It wasn't that long ago that if a horse broke a leg, euthanasia was the only course of action. Breaks are most commonly heard of in racehorses, but any horse can break a bone in its leg.
While euthanasia is often still the main option, advances in veterinary technologies and techniques mean that some horses can be saved, and may even be able to return to their work in some capacity. But saving every horse with a fracture is still a long way off. Here's why.
When a Human Breaks a Leg
If a human breaks a leg, the worst-case scenario might be surgery, possibly to place an implant (plates, pins, screws, etc.) to hold the bone together, a cast, and weeks or months of allowing the bone to heal, followed by physiotherapy. Our bodies are relatively light compared to a horse's, and our leg bones are proportionately larger for our weight, in comparison to a horse's.
We also know that we must stay off of the injured leg so that the fracture can mend properly, without stressing or damaging the healing bone. Most people, no matter how complicated their fracture, will probably survive their fracture unless there is some sort of unusual complication.
When a Horse Breaks a Leg
Unlike humans, horses have heavy bodies and light leg bones. This is the way we've developed many breeds, especially the Thoroughbreds. When bones break, they may often shatter. And it's almost impossible to surgically reconstruct the fractured leg.
While humans have some large muscles and a bit of tissue below the knee that helps to stabilize a broken bone, along with a cast, a horse has very little muscle and hardly any other tissue besides tendons, ligaments, blood vessels, and some nerves below the knee.
The lack of muscle and other tissue means that even with a cast, the broken bone has little to support it. And, it's much harder to prevent a horse from using its broken leg to bear weight. Horses stand most of the time, and a horse is likely to instinctively flee when it's startled, instead of reasoning that it must keep weight off of its fractured leg. This makes the chances of re-injury high.
Horses' Legs Bear a Lot of Stress
Horses put a huge amount of stress on their legs, especially when galloping and jumping. And, there are several bones below the knee and hock. Some of the bones are within the hoof, and when they shatter, they are far more difficult to stabilize and heal.
Over half of the horse's weight is borne on the front legs, so those bones and joints, in particular, endure a lot of stress. Even if a horse's bones are healing, other complications can set in, such as static laminitis, making it difficult for the horse to fully recover without ongoing severe pain.
Fractures That Can and Can’t Be Repaired
The less complicated the fracture, the more likely the horse will recover. Greenstick and stress fractures are incomplete fractures, and these can usually be treated successfully. Simple fractures, where there is one clean break, are more likely to heal successfully than shattered bones (or comminuted fractures).
Compound fractures, where a broken bone penetrates the skin, have a much poorer prognosis and are less likely to heal successfully without complication. Such cases are likely to be euthanized, particularly if the blood supply to the leg has been compromised. Fractures that involve joints such as the pasterns, are often irreparable. Fractures that occur above the knee are also difficult to repair.
Signs of a Horse With a Broken Leg
A horse that has fractured a leg will be in obvious distress. It will not want to bear weight on the leg and there will be swelling. The leg may appear to be crooked, or a bone may even appear to protrude through the skin.
As soon as possible, have a veterinarian examine the horse. Continued movement can worsen the fracture or cause additional injury to the horse, so it must be kept as still as possible. If the veterinarian determines the fracture can be repaired, the horse may be transported to a veterinary hospital.
Laminitis: Prevention & Treatment. American Association of Equine Practitioners
Fractures In Horses. American College Of Veterinary Surgeons