10 ways to reduce the risk of damaging these dynamic structures

Tendons connect muscle to bone via their tough, fibrous strands. Wherever animals have bones and muscles, they have these collagen-fiber structures. But tendons in horses’ legs are unique in that they store high levels of quick energy, which they release after each step, making them capable of phenomenal athletic efforts.

It’s a “brilliant” design that’s helped this rapid-reaction prey species outrun many of its predators across its evolutionary history, says Claire O’Brien, MRes, PgDip, BSc (Hons), FHEA, of the University of Limerick, in Ireland, previously a researcher at Aberystwyth University, in the U.K.

But the tradeoff for such a design is these weight-bearing tendons are especially prone to injury and reinjury, says Roger Smith, MA, VetMB, PhD, DEO, Dipl. ECVSMR, ECVS, FRCVS, professor of equine orthopedics at the U.K.’s Royal Veterinary College Hawkshead Campus, in Hatfield.

Both the deep digital flexor tendon (DDFT) and especially the superficial digital flexor tendon (SDFT) are at risk for damage, meaning months or years of time off work or even the end of a horse’s athletic career.

Ideally, we’d reduce horses’ risk of sustaining tendon damage altogether, our sources say. Here are 10 ways to help.

1. Understand biomechanics and “biothermics” of tendon function.

Tendons are viscoelastic structures, meaning they stretch, and their mechanical behavior changes depending on how far and frequently they’re stretched, Smith says. Basically, tendons efficiently provide energy when weight-bearing but break down when stretched beyond their limits.

The SDFT, for example, stretches up to 16% in high-impact situations such as jumping and galloping, Smith says.

O’Brien adds, “If you could just watch a video of a horse coming to a fence in slow-motion and see that last step before takeoff, you’d be absolutely shocked to see how much the distal limb drops down.”

A stretch extending beyond that 16%, however, can damage the fibers, says Smith. Even so, that’s not the most common cause of injury. More often, he says, tendons get repeatedly loaded to the point of heating up. Researchers estimate core SDFT temperatures reach 110 F (43.5 C) during high-
intensity training sessions, O’Brien says.

That’s certainly not what you want, since scientists have shown that tendon cells—known as tenocytes—incur microscopic levels of heat damage starting at 108.5 F (42.5 C). Over time repetitive microdamage builds up, causing injury and lameness.

In fact, it’s the microdamage—not traumatic accidents—that’s the leading cause of tendon injury and reinjury, O’Brien says.

Knowing this is an important first step in safeguarding tendons, our sources say.

2. Know the Risk Factors When Selecting Your Athlete.

Armed with that knowledge, buyers and breeders can make informed decisions when purchasing horses because good selection is a critical part of injury prevention, Smith says.

Genetics play a role in tendon quality, and researchers have even identified tendon-injury-related genes in both humans and horses, he says. Yet, while genetic information can be helpful, it’s not essential, “as the more dominant risk factors are those that the horse experiences during its career.”

The greatest risk factor is prior tendon injury, says Smith. In the case of a prepurchase exam, veterinarians should palpate for signs of previous lesions. Ultrasound can also be helpful because healed injuries are not always detectable otherwise. Old tendon injuries reveal a tendency for tendon problems, and the horse is more likely to re-injure compromised tissues.

Importantly, this does not mean people should not buy horses with these risk factors, Smith says. Rather, they should be aware of the increased risks and prepared to be more vigilant or select a lower-intensity discipline that reduces chances for tendon injury.

3. Feel, watch, and monitor tendons regularly.

Early injury in some tendons—especially the SDFT, which extends along the back of the horse’s leg from the carpus (knee) to the pastern—can be visible, says Christopher Elliott, BVSc (hons), MANZCVS, Dipl. ACVSMR, of Palm Beach Equine Clinic, in Wellington, Florida.

So, it’s up to us to “dot the I’s and cross the T’s with paying attention to any change within that tendon,” he explains. “You should know what your horse’s leg feels like every day in terms of size, shape, contour, and temperature in all four limbs.” Ultrasound exams—whether regularly in healed tendons or after detecting a potential issue, can also provide critical feedback about how the tendon is coping with training, he adds.

Smith recommends visual inspections, palpation, and even Doppler ultrasound (which measures blood flow and can pick up subtle signs the eye can’t) checks after every high-intensity workout in previously injured regions and in areas of concern. “This is currently one of the best strategies for prevention, ” he explains. While an injury can’t be avoided altogether, detecting damage as early as possible and starting treatment can prevent further damage.

4. Use Boots Wisely.

Well-placed and well-fitted boots can help protect tendons and other structures from rare traumatic injuries that could happen when the horse clips himself or hits a jump, which some horses are particularly prone to doing, O’Brien says.

Nevertheless, these acute injuries are relatively uncommon compared to the risks of repetitive microdamage caused by overheating. “We continue to use boots on the horse, knowing they can increase tendon temperature even further during sessions,” she says.

If riders prefer using boots to protect the legs from acute trauma, they should apply them shortly before intense exercise and remove them immediately afterward, she says.

Simply airing the legs should help tissue temperatures drop, notes Smith. But cryotherapy—ice packs, cold hosing, or commercial ice boots—is also particularly effective.

Ensure boots are as ventilated as possible and/or made of materials that do not generate heat, O’Brien adds.

“Riders should check that any companies promoting such features in their products are transparent about any unbiased research to support their claims,” she says.

