A horse having its foot examined for navicular disease in Washington State University's MRI.
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Navicular disease, or inflammation of the heel, is one of the most common causes of performance limiting lameness in the front legs of many different types of horses. Although it is common and veterinarians have long recognized and treated it, the cause of navicular disease is poorly understood.
"A wide variety of treatments have been used on horses with clinical signs of navicular disease, which can be described as heel pain," said Dr. Sarah Sampson, a Washington State University equine veterinarian with expertise in navicular disease and magnetic resonance imaging.
"But most treatments have proven ineffective in stopping the chronic, progressive degeneration that occurs in the navicular bone of affected horses. Many treated horses have repeated episodes of lameness that eventually result in retirement if they are performance horses."
An important advancement in diagnostic technology is changing this scenario - the use of magnetic resonance imaging, or MRI. WSU's College of Veterinary Medicine pioneered the clinical use of MRI in live horses beginning in 1996. It is currently one of only a few veterinary hospitals in the world equipped with this technology, and it has moved WSU to the forefront of veterinary medicine in the evaluation of lameness and neurological disorders.
In recent years, veterinarians have evaluated many bone and soft tissue problems with MRI technology, many of which have not been diagnosed in live horses before.
"MRI has allowed us to see tendons, ligaments, and bones in the horse's foot in ways never before possible," Dr. Sampson said. "The use of MRI to evaluate the feet of affected horses has been the biggest single step forward in understanding navicular disease in the past 50 years. Our 11 years of experience with MRI evaluations has taught us much about the disease.
"We have learned that navicular disease is not one disease, but in fact many different problems that cause the same clinical signs in horses," she said. "We have learned that MRI is often necessary in making appropriate treatment decisions in many horses. It allows us to determine the source of inflammation and pain in more than 90 percent of horses with pain that has been localized to the foot.
"Although we still treat horses with foot lameness without an MRI, our experience with it has taught us that we greatly increase the chances of helping horses return to performance once we know the cause of the problem and can apply an appropriate treatment," Dr. Sampson said.
"For example, a horse with tendonitis of the deep flexor tendon may need to be treated for tendonitis, not just navicular disease, which may have seemed appropriate based on a radiograph alone. Many horses with clinical signs of navicular disease need an MRI."
Because of the information learned from MRI evaluations of horses with navicular disease, new treatments are being developed and used.
"Now that we are recognizing other locations of damage in the horse's foot, new treatments are being developed for specific problems," Dr. Sampson said.
"These treatments need to be adequately evaluated before they can be recommended for routine use in performance horses."
Two studies are currently being conducted at WSU on two new treatments for horses with navicular disease. The first study involves assessing and treating affected horses with a new therapeutic drug for those that have navicular disease with bone edema, and the second involves a surgical procedure to help horses that have affected ligaments in the navicular region.