5 facts about pedal bone fractures [H&H VIP]

  • A marked but unexplained foot lameness may well point to a broken pedal bone. Karen Coumbe MRCVS gets the facts about these small but significant fractures

    1. Prognosis depends on the nature of the damage
    Fractures of the pedal bone are fairly common and can occur in horses and ponies of all ages, types and breeds. Yet vets are unlikely to see many of exactly the same types, so sharing information is paramount if clinics are to select the best approach to treatment.

    In a recent study published in The Veterinary Journal, 285 cases of different pedal bone fractures were collected by vets from five clinics in Austria, Netherlands, Switzerland and the UK. Horses with a fracture that did not involve the the distal interphalangeal (DIP, formerly known as the coffin joint) — like Jasper — had a better outcome, with nearly 92% returning to their original or an expected level of use.

    This same study showed that horses with a hindlimb pedal bone fracture had a significantly greater chance of successful recovery. No significant association was noted between the success rate and the horse’s age or the stage at which treatment was initiated.

    The outlook depends on how the pedal bone is damaged. Vets use a numbered system to classify the type of fracture (see box, left). Key factors are the position of the fracture line and the number of fragments. If the DIP is involved, the risk of osteoarthritis developing is greater.

    2. Everyday incidents cause most fractures
    The cause was determined in approximately half of the survey cases. Slipping or stepping on solid objects and kicking an unyielding object were the most common, followed by spontaneous occurrence during exercise, a kick and, surprisingly, road traffic accidents.

    3. Vet-farrier consultation can enhance outcome
    Immobilisation of the foot did not affect outcome, according to this survey. This is also surprising, because horses often seem more comfortable once the injured foot is supported.
    On reviewing the outcomes of less severe fractures treated conservatively (without surgery), a significant link was found between treatment method and a return to previous performance level. Of the cases treated with box rest alone, 97% had a successful outcome — compared to 81% with hoof immobilisation.

    This suggested that box rest alone, rather than additional immobilisation, had a better outcome. Any support given by a foot cast or special shoe may be less important than previously thought.

    Instead, it seems that the hoof capsule itself may be capable of sufficiently immobilising the injured area. Some vets have suggested that a half-limb cast is fitted, which would more effectively immobilise the joint above the fracture.

    If a bar shoe or cast is applied, this in turn can cause complications such as contraction to the heel. Distortion of the foot shape increases the potential for long-term lameness.

    Overall, it seems that appropriate management must be selected carefully after discussion with vet and farrier.

    4. Multiple imaging methods may be needed
    Subtle fractures can be hard to pick up on radiographs. More than one image may be required to get just the right angle, where the X-ray beam is parallel to the fracture line so that the gap shows up sufficiently clearly. My record is 11 images to find such a fracture, even when I was pretty suspicious that it was there!

    There are good reasons — economic and safety — to try to reduce the number of X-ray images, so vets may now use other sophisticated technology such as magnetic resonance imaging (MRI) or computed tomography (CT) to provide a more accurate answer.

    X-rays alone may not be a guide to the severity of the damage, as not all fracture lines show up. If in doubt, your vet may do follow up X-rays 10-14 days later to see what is happening with a painful foot.

    5. Convalescence should never be rushed
    Another challenge is that X-ray appearance and clinical healing do not always correlate. Sometimes the fracture line will remain long after the horse is sound, so a return to work should be based on clinical rather than imaging appearance. Further investigations such as nerve blocks or even a bone scan are useful to test the significance of a fracture line.

    This recent long-term survey suggested that horses should be rested for at least two months after a pedal bone injury. Even if the horse becomes sound before this time, a premature return to training might result in re-fracture or delayed union or repair (bone healing).

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