Hind limb interference is a gait abnormality
that occurs when the medial (inside) portion of a hind foot
strikes the opposite hind limb anywhere from the coronet to
just below the hock. The inside of the pastern or fetlock is
the area most often struck by the offending foot. Causes for
hind limb interference can be divided into temporary or
permanent. Temporary causes would include age and stage of
training, degree of fitness, fatigue and inappropriate
trimming and/or shoeing. Permanent causes of hind limb
interference are linked to faulty conformation. Horses with
base narrow conformation that turn out are usually candidates
for this type of abnormal gait. This type of conformation will
cause the arc of flight of the hind foot to deviate inwards
toward the opposite limb instead of moving straight ahead.
Winging inward may cause the foot to travel close enough to
the opposite limb to interfere. Interference generally occurs
at the trot. Horses with cow-hocked conformation will also
move in such a way that the flight of the foot moves inward
toward the opposing limb but because of the distance between
the hind limbs, these horses seldom interfere. The base narrow
horse will stand with its hind feet together. If you stand
behind the horse you can note the severity of the inward
flight pattern of the limb. Often when the hind foot contacts
the ground, the hock will move outwards which denotes
instability of the hind limbs with a further tendency to
interference. Most base narrow horses, and for that matter,
horses with cow-hocked conformation will have a narrow
rolled-under heel on the outside of both hind feet. As the
hind limbs bear weight, the foot rolls off on the outside heel
which allows the inside of the foot to move closer to the
opposite limb often compounding the problem.
Temporary causes of interference are often treated with
patience. As the horse matures, advances in its training
level, builds up the musculature in the hind limbs and attains
a higher degree of fitness, the intermittent signs of
interference will disappear. Often the horse is shod behind
with shoes that are too small. This reduces overall ground
surface and hind limb support causing instability which in
turn can lead to the horse occasionally striking the opposite
limb. This can be corrected simply by using a shoe that is the
appropriate size. Protective boots can be placed on the
fetlocks until any cause of temporary interference is
resolved.
Interference caused by abnormal conformation is corrected
through proper farriery. Your farrier should observe the horse
at a walk and trot to determine the flight pattern of the limb
and the severity of the interference. If you can’t see the
interference, carpenter’s chalk can be placed on the inside of
the hoof walls to determine where the interference is
occurring and if one or both feet are involved. When trimming
the base narrow horse, the medial (inside) hoof wall should be
lowered. This will normally provide more clearance when the
horse moves. A square toe shoe (angled toward the outside of
the toe) is useful as it helps to straighten the path of
flight. The shoe should be long enough to extend behind the
heels of the foot. A trailer on the outside with the shoe fit
full is beneficial if the outside heel is narrow and rolled
under. This is generally all that is needed to remedy the
interference.
If the horse has a cow-hocked conformation, whether or not it
interferes, it should be trimmed in such a manner that the
lateral (outside) hoof wall is trimmed lower. This will change
the position of the foot, allowing the toes to be more in line
with a straight flight path. Again a square toe shoe will help
the foot breakover straighter and a lateral trailer should be
used. The trailer will contact the ground first and rotate the
position of the foot straighter when landing.
In summary, to rectify hind limb interference, your farrier is
attempting to change the flight pattern of the limb, correct
any instability present and provide adequate support.
Any discussion of gait abnormalities of the hind limbs would
not be complete without discussing forging. Forging is noted
at a trot (sometimes at a walk) and happens when the toe of
the hind foot strikes the heel or bottom of the front foot on
the same side just as the front foot is starting to leave the
ground. When the toe of the hind shoe strikes the heel of the
front shoe, a constant metallic sound is heard as the horse
trots. What happens is the front foot is too slow in leaving
the ground to avoid the forward advancing hind foot.
Overreaching is a more severe form of forging where the
advancing hind limb approaches the fore limb even faster and
the toe of the hind foot lands on the heel bulb of the front
foot on the same side before the foot leaves the ground. This
will result in the shoe being pulled and the heel bulb being
lacerated (known as a heel grab).
Forging can again be caused by age, fatigue, improper riding,
degree of fitness and faulty conformation. Faults in
conformation that lead to forging are seen in a young horse
that is experiencing a surge in growth, short backed horses
with long legs, front or hind feet that are set too far under
the body, long hind limbs, and “sickle” hock conformation.
Another area that is often overlooked is forelimb lameness.
Any horse with forelimb discomfort that causes a short
“stilted” gait or lack of extension can develop forging. If an
abnormal gait is noted in the forelimb accompanied by forging,
local anesthesia can be used to block the front feet, and if
the gait improves and the forging disappears, a thorough
lameness examination should be initiated.
The treatment of forging can be thought of as a function of
timing. The intent of treatment is to speed up the breakover
of the forefeet and slow down the advancing hind feet. Again,
the horse is observed by the farrier at a walk and trot to
determine the extent of the gait abnormality. To speed up
breakover in the front limbs, any excessive toe length is
trimmed accordingly. Then a square, rolled or rocker toe shoe
is used to enhance breakover. Some feel a lighter shoe such as
aluminum is beneficial in the front feet. It’s imperative that
the appropriate size shoe is used to provide the proper ground
surface and support. Often a shoe that is too small is
mistakenly used with the thought that the horse will not pull
the shoe but in fact it compounds the problem The hind feet
are trimmed in a manner that the heels are moved back to the
widest part of the frog to create as much ground surface as
possible. A square toe shoe is used and the toe of the shoe is
set back ¼ to 3/8 inch from the outline of the hoof wall at
the toe. The heels of the hind shoes are fitted well beyond
the buttress of the foot. This type of the shoe coupled with
the trimming will tend to keep the foot on the ground longer,
i.e., decrease breakover of the hind limb.
Hind limb abnormalities often require trial and error to
correct. If a horse continues to forge despite various shoeing
modifications, then it may be necessary to determine whether
the horse is suitable for the athletic endeavor being pursued.
The one necessary requirement to eliminate forging, is a good
working relationship with a knowledgeable, competent farrier.
Dr. Steve O’Grady is a veterinarian and farrier who runs
Northern Virginia Equine in The Plains, VA. Derek Poupard a
farrier also located in The Plains, VA contributed to this
article.
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