Whitepaper: Injury prevention in Thoroughbred racehorses using safe, high-quality standing CT imaging: The Equina® by Asto CT

David Ergun 1,2, PhD, CEO

Chris Whitton 3, BVSc, PhD

Sabrina Brounts 4, DVM, MS, PhD, DACVS, DECVS, DACVSMR

Peter Muir 4, BVSc, MVetClinStud, PhD, DACVS, DECVS, FRCVS

1: Asto CT Inc., Middleton, WI USA

2: Medical Physics, University of Wisconsin-Madison, Madison, WI USA

3: Department of Veterinary Clinical Sciences, University of Melbourne, Werribee, Australia

4: School of Veterinary Medicine, University of Wisconsin-Madison, Madison, WI USA

Updated May 2026

INTRODUCTION

Repeated racing exercise can cause serious musculoskeletal injury in horses and place jockeys at risk of serious injury as well (Hitchens et al. 2016). Risk of serious injury with subsequent euthanasia can be high at certain locations across the world. In the fetlock, fractures of the condyles of the cannon bone and the proximal sesamoid bones are common causes of fatal injury. These fetlock injuries are stress fractures that occur because athletic activity has caused  accumulation of fatigue damage to bone (Muir et al. 2006, Dubois et al. 2014). In addition to resulting in deaths, these types of musculoskeletal injury can affect racing performance and result in enforced rest and early retirement and are, therefore, of substantial importance across the world (Colgate et al. 2020, 2025). For horse racing to maintain its social license with the public, it is important to minimize injuries occurring in Thoroughbred racehorses. News headlines about horse deaths and welfare concerns involving racetracks are unacceptable to the public as we have seen in recent years. Therefore, improving the welfare, quality of life, and clinical care of Thoroughbred racehorses is of utmost importance (Colgate et al. 2020, 2025).

A new standing computed tomography (sCT) system, the Equina®, (Asto CT, Middleton, WI), has been developed and deployed for imaging of the distal limbs (Brounts et al. 2022a) and head/neck (Brounts et al. 2022b) of a sedated horse in the standing position. One of the key goals is to make equine imaging simple, efficient, and effective so it can be used as part of a preemptive injury prevention program to help minimize risk of serious injuries to Thoroughbred racehorses. In Australia, Racing Victoria has used the Equina imaging system for pre-race screening of horses as part of their new safety measures supporting the welfare of horses participating in the Spring Racing Carnival in Victoria. Use of this advanced veterinary technology for early detection and management of musculoskeletal injuries, particularly fetlock stress fractures, can move us towards a new standard of care for Thoroughbred racehorses. In this paper, we provide a brief description of the key features of the Equina® system, and its use in pre-race injury prevention screening.

DETECTION OF PRE-FRACTURE PATHOLOGY

Fractures of the distal limbs of racehorses frequently arise from repetitive stress on the bones of the skeleton due to training and racing (Muir et al. 2006, Shaffer et al. 2021). While the limbs are designed for running and bearing the weight of the horse, the demands of a training program may exceed the body’s ability to repair fatigue injury and associated bone microdamage. Over time, microdamage accumulation leads to macroscopic cracking of bone tissue, and eventually a stress fracture (Muir et al. 2006). Early detection of bone fatigue injury is highly advantageous as this enables identification of horses with heightened risk of serious injury (Brown Irandoust et al. 2026). Personalized care through modification of training and specific individualized treatment can then be implemented to enable bone healing and reduction of injury risk during ongoing athletic activity.

Unfortunately, many horses that experience fatal injury during racing do not exhibit clinically detectable abnormalities during standard pre-race veterinary inspection (Stewart & Lam 2010). Standard digital radiographic imaging can detect fractures once they have begun to propagate but lacks the diagnostic sensitivity to detect subtle changes in bone associated with accumulation of microdamage and development of an incipient stress fracture (Morgan et al. 2006, Irandoust O’Neil et al. 2025a). The analysis of gait data collected during races shows potential for identifying horses developing early fatigue injury to bone (Wong et al. 2023), thus assisting veterinarians to target horses that would benefit from advanced imaging, such as Equina® by Asto CT.

In human and veterinary medicine clinician training regarding interpretation of medical images is focused on identification of structural change, not risk assessment. Whilst risk assessment for fetlock stress fracture based on subjective assessment of fetlock sCT imaging has shown promising results, objective assessment, particularly mechanical assessment, would be preferable (Brown Irandoust et al. 2026). Bone stress fractures propagate to failure because strain becomes intolerable in the fatigue injury site and is not directly related to the metabolic activity of the bone. Virtual mechanical testing (VMT) of a 3D computer model prepared from sCT imaging is an objective assessment approach (Irandoust et al. 2025b, Brown Irandoust et al. 2026) that is now available for use in injury prevention screening. Importantly, VMT directly assesses strain concentration in sites of bone fatigue injury using finite element analysis. With more research, it should be possible to define a fracture threshold that would further inform risk assessment interpretation of sCT injury prevention screening. Such knowledge will help avoid unnecessary scratching of a horse from racing as well as ensuring personalized care of horses with imminent risk of serious injury that is really needed including removing the horse from racing and providing appropriate rest to allow bone fatigue injury to heal. It would be expected that a similar approach to risk assessment for proximal sesamoid bone stress fracture (Shaffer et al. 2021, Thom et al. 2025) would be equally impactful. Collectively, this recent research suggests condylar and mid-body proximal sesamoid bone stress fractures in the fetlock should be viewed as preventable injuries in populations of Thoroughbred racehorses that are appropriately screened using sCT.

