The collateral cartilages (ungual cartilages) are flexible sheets of cartilage that protrude off the back of the wings of the coffin bones within the heel of the foot. In normal horses, these paired cartilages are firm, rubbery-feeling, flexible ridges, visible and palpable in the heel.
Sidebone refers to the hardening (turning to bone or ossification) of the collateral cartilages of the front feet. This condition rarely occurs in the hind feet.
This condition is more common in heavier horses, especially Draft, Draft crosses and Warmblood breeds. It may be related to genetic factors, and certainly is seen more in horses of certain conformation. It is commonly seen in horses of pigeon toe conformation. Pigeon toe probably contributes to unequal loading of the foot which causes ossification.
It is also seen more commonly in feet that undergo excessive concussion for whatever reason, a sign of wear and tear. In many cases, sidebone is found in sound horses that are not lame.
Horses with extensive ossification of the collateral cartilages may lose much of the normal shock absorbing function of the hoof, limiting performance and possibly causing lameness. The biggest problem with this finding is deciding on its significance in a given case of lameness and in predicting whether a horse with this finding in a purchase exam will go lame in the future. There is no known treatment to resolve or reverse this condition.
Diagnosis requires palpation of the foot, and radiographs to confirm the extent of the problem. MRI may be needed to determine specific soft tissue injuries in the hoof that are the REAL cause of lameness.
Treatment of sidebone itself is usually not needed and is not really possible anyway. Changes in shoeing and other treatments may help with pain and the mechanical stresses that contributed to the development of the sidebone in the first place. Other, concurrent injuries in the hoof should be treated or managed. These may only be defined by
Other Diagnoses Considered
Prognosis & Relevant Factors
The prognosis for painful sidebone is fair with early management of the condition and adjustments in workload and shoeing. The prognosis is poor in advanced cases associated with lameness, or with fractured sidebone. In many cases, while sidebone may exist, it is not really the cause of the lameness.
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Helpful Terms & Topics in HSVGWritten, Reviewed or Shared by Experts in Equine Health