| Recent research effort in bone remodeling has been directed toward describing interstitial fluid flow in the lacuno-canalicular system and its potential as a cellular stimulus. Regardless of the precise contents of the mechanotransduction "black box", it seems clear that the fluid flow on which the remodeling is predicated can not occur under static loading conditions. In an attempt to help continuum remodeling simulations catch up with cellular and subcellular research, this research presents a simple but novel strain rate driven remodeling algorithm for density allocation and principal material direction rotations.; An explicit finite element code was written, parallelized and deployed at the San Diego Supercomputer Center which implements the remodeling algorithm. Remodeling occurs at discrete, periodically occurring time steps. Cortical and trabecular apparent density are updated based on local strain rate, and realignment of principal material directions is driven by the local stress tensor. Stress is calculated using a path-dependent hypoelastic constitutive law, formulated with the Jaumann stress rate. The testbed for this algorithm is the proximal femur. Loading conditions were linearized around instants of peak rate of application during normal gait and stair climbing, assumed to occur with sufficient frequency to exceed the threshold cycle number for cellular remodeling activation.; Results indicate that a target strain rate for this dynamic approach is ∣ D*I ∣ = 1.7%/sec which seems reasonable when compared to observed strain rates. The dynamic stimulus, hypoelastic constitutive law algorithm produces unique and convergent equilibrium predictions for remodeling parameters in the stable range. Remodeling simulations indicate that a morpho-mechanically realistic three dimensional bone can be synthesized by applying a few dynamic loads at the envelope of common daily physiological rates, even in the absence of a static loading component.; This work constitutes the only known large-scale remodeling simulations of the proximal femur which includes the effects of both density changes and orthotropic realignment, and the first known remodeling simulation employing a dynamic remodeling stimulus. Macroscopic three dimensional analyses such as this may be of benefit to surgeons and clinicians seeking a greater understanding of the biomechanical effects of bone cysts, tumors, stress fracture, microgravity environments, and osteoporosis. |
