Lameness is a common problem in many horses. As we previously discussed there are many different causes and types of lamenesses. Navicular Syndrome is one very common disease that can be devastating to a horse’s athletic career.
Navicular Syndrome describes an inflammatory or degenerative process in the heel region, most commonly in the forelimbs. It is important to have a brief understanding of the equine forelimb anatomy to begin to understand the syndrome. The navicular bone lies behind the coffin bone and the short pastern bone inside the hoof wall. The Deep Digital Flexor Tendon (DDFT) runs down the back of the cannon bone, past the navicular bone and attaches to the coffin bone. This tendon enables flexion of the coffin joint by using the navicular bone as hinge. There are many small, but very important, structures contained within the heel region of the foot.
Navicular Syndrome is a chronic, progressive, painful disease that most commonly affects middle aged and older horses. Navicular makes up approximately 1/3 of all forelimb lamenesses diagnosed in equine medicine. The disease usually involves both legs (bilateral), but to varying degrees. Therefore, the owner most often reports lameness in only one leg, which is often intermittent.
Navicular is newly termed a “syndrome” as we recently have understood that the disease can potentially affect much more than just the navicular bone. Navicular Syndrome is due to problems that can involve the navicular bursa, deep digital flexor tendon, coffin joint, and the associated soft tissues, in addition to the navicular bone. The involved structures undergo degenerative changes resulting in inflammation and pain.
This syndrome consists of several clinical signs, including but not limited to pain in the heel region of the hoof and gait abnormalities, which are often noted as being short strided. There is often a history of a low grade, shifting leg lameness. We often are presented with horses that are thought to be painful in the shoulders. The more severely affected leg will often be held in a pointing position in front of the horse in attempt to minimize the weight on the heel area. As the disease progresses, the horse will develop under run and contracted heels and can get sole bruises, from landing on the toes instead of the heels.
The cause of Navicular Syndrome is controversial. One theory is that there is increased pressure between the Deep Digital Flexor Tendon (DDFT), coffin bone, and short pastern bone. The pressure results in inflammation which will cause the degenerative changes seen. Another theory is that there could be change in blood flow to the structures. The blood flow change is speculated to be a result of small clots blocking the blood coming to and from the navicular bone and its structures. It is also speculated that the cartilage in the associated joints becomes inflamed and causes arthritic problems.
Contributing factors that may predispose a horse to Navicular Syndrome include conformation, athletic requirements, an unbalanced foot, and poor conditioning. Conformation is suspected to be a major contributing factor. Horses with a break in the foot to pastern axis have increased pressure on the DDFT resulting in increased pressure on the navicular bone and coffin bone. The short heeled, long toed horses will have more strain on the DDFT and will increase concussion on the foot. Horses with small feet have less foot to take the impact when moving resulting in more pressure in the heel. Horses that are asked to take more impact when performing are at a higher risk. These horses include racing horses, barrel racers, team and calf ropers and jumpers.
Next article we will discuss the diagnosis, treatment, and prognosis of Navicular Syndrome. If you have any questions regarding the above information or any questions/concerns in general, please contact Twin Valley VHS at 745-6642.
Dr. Justin Noble DVM
Twin Valley Veterinary Health Services