Meeting Abstract

8.1  Thursday, Jan. 3  Strain environment, bone histomorphology, and growth in the emu femur and tibiotarsus MAIN, Russell P; Cornell University rpm74@cornell.edu

A close relationship between skeletal form and mechanics has long been hypothesized. However, many studies have only examined these relationships in adult animals, while skeletal morphology is likely influenced by interactions between skeletal form and mechanics throughout ontogeny. This study examines relationships between in vivo bone strains, bone geometry, and histomorphology in the emu femur and tibiotarsus (TBT) at different ontogenetic stages. Bone strain data were collected from the femora and TBTs of emu as they ran on a treadmill and regional cortical distributions of peak axial strains, radial and circumferential strain gradients, and longitudinal strain rates related to regional patterns in cortical growth, porosity, remodeling, and collagen fiber orientation. The distributions of axial strains in the two bones were variable during stance resulting in few regional differences in strain rates, gradients, or peak tensile strains. Peak compressive strains, however, were significantly greater in the caudal-medial regions of both bones. Cortical thickness and periosteal growth rates did not differ regionally in either bone. Bone porosity also did not vary regionally or during ontogeny. Minimal remodeling was observed in the femur throughout ontogeny, but increased in some regions of the TBT. Collagen fiber orientations were consistent through growth and regionally uniform within each bone, with primarily transverse fibers in the femur and longitudinal fibers in the TBT, despite both bones having similar axial strain environments. Small regional differences in the axial strain parameters and the shear strains dominant in both bones are likely responsible for the weak relationships observed between bone histomorphology and mechanical strain environment.