Meeting Abstract
88.1 Wednesday, Jan. 7 Changes in cortical bone stiffness and geometry in response to applied load vary with age in female mice MAIN, R.P.*; LYNCH, M.E.; SCHMICKER, T.L.; VAN DER MEULEN, M.C.H.; Cornell University; Cornell University; Cornell University; Cornell University rpm74@cornell.edu
A variety of vertebrate taxa maintain functional bone strain levels within a certain healthy range through bone modeling and remodeling. As humans age, our bones are believed to become less sensitive to the strains induced by mechanical loads, resulting in resorption to achieve what the osteocytes perceive as healthy strains. This process results in decreased bone stiffness, and hence increased strains and a greater likelihood of fracture during functional loading. To examine the sensitivity of the response of mammalian bone to functional strain levels with age and the effects of this response on bone stiffness, we applied non-invasive loads to the tibiae of 6wk, 10wk, 16wk, and 26wk old female C57Bl/6 mice for 2wks. The right tibiae served as non-loaded controls. Bone stiffness was measured as the relationship between applied load and bone strain at the medial tibial midshaft. Initial bone stiffness and changes in stiffness associated with the loading protocol were related to bone geometry and mineral content. Experimental load levels varied between groups but corresponded to +1200 microstrain tissue deformations at the medial midshaft. Following 2wks of loading, stiffness changed significantly between the loaded and control limbs in only the 10wk and 16wk old groups where, surprisingly, the control tibiae were stiffer than the loaded tibiae. Although no stiffness differences occurred with age in the control tibiae, the loaded tibiae of the 6wk old mice were significantly stiffer than the loaded tibiae in all older groups. Similarly, the loaded tibiae of the 10wk old mice were stiffer than those of the 26wk old mice. Thus, stiffness and, likely, geometric and mineral responses to applied load are age-dependent in female mouse tibiae.
