Puncture Wounds in Horses
A puncture wound in any horse is cause for serious concern. For one thing, it can be difficult to treat. For another, it carries with it the danger that the horse might contract tetanus, also known in the horse community as lockjaw. Whatever the term, the condition can result in the horse’s death. Tetanus is caused by the bacteria Clostridium tetani. However, other Clostridium strains can cause malignant edema, an acute wound infection that can result in the horse’s death.
For purposes of discussion, we will divide this article into two parts. The first will involve puncture wounds in general, and the second part will deal with serious puncture wounds to the equine foot.
There is a basic five-step approach that is essential in preventing deadly bacteria from working their mischief when a puncture wound occurs, says Glen Gamble, DVM, a Riverton, Wyo., veterinarian whose practice revolves around horses. His approach is:
- Make certain that the penetrating object and resultant debris are removed and that the hair is clipped from around the edges of the wound. (For non-foot puncture wounds.)
- Thoroughly flush the wound with antiseptic.
- Make certain the wound remains open to facilitate drainage.
- Place the horse on a seven-day treatment protocol with antibiotics, specifically procaine penicillin.
- Vaccinate the horse against tetanus.
The five steps are aimed at facilitating the healing process and heading off lockjaw or malignant edema.
The risk of infection is greater if there is no blood flow from the wound, says Gamble. Blood can wash out debris that has been left at the inner wound site. If there is no blood flow out of the wound, the debris will remain in place and might carry with it Clostridia spores. It is for this reason that flushing the wound with antiseptic after the penetrating object has been removed is highly important, he emphasized. The flushing action can substitute for blood flow in clearing debris from the site.
The rule of thumb, he said, is never tightly bandage a puncture wound or suture it completely closed. The reason for clipping away hair at the edge of the wound, he said, is to prevent it from matting and shutting off drainage, much the same way that complete suturing would.
While tetanus is the most basic worry, the less-known, but equally deadly Clostridia bacteria that cause malignant edema are reasons for concern when a puncture wound occurs, Gamble said. These Clostridia strains produce gas, toxins, and necrosis of tissue in a very short time (around the wound).
In addition, a variety of other pathogenic anaerobic bacteria can form an abscess or ascend along tendons or facial planes, said Gamble, potentially spreading up and away from the initial puncture wound.
Punctures that billow air when the horse moves, he said, can push bacteria up along muscle layers, resulting in massive abscesses. This type of wound also can push air beneath the skin.
When this occurs, he said, the horse needs to be immobilized to halt the air flow. Then the wound should be partially sutured to minimize wound edge movement. Eventually, he said, the remaining air will be absorbed.
All mammals are subject to an attack by C. tetani, but horses and humans are the most susceptible. By contrast, cats and birds are highly resistant to it. C. tetani is found in the soil and in the intestinal tract. Although it is found worldwide, there are some areas, such as the northern Rocky Mountains, where it is rare and cases of tetanus are seldom recorded.
The bacteria is anaerobic by nature and as such, can’t survive in an environment where oxygen is present. However, it not only can survive, but can flourish within a puncture wound that is shut off from oxygen. It is for that reason, said Gamble, that the wound must be kept open during the healing process, so that oxygen can help prevent the harmful bacteria from proliferating.
When C. tetani is introduced into a puncture wound that does not receive oxygen, the bacteria localize in necrotic tissue at the original site of infection and begin multiplying. As bacterial cells undergo autolysis (the destruction of cells of the body by its own serum), a potent neurotoxin is released. The toxin usually is absorbed by the motor nerves in the area and passes up the nerve tract to the spinal cord, where it causes the signs of tetanus. The toxin causes spasmodic, tonic (prolonged) contractions of the voluntary muscles by interfering with the release of neurotransmitters within the spinal cord.
There is a window of opportunity for warding off the effects of C. tetani because the incubation period varies from one week to several weeks, usually averaging 10 to 14 days.
Even if horses have been vaccinated annually for tetanus, said Gamble, a booster shot immediately in the wake of a puncture wound is important since it will serve to increase the number of antibodies that will combat the harmful toxins.
The bad news is that if the window of opportunity is missed, it could cost the horse its life. It is estimated that the mortality rate for horses which contract tetanus exceeds 80%.
Once the horse reaches the state where it is suffering violent, general spasms, is hypersensitive to sudden movement or noise, and has difficulty eating, the battle usually is over, said Gamble. The only recourse is euthanasia.
Among the horses which do recover, there normally is a convalescent period that ranges from two to six weeks. Interestingly, contracting the disease and surviving usually does not induce protective immunity for the future. Only ongoing vaccinations can do that.
