When an equine athlete suffers a sesamoid fracture, the owner will often ask his or her veterinarian that daunting question: "What’s his prognosis to return to competition?" A team of researchers recently set out to determine if, in some cases, the size and shape of a bone fragment could help veterinarians give a more accurate prognosis for a sesamoid bone fracture. They found the answer wasn’t as straightforward as they’d hoped.

The most common type of fracture in the equine forelimb is that of the proximal sesamoid bones (PSB), a pair of small, nodular bones located at the back of the fetlock. Apical fractures, which affect the upper third of the sesamoid bones, are the most common of these, and they can occur in either the medial (inner) or lateral (outer) region of the PSB. Thoroughbred racehorses are especially prone to this type of fracture due to the rigors of the sport.

In a recent retrospective study, J. Lacy Kamm, DVM, a PhD graduate student at the Colorado State University Orthopaedic Research Center in Fort Collins, and a research team assessed the geometry of apical sesamoid fractures to see if the size or shape of the bone fragment impacted the horse’s prognosis for racing. The researchers examined 110 Thoroughbred weanlings and yearlings and 56 Thoroughbreds in training that underwent arthroscopic surgery for removal of an apical PSB fragment at Rood & Riddle Equine Hospital, in Lexington, Ky., between January 1994 and December 2002.

The researchers measured the size/shape of each horse’s fracture via radiographs, and then compared the results with the animal’s postoperative race reco