Tissue Strain Transduction and Amplification at the Osteocyte as a Result of Microstructural Changes in the Bone Matrix

It is well known that bone adapts to changes in its mechanical environment and that this adaptation is controlled at the cellular level through the coordinated actions of osteoblasts, osteocytes, and osteoclasts. Osteocytes make up over 90% of all bone cells [1], and are hypothesized to be the mechanosensors in bone [2] that mediate the effects of bone loading through their extensive communication network. The application of force to the skeletal system produces several potential stimuli for osteocyte function including hydrostatic pressure, fluid flow-induced shear stress, and bone tissue strain. Previously, the basis used for studying the stimulatory effects of mechanical strain on bone cell biological responses in vitro has been the direct measurement of bone strain in humans during various physical activities [3,4]. The limitation of applying this strain magnitude data to cells in vitro, however, is that the in vivo strain gage measurements represent continuum measures of bone deformation. Clearly, at the spatial level of bone cells, cortical bone is not a continuum and microstructural inhomogeneities will result in inhomogeneous microstructural strain fields; local tissue strains will be magnified in association with microstructural features [5,6]. It is unclear as to how much of these magnified strains will be directly transmitted to the osteocyte itself. Additionally, if the osteocyte has the ability to alter its perilacunar environment [7], it is unknown what effect do these changes have on the strain that is transmitted to the osteocyte and cell process.