this study showed that the stress and stress distribution of the steel plate unit in the steel plate fixation model of Frykman Ⅷ fracture of the distal radius combined with ulnar styloid type I fracture were smaller than those of the fracture model combined with type II fracture of styloid process of ulna;the relative displacement values of the distal radioulnar joint and the ulnar styloid fracture broken end were smaller than the latter too.(3) The three-dimensional finite element model of wrist joint constructed in this study can be used to analyze the mechanical mechanism of wrist fracture. The results of finite element analysis showed that the fracture of styloid process of ulna in Frykman Ⅷ fracture of the distal radius would affect the stability of the distal radioulnar joint, especially in the case of ulnar styloid type II fracture, which can provide a certain clinical reference for the selection of operation scheme of such fracture.