The Equine Foot & Common Disorders
The old adage "No Foot, No Horse" is as true today as it was years ago.
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The extreme athletic endeavors that horses participate in, the effects of genetics and poor breeding, poor farriery practices, and their sheer size can result in diseases of the foot, some with devastating consequences. Thankfully, modern medicine is making strides in identifying, preventing and treating these diseases to return affected horses to soundness. A dedicated owner along with a knowledgeable veterinarian and farrier, in many cases, work together to achieve a sound and comfortable horse. Below we outline the basic anatomy of the foot and some common diseases that are seen. As always, if you have any questions about what you read, we are here to answer them!
Anatomy
The horse's foot is both confusing and fascinating in its structure. Think of the exterior of the hoof like your fingernail. It is a hard, keratinous substance created at the coronary band (like your cuticle) and grows out towards the ground. It is attached to the coffin bone by a very unique, interlocking structure called the corium - we know this as the "white line." The corium is a layer of blood vessels, nerves, and connective tissue. On the ground surface this corium also grows out, creating the softer sole. It is softer because it has higher water content than the hoof wall. The digital cushion is a spongy, elastic body that lies in between the coffin bone and the frog like a supportive orthotic for the horse's foot. There is a theory that it acts as a pump for getting blood to flow more completely through the foot. The navicular bone is a small bone that is situated caudally between the last two bones in the foot and the deep digital flexor tendon. Its function is as a fulcrum over which the deep flexor tendon changes direction to allow the toe to be pulled backwards. It is surrounded by a bursal fluid sac, which permits the movement to happen more smoothly. It is required, by virtue of the weight of the horse and its position in the foot, to absorb a lot of compressive force.
Image courtesy of Dechra Veterinary Products
Hoof Abscess
One of the most common causes of lameness in the horse is a hoof abscess. Frequently when a horse becomes suddenly lame, it is due to a localized accumulation of pus in the horse's hoof. Abscesses can be caused by bruises to the sole, cycling environmental conditions (wet/dry), "hot" nails, poor foot conformation, poor trimming, and penetrating wounds. Conditions such as laminitis can predispose a horse to abscesses.
Diagnosis is made by using hooftesters and lameness evaluations. Treatment usually involves soaking the affected foot in warm water and epsom salts and poulticing until the infection has been drawn out and clears. Antibiotics and anti-inflammatories (Bute) are not recommended. Chronic abscesses may require additional, more aggressive treatment.
Penetrating Wounds
The environment is full of all sorts of things for horses to hurt themselves on and they seem to be able to find them despite our best efforts. Puncture wounds of the hoof, commonly caused by nails and various other pieces of metal and objects, can be serious if the important structures of the foot are penetrated. To this end, it is extremely important to have your veterinarian out as soon as possible if you find a foreign body in the bottom of your horse's foot. Although it seems counterintuitive, DON'T PULL THE NAIL OUT!
They will most likely radiograph the foot to see where the object is in relation to the bones and joints of the foot. If there is involvement of the flexor tendons, navicular bursa, navicular bone, or coffin bone, surgical intervention and aggressive treatment are necessary for future soundness. Prompt diagnosis and treatment is important for a good prognosis for any puncture wound of the hoof. Treatment may include soaking, poulticing, immunization for tetanus, nerve block, and antibiotic therapy (local and/or systemic).
Navicular Disease
Navicular Disease occurs when this bone is unable to handle the compressive stresses put upon it. There is a highly genetic component to this disease, most notably it occurs bilaterally in big-bodied Quarter Horses 4 to 15 years old with upright conformation and small feet. Other factors may contribute to development of this disease, namely faulty foot or leg conformation, trauma to the foot, or exercise on hard surfaces. As the weight of the horse presses down on the foot during mid-stride, the navicular bone gets pushed towards the ground. At the same time, the deep flexor tendon contracts to allow the toe to be pulled backwards to complete the stride. This contraction pushes the navicular bone upwards. In a navicular bone that is predisposed or genetically weak, these opposing compressive forces cause breakdown.
What happens at the cellular level within the bone is still controversial, but what matters to us as owners is that our horse is chronically, intermittently lame. Symptoms can include lameness after working but a return to soundness when at rest, shifting of weight when standing, standing with material packed up under the heel with the toe facing downward,and a characteristic gait: the horse will walk toe-first to relieve pressure on the heel area where the pain originates.
