Institute for Biomechanics, ETH Zurich, Zurich, Switzerland.
J Biomech. 2012 Apr 5;45(6):1060-7. doi: 10.1016/j.jbiomech.2011.12.024. Epub 2012 Jan 28.
Small endosseous implants, such as screws, are important components of modern orthopedics and dentistry. Hence they have to reliably fulfill a variety of requirements, which makes the development of such implants challenging. Finite element analysis is a widely used computational tool used to analyze and optimize implant stability in bone. For these purposes, bone is generally modeled as a continuum material. However, bone failure and bone adaptation processes are occurring at the discrete level of individual trabeculae; hence the assessment of stresses and strains at this level is relevant. Therefore, the aim of the present study was to investigate how peri-implant strain distribution and load transfer between implant and bone are affected by the continuum assumption. We performed a computational study in which cancellous screws were inserted in continuum and discrete models of trabecular bone; axial loading was simulated. We found strong differences in bone-implant stiffness between the discrete and continuum bone model. They depended on bone density and applied boundary conditions. Furthermore, load transfer from the screw to the surrounding bone differed strongly between the continuum and discrete models, especially for low-density bone. Based on our findings we conclude that continuum bone models are of limited use for finite element analysis of peri-implant mechanical loading in trabecular bone when a precise quantification of peri-implant stresses and strains is required. Therefore, for the assessment and improvement of trabecular bone implants, finite element models which accurately represent trabecular microarchitecture should be used.
小型骨内植入物，如螺钉，是现代骨科和牙科的重要组成部分。因此，它们必须可靠地满足各种要求，这使得此类植入物的开发具有挑战性。有限元分析是一种广泛使用的计算工具，用于分析和优化植入物在骨骼中的稳定性。为此，骨骼通常被建模为连续体材料。然而，骨骼失效和骨骼适应过程是在单个小梁的离散水平上发生的；因此，在这个水平上评估应力和应变是相关的。因此，本研究的目的是研究在连续体假设下，种植体周围应变分布和种植体与骨骼之间的载荷传递如何受到影响。我们进行了一项计算研究，在该研究中，将松质螺钉插入小梁骨的连续体和离散模型中；模拟轴向加载。我们发现离散骨模型和连续体骨模型之间的骨-植入物刚度有很大差异。它们取决于骨密度和应用的边界条件。此外，螺钉向周围骨骼的载荷传递在连续体和离散模型之间有很大差异，尤其是在低密度骨中。基于我们的发现，我们得出结论，当需要精确量化种植体周围的应力和应变时，连续体骨模型在分析小梁骨中种植体周围机械载荷的有限元分析中用途有限。因此，为了评估和改进小梁骨植入物，应该使用能够准确表示小梁微观结构的有限元模型。
