Institute of Structural Mechanics, University of Rostock, Albert-Einstein-Str. 2, 18059, Rostock, Germany.
Biomechanics and Implant Technology Research Laboratory, Department of Orthopaedics, Rostock University Medical Center, Rostock, Germany.
J Mech Behav Biomed Mater. 2022 Feb;126:105059. doi: 10.1016/j.jmbbm.2021.105059. Epub 2021 Dec 26.
Periprosthetic femoral fractures (PFF) around total hip replacements are one of the biggest challenges for orthopaedic surgeons. To understand the risk factors and formation of these fractures, the development of a reliable finite element (FE) model incorporating bone failure is essential. Due to the anisotropic and complex hierarchical structure of bone, the mechanical behaviour under large strains is difficult to predict. In this study, a state-of-the-art subject specific FE modelling technique for bone is utilised to generate and investigate PFF. A bilinear constitutive law is applied to bone tissue in subject specific FE models of five human femurs which are virtually implanted with a straight hip stem to numerically analyse PFF. The material parameters of the models are expressed as a function of bone ash density and mapped node wise to the FE mesh. In this way the subject specific, heterogeneous structure of bone is mimicked. For material mapping of the parameters, computed tomography (CT) images of the original fresh-frozen femurs are used. Periprosthetic fractures are generated by deleting elements on the basis of a critical plastic strain failure criterion. The models are analysed under physiological and clinically relevant conditions in two different load cases re-enacting stumbling and a sideways fall on the hip. The results of the analyses are quantified with experimental data from previous work. With regard to fracture pattern, stiffness and failure load the simulations of the load case stumbling delivered the most stable and accurate results. In general, mapping of material properties was found to be an appropriate way to reproduce PFF with finite element models.
全髋关节置换术后股骨假体周围骨折（PFF）是骨科医生面临的最大挑战之一。为了了解这些骨折的危险因素和形成机制，开发一种包含骨失效的可靠有限元（FE）模型至关重要。由于骨骼具有各向异性和复杂的层次结构，因此很难预测大应变下的力学行为。在这项研究中，利用一种最先进的骨骼特定FE 建模技术来生成和研究 PFF。在五个人体股骨的特定于个体的 FE 模型中，应用双线性本构定律来模拟骨组织，这些模型被虚拟地植入直髋关节柄，以数值分析 PFF。模型的材料参数表示为骨灰密度的函数，并映射到 FE 网格的节点上。通过这种方式，模拟了骨骼的特定于个体的、异质结构。对于参数的材料映射，使用原始新鲜冷冻股骨的计算机断层扫描（CT）图像。根据临界塑性应变失效准则，通过删除元素来产生假体周围骨折。根据两种不同的加载情况，对模型进行分析，模拟绊倒和髋关节侧方跌倒的生理和临床相关条件。分析结果与以前工作的实验数据进行定量比较。就骨折模式、刚度和失效载荷而言，绊倒加载情况的模拟结果最稳定和准确。一般来说，用有限元模型再现 PFF 时，材料特性的映射被认为是一种合适的方法。
