The skeleton is the essential framework that supports all the organs and tissues in the body. It also works in conjunction with muscles, tendons and ligaments to allow movement.
Because of this, fractures are one of the most serious injuries a horse can sustain.
There are two types of bone fractures:
- Pathological fractures occur when a disease process weakens the bone. For example, deficiencies in minerals such as calcium, bone cancer and infection can all lead to pathological fractures.
- Traumatic fractures are caused by excessive force that overwhelms the bone’s strength.
Some of the best information about the risk of fractures in horses comes from studies on racehorses because many jurisdictions collect injury data.
Fractures remain the leading cause of euthanasia of racing horses on racetracks. Of all the 205 bones that comprise the horse’s skeleton, racehorses most often fracture their pelvis during training and lower legs during races.
Fractures of the coffin bone in the hoof have the best prognosis of all lower leg fractures.
It is equivalent to the last bone in the tip of your finger, only with the nail wrapped all the way around. Securely encased in the hoof wall (hence the name coffin), these small wedge-shaped bones can fracture from sudden, high intensity impact.
Horses with this type of fracture can be managed with shoeing or casting and may heal with the potential for good return to function.
Fractures further up the leg are not as lucky. Those involving the pastern or cannon bones usually result in euthanasia.
Horses with fractures are acutely and severely lame with heat and swelling over the affected bone. Instability may be obvious, depending on the site of the fracture.
However, it can be more challenging to diagnose if thick layers of muscle cover the affected bone, such as the hip.
Another common fracture occurs in horses that rear and fall over backward. These horses are at risk of breaking a thin bone that supports the brain in the skull.
Horses can survive fractures of this skull bone, but there is a high risk of death or severe brain injury. Affected horses may have bleeding from the nose and abnormal behaviour including paralysis.
Fracture treatment and prognosis depend on the severity of the break and the bone involved.
Bone fractures must be immobilized with casting, splinting or surgery for the best chance of healing.
They may not heal if there is movement at the fracture site, infection or poor blood supply. For these reasons, fractures of the lower limb, other than those of the coffin bone, are difficult to treat in horses.
Surgical repair of simple fractures are possible, but the horse needs to successfully recover from general anesthesia and tolerate stall rest to have any hope of healing.
There is also risk of founder in the supporting leg, which is why euthanasia is often the only humane option.
Many fractures result from obvious trauma such as being kicked by another horse, but other fractures seem to occur out of the blue.
Some researchers believe that accumulated micro-damage from overuse or not enough exercise are contributing factors.
Studies in racehorses found that a lack of high-speed training before racing increases the risk of fracture.
On the other hand, horses that are frequently worked at high speeds for longer distances are also at a greater risk.
Horses that run on firm ground are also more likely to fracture their legs. The reason for this is probably related to bone remodelling.
Bones are made of collagen with deposits of calcium, phosphorus and other minerals, which give bones their strength.
Despite this rigidity, bones are constantly being remodelled.
Specialized digestion cells break down old bone, and regenerative bone cells then lay down new bone in response to the forces applied to them.
Bones may not remodel to meet the needs of high performance without the right type of exercise in the right amounts. Horses that never run have not had the right types of stress on their bones to stimulate remodelling to accommodate high speed running. As well, horses that run too much may not have enough time to heal microscopic damage.
Many factors contribute to fractures, but this racehorse data suggests that performance horse owners who expect bursts of high speed should consider incorporating small amounts of high-speed training with sufficient low-speed work in between to allow for healing and bone remodelling.