title: Ex vivo simulation of in vivo strain distributions in the equine metacarpus.
abstract: The objective of this study was to examine several simple ex vivo loading conditions for the equine metacarpus, and to evaluate their ability to reproduce the mid-diaphyseal bone surface strain distributions previously reported in vivo at the walk and trot. Distributed axial compressive loads, and 9 different axial compressive point loads at -7.5 kN and -15 kN were applied to metacarpal-distal carpal bone preparations from 6 Thoroughbred horses, aged 1-5 years. The resulting dorsal, medial, palmar, and lateral mid-diaphyseal bone surface axial and shear strains were compared with previously reported in vivo surface strain distributions using a root mean square error (RMSE) protocol. The effects of loading condition and load magnitude on RMSE were assessed with a mixed-model analysis of variance. There were significant differences between loading conditions, and, in most cases, between load magnitudes, in the fit of the ex vivo to the in vivo strain distributions. In vivo mid-diaphyseal bone surface strain distributions at the walk can be well approximated ex vivo by a distributed axial compressive load, or by a point load positioned 0.5 cm medial to the sagittal midline, at -7.5 kN loads. In vivo mid-diaphyseal bone surface strain distributions at the trot can be well approximated by the -15 kN loads applied to the same locations. These simplified loading conditions can be used in designing biologically relevant loading protocols for ex vivo mechanical testing studies, as well as in developing boundary conditions for finite element analysis. As such, these loading conditions may be considered as tools to be used as a means of replicating in vivo loading conditions during the initial design and testing stages in the development of fracture fixation devices, as well as in the theoretical mechanical analysis of the metacarpal structure.
authors.affiliation: Department of Anatomy, Physiology, and Cell Biology, School of Veterinary Medicine, University of California, Davis 95616, USA.
authors.forename: C M
authors.initials: CM
authors.lastname: Les
authors.forename: S M
authors.initials: SM
authors.lastname: Stover
authors.forename: K T
authors.initials: KT
authors.lastname: Taylor
authors.forename: J H
authors.initials: JH
authors.lastname: Keyak
authors.forename: N H
authors.initials: NH
authors.lastname: Willits
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D002350:Carpus, Animal / Q000502:physiology*; D005260:Female; D005684:Gait; D006736:Horses / Q000502:physiology*; D008297:Male; D008663:Metacarpus / Q000502:physiology*; D008954:Models, Biological; D012016:Reference Values; D016474:Weight-Bearing