Manipulating load-induced fluid flow in vivo to promote bone adaptation

Mechanical stimulation is critical to maintaining bone mass and strength. Strain has been commonly thought of as the mechanical stimulus driving bone adaptation. However, numerous studies have hypothesized that fluid flow in the lacunar-canalicular system plays a role in mechanoadaptation. The role of fluid flow compared to strain magnitude on bone remodeling has yet to be characterized. This study aimed to determine the contribution of fluid flow velocity compared to strain on bone adaptation. We used finite element modeling to design in vivo experiments, manipulating strain and fluid flow contributions. Using a uniaxial compression tibia model in mice, we demonstrated that high fluid flow velocity results in significant bone adaptation even under low strain magnitude. In contrast, high strain magnitude paired with low fluid velocity does not trigger a bone response. These findings support previous hypotheses stating that fluid flow is the principal mechanical stimulus driving bone adaptation. Moreover, they give new insights regarding bone adaptative response and provide new pathways toward treatment against age-related mechanosensitivity loss in bone.