Clinical science has made significant strides over the past 30 years to help us understand why catastrophic injuries occur. This has led to techniques and practices that enable veterinarians to identify many at-risk horses. | Photo: Courtesy University of Pennsylvania School of Veterinary Medicine

More than 80% of life-threatening injuries Thoroughbreds sustain at racetracks are the result of limb fractures. Losing horses this way is a significant issue for racing in terms of horse welfare and owner finances.

Most fractures happen during galloping without any apparent inciting event. Many scientific studies over the past 25 years have shown that these injuries are the consequence of repetitive stress injuries to the skeleton due to the repeated large loads associated with high-speed work.

Bone tissue can detect the type of loads and forces placed on it and respond through a biological process called bone adaptation. This process strengthens the bone so it is better able to withstand the new loads and forces. However, adaptation is not instant, and as part of the process, some areas of bone will become weaker before they become stronger. If the horse continues to do repeated high-intensity exercise during this phase, microdamage accumulates and can lead to small, incomplete stress fractures, also called “bone fatigue