Bruising on the volar surface of the foot usually is a common cause of lameness in horses.
It is caused by direct injury from stones, irregular ground, or other trauma. Poor shoeing, especially in horses with flat feet or dropped soles, predisposes to bruising, usually around the periphery of the sole. Bruising may or may not be associated with lameness, but if it becomes chronic, the affected area can become infected. Persistent, nonresponsive bruised sole suggests pedal osteitis.
A “corn” is a specific type of bruising that is seen in the sole at the buttress (ie, the angle between the wall and the bar). It is most common in the forefeet on the inner buttress and is usually associated with the heel of a shoe that was improperly placed or left on too long and caused pressure on the sole. Shoes that have been fitted too closely at the quarters can also cause corns. Faulty foot conformation, straight walls that tend to turn in at the quarters, or contracted feet may predispose to corns. Other causes include excess trimming of the sole (which exposes the sensitive tissue to contusion) or neglect of the feet to the extent that they become long and irregular.
Corns are described as dry when only mild inflammatory changes exist, as moist when there is excess inflammatory exudate, and as suppurative once they become secondarily infected. When the foot is raised and the solar surface freed of dirt and loose horn, a discoloration, either red or reddish yellow, is noted. Supporting-leg lameness is an early sign, but lameness is not always seen. Tapping with a light hammer over the area or applying pressure with a hoof tester usually causes discomfort. If infection is present, pain is pronounced when pressure is applied with hoof testers; if not promptly treated, a tract may extend through to the coronet to produce a suppurating sinus.
The prognosis is favorable. In uncomplicated dry corns, relief from pressure on the affected area is the first consideration. This can be achieved by shortening the toe if it is too long and by applying a bar shoe to promote frog pressure. A three-quarter-bar shoe may be of value in relieving pressure. If the corn is suppurating, it should be drained immediately by a surgical opening directly through the sole. After drainage, the foot should be dressed to permit drainage. Hot foot baths and poultices may be helpful. The horse should be kept in a dry, clean box stall. After infection is controlled, the cavity can be packed with sterile gauze and topical antibiotic ointment, and a metal, rubber, or leather sole placed between the shoe and the foot. Parenteral antibacterial therapy is of questionable value unless systemic illness is present.