Pedal bone fractures

Despite many recent advances in veterinary care, the outlook is often hopeless when a horse breaks a bone in its leg, as it can be impossible or difficult and expensive to repair. At best, the horse will have to be retired and at worst, it will need tobe destroyed. And even if the horse survives and is sound, there is always cause for concern that it will never return to the same level of work it was at before the injury.

Pedal bone fractures

The horse’s foot contains a single large bone (pedal bone), with a smaller bone just behind it at the back of the foot (navicular bone). Frequently, pedal bone fractures are an exception to the gloomy prognosis for fractures in the horse. And when the injury is diagnosed promptly, and treated correctly, the prognosis for full recovery can be excellent. Pedal bone fractures often occur as a result of a sudden traumatic injury to a horse’s foot. Such injuries can happen following horses kicking out against solid objects, such as walls or cross-country fences, or during normal ridden exercise if the foot lands awkwardly on an uneven surface. Occasionally, horses may fracture their pedal bones as a result of a severe penetration by a nail or sharp stone.

Following a pedal bone fracture, the horse is often extremely lame and may not be able to bear weight on the affected leg. The hoof may feel hot and inflamed and any pressure or percussion (ie tapping) of the foot can be severely resented by the injured horse.

Unfortunately, the signs shown by a horse with a pedal bone fracture can mimic common conditions, such as abscesses or severe bruising, so it is possible to overlook the fracture.

X-ray diagnosisThe vet usually diagnoses a pedal bone fracture by taking an X-ray of the affected hoof. Unfortunately, the injury can be extremely difficult to identify in the first few days after it takes place. Initially, the fracture appears as a hairline crack on an X-ray film. Consequently, it may not be identified soon after the injury, despite the vet taking several X-rays at different angles.

If your vet is suspicious of a pedal bone fracture but is unable to identify it, it is normal to box rest the horse for 7-10 days before repeating the X-rays. By this stage, the fracture is often much clearer on the film because the bone usually dissolves close to the fracture as part of the healing process.

Occasionally, pedal bone fractures are suspected, but, despite taking numerous X-rays, the vet is unable to make a definitive diagnosis. They may then perform nerve blocks to confirm that the pain is definitely coming from the foot.

A bone scan (gamma scintigraphy) is another diagnostic option, although X-rays are usually sufficient.

Special shoes

Treating pedal bone fractures depends on the age of the horse, the type of fracture and the preference of your vet. But box rest is the most important part of the treatment.

The duration of rest is variable, though 2-3 months of total box rest, followed by 2-3 months of controlled exercise from the box, is required to allow the bone to heal.

It is also important that the foot is immobilised to prevent movement of the bone. Every time a horse bears weight on its foot, the hoof wall expands slightly, which allows movement of the pedal bone and leads to a delay

in any healing. The simplest way to immobilise a hoof is to shoe the horse with a bar shoe with quarter clips, which will prevent this expansion.

Occasionally, a rim shoe may be used for the same reason. A piece of sheet metal is welded around the foot and and the foot sits within the rim. Expansion of the foot can be prevented further by applying acrylicmaterials between the foot and the rim shoe.

Probably the best way to prevent foot expansion is by applying a cast to the limb. Various types of cast can be used, such as enclosing the hoof alone, enclosing the hoof and pastern or enclosing the whole limb below the hock or the knee.However, casts can cause complications, so it is still common to use a bar shoe alone.

Essential surgery

Sometimes, surgery is necessary. When the pedal bone is cracked straight down the middle, placing a screw across the joint to compress the two pieces of bone back together can be an excellent technique to speed its healing. This allows a quicker return to soundness and work. However, despite this, placing the screw into the bone in the hoof can have serious complications, such as infection.

Surgery is also often required when there has been a penetrating wound to the foot, fracturing part of the bone which subsequently becomes infected. In such cases, the fractured piece of bone often loses its blood supply and dies off. The horse’s body then recognises the piece of bone as foreign material, which causes a persistent infection of the foot. The only cure for this is to remove the dead piece of bone surgically through either the sole or wall of the hoof.

Outlook

The prognosis for pedal bone fractures is generally good, but this depends on whether the fracture enters the coffin joint (the joint between the pedal bone and the short pastern bone). Acertain number of horses with such fractures end up with severe osteoarthritis of the joint, for which there is little successful treatment available.

One of the most difficult decisions for vets dealing with pedal bone fractures is when the horse can restart exercise. This decision is made more difficult as X-rays can be of little assistance – often, the fracture line is still obviously visible on X-rays many years after the horse has become sound and is back in full work.

In many instances, the decision of when to return a horse to work is made purely on the clinical progress of the horse and its degree of soundness, with follow-up X-rays providing little, and often conflicting, information.