Navicular syndrome (or navicular disease, or caudal heel pain syndrome) is a degenerative condition of structures in the horse's heel. The navicular bone lies at the back of the heel, and the deep digital flexor tendon runs down the leg and wraps under the navicular bone before anchoring to the coffin bone. Pain results from changes in the bones, bursa (fluid-filled joint structures designed to absorb shock and reduce friction), tendons, and ligaments in this area.
No one knows precisely what causes navicular syndrome.
Lameness is the classic sign of navicular syndrome. This can appear suddenly, but a more common pattern is mild lameness that becomes progressively worse over time. A horse with navicular syndrome feels pain in the heels of the front feet, and its movements reflect attempts to keep pressure off this area. At rest, the more painful foot is often "pointed," or held slightly in front of the other forefoot, thus bearing little or no weight. Because the horse tries to impact the ground flat-footed or toe-first instead of the more normal heel-first pattern, the gaits are short-strided and stiff. A horse with navicular syndrome has difficulty turning sharply, going downhill, and moving on rocky or hard ground. Picking up one front foot for trimming or shoeing is painful because weight is concentrated on the other foreleg, and affected animals may become quite uncooperative during farrier visits.
While there's no guarantee that a particular horse will or will not develop navicular trouble, the problem is most common in stock-type horses (Quarter Horses, Paints, Appaloosas). There is a fairly high incidence in Thoroughbreds and some warmblood breeds. Arabians, on the other hand, are rarely affected. Lameness from navicular syndrome is most often diagnosed in horses between the ages of seven and fourteen.
No one knows precisely what causes navicular syndrome. Like some other lamenesses, a combination of factors is probably to blame. Conformation seems to be important, with more cases occurring in horses with heavy bodies, upright pasterns, and small hooves. A large number of affected horses have a history of work involving front-leg impact (jumping, cutting, roping, and reining) or increased concussion (parade work or other use involving hard or rocky surfaces). Suspicion has also been directed at irregular farrier care, unbalanced hooves, and shoeing practices that reduce contact between the frog and the ground. A common thread seems to be the combination of increased stress and limited oxygenation of structures in the heel area, but the exact cause of tissue damage and inflammation has not yet been determined.
Consultations with a veterinarian and a farrier are the first steps in combating navicular syndrome. While there is no cure, a prompt diagnosis allows treatment—farrier, medical, or surgical—to begin early in the course of the disease. Proper trimming and therapeutic shoeing can provide relief for many horses. Farrier care is aimed at correcting broken-back or broken-forward pastern angles and normalizing underrun or contracted heels. Generally a shortened toe, either through trimming or shoe design, is a goal. Heel support afforded by egg bar or wide-web shoes reduces pain in some horses, and a shock-absorbing polyurethane shoe from Switzerland is being tested as a possible therapeutic aid. Overall, proper trimming and shoeing can relieve discomfort in about 30% of horses with navicular syndrome.
Polysulfated glycosaminoglycans and hyaluronic acid sometimes lead to improvement, possibly by inhibiting enzymes involved in tissue breakdown. Anti-inflammatory medications can be injected into the heel area or given orally for pain relief. Medical treatment combined with therapeutic shoeing can help about 60% of affected horses.
Palmar digital neurectomy, a surgical procedure to sever the nerves to the painful area, is a last resort in treating navicular syndrome. This option eliminates sensation in the rear third of the foot, thus ending pain and lameness, but it is not a permanent cure. Degenerative changes continue to occur within the hoof, and about one-third of treated horses are lame again within two years.
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