Tendonitis develops when the fibres that a tendon is composed of are strained or torn, either through being overstressed or from trauma. As the horse’s body attempts to heal the injury, it causes swelling and heat – the classic signs of inflammation.

This condition is a common problem for competitive horses, said Dr. Aimie Doyle, professor in Large Animal Surgery at the Atlantic Veterinary College. Working at speed is a major risk factor. For racehorses, the incidence of tendonitis is reported to be about 43 per cent, but dressage, jumping and eventing horses also have high rates of injuries to tendons. Dr. Doyle noted that western performance horses may be at increased risk for tendonitis depending on their specific activity. For instance, activities with quick starts and stops such as cutting or reining would be at higher risk than those without, such as barrel racing or calf roping, where more chronic ligament injuries or osteoarthritis tend to be more common. “Any veterinarian working with equine athletes will see this injury with some degree of frequency,” she said.

Tendonitis is a serious condition. It can cause severe pain and lameness for the horse. Even worse, more than 60 per cent of horses that develop the condition will re-injure themselves within a year, either in the same spot or a different tendon. That’s why a focus on prevention makes good sense.

Dr. Judith Koenig, a professor with the Ontario Veterinary College who specializes in Equine Sports Medicine, said understanding how tendons work and what causes inflammation can help horse owners understand how to prevent and treat it. She explained that tendons are designed to store energy for the muscles and then release it, like a spring. Each tendon is made up of many fibres that work together.

When there is excessive repetitive strain on the tendons, these fibres can be damaged or altered. In fact, Dr. Koenig said a deterioration in the core of the tendons, leading to a thickening, can be seen with ultrasound before tendonitis becomes obvious. While this deterioration may be related to age, Dr. Koenig said some racehorses have the problem by age three or four. At this early stage, the horse is not necessarily lame.

“The theory is that tendonitis can be caused by excessive repetitive strain on the tendons, especially when the forces are not evenly distributed,” she said. Since racehorses run in one direction only, there is increased and repeated strain on the inside foreleg producing the high incidences of tendon injuries in that sport. The initial deterioration and inflammation worsens and the fibres actually develop tears and small holes.

What Tendon?

Run your hand down the back of your horse’s leg – either front or back. From the knee or hock to the fetlock, you’ll feel the superficial digital flexor tendon (SDFT); it attaches to the bone just above the hoof. Normally, the tendon is straight and feels almost like a thin rubber hose under the horse’s skin – firm, but not hard like a bone.

Underneath that easy-to-find tendon, running from the knee to the bottom of the hoof is the deep digital flexor tendon (DDFT). The SDFT is the tendon affected in more than half of the cases of tendonitis, so it’s worth getting to know how they feel normally. Tendonitis is also more often seen in the front legs than the hind legs.

Prevention Strategies

Ensuring that the horse’s foot is balanced will minimize strain on the tendons. “If the horse has a conformation problem so that he is always landing a bit on one side of his hoof first, for example, or if his feet have not been properly trimmed or shod, so they are unbalanced, the risk of developing tendonitis is higher,” said Dr. Koenig.

Another possible cause of uneven forces affecting the tendon is riding over uneven ground, deep sand or mud, especially at speed.

Tendons are a part of the entire system that moves the horse, and for the tendon to do its job safely and effectively, it needs to be connected to muscles that are strong enough for the work required of the horse.

“Conditioning of the horse is very important to protect the tendons,” said Dr. Koenig. Expecting your horse to do new, difficult movements or increase his speed too quickly will increase his risk of injury. Instead, work with your trainer to develop a program that will gradually move the horse to higher levels of fitness.

It’s also important to be aware of your horse’s fatigue. Tired muscles are weaker muscles, and force the system to rely too much on the tendons. Your horse may be capable of jumping three feet or doing short gallops, but pushing him to keep working when his muscles are becoming tired can cause a tendon problem or injury. Try to watch for signs that your horse is reaching his limits and slow down, take a long break or stop.

Competition can be especially hazardous, because the excitement and lure of the prize may encourage the rider to push the horse harder. “Unless you are confident that your horse is fit enough, don’t compete,” Dr. Koenig cautioned.

Cold muscles are also weaker and won’t stretch as well as when they are warmed-up – again, putting more tension on the tendons. Ten or 15 minutes of walking or trotting slowly before you begin more intense work will allow the muscles to work the way they are supposed to, and protect the tendons.

Dr. Koenig suggests this should be part of your everyday grooming and tacking-up routine: run your hand over the back of each of your horse’s legs. You are trying to detect any heat, thickening or swelling where the tendons are – fairly easy in the case of the SDFT, but tougher when it comes to the DDFT, which attaches directly onto the bone, between the splint bones below the SDFT.

If the horse seems to flinch or react as though in pain to the pressure of your hand, that could be another sign, according to Dr. Doyle. “I think early detection of the sub-clinical diseases – inflammation but not to the point we have fibre tearing – is the best way to prevent the injury from progressing to severe tendonitis,” she said.

