J.D. Wheat Veterinary Orthopedic Research Laboratory

Catastrophic Injuries in Racehorses

We have...
  • discovered that most fatalities due to a skeletal injury are predisposed by horses training or racing with a pre-existing injury (Figure 1)
  • demonstrated risk factors for some injuries include …
    • hoof conformation
    • toe grabs
    • training intensity
    • lay-up enhanced
    • diagnostic techniques for detection of mild injuries

Recently, we have discovered that pre-existing injuries also play a role in fractures of the proximal sesamoid bone that result in fetlock breakdown, the most common cause of death in Thoroughbred and Quarter Horse racehorses. With knowledge that catastrophic injuries are the acute manifestation of a more chronic process, we continue to work on understanding injury development to determine strategies for injury prevention.

Collaborations among the California Horse Racing Board Postmortem Program, California Animal Health and Food Safety Laboratory system, Thoroughbred and Quarter Horse racing industries, our research laboratory, and research funding organizations (Center for Equine Health, UCDavis; Grayson-Jockey Club Research Foundation; Pacific Coast Quarter Horse Association; Southern California Equine Foundation; USDA; and private donors) make this work possible.



Photo: Injuries Chart

Figure 1. The majority of fatalities due to fracture of a long bone are due to transient weakening associated with attempted healing of a pre-existing stress fracture.



Stover SM, Johnson BJ, Daft BM, Read DH, Anderson M, Barr BC, Kinde H, Moore J, Stoltz J, Ardans AA
. An association between complete and incomplete stress fractures of the humerus in racehorses. Equine Veterinary Journal, 1992;24(4): 260-3.

Johnson BJ, Stover SM, Daft BM, Kinde H, Read DH, Barr BC, Anderson M, Moore J, Woods L, Stoltz J. Causes of death in racehorses over a 2 year period. Equine Veterinary Journal, 1994;26(4): 327-30.

Estberg L, Gardner IA, Stover SM, Johnson BJ, Case JT, Ardans A. Cumulative racing-speed exercise distance cluster as a risk factor for fatal musculoskeletal injury in Thoroughbred racehorses in California. Preventive Veterinary Medicine, 1995;24: 253-63.

Estberg L, Stover SM, Gardner IA, Johnson BJ, Case JT, Ardans A, Read DH, Anderson ML, Barr BC, Daft BM, Kinde H, Moore J, Stoltz J, Woods LW. Fatal musculoskeletal injuries incurred during racing and training in thoroughbreds. Journal of the American Veterinary Medical Association, 1996;208(1): 92-6.

Kane AJ, Stover SM, Gardner IA, Case JT, Johnson BJ, Read DH, Ardans AA. Horseshoe characteristics as possible risk factors for fatal musculoskeletal injury of thoroughbred racehorses. American Journal of Veterinary Research, 1996;57(8): 1147-52.

Hornof WJ, Stover SM, Koblik PD, Arthur RM. Oblique views of the ilium and the scintigraphic appearance of stress fractures of the ilium. Equine Veterinary Journal, 1996;28(5): 355-8.

Estberg L, Stover SM, Gardner IA, Drake CM, Johnson B, Ardans A. High-speed exercise history and catastrophic racing fracture in thoroughbreds. American Journal of Veterinary Research, 1996;57(11): 1549-55.

Haussler KK, Stover SM, Willits NH. Developmental variation in lumbosacropelvic anatomy of thoroughbred racehorses. American Journal of Veterinary Research, 1997;58(10): 1083-91.

Estberg L, Stover SM, Gardner IA, Johnson BJ, Jack RA, Case JT, Ardans A, Read DH, Anderson ML, Barr BC, Daft BM, Kinde H, Moore J, Stoltz J, Woods L. Relationship between race start characteristics and risk of catastrophic injury in thoroughbreds: 78 cases (1992). Journal of the American Veterinary Medical Association, 1998;212(4): 544-9.

