Tendons: Injuries & Healing

Many horse owners can point to a tendon on their horses’ legs, but aren’t quite sure what it is. In anatomical terms, a tendon is a connective cord made of collagen that joins a muscle to a bone. A ligament is similar, but joins two bones. A horse’s tendons are very strong; they are also elastic and can absorb a significant amount of energy.

But their strength doesn’t mean they are impervious to injury. In fact, Dr. Judith Koenig of the Ontario Veterinary College in Guelph, Ontario, said that tendon injuries are one of the biggest orthopedic problems besides arthritis in horses. And while sports activities are the main causes of tendon injuries, the Canadian winter can also pose its own risks.

The tendon most likely to be problematic is the superficial digital flexor tendon (SDFT), which Dr. Koenig explained is similar to the Achilles tendon that runs behind the heel in a human body. In a horse, this tendon runs up the back of each leg, from above the fetlock to the knee or hock. A 2010 UK study found that between 75 and 93 per cent of the cases where tendons were injured involved this particular tendon and almost always the ones in the front legs.

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Dr. Koenig explained that this tendon, because of its ability to stretch and compress, is like a spring. “It stores a ton of energy,” she said. “As the horse gets older, the core can begin to deteriorate and that makes it more susceptible to injury.”

Tendons can be damaged in several ways. The most common is by “mechanical overload” – the ongoing and repeated hard exercise breaks down the tendon. Horses can also suffer damage to tendons from being hit or struck in that area – a hard kick by another horse, for example, or in a fall or accident. Finally, a sudden stress or overstretching of the tendon, such as a horse slipping and twisting his leg, can also cause injury.

The main cause of tendon problems, according to Dr. Koenig, is participation in sports. “All sports put horses at risk,” she said. Different disciplines are likely to put more strain on different tendons. For example, racing horses are most likely to injure the SDFT and horses competing in dressage may have problems with the deep digital flexor tendon (DDFT).

Another potential cause of injury can be holes in fields or pastures. “It’s frustrating when a horse is turned out and comes back with a bowed tendon,” said Dr. Koenig.

Winter Risks

The paddock can be especially risky in winter, according to a bulletin from the University of Minnesota extension. The authors point out several areas of concern:

Deep, heavy or wet snow: Being ridden or turned out in deep snow can cause tendon injuries, as it puts a great deal of strain on the horse’s legs, especially if he is not very fit. It’s like a person trying to run in deep, damp sand. Deep snow can also hide hazards such as rocks, forgotten buckets or posts, etc. The extension experts recommend clearing snow from paddocks and pastures if possible, and avoiding riding in deep snow.

Be careful when removing snow to avoid piling it in drainage areas, septic tanks areas and other locations where it could either get into rivers or drinking water when it melts. This snow will likely contain manure, feed, bedding and other contaminants that could cause problems for water systems. You also want to be sure it won’t cause flooding of any buildings when it melts.

Frozen ground: Frozen ground has no “give,” so the concussion forces on the horse’s feet and legs are higher than during the summer months, meaning greater strain on the tendons. (There is also a higher risk of the soles of the horse’s feet becoming bruised.) Keep to a slower pace if riding outdoors; most indoor riding arenas will have softer footing.

Icy spots: Slips and falls on the ice can cause serious injury to the horse’s tendons. It’s helpful to inspect the stable and paddocks daily to see where ice has formed, and take precautions.

Putting sand on any icy spots is one of the most common ways to increase traction and protect horses from injury. There are, however, a couple of things to be careful about: it’s dangerous for horses to ingest sand, so keep any feed well away from the area. Also, don’t ever mix sand and salt for spreading on the ice, because the horses are likely to attempt to eat the salt and end up ingesting sand as well. Fresh manure and wood ash are also useful for helping to melt ice and improve traction.

Wood shavings, hay and straw are sometimes scattered over ice with the goal of making it safer, but research has shown that this does not improve traction – these items just slide over the ice – and should not be used.

Hoof Care: The barefoot horse generally has better traction on ice and snow than one in ordinary shoes. But shod or not, horses in winter are at risk of getting balls of compacted ice or snow trapped in their hooves. These hard-packed and slippery balls make it hard for the horse to move around without slipping or falling, and add significant strain to the animal’s joints and tendons.

Even if you are not riding, your horse’s hooves should be picked out daily if there is snow on the ground, to prevent this problem.

