Navicular syndrome
It most commonly describes an inflammation or degeneration of the navicular bone and its surrounding tissues, usually on the front feet.
This finding, and the associated biochemical changes, have led some researchers to conclude that there are elements in navicular disease common to osteoarthritis, and to suggest similar therapeutic regimes.
Constant compression can also increase the bone density directly under the cartilage surfaces, especially on the flexor side.
Some experts believe that the degenerative process begins with excess tension placed on these ligaments, causing strain and inflammation.
If the ligament continues to be strained, it can thicken and permanently reduce blood flow to the navicular bone.
The navicular bone, in response to both the increased pressure and overall decreased blood supply, would absorb mineral from its center.
Recent research has found correlations between "toe-first landing" of the hooves and navicular problems, due to excessive strain put on the deep digital flexor tendon, as a consequence of misalignment of the lower joints.
[citation needed] Toe-first landing, usually seen as a consequence of navicular disease, may actually be a cause or at least a contributing factor to the onset of tendon inflammation and bone modifications.
Toe-first landing is often caused by frog and heel overtrimming, long toes, and/or poor shoeing.
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.
[8] Mary Thompson, a vertebrate paleontologist at Idaho Museum of Natural History, has found evidence in many species of early horses and concludes, "The results of this study strongly suggest that man’s intervention (whether by increased usage or improper breeding practices) may not be the sole cause of the syndrome", although she cautions that her results are preliminary.
[9][10] Working on steep hills, galloping, and jumping all contribute to navicular syndrome, as they place greater stress on the DDF tendons, and may cause overextension of the pastern and coffin joints.
This might explain why the syndrome is seen more frequently in Thoroughbreds, American Quarter Horses, and Warmbloods as opposed to ponies and Arabians.
Affected horses display a "tiptoe" gait – trying to walk on the toes due to heel pain.
[12] People on both sides agree that proper hoof shape and angle are an important long-term management plan for a horse with navicular disease.
[16] Advocates of barefoot trimming cite recent studies which show that removing the shoes can help alleviate the symptoms of navicular disease, and in some cases, reverse some of the damage done to the hoof.
[17] It is not uncommon to find horses whose navicular disease is completely manageable through corrective barefoot trimming.
[12] However, this may require a transition period lasting from weeks to years where the horse may remain lame,[6] or may never become sound.
Anti-inflammatory drugs are used to treat the pain, and can help the lameness resolve sometimes if shoeing and training changes are made.
The use of intramuscular glycosaminoglycans has been shown to decrease pain in horses with navicular disease, but this effect wanes after discontinuation of therapy.
[25] Gallium nitrate (GaN) has been hypothesized as a possible treatment for navicular disease, but its benefits have not been confirmed by formal clinical studies.
In this procedure, the palmar digital nerves are severed, so the horse loses sensation in the back of the foot.
After the neurectomy, if the horse becomes injured in the area the injury may go undetected for a long period of time, which risks the animal's health.
In fact, though the time periods vary based on the individual horse and surgical method utilized, these nerves often regenerate and return sensation to the afflicted region within two to three years.
