Navicular Syndrome

Description

The navicular bone is a small bone in the foot of the horse that is held in place by ligaments. Because of the complexity of the interacting structures of the foot, a number of problems can arise if any damage or pathology occurs to disrupt the functions within the foot. Since the forelimbs bear between 60 to 65% of a horse's weight, the inner workings of the hoof are important to the soundness of the horse.

To understand the underlying problems of navicular syndrome, it is important to understand the horse's anatomy. The navicular bone lies behind the coffin bone and under the small pastern bone. The deep digital flexor tendon runs down the back of the cannon and soft tissue in that area and under the navicular bone before it attaches to the back of the coffin bone. The digital flexor tendon flexes the coffin joint and the navicular bone acts as a fulcrum.

The navicular bone is supported by several ligaments. The impar ligament attaches the navicular bone to the coffin bone. The bones are cushioned by cartilage. A small sac, the navicular bursa, protects the digital flexor tendon and navicular bone from abrasion as they work together.

Navicular syndrome occurs when inflammation or degeneration of the navicular bone and its surrounding tissues and ligaments prevents the smooth interaction necessary for the horse to stand, walk, trot, or gallop. This syndrome is usually a chronic bilateral foreleg lameness that can occur in horses of all ages. Quarterhorses, thoroughbreds, and warmblood breeds seem most susceptible.

Symptoms

• Heel pain
• "Tiptoe" gait
• Lameness

Causes

Two theories, one of predisposition, and the other, a genetics theory, are the subject of ongoing debate among veterinarians.

Studies show that the smaller the foot on a large horse, the more apt the horse is to develop navicular syndrome.

The activity of the horse is also seen as a factor. Activities, such as barrel racing, that put stress on the horse's foot may lead to navicular syndrome.

Genetic predisposition that relates to the conformation of the foot and the natural angle of the pastern may also be a factor. The more upright the pastern is, the more likely the horse is to develop navicular syndrome.

Prevention

Keeping a horse's feet in proper neurological and bio-mechanical balance is the best prevention. Trimming the hooves regularly and carefully, and exposing the horse to stimulus to improve hoof form is vital.

Proper shoeing by a farrier who is experienced in designing shoes that provide support for the heels and counteract tendencies such as rolled toe problems can be helpful. Horses with upright feet may need their heels lowered and a shoe that will allow their heels to spread.

Regular exercise that maintains fitness is preferable to rough workouts on rugged terrain and hard surfaces. If a horse has any predisposition to navicular syndrome, controlling the frequency of jumps is also important.

Treatment

The prognosis for a horse with navicular syndrome is guarded. By the time the problem is recognized, degeneration of the tissues, ligaments, and bone structure may be well-advanced. Management of the condition involves alleviating pain and slowing progress of the degeneration.

The services of a veterinarian to confirm the diagnosis, the extent of the degeneration, and the needs of the horse will help inform the best course of treatment in each case.

Anti-inflammatory drugs used to treat the pain include corticosteroids, NSAIDS, and other joint medications. Anticoagulants to improve blood flow are often used along with vasodilators to improve the flood flow into the vessels of the hoof. .

Proper trimming of the hooves and shoeing are important in long-term management of navicular syndrome. An experienced farrier can select or design shoes that will improve the neurological and mechanical balance of the foot depending on the conformation of the horse's hooves.

In some cases, surgery may be recommended after all other options have been considered. The palmar digital nerves may be severed so the horse loses sensation in the back of the foot. Because of possible complications, including infection, continuation of the lameness, and the loss of the horse's ability to feel pain if injured, most veterinarians are reluctant to take this approach.

Another procedure, navicular suspensory desmotomy, during which the ligaments supporting the navicular bone are severed, is successful about 50% of the time.

Usually, a horse diagnosed with navicular syndrome will need a careful evaluation and development of the best exercise program possible to relieve pain and slow the progress of the condition.

Swimming and slow, long-distance work are often recommended, along with a reduction of work on irregular, hard surfaces or terrain, and either a reduction in frequency of jumping or eliminating jumping altogether in order to prevent further injuries.