The potential role of the misstep, and other footfall insights in horses

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It is research than can literally be called groundbreaking. Scientists are applying inertial sensors and other technologies to learn more about the interaction between horse hooves and the ground.

The findings are adding more important pieces to the puzzle around the stresses and strains on the legs of horses, and the causes of injuries.

The findings also raise questions, such as the potential role of a bad step – hitting uneven ground or simply a misstep – in causing breakdowns.

Work in the field has been continuing in the laboratory of Dr Jeff Thomason at the Ontario Veterinary College for years.

As well as exploring how the hoof interacts with the ground, his team has also examined the shock and forces acting on the horse’s leg.

Studies have been conducted using a wide variety of surfaces and conditions in racing and various sport horse disciplines.

Thomason has been measuring joint loading since 1985 when he put his first strain gauges on a hoof.
Each study adds to the growing body of knowledge, which ultimately serves to optimize surfaces in order to reduce sports injuries.

Ontario Veterinary College student Alexis Szpakowski presented her findings on the interaction between body size and surface type on hoof loading at the recent International Society for Equitation Science conference at the University of Guelph.

Szpakowski’s study included 10 horses of varying breeds and ranging in size from about 356kg to 673kg.

Three strain gauges and an accelerometer were glued to both front hooves to measure the strain, as a surrogate of force, and acceleration experienced by the hoof while the horse is in motion.

The same rider piloted each horse at a trot on two surfaces – an indoor arena with a firm sand mix, and a soft sand outdoor ring.

Loading measurements were recorded from impact, slide, and mid-stance for a minimum of 10 stances.

When comparing the two surfaces, preliminary results reveal the loading measurements for impact, slide and force at mid-stance were all lower for the soft sand ring by 10 to 60%.

A horse fitted with sensors to monitor its footfall.

Results concerning the size of the horse revealed that slide values were not affected by size. However, impact accelerations decreased in the firmer sand mix indoors but not in the softer sand outdoors.

Mid-stance loading increased as the weight of the horse increased in the soft sand outdoors but not on the firmer surface indoors.

This result was not immediately intuitive for the researchers and suggests that larger animals experience more mid-stance loading on softer surfaces.

“Footing is very important simply because the characteristics of each surface directly affect the loading of the hoof,” Szpakowski says.

“I loved the hands-on aspect of data collection in this study and how even preliminary results, such as mine, can contribute to a growing body of knowledge to improve equine health and help reduce injuries related to footing including lameness and limb fractures.”

Thoroughbred limb-loading study

Graduate student Danielle Halucha, also with the college, presented findings at the conference from her study on asymmetrical limb loading in thoroughbred racehorses as a possible cause for injury.

Under the direction of Thomason, Halucha’s study set out to quantify mechanical changes in loading comparing both forefeet of Thoroughbred racehorses among various locomotory conditions that are normal for training and racing: speed, lead (left lead or right lead), and curve (turn or straight).

The aim was to identify changes within locomotory condition that are sufficiently large to be implicated in the cause of injuries for which the conditions are known risk factors.

In this study, comparing loading of the forelegs, Halucha explained: “Mid-stance stood out as having the greatest average percentage change for both means and variances compared to other phases of the horse’s stride.”

When the hoof is on the ground, this stance is divided into four phases: primary impact, secondary impact, midstance, and breakover, during which the hoof experiences different forces and accelerations.

Each phase is associated with a risk factor for injury; however, it is difficult to identify the mechanical cause of injury.

When Thomason’s team attaches hoof sensors and accelerometers, more than 30 measurements are being taken per footfall – all to do with shock and loading and the timing thereof.

Halucha’s study looked at risk factors for injury and loading of the hoof under different conditions. These conditions were chosen from the Equine Injury Database and current epidemiologic studies conducted on North American racehorses.

“There are many risk factors for injury in North American racing that have already been documented through various epidemiologic studies,” Halucha says.

“Some of these include the age of the horse, experience and the racing surface. However, the underlying mechanical cause of injuries is not well understood. In order to minimize the risk of mechanical injuries, we must understand what, in regards to mechanical loading, is changing or going wrong.”

Significant differences in the variances were noted in her study, raising the possibility that some degree of unpredictability in loading should be further investigated when addressing the causes of injury.

“I would love to go back and examine the outliers and potential outliers more closely and see what information they might hold,” she said.

“With regards to biomechanics research in general? I think that by continuing to dissect out the complexities of loading and what can affect it, we are getting closer to the potential mechanical causes of injury.”

The idea that the horse “took a bad step” suggests that the variability and the outliers in the data set collected might provide more information than the magnitude of loading or mean changes in loading when identifying risk factors for injury.

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