Sesamoid Fracture Prognosis Favorable

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The horse’s fetlock joint has the potential for a large range of motion. The sesamoid bones are two macadamia-nut-shaped bones that sit at the back of the fetlock and are the attachment for the suspensory ligament from above, and the origin of the distal sesamoidean ligaments that travel down to attach to the pastern bone. These ligaments travel up and down as the fetlock flexes and relaxes.

Because of the constant tug on the sesamoids from ligaments above and below, fractures can occur. If they fracture in the lower portion of the bone (toward the ground, base fractures), surgery isn’t an option because the complexity of the anatomy means that trying to get at these fractures causes more damage than it can help. Top/apex fractures, though, can be approached surgically.

Sesamoid-bone fractures are an occupational hazard of athletic horses but can occur in young horses as well. A study performed by the Rood and Riddle Hospital in Kentucky looked at the long-term outcome for 151 Thoroughbred weanlings and yearlings who had surgical removal of apical sesamoid fracture fragments. Of these horses, approximately 92% had fractures in the hind limbs, 8% in the front. Of the horses with front leg sesamoid fractures and subsequent surgery, 55% made it to a racing career, but 86% with operated hind leg sesamoid fractures did. Their performance at the track was equivalent to that of other foals from their same dam.

A limitation of this study is that we don’t know if the horses that didn’t race had a problem related to their prior sesamoid fracture and surgery or a totally unrelated problem. However, looking only at odds, the percentage of youngsters that had sesamoid fractures with surgery and eventually made it to the races was actually higher than for all foals of their dams overall (84% versus 78%). This suggests that the prospect for an athletic career after surgery for a hind leg sesamoid bone fracture in a young horse is good.