Equine Navicular Syndrome

Description

Navicular Syndrome is a soundness problem in horses, and not an actual disease.

Navicular Syndrome, which begins with inflammation of the bursa between the Navicular bone and the tendon of the deep digital flexor, is a common cause of lameness in horses.

A. Flexor Tendon
B. Navicular Bone
C. Navicular Bursa

Navicular Syndrome is one of the most common causes of lameness in horses and usually affects both forefeet. However, one foot may have more damage than the other. The Flexor Tendon adjacent to the Navicular Bursa may he progressively destroyed and rupture. The Flexor Tendon flexes the joints of the foot moving the toe down and back. Horses with poor conformation of the forelimb are more likely to develop Navicular Syndrome.

When the foot is placed upon the ground, the weight forces the Navicular Bone back against the Flexor Tendon. Horses with small feet have a smaller area to distribute weight. Consequently, more pressure is placed upon the Navicular Bone.

Symptoms

While walking, a horse with Navicular Syndrome tends to place its weight on the toe to avoid pressure on the heel area which contains the inflamed Navicular Bone and Bursa. The horse may stumble frequently. Since the horse does not place weight on its heel, it will take longer to stop.

While standing, the horse tends to shift its weight continuously. This relieves pressure and the pain on its heel. Because the horse will place its weight on its toes when moving, its gait is rough and gives the appearance of lameness in the shoulder.

Lameness and pain are usually mild but worsen when the horse is worked on a circle. The lameness may disappear after a rest.

Because there may be poor circulation in the feet, after several months of pain, the feet may begin to change shape, especially the foot that has been experiencing the most pain, which tends to become more upright and narrow.

Diagnosis

Many veterinarians use hoof testers to diagnose Navicular Syndrome. When pressure is applied with a hoof tester over the frog area, and the horse may flinch in pain if Navicular Syndrome is present. The veterinarian should also test the hind feet with hoof testers to compare the reaction with the forefeet.

A locally injected anesthetic that temporarily blocks the nerve to the affected foot will relieve pain. This helps the veterinarian to determine if Navicular Syndrome exists. If a lame horse walks normally after the injection, the lameness is probably located in the Navicular area.

Treatment

Degenerative changes are not reversible. Managing the condition by alleviating pain and slowing degeneration is the best course of action.

Corrective shoeing by an experienced Farrier is helpful. A bar placed across the heels aids in relieving the pressure on the heels. Rasping the quarters of the hoof wall or cutting grooves in the wall aids in relieving foot contraction. Rubber frog supports may be a better method of restoring frog pressure.

Vasodilator drugs can improve the blood flow into the vessels of hoof.

Cutting the nerves that supply the Navicular area is an effective treatment for pain. A neurectomy (more commonly called nerving) is controversial surgery which severs the palmar digital nerves so the horse loses sensation in the back of the foot. The procedure is usually performed on both front feet.

Complications can include infection of the wound, lameness if the nerves regrow or small branches of the nerves are not removed, and neromas.

After a neurectomy, a polo pony's feet should be inspected regularly by a Farrier or veterinarian. Neurectomy lowers the market value of a horse and may make a polo pony unsafe for playing in a game.

The outlook for horses with Navicular Syndrome is unfavorable in most cases. However, the methods of treatment may be sufficiently effective to reduce the horse's suffering and extend its useful service.