Equina® is readily available and is being increasingly used for routine lower limb imaging in horses. High throughput low-cost screening of large numbers of horses with sCT is now possible, which makes it attractive for injury prevention in racing Thoroughbreds. Equina® sCT imaging has the diagnostic sensitivity required for detection of early signs of fatigue damage to bone (Irandoust et al. 2025a, Brown Irandoust et al. 2026), and is an ideal tool for detection and monitoring for early bone injury, thereby reducing horse deaths from stress fracture injury. Reduction in high-speed falls during racing will also reduce jockey injury (Hitchens et al. 2016).

EQUINA IN USE TODAY FOR PRE-RACE SCREENING

The Melbourne Cup is the most watched horse race in Australia. For many people it is the only race they watch all year so injuries that occur in the race are highly publicized. In recent years international horses have made up an increasing proportion of the field and injuries in these horses have been a particular problem. A cluster of deaths due to catastrophic limb injuries consisting of 5 horses in a period of 10 years resulted in increased veterinary scrutiny of horses competing in the Melbourne Cup and the Carnivals that surround this race. Investigation of these deaths found that a large proportion of the fatally injured horses had pathology that would likely have been detected by sCT examination before the incident.

For this reason, Racing Victoria introduced mandatory pre-race screening with advanced imaging for horses competing in the Melbourne Cup in 2021 as one of several measures aimed at reducing injury risk. All four fetlocks of each horse entered in the Melbourne Cup, and all international horses in Racing Victoria’s quarantine center are scanned. In 2022, this involved a total of 40 horses being scanned, with 38 being scanned in a 10-day period. Three horses (7.5%) were withdrawn based on their sCT scan findings. Over the last five years, no fatalities have occurred in the Melbourne Cup with this approach to injury prevention screening.

sCT screening will not eliminate risk of injury as racing Thoroughbred horses has a standard level of risk associated with the activity. However, sCT screening by Racing Victoria for Melbourne Cup finalists over the last 5 years suggests that use of sCT as part of an injury prevention program is effective and substantially reduces the risk of serious or fatal injury.

In addition to screening for specific races, Racing Victoria has also introduced a subsidy scheme to reduce the cost of advanced imaging for all racehorses and, therefore, increase its use throughout the year to further reduce the risk of severe injury. Implementing low-cost screening is particularly helpful for low value horses, as bone fatigue injury commonly affects all grades of racing Thoroughbreds.

Pre-race screening CT scan of a Thoroughbred racehorse ahead of the Melbourne Cup.

TRANSFORMING THE STANDARD OF CARE IN INJURY PREVENTION

Development of the Equina® imaging system has broad implications across the equine community. By offering sCT at either a local veterinary clinic or a training center, it can preserve the quality of life, support a successful athletic career, and enhance the financial value of the horses. Equina® can be incorporated into several parts of routine racehorse practice.

These include:

• Pre-purchase imaging of yearlings or older racehorses

• Pre-race screening for elevated risk of serious musculoskeletal injury in racehorses actively training and racing to assess fitness to race. The ability to image many horses in a short period of time with no disruption of training activity makes the Equina® an ideal imaging system for this type of screening. Racing Victoria in Australia has implemented these safety measures already.

• Evaluation of horses exhibiting lameness or gait change, such as reduction in speed or stride length (Wong et al. 2023). Identification of structural changes associated with early bone fatigue injury can enable personalized clinical care, modification of training, and prevention of serious musculoskeletal injury.

• Enabling use of a 3D printed patient-specific transcondylar drilling guide to optimize transcondylar screw placement in the standing horse, a treatment that is being increasingly used for parasagittal groove subchondral bone injury to prevent propagation of a condylar stress fracture.

• Longitudinal monitoring of racehorses with concerning fatigue injury, since fracture risk can change rapidly over time.

SUMMARY

Improving the health and welfare of Thoroughbred racehorses through prevention and diagnosis of serious or fatal musculoskeletal injury is a critical current need in the Thoroughbred racehorse industry. The evolution of sCT scanning in the equine veterinary world has moved to wide bore gantries, rugged, quick, easy use, and high throughput performance. The Equina imaging system is readily available and addresses a current public concern about the health and welfare of the Thoroughbred racehorse. By developing an easy-to-use affordable sCT system, Asto CT is opening the door for best-in-class limb imaging for all Thoroughbred racehorses.