5. Use evidence-based training.

Progressive training programs based on scientific evidence contribute to core and muscle strength while preventing overwork-related fatigue, Elliott explains: “We know that too much exercise or inappropriate exercise increases risk factors for orthopedic injury, particularly in the soft tissues.”

Horse owners must also allow appropriate recovery time between training sessions, especially before advancing to more strenuous exercise, O’Brien adds. “Tendons need the chance to recover between the cyclical bouts and to have enough variety in the training and surfaces to allow time to recover in between sessions that tend to induce greater strain, like show jumping, galloping, and any kind of high-intensity work,” she says.

Furthermore, to limit repetitive movement that can strain the same tissues repeatedly, Elliott also recommends cross-training in different disciplines and on a variety of footing.

“Statistics have shown that the majority of tendon injuries occur during the training program, not during competitions,” O’Brien says. “It’s a difficult balancing act, but just make sure your program is as evidence-based, varied, and appropriate as possible.”

Warming up might or might not benefit horses’ weight-bearing tendons, because—unlike humans—they spend so much time standing, says Smith. More research into warmup’s effects on tendon health is needed, he adds, but it remains essential for general musculoskeletal health, especially the joints.

Meanwhile, breeders and trainers should follow evidence-based conditioning programs that help young horses’ tendons adapt to athletic work, Smith adds. “You’ve got to encourage animals to exercise in a controlled fashion when they’re young, while those tendons are still adaptable—which is when they’re growing,” he says.

6. Recognize Your Horse’s Fitness.

Tendons don’t work individually. Therefore, our sources say it’s important to maintain a “whole horse” view of the animal when managing tendon health.

Owners must recognize the overall health and fitness of their horses “to ensure that the legs are as orthopedically comfortable as they can be,” Elliott says.

O’Brien and Smith agree. “We need to be objectively monitoring the training we’re making horses undergo,” says O’Brien, whether that’s tracking our distance, gaits, speed, and other stats with an equestrian smartphone app, or going higher tech, under veterinary supervision, with heart rate and other monitors. 

7. Notice Hoof Shapes and Angles.

The horse’s hoof angle could make a significant difference in tendon strain, says Elliott. “You need well-balanced, well-
maintained feet that have a nice, short breakover and are appropriate to the specific sports discipline,” he says. (Experts define breakover as the moment the heels leave the ground and begin to rotate over the toe.)

Critically, people need to understand how bar shoes, wedges, or anything that elevates the heel could affect various tendons, says Aimee Colbath, VMD, MS, DACVS-LA, assistant professor in the section of large animal surgery at Cornell University College of Veterinary Medicine, in Ithaca, New York.

Heel elevation reduces strain on the DDFT, which can create more strain on the SDFT. “This is a common misconception, and it’s a bit counterintuitive,” she says.

Still, it makes anatomical sense, she adds. The DDFT attaches to the third phalanx, or coffin bone, but the SDFT attaches at the upper portion of the second phalanx, or short pastern bone. “By raising that foot up, you’re … raising the thing that the DDFT attaches to,” she says. “That’s not true for the SDFT.”

Smith says we need more scientific evidence linking injury risk and specific shoeing techniques. Depending on the horse’s conformation, there is a lot that can be done with such techniques to help him.

8. Think Smart About Footing.

Footing science is complex; even researchers don’t always agree on what’s best. In part, that’s because surfaces affect different tendons in a variety of ways.

For example, deeper, softer, more “sinkable” ground might contribute to higher strains on the SDFT, says Colbath. But other scientists studying racehorse injury risk suggest the opposite. In the latter situation this is thought to be because softer ground slows racehorses, which reduces peak tendon loading. In other disciplines, with lower maximal speeds, we might not see the same effect.

As a rule, owners should seek out consistent footing. “Avoid uneven surfaces, poorly maintained surfaces, or surfaces that are either too hard or too soft,” Elliott says.

9. Believe in Time Off.

Researchers have shown that tendons such as the SDFT undergo significant structural changes after intense workouts—with maximal changes at 48 hours. “The tendon is really doing a lot of hard work trying to repair any of the minor damage that occurred,” O’Brien explains.

When SDFTs have 72 hours to recover, they appear as they did prior to the workout on ultrasound imaging. This suggests good, strong repair, she says.

By contrast, a lack of sufficient recovery time could lead to even more microdamage. “So, if you were to, say, gallop the horse on a Monday and then do show jumping on Wednesday, research would lead you to believe that you may be more likely to cause a significant rupture of that tendon than if you’d let it rest for three days,” she says.

Meanwhile, owners of horses recovering from tendon injuries must respect and follow the rest and rehab programs their vets provide, Elliott adds. These can last months and follow a slowly progressive return to exercise, which allows the tendon to fully heal.

10. Support and Follow Ongoing Tendon Research

Many scientists worldwide are studying how to protect horses’ tendons from and treat injuries. Several studies are already underway—such as investigating genetics, risk factors, the influence of footing and shoeing, and biomarkers of early pre-lesion changes. These all could offer important insight into how we manage our athletes for optimal tendon health.

Smith’s team, for example, is currently developing molecular inhibitors designed to stop the progression of tendon degeneration while it’s still at a microscopic phase. This approach could address damage before anyone even notices it or it escalates to injury.

Individuals interested in supporting research can donate to their favorite vet school or charity that supports equine research.

Take-Home Message

Tendon injuries might be a common curse among sport horses, but that doesn’t mean they have to be. With foresight and a strong, evidence-based preventive strategy in place, owners and riders can reduce the risks of their horses sustaining damage to these dynamic structures.