Influence of intramedullary pressure on fluid flow in Haversian canals and lacuno-canalicular network

The seepage behavior of bone fluid is the main pathway of osteocyte metabolism, and the pore pressure, fluid velocity, and fluid shear stress generated by it are the main fluid flow stimuli perceived by mechanically sensitive osteocytes. However, the impact of intramedullary pressure (IMP) on the fluid behavior of interstitial fluid in bone remains unclear. The purpose of this study was to evaluate the effect of IMP on the fluid flow behavior in the Haversian canals and lacuno-canalicular network (LCN). This study established a multiscale finite element model of bone tissue based on the theory of poroelasticity, considering the interconnection of different pore scales such as bone marrow cavity, Haversian canals, and LCN. The effects of IMP frequency and amplitude on Haversian canal pore pressure (p_Hc) and flow velocity (v_Hc), as well as on LCN pore pressure (p_lc), flow velocity (v_lc), and fluid shear stress (τ), were analyzed. In this model, we assumed that IMP is a pulsating liquid pressure that is synchronized with arterial blood pressure and respiration, located within the bone marrow cavity and acting on the inner wall of bone tissue. We considered the stepwise conduction of pore pressure at different pore scales. As the initial pressure condition of the overall model, IMP was calculated to obtain p_Hc and v_Hc, while p_Hc was calculated as the initial pressure condition of the next scale model to obtain p_lc, v_lc, and τ. The results indicated that IMP had a significant impact on the fluid flow of bone. The p_Hc and p_lc significantly increased with the increase in IMP amplitude, and the frequency of IMP had a significant impact on the peak p_Hc over time. The multilevel pore model established in this study provides a more accurate analysis of the fluid flow behavior within bones, which is of great significance for a deeper understanding of bone internal force conduction and is crucial for a better understanding of bone adaptation based on IMP.