Humeral Stress Fractures and Return to Racing (AAEP 2011)

A stress fracture is a stress fracture, regardless of its location, right? Well, not necessarily; in some cases, a fracture's location in a bone could have implications for whether the horse will return to his previous level of work or whether his career will be cut short. A research team recently examined whether the location of a stress fracture within the humerus impacted racing prognosis. Nicole Fawns, DVM, a fellow in the Comparative Orthopaedics Research Laboratory at the University of Pennsylvania School of Veterinary Medicine, presented the results at the 2011 American Association of Equine Practitioners convention, held Nov. 18-22 in San Antonio, Texas.

"Stress fractures are a major cause of lameness and result in significant economic loss within the Thoroughbred racing industry," Fawns explained. "The objectives of this study were to characterize stress fractures in the humerus and to describe post-injury racing performance."

Fawns and colleagues completed the retrospective study at Rood & Riddle Equine Hospital, in Lexington, Ky., using medical records from 88 Thoroughbred racehorses referred to the clinic from 1990 to 2010. Each of these horses had been diagnosed with a stress fracture of the humerus via radiography or nuclear scintigraphy.

"The influence of fracture location on racing performance was made by evaluating total earnings, total starts, average earnings, highest class raced, and length of time from injury to next race," Fawns added.

Fawns' key findings included:

  • Seventy-four percent of affected horses raced after recovering from the fractures;
  • A greater percentage of horses that raced pre-injury raced after recovery than horses that did not race prior to injury (83%);
  • The average length of time between injury and racing following recovery was 285 days;
  • The location of the lesion within the humerus and affected forelimb had "no significant influence" on the majority of racing variables evaluated;
  • Horses started significantly more races after injury, but overall the horses raced in a lower class than they did prior to injury;
  • Average earnings per start decreased significantly post-injury; and
  • Bilaterally affected horses (those with stress fractures in both legs) had "identical" fracture locations in both legs.

Still, Fawns et al. concluded that the affected limb and the location of the stress fracture within the humerus had no significant effect on return to racing, but did impact racing performance.  

"Our results indicate that humeral stress fracture—regardless of location or limb affected—had a negative impact on racing performance but did not preclude return to racing" she explained. "The significant drop in class, increase in number of starts, and decrease in average earnings is multifactorial; (other) variables—including increasing age—negatively affect racing performance."

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.

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