Keratomas are locally invasive (non-spreading) tumors comprised of keratin, the primary substance making up the hard wall of the hoof. They are located between the coffin bone (3rd phalanx) and the hoof wall. Keratomas are fairly uncommon, but can be a significant source of lameness when the mass extends to the sole of the hoof. The tumors grow anywhere within the hoof capsule, exerting pressure upon and displacing the coffin bone opposite of the tumor’s contact with the hoof wall. They are most common in the toe, but may exist in either quarter. Any foot may be affected.
The cause of Keratomas remains elusive, but some experts speculate that the tumors form in response to a previous insult to the coronary band. The coronary band is the junction between the hoof and the pastern and contains the epidermal cells responsible for making keratin.
In some cases, there is a visible bulge in the hoof wall at the site of the keratoma. The white line may deviate toward the frog, or may separate leaving the hoof susceptible to infection. In many cases however, there is no outward clue to the tumor’s existence other than unattributable lameness. A hoof tester may be helpful to reveal pain at the site of the mass. X-rays are used to confirm the diagnosis.
Keratomas, once diagnosed, require surgical removal under a general anesthetic. The hoof wall is removed to reveal the keratoma tumor, which is also excised as fully as possible to prevent re-growth. The defect created in the hoof is then packed with betadine soaked gauze, and the entire foot is wrapped to prevent contamination of the wound by soil and pathogens. A farrier can then build a special plate that covers the defect and is attached by removable screws. This facilitates changing of packing gauze every 3 days and keeps contamination out while the hoof heals.
Before surgery, if the horse was not current on tetanus vaccination, it will be administered to prevent the often fatal disease caused by bacterial infection of deep wounds. Afterward, the horse may receive antibiotics to prevent bacterial infection overall. It can take many months for the hoof to completely heal after Keratoma surgery, so diligence and patience are required to a great extent.