Cause:
Navicular disease occurs almost exclusively on the front legs, because two thirds of the weight of the horse (and riders) rests on the front legs. Because of this the navicular area of the front legs gets rather overloaded and damage arises. With enough rest the damage can disappear. But such damage leaves behind a scar and in a complex structure like the navicular of the horse, where everything has to be supple and elastic, this scar can encourage irritation on the long run and so also new damages. And so more and more scar tissue arises and the navicular becomes less supple.
There are many theories concerning the arising of navicular disease.
Overload in combination with a sensitivity that is hereditary is mostly seen as a possible cause. Especially the in Western Europe breed and populair Warmblood seems to be sensitive for this condition. The disease is usually established at a pretty young age from 5 to 7 years. Horses of that age het loaded more heavily which can lead to the complaints.
Symptoms:
Horses with navicular disease mostly have a changing, recurring, light lameness with regularly an increased tendency to stumble. In these horses we often see, after a while, that the most affected hoof becomes steeper, because the horse is going to relieve the backside (the navicular area) and because of this it won't wear as fast.
Diagnosis and treatement:
In the lameness examination usually stands out that the lameness gets much worse if the horse has to trot on a small place with a hard ground with the painful leg as the inside leg. Because of this there is more weight on the inside leg and so on the affected navicular.
If this is the casen we anaesthatize the nerve of the navicular with a local injection to be sure that the cause of the lameness is here. If there is an obvious improvement of the lameness after the anaesthesia or the animal becomes irregular to the front leg, then the next step is to establish how bad the navicular is affected. Usually this is done by making two x-rays per leg where the hoof joint and radius bone can be judged Then it is desirable in some cases to examen the deep flexor tendon and bursa with an ultrasound. This requires some preparation of the hoof by making it thinner in shape and weaking the radius so that the sound rays of the scan can penetrate more easy. For this is a day in the hospital desirable.
Depending on the degree of damage within the navicular area, the purpose of the horse and the position of the foot, a treatement plan can be made and a prognosis for the continuance of the disease can be given.
Especially horses with flat feet and underrun heels react usually very good on putting the hoof "steeper" and a "round" eggbar with maybe an insole and a "hoof pad" ( = a bouncy cushion). Because of this the navicular area will be relieved.
Besides that there are plenty anti-inflammatories and "lubricating" product that can be injected (local) and/or be given over the food. Mostly these products are expensive and they only have an effect during the period that you use it. However sometimes such a treatement can give just that bit of extra that the horse needs to walk normal again.
If the foot has already grown steeper and/or the damage has worsened, then can surgery be a last solution. This can only be done if during the lameness examination has been established that the horse isn't lame anymore after anaesthatizing the nerve of the navicular; During the surgery that same nerve will be cut at the same height, which will only make sense if that is where the pain is. After this surgery the horse will stay numb forever at the back half of the hoof, which makes a daily control, by the owner, for conditions and damages necessary. Horses that have had this surgery can never participate in a sport anymore. In a few cases the damages can expand slowly again after the surgery, so that the horse will walk lame again eventually.
At the end preventing that the navicular gets overloaded is the best. Trimming at the right time (also during breeding) and not letting the foot grow unnecessary flat with underrun heels can contribute to that. Training on a solid ground where a part of the weight is being shifted to the hindquarters and not letting the horse jump high obstacle at a too young age are things where you must pay attention to.
» Scientific info » Navicular
