Assessment of the multifactorial causes of atypical femoral fractures using a novel multiscale finite element approach

• Published in: Bone (New York, N.Y.) N.Y.), 2020-06, Vol.135, p.115318-115318, Article 115318
• Main Authors: Demirtas, Ahmet, Rajapakse, Chamith S., Ural, Ani
• Format: Article
• Language: English
• Subjects: Atypical femoral fracture; Cortical bone microstructure; Femoral geometry; Material heterogeneity; Multiscale finite element modeling
• ISSN: 8756-3282; 1873-2763
• DOI: 10.1016/j.bone.2020.115318

Atypical femoral fracture (AFF), which is a low energy fracture in the subtrochanteric or diaphysis region of the femur, has multifactorial causes that span macro- to microscale mechanisms including femoral geometry, cortical bone composition and structure. However, the extent of individual and combined influence of these factors on AFF is still not well understood. As a result, the aim of this study is to develop a multiscale fracture mechanics-based finite element modeling framework that is capable of quantifying the individual and combined influence of macroscale femoral geometrical properties as well as cortical bone microscale material properties and structure on AFF. In this study, three different femoral geometries with two different cortical bone microstructures, and two different material property distributions were investigated by first determining the critical AFF locations in the femur using macroscale stress analysis and then performing coupled macro-microscale fracture simulations. The simulation results showed that femoral geometry led to substantial differences in crack growth independent of cortical microstructure and tissue level material properties. The results suggest that multiple femoral geometrical properties, including neck-shaft angle and curvature, may contribute to the fracture behavior at AFF sites rather than a single macroscale geometrical feature. Osteonal area had a significant effect on microcrack propagation at AFF sites independent of microscale material property distribution and femoral geometry. In addition, cortical bone tissue level material heterogeneity improved the fracture resistance independent of femoral geometry and cortical microstructure. In summary, the computational approach developed in this study identified the individual, combined, and relative influence of multiscale factors on AFF risk. The new framework developed in this study could help identify the governing multiscale mechanisms of AFF and bring additional insight into the possible association of long-term bisphosphate treatment with AFF. [Display omitted] •A multiscale fracture mechanics-based finite element model of AFF was developed.•Multiple femoral geometrical properties influenced AFF rather than a single feature.•An increase in osteonal area improved the fracture resistance at AFF sites.•Increased material property heterogeneity increased the resistance to AFF.