The majority of career-ending health concerns in Thoroughbred racehorses are attributed to musculoskeletal injuries. Very importantly, of these injuries, a small subset can be life-threatening to both horses and jockeys if they occur during high speed exercise or racing. Although the industry has achieved a reduction in fatal injury rates in Thoroughbred racing over the past decade, understanding the causes and development of lower forelimb bone fractures that lead to these catastrophic musculoskeletal injuries (CMI) remains one of the highest safety and welfare priorities in horse racing.

The metacarpophalangeal joint (MCP), widely referred to as the fetlock joint, is the most common site of serious orthopedic injuries in Thoroughbred racehorses. Specifically, significant clinical and research efforts have focused on the proximal sesamoid bones (PSBs), as they account for an estimated 45-50% of fatal injuries among U.S. Thoroughbred racehorses.

The Musculoskeletal Research Group at the University of Kentucky (UK), in collaboration with veterinary practitioners, racing regulators, racetracks and scientists at other universities, has ongoing studies in a number of areas that all aim to support and advance the orthopedic health of racehorses and, indeed, all equine athletes. One of these research projects is the PhD dissertation research focus of graduate student Grace Camp. Her project involves the collection and analysis of postmortem computed tomography (CT) forelimb scans from horses that have died on Kentucky racetracks or training facilities that either sustained a CMI or died for reasons unrelated to a CMI (sudden death, colic, etc.). Each scan is assessed for bone lesion pathology across a total of 105 forelimb anatomical sites, from the distal radius to the navicular bone. To date, 1,644 CT scans from 431 horses have been collected, resulting in more than 98,000 anatomical site assessments. This large-scale dataset enables the research team to utilize “big data” strategies and advanced machine learning or data mining techniques to identify and characterize bone lesions and fracture patterns from a large sample set perspective.

Catastrophic PSB fractures have commonly been reported to occur biaxially, but at the same time exhibit distinct fracture configurations between the medial and lateral PSB. With Thoroughbred racehorses, the repetition of fracture locations and patterns that are often observed indicate that consistent pathological processes are important as opposed to random “bad step” events. Advancing our understanding of these processes should facilitate efforts to more effectively identify horses at higher risk of bone fracture, while also providing a foundation of knowledge to improve training methods, diagnostic approaches and therapeutic strategies. Large sample sets will help in learning how to better distinguish between normal and pathological PSB changes associated with high-speed locomotion exercise, while also providing the statistical power to resolve biomedically important relationships.

Veterinary clinicians routinely use advanced diagnostic imaging techniques to evaluate and monitor patient health. In addition to the diagnostic value of these medical images for the specific patient, the captured radiometric data provide details on bone structure, texture and often skeletal adaptation over time. Camp, who earned her undergraduate degree in Equine Science and Management at UK, seeks to extract meaningful information using powerful new computational methods. Her research aims and experimental plans apply biomedical image analysis techniques from a “big data” perspective to investigate three-dimensional size and structural parameters and image-based features of PSBs from CT images, with the goal of identifying and characterizing bone features or patterns of bone alterations that may predispose an equine athlete to a CMI or indicate an elevated risk or susceptibility for a CMI.

Further research into the relationship between bone structure and lesion pathology in PSBs could open new avenues to enhance musculoskeletal health in Thoroughbred racehorses. The insights gained from this medical imaging study and others being conducted around the world have the potential to improve our ability to identify structural features associated with pathological changes and fractures in PSBs. The ultimate goal is to enhance the sensitivity and specificity of detection, monitoring and prevention of serious musculoskeletal injuries in Thoroughbred racehorses and all equine athletes.

This is an excerpt from Equine Disease Quarterly, Vol. 35, Issue 3, funded by underwriters at Lloyd’s, London, brokers, and their Kentucky agents. It was written by Grace Camp, MS, PhD student at the University of Kentucky’s Gluck Equine Research Center, in Lexington, and James N. Macleod, VMD, PhD, professor at the Gluck Equine Research Center.