Shoe Boil
by Frosty Franklin, DVM
Edgecliff Equine Hospital • S. 1322 Park Road, Spokane, WA 99212 • 509/924-6069

Shoe boil, capped elbow, and olecranon bursitis are all terms that describe a movable swelling that can occur at the point of the elbow in the horse. The swelling can be of variable size and can affect one or both elbows. The lesion usually occurs as a result of trauma caused by the heel of the foot hitting the point of the elbow while the horse is lying down. In gaited horses, occasionally the foot strikes the elbow while the horse is in motion.

The lesion is an acquired subcutaneous bursa. A bursa is a flattened, closed fluid sac that develops at points of pressure or friction. Bursae are lined with cells that produce fluid somewhat like the fluid within joints.

When the point of the elbow is traumatized a fluid filled swelling may occur, sometimes quite suddenly. In the acute stage the swelling may be mildly painful and there usually is little or no lameness. In the chronic stages the swelling becomes rather firm and is composed primarily of fibrous (scar) tissue. The resulting fibrous mass is painless and does not interfere with function. However, a shoe boil can be quite disfiguring and cause a significant cosmetic problem. Occasionally, following needle aspiration and injection of various medications the shoe boil (bursa) will become infected. The infected shoe boil usually forms a painful abscess and ruptures. The lesion is then characterized by a draining tract and develops of a mass of granulating tissue.

The first principle of treatment of olecranon bursitis is prevention of further trauma to the elbow. Deeply bedding the stall, apply a large doughnut-looking roll to the pastern of the injured limb or cross tying the horse are all means to prevent further trauma to the region of the elbow. Sometimes, early recognition and prevention of further injury to the point of the elbow will allow the lesion to resolve.

An acute shoe boil can be injected with a corticosteroid two or three times on a weekly basis. My cortisone of choice for this lesion is Betasone. If the inciting trauma can be removed and the bursa has not developed scar tissue the result will be a cosmetically acceptable small nodule of fibrous tissue at the point of the elbow.

If the shoe boil is a large fibrous mass or there is a mass of draining, granulating tissue then en bloc surgical removal in the standing horse is advocated. The horse should remain standing for two to three weeks following the surgery to prevent stress on the suture line and to optimize the chances for surgical success.

Many other treatments have been proposed for the treatment of shoe boils. None of the treatments work all the time. En bloc surgical remove is not an easy surgery and expensive. Three weeks of cross tying may be impossible for some horses without daily tranquilization. Prevention by avoiding shoes will long trailers, deep bedding, and early recognition makes good common sense to me.