Background: Bone remodeling in the elderly is no longer balanced. As a result, the morphologies and mechanical properties of bone at different scales will change. These changes would affect the mechanical responses of bone, which might exacerbate the imbalance of bone remodeling and even cause age-related bone diseases.
Methods: Considering those changes, multiscale finite element (FE) models of bone in the young and the elderly were developed that included macroscale (proximal femur), mesoscale (cortical bone), microscale (Haversian system) and sub-microscale (osteocyte-lacuna-canaliculus-extracellular matrix system, OLCES). The stress and strain distributions at different scales and transmissions among different scales were investigated.
Results: The stresses of the elderly at macroscale, mesoscale and microscale were higher than those in the young by 23.7%, 62.5% and 8.0%, respectively, and the stresses of the elderly and the young at sub-microscale were almost the same. The strain of the elderly at macroscale, mesoscale, microscale and sub-microscale were higher than those in the young by 48.6%, 56.8%, 11.9% and 25.1%, respectively. The stress and strain transmission rates (ηand η) from mesoscale to microscale were decreased by 1.8%, and 2.5% than those from macroscale to mesoscale in the elderly, respectively; but increased by 13.8%, and 4.7% in the young, respectively. η from microscale to sub-microscale in the elderly was higher than that in the young by 21.3%.
Conclusions: Degeneration of cortical bone mechanical property in the elderly causes increases in stress and strain at macroscale and mesoscale. The reduction of lacunar number in the elderly is not conducive to the mechanical transmission from mesoscale to microscale. The differences in stress and strain at microscale between the young and the elderly are smaller than those at macroscale or mesoscale. The strain stimulus sensed by osteocyte in the elderly is not weakened compared with that in the young.
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