The diagnosis of navicular disease can be made with diagnostic nerve blocks and radiographs, although sometimes the x-ray findings are subtle. If no changes are seen on x-ray, an MRI (Magnetic Resonance Imaging) may be necessary.
Treatment is usually frustrating and can include rest and anti-inflammatory drugs; though in most cases the lameness will return when work is resumed. Correcting imbalances of the foot with trimmings and shoeing is imperative. Intra-articular corticosteroid injections can be very effective for short term relief but the length of time of relief depends upon the severity of the disease. Surgical removal of the nerves that supply pain sensation to the navicular area (neurectomy) is more invasive, but usually the most effective way to manage true navicular disease. This does not cure the disease, but merely takes away the pain and allows the horse comfort and the ability to work. There are several complications to this surgery so a consult with your veterinarian is a must before this step is taken. The duration of relief varies from horse to horse and is dependent upon surgical technique and adherence to post-surgical recommendations.
Pedal Osteitis
Caused by repeated concussion, chronic bruised soles, and laminitis, pedal osteitis is inflammation and demineralization of the pedal (coffin) bone and the resulting inflammation of the structures of the sole of the front feet. Most commonly seen in performance horses, it is especially seen in horses who work on hard footing.
Symptoms may include a stilted, shuffling gait and sensitivity over the whole bottom of the foot. Both front feet may be affected and therefore overt lameness may not be noticeable. Pedal Osteitis is diagnosed by nerve blocks and radiographs, where demineralization of the coffin bone can be seen. Treatment includes rest and anti-inflammatory drugs as well as correct trimming and shoeing with pads to relieve sole concussion.
Coffin Bone Fractures
An injury that occurs due to concussion during exercise or in racing, a fracture of the coffin bone results in a sudden onset of lameness. Typically through the lateral wing of the coffin bone, it can extend into the coffin joint; some fractures can occur in the main body of the coffin bone (as seen in the picture to the right). Diagnosis is made with examination, nerve block and radiographs. On exam the foot will be painful when compressed with hoof testers and turning or pivoting the horse will make the lameness worse. X-rays immediately after injury may not show the fracture but when repeated 48-72 hours later may reveal the injury and the extent of damage, including if the coffin joint is involved. Some horses may appear to return to relative soundness after 48 hours of stall rest but will still have a fracture present that does not extend into the joint.
Treatment for fractures that do not involve the coffin joint includes 6-9 months of rest, often resulting in a return to soundness, though the fracture will still be visible on x-ray (fractures typically heal with a fibrous union). For fractures involving the the joint, horses younger than 3 will usually heal well with 12 months of rest.
Horses over 3 years may require surgery to insert a screw to promote healing of the bone and can have a less favorable prognosis. A common surgical complication is infection and a second surgery is required to remove the screw in order to return the horse to soundness. For all horses, a plain bar shoe with clips on each quarter to limit expansion and contraction of the heels is recommended.
Quartercracks
Most common in racehorses, quartercracks are a split in the hoof wall starting at the coronary band and running straight down the hoof. These can be caused by trauma, poor conformation, or excessively dry hooves. Quartercracks may also be caused by trauma to the coronary band resulting in a build up and overlap of the hoof wall. Affected horses may or may not show lameness but if an infection develops, lameness will occur.
The most effective way to decrease pain and promote hoof growth is to unweight the hoofwall caudal to the quartercrack. This can be done with corrective shoeing, "floating" the hoofwall at the ground surface or surgical removal. Other treatments include application of a counterirritant to the affected section of the coronary band to encourage growth and patching of the hoofwall.
Sidebone
Sidebone is the ossification, or hardening into bone, of the cartilages of the coffin bone. Seen frequently in hunter/jumpers, it is commonly caused by uneven concussion to the quarters of the feet though it is thought there may be an inherited predisposition to sidebone. It can also occur with trauma or improper shoeing that inhibits the movement of the quarters.
Lameness due to sidebone is rare unless a secondary infection occurs; this is called "quittor". Sidebone is mostly a secondary finding when radiographing the foot for any reason.
While palpation of the cartilages of the coffin bone may reveal a loss of flexibility, radiographs are the only way to confirm diagnosis. Corrective trimming and shoeing focusing on balancing the foot and promoting expansion of the hoofwall and quarters to protect the foot from uneven concussion is the primary treatment.
Laminitis
For an in-depth review of laminitis, follow this link.