What Is Navicular Disease in a Horse?

Navicular disease (also called navicular syndrome) refers to any lameness in the area surrounding a tiny, wedge-shaped bone called the navicular, located in the lower part of a horse's foot. When this bone is compromised because of excess pressure or poor circulation, lameness can result. Sometimes the cure is as simple as changing the angle of the hoof, but other times long-term adjustments may be necessary to ensure the horse's soundness.

  1. The Navicular Bone

    • The navicular is a small, flattened bone in a horse's foot that acts kind of like a balancing point, distributing pressure between the tendons and the bones. Navicular disease typically originates in the navicular bursa, the fluid-filled sac that lies behind the bone and serves to reduce friction between the bone and the attached tendons. When this sac becomes inflamed, it reduces the cushion between the bones and the tendons, which in turn applies more pressure to the bone itself.

    Navicular as a Circulatory Problem

    • One way navicular disease may develop is through circulatory problems resulting from compromised blood flow through the navicular bone. Correct shoeing (as opposed to corrective shoeing) and therapies designed to increase circulation can help the bone recover.

    Navicular Disease as a Result of Excess Pressure

    • Because the navicular bone is located at the point where the foot flexes, it acts as a balancing point, providing needed leverage for the tendons that support the ankle bones. It is thought that over time, excess pressure on this bone and its surrounding cushions (the bursa) reduces its effectiveness, resulting in lameness.

      Large horses with feet that are too small are especially prone to excess pressure here, as are horses with poor conformation and those whose hooves that have grown long enough the heel has dropped, applying more pressure to the ankle region. Repeated concussion on hard surfaces is also a cause of navicular damage.

    Symptoms of Navicular Pain

    • Clinical signs of lameness in the navicular area are walking on the toes rather than applying pressure to the heel, standing with feet farther underneath in an attempt to relieve pressure to the foot, visibly favoring a foot while moving, contracted heels due to decreased circulation and a rough gait as a result of a shortened stride.

    Determining the Cause

    • Your veterinarian will use a tool called a hoof tester to apply pressure to the fog (fleshy area on the underside of the hoof) and the hoof wall in an attempt to isolate the soreness. He will also observe the horse's movement, looking for a shortened stride and a tendency to apply more pressure to the toe than the heel.

      He might also do a flexion test, which involves holding the foot while bending it at the ankle joint (fetlock and pastern) for 90 seconds, then releasing it and trotting the horse. A horse that is lame for at least a few strides is experiencing pain in the navicular area. Other methods of diagnosis involve nerve blocks and X-rays.