Bone Chips in the Knee and Racing Potential (AAEP 2010)

Before purchasing a yearling it's important to review his health records to ensure he is healthy and sound enough for a successful racing career. Jennifer L. Higgins, DVM, gave potential buyers insight into specific lesions that could reduce a horse's career earnings when she presented a retrospective study on the subject at the 56th Annual Convention of the American Association of Equine Practitioners, held Dec. 4-8 in Baltimore, Md.

Higgins, an associate veterinarian at Northern Lakes Veterinary Hospital in Ashland, N.H., completed the study with a team from Rood & Riddle Equine Hospital in Lexington, Ky., when she was an ambulatory intern. The team reviewed more than 5,000 radiographs of Thoroughbred yearlings offered for public sale from 2004 to 2007. They examined bone fragments located in the back of the horses' knees on the articular surfaces of the accessory carpal bone that were previously considered to be a mild problem, hoping to determine whether these fragments affected racing prognosis.

The researchers narrowed their focus to 45 yearlings that met their inclusion criteria. Of these 45 case studies, 23 horses had lesions in the left knee, 19 in the right, and three had lesions in both knees. Due to the retrospective nature of the study, there was no way of knowing how or when the horses sustained the lesions.

They then pulled complete race records on the 45 horses, mainly focusing on the number of starts, earnings per start, and career earnings.

"We compared these records to those of (siblings on) their dam's side," Higgins said. The comparison with the maternal siblings allowed the researchers to have controls in the study.

Higgins and colleagues revealed that the lesions in the accessory carpal bones didn't have an effect on the number of starts the study horses made, but they had an appreciable effect on career earnings.

"Both the study horses and their siblings made it to race," Higgins said. "But the study horses made significantly less money per start than the siblings during their 2- and 3-year-old campaigns."

Higgins noted that the siblings made roughly, on average, $1,500 more per start over their 2- and 3-year-old campaigns than did the case horses. Subsequently, the siblings had higher career earnings than the study horses.

Higgins did point out that the small study size may have impacted the results. She added that there was no way of knowing how long fragments had been in joints at the time the radiographs were taken, so it was unclear if fragment chronicity impacted the results.

"Racing is complex and outcomes are influenced by multiple factors," Higgins said. But, she added, in this study bone fragments of the accessory carpal bone had a significant negative impact on racing performance.

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

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