Predisposed to injury: Different sports carry different risks for horses

Researchers have found a difference in the prominence of injuries in show-jumping horses depending on whether they are elite or non-elite competitors. Getty ImagesIt's no surprise that horses competing in different sports are predisposed to specific injuries. In fact, the type and site of injury may even reflect the type and level of performance, according to one study: “Horses training for different sports are likely to load different anatomical structures and load these in different ways between different sports and between elite and lower level. It could, therefore, be expected that horses working in any single sport would have a particular type of injury predisposition at specific anatomical sites.”1

Older sport horses typically suffer from repetitive-type injuries: exacerbation of osteoarthritis due to sprains or strains involving the soft tissues around compromised joints, says Duncan Peters, DVM, MS, DACVSMR, associate professor of large animal clinical sciences at Michigan State University's College of Veterinary Medicine. “All of a sudden you get an acute overload, and you see soft tissue injuries associated with the joint capsule or the collateral ligaments,” he says. “Those injuries are more acute, even though you have some underlying osteoarthritis.”

Many of these horses may have undergone some type of injury in the past, healed from it, and then continued on in their careers, Peters says. “That's different than what we see in younger racehorses and some of the Western performance horses that will compete as 2- and 3-year-olds and then experience orthopedic problems while they are still going through development.”

In sport horses these injuries may be mistaken for poor or waning performance or an inability for the horse to attain its full potential.

Event and performance level factors

So how does sport category and performance level correspond to diagnosis? According to the 2006 study, researchers saw “a significant difference between anatomical site injured and sport category, including a high risk of forelimb superficial digital flexor tendon injury in eventing and elite show jumping, distal deep digital flexor tendon (DDFT) injury in elite show jumping, and hindlimb suspensory ligament injury in elite and nonelite dressage. There was a low risk of tarsal injury in elite eventing and proximal DDFT injury in dressage.”1

As for performance level, researchers discovered that elite and non-elite competitors were often predisposed to different injuries:1

> Elite show jumping horses (those that routinely compete over 1.4-meter or higher fences) most frequently injured the suspensory ligament, followed by the DDFT.

> Non-elite show jumping horses frequently injured the navicular bone and ligaments.

> Dressage horses at both performance levels showed the most frequently injured site at the suspensory ligament, predominantly in the hind limb. This was followed by the tarsus for elite-level horses.

> The superficial DFT was injured six times more frequently in elite event horses than non-elite horses and navicular bone and ligament injuries were equal for both performance levels in eventing.

> For endurance horses, the tarsus was the most frequently injured site.1

Likewise, researchers showed a strong correlation between specific orthopedic injuries and individual sports:1

> Suspensory ligament injury occurs most frequently for dressage horses.

> Proximal sensory desmitis occurs most frequently for show jumping, dressage and eventing.

> The tarsus is most frequently injured in elite dressage and endurance horses.

> Forelimb superficial DFT injury is most frequently detected in elite show jumping horses.

> DDFT injury in forelimbs of horses is seen in most sports.

For both elite and non-elite dressage horses, the hindlimb suspensory ligament is the most frequent site of injury compared with other sport horses. Getty Images> Elite show jumpers had the greatest proportion of injuries at a distal location. For other sports, injuries occurred more frequently within the digital flexor tendon sheath, proximal to the pastern.

> Injuries to the navicular bone occurred more frequently than injury to the associated soft tissues (bursa, DSIL, CSL and distal DDFT). Non-elite dressage horses had the most navicular bone injuries, followed by elite eventing.

Progression of orthopedic injury

As older sport horses advance in their careers, there is a progression of problems, such as osteoarthritis, Peters says. “We then get to a point where there is enough instability or wear and tear of the articular surface that all of a sudden the horse experiences pain related to the bone, and the deteriorating joint can no longer take up the absorption, or the concussion of the discipline, whether competing in dressage or other sport horse events.”

