Multi-scale modeling of the human vertebral body: comparison of micro-CT based high-resolution and continuum-level models.

The overall goal of this study was to assess the mechanistic fidelity of continuum-level finite element models of the vertebral body, which represent a promising tool for understanding and predicting clinical fracture risk. Two finite element (FE) models were generated from micro-CT scans of each of 13 T9 vertebral bodies--a micro-FE model at 60-micron resolution and a coarsened, continuum-level model at 0.96-mm resolution. Two previously-reported continuum-level modulus-density relationships for human vertebral bone were parametrically varied to investigate their effects on model fidelity using the micro-CT models as a gold standard. We found that the modulus-density relation, particularly that assigned to the peripheral bone, substantially altered the regression coefficients, but not the degree of correlation between continuum and micro-FE predictions of whole-vertebral stiffness. The major load paths through the vertebrae compared well between the continuum-level and micro-FE models (von-Mises distribution), but the distributions of minimum principal strain were notably different. We conclude that continuum-level models provide robust measures of whole-vertebral behavior, describe well the load transfer paths through the vertebra, but provide strain distributions that are markedly different than the volume-averaged micro-scale strains. Appreciation of these multi-scale differences should improve interpretation of results from these sorts of continuum models and may improve their clinical utility.