The Navicular bone, from its position in the center of the foot, and the important protection it receives from the surrounding surfaces, is seldom visited by disease or injured in an accident.  It is protected at either end by the wall and wings and cartilages of the coffin bone, and on its upper face by the lower pastern bone.  Underneath, where there is the greatest risk of injury, it is protected by the flexor perforans, the plantar cushion, and the frog. 

In this disease the flexor perforans becomes ulcerated where it slides over the under face of the Navicular bone (at times involving the sesamoid sheath in the process).  The severe pain experienced by the horse is from its play over the rough, diseased portion of that bone.  This disease is sometimes inherited, but once contracted it is incurable.  However, a great deal may be done to ease the pain in the animal.  I believe that two thirds of Navicular disease is caused by improperly dressing the hoof, cutting the frog away, weakening the bars, and thinning the soles.  This is then exacerbated by riding over uneven surfaces, which provokes inflammation of the tissues and membranes of the foot.  The effects of Navicular disease is the shrinkage of the outer wall upon the living parts of the foot, immediately below the coronary band, crowding the cartilages in and stopping the circulation.  The foot becomes dry, hard, and feverish.  The wall becomes thick and deep.  The white line across the heel shows where the foot should be reduced around the base.  When the disease becomes well established, the horse manifests it by continual restlessness, standing on one foot and holding the other backward, with the heel elevated and the toe touching the ground, or by twisting the toe out and resting the heels of one on the coronet of the other; and by constantly shifting and flexing the fetlock and knee.

Not one third of the cases of navicular disease that I have seen are chronic.  Many cases that are wrongly termed navicular disease should be considered only navicular joint lameness, which if allowed to run might become chronic, but are curable if treated in time.
In dressing the foot, proceed as normal, then after properly leveling and balancing the hoof, open up the commissures and pare out the sole within safe limits.  If the frog projects above the heel, pare it flat on the ground tread.  In most instances the bar shoe can be used with satisfactory results.  I often will use a composite shoe in these cases due to their added shock absorption. 

After nailing on the shoe stand the horse in soaking tubs of warm water, two hours per day, for a week to ten days.  Also place warm water bandages around the coronet band.  The shoe should extend as well back from the heel as can be safely worn, and by this method of shoeing, much relief will be afforded the horse.  Reset the shoes every two to three weeks to keep down the surplus growth.