Gradient mechanical environments modulate intra-osteonal fluid flow: a three-dimensional finite element study.

Objective: Interstitial fluid flow within the osteonal lacunar-canalicular system (LCS) is crucial for osteocyte mechanotransduction and bone remodeling. This study aims to develop a three-dimensional finite element model of an osteon with gradient-varying boundary conditions to systematically investigate how mechanical loading, outer wall constraints, and pulsatile blood pressure modulate intra-osteonal fluid flow. Methods: This study constructs a three-dimensional finite element model to systematically analyze the dynamic responses of fluid flow behavior under gradient boundary conditions. Gradient parametric analyses were performed by varying: (1) axial strain amplitudes (250-5000 με) to simulate different activity levels; (2) radial displacement constraints at the outer wall (0- 0.042 μm) to represent confinement by surrounding tissues; and (3) pulsatile blood pressure amplitudes (A = 0-2.5) at the inner wall to mimic physiological to hypertensive conditions. The resulting pore pressure, fluid velocity, and fluid shear stress (FSS) distributions were analyzed. Results: All parameters exhibited axisymmetric distributions. Peak pore pressure, fluid velocity, and FSS increased nearly linearly with strain magnitude, ranging from 1.7×10 Conclusion: The gradient boundary condition approach effectively quantifies the differential and synergistic effects of mechanical load, structural constraint, and vascular pressure on the osteonal fluid environment. These findings provide a quantitative framework for understanding mechanotransduction in bone and may inform clinical strategies for managing bone adaptation and disease.