Whereas diffusion has been shown to be the major contributing mechanism for mass transfer in the extravascular spaces of organs and soft tissues, it is unlikely that diffusion alone can account for sufficient molecular transport in the porous yet relatively impermeable tissue of cortical bone. An alternate mechanism for such mass transfer is intrinsic to the functional role of cortical bone in transferring loads within the musculoskeletal system. Namely, it has been proposed that mechanical loading causes minute deformations within the poroelastic tissue of cortical bone, resulting in extravascular fluid displacements. This biophysical phenomenon is referred to as load-induced interstitial or extravascular fluid flow.
In order to establish the role of convective transport mechanisms for maintenance of healthy bone metabolism and to investigate the potential role of convective transport (via load-induced fluid flow) for processes associated with functional adaptation, we developed a theoretical osteon model based on finite element methods. A study designed to simulate short term transport (circa 1 second or half a gait cycle) in a single osteon corroborated the hypothesis that diffusion alone is insufficient for molecular transport between the blood supply and remotely lying bone cells. Simulations of long term transport (circa one day) showed that convection via load-induced flow can be expected to improve this transport significantly.