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Navicular Disease
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Introduction
Navicular disease is one of the most common cause of front limb lameness. It is easy to diagnose, but frustrating to treat. The owner often thinks the horse has a sore shoulder, because it will shorten the length of its stride and move with a choppy gait.
The navicular (distal sesamoid) bone sits behind the coffin (distal phalanx) bone and is the smaller of the two bones in the horses' foot and is held in place by tendons and ligaments.
The navicular bone has two functions:
• To protect the joint and tendons from pressure and concussion (the navicular bone acts as a pulley on the deep digital flexor tendon, which takes some of the stress off the coffin bone).
• To act as a valve for blood flow to the coffin bone and corium inside the hoof.
If the hooves are not properly cared for, the navicular bone becomes immobile, resulting in poor blood flow within the hoof. Specific problems that are likely to result in immobilization of the navicular bone include high heels, overlaid bar, long toes and improper shoeing. Navicular syndrome, also known as Caudal Heel Syndrome, is a degenerative process that can affect the bone, bursa or tendon. Navicular disease occurs almost exclusively in the front feet and usually affects both fee.
Skeleton of a horse. C= Navicular Bone
Causes
There are many possible causes for navicular syndrome. One is thought to be increased pressure inside the bone causing pain. There is also a chronic form of the disease thought to be caused by adhesion (scar tissue) between the navicular bursa and the deep digital flexor tendon. Another cause of chronic navicular disease is arthritis of the navicular bone and associated structures.
Increased pressure inside the bone is thought to cause the horse pain. Concussion may also aggravate the problem. If the horse has to work on a rough or hard surface, the constant pounding of the hoof increases the pain. Other factors such as conformation, foot size, improper trimming of the hoof and obesity can all lend to navicular disease.
Navicular disease usually affects fast-growing, large horses, such as Thoroughbreds, Quarter horses, warmbloods and some Standardbreds. Ponies, Arabians and draft breeds are usually not affected.
Signs
Navicular syndrome causes a gradual and progressive increase in lameness of the front legs. Due to the gradual nature of onset, navicular problems are difficult to detect until the condition is advanced.
While walking, the horse with navicular syndrome tends to place its weight on the toe to avoid placing pressure on the heel area, which contains the inflamed navicular bone and bursa. Since the horse will not place weight on the heel, it takes longer to stop the stride. While standing, a horse with navicular syndrome tends to shift its weight continuously to relieve pressure and pain within the heel. A horse with navicular syndrome is often lame after work; however, the lameness may disappear with rest. Due to comparably poor circulation in the feet of many horses with this condition, the heels and adjacent hooves may become smaller and contract.
Typically most victims are between two and 10 years old. Sometimes the problem is the horse is too big for the size of its foot. It is not always "big horse, small foot" though, nor is it really use-specific, but affected horses are usually athletic. Horses used to race, rope, compete in dressage, or barrel race are normally those which show the signs of intermittent front leg lameness associated with navicular disease.
Some of the methods veterinarians use to diagnose navicular disease are hoof testers, to detect pain in the heel area, radiographs to look for changes in the bone or bursa of the navicular bone, nuclear scintigraphy to detect bone and/or soft tissue inflammation, and heel nerve blocks. A lame horse that exhibits soundness after a heel nerve block may have navicular disease.
Once the veterinarian has diagnosed navicular disease, there are a few treatment options. Corrective shoeing with an "egg-bar" shoe is one. This type of shoe gives extra support to the heel. These shoes are usually made out of aluminum because it is a lighter material than regular steel bar stock. The owner should allow four to six weeks to determine if the change of shoes will be a viable treatment. If the bone has already started to change because of the
disease, corrective shoeing may not help. Medications to increase the blood supply may also be given.
Navicular disease may also cause secondary lameness. The coffin joint may swell and become sore as a result of the problem with the navicular bone. Analgesic or other drugs for pain may be given, but caution should be used. Some of these drugs may cause ulcers and renal disease.
As a last resort, the nerve supplying the back of the heel may need to be surgically cut. If done correctly this is a safe procedure because the nerve to the toe is left intact. Therefore the horse is aware of its foot placement.
Reducing the risk of navicular syndrome
Good foot care is very important to help prevent and treat this disease. The feet must be kept clean and properly trimmed and shod. Keeping the horse in good physical shape is also important.
• Obesity only aggravates navicular disease. Excess weight puts pressure on the weight-bearing joints. If overweight is contributing towards your horse’s pain, your veterinarian will recommend a suitable diet.
• Exercise is an important component of healthy living. Exercise helps reduce pain, prevents further joint damage and can help your horse maintain a healthy weight. Disuse of a sore joint will cause the muscles around it to weaken, resulting in pain. A little exercise taken frequently is recommended.
• Some horses, particularly working animals, do not get adequate rest for optimum healing. Your veterinarian will be able to advise you on how much rest your horse requires during the healing period. • Improper shoeing can cause many joint and muscle problems and is a significant factor in the progression of navicular disease. An experienced farrier can help assess whether your horse’s shoeing is contributing towards the condition. Your veterinarian may be able to suggest a farrier who is capable and well respected.
In some breeds, navicular disease may have an hereditary or genetic component. To help reduce the incidence, it may be wise to not breed horses confirmed as having the condition.
