Association between long periods without high-speed workouts and risk of complete humeral or pelvic fracture in Thoroughbred racehorses: 54 cases (1991–1994)

Tracey K. Carrier From the J. D. Wheat Orthopedic Research Laboratory. Department of Anatomy, Physiology, and Cell Biology (Carrier, Stover), the California Veterinary Diagnostic Laboratory System (Estberg, Johnson, Read, Ardans), and the Department of Medicine and Epidemiology (Gardner), School of Veterinary Medicine, University of California, Davis, CA 95616-8732.

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Leah Estberg From the J. D. Wheat Orthopedic Research Laboratory. Department of Anatomy, Physiology, and Cell Biology (Carrier, Stover), the California Veterinary Diagnostic Laboratory System (Estberg, Johnson, Read, Ardans), and the Department of Medicine and Epidemiology (Gardner), School of Veterinary Medicine, University of California, Davis, CA 95616-8732.

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Susan M. Stover From the J. D. Wheat Orthopedic Research Laboratory. Department of Anatomy, Physiology, and Cell Biology (Carrier, Stover), the California Veterinary Diagnostic Laboratory System (Estberg, Johnson, Read, Ardans), and the Department of Medicine and Epidemiology (Gardner), School of Veterinary Medicine, University of California, Davis, CA 95616-8732.

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Ian A. Gardner From the J. D. Wheat Orthopedic Research Laboratory. Department of Anatomy, Physiology, and Cell Biology (Carrier, Stover), the California Veterinary Diagnostic Laboratory System (Estberg, Johnson, Read, Ardans), and the Department of Medicine and Epidemiology (Gardner), School of Veterinary Medicine, University of California, Davis, CA 95616-8732.

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Bill J. Johnson From the J. D. Wheat Orthopedic Research Laboratory. Department of Anatomy, Physiology, and Cell Biology (Carrier, Stover), the California Veterinary Diagnostic Laboratory System (Estberg, Johnson, Read, Ardans), and the Department of Medicine and Epidemiology (Gardner), School of Veterinary Medicine, University of California, Davis, CA 95616-8732.

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Deryck H. Read From the J. D. Wheat Orthopedic Research Laboratory. Department of Anatomy, Physiology, and Cell Biology (Carrier, Stover), the California Veterinary Diagnostic Laboratory System (Estberg, Johnson, Read, Ardans), and the Department of Medicine and Epidemiology (Gardner), School of Veterinary Medicine, University of California, Davis, CA 95616-8732.

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Alex A. Ardans From the J. D. Wheat Orthopedic Research Laboratory. Department of Anatomy, Physiology, and Cell Biology (Carrier, Stover), the California Veterinary Diagnostic Laboratory System (Estberg, Johnson, Read, Ardans), and the Department of Medicine and Epidemiology (Gardner), School of Veterinary Medicine, University of California, Davis, CA 95616-8732.

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Objective

To determine whether a two-month or longer period without official high-speed workouts (lay-up) is associated with humeral or pelvic fracture in Thoroughbred racehorses.

Design

Retrospective study.

Animals

Thoroughbred racehorses in California that were euthanatized because of a complete humeral or pelvic fracture.

Procedure

Age, sex, activity, number of lay-ups, number of days from a race or official timed workout to fracture, number of days from end of last lay-up to fracture, mean duration of lay-ups, and total number of days in race training were compared between horses with humeral fractures and horses with pelvic fractures. A case-crossover study was used to estimate relative risk for fracture of the humerus or pelvis occurring within hazard periods of 10 and 21 days following lay-up, compared with periods following more regular participation in official racing or timed workout events.

Results

Horses with pelvic fractures were more often female, older, and had 0 or ≥ 2 lay-ups. Horses with humeral fractures were typically 3-year-old males that had 1 lay-up. Horses with pelvic fractures had more total days in race training, fewer days from last exercise event to fracture, and a greater number of days from end of last lay-up to fracture than horses with humeral fractures. Return from lay-up was strongly associated with risk for humeral fracture during hazard periods of 10 and 21 days (relative risk = 71 and 45, respectively).

Clinical Implications

Risk of humeral fracture may be reduced if horses are cautiously reintroduced into race training after lay-up. (J Am Vet Med Assoc 1998;212: 1582–1587)

Objective

To determine whether a two-month or longer period without official high-speed workouts (lay-up) is associated with humeral or pelvic fracture in Thoroughbred racehorses.

Design

Retrospective study.

Animals

Thoroughbred racehorses in California that were euthanatized because of a complete humeral or pelvic fracture.

Procedure

Age, sex, activity, number of lay-ups, number of days from a race or official timed workout to fracture, number of days from end of last lay-up to fracture, mean duration of lay-ups, and total number of days in race training were compared between horses with humeral fractures and horses with pelvic fractures. A case-crossover study was used to estimate relative risk for fracture of the humerus or pelvis occurring within hazard periods of 10 and 21 days following lay-up, compared with periods following more regular participation in official racing or timed workout events.

Results

Horses with pelvic fractures were more often female, older, and had 0 or ≥ 2 lay-ups. Horses with humeral fractures were typically 3-year-old males that had 1 lay-up. Horses with pelvic fractures had more total days in race training, fewer days from last exercise event to fracture, and a greater number of days from end of last lay-up to fracture than horses with humeral fractures. Return from lay-up was strongly associated with risk for humeral fracture during hazard periods of 10 and 21 days (relative risk = 71 and 45, respectively).

Clinical Implications

Risk of humeral fracture may be reduced if horses are cautiously reintroduced into race training after lay-up. (J Am Vet Med Assoc 1998;212: 1582–1587)

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