A short, choppy stride; standing with one foot pointed ahead of the other; forefoot lameness that’s easily seen on hard ground or when the horse is moving on a circle; increased stumbling. These are all common signs in a horse with navicular syndrome, defined as discomfort in the front heel area related to pain around the navicular bone or the tendons and other structures in the navicular area.
The navicular bone or bursa, deep digital flexor tendon, and various ligaments may be involved. In previous years, it was believed that arthritic changes to the navicular bone were the source of pain, but more recent studies have shown that this is not always the case.
The deep digital flexor tendon ties into the coffin bone and runs over the lower surface of the navicular bone in the rear part of the hoof before turning to go up the horse’s leg. The tendon is under tension as the horse moves, and any factor that increases this stress or impedes smooth action can lead to inflammation and pain in the heel area.
Inflammation can result from wear and tear as a horse ages, and the syndrome is most commonly seen in older horses. While it can be found in horses of any breed, the incidence is highest in Quarter Horses, Warmbloods, and Thoroughbreds. Any horse with a large, heavy body and small hooves is at an increased risk for foot problems, including navicular syndrome.
Another conformation factor that increases the chance of a horse developing navicular syndrome is an incorrect pastern angle that does not match the angle of the hoof. If the mismatched angles cause the deep digital flexor tendon to be excessively stretched as it runs over the navicular bone, there is increased pressure on the navicular bone, cushioning bursa, and surrounding structures. Delays in regular hoof trimming and resetting of shoes can contribute to the problem. Horses with long toes and low or underrun heels have the same risk, regardless of whether conformation or poor hoof care is the cause.
Radiographs of the navicular bone may be somewhat helpful in diagnosing navicular syndrome, although decades of radiographs have failed to show a clear relationship between bone changes and heel pain. Magnetic resonance imaging is more useful in showing problems in the soft tissue structures around the navicular bone.
Navicular syndrome can be managed to reduce the horse’s pain and minimize excessive stress on the deep digital flexor tendon. A layup period in a stall or small paddock can allow the painful structures to rest and recover. Keeping horses at the correct body weight is important, as obesity increases the load on a horse’s hooves and tendons. Regular hoof trimming is important to establish and maintain the correct angle of the hooves and pasterns. Therapeutic shoeing can improve the horse’s comfort by improving balance and breakover. Some horses benefit from pain medications and/or corticosteroid injections to the coffin joint or the navicular bursa.
In cases of severe, intractable pain, owners and veterinarians may lean toward neurectomy (severing the nerves to the painful area). While this procedure allows the horse to work without discomfort, it also means that the horse will not feel sole bruises, abscesses, laminitis, and other conditions that may need veterinary care and would normally be signaled by lameness.
One or more of these treatment steps can allow many horses with navicular syndrome to become more comfortable and return to some level of work. However, the syndrome can never truly be cured, and management should be designed to avoid an increase in stress and inflammation in the affected structures.