The long toe, low heel conformation places constant stress on the navicular bone, even as the horse is standing. Upright feet increase concussion, especially in the heel region of the hoof where the navicular bone is located. Excess concussion cannot be absorbed as well by the structures designed to do so (the frog, heels, and digital cushion), so more impact is transmitted to the structures within the foot. Poor hoof shape is usually inherited, although poor shoeing and trimming can contribute to these shapes. With the long toe, low heel conformation can come contracted heels (narrowing of the heel) which further compresses the navicular bone along with sheared heels adding more stress to the tendons and navicular bones. Shoeing
Poor trimming, shoe selection, or inappropriate shoe attachment are well-known causes of lameness, and navicular disease is fairly common in the modern-day domesticated horse. However, it is also seen in wild horse populations. Those who advocate "barefoot trimming" of domestic horses propose that in nature, a horses hoof is designed to expand and contract as the horse moves. This expanding and contracting acts as an auxiliary blood pump, and aids the circulation of blood to the lower extremities. When an inflexible metal shoe is improperly attached to the hoof, the hoof can no longer work as designed, and blood flow is inhibited. However, evidence of navicular degeneration has been established in the fossil record of early horses.
This may be due to strain and inflammation of the ligaments supporting the navicular bone, reduced blood flow and increased pressure within the hoof, damage to the navicular bursa or DDF tendon, or from cartilage erosion. Affected horses display a "tiptoe" gait - trying to walk on the toes due to heel pain. They may stumble frequently. The lameness may switch from one leg to another, and may not be consistent. Lameness usually occurs in both front feet, although one foot may be more sore than the other. Lameness is usually mild (1–2 on a scale of 5). It can be made worse when the horse is worked on a hard surface or on a circle. After several months of pain, the feet may begin to change shape, especially the foot that has been experiencing the most pain, which tends to become more upright and narrow. Treatment and prognosis
No single treatment works for all cases, probably because there is no single cause for all cases. The degenerative changes are usually quite advanced by the time the horse is consistently lame, and these changes are believed to be non-reversible. At this time, it is best to manage the condition and focus on alleviating pain and slowing the degeneration. Trimming
Putting the foot into proper neurological and biomechanical balance is crucial. Often navicular horses have long toes and underrun heels with very little inner wall depth or strength. Exposing the horse to proper stimulus to improve hoof form and structure is also vital.