Sesamoid Injuries

Two little bones sitting at the back of the fetlock both amaze and confound veterinarians. The sesamoids, as they’re called, anchor the suspensory apparatus that allows a horse’s foot and fetlock to move properly. Yet their location and anatomy make them vulnerable to injuries that can be difficult to repair and even catastrophic.

 

Given the sesamoids’ location, it isn’t surprising that high speeds can lead to fractures and soft tissue injuries. In a racehorse, for example, the fetlock can sometimes extend to the point that the sesamoid bones actually make contact with the ground. If the pressure is too great, those bones can shatter to a point that requires euthanasia.

 

“Horses have two proximal sesamoid bones on each limb,” says Jeff Blea, DVM, racetrack practitioner and current American Association of Equine Practitioners president. “They, together with the cannon bone and long pastern, make up the fetlock joint.” 

 

Blea explains that the sesamoids are surrounded by an intricate system of ligaments. The suspensory ligament begins at the top back of the cannon bone, runs down the cannon bone, and splits into two branches—one attaching to each sesamoid. Other ligaments connect the sesamoids to each other, and the distal sesamoidean ligaments extend down to the pastern bones. “If you look at it from a physiological standpoint, it’s a highly mechanical area,” says Blea. “It’s an area that is susceptible to increased tension, increased force, and increased pressure.”