Stewart T, Jin Z M, Shaw D, Auger D D, Stone M, Fisher J
Department of Mechanical Engineering, University of Leeds.
Proc Inst Mech Eng H. 1995;209(4):225-31. doi: 10.1243/PIME_PROC_1995_209_349_02.
The tibio-femoral contact area in five current popular total knee joint replacements has been measured using pressure-sensitive film under a normal load of 2.5 kN and at several angles of flexion. The corresponding maximum contact pressure has been estimated from the measured contact areas and found to exceed the point at which plastic deformation is expected in the ultra-high molecular weight polyethylene (UHMWPE) component, particularly at flexion angles near 90 degrees. The measured contact area and the estimated maximum contact stress have been found to be similar in magnitude for all of the five knee joint replacements tested. A significant difference, however, has been found in maximum contact pressure predicted from linear elasticity analysis for the different knee joints. This indicates that varying amounts of plastic deformation occurred in the polyethylene component in the different knee designs. It is important to know the extent of damage as knees with large amounts of plastic deformation are more likely to suffer low cycle fatigue failure. It is therefore concluded that the measurement of contact areas alone can be misleading in the design of and deformation in total knee joint replacements. It is important to modify geometries to reduce the maximum contact stress as predicted from the linear elasticity analysis, to below the linear elastic limit of the plastic component.
在2.5 kN的正常负荷下，使用压敏膜对目前流行的五种全膝关节置换假体的胫股接触面积进行了测量，并在几个屈曲角度下进行了测量。根据测量的接触面积估算了相应的最大接触压力，发现其超过了超高分子量聚乙烯（UHMWPE）部件预期发生塑性变形的点，特别是在接近90度的屈曲角度时。在所测试的五种膝关节置换假体中，测量的接触面积和估算的最大接触应力在大小上相似。然而，对于不同的膝关节，通过线性弹性分析预测的最大接触压力存在显著差异。这表明在不同的膝关节设计中，聚乙烯部件发生了不同程度的塑性变形。了解损伤程度很重要，因为发生大量塑性变形的膝关节更有可能遭受低周疲劳失效。因此得出结论，仅测量接触面积在全膝关节置换假体的设计和变形方面可能会产生误导。根据线性弹性分析预测，修改几何形状以将最大接触应力降低到塑性部件的线性弹性极限以下非常重要。
