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Anterior Cruciate Ligament Injuries are
relatively common in dogs. This article
will discuss what the problem is and how we fix it.
The knee joint is a very complex structure. In dogs,
this joint is sometimes called the stifle. The end of
the thigh bone, or femur, rests precariously on the top
tibia, or lower leg bone. The ends of each bone
are covered with a thin layer of cartilage called articular
cartilage. There is a cartilage pad called the
meniscus in between to cushion the bone ends. The
whole thing is held together by ligaments.
Of particular interest is the cranial cruciate ligament.
There are two cruciate ligaments, named cruciate
because they cross each other. They are located
inside the joint in between the femur and the tibia, and
together they keep the femur sitting squarely on top of
the tibia. One of the cruciate ligaments is
located more to the front, and is called the cranial
cruciate ligament, cranial referring to it's forward
position. An annoying bit of anatomical tradition
allows this ligament to be called either the cranial or
the anterior cruciate ligament. In veterinary
medicine, it is generally called the anterior cruciate
ligament and is often abbreviated ACL. It's
partner is the caudal cruciate ligament.
If one of the cruciate ligaments were to break, the two
bones would be able to slide back and forth freely on
each other. This is
exactly what happens, too. Because of some
peculiarities in the anatomy, it is almost always the
ACL that breaks and not the caudal cruciate ligament.
When the ACL ruptures, the joint becomes unstable and
painful. If not treated, severe, debilitating
arthritis will develop.
There are two reasons the ACL can break. The first
was is for a healthy ACL to be severely traumatized.
The trauma can be a mis-step, a fall, a twist, or a
sudden wrench. This would be a
of injury. We see this type of acute injury most
commonly in young, athletic dogs.
The other way an ACL can fail is by slow degeneration.
In some middle-aged, somewhat overweight, less active
dogs the ACL will begin to degenerate slowly over years.
Eventually it fails entirely, and failure may occur
during something as non-stressful as a walk around the
block. Often, these knees will have developed
advanced arthritis before the ACL ever fails.
These dogs often rupture the ACL in the other leg within
a few years as well. In my practice, the slow,
degenerative ACL injuries outnumber the acute traumatic
It is thought that poor knee conformation is the root
cause of most ACL
ruptures, especially of the slow degenerative ones.
If an x-ray of the knee is taken, it can be seen that
there is an angle formed between the top of the tibia
and the shaft of the tibia. This angle is called
the Tibial Plateau Angle. In the image it is 25
degrees. This angle is important because if it is
too high, there will be excessive strain on the ACL and
that will lead to instability and ACL rupture.
While there is a lot of support for this theory, in
reality the issue is not that cut-and-dried. Many
dogs with ACL ruptures have normal Tibial Plateau
Angles. In fact, the data show that in general,
dogs with ACL ruptures really don't have significantly
steeper Tibial Plateau Angles than dogs without ACL
ruptures. Most veterinarians do agree that dogs
with ACL ruptures with steep Tibial Plateau Angles pose
This forms the basis for one method of ACL Rupture
treatment. There have been several procedures
developed that changes the slope of the tibial plateau.
The most common of these procedures, the Tibial Platuau-Leveling
Osteotomy, or TPLO, involves cutting the tibial in two,
rotating the plateau, and plating it back together.
The ACL itself is not repaired, or even touched, in this
procedure. The new tibial plateau
is what stabilizes the joint.
The surgeons who pioneered this technique, in a highly
controversial move, actually patented the procedure, and
then made a fortune selling equipment and running
training schools. Although the patent has now
expired, because of the technical nature of the
procedure and the expensive instrumentation required, it
still is mainly done by specialist surgeons. It
has the advantage of a rapid recovery and in general
good results, but has the disadvantage of being more
costly to perform. Most referral surgeons charge
somewhere in the neighborhood of $1,500 to $2,500 to
perform a TPLO.
The second way to treat ruptured ACL's is to implant a
synthetic ligament. This technique is much older
than the TPLO, although it has undergone many
refinements over the years to make it work even better.
The technique is
sometimes abbreviated LI for Lateral Imbrication.
The most recent refinement of the technique is called
the Tightrope Procedure, named after the hardware that
is used. Modeled after a technique for repairing
ankle injuries in humans, an ultra-strong 21st-century
braided material is implanted through holes drilled in
the bones themselves to take over the function of the
damaged ACL. In my hands, the Tightrope Procedure
provides significant advantages over some of the older
LI techniques. I find that most of my Tightrope
patients walk out of the clinic the day after surgery
better than they walked in. The Tightrope
Procedure is still quite new, and long-term follow-up is
not available, but so far it seem to be outperforming
the previous LI procedures, and short-term it seems to
be outperforming the TPLO in many cases. The
Tightrope Procedure has the advantage of being done
locally here in our clinic, unlike the TPLO which
requires referral to Salt Lake or Boise. Aslo, the
Tightrope costs less, currently from $900 to $1,100.
This is more than some of the older LI techniques
because of the cost of the new implants. However,
it is worth it because of the superior performance of
the new implants.
