Converging-diverging shape configuration of the diaphysis of equine third metacarpal bone through computer-aided design

Abstract

The shape of the diaphysis of the equine third metacarpal bone (MC3) has a substantial influence on its mechanical properties. The connection between bone shape and bone adaptive responses is likely to be useful in forecasting the response of MC3 to a training program as well as predicting its internal loading. A variety of geometrical parameters including cortical area (A), width of dorsal cortex (D), palmar cortex (P), medial cortex (M), lateral cortex (L), medulla in dorsopalmar plane (Md), and medulla in lateromedial plane (M1) in three main cross sections (slices) within the diaphysis of 27 Thoroughbred horses aged from 12 hours to 15 years were measured using computer-aided-design and were analysed using t-tests and ANOVA test (performed in statistical MATLAB codes). Shape indices ([D/P] × [(D+P)/ Md]), H (D+Md +P), and V (M+ M1 +L) were also calculated. For all the samples, the values were plotted for a slice taken from around the mid-point of the shaft, and from two others taken at 3 cm proximally and distally from the middle slice. Cortical area decreased from proximal to distal slices in the majority of the specimens, except for all the foal samples where the area fluctuated and showed a converging-diverging shape. A similar trend was observed for one of the adult horses. To investigate converging-diverging shape configuration, a two-degree polynomial function was fitted to the plots of geometrical parameters and then the curvature (k) of these fitted curves was quantified and compared to assess the significant changes. Previous research showed that 0.5 mm differences in thickness of the midshaft dorsal cortex have a significant effect on local strain in vivo. Variations in the geometrical parameters of the midshaft metacarpus have a dramatic impact on the internal loading of the MC3 and should be considered in designing equine training programs in attempts to predict and prevent bone damage.