Gamble and a number of other veterinarians suggest that mares be vaccinated during the last six weeks of pregnancy to confer protection to newborn foals through colostrum, and that foals begin vaccination at five to eight weeks of age.
Foot Puncture Wounds
While all puncture wounds pose a threat to a horse’s well-being, perhaps the most insidious of all are punctures of the equine foot. Some of which need surgical attention.
Dealing with that aspect of puncture wounds during last year’s AAEP meeting in Albuquerque, N.M., was G. Lynn Richardson, MS, DVM, Dipl. ACVS, of Equine Referral Services in Rancho Santa Fe, Calif.
There is no predilection for puncture wounds of the foot in horses based on age, breed, sex, or type of activity in which affected horses are involved, Richardson said by way of introduction.
Sometimes, he told his listeners, a puncture wound in the foot area can be difficult to locate. Penetrating wounds of the coronary band, for example, can be overlooked if the hair is long in this region or if wound drainage or local swelling is not yet present.
The same can be true of the bottom of the foot, where dirt and other foreign material can mask the entry wound made by a sharp object. Of course, if that object is protruding from the foot, determining location of the wound site is not difficult.
Trimming the bottom of the foot and paring away superficial layers of horny tissue will usually reveal a puncture tract, especially if it is more than a few hours old, Richardson said.
A hoof tester can help locate the site of injury. Normally, there will be a pain reaction when pressure is brought to bear at the entry site. Puncture wounds to the frog can be difficult to find because the elastic nature of the frog serves to seal the hole.
If the puncture wound penetrates deeply into the foot, Richardson said, the treatment of choice often is surgical debridement (the removal of foreign material along with devitalized or contaminated tissue).
For punctures in the toe and quarter regions, he said, a hoof knife should be used to remove at least one to two centimeters of the sole around the site of the puncture. The horny tissue of the bar should also be removed when the puncture is in the heel region.
For wounds involving the frog and its sulci (the groove around the frog), says Richardson, the cornified tissue overlying this area and the adjacent bar must be removed.
A sterile probe, he said, should be inserted into the wound so that the entire tract can be identified for removal during surgery. If the wound involves only the digital cushion (heel area), a tapered core of tissue that includes the tract should be removed with a scalpel.
If the puncture wound is of such a depth that it reaches the deep digital flexor tendon, the surgical procedure is more involved and the prognosis for the horse’s complete recovery is not so bright.
A wound penetrating the deep digital flexor tendon, said Richardson, should be approached in a manner similar to the approach taken when penetration of the frog or sulci occurs.
Treating the injury soon after it appears is one of the keys to success, Richardson said.
Horses treated with appropriate surgical debridement within four days after the injury have a better chance at a successful outcome than horses not receiving appropriate treatment by this time. Horses that have a hind leg affected are more likely to return to their previous activities. When the deep flexor tendon is punctured or the structures surrounding the navicular bursa are involved, the prognosis is more guarded.
A puncture wound to the front foot can be more difficult to heal because the horse carries up to 65% of its weight on the front end. As a result, it is difficult for the horse to ease pressure on the injured digit, something that is possible when the injury is to a rear foot.
Richardson also emphasized that all puncture wounds of the foot should be treated as though they were extremely serious; even career-threatening.
The most common mistake made in the management of this type of injury is a conservative approach to the treatment of the puncture wound, especially if it involves the deep flexor tendon or the structures adjacent to the navicular bursa, he said. Deep puncture wounds of the foot should be handled on an emergency basis with appropriate diagnostic imaging to confirm the extent of the injury, followed by surgical debridement of the affected tissues.
Adjunct medical management with systemic anti-inflammatory and anti-microbial agents, along with appropriate local wound management, is the preferred method of management for this type of injury, he continued. Conservative management can be successfully used to manage this type of injury when superficial; however, when the puncture wound is deep, medical management is only temporarily effective. Delay of surgical debridement and drainage of the wound may adversely affect the prognosis.
The take home message from Gamble and Richardson is that all puncture wounds are serious, and if not treated in the early stages, can ruin a horse’s performance career or even cost its life. The importance of annual tetanus booster shots can’t be over-emphasized.
About the Author
Les Sellnow is a free-lance writer based near Riverton, Wyo. He specializes in articles on equine research, and operates a ranch where he raises horses and livestock. He has authored several fiction and non-fiction books, including Understanding Equine Lameness and Understanding The Young Horse, published by Eclipse Press and available at www.exclusivelyequine.com or by calling 800/582-5604.