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Navicular Syndrome:

Shoeing Methods

Tom Stovall, AFA Journeyman Farrier

Usual disclaimers. See your veterinarian for diagnosis and treatment of
any pathology. This post is to be considered information only and is not
specific to any individual or type.

                 
Navicular Syndrome: lameness in the rear third of a front foot which
will block out with a posterior digital nerve block, usually both fronts
involved, although sometimes not evident until one is blocked.

All methods of shoeing for NS are palliative in nature. A farrier can't
cure or correct anything, he can only relieve the symptoms to some
degree. One hears the term "corrective shoeing" used in the treatment of
NS horses however, "corrective" is a misnomer: no method of shoeing will
correct the condition.

Shoeing for NS must meet several criteria if it is to be successful: it
must decrease pressure on the navicular bone from the deep flexor
tendon, it must enhance breakover, and it must protect the rear third of
the foot from environmental pressure.

The primary method of shoeing the NS horse is to stand them up and
turn them over. This means that the farrier will do whatever he can to
increase the angulation. Increased angulation can be accomplished by
several methods: cutting the toe, raising the heels, and setting the
shoe under. Since the farrier is unable to grow hoof, raising the heels
is accomplished through the usage of wedge pad(s) and various types of
non-traction calks; e.g., roll calks, wedge calks, etc.

Why increased angulation? Because this relieves the pressure exerted
upon the navicular bone by the deep flexor tendon which uses the
navicular bone as a fulcrum before it inserts into P3 (os pedis).

Increased angulation relieves pressure from the DFT, but how is turnover
enhanced? Several methods. First, through choice of configuration of
shoe materials; i.e., the use of half-rounds, aluminum (which becomes a
de-facto half-round with wear) and hot-rasping the ground surface of the
toe of a conventional shoe. Secondly, and most important from the
standpoint of enhanced turnover, the shoe must be set under so that an
imaginary line from the front of the fetlock, bisecting the toe, to the
ground, is as short as possible.

                    /                          /
                  /                          /
                /                          /
              /              |           /               |
            /________________|          |________________|
          =====================          ==================
                  normal                     set under

By setting the shoe under, turnover is enhanced, and pressure on the DFT
is reduced as a direct result. The obvious limiting factor to setting
the shoe under is the white line; however, the shoe can be set under to
the posterior edge of the white line if necessary. Note that the toe is
"chopped off" rather than "feathered" to the coronary band in an effort
to make the foot look "pretty". Excessive rasping, aka, "feathering the
toe", destroys the structural integrity of the hoof.

The easiest method of protecting the rear third of the foot is the use
of a bar shoe. Underslung, low-heeled horses respond best to
conventional (track-style) egg bars, probably because the increased
support relieves pressure exerted by the DFT. Upright horses respond
better to the more circular style of egg bars or straight bars. All
styles may be configured with a "frog cradle" which protects the frog
from environmental pressure; however, it's more efficient to use a wedge
pad or bar wedge pad to accomplish the same result.

We've all heard the old wive's tale: "A horse can't run in bar shoes".
Horsefeathers! A horse that *needs* bar shoes, can't run without them.

The aforementioned methods of farriery may be used individually or in
combination. A horse with minor symptoms might be shod with half-rounds
slightly set under; a horse with serious problems, with aluminum egg
bars set under as much as possible and three degree bar wedge pads.

Navicular problems range in severity from a slight bruise to the
navicular bursa to a fractured navicular bone. They are all treated in
much the same manner: palliative farriery in conjunction with the
veterinary prescription of vasodilators when applicable. Due to
farrier/veterinary cooperation resulting in increased knowledge
relative to the diagnosis and treatment of this syndrome, horses which
would have been euthanized 20 years ago are now dying of old age after
leading full, active lives.

Sometimes, all methods of palliation fail and a poster digital
neurectomy becomes the only viable alternative to euthanasia. One of
the methods of accomplishing a posterior digital neurectomy is the
application of extreme cold to the nerve tissue, hence the term:
"freezing". The usual method is to sever the medial and lateral
posterior digital nerves. The lay term for this procedure is "nerved".

The need for a neurectomy is considered to be established when all other
means of shoeing and/or pain relief are exhausted.


 * SLMR 2.1a * "For want of a nail, the shoe was lost..."

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