Navicular
Disease: To be Feared or Treated?
by Julie Cary, DVM, MS
Diplomate, American College of Veterinary Surgeons
Associate, Cave Creek Equine Surgical Center
Navicular disease is a term that induces
horror and panic in many horse owners. Fortunately, with advancing
technology, the condition is not one that should be feared as much.
Most veterinarians now refer to the condition as palmar or heel
pain. This more accurately reflects the nature of the condition.
How is Navicular disease diagnosed?
Heel pain is defined as a lameness
originating in the back half of the horse’s foot which blocks to a
palmar digital nerve block. This is the area where the navicular
bone resides, as well as several other soft tissue structures. There
are certain types of hoof conformation or shoeing imbalances that
can predispose an individual to developing pain in the back of the
foot. The first line of diagnostics include taking radiographs of
the foot. The classic navicular disease will have bone changes that
can be seen on radiographs, such as bone spurs, holes in the marrow
cavity, roughening of the flexor surface of the navicular bone, or
thickening of the marrow cavity.
Unfortunately, radiographs do not reveal what is going on with the
soft tissue structures. We now know that many times, the soft tissue
injury precipitates the changes to the navicular bone. If we can see
the soft tissue damage and manage it appropriately, we can better
manage the horse and its lameness. Ultrasound can be used to image
many of the structures within the foot including the deep digital
flexor tendon, navicular bursa, and the small supporting structures
of the navicular bone. The problem is that ultrasound of the foot
can only be performed through a couple of windows (the frog and
through the back of the heel bulbs) and requires considerable
practice on the part of the veterinarian to diagnose the condition.
Recently, MRI has been used to document more conclusively the
problems in the foot. Washington State University has been studying
horses with palmar heel pain for the past seven years using MRI.
Several practices have recently added MRI to their diagnostic
capabilities. We have learned a wealth of knowledge from this
modality. Interestingly, the majority of cases seen at one
institution, which have been worked up by several veterinarians
prior to referral, have turned out to be damage to the deep digital
flexor tendon as it curves around the navicular bone and inserts on
the coffin bone. These cases need to be rested and rehabilitated
much the same was as a bowed tendon.
How is Navicular disease treated?
Treatment of heel pain includes corrective
shoeing to ensure the foot is balanced and to minimize the stress on
the soft tissue structures. Other treatments include pain modulation
and anti-inflammatory medication, which is usually in the form of
phenylbutazone. Isoxsuprine is a medication that is often used in
cases of heel pain. The purpose of the medication is to help improve
blood flow to the area. Also, treating the coffin joint or navicular
bursa with hyaluronic acid with or without a cartilage friendly
steroid can help with certain types of pathologic changes.
Some people advocate the use of “nerving” these horses. Nerving
entails removing a chunk of nerve from the palmar digital nerve so
that the horse can not feel the back 1/2 of the foot. This does not
stop the disease process, and can contribute to its worsening in
some circumstances. The nerve will eventually grow back in one to
five years. It is the author’s opinion that nerving should only be
performed on horses that do not respond to any other treatments and
who have a finite career time required.
End stage navicular disease is a complex of problems associated with
both the soft tissue and bone in the heel region of the foot. The
most common is that the deep digital flexor tendon becomes stuck to
the navicular bone which then interferes with the pulley function of
the DDFT. Every time the horse steps it pulls on those soft tissue
attachments. This is why many of the horses with this condition take
extremely short steps with their front feet.
What is the prognosis for Navicular disease?
The key to palmar foot pain is early and
accurate diagnosis. Lameness that has been noticed for a short
period of time is much more likely to be resolved than lameness
present for a long time. Getting an accurate diagnosis of the
offending structure or structures helps more effectively treat the
problem. Veterinarians with a special interest and understanding of
feet are extremely helpful in diagnosing and treating these types of
cases.
