It's no secret that the proximal sesamoid bones, which form the back part of the pastern, are a big vulnerability for racehorses. Fractures of the sesamoid bones or failures of the suspensory ligament apparatus that holds them in place are associated with 30 to 50 percent of fatal injuries in Thoroughbred racehorses. So, while we wait for better methods to detect impending injury to those structures, how do we better protect those bones?
(Read more about research on sesamoid bones and their role in a horse's movement in this Paulick Report feature from January 2021.)
Farrier Steve Stanley, who has worked on racing Thoroughbreds and Standardbreds for some four decades, offered a few suggestions at a recent virtual edition of the Tex Cauthen Memorial Seminar focusing on racing safety.
A few takeaways from Stanley's presentation:
- Soft tissues like the ligaments and tendons probably strengthen faster in response to training than bone, which leaves already-vulnerable bones like the sesamoids in a comparatively weaker position. Stanley said horses with sesamoid fractures tend to be younger and less fit.
- Stanley also cited research that showed these injuries were more common in front limbs for Thoroughbreds and hind limbs for Standardbreds, probably reflecting the differences in load distribution between the two race types.
- It's not news that toe grabs come with risk, but it may surprise you how much risk they create for horses' safety. Stanley cited a post-mortem study on Thoroughbreds which found that those with a 6 millimeter long grab were 15.6 times more likely to have a suspensory apparatus failure than a horse running without a toe grab. Grabs of 4 millimeters were 6.5 times more likely to have a failure. For some time now, safety experts have suggested states limit toe grabs to 2 millimeters or less. As with anything in racing, different jurisdictions have different rules about maximum toe grab length.
Toe grabs were originally intended to help horses handle a racing surface better, like a soccer cleat on a grass field. The trouble with them, Stanley said, is they drive the toe farther into the track surface than it would normally go, halting the natural sliding of the foot across the ground. That pressure pushes back against the rest of the leg, creating excess flexion through the fetlock and the coffin joint, pulling harder against that stretchy ligament.
What many people may not realize is that rim pads or elevated heels, which like toe grabs are aimed at increasing traction, may also place the suspensory apparatus under stress.
- Stanley detailed his personal experience with other types of shoe construction that could impact traction similarly to a toe grab. Stanley was part-owner on a Standardbred mare who pulled a shoe in the paddock before a race and he replaced it with a Sigafoos shoe which is a glue on shoe with a rim pad. The mare performed poorly and began interfering during the race, which was uncharacteristic for her. That rim pad, he later realized, could also reduce the slide phase of the shoe, and he believes if you're going to use a Sigafoos, you should remove any toe grab from the equation.
- When considering the length of the toe grab on a horse, Stanley pointed out that everything is relative. Usually the shoe itself is made of aluminum, while the toe grab is steel. Since aluminum wears down faster than steel, a toe grab could theoretically increase in height toward the end of a shoeing cycle as the shoe around it recedes.
- The leverage action of a toe grab can also change as a horse's foot grows because its position shifts as the foot grows. In return, the grab can change the forces going back to the coronary band guiding future growth. Stanley questioned whether these changes in leverage might not also be impacting the soft tissues in the hoof and lower leg, though he was unable to find existing research studying these impacts.
- The tendency to trim horses with long toes and low heels can also increase pressure on these soft tissues. Often, Stanley said, this is done with the intent of making a horse's stride longer, but instead it actually increases the duration of a stride and the effort the horse must take to work.
Stanley believes that many of the serious soft tissue injuries to the suspensory apparatus come as the result of fatigue, and an increased duration of stride seems likely to exacerbate fatigue of the ligaments and tendons.
- In the end, from the farrier's perspective, Stanley said it all comes down to maintaining the hoof/pastern angle. Up-close photographs of horses' fetlocks before and after the application of shoes with these various devices show changes in the angle of the horse's soft tissues to the foot and to the ground. Farriers should aim to maintain those natural angles as much as possible.
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