If your horse needs to be shod, ask your farrier to use snow pads and studs to reduce the risk of slipping on ice and of snow balling up in the hoof.

When Tendons Are Injured

The typical sign of a tendon injury is the “bowed tendon” – the back of the horse’s leg is swollen and the tendon curves outwards. The horse is likely to be very lame and, if you touch the swollen area, he will usually react with signs of pain. It is likely also to feel hot to the touch.

Dr. Koenig said prompt treatment of any suspected tendon injury is essential. She advises horse owners to start by applying cold to the injured tendon to reduce inflammation. This may be easier than usual in the winter – a towel full of snow, for example, may be applied. A bucket of ice water or even a cold water hose run over the area are alternatives (there are also commercial ice boots and other tools to keep the area cold). Remember that this should only be applied for a maximum of 20 minutes, and then a support bandage should be applied. Repeat the cold treatments every few hours, for just 20 minutes each time, and then wrap again, for the next three to five days.

The support bandage helps by putting firm pressure on the tendon and can reduce edema (accumulation of fluid) around the injured area. The bandage, though, doesn’t really protect the tendon from the forces exerted as the horse walks around, so in very severe cases a veterinarian may decide to put a cast on the leg as it heals.

The third step to take to reduce inflammation and encourage healing is to treat with an anti-inflammatory medicine such as phenylbutazone, said Dr. Koenig.

Many tendon injures are found to be the result of a series of minor traumas. Any tendon injury should, therefore, be taken seriously, as it has the potential to become a more significant problem. “The best way to assess the injury is to have an ultrasound done,” Dr. Koenig explained.

With information from an ultrasound to provide guidance, your veterinarian will help you develop a long-term controlled exercise program to promote healing (see chart on page 16). “We now have good research to show that this is more effective than just turning the horse out,” said Dr. Koenig. “The quality of the new tissue that grows during healing is superior when you follow this kind of program.”

The Healing Process

For an SDFT injury, most horses will be back to full use in about nine to 12 months. The first few days after the injury should be spent in stall rest. After that, the owner can begin daily hand walking of the horse, slowly increasing the duration. Within a few weeks, the horse might be able to trot for one minute before returning to a walk; when that’s going well, it can be extended to two minutes of trotting. “Eventually you’ll be able to have the horse canter and finally work at speed,” said Dr. Koenig.

The horse’s healing should be re-checked with ultrasound throughout the process, said Dr. Koenig. The information provided will guide the veterinarian in recommending how slowly or quickly the intensity of exercise should be increased. “I find people often underestimate how important this process is,” she added.

In some cases, surgery may be needed to remove damaged tissues and help the tendon to heal. Again, this will need to be followed by a progressive exercise program. Even after the horse has returned to normal work, he or she is likely to be more susceptible to future tendon injuries.

A little extra care in the stable and paddock in the winter may protect your horse’s tendons from unexpected problems. And when the weather warms up again, be sure to gradually work up to more intensive exercise to reduce the risk of tendon damage from overwork as well.

New Research: Stem Cell Hope

Dr. Judith Koenig is researching new approaches using stem cells to promote the healing of injured tendons in her work at the Ontario Veterinary College. Stem cells are special cells that have the ability to become other types of cells; they can be found in bone marrow, in fetal tissue and in the blood contained in the umbilical cords of newborn mammals. Many new parents will opt to bank the umbilical cord blood of their babies, in case the child (or a close relative) develops a disease later that could be treated with those stem cells.

The technique Dr. Koenig is using, in collaboration with Dr. Thomas Koch, involves taking umbilical cord blood from newborn foals and extracting the stem cells that are known to be the most effective against inflammation. These cells are then injected into the injured tendon on an unrelated horse.

“Most of the horses we are testing this with have tendon injuries that do not have a good prognosis,” Dr. Koenig said. This is usually repeated several times.

Dr. Koenig said the results so far have been positive. “The quality of healing is much better than usual, at least in the beginning after the injection. But it is not as impressive in the long run, which is why we are now repeating the injections as time goes on.”

Other veterinarians conducting similar research have tried injecting the stem cells into the horse’s artery near the injury, rather than directly into the tendon. “They found that the stem cells would actually travel to the injured tendon tissue,” said Dr. Koenig.

How do the stem cells work in promoting healing? Dr. Koenig said the mechanism isn’t known for sure, but some think they may enhance growth by recruiting other cells to come in to the area and by attracting more stem cells.