Breakdown Injuries in Thoroughbred Race Horses: Perspectives on Solutions
David M. Nunamaker, VMD, DACVS
They Shoot Horses, Don’t They, a movie in the late 1960s, portrayed the lives of a disparate group of contestants engaged in a grueling dance marathon. The movie’s title however, conveyed to many people the end result of injury associated with horse racing. It is a misconception since great strides have been made in the treatment of catastrophic breakdown injuries. Success, however, may still be uncertain depending on the specifics of the injury, the experience of the treating team and factors termed luck or fate.
Catastrophic breakdown injuries resulting in death occur with a relatively constant frequency and average about 1.5 horses per thousand race starts. The number of catastrophic injuries treated is often related to economics. Inexpensive horses with little value as breeding animals are often discarded without attempts at treatment. This slowed veterinary advancements in the treatment of these injuries, but improved results were seen over time with more experience and better tools. Although treatment is often possible, prevention is preferable, and it is helpful to know just what you are preventing. In a California study, 83% of fatal injuries in races were musculoskeletal injuries; 80% were related to the proximal sesamoid bones and the third metacarpal bone. Only 56% of the injuries during training involved these bones.
It is important to develop solutions to prevent injury and test these ideas using hypotheses driven research programs. In an era of “evidence-based medicine” the equine industry is often quick to make expensive decisions that are not based on research results, such as expenditures for the poly track. What evidence led to spending millions on these new facilities? Is track surface a way to address some flaw in our training programs or perhaps the problems associated with toe grabs? If so it might be cheaper and more realistic to identify and solve the problems.
Evidence-based research has led to an understanding of the pathogenesis and pathomechanics of bucked shins and a greater understanding of bone modeling and remodeling associated with training on various track surfaces in young horses. Prospective and retrospective studies demonstrated significant reduction in the incidence of bucked shins with slight changes in training methods reducing the incidence from 70-90% to less than 5% in the hands of knowledgeable trainers. As a bonus the decrease in the incidence of bucked shins also decreased the incidence of stress fractures in the cannon bone. Approximately 10% of the catastrophic cannon bone fractures are a sequella to these stress fractures. If adopted, elimination of bucked shins eliminates stress fractures and hence would reduce the breakdown injury rate by 10%. Therefore evidence-based research could be responsible for decreasing bucked shins and eliminating this form of breakdown injury.
Studies of risk factors for different shoeing modalities have shown a 17 times greater risk for condylar fractures with horses wearing shoes with regular toe grabs. The risk for traumatic disruption of the suspensory ligament increased 15.5 times and the risk for fatal injury increased 3.5 times with the use of toe grabs as compared to rim shoes. If the results of this study were correct the elimination of toe grabs on racehorses might decrease the fatal musculoskeletal injury rate by about 3 fold. Studies in our laboratory using accelerometers showed accelerations on the hoof up to 450 g when horses were running at racing speeds with toe grab shoes while specially designed shoes reduced the accelerations by 100g. This shows the adaptability of the horse’s foot since whole body accelerations above 100g are generally not compatible with life. It also points to an avenue of research that may be quickly productive.
What was the shoeing status of recent horses that suffered catastrophic injuries? Did they land on their heels, flat footed or on their toes when they ran? Do these breakdown injuries occur when the foot strikes the ground or when the foot leaves the ground? Our acceleration data suggests that the injury could as well occur when leaving the ground rather than striking it. Can you develop an interface with the racing surface that supports and protects the foot and the horse? Is poly track the answer?
Horses break down while in training and racing; different trainers have different histories and incidence rates. Many questions need to be answered before a thorough understanding of breakdown injuries occurs. The answers lie in evidence-based medicine with hypothesis testing using research methodology. Answers will come gradually but it would behoove the industry to move aggressively to institute change where evidence exists. When dealing with a death rate of 0.15%/start associated with racing it is necessary to have industry-wide cooperation and large studies to make headway.
To start this effort I would suggest testing the null hypothesis that toe grabs have no effect on death rate. This could be done through a single state’s racing commission or a multi-state effort and would be fair for all competitors. The industry would be shown, as doing something worthwhile to study/solve the problem and data would provide the evidence to include or exclude toe grabs on the racetrack. It would be cheaper than installing a polytrack, and might save a few hundred horse lives.