Orthotropic modelling of the skeletal system

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Title: Orthotropic modelling of the skeletal system
Authors: Martins Da Silva Geraldes, Diogo Miguel
Item Type: Thesis or dissertation
Abstract: The femur‘s shape, geometry and internal structure are the result of bone‘s functional adaptation to resist the mechanical environment arising from different daily activities. Many studies have attempted to explain how this adaptation occurs by embedding bone remodelling algorithms in finite element (FE) models. However, simplifications have been introduced to the representation of bone‘s material symmetry and mechanical environment. Trabecular adaptation to the shear stresses that arise from multiple load cases has also been overlooked. This thesis proposes a novel iterative 3D adaptation algorithm to predict the femur‘s material properties distribution and directionality of its internal structures at a continuum level. Bone was modelled as a strain-driven adaptive continuum with local orthotropic symmetry and optimised Young‘s and shear moduli. The algorithm was applied to the Multiple Load Case 3D Femur Model, a FE model of a whole femur, with muscles and ligaments spanning between the hip and knee joints included explicitly. Several artificial structures were included to allow for more physiological modelling of the femur‘s mechanical behaviour. Multiple load cases representing different instances of daily activities were considered. The model‘s positioning and applied inter-segmental loading were extracted from a validated musculo-skeletal model. The mechanical envelope produced by the FE model was matched up with published studies and the model‘s suitability as a platform for the prediction of bone adaptation was confirmed. The resulting material properties distributions were compared against CT data of a human femur specimen and published studies. Furthermore, the predicted directionality of the femur‘s internal structures was validated by comparison with micro CT data of the proximal and distal regions of the same specimen. It was concluded that the proposed model can reliably produce the observed optimised structures in the femur. It is recommended that multiple activities and different instances of each load case should be considered when attempting to model bone‘s adaptation. The final result of this work is a physiological orthotropic heterogeneous model of the femur. This method has the potential to be an invaluable tool in achieving a more thorough understanding of bone‘s structural material properties, improving the knowledge we have of its mechanical behaviour.
Issue Date: Nov-2012
Date Awarded: Mar-2013
URI: http://hdl.handle.net/10044/1/13813
DOI: https://doi.org/10.25560/13813
Supervisor: Phillips, Andrew
Department: Civil and Environmental Engineering
Publisher: Imperial College London
Qualification Level: Doctoral
Qualification Name: Doctor of Philosophy (PhD)
Appears in Collections:Civil and Environmental Engineering PhD theses

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