The proximal sesamoid bones are two bones that make up the back part of the fetlock joint. They are also an integral part of the suspensory apparatus of the limb. The suspensory ligament attaches to them from above, and distal ligaments anchor them to the pastern bones below.
When the fetlock is overextended, the suspensory apparatus is overloaded, excessive tension develops across the bones and they can fracture. This is most commonly seen in racehorses. It is more common in severely fatigued horses at the end of a race.
Weakness within the sesamoid bones predisposes to this kind of fracture. The fracture can also occur in foals that overexert after a long period of confinement.
Diagnosis requires lameness exam, nerve blocks and x-ray. Ultrasound is of value in determining extent of soft tissue injury (especially suspensory ligament injury), which is often present.
X-ray determines the precise configuration of the fracture. This knowledge is needed in order to determine the best treatment plan and prognosis.
Treatment depends on the specific fracture, when the fracture occurred, and the horse’s response to injury. Some heal well with months of rest and no other treatment. Others require surgical removal, whereas mid-body fractures are often screwed together. Your vet will provide these options based on the specific nature of the fracture.
Other Diagnoses Considered
Prognosis & Relevant Factors
There are a variety of fracture types that affect these bones. Each carries a different prognosis. The prognosis varies from good for small apical (upper) fractures to poor for severe body fractures. Horses that have suspensory ligament and distal ligament involvement also tend to have a worse prognosis.
In some cases, an old fracture can be discovered in an otherwise sound horse, usually in a pre-purchase examination. While these horses may be healed clinically, the x-ray fracture line in a fractured sesamoid may persist.
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