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Navicular Disease: A New Approach to a Pain in the Heel

Pet Column for the week of September 22, 2003

Office of Public Engagement
2001 S. Lincoln Ave.
Urbana, Illinois 61802
Phone: 217/333-2907
Ann Marie Falk
Information Specialist

There's nothing worse than heading to pasture for an early morning ride and seeing your horse limping toward you. Navicular disease-or heel pain-could be the culprit.

Strictly speaking, "navicular disease" is pain or lameness that results from a problem with the navicular bone, but the term is loosely used to mean any pain or lameness that comes from the heel, including that arising from soft tissue structures. "Heel pain" is a more accurate term for this problem, and researchers at the University of Illinois Veterinary Teaching Hospital in Urbana are exploring the use of shock wave therapy to treat it.

"Horses with this type of lameness do not want to put weight on their heels. Owners describe the horse stumbling from landing with the toe first into the ground. The heel may or may not be sore to hoof testers. The most common site of heel pain is in the forelimbs, and usually both legs are affected," explains Dr. Allison Stewart, an equine surgeon at the teaching hospital.

When the navicular bone is involved, the onset is gradual and the disease is progressive. Heel pain caused by injury to the soft tissue around the navicular bone most commonly involves the deep digital flexor tendon or the suspensory ligament to the navicular bone.

Quarter horses are anatomically predisposed to navicular disease. These horses have a natural upright pastern, which causes the hoof wall to be at a much lower angle than the pastern. Hunter/jumpers are more likely to strain soft tissue tendons or ligaments.

"To find the cause of lameness, we block nerves in different areas of the leg. If a horse goes sound after an injection of local anesthetic to the heel, then the problem is in the heel. Now the questions is 'Is this a bone or soft tissue problem?' The next step is to take radiographs (X rays) of the navicular bone, where problems are easier to spot," notes Dr. Stewart.

Ultrasound is a good diagnostic tool to use in the pastern to look for a soft tissue problem when radiographs don't implicate the bone. Nuclear scintigraphy, or a "bone scan," gives a view of both bone and soft tissue. It identifies "hot spots" of damage or turnover of bone or soft tissue. A bone scan is very sensitive and can help pinpoint the location of injury if radiographs and ultrasound aren't helpful.

Magnetic resonance imaging (MRI) is the most definitive diagnostic approach, providing the most information about the foot. Unfortunately few equine patients have access to MRI.

The first step in both treatment and prevention is corrective shoeing. With the help of a farrier, the heel is elevated and the hoof wall is put in alignment with the pastern and the angle of the shoulder. The foot is now balanced; it is not landing more on either the inside or outside of the hoof. The stress of walking is now directed away from the heel.

"If the navicular bone is the problem, the disease will be degenerative and will worsen with time. Ligament and soft tissue injuries will heal with rest, but these horses are prone to re-injury. Non-steroidal anti-inflammatory drugs are given initially to help break the pain-inflammation cycle and promote healing," says Dr. Stewart.

Other medications thought to promote healing, such as glucosamine, are often added to the treatment regimen. Some veterinarians will use medication to dilate blood vessels in the heel. These methods of treatment, not currently supported by scientific trials, are tried when a horse does not respond to traditional approaches. Neurectomy, transecting the nerves that go to the heel, will eliminate the pain but does not solve the problem.

A new treatment approach in navicular disease is shock wave therapy. The two main forms of shock wave therapy are pneumatic (air-driven) and piso-electric. Both generate radial waves through the tissue. It has been documented in other areas that shock waves therapy near the site of a fracture stimulates healing. The use of shock wave therapy over nerves has been shown to relieve pain for 6 to 8 weeks. To penetrate the foot, the shock wave must go through the frog (center portion of the bottom of the hoof).

"Currently we are beginning clinical trials of shock wave therapy. The trial is designed to determine whether shock wave therapy promotes healing of the tendons, ligaments, and bones causing heel pain or whether it just provides pain relief," says Dr. Stewart.

Contact your local veterinarian for more information about navicular disease or concerns about your horse. To learn about the shock wave clinical trial, please call the University of Illinois Veterinary Teaching Hospital at 217/333-2000.