How much do you know about Navicular disease?
Navicular disease, or navicular syndrome, is an umbrella term for a collection of fairly common conditions causing inflammation or degeneration of the navicular bone and surrounding structures in a horse's foot. It causes chronic, progressive lameness and generally affects the horse's front feet.
A small, flat, canoe-shaped bone that lies across the back of the coffin joint and beneath the small pastern bone, the navicular bone attaches via ligaments to both the pedal bone and pastern joint. The deep digital flexor (DDF) tendon, which flexes the coffin joint, crosses the lower portion of the navicular bone and functions like a pulley.
There is cartilage between the navicular bone and the coffin joint, and between the navicular bone and the DDF tendon. Between the DDF tendon and the navicular bone also lies a small, fluid-filled sac called the navicular bursa. It cushions the tendon and the bone as the former moves over the latter.
Exactly what causes navicular disease is unknown; consequently, there is no guaranteed measure of prevention. Evidence of the disease is present in the fossil record of early horses, as well as in populations of wild horses, so it is not strictly a disease of domesticated horses.
What is known is that damage to the navicular bone, such as that caused by repeated compression, can erode the cartilage that protects it, making that cartilage less effective as a shock absorber. In some cases, the cartilage can erode enough to expose the bone underneath it, making the navicular bursa and DDF tendon vulnerable to the negative consequences of friction between the navicular bone and the DDF tendon (a condition called navicular bursitis).
There are many manifestations of navicular disease; in general, any damage to, or degeneration of the navicular bone itself, the DDF tendon, the navicular bursa, or any of the navicular ligaments can present as low-grade, recurrent pain and lameness, and fall under the term "navicular disease."
Jumping, regular exercise on hard ground, work on steep hills, galloping, and circle work all place more stress on the DDF tendons, as well as the pastern and coffin joints, and put the horse at risk for developing navicular disease.
Furthermore, a horse needs to be in motion to maintain healthy blood flow to the hoof. When a horse is moving, the navicular bones are stressed intermittently, so horses that spend a great deal of time standing, such as those kept in stalls with little or no turnout, are potentially at greater risk of suffering insufficient blood flow to the hooves and overstressing the navicular bones.
A horse's conformation can also contribute to the likelihood that the horse will develop navicular syndrome. A downhill build, upright pasterns, small, narrow, and/or upright feet, and long toes with low heels are potential conformational shortfalls that can increase the likelihood of the disease.
Symptoms of navicular present as mild, recurring lameness that comes and goes when the horse is exercised in a manner that increases stress on the affected region, such as exercise on hard surfaces or in a small circle. The lameness can be bilateral, though in some cases, one foot is more affected than the other. In such instances, horses often stand with the painful foot slightly in front of the other. Heel pain, or the appearance thereof, is another potential indicator of navicular disease; affected horses sometimes avoid placing weight on their heels by setting their toes down first.
Navicular disease can be treated, but not cured, and it is progressive. Horses diagnosed with navicular disease will generally need an adjustment - reduction - in their workload, and many, especially performance horses, will not be able to continue performing at previous levels.
In addition to recommending corrective shoeing, the treating veterinarian may take x-rays, administer short and/or long-term pain medication, and inject the affected region with corticosteroids and other medications depending upon the severity of the disease.