Orthopaedic Research Laboratory, Radboud University Nijmegen Medical Centre, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands.
J Biomech. 2011 Feb 24;44(4):780-3. doi: 10.1016/j.jbiomech.2010.10.037. Epub 2010 Nov 12.
Aseptic loosening at the implant-cement interface is a well-documented cause of failure in joint arthroplasty. Traditionally, the strength of the implant-cement interface is determined using uni-axial normal and shear loading tests. However, during functional loading, the implant fixation sites are loaded under more complex stress conditions. For this purpose, the strength of the implant-cement interface under mixed-mode tensile and shear loading conditions was determined in this study using interface specimens with varying interface roughness. For the lowest roughness value analyzed (R(a)=0.89 μm), the interface strength was 0.40-1.95 MPa at loading angles varying between pure tension and shear, whereas this was 4.90-9.90 MPa for the highest roughness value (R(a)=2.76 μm). The interface strength during pure shear (1.95-9.90 MPa) was substantially higher than during pure tension (0.58-6.67 MPa). Polynomial regression was used to fit a second-order interpolation function through the experimental interface strength data (R²=0.85; p<0.001), relating the interface strength (S [MPa]) to the interface loading angle (α [degrees]) and interface roughness (R(a) [μm]): S(α,R(a))=0.891R²(a)+0.001α²-0.189R(a)-0.064α-0.060. Finally, an interface failure criterion was derived from the interface strength measurements, describing the risk of failure at the implant-cement interface when subjected to a certain tensile and shear stress using only the interface strength in pure tensile and shear direction. The findings presented in this paper can be used in numerical models to simulate loosening at the implant-cement interface.
在植入物-水泥界面处的无菌松动是关节置换术失效的一个有充分记录的原因。传统上，使用单轴法向和剪切加载测试来确定植入物-水泥界面的强度。然而，在功能负载下，植入物固定部位承受更复杂的应力条件。为此，本研究使用具有不同界面粗糙度的界面标本，在混合模式拉伸和剪切加载条件下确定了植入物-水泥界面的强度。对于分析的最低粗糙度值（R(a)=0.89 μm），在纯拉伸和剪切之间变化的加载角度下，界面强度为 0.40-1.95 MPa，而对于最高粗糙度值（R(a)=2.76 μm），界面强度为 4.90-9.90 MPa。在纯剪切（1.95-9.90 MPa）时的界面强度明显高于纯拉伸（0.58-6.67 MPa）时的界面强度。使用多项式回归通过实验界面强度数据拟合二阶插值函数（R²=0.85；p<0.001），将界面强度（S [MPa]）与界面加载角（α [°]）和界面粗糙度（R(a) [μm]）联系起来：S(α,R(a))=0.891R²(a)+0.001α²-0.189R(a)-0.064α-0.060。最后，从界面强度测量值中推导出了界面失效准则，该准则描述了当仅在纯拉伸和剪切方向上的界面强度时，植入物-水泥界面在受到特定拉伸和剪切应力时失效的风险。本文提出的研究结果可用于数值模型，以模拟植入物-水泥界面的松动。
