Sesamoid Fractures: Size, Shape, and Racing Prognosis

The most common type of fracture in the equine forelimb is that of the PSB

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 record. The average earnings per start and total number of starts after surgery were used in the comparisons.

After reviewing the results, the authors found that the size and shape of the apical fracture in the PSB did not affect the racehorses' prognoses. A horse's average earnings and total postoperative starts appeared to have no relationship to the size or shape of the PSB fragment. Some horses in the study that had the largest fracture fragments removed went on to race successfully, the team noted.

The study authors did state that "presumably there is a size (of fracture) that will begin to affect the prognosis for racing ... but the threshold was not identifiable in this group."

From the current study the authors concluded that the only reliable tool for predicting racing prognosis is the anatomical location of the fractured sesamoid: Horses with fractures in the inner region of the PSB in the forelimb had the least favorable prognosis of all the fractures examined.

The study, "Size and Geometry of Apical Sesamoid Fracture Fragments as a Determinant of Prognosis in Thoroughbred Racehorses," was published in July in the Equine Veterinary Journal. The abstract is available online.

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