Just as the human cuticle generates a fingernail, the coronet band generates a horse’s hoof wall, which grows down over the hoof. However, unlike a cuticle, the hoof wall grows while keeping the coffin bone suspended within the hoof via the laminar attachments, all while bearing the full weight of the horse – a miraculous mechanism.
The coronary band cells produce the horn material of the hoof wall, called keratin.
Abnormal cell growth here can result in a “core” of abnormal hoof wall that grows along the inside of the hoof wall, resulting in a tubular mass called a keratoma. While not cancer, keratoma is often classed as a benign tumor of these horn producing cells.
The cause of keratoma is not entirely understood. It is thought that injury to the coronet predisposes to its development, but keratomas are also seen in horses with no history of injury.
Keratoma is rare, and usually causes mild to moderate lameness. In some cases, it is found as an incidental finding and not associated with lameness. Pain and lameness that results from keratoma probably originates from pressure on the sensitive laminae inside of the hoof wall.
A keratoma on the hoof wall can sometimes be seen on the sole as an inward deviation of the white line. Sometimes a bulge develops in the hoof wall overlying the keratoma.
Radiography is an important diagnostic and can reveal bone loss of the coffin bone margin, resulting from pressure caused by the mass. MRI is the most reliable diagnostic and usually shows the full extent of the mass.
Treatment involves surgical removal of the cylindrical keratoma, usually by removal of the overlying hoof wall.
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Prognosis & Relevant Factors
The prognosis is good with surgical removal of the keratoma. Usually, the overlying hoof wall is also removed at surgery.
Special shoeing and bridging repair of the hoof wall may be required to stabilize the hoof capsule as the hoof grows out.
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