Navicular disease is a degenerative disorder of the navicular bone that is predisposed by faulty foot conformation. In horses affected by this disease, increased amount of blood and accumulation of an excessive amount of watery fluid in the cavity of the bone cause venous hypertension, bone pain, and lameness.
Navicular disease is an inflammation of bursa, deep flexor tendon and navicular bone. Bone and tendon develop adhesions which cause pain and lameness. The genetic predisposition to navicular disease is proven nowadays, but otherwise, what causes it is still unclear. Horses with navicular disease have an increased load on the navicular bone in early stance. This has been suggested to be a response to pain in the heel region. The horse responds to heel pain (including pain in the navicular region) by contracting the deep digital flexor muscle to unload the heels. This increases the compressive load on the navicular bone, which may cause damage to the overlying flexor cartilage, which is then painful and identified as navicular disease.
Occasional lameness which decreases on rest and after work (horse warms up); standing with affected toe pointed; shuffling gait, especially if both forefeet affected. On X-ray navicular bone has ragged edge and areas of rarefied bone and nerve block. Navicular syndrome can be treated in a variety of ways. This is related to the fact that it has a variety of causes. Treatment may include stallrest, non-steroidal anti-inflammatory drugs, and orthopaedic shoeing plus intrabursal injections of short-acting corticosteroids and hyaluronic acid.
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Many veterinarians recommend shoeing as the primary therapy. Shoeing is performed to correct preexisting problems, enhance physiologic function of the foot, and ease breakover of the foot. Shoeing is reported to be most effective when performed within 8 months of the first signs of lameness. Nonsteroidal anti-inflammatory drugs are not used unless radical changes have been made in the shoeing. Approximately 75% of the horses improve in their performance. If therapy does not improve the horse within 6 to 12 weeks, surgery may give permanent relief.
The disease is progressive, and affected horses eventually will need to be retired because of lameness. Often horses with navicular disease remain undiagnosed until the disease has advanced to the stage where problems exist in the foot or to where the conformation-balance of the hoof is irrecoverable. The key to controlling the disease is prevention by maintaining good overall hoof husbandry.