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Navicular disease is a progressive degenerative condition involving the navicular bone, the bursa and the deep digital flexor tendon (DDFT) of one or, more commonly, both front feet.

Itis a complex syndrome with a multitude of symptoms, possible causes and forms of treatment. Horses with the condition frequently have degenerative joint changes elsewhere in their limbs, which may explain the poor success rate in treating this disease.

Some people believe that the lameness is caused by pain arising from the soft tissue structures of the heel, rather than the navicular bone itself.

Causes of navicular

There are three main schools of thought about navicular syndrome, whose causes probably reinforce each other.

• Concussion and trauma to the bone, bursa and ligaments, usually associated with horses with “long toe, low heel” conformation.
• Disruption of the blood supply within the navicular bone which leads to a painful degeneration (necrosis).
• Part of a more generalised arthritis.

Factors common to all three include poor conformation, foot shape and hoof/pastern axis – either collapsed or too upright – plus strenuous work combined with long periods standing in a stable.

Diagnosis and treatment

To diagnose navicular syndrome, the vet will look at the clinical signs, take X-rays and use scintigraphy. There are three main ways of treating navicular syndrome.

Reduction or abolition of pain:

• Painkilling drugs, such as ‘bute’, are commonly used, but many equestrian sporting bodies prohibit them.
• Injecting cortisone or hyaluronic acid into the navicular bursa can provide good, although temporary, pain relief. Adverse reactions may occur.
• Cutting the nerves supplying the back of the foot (a neurectomy) will improve many horses. This treatment has many potential complications.

Improving the navicular blood supply:

• Isoxsuprine: this dilates the arteries and is administered orally.
• Warfarin: this reduces blood viscosity, thereby improving the blood flow. Clotting time must be monitored continuously when using Warfarin, to reduce the risk of serious haemorrhage. It is not compatible with many other drugs, including ‘bute’.

Redefining foot balance:

This is the most essential part of any treatment programme. The aim of corrective trimming and shoeing is to re-establish and maintain a straight hoof/pastern axis, to shorten the toe where necessary and to encourage growth and expansion at the heel. It can be a long process and shoeing with heel wedges may sometimes be used in the interim.

• Egg-bar shoes are useful for collapsed heels and are often combined with rolled toes to reduce the leverage on the toe at the breakover part of the stride.
• Four-point shoes are square-toed and set back from the toe of the foot to about 1inch in front of the frog, altering the breakover point and reducing heel pressure.