Ex vivo simulation of in vivo strain distributions in the equine metacarpus.

The research focuses on analyzing different loading conditions on horse metacarpal bones to simulate the strain experienced during walking and trotting. The outcomes of this study could help design relevant load protocols for mechanical testing studies and finite element analysis, and recreate in vivo conditions in the initial phases of testing and designing fracture fixation devices.

Study Overview

• The study aimed to replicate and analyze the strain distribution experienced by the metacarpal bones of horses during walking and trotting by creating several ex vivo loading conditions. This was done by applying distributed axial compressive loads, or compressive point loads at -7.5 kN and -15 kN, on metacarpal-distal carpal bone preparations from 6 Thoroughbred horses aged 1-5 years.

Methodology

• The dorsal, medial, palmar, and lateral mid-diaphyseal bone surface axial and shear strains were then compared with previously reported in vivo surface strain distributions using a root mean square error (RMSE) protocol.
• Using mixed-model analysis of variance, the study analyzed the effects of load magnitude and loading conditions on RMSE to understand whether the strain distributions could be well approximated ex vivo.

Findings

• There existed significant differences between loading conditions and in most cases, between load magnitudes, regarding the suitability of the ex vivo to the in vivo strain distributions.
• The researchers found that strain distributions experienced during walking could be accurately approximated by utilizing 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 the ex vivo setting.
• The same in vivo strain distributions experienced while trotting could be replicated by applying -15 kN loads at the same locations in an ex vivo environment.

Implications

• The findings validate these ex vivo loading conditions as an efficient tool that can be utilized in the initial phases of designing and testing fracture fixation devices, and for theoretical mechanical analysis of the metacarpal structure.
• This approach could also be used to develop relevant boundary conditions for finite element analysis and to plan mechanically relevant load protocols for ex vivo testing studies.