Pin Firing

I am about to purchase a gelding who is off the track. I notice he has lines of scars on his cannons that the owner says are from "pin firing." What is pin firing, what is its purpose, and how often is it performed? Is there any long-term damage as a result?   via e-mail

Pin firing or thermocautery has therapeutic value for certain conditions in the horse. When done properly, the AAEP considers pin firing an acceptable form of therapy.

(Editor's note: In 2006, the AAEP updated its position on pin firing to read: “Thermocautery may have therapeutic value for certain conditions in the horse. When applied judiciously and in conjunction with appropriate analgesia and aftercare, the AAEP considers the modality an acceptable form of therapy in cases that have proven refractory to conventional treatment.”)

Pin firing is a therapy that uses a small, red-hot probe to cause cauterization (burning) of tissue in horses with chronic injuries to produce an abundant, serous inflammatory process. As opposed to other inflammation processes such as infections or bruising, serum has little or no fibrin (clotting material) or cellular content and does not coagulate. Firing causes maximal exudation, or oozing, and minimal tissue degeneration. The flooding of serum seems to flush out any chronic irritation, and it does not displace old scar tissue.

Firing is done more often in racehorses than in other performance horses, and has been used for more than a century in conditions of recurring injuries such as a splint, curb, or chronic bowed tendon. The process is performed under sedation and local anesthesia, and the pain inflicted is fairly short-lived and usually well-tolerated by the patient.

Here is a typical example of the cycle of a horse which warrants pin firing. A Standardbred horse might, in horseman's terms, "pop" a curb, or show inflammation in the plantar ligament. The horse is rested, the inflammation seems to disappear, and the horse begins light exercise again. When the horse reaches training level, the leg becomes inflamed again, and the curb becomes a chronic injury.

The driving idea behind firing is that it makes chronic inflammations acute and allows them to heal. When the body responds to the new injury of firing, which is performed over the old injury, it responds in a different way than the initial injury. I feel that until the condition is made acute, it will not heal.

According to George B. McKillip in the American Veterinary Medical Association Proceedings from 1913, "firing has for its chief aim in the treatment of these cases the removal of solid exudates. It does this by bringing into the inflamed zone a great volume of normal body fluid which contains the necessary materials for the removal of the deposits. The free mobility of the exudate from the firing and its freedom from solids permits it to execute these functions and transport the products away without permanently embarrassing the tissue with is own presence."

It is important that if a practitioner fires one leg that he pays special attention to the opposite leg. Otherwise, the horse will place excessive weight on the unaffected leg and strain that one. Many times, both of the front or hind legs are done at the same time, for it seems what injury occurs in one leg will also appear in its partner.

Following firing, specific nursing care is necessary. This involves a strict regimen of ointments and keeping the area clean. The horse must have time off, from six months to a year, depending on the condition. A splint or a curb doesn't take as much time as a bowed tendon to heal. Once the horse is able to walk comfortably on the leg, it should be allowed to do so, just as one would walk on a sprained ankle to build strength after the injured joint is able to bear weight.

Pin firing is common with some practitioners, but it is not generally taught today in veterinary schools. Quality firing takes experience--a good vet can examine a condition and an ultrasound of the leg, see a chronic condition, and recommend the procedure. As veterinary medicine has become more specialized, there are a lot of people who have fired many horses. They might have had good results, some vets are not very anxious to spread the word of their service, for it is not an aesthetically pleasing process. It's easier to convince owners to have their horse pin fired after they've seen the horse go from performing at its peak to not performing at all. Then they are seeking a permanent solution, and might overlook the appearance of the actual procedure, and find the process is effective. For clients who have not experienced success with firing, the procedure might seem very archaic.

The only problem one might have as a result of firing is if the process does not allow circulation between the areas of the cautery, in which case the skin will die. Points of firing are placed far apart for this reason. White hairs might appear at the points of firing, and in show horses this would not be desirable. In addition, the practitioner must be very careful not to cauterize either over or through superficial blood vessels, or close to a joint capsule.

In my years of practice, I never saw any long-term damage as a result of pin-firing. What I did see was long-term help for the performing horse, which includes anything from the racehorse to the hunter-jumper.

About the Author

Clyde Johnson, VMD

J. Clyde Johnson, VMD, is a past president of the American Association of Equine Practitioners.

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