Traction or Trauma?

Some astute horsemen have long alleged that certain styles of horseshoes might predispose a racehorse to catastrophic injury, often resulting in euthanasia of the athlete. A recently completed study at the University of California, Davis, supports the hypothesis that some shoe types might predispose a horse to musculoskeletal injury.

"We are very excited about the results of the study," exclaimed Albert J. Kane, DVM, MPVM, lead veterinarian for the study. "We have not only identified types of shoes that may increase a horse's risk for injury, but also alternative shoes that may help prevent injury."

The study was conducted at the University of California, Davis, School of Veterinary Medicine's Orthopedic Research Laboratory by Kane under the guidance of Susan M. Stover, DVM, PhD, and Ian A. Gardner, BVSc, MPVM, PhD. It was funded by the Grayson-Jockey Club Research Foundation, the California Center for Equine Health and Performance, Oak Tree Racing Association, the State of California satellite wagering fund, Mr. and Mrs. Amory J. Cooke, and the Hearst Foundation.

Shod hooves were obtained from Thoroughbreds submitted for postmortem examination to the California Veterinary Diagnostic Laboratory System through the California Horse Racing Board Postmortem Program. All of the study's horses were injured at California tracks either while racing or training, or while training at a certified training center. The horses' injuries were so severe that the animals were euthanized at the track.

Kane's investigation included checking all four hooves and recording the presence of toe grabs and whether they were low, regular, or high; recording the presence or absence of rim shoes; categorized injury outcomes, including any fatal injury resulting from the tendons, ligaments, bones, or a suspensory apparatus failure--suspensory ligament ruptures or sesamoid fractures.

Of the horses which suffered catastrophic injuries, 51% had a suspensory apparatus failure, the most common catastrophic injury. The control horses which served as the comparison group died in the same time frame as the study horses, but from illnesses unrelated to musculoskeletal injuries, such as colic.

The objective of the case-control study was to determine if toe grabs and rim shoes are associated with an increased risk of catastrophic musculoskeletal injury. Kane and his colleagues specifically wanted to determine if traction devices contribute to the occurrence of suspensory apparatus failure in racehorses.

The research included recording the various types of shoes the horses were wearing at the time of the fatal injury--aluminum or steel shoes, flat shoes, or shoes with traction devices--the kind of traction devices, and whether the toe grabs were low, regular, or high. They also noted whether or not the horses were wearing therapeutic pads. The study found that most of the horses were shod with low toe grabs on the front and regular grabs on the back.

"We found that the higher the toe grab, the greater the risk of injury," said Kane. "The odds of sustaining a catastrophic suspensory apparatus failure were 16 times greater for horses shod with regular toe grabs compared to horses shod without toe grabs. The odds of any type of fatal injury were three times higher with regular grabs when compared to horses shod without grabs; and the odds were twice as high with low grabs."

Kane said adding toe grabs might give a horse more traction, but at the same time those traction devices can have a jarring effect on the distribution of forces and patterns of movement in the lower limbs of performance horses. He suspects the higher toe grabs increase the forces transmitted to the leg. High toe grabs add eight millimeters to the height of the toe, regular grabs add six millimeters, and low grabs add four millimeters. It was determined that the added height changes the geometry of the hoof as it contacts the ground. It also changes the angles of the joints as they support the weight of the horse in a manner similar to the undesirable long toe, low heel hoof conformation that develops in many Thoroughbred racehorses.

Because toe grabs elevate only the toe of the hoof, the hoof is unbalanced from toe to heel. This changes the natural position of the horse's toe during the weight-bearing part of the stride and can change the forces traveling up the limb. Where a flat shoe disperses the concussion up the limb, toe grabs and/or calks concentrate the concussion at the toe or heel.

"Nature designed a horse's action so the hooves slide a little upon impact," Kane said. "This very small amount of sliding or slipping allows some of the shock of impact to dissipate, lessening the force as it travels up the leg. The extreme types of traction devices work against the way a horse was meant to move."

Kane was adamant in adding that the study wasn't designed to tell us how toe grabs increase the risk of injury--it was designed to establish a link between toe grabs and the risk of injury.

"Now we know to focus future research efforts on the effects of toe grabs and how they affect a horse's legs," he said.

Considering that about 85% of all racehorses compete wearing toe grabs, Kane's study could have a large impact on the incidence of injuries in racing.

"An injury is like a pie made up of several factors such as conformation, shoes, exercise history, track condition, or pre-existing mild injuries, such a stress fracture," Kane explained. "Bring some of these factors together and you have an injury. Eliminate one of the factors and the injury may not be as serious, or may not occur at all. Specific injuries have different causes. Although there isn't one single cause for most injuries, it does appear that horses wearing toe grabs are more likely to suffer a fatal musculoskeletal injury."

While shoes with toe grabs might predispose a horse to injury, the study also found that rim shoes might help prevent injury. Rim shoes offer some of the traction of toe grabs without the unbalanced concussion. Rim shoes raise the hoof off the ground, but do so evenly. The hoof remains flat and the force remains constant around the entire circumference of the hoof.

"Rim shoes may actually have a protective effect against injury," Kane said. "They are an attractive alternative to toe grabs because they provide a horse with traction, but do so without the risk posed by other traction devices."

When Kane believes a racehorse needs increased traction, for whatever reason, he recommends shoeing with a balanced traction device that is not too severe, such as an inner rim shoe with a low toe grab, or better still, no toe grab.

"A lot of what we found in the study was not a surprise," he said. "However, the study gives us concrete evidence to be able to say, 'Hey, let's take notice of this and make modifications to prevent injury.' "

Perhaps the most exciting finding Kane noted was that by simply changing shoe type, trainers and farriers can greatly lower a horse's risk of injury. Making these changes is not costly and might save a horse owner thousands of dollars in veterinary bills and medications, and perhaps a horse's life.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.