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Abstract
Osteoporosis-related vertebral fractures represent a major public health problem.
Anatomy-specific CT-based finite element (FE) simulations could help in identifying
which vertebrae have the highest risk of fracture and thus help to decide upon the
need for vertebroplasty or other surgical intervention. Continuum level FE simulations
require effective macroscopic material properties of the vertebra. Micro finite element
(microFE) models can be used to circumvent the difficult experiments that are necessary
to determine these effective properties. From a quantitative point of view, these
microFE models depend critically on the chosen trabecular tissue properties. The question
remains whether linear elastic microFE models of vertebral trabecular bone with and
without specimen-specific tissue properties yield similar results as non-destructive
macroscopic experiments under moist conditions. microFE models were set up from microCT
scans with specimen-specific or average tissue moduli measured by nanoindentation
under dry and wet testing conditions. Non-destructive macroscopic mechanical compression,
tension and torsion tests were performed. Experimentally obtained and simulated apparent
stiffnesses were compared. No significant difference was found when comparing microFE
simulations with wet tissue properties and experiments for tension, compression and
torsion (p>0.05). Concordance correlation coefficients were high for tension and compression
(r(c)(wet)>or=0.96,p<0.05) but moderate for torsion (r(c)(wet)=0.81,p<0.05). The agreement
between simulation and experiment was confirmed by Bland-Altman plots which showed
mean differences <or=10MPa. Surprisingly, the agreement between simulation and experiment
was not reduced by using an average tissue modulus. The results indicate that valid
microFE models can be set up using average tissue properties obtained under wet indentation
conditions.
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