This condition causes lameness in horses, consistently in the front legs. Commonly it will start with a slow onset of lameness in front, sometimes in one, then the other front leg, eventually to both at the same time. The horse develops a short, choppy stride seen easiest at the trot.
The cause is not fully understood yet – but current thought is that it is caused by poor blood circulation to the navicular bones resulting in poor oxygen and nutrient supply to these bones so they start to degenerate, resulting in a lame horse.
Diagnosis is made via history and physical signs. The horse has front foot lameness centred on the navicular area with no other obvious causes. In the past, diagnosis was based on changes seen in the navicular bone on xrays – this has been shown to be quite wrong.
Some xrays of navicular bones in horses with no current or history of lameness show quite obvious changes – these horses can not be diagnosed with navicular syndrome. Similarly, some horses with correct histories of lameness onset pointing to navicular syndrome, and show pain in the navicular area to hoof testers that is blocked out with local anaesthetic, have no changes visible on xray in these bones – but they are highly likely to have navicular syndrome. Because the cause of navicular syndrome is not fully understood, there is no known prevention regime at this time. With what is known, it makes sense to make sure your horses hooves are orrectly trimmed and shod, to avoid over-extension of the fetlock joint; also that your horse is conditioned properly for the exercise it is to do.
Treatments currently used are not all successful. A combination of proper shoeing, anti-inflammatory drugs (eg phenylbutazone) and a drug called isoxsuprine which increases circulation to the bone has been successful to varying degrees. Neurectomy (cutting and removing a segment) of the branches of the posterior digital nerve that serve the navicular area has been used as a last resort quite successfully – but there are dangers with this surgery for the horse. Note, the new Animal Welfare Bill in NZ deems it illegal to use a neurectomised horse for competition. Talk to your vet if you suspect your horse has this problem.