膝内翻对踝关节接触特征影响的有限元分析

Effect of different knee varus angle on the ankle joint contact characteristics: a finite element study

目的应用有限元分析的方法研究膝内翻不同角度对踝关节接触特征的影响。方法利用逆向建模技术,将正常成人志愿者右下肢三维CT数据在Mimics 10.0、Geomagic 7.0软件中对相关组织进行重建,将三维模型导入Hypermesh 10.0软件中进行网格划分,利用其Morph功能改变股胫角分别生成0°、5°、10°、15°、20°、25°、30°膝内翻模型,在Abaqus 6.9中添加受力工况,进行有限元分析。结果建立的下肢三维有限元模型,共75 230个节点、204 745个单元。0°模型胫距关节总接触面积为264.65 mm2,接触应力主要分布在前内、前外、后外3个象限。在10°模型中,前外、后外2个象限的接触应力明显减小,前内及后内象限的接触应力显著增大,与0°模型比较差异有统计学意义(P<0.05)。30°模型与0°模型比较,接触应力区的图形相似,应力值差异有统计学意义(P<0.01)。与0°模型比较,应力区中心曲线在10°模型中内移约2.44 mm,20°模型中外移约3.47 mm,30°模型外移4.26 mm。在20°模型中外踝-距骨接触面的应力值为1.67 MPa,至30°模型该应力值增大至3.42 MPa。结论膝内翻不仅影响膝关节的应力分布,而且使胫距关节峰值应力增大、外移,足底部出现代偿性外翻,诱发创伤性关节炎及扁平足。

Objective To analyze the effects of different knee varus angle on the stress and contact area at the ankle using the finite element（ FE） method. Methods Using reverse modeling technology, Helical CT scan images of the right lower limb of the volunteer were obtained to reconstruct a three dimensional model of the limb by using Mimics 10. 0 and Geomagic 7. 0 software. And then the model was imported into Mesh of Hypermesh 10. 0 software, through the Morph function, the femoral tibial angle were changed to generate models with different knee varus angle respec-tively （0°,5°,10°,15° ,20° ,25° ,30° ） , added stress condition and boundary conditions in Abaqus 6. 9 software and calculated the von Mises stress distributions and contact area on each part of the ankle joint. Results Three-dimen-sional finite element models of the lower limb was established with 75 230 nodes and 204 745 units. The contact area of tibiotalar joint was 264. 65 mm2 in 0° model, the contact stress mainly distributed in the quadrants of anteromedial （AM） anterolateral（ AL） posterolateral（PL） . In 10°degree model, the stress reduced in AL and PL,but increased in AM and posteromedial（ PM） significantly（ P 〈 0. 05 ） . In 30° model, the contact stress area were similar to 0° model,but the stress values had statistical significance （ P 〈 0. 01） . Compared with the 0° model, the center curve ofthe 10° model moved to the inside about 2. 44 mm, but the curve of 20° model moved outside about 3. 47 mm and 4. 26 mm in 30° model. The contact stress of lateral talar was 1. 67 MPa in 20° model and 3. 42 MPa in 30° model.Conclusions Knee varus not only affects the stress distribution of the knee, but also increases the stress of the ankle and changes the stress distribution, and induces the traumatic arthritis and flatfoot.Key words knee varus;ankle joint;finite element analysis;traumatic arthritis