At the rear side of the pastern on each equine limb are two small sesamoid bones that provide anchor points for the two branches of the suspensory ligament. As elements of the pastern joint, the sesamoids are under stress each time the horse takes a step.
Like other parts of the horse’s skeleton, these bones respond to weight-bearing and become stronger as the horse exercises, but this is a gradual process that takes time. Moving ahead too fast with a young horse’s training program can lead to fractures in the sesamoid bones if conditioning lags behind the demands of strenuous exercise. Conformation faults and shoeing problems can also be contributing factors if a horse develops a problem with a sesamoid bone. Likewise, lameness in the opposite leg can make a horse put more weight on the sound leg, increasing stress on bones and tendons.
Treatment for a fractured sesamoid depends somewhat on what part of the bone is broken. Fractures at the top of the bone can sometimes be treated by surgically removing the broken tip, while breaks in the middle or bottom part of the bone have a less positive prognosis. If the bone has broken into several small pieces, repair is rarely successful and affected horses are often euthanized.