Navicular disease

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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.



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