Our knowledge of the causes of foot pain, and therefore navicular disease in horses, has increased 10-fold in the past decade.

Previously, if nerve-blocks revealed that a horse had localised pain in the back third of its foot, it was usually attributed to navicular.

Similarly, if an X-ray revealed a large, cyst-like structure penetrating the back shell of the navicular bone, navicular disease was to blame.

However, many horses who also had localised pain in this region, but no detectable X-ray changes, were also diagnosed, incorrectly, with so-called navicular syndrome.

Vets recognised it was possible that the ligaments supporting the navicular bone might also experience strain. They knew this because of the presence of new bone formation at the point where the ligaments attach to the navicular bone, but there was no proof until magnetic resonance imaging revolutionised vets’ ability to reach more specific diagnoses for foot lameness.

This new technology has provided vets with the ability literally to look inside a horse’s foot.

We now know that there are a variety of different injuries that can affect the navicular bone: primary pain can occasionally arise from the supporting ligaments or the deep digital flexor tendon that passes over the back of this area and coffin joint pain or injury to its collateral ligaments can result in similar clinical signs to those seen in so-called navicular syndrome.

In horses with sidebone (ossified cartilage of the coffin bone) it may be that the sidebone itself is injured, or that the ligaments associated with the sidebone have sustained damage.

So navicular syndrome is not a true diagnosis. A more detailed lameness investigation should be carried out when the signs are vague and the diagnosis unclear as there may be more complex underlying causes of the pain.

For the full article on navicular disease, including case studies, see the current issue of Horse & Hound (27 May, ’10)