If you detect heat or swelling before your ride, change your plan, Dr. Koenig advised. “Put the horse in a stall and call your vet,” said said. “Turning the horse out in the pasture isn’t a good idea, because he can make the injury worse.” It’s much better to start treating this condition when it’s only minor than to wait too long and have serious damage to the horse’s tendon.

If your horse seemed fine during the pre-ride check, but shows signs of inflammation when you check again as you remove his tack and get ready to turn him out, putting him in the stall to rest is a good idea. Dr. Doyle said this probably means you need to adjust your horse’s training plan to prevent more severe injury.

Diagnosing a Problem

If one of your pre-ride checks doesn’t go well, and you call out your vet, what’s he or she likely to do to determine if tendonitis really is the problem? The physical exam may help rule it in or out, said Dr. Doyle. “Palpating the area may reveal swelling or heat.”

Dr. Koenig added that sometimes nerve blocks are needed to determine where the horse’s pain or lameness is originating. “Ultrasound is the definitive test, though,” she said.

Dr. Doyle explained that areas where the fibres in the tendon are strained or inflamed will appear as darker areas in the scan. (Normal tendon tissue looks white in an ultrasound.) If there are actual ruptures, tears or holes, these injuries will look completely black and are referred to as “core lesions” (see page 20). Other indications that can be seen on ultrasound are fluid in the sheath around the tendon (known as effusion) and an increase in the diameter of the tendon.

What happens next? The first goal is to reduce the horse’s pain and the inflammation. Anti-inflammatory medication is indicated, advised Dr. Doyle, and other steps such as icing, hosing the inflamed area with cold water, poulticing and supportive wrapping may be recommended. Your veterinarian will work with you to develop a plan depending on what’s going on in the tendon and the facilities you have at your stable. Strict stall rest is also critical during this stage.

Rest & Rehabilitation

Once the inflammation has begun to subside, the rehabilitation process begins. Your veterinarian will prescribe a program that gradually increases the amount of exercise the horse gets, and will assess the changes using ultrasound every two or three months. The program may take up to 12 months.

The horse shouldn’t be given free access to turn out until the veterinarian advises it, Dr. Doyle added. This gradual program is crucial to the horse’s successful recovery and patience is essential – trying to rush the process can lead to more severe injuries or a delay in the recovery process.

Depending on the injury, your veterinarian may suggest additional treatments that are used while the horse is in the recovery period.

Treatment Options

Developing treatments for tendon injuries has been a focus of Dr. Koenig’s research work. She says for core lesions, where there is an actual hole in the tendon, she likes to use stem cells. These cells are taken from the umbilical cords of newborn foals and can be injected directly into the lesion, with ultrasound used to guide the process. If the injuries are more diffuse, she may inject the stem cells into an artery instead. Her research has shown that stem cells injected this way will actually move to the injured areas. Both of these treatments can be costly.

Another option is to inject platelet-rich plasma (known as PRP), which can stimulate the growth of new, healthy tissue in the tendon.

Therapeutic laser treatments and extracorporeal shockwave treatments are also used to speed up the healing process.

In some cases, surgery may be recommended to repair the injured tendon.

These treatments are done along with the controlled exercise program – that’s still critical! – and the results are assessed when the regular ultrasound checks are done. Dr. Koenig described one case where the horse’s tendon looked as good after three months of rehab with an injection of stem cells as she would expect a horse with no additional treatments to look after six months.

These treatments are more likely to be successful if started as soon as possible after the tendonitis develops – another reason for careful monitoring to catch the condition early.

The Post-Tendonitis Future

Will your horse ever return to his competitive glory days after he’s had tendonitis? The answer to that depends in part on the sport you have been competing in. About 80 to 90 per cent of jumpers and dressage horses are able to return to previous levels of competition after treatment and rehabilitation. For racehorses or eventers, though, the rate is only 60 to 70 per cent.

And it should be kept in mind that because he’s already had tendonitis once, your horse is predisposed to a second bout.

Some owners, acknowledging the risk, will move their horses to a different sport or activity that puts less strain on the tendons.

The other factor is the severity of the injury and any underlying causes. If, for example, the tendon injury was caused by the horse’s conformation, his risk of re-injury will be even higher.

New prevention strategies may be available in the future. Dr. Doyle said researchers are looking at the genetic factors linked to higher risks of tendon injury, hoping to identify the risk factors that could be eliminated by selective breeding. Others are studying how horses are trained and conditioned to develop programs that will strengthen tendons and reduce the risk in that way.

“Each situation and each injury is unique, and the length and type of controlled rehab program and adjunctive therapies recommended may differ for each one,” said Dr. Doyle. “It’s important to assess healing with your veterinarian regularly for the best chance of a positive outcome.”

Bow-ing Out

When tendonitis hits the superficial digital flexor tendon, the swelling may cause it to look “bowed,” explained Dr. Doyle. That means it curves outward when viewed from the side, as opposed to running straight up and down between fetlock and knee.

Even after the tendon injuries have healed, the thickened tissue may remain, so the bowed tendon is still apparent.

This is rarely seen in the deep digital flexor tendon, because it is located closer to the inside of the leg.