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Abstract
Non-destructive 3D micro-computed tomography (microCT) based finite element (microFE) models are used to estimate bone mechanical properties at tissue level. However, their validation remains challenging. Recent improvements in the quantification of displacements in bone tissue biopsies subjected to staged compression, using refined Digital Volume Correlation (DVC) techniques, now provide a full field displacement information accurate enough to be used for microFE validation. In this study, three specimens (two humans and one bovine) were tested with two different experimental set-ups, and the resulting data processed with the same DVC algorithm. The resulting displacement vector field was compared to that predicted by microFE models solved with three different boundary conditions (BC): nominal force resultant, nominal displacement resultant, distributed displacement. The first two conditions were obtained directly from the measurements provided by the experimental jigs, whereas in the third case the displacement field measured by the DVC in the top and bottom layer of the specimen was applied. Results show excellent relationship between the numerical predictions (x) and the experiments (y) when using BC derived from the DVC measurements (UX: y=1.07x−0.002, RMSE: 0.001mm; UY: y=1.03x−0.001, RMSE: 0.001mm; UZ: y=x+0.0002, RMSE: 0.001 mm for bovine specimen), whereas only poor correlation was found using BCs according to experiment set-ups. In conclusion, microFE models were found to predict accurately the vectorial displacement field using interpolated displacement boundary condition from DVC measurement.
Highlights
Bone tissue is a complex hierarchical material (Cowin, 2001)
The findings reported by Zauel et al (2006) suggest that homogeneous isotropic microCT based finite element (microFE) models is not reliable in predicting transverse displacement
The aim of this study was to determine the accuracy of microFE models, generated from micro-computed tomography (microCT) data, in predicting the displacements of cancellous bone specimens subjected to compression, when sufficiently accurate full-field displacement measurements are used for the validation, and appropriate boundary conditions are simulated
Summary
Bone tissue is a complex hierarchical material (Cowin, 2001). The interaction between bone mechanical stimuli and the biological function driven by the cell activity becomes more evident (Viceconti, 2012). The microCT based finite element (microFE) method has become a popular tool for non-destructive structural analysis of cancellous bone tissue (Hollister et al, 1994; van Rietbergen et al, 1995; Verhulp et al, 2008). The method involves the direct conversion of the 3D voxels of micro-computed tomography (microCT) images of the bone tissue (Feldkamp et al, 1989) into shaped and sized hexahedral elements. As microCT imaging has the ability to accurately resolve bone morphology in great detail (Bouxsein et al, 2010), specimenspecific microFE models that represent the structure of the specimen can be generated (Ulrich et al, 1998)
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