Mineral heterogeneity affects predictions of intratrabecular stress and strain G.A.P. Renders a,b,n , L. Mulder c , L.J. van Ruijven a,b , G.E.J. Langenbach a,b , T.M.G.J. van Eijden a,1 a Department of Functional Anatomy, Academic Center for Dentistry Amsterdam (ACTA), University of Amsterdam and VU University Amsterdam, Gustav Mahlerlaan 3004, Room 12N13, 1081 LA, Amsterdam, The Netherlands b Research Institute MOVE, Amsterdam, The Netherlands c Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands article info Article history: Accepted 11 October 2010 Keywords: Biomechanics Degree of mineralization Finite element model Mechanical loading MicroCT abstract Knowledge of the influence of mineral variations (i.e., mineral heterogeneity) on biomechanical bone behavior at the trabecular level is limited. The aim of this study is to investigate how this material property affects the intratrabecular distributions of stress and strain in human adult trabecular bone. Two different sets of finite element (FE) models of trabecular samples were constructed; tissue stiffness was either scaled to the local degree of mineralization of bone as measured with microCT (heterogeneous) or tissue stiffness was assumed to be homogeneous. The influence of intratrabecular mineral heterogeneity was analyzed by comparing both models. Interesting effects were seen regarding intratrabecular stress and strain distributions. In the homogeneous model, the highest stresses were found at the surface with a significant decrease towards the core. Higher superficial stresses could indicate a higher predicted fracture risk in the trabeculae. In the heterogeneous model this pattern was different. A significant increase in stress with increasing distance from the trabecular surface was found followed by a significant decrease towards the core. This suggests trabecular bending during a compression. In both models a decrease in strain values from surface to core was predicted, which is consistent with trabecular bending. When mineral heterogeneity was taken into account, the predicted intratrabecular patterns of stress and strain are more consistent with the expected biomechanical behavior as based on mineral variations in trabeculae. Our findings indicate that mineral heterogeneity should not be neglected when performing biomechanical studies on topics such as the (long-term or dose dependent) effects of antiresorptive treatments. & 2010 Elsevier Ltd. All rights reserved. 1. Introduction The biomechanical behavior of bone depends not only on its microarchitecture but also on its mineral content (Currey, 1984; Hodgskinson et al., 1989; Zysset et al., 1999). In trabecular bone, e.g., microarchitecture is correlated to the apparent stiffness, i.e., Young’s modulus of bone tissue (Liu et al., 2006). However, we recently have shown that variations in the degree of mineralization of bone (DMB) could explain up to 29% of the variance in the apparent stiffness, emphasizing the importance of this material property (Renders et al., 2008). Knowledge of the biomechanical influence of DMB at the trabecular level is still limited and needs to be expanded. As a result of the continuous bone remodeling process, trabe- cular bone tissue is composed of so-called bone packets, each with its own mineral content corresponding to its tissue age. A highly specific distribution of the mineral content throughout trabecular bone has been found with Fourier transform infrared microspec- troscopy (Paschalis et al., 1997) and back-scattered electron microscopy (Boyde et al., 1993; Ciarelli et al., 2003; Roschger et al., 2003; Fratzl et al., 2004). At the trabecular surface, the site where remodeling predominantly occurs, relatively younger tissue with a low DMB is found. Whereas, the relatively older and more mineralized tissue is found with increasing distance from the trabecular surfaces (Roschger et al., 2003). Although accurate, these methods are limited by their inability to measure the mineral distribution in three dimensions. This problem can be overcome with micro-computed tomography (microCT) that considers the three-dimensional structure and thus the true spatial distribution of DMB (Nuzzo et al., 2002; Mulder et al., 2004). Indeed, several microCT studies have confirmed that mineral heterogeneity exists at the trabecular tissue level in both developing bone (Mulder et al., Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jbiomech www.JBiomech.com Journal of Biomechanics 0021-9290/$ - see front matter & 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jbiomech.2010.10.004 n Corresponding author at: Department of Functional Anatomy, Academic Center for Dentistry Amsterdam (ACTA), University of Amsterdam and VU University Amsterdam, Gustav Mahlerlaan 3004, Room 12N13, 1081 LA, Amsterdam, The Netherlands. Tel.: +31 20 59 80 887. E-mail addresses: g.renders@acta.nl (G.A.P. Renders), L.Mulder@tue.nl (L. Mulder), l.v.ruijven@acta.nl (L.J. van Ruijven), g.langenbach@acta.nl (G.E.J. Langenbach). 1 Passed away. Journal of Biomechanics 44 (2011) 402–407