Dr. Judith L. Mulholland

The classic navicular syndrome shape is a long foot, wider at the toe than the quarter with narrow contracted heels and frog. The hoof wall angle at the quarters is upright and in this case the toe is long and the heels are short and so is the shoe. This is not how to shoe for a good result. This horse was very lame.		This horse has no heels at all! Ideally allowing for some decrease in tension on the deep digital flexor tendon will offer some relief from the pain of navicular syndrome. The low heels will make the problem worse.		After rebuilding some heel with Equithane and dressing the toe from the front of the foot to move the point of breakover back under the leg, shoes were fitted with a graduated heel, a thinned and bevelled toe and greater length under the heels. This horse improved.

It is important to mention that farriery trends vary throughout the world vary, and that what is considered normal practice in one country or location may be considered very abnormal in another. For example, contacted feet with long, upright heels may be common in Europe where horses are stabled during winter. In Australia, most horses live in paddocks until 2 years of age, and flat feet and underrun heels are common in many areas. These predisposing factors are due to a combination of genetically inherited foot conformation, breed, overall management, diet, exercise, stabling, frequency of farriery care and the skill of the farrier. Genetic and environmental variety is reflected in the varying causes of navicular syndrome. Farriery, breed and management are significant factors influencing whether a horse does develop navicular syndrome, and just like laminitis, the risk of a horse developing navicular syndrome is reduced by improved farriery and horse management practices.

A chronic degeneration of the navicular bone in which there is damage to its flexor surface and the overlying flexor tendon in the front feet of the horse. There may be an accompanying navicular bursitis and osteophyte (bony outgrowth) formation. The syndrome is characterised by intermittent lameness (Blood and Studdert, 1999).

Symptoms

It is common for the earliest symptoms of the disease to go unnoticed. The onset is slow, and is usually diagnosed only when chronic changes have developed. Seventy percent of horses with confirmed navicular disease have a history of forelimb lameness. This includes shuffling gait and restricted stride for more than 3 month's duration. Pointing the toe is sometimes observed in paddocked or stabled horses. Digging the toes lower than the heels and pillowing bedding under the heels to gain relief can be symptoms in more advanced cases. Early diagnosis is vital for a prolonged, active career. The earlier the diagnosis, the better the chance of treatment providing long-term relief from lameness. The high risk groups are Quarter horses, Thoroughbreds and Warmbloods. The risk to these groups is greatly reduced when all the contributing factors are addressed. Proper equine management is the best preventive measure.

Chronic symptoms

In many cases, no classic signs of navicular disease are observed and diagnosis is made when all other avenues for the cause and treatment of poor performance have been exhausted. Degeneration of the navicular bone results in a low-grade ache, particularly when standing about. The lame horse advances the affected hoof to rest it on the toe. If both front hooves are affected, the horse will point them alternately. During exercise the horse often improves once it has warmed up. These horses are usually better when ridden or exercised daily, and worse when given time off. Because of pain in the posterior (back) half of the foot, the horse tries to minimise pain by avoiding landing on the heel first, as a normal horse does. Navicular horses have a tendency to try to land on the toe, causing a stumbling, shuffling gait that kicks up small puffs of dirt and ultimately causes excessive wear on the toe of the shoe. Alterations to footfall and function lead to a contracted, upright hoof with a recessed frog. The hoof may also have a heavily worn toe in some cases. When turned out to pasture the foot may develop a club foot shape with a concave (dished in) wall at the toe.

Diagnosis

A diagnosis may require modern methods such as nuclear scintigraphy before an approximate area of the distal limb is isolated and a diagnosis is reached. Diagnosis can usually be confirmed by a combination of several of the following techniques: Flexion testing, blocking the nerves which supply the navicular bone, X-rays and palpation of the foot with hoof testers and observation of how the horse moves, how the feet land and of changes to the hoof capsule over time. These factors are combined with assessment of the hoof shape, size and angle, combined with movement and behaviour. One of the best clues is the history from the owner or rider. This gives valuable information and helps when trying to give an accurate diagnosis. Another important point in forming a long term prognosis for the horse owner is the response to treatment. Some horses respond very well to improved shoeing and little other medical treatment is required. Some horses don't respond significantly and medical therapy may form part of the long term management in these cases.