Combined implications of bone′s structural and material impairment following renal transplantation assessed by μMRI based finite-element modeling

INTRODUCTION: High-resolution magnetic resonance imaging (μMRI) based micro-finite-element (μFE) modeling at peripheral sites is emerging as an attractive means to assess short-term alterations in bone’s mechanical competence caused by disease or in response to intervention [1, 2]. In this approach, subject-specific bone’s 3D micro-architecture derived from in-vivo μMRI is taken as input to a finite-element model. Ordinarily, bone tissue is assumed to have a constant elastic modulus (~15 GPa) because μMRI-based in-vivo measures of bone mineralization are not yet available. As a consequence, μMRI-based μFE analysis is not sensitive to possible changes in bone-mineral density (BMD) observed in patient populations such as those with end-stage renal disease (ESRD) following renal transplantation (RTxp) [3]. On the other hand, BMD alone correlates poorly with fracture risk [4, 5], which is markedly greater in ESRD than in general population [6, 7]. The purpose of this study is to examine the feasibility of generating μMRI-based μFE models with subject-specific tissue modulus by incorporating peripheral quantitative computed tomography (pQCT)-derived cortical and trabecular bone BMD measures, thereby making the approach suitable for capturing the temporal variations in bone’s mechanical competence resulting from simultaneous structural and material alterations. Towards this goal, we computed the cortical and trabecular bone stiffness of the distal tibia in RTxp recipients as part of an ongoing longitudinal study via a μMRI-based μFE modeling with subject-specific tissue modulus and compared the results to those obtained when a constant tissue modulus is assumed.