title: Consideration of multiple load cases is critical in modelling orthotropic bone adaptation in the femur.
abstract: Functional adaptation of the femur has been investigated in several studies by embedding bone remodelling algorithms in finite element (FE) models, with simplifications often made to the representation of bone's material symmetry and mechanical environment. An orthotropic strain-driven adaptation algorithm is proposed in order to predict the femur's volumetric material property distribution and directionality of its internal structures within a continuum. The algorithm was applied to a FE model of the femur, with muscles, ligaments and joints included explicitly. Multiple load cases representing distinct frames of two activities of daily living (walking and stair climbing) were considered. It is hypothesised that low shear moduli occur in areas of bone that are simply loaded and high shear moduli in areas subjected to complex loading conditions. In addition, it is investigated whether material properties of different femoral regions are stimulated by different activities. The loading and boundary conditions were considered to provide a physiological mechanical environment. The resulting volumetric material property distribution and directionalities agreed with ex vivo imaging data for the whole femur. Regions where non-orthogonal trabecular crossing has been documented coincided with higher values of predicted shear moduli. The topological influence of the different activities modelled was analysed. The influence of stair climbing on the properties of the femoral neck region is highlighted. It is recommended that multiple load cases should be considered when modelling bone adaptation. The orthotropic model of the complete femur is released with this study.
authors.affiliation: Structural Biomechanics, Department of Civil and Environmental Engineering, Skempton Building, Imperial College London, London, UK. geraldes@imperial.ac.uk.|Biomechanics Group, Department of Mechanical Engineering, City and Guilds Building, Imperial College London, London, UK. geraldes@imperial.ac.uk.
authors.forename: Diogo M
authors.identifier: 0000-0002-0320-6368
authors.initials: DM
authors.lastname: Geraldes
authors.affiliation: Structural Biomechanics, Department of Civil and Environmental Engineering, Skempton Building, Imperial College London, London, UK.|Department of Mechanical Engineering, Sir Frederick Mappin Building, Mappin Street, The University of Sheffield, Sheffield, UK.|INSIGNEO Institute for In Silico Medicine, The Pam Liversidge Building, The University of Sheffield, Sheffield, UK.
authors.forename: Luca
authors.identifier: 0000-0003-1402-5359
authors.initials: L
authors.lastname: Modenese
authors.affiliation: Structural Biomechanics, Department of Civil and Environmental Engineering, Skempton Building, Imperial College London, London, UK.
authors.forename: Andrew T M
authors.identifier: 0000-0001-6618-0145
authors.initials: AT
authors.lastname: Phillips
mesh_terms: D000203:Activities of Daily Living; D000222:Adaptation, Physiological; D015519:Bone Density / Q000502:physiology; D055119:Elastic Modulus; D005269:Femur / Q000502:physiology*; D020342:Finite Element Analysis; D006801:Humans; D008954:Models, Biological; D016138:Walking / Q000502:physiology; D016474:Weight-Bearing / Q000502:physiology
keywords: Biomechanics; Bone adaptation; Bone remodelling; Daily living activities; Femur; Finite element modelling; Multiple load cases; Musculoskeletal; Orthotropic; Shear modulus; Young’s modulus