title: Elastic modulus varies along the bovine femur.
abstract: Bone is a heterogeneous material and its mechanical properties vary within the body. Variations in the mechanical response of different bone samples taken from the body cannot be fully explained by only looking at local compositional information at the tissue level. Due to different states of the stress within bones, one might expect that mechanical properties change over the length of a bone; this has not been a matter of systematic research in previous studies. In this study, the distribution of the tissue elastic modulus along the bovine femur is investigated using three-point bending tests. Two bovine femora were split to seven and eight blocks from proximal to distal metaphysis, respectively and twenty beam shaped bone samples were extracted and tested from each block. Based on our findings, the longitudinal elastic modulus follows a gradient pattern along the bovine femur as it increases along the bone from the proximal metaphysis to mid-diaphysis and then decreases toward the distal metaphysis again. Considering long bones to be subjected to bending loads, this mechanism alters the bone structure to support load in the regions where it is needed; similar as outlined by Wolff's law. In another part of this study, microfocus X-ray computed tomography (μCT) was found unable to predict the same trend of changes for the elastic modulus via image-based or density-based elastic moduli calculations. This is insofar important as conventional finite element models of bone are often directly shaped from μCT data. Based on our findings, it seems that current computed tomography based finite element models generated in this manner may not adequately capture the local variation of material behavior of bone tissue, but this may be improved by considering the changes of the elastic modulus along the femur.
authors.affiliation: Bioengineering Science Research Group, Engineering Sciences, Faculty of Engineering and the Environment, University of Southampton, Southampton SO17 1BJ, UK. Electronic address: Nobakhti.s@husky.neu.edu.
authors.forename: Sabah
authors.initials: S
authors.lastname: Nobakhti
authors.affiliation: μ-VIS X-Ray Imaging Centre, Faculty of Engineering and the Environment, University of Southampton, Southampton SO17 1BJ, UK. Electronic address: O.Katsamenis@soton.ac.uk.
authors.forename: Orestis L
authors.initials: OL
authors.lastname: Katsamenis
authors.affiliation: Supply Chain and Information Management Group, D'Amore-McKim School of Business, Northeastern University, 360 Huntington Avenue, Boston, MA 02115, USA. Electronic address: N.zaarour@northeastern.edu.
authors.forename: Nizar
authors.initials: N
authors.lastname: Zaarour
authors.affiliation: Bioengineering Science Research Group, Engineering Sciences, Faculty of Engineering and the Environment, University of Southampton, Southampton SO17 1BJ, UK. Electronic address: G.limbert@soton.ac.uk.
authors.forename: Georges
authors.initials: G
authors.lastname: Limbert
authors.affiliation: Bioengineering Science Research Group, Engineering Sciences, Faculty of Engineering and the Environment, University of Southampton, Southampton SO17 1BJ, UK; Institute of Lightweight Design and Structural Biomechanics, Vienna University of Technology, Getreidemarkt 9, A-1060 Vienna, Austria. Electronic address: Philipp.thurner@tuwien.ac.at.
authors.forename: Philipp J
authors.initials: PJ
authors.lastname: Thurner
mesh_terms: D000818:Animals; D002417:Cattle; D055119:Elastic Modulus; D005269:Femur / Q000502:physiology*; D020342:Finite Element Analysis; D013314:Stress, Mechanical; D014057:Tomography, X-Ray Computed
keywords: Cortical bone mechanics; Micro-CT gray-level to elastic modulus conversion; Micro-computed tomography