Estimates of the peak pressures in bone pore water

The maximum pore fluid pressures due to uniaxial compression are determined for both the vascular porosity (Haversian and Volkmann's canals) and the l acunar-canalicular porosity of live cortical bone. It is estimated that the peak pore water pressure will be 19 percent of the applied axial stress in the vascular porosity and 12 percent of the applied axial stress in the la cunar-canalicular porosity for an impulsive step loading. However, the esti mated relaxation time for the vascular porosity (1.36 mu s) is three orders of magnitude faster than that estimated for the lacunar-canalicular porosi ty (4.9 ms). Thus, under physiological loading, which has a stress rise tim e generally larger than I ms, pressures higher than the vascular pressure c annot be sustained in the vascular porosity due to the swift pressure relax ation in this porosity (unless the fluid drainage through the boundary is o bstructed). The model also predicts a slight hydraulic stiffening of the bu lk modulus due to longer draining time of the lacunar-canalicular porosity. The undrained bulk modulus is 6 percent higher than the drained bulk modul us in this case.