Veterinary Topics: Horses and nails do not mix
Damage depends on where a nail punctures a hoof and what structures it encounters
A TRAUMATIC puncture to the hoof involving an old rusted nail is one of the worst things that can happen to your horse. However, try as you might, it is almost impossible to make pastures totally safe. Rain, erosion, and other environmental factors cause buried nails and debris to come to the surface. Fence and building repair and other construction projects in and around pastures are a constant source of nails, staples, wire, and other possible penetrating objects. Sheet-metal and tin roofs are often subjected to high winds during winter and summer storms that can loosen and dislodge roofing nails that find their way into fields and paddocks. Despite all you do, horses occasionally step on nails.
A nail in a horse's foot is a lot like an iceberg: Often the most dangerous part is what you do not see. The majority of the damage is done when the nail penetrates the hoof. The severity of the problem, treatment, and the eventual outcome are largely determined by where the nail goes and what structures it encounters. Here are basic rules to follow when you find your horse limping in from the field:
- Resist the urge to pull the nail out;
- Try to restrain the horse from moving since continued walking on the nail can drive it farther into the foot and increase the damage; and
- Contact your veterinarian immediately and describe the location of the nail and its angle of entry into the foot.
Because radiographs are crucial to determining exactly where the nail is, the veterinarian will need access to electricity in order to take X-rays. If the horse is not near an electric outlet, you may need to walk the animal into a barn or close to a stable. A wooden block or pad can be taped to the hoof around the nail to elevate the hoof off of the ground and to allow the horse to walk a short distance without putting additional pressure on the nail.
Nail dislodged
An even more potentially dangerous situation occurs when the horse has stepped on a nail and has already dislodged that nail before you find it. This can happen when a horse moves through grass or brush and steps on a nail that is protruding from a board or other object. The nail penetrates but does not remain in the foot. Often the horse is only mildly lame initially, and the owner might not notice the true extent and seriousness of the problem.
The nail might have penetrated the sole and damaged the coffin joint, the navicular bursa (a fluid-filled sac between the navicular bone and the deep digital flexor tendon), or the coffin bone itself. Because there is no nail to call the injury to someone's attention, the horse often is thought to have merely a bruise or a sole abscess. Diagnosis and treatment is not sought until 24 to 48 hours later when lameness is severe and, unfortunately, when much of the damage has already been done.
By taking a sample of the fluid from the coffin joint or bursa, a veterinarian can determine if bacteria are present, indicating a puncture, and treatment can be started. Newer technology such as nuclear scintigraphy and magnetic resonance imaging (MRI) provides veterinarians with a means of diagnosing what might have happened in the hoof, such as a nail puncture, even after the injury has occurred and the nail may be long gone.
Five cases of foot lameness were presented at the American Association of Equine Practitioners convention in December. They involved horses that had foot problems that were obscure or difficult to determine without conclusive evidence of any penetrating injury. MRI was used in the cases to determine the cause of the foot damage, and the modality allowed clinicians to see the actual path of the penetration. As this diagnostic technology becomes more available, veterinarians will be able to do a much better job of identifying hoof-puncture injuries in horses that do not present with a nail in the foot.
Antibiotic therapy
In a horse that has a nail still in the hoof, the nail can be removed once good-quality radiographs are taken. Save the nail because it might be helpful in measurements and in determining the actual path. The nail hole should be pared out and opened to allow easy cleaning and flushing. The foot should be packed with magnapaste (Epsom salt poultice), ichthymol, or other medicated poultice and then wrapped.
Because nails are usually contaminated with soil bacteria, tetanus is a concern with puncture wounds. If the horse's vaccination is current, he should be given a booster of tetanus toxoid. If you are unsure when the horse received his last tetanus shot or it has been a significant time since then, he should receive tetanus antitoxin instead.
Antibiotic therapy is the next step. A penetrating nail injury is usually associated with a number of different types of bacteria, so the antibiotic should be both broad-spectrum (active against many bacterial strains) and strong. A combination of penicillin and gentamicin or kanamycin is the standard treatment.
It was previously thought that systemic use of these antibiotics (injection into the muscles or the vein to produce a concentration in all organ systems in the animal) produced acceptable levels in the coffin joint, navicular bursa, and the fluid in the sheath surrounding the deep digital flexor tendon. Newer research has called this idea into question and has produced other methods to achieve high antibiotic levels in structures at risk following nail penetration.
Regional perfusion is a method of delivering antibiotics to a specific area of the body. Two types of perfusion currently are used in horses.
The first, arterial perfusion, uses the horse's arteries. A tourniquet is placed around the horse's leg above the site to be treated. A cannula or catheter is inserted into an artery and antibiotics are injected. The stronger arterial blood pressure forces antibiotics in high concentration into the area of concern, and the tourniquet slows the leakage of the drugs from that area via the veins.
The second method is osseous perfusion. According to Andy Parks, Vet. M.B., a board-certified surgeon at the University of Georgia Veterinary Medical School, "Regional perfusion can also be done via the osseous method, where a hole is drilled into the cannon bone of the affected leg, a tourniquet is placed above the hole, and a catheter is placed into the hole and antibiotics are infused."
Both methods of perfusion deliver high levels of antibiotics to a smaller, specific area and reduce the effects of those antibiotics on other parts of the body, such as the intestinal tract. The ability to concentrate antibiotics in this way increases the chances of killing bacteria introduced by a penetrating injury and reduces the need for further procedures used to open the area and flush out infection.
"Regional antibiotic perfusion is making it possible in some cases to avoid surgical treatment of septic navicular bursitis [infection of the navicular bursa due to penetrating infection]," Parks said.
Standard procedure
The standard surgical procedure for a penetrating foot wound involves cutting a hole in the bottom of the horse's sole to allow access to the deep digital flexor tendon and the infected tissue surrounding it. Damaged tissue is removed and the hole is cleaned, flushed, and infused with antibiotics. The hole is packed and a special shoe, often called a "hospital plate," is put on the horse. The shoe allows the veterinarian to unscrew and open the bottom of the sole and treat the foot and then to close the plate and keep the hoof protected.
This procedure is called a deep digital flexor tenectomy, but was commonly known as "street-nail surgery" back in the days when cart horses commonly encountered nails in the city streets.
The street-nail procedure will usually remove the infection in the foot, but it is commonly associated with adhesions on the flexor tendon, and many horses never return to full function after the surgery. Ted Stashak, D.V.M., a surgeon associated with Colorado State University's College of Veterinary Medicine, describes the tenectomy surgery as "radical and the prognosis for complete recovery is guarded."
Research has once again provided a possible improvement though. "An alternative surgical approach," according to John Lugo, D.V.M., surgeon at Auburn University's College of Veterinary Medicine, "is to open the digital bursal sac and to insert a small endoscope into that space to lavage [flush] the area, clean out any infection, and to remove any damaged tissue."
An endoscope is a small, tube-like instrument that contains a fiberoptic scope that allows the surgeon to see deep into tissues and joints in the body. The endoscope also contains a port or channel through which small scissors, forceps, and other instruments may be passed. This allows the surgeon, working with controls that resemble those of a video game and watching the procedure on a monitor, to manipulate tissue and perform surgery inside the body. This endoscopic surgical repair of damaged foot tissue, along with regional antibiotic perfusion, is currently replacing previous methods of treating traumatic foot punctures.
"We can often achieve the same degree of tissue cleansing and flushing accomplished with a street-nail operation," said Lugo, "but without almost any of the adhesions and other potentially crippling complications of that surgery".
Kenneth L. Marcella, D.V.M., is a practicing veterinarian in Canton, Georgia.