REFERENCES

Brown, N., Irandoust, S., Thom, E.J., Whitton, R.C., Henak, C.R., Muir, P. (2026). Risk assessment for condylar stress fracture in elite racing Thoroughbreds using standing computed tomography-based virtual mechanical testing. Equine Vet J. 2026, epub.

Brounts, S.H., Lund, J.R., Whitton, R.C., Ergun, D.L., Muir, P. Use of a novel helical fan beam imaging system for computed tomography of the distal limb in sedated standing horses: 167 cases (2019-2020). J Am Vet Med Assoc. 2022a;260:1351-1360.

Brounts, S.H., Henry, T., Lund, J.R., Whitton, R.C., Ergun, D.L., Muir, P. Use of a novel helical fan beam imaging system for computed tomography of the head and neck in sedated standing horses: 120 cases (2019-2020). J Am Vet Med Assoc. 2022b;260:1361-1368.

Colgate, V.A., Carpenter, R., Kawcak, C., Muir, P. Palmer, S., Parkin, T., Powell, S.E., Ramzan, P., Riggs, C.M., Spriet, M., Stover, S.M., Whitton, C., Marr C.M. Science-in-brief: Risk assessment for reducing injuries of the fetlock bones in Thoroughbred racehorses. Equine Vet J. 2020;52:482-488

Colgate, V.A., Riggs, C.M.; FRAT Group II. IFHA Global Summit of Equine Safety and Technology: Fracture prediction and prevention. (2025). Equine Veterinary Journal, epub. doi: 10.1111/evj.14458.

Dubois., M-S., Morello, S., Rayment, K., Markel, M.D., Vanderby, Jr., R., Kalscheur, V.L., Hao, Z., McCabe, R.P., Marquis, P., Muir, P. Computed tomographic imaging of subchondral fatigue cracks in the distal end of the third metacarpal bone in the Thoroughbred racehorse can predict crack micromotion in an ex-vivo model. PLoS One 2014;9:e101230.

Hitchens, P.L., Hill, A.E., Stover, S.M. The role of catastrophic injury or sudden death of the horse in race-day jockey falls and injuries in California, 2007-2012. Equine Vet J 2016;48:50-56.

Irandoust, S., O’Neil, L., Stevenson, C.M., Franseen, F.M., Ramzan, P.H.L., Powell, S.E., Brounts, S.H., Loeber, S.J., Ergun, D.L., Whitton, R.C., Henak, C.R., Muir, P. Comparison of planar digital radiography and helical standing computed tomography for assessment of condylar stress fracture risk in Thoroughbred racehorses. Equine Vet J. 2025a;57:723-736.

Irandoust, S., Whitton, R.C., Henak, C.R., Muir. P. Tuning and validation of a virtual mechanical testing pipeline for condylar stress fracture risk assessment in Thoroughbred racehorses. Royal Society Open Science. 2025b;12:241935.

Morgan, J.W., Santschi, E.M., Zekas, L.J., Scollay-Ward, M.C., Markel, M.D., Radtke, C.L., Sample, S.J., Keuler, N.S., Muir, P. Comparison of radiography and computed tomography to evaluate metacarpo/metatarsophalangeal joint pathology of paired limbs of Thoroughbred racehorses with severe condylar fracture. Vet Surg 2006: 35:611-617.

Muir, P., McCarthy, J., Radtke, C.L., Markel, M.D., Santschi, E.M., Scollay, M.C., Kalscheur, V. L. Role of endochondral ossification of articular cartilage and functional adaptation of the subchondral plate in the development of fatigue microcracking of joints. Bone 2006;38:342-349.

Shaffer, S.K., To, C., Garcia, T.C, Fyhrie, D.P., Uzal, F.A., Stover, S.M. Subchondral focal osteopenia associated with proximal sesamoid bone fracture in Thoroughbred racehorses. Equine Vet. J. 2021;53:294-305.

Stewart, B.D., Lam, K.H. Racing injury risk assessment at official pre-race veterinary inspections in Hong Kong Jockey Club. Proceedings of the 18th international conference of racing analysts and veterinarians; New Zealand 2010: p. 296-297.

Thom, E.J., Irandoust, S., Henak, C.R., Muir, P. Fatigue injury in the proximal sesamoid bones of Thoroughbred racehorses is associated with palmar osteochondral disease in the condyles of the third metacarpal bone. 2025 ORS Annual Meeting, Phoenix.

Wong, A.S.M., Morrice-West, A.V., Whitton, R.C., Hitchens, P.L. Changes in Thoroughbred speed and stride characteristics over successive race starts and their association with musculoskeletal injury. Equine Vet Journal 2023;55:194-204. 

©2026 Asto CT Inc – All rights reserved. Asto CT and Equina are trademarks of Asto CT. Drs. Ergun, Brounts and Muir have financial interest in Asto CT.