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No DescriptionACL Injuries

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 of the 
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 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 isNo Description 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 Joe-Namath-fades-back-in-the-pocket-and-is-blindsided-by-Mean-Joe-Green-type 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 ACL injuries.

It is thought that poor knee conformation is the root cause of most ACNo DescriptionL 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 special problems.

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 No Descriptionanatomy 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 the No Descriptionjoint 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,No Description 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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