Pastern Angles

[Linda_Merims@ne.3com.com]

Karen Psychninja@aol.com said:
> The mare I'm looking at is 12, registered arab, and
> extremely calm.  I've got a youngster right now, and
> have been looking for a nice quiet horse for not so
> experienced friends to ride along.  The most this mare
> would ever do is probably a 25 at a ctr pace.  I had
> the vet out for a prepurchase exam, and he suggested
> I have a farrier look at her before I made any decisions.
> The problem he saw was a possible club foot.  Now I've had
> several different opinions as to what that means.  Is it
> more concerning the pastern angle (hers are 60 degrees
> bilaterally) or the slope of the hoof wall?  (one foot
> is smaller than the other, and the angle is considerably
> more vertical on that foot).  Her filly has the same kind
> of conformation.  How big a problem is this really?

Congradulations.  I can tell you have encountered your
first club foot:  everybody is telling you something
different.

A "club foot" means that, for reasons that are only now
becoming understood, the deep flexor tendon that attaches
to the back of the coffin bone and ends in a major muscle
in the forearm is pulling back on the coffin bone.  This
causes the coffin bone to rotate downward so that its
bottom is no longer parallel (or approximately parallel)
to the ground.

This has several side effects:

 - the front of the hoof takes on a dished appearance

 - the blood supply to the front of the coronary band
   is restricted causing the heels of the hoof to grow
   faster than the front

The result is a dished hoof with an upright, boxy appearance.
The effect on the pastern angle is secondary; the hoof no
longer blends smoothly into the pastern at the same angle, but
makes a fairly abrupt angle downward.

Current thinking (and thinking on club foot changes every
decade, which makes it challenging for both vets and farriers
to keep up) is that there are two general types, and
two general causes of club foot.  (I'm leaving out
congenital contracture.)

Genetic

This kind of club foot very decidedly runs in families.
It emerges slowly over the foal's first year, with the
foot just slowly going wrong.  The owners begin to
notice it at about 6 months, and vets tend to get called
in at about 8 months to a year.  It is probably present
much earlier.  Unilateral. Since you say that this mare's
foal has the same club foot, my guess would be that she has
the genetic form.

Contracted Tendon

This phenomenon tends to happen quite suddenly.  The
foal experiences some kind of pain.  Often this is due
to osteochondrosis in the joints due to the unfortunate
combination of high carbohydrate diet (lots of grain)
fed to induce rapid growth, aggravated in some breeds
(like Morgans) by a natural thriftiness that can't
tolerate the rich diet, and a probable genetic tendancy
to react by contracting.  The foal takes the weight off
the foot to ease the pain.  For some reason, the muscle in
the forearm contracts and the owner comes out one
morning to discover that, literally overnight, the foal
is standing up on the tip of its toes, or even buckled over
onto the front of its hoofs.  Can happen at any time in
the foals' first year, but tends to happen before 6
months.  Can be unilateral or bilateral.  Unlike the
genetic form, at this stage there is nothing wrong with
the shape of the foot, it is pulled back.
Treatment of contracted tendon is twofold:

  - Ease and remove the source of the horse's pain.  Since
    the contracture can be due to joint disease, treat
    the joint disease.  There is some research that
    shows that treatment with antibiotics is helpful.

  - Desmotony of the inferior check ligament.  This is
    surgery under anesthesia to sever the check ligament
    that connects the deep flexor tendon to the cannon
    bone about 1/3 of the way down from the knee to the
    fetlock.  Varies in effectiveness; usually provides
    about 1/4 inch of "release."  Followed by shoeing
    with extended toe shoes to coax the foot back to
    normal angle.

Some acquired contractures heal completely and you'd never
know anything had happened to the foal.  Many horses show
some residual sign of their contracture as foals.  The foot
never does get back to completely proper alignment and as the
horse matures it settles in as a club foot virtually
indistinguishable from a genetic club foot.  The foot is
always slightly dished, the angle is always more upright,
and the heel always grows a bit faster.

Treatment of genetic club foot involves trimming the
heel frequently so that it doesn't grow completely
out of whack with the other foot, and possibly desmotony
of the inferior check ligament.  The surgery tends to be much
less effective in the case of genetic club foot, probably
because the horse has had it so much longer and the
surgery is usually done later when the horse is nearing or
past a year in age.  (In a study of contracted Standardbred
foals, no foal who had its check ligaments cut after 6
months started a race.)

