The navicular bone horse is one of the most common causes of lameness in horses and is a chronic disease that affects the front feet. The navicular bone has an extremely complex blood supply which provides vital oxygen and nutrients to the bone, the navicular bursa, the deep digital flexor tendon (DDFT), and the navicular ligaments. Damage to any of these structures will lead to pain, inflammation, and deterioration of the navicular bone.
Navicular disease is most often caused by limited blood flow to the navicular bone and/or trauma to the navicular bones, navicular bursa, DDFT, and navicular ligaments. The resulting damage to the navicular bone is called “dysostosis” and can result in a collapsed or fractured navicular bone.
Damage to the navicular bone and associated structures can also be caused by abnormal foot conformation, repetitive stress on the forelimbs or the hoof, or poor shoeing. The navicular bone is located on the back half of the foot and has multiple nerves that are sensitive to pressure. These nerves, along with a well-placed heel plate, help prevent shock from traveling directly through the navicular bone and frog to cause pain and injury.
A horse that has navicular bone problems will generally show signs of low-grade bilateral lameness. As the disease progresses, the horse may become more and more frequently lame, especially in the morning or after a strenuous work out. Eventually, the horse will start to work out of the lameness and will only show a slight limp when walking or trotting.
X-rays, ultrasound, and magnetic resonance imaging are all diagnostic tools to assess the condition of the navicular bone and surrounding structures. However, the most reliable test is a nerve block. A navicular nerve block involves injecting a local anesthetic around the nerves on the back half of the foot that surround the navicular bone. Once the area is numb, the veterinarian can usually determine where the lesion in the navicular bone and/or the deep digital flexor tendon is located. The lameness of the horse will typically “switch feet” once the area is blocked and this allows the veterinarian to pinpoint the area of injury and begin treatment.
Once the navicular area has been identified, several treatments have been developed to improve and prolong your horse’s soundness. Corrective shoeing, NSAID therapy, navicular bursa injections, and coffin joint injections have all shown to improve soundness in navicular patients. The key is to catch the problem early, before it gets worse. With regular veterinary checkups and proper hoof care, most horses can live out their athletic careers comfortably for a long time with navicular disease.