Computational biomechanics of the distal tibia from high-resolution MR and micro-CT images

The mechanical properties of bone estimated by micro-finite element (μFE) analysis on the basis of invivo micro-MR images (μMRIs) of the distal extremities provide a new tool for direct assessment of the mechanical consequences of intervention. However, the accuracy of the method has not previously been investigated. Here, we compared μFE-derived mechanical parameters obtained from μMRIs at 160 μm isotropic voxel size now achievable in vivo with those derived from 25 μm isotropic (reference) μCT images of 30 cadaveric tibiae from 15 donors (4 females and 11 males, aged 55–84 years). Elastic and shear moduli estimated from 5 mm3 subvolumes of trabecular bone (TB) derived from μMRIs were significantly correlated with those derived from volume-matched reference μCT images (R2 = 0.60–0.67). Axial stiffness of whole-bone sections (including both cortical and trabecular compartments) derived from μMR-based models were highly correlated (R2 = 0.85) with those from high-resolution reference images. Further, μFE models generated from μCT images after downsampling to lower resolutions relevant to in vivo μMRI (100–160 μm) showed mechanical parameters to be strongly correlated (R2 > 0.93) with those derived at reference resolution (25 μm). Incorporation of grayscale image information into the μMR-based μFE model yielded slopes closer to unity than binarized models (1.07 ± 0.15 vs. 0.71 ± 0.11) when correlated with reference subregional elastic and shear moduli. This work suggests that elastic properties of distal tibia can be reliably estimated by μFE analysis from μMRIs obtainable at in vivo resolution.