Unravelling the Mysteries of Navicular Disease

• The DDFT increases pressure against the navicular bone;
• There is an increase in contact of the navicular bone with P2; and
• Finally, tension of the collateral and impar ligaments also increases.

With a poorly balanced foot or poor foot conformation, the navicular bone is subjected to abnormal forces causing inflammation and degeneration. It is also theorized that there is a hereditary component to this disease as well.  

The resulting lameness is most commonly bilateral (affecting both feet) in the forelimbs, but it is occasionally seen in the hind limbs. It can be slowly progressive and insidious in its onset as a bilateral lameness; however, it can also arise as acute, severe, unilateral limb lameness.

Researchers have found that the most commonly affected breeds include Quarter Horses, Thoroughbreds, and European Warmbloods. Quarter Horses tend to have narrow, upright feet that are small relative to their body size. Many European Warmbloods also have tall, narrow feet. Thoroughbreds tend to have feet that are flat with low, collapsed heels. Navicular disease is least commonly seen in Arabians, ponies, and draft breeds.

Diagnosis of navicular disease can be challenging due to the location of the navicular region within the hoof capsule as well as the numerous structures that could be the source of the resultant pain. To begin diagnosis, your veterinarian will start by performing a lameness exam to locate where the pain is emanating from. This is done by watching the horse during a moving evaluation on hard and soft surfaces, as well as in straight lines and in circles. This moving evaluation is most commonly done in-hand; however, your veterinarian may ask to see the horse under saddle. A series of flexion tests will be performed. Hoof testers will be placed on each foot in search of sensitive areas.

When the area of concern is identified, your veterinarian will perform one or more nerve blocks to confirm. A nerve block is performed by instilling a local anesthetic, such as carbocaine, alongside a nerve, temporarily desensitizing it. After the nerve block is performed, the horse continues the moving evaluation to verify whether or not the nerve block affected the lameness. If the horse is no longer showing lameness, your veterinarian has confirmed the area of the limb where the pain is originating. When navicular disease is suspected, a palmar digital nerve block will resolve the pain. This nerve block desensitizes many structures within the hoof capsule including the navicular bone and its surrounding structures.