Inside the hoof, the horse’s foot contains a single large bone (the pedal bone), with a smaller bone just behind it at the back of the foot (the navicular bone), and the bottom part of the short pastern bone, which forms the distal interphalangeal or coffin joint with the pedal bone.
While improvements have been made in the treatment of bone fractures in horses in recent years, they typically remain difficult and expensive to repair, but pedal bone fractures are an exception to this. When the injury is diagnosed promptly, and treated correctly, the prognosis for full recovery can be excellent.
Causes of pedal bone fractures
Pedal bone fractures often occur as a result of a sudden traumatic injury to a horse’s foot. Such injuries can happen as a result of 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 of the hoof capsule by a nail or sharp stone.
Pedal bone fracture signs
Following a pedal bone fracture, the horse is often noticed to suddenly go extremely lame and may be unable to bear any weight on the affected leg. The hoof may feel hot as a result of inflammation and any pressure or percussion (i.e. tapping) of the foot resented by the injured horse. These signs can also show when a horse has an abscesses or severe bruising of the sole, which can lead an owner to assume the injury is less serious than it is. A vet should be called as a matter of urgency to any horse that is non-weight bearing on one leg.
Diagnosing a pedal bone fracture
The vet usually diagnoses a pedal bone fracture by taking an X-ray of the affected hoof, especially if or when the other likely diagnosis for foot lameness, namely a bruised foot or sub solar abscess have not been detected. Unfortunately, these fractures can be difficult to identify in the first few days after it occurs. Initially, the fracture appears as a hairline crack on an X-ray film. Consequently, it may not be spotted despite the vet taking several X-rays at different angles.
If your vet is suspects a pedal bone fracture, but is unable to locate 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. The vet may then perform nerve blocks to confirm that the pain is definitely coming from the foot, but there are inherent risks in numbing a foot with a suspected fracture, so other investigations may be considered.
A bone scan (gamma scintigraphy) is another diagnostic option, although X-rays are usually sufficient. Occasionally MRI might be considered to rule out other pathology, such as collateral ligament injuries.
Treating a pedal bone fracture
The most appropriate treatment for a pedal bone fracture 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 and anti-inflammatory drugs are typically given.
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 typically required to allow the bone to heal.
It can help if the foot is immobilised during this period 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 healing. The simplest way to immobilise a hoof is to shoe the horse with a bar shoe with quarter clips, which will minimise this expansion.
Occasionally, a rim shoe may be used for the same reason. A piece of sheet metal is welded around the foot so the foot sits within the rim. Applying acrylic materials between the foot and the rim shoe will further prevent expansion of the foot.
One option to prevent foot expansion is to apply 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 many cases are managed by using a bar shoe alone.
Surgery for pedal bone fractures
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 and allow a quicker return to soundness and work. However, placing the screw into the bone in the hoof has risks of serious complications, such as infection.
Surgery is most frequently required when there has been a penetrating wound to the foot, fracturing part of the bone that 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. It can be difficult to effectively remove the infected and damaged bone, whilst leaving sufficient healthy tissue for the horse to recover and weight bear fully.
Pedal bone fracture prognosis
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). Some 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 clearly 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.
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