from the Vet Corner Archives
Part of Horse Previews Magazine website. Posted on 10/2000; 2:00:00PM.
Veterinary Corner 10/00: Hoof Abscesses
by Frosty Franklin, DVM
Edgecliff Equine Hospital
S. 1322 Park Road, Spokane, WA 99212 * 509/924-6069
The horse's hoof is a very durable, tough structure that is constantly renewing. The hoof is always in contact with the environment and, as such, experiences a wide variety of traumatic insults that occasionally damages the hoof and enclosed structures. One of the most common problems occurring to the hoof is the introduction of bacteria and other microorganisms to the sensitive structures within the hoof. A hoof abscess is the result.
A hoof abscess, in my mind, is either a direct hoof abscess caused by penetrating wounds or an indirect hoof abscess caused by the migration of moisture and bacteria into fissures and cracks along the white line.
Almost always when the horse is acutely lame to the point where weight bearing on the affected limb is difficult, the diagnosis is a hoof abscess. Rarely, that non weight-bearing stance is caused by a fractured bone somewhere within that affected limb. By examining the foot for heat and swelling just above the foot in the pastern and fetlock and by evaluating the digital arterial pulses the owner can quickly rule in or rule out a hoof abscess.
In talking with my clients I was amazed to find a large percentage of horse owners that are not aware of the importance of being able to check for the presence of pulses within the digital arteries. In the normal resting horse the digital arterial pulses are not palpable. The digital arteries are present on each side of the pastern. The digital vein is visible on each side of the pastern in most horses, especially if the hair on the pastern is clipped. The digital artery is just slightly posterior to the vein, the vein being a good visual landmark. Whenever inflammation or infection occurs in the foot, the pulses in the digital arteries are obvious to anyone that feels for them. It would be a good idea for horse owners to become familiar with the digital arterial pulses and how to palpate for them. Ask your veterinarian for help if you are confused about the anatomy. Check your horse right after exercise, because then the pulses are palpable.
Penetrating wounds of the hoof can be very serious and should be treated as a potential career ending or life-threatening wound. It is difficult to tell which of the vital structures of the foot have been injured and contaminated with microorganisms. Penetrating wounds of the middle third of the frog are particularly scary because in this region the navicular bone and bursa are present, as well as the deep flexor tendon and the coffin joint. Some of the puncture wounds to the hoof are well hidden by the spongy, elastic frog or the dark dirt-filled sulci and go undetected. In other cases, the nail is simply removed, some iodine squirted in the wound and the incident is not taken seriously and several days may have lapsed before treatment is sought. By then a very serious situation has precipitated requiring surgery, long-term antibiotic therapy, and special hoof care with only a fair chance of returning to full use. In one study, 12 of 38 horses with puncture wound to the navicular bursa or navicular bone returned to satisfactory function.
Fortunately, indirect hoof abscess are much more common. In our practice, they occur when the footing is wet. Defects and fissures in the white line allow the moisture, manure and bacteria access to the sensitive structures to form this type of abscess. These abscesses are relatively easy to treat if the fissure is readily located. These fissures and the structurally comprised white line are common in chronic laminitic (foundered) horses. The "stretched" or widened, pithy white line does not have the integrity of a normal white and allows filth access to the sensitive tissues of the foot. Horses that are recently trimmed and then exposed to muddy/mucky corrals also seemed to be predisposed to a indirect hoof abscess. The infection that gains access to the foot through the white line may travel up the sensitive lamina underneath the hoof wall forming a "gravel" that drains at the coronet. Or much more likely, the infection involves the sole and becomes a sole abscess. This type of hoof abscess is very painful but usually resolves within a few days with proper treatment.
Diagnosing indirect hoof abscess is usually straightforward. Examining the foot for heat, pain, and swelling. Removing the shoe, and proper cleaning of the hoof with a hoof pick and hoof knife is essential. Paying particular attention to the coronet, frog, sulci, and the white line. The hoof testers can be very useful or they can make the horse very defensive because you apply them too forcefully at the beginning. Once the black line or fissure is identified the line is followed with the hoof knife and most of the time grayish exudate will drain the abscess.
Establishing surgical drainage is the most important aspect of therapy. A small loop knife works well. Once a small drainage hole is created the foot may be soaked in hot Epsom salt solution (2 cups per gallon of very warm water). Instead of soaking, I usually apply Magnapaste ointment and bandage the hoof. Magnapaste is an osmotic and "draws" the abscess. Recently, over the bandage I have been applying a new product called the "Equine Slipper." The Equine Slipper has a thick leather bottom and the upper part is breathable cordura nylon with handy Velcro fasteners. It seems to protect the bandage and keeps the hoof clean. Tetanus toxoid should be administered if the horse has not been vaccinated within the last 6 months. I usually prescribe phenylbutazone: 2 grams daily for 6 days.
Penetrating wounds or direct hoof abscess are managed more intensely. The penetrating object is best left in place. The veterinarian is summoned and the hoof radiographed. Even then, evaluating all the structures involved is difficult. Dr. Schneider at Washington State University College of Veterinary Medicine is using MRI to evaluate the structures of the foot damaged by puncture wounds. The more information one can delineate the more accurate the diagnosis and prognosis. Treatment of these direct abscesses many times is difficult. Surgical curettage of bone infections to the third phalanx or navicular bone caused by nails puncturing the bone, debriding the deep flexor tendon and drainage of the navicular bursa or joint lavage of the coffin joint are procedures requiring expertise and considerable expense. The prognosis is guarded to unfavorable in many cases. If the penetrating object does not encounter a vital structure as around the periphery of the hoof, most of the time the prognosis for complete recovery is good.
Some hoof abscess can be prevented. Start by keeping the barnyard and stable free of nails and other sharp objects that can penetrate the hoof. They are the number one cause of penetrating injuries to the foot.
Should an acute lameness occur, seek veterinary attention early. Early treatment usually has a higher success rate.