In addition to osteoarthritis, these horses can experience a range of progressive conditions, including:

Ligament problems. Sport horses are diagnosed with ligament issues that tend to occur more at the attachments and at the ligament or tendon extremities, i.e., proximal suspensory problems, which are common in dressage horses, jumpers and event horses.

“These injuries may be the result of ongoing stress on that area that, over time, creates problems with the ligament attachment,” Peters says. “We then start to get some remodeling, some bone and ligament pain associated with those attachments. We'll see it in the proximal suspensory region and commonly at the sesamoid bones around the ankles. We'll see branch suspensory ligament problems, which are certainly different than what they see in racing horses. In sport horses, it's an accumulative effect of aging, time and miles, rather than a catastrophic breakdown-an overload-fatigue-type injury as seen in younger racing Thoroughbreds.”

In performance horses, there is a little different pathology or etiology of the damage to the ligament. “The result is that you have a lameness and/or dysfunction, and the horses are not able to do their job,” Peters says.

Tendon injuries. Sport horses don't typically experience acute enlarged tendons or big core lesions that occur from racing. “We see tendonitis that may be associated more with a weakening or degeneration of the tendon over time,” Peters says. “We see damage in the areas of the deep flexor tendon, over the navicular bone and into the attachment at the bottom of the foot.” Sport horses may experience some tendon injuries in the mid-cannon area and also racing-type injuries, but not as often. “Most of our tendon injuries are related to margin tears rather than the core-type lesions that you may get in the young horse.”

Some of those tendon injuries are traumatic, where the horse directly hits those areas, and others occur over time, causing micro-overloading and weakness in those areas.

Hock injuries. Common hock problems include osteoarthritis, or degenerative joint disease, affecting the lower joints of the hock. This is usually due to the stresses in this area that, over time, cause remodeling of the joint surfaces and the surrounding bony structures. There can be low-grade pain (subclinical) associated with this bony remodeling that is insidious in nature until it progresses to an outright discomfort and lameness. In addition, there can be some acute stress of the compromised joint during performance that results in soft tissue inflammation and pain. “In sport horses, we often see a change in performance with the underlying degenerative joint conditions,” Peters says. “The horse will not jump or perform as well as he used to, for example, or he may jump to the left consistently. A dressage horse may suddenly have trouble with lead changes, or an event horse may struggle with his collection or lateral movement in his dressage work.”

Back pathology. “We are appreciating these injuries more and more,” Peters says. “A lot of back problems are related to osteoarthritis of the articular facets and repetitive stress on those areas where there is some instability. The body tries to take care of it the best it can either by laying down some scar tissue or new bone.”

Improper tack and saddle fit can also cause sore backs and muscle spasms. “And a horse in training for dressage or three-day eventing has a rider aboard for a longer period of time than an exercising racehorse. Additionally, most sport horses carry a greater percentage of their body weight, in rider and equipment, during training and competition in comparison to racehorses.”

Stress fractures and other injuries. Sometimes remnants of past injuries from an earlier career can appear later in the horse's life. “Some retired racehorses get a second career as event, jumping or dressage horses,” Peters says. “So we appreciate that some old horserace injuries, like stress fractures or ligament desmopathies, may be a problem as those sport horses advance their careers. In some of these horses we see dorsal spinous process impingement, or some early arthritis that may have developed because of the excessive extension-flexion of the back that occurs with the galloping gait.”

Some of these problems can be locally painful and metabolically active, showing up with nuclear scintigraphy (bone scan), Peters says. “Many of them are incidental findings, as the injuries have since healed, and the horse is able to pursue his new career. It's not uncommon to see something abnormal on a radiograph or ultrasound that isn't really affecting the horse.”

Summary

In conclusion, researchers conclude that show horses competing in specific sports are at greater risk of injury at specific anatomical locations than horses used for general purpose riding.1

Reference

1. Murray RC, Dyson SJ, Tranquille C, Adams V. Association of type of sport horse and performance level with anatomical site of orthopedic injury diagnosis. Equine Exercise Physiol 7, Equine Vet J Suppl 2006;36:411.