Effects of osteocyte orientation on loading-induced interstitial fluid flow and nutrient transport in bone

Changes in osteocyte spatial arrangement and orientation that are associated with aging and certain bone diseases have attracted much attention. The purpose of the current study is to demonstrate effects of osteocyte orientation on the deflection of fluid flow in bone by modeling osteocytes rotated by 0 & DEG;, 30 & DEG;, 45 & DEG;, 60 & DEG;, and 90 & DEG; relative to the bone fluid flow axis. The lacuno-canalicular network was assumed to be regularly arranged and uniformly distributed and the osteon was defined as a representative cubic periodic unit cell (CPUC) at the microscale level. Calculation of canaliculi number and distribution around the osteocyte enabled estimation of osteon microstructural parameters toward the establishment of an osteon poroelastic finite element model to investigate specific loading-induced interstitial fluid flow and nutrient transport parameters in the bone under different boundary conditions and loading types. The results showed that osteocyte orientation under loading conditions approximating normal physiological loads markedly influenced predicted osteon maximum fluid pressure (p), fluid velocity (v), and fluid shear stress (tau) values. Moreover, results showing the nonuniform distribution of p and tau values within the osteon wall indicated that osteocyte orientation and canaliculi three-dimensional distribution were important parameters for predicting the degree of anisotropy of lacuno-canalicular system permeability, of anisotropy of lacuno-canalicular system permeability, while also demonstrating that osteocyte orientation had little effect on nutrient transport. Furthermore, loading type and lacuno-canalicular tortuosity effects on osteon fluid flow were greater than osteocyte orientation-associated effects. The results of this study may help researchers accurately quantify bone fluid flow behavior to enhance understanding of mechanotransduction mechanisms in bone.