Orthopaedic Research Laboratory, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
J Mech Behav Biomed Mater. 2011 Oct;4(7):1492-503. doi: 10.1016/j.jmbbm.2011.05.019. Epub 2011 May 13.
In cemented total hip arthroplasty, the cement-bone interface can be considerably degenerated after less than one year in vivo service; this makes the interface much weaker relative to the direct post-operative situation. It is, however, still unknown how these degenerated interfaces behave under mixed-mode loading and how this is related to the interface morphology. In this study, we used a finite element (FE) approach to analyze the mixed-mode response of the cement-bone interface taken from postmortem retrievals. We investigated whether it was feasible to generate a fully elastic and a failure cohesive model based on only morphological input parameters. Computed tomography-based FE-models of postmortem cement-bone interfaces were generated and the interface morphology was determined. The models were loaded until failure in multiple directions by allowing cracking of the bone and cement components and including periodic boundary conditions. The resulting stiffness was related to the interface morphology. A closed form mixed-mode cohesive model that included failure was determined and related to the interface morphology. The responses of the FE-simulations compare satisfactorily with experimental observations, albeit the magnitude of the strength and stiffness are somewhat overestimated. Surprisingly, the FE-simulations predict no failure under shear loading and a considerable normal compression is generated which prevents dilation of the interface. The obtained mixed-mode stiffness response could subsequently be related to the interface morphology and subsequently be formulated into an elastic cohesive zone model. Finally, the acquired data could be used as an input for a cohesive model that also includes interface failure.
在骨水泥型全髋关节置换术中，骨水泥-骨界面在体内使用不到一年后就会发生明显退变，这使得界面相对于直接术后情况变得脆弱得多。然而，目前尚不清楚在混合模式载荷下这些退变的界面是如何表现的，以及这与界面形态学有何关系。在这项研究中，我们使用有限元（FE）方法分析了来自尸检标本的水泥-骨界面的混合模式响应。我们研究了是否可以仅基于形态学输入参数生成完全弹性和失效的内聚模型。基于计算机断层扫描的尸检水泥-骨界面的 FE 模型被生成，并且确定了界面形态。通过允许骨和水泥组件的开裂并包括周期性边界条件，使模型在多个方向上加载直至失效。所得的刚度与界面形态有关。确定了包含失效的封闭形式混合模式内聚模型，并将其与界面形态相关联。FE 模拟的响应与实验观察结果相当吻合，尽管强度和刚度的幅度有些高估。令人惊讶的是，FE 模拟预测在剪切载荷下不会发生失效，并且会产生相当大的法向压缩，从而防止界面的扩张。随后，可以将获得的混合模式刚度响应与界面形态相关联，并将其公式化为弹性内聚区模型。最后，可以将获得的数据用作包含界面失效的内聚模型的输入。
