Risk Factors for Catastrophic Fractures

At the American Association of Equine Practitioner's Blue-Ribbon Panel Research Meeting in Ft. Collins, Colo., Ellen Singer, DVM, DVSc, Dipl. ACVS and ECVS, MRCVS (epidemiology), of the University of Liverpool, discussed identifying risk factors that contribute to fatal distal limb fractures in the racing horse.

The most common fracture sites include the lateral condyle of the cannon bone, the long pastern (proximal phalanx or P1) bone, and the sesamoid bones in the fetlock. In the United Kingdom, there are a variety of racing surfaces and speeds that incur fractures: flat turf, all-weather flat track, hurdle race (flimsy and slanted jumps approximately 3 feet high), steeplechase with substantial fences ranging 3'7" to 4' in height, and National Hunt races on turf over fences with older horses. Cannon bone fractures of the lateral condyle are the most common of all the fractures, and they are seen especially in hurdle races. P1 fractures are most prevalent in steeplechase and hurdle races, while biaxial sesamoid fractures are more common in all-weather track races (such as those run in the United States).

anatomy of the distal limb

Singer noted that specific training factors increase the risk of lateral condylar fractures. Horses with no gallop training (considered breezing in the United States) had an increased risk, whereas horses with too much gallop work were at a slight increased risk.

The distance galloped in training is significant, with horses that did not do gallop work in training being more at risk for fracture. As gallop work increased up to 8-10 furlongs each week, the risk of fracture decreased. If a horse's gallop training is increased from only 5 furlongs per week up to 10 furlongs per week, then the risk of fracture decreases by half.

Singer stressed that horses must be trained at speed if they are expected to race at speed.

An increase in the number of runners in a race is also associated with increased fracture risk, and an increased length of race also amplifies fracture risk, possibly due to bone fatigue.

Singer said there is a risk of lateral condylar fracture if a horse's first race started at 3-4 years of age, and this is likely related to less bone training at an early age. But, as number of years in training increase, the risk of lateral condylar fracture decreases, up to age 3-4 years. Racing in softer footing decreased risk compared to firmer ground, possibly due to increase in speed and concussion on a hard surface.

P1 fracture risk is associated with distance galloped per week. Those horses in training for longer periods have less risk, while colts have an increased risk relative to fillies. Use of certain gallops or trotting on tarmac increased risk. Firmer going on the day of a race increased the risk, especially for cannon bone fractures.

Biaxial sesamoid bone fractures were more prevalent in horses running on an all-weather track as opposed to turf. There were no training risk factors that affected this risk, but Singer reported an increase in number of runners or length of race did demonstrate some small influence.

There are very few risk factors consistent among these fracture types; however, some consistencies were seen with size of the field of horses running in the race and the type of going: The softer the terrain, the less risk of fracture. Based on this, the industry has changed its management of terrain by increasing irrigation and watering to aim for softer footing. Singer also commented that the risk of tendon injury increases on firm ground, more likely due to increased speed. Also, the faster the horses go, the greater the risk of falling, with its attendant potential for any kind of injury.

Singer recommends that future investigation should concentrate on lateral condylar cannon bone fractures and P1 fracture as these have the greatest impact on the industry. It is of value to investigate training methods and the relationship of fractures to canter/gallop ratios, as well as the relationship of racing to training. Recording of accurate training information could be improved with the use of GPS to log distance and speed.

About the Author

Nancy S. Loving, DVM

Nancy S. Loving, DVM, owns Loving Equine Clinic in Boulder, Colorado, and has a special interest in managing the care of sport horses. Her recent book, All Horse Systems Go, is a comprehensive veterinary care and conditioning resource in full color that covers all facets of horse care (available at Shop.TheHorse.com or by calling 800/582-5604). She has also authored the books Go the Distance as a resource for endurance horse owners, Conformation and Performance, and First Aid for Horse and Rider in addition to many veterinary articles for both horse owner and professional audiences.

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