The last thing you want to do with a club foot is what
farriers were doing left and right in the 1980's:  try
to "stretch the tendon" by trimming the heels down, even
gradually, to match the "normal" foot.  This tends to
aggravage the secondary effects of a club foot described
later.

But all this is water under the bridge with the mare you
are looking at.  She's mature and has carried her club foot
for years.

The thing to realize is that there are *degrees* of club
footedness.  There's even a Grade I, Grade II, Grade III,
and Grace IV taxonomy to characterize it.  All are based
upon how much the coffin bone is rotated back from where
it should be.

  Grade I's are almost unnoticeable from the outside.
  There's no dish.  The horse travels evenly and
  normally.  It may just be a little more upright and
  the heel grows just a little faster.

  Grade II's have a dish.  The horse may travel slightly
  shorter on that leg and have a tendancy to stub its toe
  and stumble.  You have to keep after the heel or the club
  foot will get way out of alignment with the normal foot.

  Grade III's have a pronounced dish.  The foot is nearing
  vertical.  The horse travels very short and likely
  bobs its head at the trot.

  Grade IV's are when the front of the horse's foot is *past*
  vertical.  Grade IV's are in rough shape.  I've seen only
  one adult horse in my life carrying a Grade IV club foot.

A club foot is susceptible to two kinds of deterioration,
both of which can be serious to the horse's long term soundness.
The only way to tell whether this deterioration has set in
is X-rays.

First, when the coffin bone in a club foot rotates down,
it nonetheless remains attached to the front wall of the
hoof through the laminae.  The worse the club foot and
the greater the concussion it suffers through the horse's
working life, the laminae start to tear and the coffin bone
begins to separate from the hoof wall itself in a kind of
mechanical founder.

Second, because the deep flexor tendon is restraining the
coffin bone from fully extending, the toe of a club foot
tends to land first, jabbing the front of the coffin bone.
Again, depending on how bad the club is, how carefully
the horse has been trimmed, and the strain of its working
life, the front rim coffin bone begins an arthritic degeneration
and will "remodel" itself.  Instead of being comparatively
smooth, the coffin bone rim becomes jagged, there are uneven
calcium deposits, and even sometimes a little toe spur of
bone develops.  The horse can be in considerable pain.

So, if the horse you are looking at is a Grade I, travels
even and sound, doesn't trip, and x-rays reveal that no
coffin bone degeneration or separation from the hoof wall
has set in, then she's probably fine.  You'll need a good
farrier!  Getting the angles right (which other people have
described very well) is tricky.  Again, the very LAST thing
you want to do is trim the heel down to match the normal
foot.  Tendons are not very stretchable.  Lowering the heel
puts immense tension on the deep flexor and the result is to
jam the toe harder, and the constant pull of the horse's weight
and motion tears the laminae!  You want a trim that will
cause the horse's foot to land flat.  The "good" foot may
have to be trimmed higher than normal just so that the
horse will go even.  (This is what was done to my 19 year
old Morgan who has a grade 1 to 1 1/2 club foot.  It has
had some interesting long term effects, like sidebone, on
the *good* foot.)

But if it is a Grade II, the horse travels a tad short or
maybe stumbles a bit, and X-rays show that changes have
begun to set in, then I wouldn't count on her to stay sound
making even 25's.

And since you say her daughter has the same club foot, I
would not breed her.

Lastly, several people have mentioned the "grass foot"
theory of club footedness.  I wouldn't claim that always
grazing with, say, the left foot forward and the right
foot back, didn't cause club footedness in some horses.
(Incidentally, for reasons nobody understands, 70% of
club feet are in the right fore.)  However, the problem
with the grass foot theory is that it is the perfect
chicken-and-egg theory.  Does the horse become club footed
because it grazes one-sided?  Or does the horse graze
one-sided because it is contracted and it is most comfortable
for the horse to keep the contracted foot underneath him,
and not extended?  I'd love to see an experiment where foals
who were starting to go wrong were hobbled to force them to
graze on the other foot and see if it corrected anything.

Linda B. Merims
and Merry Daystar (grade 2.5 and buried at 5 because of it)
and Townshend Night Star (grade 1 and going strong at 19)
lbm@ici.net
Linda_Merims@ne.3com.com
Massachusetts, USA




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