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Two unrelated but complementary studies recently examined the risks and underlying pathology of catastrophic proximal sesamoid bone fractures in racehorses. A 5-year prospective study in the United Kingdom examined the incidence of sesamoid bone fractures and explored risk factors related to horse and race characteristics. While only 31 horses sustained this specific injury in almost 500,000 starts, the risk of injury for horses racing on all-weather flat tracks was 4 times higher compared with horses racing on turf. Horses with fractures were 5 ½ years of age on average and had started an average of 28 races prior to the injury.
A California study also examined horses with catastrophic sesamoid bone fractures but focused more on the underlying pathology. The sesamoid bones of horses that sustained fractures were found to have more porosity and excessive remodeling compared to controls. The authors concluded horses that sustained sesamoid fractures had adapted to the high mechanical loading characteristic of racing and race training but excessive remodeling left them more susceptible to injury.
Both of these studies suggest that catastrophic sesamoid bone fractures are the end result of a significant period of training and racing. Most of these injuries show evidence of pre-existing pathology attributable to remodeling and an imperfect or incomplete adaptation to mechanical loads that failed to compensate for the demands of race training. Further study could help identify horses at increased risk for injury so training and racing schedules could be modified to accommodate successful adaptation and…