A validated specimen specific finite element model of vertebral body failure

Numerical models are widely used to evaluate the mechanical behaviour of vertebral bodies (VB)subject to different loading conditions. The validity of the vast majority of these is confined to the elastic region, and here good agreement with experimental data has been demonstrated. However this approach is poorly predictive of plastic failure. Thepresent study aims to address this limitation and simulate the onset of yield. Six porcine VBs (from C2 to C7) were dissectedfrom a spine specimen, potted in PMMA bone cement and Micro-CT imaged using a Nikon XT225 ST scanner (Nikon Metrology UK, Hertfordshire, UK). A compressive load was applied to each specimen with an Instron 5967, 30 kN materials testing machine (Instron, High Wycombe, UK) at a rate of 1000 N/min. Specimen-specific FE models of all specimens were created by segmenting and meshing the micro-CT images (ScanIP, Simpleware, UK), material properties were assigned from the grayscale value and the compression experiment was repeated in-silico. Conversion factors for the Young’s modulus (kE), the Yield stress (ky), the Tangent (ktan) and the density (kρ) were determined for the grayscale values to minimise the error between experimental and numerical load-displacement behaviour. This allowed an excellent match between experiment and simulation results. The difference between experimental and numeric results for vertical displacement was typically 1% at 2000 N, between 1.5 and 3 % for 4000 N and between 2 and 3% for 5000 N, the latter typically representing the onset of yield.In this study, a technique allowing the prediction of the load-displacement behaviour of VBs subject to compression was developed. The novelty in the proposed approach rests with the fact that the onset of yield, crucial in determining subsequent failure modes, can also be modelled. This paves the way for more accurate FEA models aimed at predicting the failure modes of the spine.