一种新型膝关节假体在步态过程中接触应力的有限元仿真

目的对一种使用新方法设计的新型人工膝关节假体进行有限元模拟分析,研究改变关节假体外髁关节面的扭转角度对改善人工膝关节假体力学环境的影响。方法依据志愿者提供的膝关节CT测量数据,建立3个膝关节假体模型,内侧股骨髁在冠状面保持圆曲线,外侧股骨髁根据冠状面轮廓曲线的扭转角度不同,分为0°、10°、20°(分别命名为模型1、2、3)。将假体模型导入有限元软件,输入自然人体膝关节的运动步态信息为加载工况,模拟步态过程中膝关节假体的运动状态,并将通过模拟得到的髁间应力同使用接触力学理论公式得到的应力计算结果进行对比。结果 3组模型的最大应力出现在步态13%处,此时关节轴向力最大(2.6 kN)。模型1内、外髁最大应力分别为35.5、30.6 MPa,模型2内、外髁最大应力分别为38.4、32.6 MPa,模型3内、外髁最大应力分别为38.3、43.1 MPa。模型2、3的应力曲线相比模型1变化较为平缓。模拟得到的应力曲线与理论计算曲线的趋势相同,但个别步态时刻处有差异。结论通过增大人工膝关节假体外髁曲面的扭转角度可以改善膝关节力学环境,经过改进的膝关节假体在步态过程中对胫骨衬垫的应力突变减少,可以延长假体的使用寿命。

Finite element simulation of contact stress on a novel total knee prosthesis during gait cycle

Objective To perform finite element analysis on a type of newly designed total knee prosthesis, and investigate the influence from changing twist angle of the lateral condyle surface on mechanical environment of the knee joint. Methods Based on CT measurement data from a volunteer, 3 artificial knee prostheses with the same medial condyle were established. In Model 1, the twist angle of lateral condyle surface was 0°, while 10° and 20° in Model 2 and Model 3, respectively. The prosthesis models were imported into finite element software and applied with gait cycle data to simulate the motion of knee prosthesis during the gait cycle. The simulated stress results in the knee joint were then compared with the calculated results, which were obtained from theoretical formula of contact mechanics. Results The maximum stress of 3 models appeared at 13% of the gait cycle, when the axial force (2.6 kN) was also the maximum. The maximum stresses of medial and lateral condyle in Model 1, Model 2 and Model 3 were 35.5 and 30.6 MPa, 38.4 and 32.6 MPa, 38.3 and 43.1 MPa, respectively. The stress curves of Model 2 and Model 3 during the gait cycle were relatively smooth compared with those of Model 1. The simulated stress trend was basically similar to the theoretical calculation, except at a few moments in the gait cycle. Conclusions The mechanical environment of the total knee prosthesis can be improved by twist angle of the lateral condyle surface. This newly designed prosthesis can preserve implants from abrupt change of the stress during the gait cycle and prolong the service life of prostheses.