title: Knee loading dynamically alters intramedullary pressure in mouse femora.
abstract: Dynamic mechanical loads have been known to stimulate bone formation. Many biophysical factors such as number of daily loading cycles, bone strain, strain-induced interstitial fluid flow, molecular transport, and modulation of intramedullary pressure have been considered as potential mediators in mechanotransduction of bone. Using a knee loading modality that enhances anabolic responses in mouse hindlimb, we addressed a question: Do oscillatory loads applied to the knee induce dynamic alteration of intramedullary pressure in the femoral medullary cavity? To answer this question, mechanical loads were applied to the knee with a custom-made piezoelectric loader and intramedullary pressure in the femoral medullary cavity was measured with a fiber optic pressure sensor. We observed that in response to sinusoidal forces of 0.5 Hz and 10 Hz, pressure amplitude increased up to 4-N loads and reached a plateau at 130 Pa. This amplitude significantly decreased with a loading frequency above 20 Hz. To confirm alteration of intramedullary pressure, real-time motion of microparticles in a glass tube inserted to the femoral medullary cavity ex vivo was visualized. Taken together, these data reveal that knee loading dynamically alters intramedullary pressure as a function of loading intensities and frequencies.
authors.affiliation: Department of Biomedical Engineering Indiana University - Purdue University Indianapolis, Indianapolis, IN 46202, USA.
authors.forename: Ping
authors.initials: P
authors.lastname: Zhang
authors.forename: Min
authors.initials: M
authors.lastname: Su
authors.forename: Yunlong
authors.initials: Y
authors.lastname: Liu
authors.forename: Andrew
authors.initials: A
authors.lastname: Hsu
authors.forename: Hiroki
authors.initials: H
authors.lastname: Yokota
mesh_terms: D000818:Animals; D005260:Female; D005269:Femur / Q000502:physiology*; D006614:Hindlimb / Q000502:physiology*; D007596:Joints / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D008863:Microspheres; D013314:Stress, Mechanical; D016474:Weight-Bearing