So which technique is better? Initially, it was
widely believed that the TPLO technique was better in
all situations. However, recent studies are
starting to show that TPLO and LI do not differ that
much, and patients having either technique can
experience excellent results. The advent of the
new Tightrope technique makes the picture even less
clear. Although there are lots of opinions out
there, my opinion is that the jury is still out on this
one. Both techniques can be used with excellent
results in many dogs.
However, there are some situations where there is a
clear choice. Almost everybody agrees that the TPLO is best for very large dogs (75 pounds and up), and
for meduim and large dogs that are very active or have
abnormally steep tibial plateau angles. And almost
everyone agrees that the LI technique is best for small
dogs, say 45 pounds and down. The Tightrope
technique shows promise in some of the larger dogs as
well. I believe the Tightrope is an
acceptable alternative for even large dogs when
financial constraints prohibit the TPLO procedure,
although the chances of having a less-than-ideal
outcome are higher the bigger the dog gets, the more
active he is, or the steeper the tibial plateau angle
gets. There are some practitioners who disagree
with this opinion.
The real problem is which technique is better for the
dogs in the middle, who weight from 45 to 75 pounds.
Again, there are lots of opinion out there. My
personal opinion is that TPLO is slightly better than LI
for these dogs, and if finances are not an issue I
recommend TPLO. The bigger your dog is, the more
active he is, or the steeper the tibial plateau angle,
the more strongly I recommend TPLO.
However, TPLO can cost twice as much, and I do not feel
that it is twice as good in dogs in this weight range.
I have had excellent success with the LI technique in
many dogs this size. With the older LI techniques,
the dogs regain good function within two months. With
the new Tightrope technique, most dogs walk out of the
clinic the day after surgery with less pain than they
walked in. With TPLO, the recovery is quicker than
the old LI techniques, but not as fast as the Tightrope.
It must be noted that there are rare instances of
catastrophic, limb-threatening complications with TPLO
that we do not experience with the LI technique.
This is because the bone is actually sawn in half, and
if the plate fails for any reason, operative error,
faulty implant, crazy patient, rub of the green,
whatever, there will be big problems. If LI or the
Tightrope is done and does not work out well, a TPLO can
then be performed later and improve the situation if
done within a reasonable time frame.
An important part of either surgery is the examination
of the meniscus. You will recall that the meniscus
is a cartilage cushion thet fits in between the ends of
the femur and the tibia. When the ACL ruptures and
becomes unstable, the meniscus becomes vulnerable to the
shear forces of the two bones moving in abnormal ways.
Again, anatomical peculiarities make it so that it is
always the medial side of the meniscus that tears in
dogs. The joint is surgically opened, and the
medial meniscus is examined. If a tear is found,
it must be removed, as the meniscus does not heal by
itself. If the tear is severe, the entire medial
meniscus must be removed.
The operated area heals by forming fibrocartilage, which
is a version of scar tissue. It is not as good as
the original meniscus, but it is better than leaving the
torn meniscus. It takes some time for this healing
to happen, so that joints with a torn medial menuscus
heal slower, and the final result is not as good as in
joints without a torn meniscus.
ACL Surgery is fairly painful. We take care to
provide excellent pain control for our ACL surgery
patients. We always use pre-emptive pain
medications including morphine-like drugs, intre-operative
pain drips, epidural pain medication, and intra-joint
anesthetics. Post-op we continue the pain drips
and non-steroidal anti-inflammatories. With good
pain control, our patients experience a more rapid
return to function.
Post-op care consists of controlled activity. Knee
surgery is all about physical therapy. Many
physician surgeons have their knee patients walking the
day of surgery, and so do we. We want our patients
to be up and walking,
but not putting stress on their new knees. Most
dogs will carry the leg for days to a few weeks,
gradually starting to touch the toe down, then gradually
bearing more and more weight as the weeks pass. We
want early, active movement but no excessive strain.
This means that our ACL patients should be free to walk
around the house, but can't run, can't climb or go
down flights of stairs, can't jump up and down
from furniture, and can't be allowed outside without
being on a leash for the first month. We will
allow leash walks the first month as soon as their
progress allows. The second month is usually spent
gradually increasing their activity.
Dogs with torn ACL's that have surgery do much better
than dogs that don't. Often, they return to normal
function. However, some patients don't. Dogs
that have acute, traumatic ACL tears do the best.
Their knees were in good shape before the tear, and they
are more likely to have normal tibial plateau angles.
These dogs will develop arthritis as they age, but in
ngeneral do very well. However, the dogs with
degenerative ACL tears may not do so well. They
often have considerable arthritis in their knees before
the ACL gets around to tearing. They are also more
likely to have abnormal tibial plateau angles.
While surgery on these knees cannot repair the arthritis
that is already there, surgery can reduce the amount of
further degeneration that occurs. Even so, these
patients often experience considerable arthritis in
their damaged knees even with surgery. I do feel,
however, that they are much better with surgery that
they would have been without it.
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