Clinical CT-based assessment of trabecular bone shear modulus using nonlinear finite element modelling

Abstract

Osteoporosis is an age-related bone disease causing increased bone loss and enhanced bone fragility and fracture-risk. Osteoporotic imaging plays important roles in quantitative assessment of bone quality, strength, and fracture-risk, and plays important roles in evaluating disease severity and treatment planning. High-resolution CT imaging on dedicated scanners is used for finite element (FE) analysis (FEA) of trabecular bone (Tb) microstructure. However, Tb micro FEA on clinical CT imaging is challenging and yet to be established due to difficulties with binary segmentation of Tb at relatively low-resolution. Here, we present a CT-based material density adjusted nonlinear FEA method for computing Tb shear modulus, while avoiding explicit segmentation of Tb micro-network. FE meshes were constructed over upright cylindrical VOIs derived from CT scans after alignment of tibia axes with the image axes. Image voxels were modelled as cubical mesh elements, and their mechanical properties were derived from their CT-derived ash-density. Tibiofemoral direction was used to define shear loading directions. The method was optimized and evaluated using clinical CT and micro-CT scans of cadaveric ankle specimens (n = 10). FEA stress propagation along Tb microstructures and nominal leakages over marrow space was confirmed. CT-derived shear modulus values were highly reproducible (ICC = 0.98) and high linear correlation (r ≥ 0.83) was observed with micro-CT-derived reference values. Nonlinear FEA using clinical CT imaging will broaden the scope of micro-mechanical analysis of Tb network at relatively low in vivo resolution alleviating the need for binary segmentation of Tb, while accounting for microdistribution of bone minerals.