Horses are very vulnerable to puncture wounds in the foot given the sheer number of fence nails, horseshoe nails and general pointy stuff that accumulates in stables, yards and paddocks. The problem with “stepped on a nail” is that there are several vital structures just beneath the sole that are easily penetrated by a nail tip. This means that the area is not only physically damaged, it also is contaminated with a mixture of dangerous bacteria, including, for example, E. coli and clostridium tetani, which can lead to devastating septic infections and even tetanus.
Path of Destruction
Nails can penetrate the hoof anywhere on the sole, bars and frog. The extreme pressure placed on the nail as well as the density of the internal structures of the foot, means that the nail can bend quite significantly, and take an unexpected angle as it travels deeply into the tissues. This makes it impossible to estimate how much of the nail actually went in, by simply looking at the entry point.
For instance, let’s say we have case where a three-inch nail appears to have gone straight into the foot, but, upon examination, we discover that just below the sole it took an abrupt angle and tracked along the solar surface without getting into anything vital. In a less fortunate circumstance, we find that a small, relatively short nail has entered the sole next to the frog at a very shallow angle, but investigation proves that it penetrated the navicular bursa, a small sack of synovial fluid that lies between the navicular bone and deep digital flexor tendon. These are two very different situations, with differing prognoses.
What’s the Damage?
The only way to determine the damage a penetrating object has caused to the foot is through diagnostic imaging, which is much easier to perform if the foreign object is still in place. So, if you pick up your horse’s foot and spot a protruding object, resist the urge to pull it out straight away! The only exception would be if the object sticks out past the bottom of the foot, meaning that it will be pushed in even further every time the horse takes a step. In this case, try to identify as exactly as possible where it entered the foot, and use pliers to pull it out as smoothly as possible. Then apply a protective self-adhesive elastic bandage (like Vetrap䋢), to prevent more dirt and debris from packing into the hole. Keep the nail handy so your vet can examine the length of it and any bends in the shaft.
Ideally, if you see a nail in the foot, you should leave it in place, apply a protective bandage or put a clean boot on to prevent further contamination of the sole, and call your vet right away. Leaving the nail in place will allow the vet to take x-rays of the foot before removal, which helps to identify exactly what structures have been penetrated, and to plan the most appropriate strategy for dealing with the situation. In reality, most vets aren’t called out until the nail has already been removed, sometimes after several days have passed.
It is also possible for a puncture to occur and leave no object behind. This can happen when a board comes down in the paddock and the horse steps on a nail, punctures the foot, then leaves the nail behind in the board as they lift their foot. It can also happen when a horse steps on one of the nails in their own shoe while in the process of accidentally pulling it off.
If the horse is unlucky enough to have the nail driven directly into bone, lameness is immediate and obvious. In other cases, when owners aren’t aware that a puncture has occurred, or if they saw the nail and pulled it out because it didn’t seem to go in very far, the horse may not look very sore for two or three days. This is because it takes several days for infection to develop, and build up painful pressure and inflammation in the affected structures. In these situations, it can be very challenging to find the entry point and tract of the penetrating object, because the area quickly packs up with debris and becomes essentially invisible.
Once the vet has examined the foot and the object, they can decide if it is necessary to perform more diagnostics to determine how much damage has occurred. A common procedure is to inject contrast media into the tract and use x-rays to follow the path of the contrast fluid along the path of the puncture. Contrast media is a clear liquid solution that shows up as opaque (white) on x-rays, making it indispensable for identifying puncture tracts as well as determining the extent of wounds, synovial structures, cysts and other unusual body cavities with uncertain margins.
Injection of the navicular bursa, or any of the local synovial structures such as the digital tendon sheath and coffin joint, with dirt and bacteria creates a potentially life-threatening infection. Urgent care, often including surgical flushing and intensive antibiotics, is required to save the horse from permanent lameness and ongoing complications in serious cases. The longer treatment is delayed, the worse the prognosis, so it is critical that any involvement of the navicular bursa, tendon sheath or coffin joint is identified and treated as quickly as possible.
In some situations, when a puncture is suspected, but cannot be identified, your vet may have to draw synovial fluid out of the coffin joint, navicular bursa or tendon sheath, to see if the cell count and protein levels in the fluid are suspicious for infection. Vets can also use MRI (magnetic resonance imaging) to determine the path a penetrating object has taken in the foot, because they are able to identify all of the individual soft structures within the foot and determine which ones have been compromised.
What Happens Next?
If significant injury and contamination of a synovial structure has occurred, the vet may recommend referral to a hospital facility for surgery to thoroughly clean up the area, followed by intensive antibiotic therapy. Less severe situations can be managed on the farm, which would include your vet debriding and opening up the tract to help drainage, followed by stall rest, poulticing the foot, a tetanus booster and antibiotics. Specific antibiotic choice depends on the severity of the puncture and ability of the handler to administer oral or injectable medications.
You will certainly be instructed to apply a poultice to the foot to encourage drainage of contaminated material from the hole and prevent it from closing over too quickly. Clay and mud poultices are not appropriate for this purpose, as they will pack into the hole and further contaminate the wound. A better choice is a medicated pad-type poultice such as Animalintex. It will keep the area clean while gently drawing out infection and providing a mild astringent effect. There are many techniques for applying a durable and effective foot bandage, as well as several types of poultice boots available to make this process even easier. (See the September/October issue for instructions on how to apply a foot bandage.)
The prognosis for successful recovery from a puncture wound in the foot depends on quick action to identify the path of the nail and treatment of potential synovial sepsis, as well as mechanical damage to the foot and diligent aftercare to ensure proper poultice application and medication during the critical early period to prevent infection from establishing.