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    AskTheVetNavicular disease is an ugly term in the equine world. It is a dreaded condition that makes people cringe, and if they are looking to buy your horse, they will turn and run at the first mention of the term. Before we discuss the disease, we should talk about what the navicular bone is.
    The navicular bone is a small bone in the hoof. Its function is to act as a pivot point for the deep digital flexor tendon. This tendon is what brings the hoof back when the horse is moving. This little bone is not meant to bear any weight in the horse, just make it easier for that tendon to slide around the curve of the lowest part of the digit.

    With navicular disease, there can be three different processes occurring. First, you can have degeneration of the bone. Second, you can have sclerosis, or thickening, of the bone. Lastly, you can have navicular bursitis. An additional cushion to the tendon gliding along the bone is a fluid filled sac called the navicular bursa. With “bursitis”, the bursa is inflamed and a source of pain.

    Clinical signs of navicular disease can vary. Most often, the horses are more comfortable on the straight and flat, versus turning and downhill. Of ten, the disease affects both front feet. The gait of the horse tends to be “choppy” or “stabbing” the front feet into the ground. It is extremely rare to have issues with this bone in the hind feet.

    Diagnosis usually starts with a lameness exam by your veterinarian. They will usually watch the horse move on the straight and lunging. Next, I usually go over the hooves with my hoof testers. They apply pressure to different areas of the hoof, looking for discomfort. Some horses with navicular are sore to the testers, some are not. Next, I usually will do peripheral nerve blocks. This involves putting a small amount of local anesthetic adjacent to the nerves running down the leg. A vast majority of navicular horses respond very well to the lowest block we typically do. This lowest block tells us we have discomfort in the heel of the hoof.

    Now that we know where to look for the problem, we want to see it. In the field, we can do radiographs (X rays). With degeneration or sclerosis, usually we can see that. With bursitis, we cannot. Depending on the budget of the owner, the exam may end there with a diagnosis of navicular. More recently, we have gained access to better imaging tools, but they also cost more. MRI is an excellent tool for imaging of the hoof. It uses a giant magnet to get images instead of X rays. The images are more detailed and they also visualize soft tissue structures. With the commonplace use of MRI these days, many cases previously diagnosed as navicular have actually been found to have some soft tissues problems in the adjacent areas that have been misdiagnosed. Other tools that can be used to evaluate the foot are ultrasound and nuclear scintigraphy. Most of you know about ultrasound or sonograms, but nuclear scintigraphy is not talked about as much. It involves injecting a radioactive dye into the horse and then using a special camera to see where in the body it is more concentrated. With inflammation you have increased blood flow, therefore you see more of the dye.

    Now that we have a diagnosis of navicular, what do we do? Most likely, the first thing your veterinarian will recommend will be some shoeing changes. There are different approaches you may try first, but in my experience, there is not a one-size-fits-all solution to the problem. Sometimes it will involve a little of trial-and-error to see what makes the horse the most comfortable.

    After changing how the horse is shod, veterinary treatments will come into play. Here is a list of different things that may play a role in your horse’s therapy. Usually, a combination of them is what works best for me:

    * Anti-inflammatories — Phenylbutazone(Bute), firocoxib(Equioxx), flunixin(Banamine) and ketoprofen(Ketofen) are popular ones. Their goal is to reduce inflammation, thereby reducing pain
    * Medications to improve blood flow — Aspirin is sometimes used to increase bloodflow by making the platelets in the blood less likely to stick to each other. Isoxsuprine may be used to dilate blood vessels. It has also been found to relieve some pain.
    * Bisphosphonates – Among this newest group of drugs to be used to treat navicular, the two most used in horses are OsPhos and Tildren. They both work by inhibiting the breakdown of the bone to allow it to be rebuilt faster. They are drugs to be administered only by your veterinarian, as they have some potentially dangerous side effects. They have been successful in helping a lot of horses with this condition.
    * Shockwave therapy — Another modality that may give your horse relief from the discomfort.
    * Steroid injections-If you have a horse with navicular bursitis, injecting the bursa with steroids to reduce the inflammation often times helps. An alternate that is sometimes tried is to inject the coffin joint which may connect to the bursa.
    * Surgery — Often considered a salvage procedure is a palmardigital neurectomy. It involves cutting the nerves to the heel of the horse. This removes the pain associated with the disease and has given many horses more years to be pain-free.

    No matter which way you and your veterinarian go, the goal should be to limit the progression of the disease and keep your horse as comfortable as possible. This may require you to change your horse’s profession. Hopefully this gives you a little insight to some of the possibilities of dealing with navicular disease.

    ~Dan

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