The response of equine cortical bone to loading at strain rates experienced in vivo by the galloping horse.

This study examines how the rate of strain (i.e. the speed of loading) affects the mechanical properties of horse bone (specifically “cortical bone”, or compact bone). Main findings include that strain rates increase the bone’s mechanical properties to a certain point, after which they cause a decrease in the bone’s ability to withstand the strain and absorb energy; this results in the bone becoming brittle and prone to catastrophic fractures.

Study Overview

The study firstly recognizes the fact that the performance and behavior of cortical bone under strain or load is strain rate-dependent. This refers to the dependency of the bone’s behavior on the rate at which the load is applied. The strain rates that a horse bone endures – particularly within galloping horses – significantly exceed those found in any other species.

• The study aimed to measure how strain rates between 0.0001 and 1 sec-1 influence the mechanical properties of equine cortical bone.
• The research found that initially, the increase in strain rates resulted in enhanced mechanical properties of the bone.

Critical Findings

However, the study also reveals that there’s a limit or a critical value to the strain rate’s positive impact on the bone’s mechanical properties.

• Post this critical value, any further increase in the strain rates resulted in reduced strain to failure and the capacity of energy absorption.
• This critical rate occurred around 0.1 sec-1, which interestingly aligns with the in vivo range for a racing horse in full gallop.

Implications of Brittle Deformation

The stress-strain curves used in this research revealed a transition point in bone deformation. Past the critical strain rate, the deformation transforms from pseudo-ductile to brittle.

• The term “pseudo-ductile” refers to the initial phase where the bone can withstand strain.
• If the bone becomes “brittle” from too much strain, it is more likely to undergo catastrophic failure or damage under load. This condition has severe implications, with the risk of bone fracture and destruction of the animal.

This study emphasizes the need for understanding different strain rates on horse bones, specifically in scenarios like horse racing, to prevent injuries and ensure the health and safety of the racing equine.