Inflammation from strain of the impar ligament can decrease blood flow to and from the navicular bone, as the major blood vessels supplying the bone run up and down this area. If the ligament continues to be strained, it can thicken and permanently reduce blood flow to the navicular bone. Because veins are more easily compressed than arteries, blood flow to the bone would be less obstructed than blood flow from the bone. This would cause a buildup of pressure within the navicular bone. The navicular bone, in response to both the increased pressure and overall decreased blood supply, would absorb mineral from its center. Excess tension can also cause exostoses where the ligaments attach to the navicular bone, giving the bone a "canoe" shape. If tension is extreme, the ligaments may actually tear. 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. 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. Contributing factors
Conformation
Certain conformational defects may contribute to navicular syndrome, especially defects that promote concussion. These include upright pasterns, small feet, narrow and upright feet, significant downhill build (commonly seen in American Quarter Horses), and long toes with low heels (commonly seen in Thoroughbreds).
This procedure should only be performed if it will eliminate the lameness associated with navicular syndrome, and only after all other options have been explored. The procedure is usually performed on both front feet. Complications can include infection of the wound, continuation of the lameness (if the nerves regrow or if small branches of the nerves are not removed), neuromas, and rupture of the deep digital flexor tendon. 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 animals health. Due to this, the feet should be cleaned and inspected regularly. Neurectomy tends to lower the market value of a horse, and may even make the horse ineligible for competition. Neurectomy is controversial. The most common misconception about "nerving" a horse is that it will permanently solve the lameness/pain issue. 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. In navicular suspensory desmotomy, the ligaments supporting the navicular bone are severed. This makes the navicular bone more mobile, and thus reduces the tension of the other ligaments. It is successful about half of the time. Prognosis
The prognosis for a horse with navicular syndrome is guarded. Many times the horse does not return to its former level of competition. Others are retired.