Over Christmas, my brother and I discussed the dodgy genes we’ve both inherited – bottle neck shoulders, slabs for hands, and protruding accessory navicular bones. Yep, that’s right. My brother and I are part of 10% the population who have an extra bone on the inside of their foot. Luckily for us, our feet aren’t that lumpy. I wonder what the diagnosis would be if we were horses!
Navicular Syndrome in equines is a different matter altogether. The navicular bone, of which we’re learning more about every day, is a small bone within the hoof capsule, just behind the coffin bone. In college we were told that the bone was similar to that of a ship – navy, naval, navicular. See the memory cue here?
The function of the navicular bone is to provide a smooth surface over which the deep digital flexor tendon can change angle so asto attach to the coffin bone. This is where problems begin to arise.
We learnt at college, and sadly I’m probably out of date in this knowledge now, that navicular syndrome is when a reduction of blood supple to the navicular bone causes the bone to deteriorate; and the surface no longer be smooth and flat, but pitted and full of holes. This means that the tendons can no longer glide over the bone, but rather jerk and judder over, injuring the tendon itself and causing inflammation and pain. Nowadays we know that there are numerous other problems that are associated with the area of the navicular bone, and diagnostic techniques no longer leave us guessing.
Navicular syndrome typically affects both front feet to varying degrees. One foot is usually more painful, so lameness of a single leg is often identified first.
Horses with Navicular Syndrome have shorter strides, and the inside leg on a circle is usually lamer of the two. Due to the pain coming from the heel, the foot is usually placed toe-heel instead of the usual heel-toe landing. As the area of pain is within the hoof capsule there is very little to see or feel, but the degree of lameness will intensify with work.
A vet will nerve block to identify that it is the heel area that is causing the pain, and X-ray to discover the reason behind the pain. This could be enlargements of the vascular channels or synovial fossa within the navicular bone; cyst-like lesions within the navicular bone; calcification of the ligaments associated with the navicular bone; bone disease affecting the coffin joint in the area of the navicular bone; degeneration of the flexor surface of the navicular bone; degeneration of the flexor tendon in the area of its passage over the navicular bone; fractures of the navicular bone, or a combination of factors.
The treatment for Navicular Syndrome is varied, ranging from conservative to aggressive depending on the cause and amount of damage. Of course all horses are individual, so respond to treatment in a different way, regardless to the extent of damage.
Changing the shoes so that they best support the heel is one of the most popular methods of treatment, along with anti inflammatory medication. The first goal of the farrier is to gradually get the foot back into balance; correcting the hoof-pattern axis and supporting contracted heels. Blood flow to the area should also be promoted to improve the overall health of the foot, so shoes shouldn’t be too tight fitting, have wide branches to allow the hoof to expand, and the nails shouldn’t be to close to the heel. Bringing the toe under, using square toed shoes, and bringing the breakover point further back will reduce stress on the limbs. Some people use egg bar shoes, or small wedges to help the hoof action.
A last ditch attempt to keep your horse athletic is to de-nerve their foot, which means they can no longer feel pain, be it navicular or abscess, whatsoever in the foot. An extreme treatment in my opinion.
Overall Navicular Syndrome doesn’t mean the end of their working life, but it is degenerative, so the sooner it is monitored and the horse supported the better to help keep the mobile for as long as possible.