Pin firing is a centuries-old veterinary practice in which heated metal needles are pressed into a horse’s skin over an injured tendon or bone. The idea behind it is that deliberately burning the tissue will trigger an inflammatory response that speeds healing. Despite its long history in horse racing, clinical research has shown pin firing does not work and can actually make injuries worse. It is now banned or heavily restricted in most major racing jurisdictions.
How Pin Firing Works
The procedure falls under a category called “counterirritation,” a broad approach based on the theory that creating a new injury near a damaged structure will flood the area with blood flow and healing factors. In pin firing specifically, a veterinarian heats a metal instrument with a pointed tip and presses it into the skin overlying an injured tendon or ligament, typically on the lower leg. The burns are applied in a grid-like pattern of small dots.
The tissue temperature at the point of contact reaches 60°C (140°F) or higher. At that temperature, collagen fibers break down and cells in the treated area die. The body then launches a wound-healing response: clearing out the dead tissue debris and replacing it with scar tissue. Proponents historically believed this process would strengthen the underlying tendon or bone. Pin firing was most commonly performed on racehorses with shin soreness (stress on the cannon bone) or tendon strains, conditions that are extremely common in Thoroughbred racing.
Other forms of the same concept include “line firing,” where a blade-shaped iron is dragged across the skin in rows rather than dots, and “freeze firing,” which uses liquid nitrogen instead of heat. Chemical blistering agents, such as iodine-based liniments applied to the skin or injected around the tendon, are a related approach. All of these aim to provoke the same controlled inflammatory reaction.
What the Research Actually Found
The most thorough investigation into firing was a five-year clinical and experimental study known as the Silver and Rossdale Report. Researchers compared multiple treatments for tendon injuries, including rest alone, line firing, pin firing, tendon splitting, and carbon fiber implantation. They tracked healing using pathological analysis of the tendon tissue itself.
The results were clear: cautery either failed to speed up healing or actively slowed it down. Tendons took at least 15 months to heal regardless of treatment. Pin firing was singled out as especially harmful. When the heated needles penetrated deep enough to reach the actual tendon, they caused additional damage that prolonged the healing process. The study concluded that “pin firing and tendon splitting are detrimental.”
The theoretical basis for the procedure also fell apart under scrutiny. Cauterization did not increase blood flow to the tendons themselves. In fact, vascularity in the tendon was reduced for the first several days after firing. While the procedure did stimulate new blood vessel growth in the surrounding skin and soft tissue, that increased circulation never reached the injured structure it was supposed to help. Researchers also raised concerns that firing could create restrictive adhesions between tendons and their surrounding sheaths, limiting the tendon’s ability to glide freely and potentially causing new problems.
What likely created the illusion that pin firing worked was the enforced rest that followed it. After being fired, horses were typically turned out to pasture for months. That prolonged rest period is genuinely beneficial for tendon healing, and horses often did return to soundness. But they improved because of the time off, not the burns.
Why It Persisted for So Long
Pin firing survived in horse racing for decades after evidence mounted against it, largely because of tradition and a logical-sounding but incorrect theory. Trainers who had used the practice their entire careers pointed to horses that recovered after being fired, not recognizing that the rest period deserved the credit. The visible scarring on a horse’s legs also served as a kind of signal to buyers and trainers that an injury had been “treated,” which carried social weight in racing culture even when the treatment itself was ineffective.
The procedure also persisted because tendon injuries in racehorses are notoriously difficult to treat. When effective options are limited, people are more willing to try anything, and less likely to question whether it works.
Legal Status in Racing
Pin firing is now prohibited under U.S. federal racing rules. The Horseracing Integrity and Safety Authority (HISA), which sets nationwide standards for American racing, classifies pin firing alongside practices that “induce inflammation and pain with the intent to speed healing of injured structures.” Under HISA rules, pin firing of any structure is a prohibited practice. Horses from the 2023 foal crop onward cannot participate in a covered race or timed workout if they have been pin-fired on their shins or freeze-fired on the front of the cannon bones. These procedures cause permanent, visible changes to the horse, and the rule is designed to deter anyone involved in a horse’s care from performing them.
The Australian Veterinary Association takes an even harder line, stating that traditional forms of thermocautery, including pin firing, line firing, and freeze firing, “must not be used in any circumstances in any animal, by veterinarians or other persons.” The practice is also banned or effectively eliminated in the United Kingdom and most of Europe.
Modern Alternatives for Tendon Injuries
Over the past two decades, regenerative medicine has largely replaced older approaches to equine tendon and ligament repair. The most widely used option is platelet-rich plasma (PRP), where a concentrated portion of the horse’s own blood is injected directly into the injured tendon. Randomized trials have shown that PRP improves lameness scores and helps organize the healing tissue into a more functional structure.
Other regenerative treatments include stem cell therapy, where cells are harvested from the horse’s bone marrow and injected into the injury site, and bone marrow aspirate concentrate, which contains a mix of growth factors and stem cells. Extracorporeal shockwave therapy, which delivers focused pressure waves through the skin, is another common approach. Long-term return-to-work rates appear comparable across PRP, shockwave therapy, and bone marrow concentrate treatments, giving veterinarians several evidence-based options depending on the type and severity of injury.
The single most important factor in tendon healing remains controlled rest and a gradual return to exercise. Modern rehabilitation programs use ultrasound imaging to monitor tendon repair over months, adjusting the horse’s workload based on how the tissue is actually progressing rather than relying on a fixed timeline or the appearance of the leg.