Estberg L, Gardner IA, Stover SM, Johnson BJ. A case-crossover study of intensive racing and training schedules and risk of catastrophic musculoskeletal injury and lay-up in California thoroughbred racehorses. Preventative Veterinary Medicine, 1998;33(1-4): 159-70.

Carrier TK, Estberg L, Stover SM, Gardner IA, Johnson BJ, Read DH, Ardans AA. Association between long periods without high-speed workouts and risk of complete humeral or pelvic fracture in thoroughbred racehorses: 54 cases (1991-1994). Journal of the American Veterinary Medical Association, 1998;212(10): 1582-7.

Haussler KK, Stover SM. Stress fractures of the vertebral lamina and pelvis in Thoroughbred racehorses. Equine Veterinary Journal, 1998;30(5): 374-81.

Haussler KK, Stover SM, Willits NH. Pathologic changes in the lumbosacral vertebrae and pelvis in Thoroughbred racehorses. American Journal of Veterinary Research, 1999;60(2): 143-53.

Hill AE, Stover SM, Gardner IA, Kane AJ, Whitcomb MB, Emerson AG. Risk factors for and outcomes of noncatastrophic suspensory apparatus injury in Thoroughbred racehorses. Journal of the American Veterinary Medical Association, 2001;218(7): 1136-44.

Hill AE, Carpenter TE, Gardner IA, Stover SM. Evaluation of a stochastic Markov-chain model for the development of forelimb injuries in Thoroughbred racehorses. American Journal of Veterinary Research, 2003;64(3): 328-37.

Le Jeune SS, Macdonald MH, Stover SM, Taylor KT, Gerdes M. Biomechanical investigation of the association between suspensory ligament injury and lateral condylar fracture in thoroughbred racehorses. Vet Surg, 2003;32(6): 585-97.<,/

Gross DK, Stover SM, Hill AE, Gardner IA. Evaluation of forelimb horseshoe characteristics of thoroughbreds racing on dirt surfaces. Am J Vet Res, 2004;65(7): 1021-30.

Hill AE, Gardner IA, Carpenter TE, Stover SM. Effects of injury to the suspensory apparatus, exercise, and horseshoe characteristics on the risk of lateral condylar fracture and suspensory apparatus failure in forelimbs of thoroughbred racehorses. Am J Vet Res, 2004;65(11): 1508-17.

Anthenill LA, Stover SM, Gardner IA, Hill AE, Lee CM, Anderson ML, Barr BC, Read DH, Johnson BJ, Woods LW, Daft BM, Kinde H, Moore JD, Farman CA, Odani JS, Pesavento PA, Uzal FA, Case JT, Ardans AA. Association between findings on palmarodorsal radiographic images and detection of a fracture in the proximal sesamoid bones of forelimbs obtained from cadavers of racing Thoroughbreds. American Journal of Veterinary Research, 2006;67(5): 858-868.

Anthenill LA, Stover SM, Gardner IA, Hill AE. Risk factors for proximal sesamoid bone fractures associated with exercise history and horseshoe characteristics in Thoroughbred racehorses. American Journal of Veterinary Research, 2007;68(7): 760-771.

Stover SM, Murray A. The California Postmortem Program: leading the way. Vet Clin North Am Equine Pract, 2008;24(1): 21-36. Entwistle RC, Sammons SC, Bigley RF, Hazelwood SJ, Fyhrie DP, Gibeling JC, Stover SM. Material properties are related to stress fracture callus and porosity of cortical bone tissue at affected and unaffected sites. J Orthop Res. 2009

Anthenill LA, Gardner IA, Pool RR, Garcia TC, Stover M. Focal lesions likely predispose midbody fracture of proximal sesamoid bones in Thoroughbred racehorses. American Journal of Veterinary Research. 2009 IN PRESS

Entwistle RC, Sammons SC, Bigley RF, Hazelwood SJ, Fyhrie DP, Gibeling JC, Stover SM. Material properties are related to stress fracture callus and porosity of cortical bone tissue at affected and unaffected sites. Journal of Orthopaedic research 2009;27(10):1272-9.