Navicular Disease Explained

Introduction to Navicular Disease
While most refer to this equine problem as navicular disease it is actually better understood as a syndrome instead. A broad explanation of the syndrome would be that it affects the navicular bone and the surrounding tissues. More often than not it is present in the front feet of horses and can lead to both debilitating and disabling lameness.

Where and what is the Navicular Bone?
Having a good understanding of the forearm of a horse will help to make understanding this syndrome easier. For one thing, the navicular bone is also known as the Distal Sesamoid. You will find it at the back of the coffin bone and beneath the pastern bone. It is here where you find the deep digital flexor tendon, or DDF. This tendon lies behind the cannon and tissue and passes under the navicular bone as well. Its main purpose is to flex the joint. The navicular bone's function is that of fulcrum (i.e. A support) over which the tendon passes.

There is no known single cause for navicular syndrome or disease. There is no shortage of opinions and theories surrounding the problem however. Generally speaking, navicular disease can be explained in two main points, namely:

1. Compression Of The Navicular Bone
Along with the compression of the navicular bone, the deep digital flexor tendon is also compressed. This results in degeneration of the cartilage as well. Over time the cartilage becomes flatter and less effective at absorbing shocks. Also, along with this degeneration comes erosion of the cartilage as well.

Degeneration of the cartilage is common in navicular horses. An equine vet will tell you that there is a similarity between the syndrome and osteoarthritis. Because of the similarities treatment is generally very similar as well.

Because the cartilage is reduced and eroded with time, the bone underneath it can become exposed. When there is no more cartilage covering the navicular bursa and the deep digital flexor tendon, damage is sustained, which is caused because of the friction with the navicular bone. As a result swelling of the bursa (called navicular bursitis) is known to occur.

2. Tension On Supporting Ligaments
Some in equine vet circles have discovered through research that the degeneration process starts with excessive tension being placed on the ligaments. Because of the tension strain and swelling result, and this in turn results in a decrease of blood flow both to and from the navicular bone. If strain is consistent and results over a prolonged period of time, the ligament can become thicker and the blood flow will be permanently affected in this way.

You can generally spot a horse with navicular disease/syndrome. Those that are prone to it will experience both severe pain and even lameness. The lameness might be mild and intermittent, or it might be much more severe and debilitating. It is generally believed among researchers that the lameness actually results because of the swelling and the strain on the ligaments that support the navicular bone. Decreased blood supply, plus greater pressure in the hoof, leads to navicular bone damage as well as damage to the deep digital flexor tendon.

You can spot an affected horse by the characteristic tiptoe gait. This is in a bid to ease the pain in the heel. Affected horses are known to stumble quite a lot, with lameness alternating between the legs. More often than not the lameness tends to occur in both front feet, although one might cause more discomfort to the horse than the other.

Navicular horses experience mild lameness that is worsened if they are worked on hard or steep surfaces. As time passes one will notice that the feet actually change shape, with the one that has been the most affected showing the most amount of change.