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

The mechanical properties of bone estimated by micro-finite element (mu FE) analysis on the basis of in vivo micro-MR images (mu MRIs) 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 mu FE-derived mechanical parameters obtained from mu MRIs at 160 mu m isotropic voxel size now achievable in vivo with those derived from 25 pm isotropic (reference) mu CT images of 30 cadaveric tibiae from 15 donors (4 females and 11 males, aged 55-84 years). Elastic and shear moduli estimated from 5 mm(3) subvolumes of trabecular bone (TB) derived from mu MRIs were significantly correlated with those derived from volume-matched reference mu CT images (R(2) = 0.60-0.67). Axial stiffness of whole-bone sections (including both cortical and trabecular compartments) derived from mu MR-based models were highly correlated (R(2) = 0.85) with those from high-resolution reference images. Further, mu FE models generated from mu CT images after downsampling to lower resolutions relevant to in vivo mu MRI (100-160 pm) showed mechanical parameters to be strongly correlated (R(2)>0.93) with those derived at reference resolution (25 pm). Incorporation of grayscale image information into the mu MR-based mu FE 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 mu FE analysis from mu MRIs obtainable at in vivo resolution. (C) 2010 Elsevier Inc. All rights reserved.