Bone Chips: Prevalence and Effect on Racing Career (AAEP 2010)

In the first study of its kind performed on 2-year-old Thoroughbred racehorses, Daniel T. Meagher, DVM, MS, Dipl. ACVS, of Valley Equine Associates, in Ranson, W.Va., set out to determine the prevalence of radiographic lesions and their effect on race performance. A similar study was previously carried out on radiographic abnormalities in yearlings, but Meagher's study was the first to examine the prevalence of abnormalities in 2-year-olds and what effect they had on their racing careers.

At the 56th Annual Convention of the American Association of Equine Practitioners, Meagher presented the current study in which he and his colleagues examined carpal, fetlock, stifle, and hock radiographs associated with 2-year-olds in training sales from 1997 to 2001 in Barretts Equine Limited's repository. Barretts, a Thoroughbred auction company based in Pomona, Calif., gave Meagher access to these radiographs for the research.

Of the 953 sets of radiographs examined, 69% (654 horses) had no evidence of lesions and served as controls, and the remaining 31% (299 horses) with lesions were considered cases. Meagher noted that 63% of the case horses were male, and that 11 horses had lesions in more than one region (in both the knee and the fetlock, for example).

Meagher's findings revealed that the case horses were statistically less likely to start a race or earn money. "Eighty-six percent of (case) horses raced, while 91% of control horses raced," he said.

"Specific radiographic abnormalities were associated with lower race performance," Meagher wrote. "However, none of the individual lesions prevented all affected horses from racing."

The researchers revealed that lesions in the fetlock area were the most common, with approximately 40% of the case studies (121 horses) showing such lesions. Meagher noted the most drastic difference in performance between case and control horses involved horses with a forelimb proximal P1 chip fracture (a chip in the upper portion of the long pastern bone)--a less commonly found, but still significant lesion.

"A study examining the effects of arthroscopic removal of P1 chips in race horses shows that the prognosis is favorable following removal," he observed. "Therefore, the assumption is that proximal P1 chips are not a big deal on pre-sale radiographs, and this (information) may refute some of that dogma.

"However, caution must be taken in interpreting these results, as no knowledge of pre- or post-sale surgery was known," he advised.

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