Micro Finite Element models of the vertebral body: Validation of local displacement predictions

PLoS One. 2017 Jul 11;12(7):e0180151. doi: 10.1371/journal.pone.0180151. eCollection 2017.

Abstract

The estimation of local and structural mechanical properties of bones with micro Finite Element (microFE) models based on Micro Computed Tomography images depends on the quality bone geometry is captured, reconstructed and modelled. The aim of this study was to validate microFE models predictions of local displacements for vertebral bodies and to evaluate the effect of the elastic tissue modulus on model's predictions of axial forces. Four porcine thoracic vertebrae were axially compressed in situ, in a step-wise fashion and scanned at approximately 39μm resolution in preloaded and loaded conditions. A global digital volume correlation (DVC) approach was used to compute the full-field displacements. Homogeneous, isotropic and linear elastic microFE models were generated with boundary conditions assigned from the interpolated displacement field measured from the DVC. Measured and predicted local displacements were compared for the cortical and trabecular compartments in the middle of the specimens. Models were run with two different tissue moduli defined from microindentation data (12.0GPa) and a back-calculation procedure (4.6GPa). The predicted sum of axial reaction forces was compared to the experimental values for each specimen. MicroFE models predicted more than 87% of the variation in the displacement measurements (R2 = 0.87-0.99). However, model predictions of axial forces were largely overestimated (80-369%) for a tissue modulus of 12.0GPa, whereas differences in the range 10-80% were found for a back-calculated tissue modulus. The specimen with the lowest density showed a large number of elements strained beyond yield and the highest predictive errors. This study shows that the simplest microFE models can accurately predict quantitatively the local displacements and qualitatively the strain distribution within the vertebral body, independently from the considered bone types.

MeSH terms

  • Animals
  • Elastic Modulus / physiology
  • Finite Element Analysis*
  • Lumbar Vertebrae / physiology
  • Stress, Mechanical
  • Swine
  • Thoracic Vertebrae / physiology*

Grant support

This study was partially supported by Sheffield Hospital Charity (grant number: 141515-1; ED, MV; http://www.sheffieldhospitalscharity.org.uk/), the Engineering and Physical Sciences Research Council (MultiSim project, grant number: EP/K03877X/1; MV; https://www.epsrc.ac.uk/), the Royal Society (grant number: RG130831, GT; grant number: RG150012, ED; https://royalsociety.org/), and the European Society of Biomechanics (ESB mobility award 2014; VD; https://esbiomech.org/). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.