Cortical bone periosteocytic space morphology can affect osteocyte-level mass flows and shear stresses

This work investigates the interstitial fluid flow through the osteocytic-lacunar-canalicular system of cortical bone. The study assumes that it is a dynamic environment that undergoes continuous morphological changes. The model employed is a typical canaliculus (an annular region filled with a gel-like matrix that has a characteristic external diameter of 200 nm and a characteristic length of 35 urn which connects two bone cells - osteocytes). Two canalicular morphological changes are investigated - local constrictions and permeability alterations. The continuity and Brinkman equations are solved for this model, analytically and numerically. The results indicate that pericellular morphology modifications can significantly alter mass flows and shear stresses around osteocytes. Similar mechanisms, if present in vivo, may lead to changes in solute fluxes and in the loads applied to the cells and affect the manner in which osteocytes perceive their environment, react and result in bone adaptation processes. Furthermore, they may provide further explanation to the fundamental paradox that the strains applied to whole bone (tissue-level) in vivo are much smaller than the strains necessary to activate bone-cell signaling in cell cultures.