By Brian Beale, DVM, Diplomate ACVS, Gulf Coast Veterinary Specialists

Did you know the dog and cat each have 2 knees….just like us!  Injury to the knee is the most common cause of lameness and pain in both dogs and cats.  A tear of the anterior cruciate ligament (ACL) is often the culprit.  ACL tears occur frequently in man, but it is even more common in dogs.  If left untreated, life long arthritis can ensue causing permanent pain and loss of function of the affected knee.

How do you know if your pet has a knee problem?

It’s not always easy. Some dogs will have an obvious limp and may even carry a hind leg.  Others show much more subtle signs such as decreased activity, difficulty rising, sitting off to the side or reluctance to jump.

Why is the Anterior Cruciate Ligament important?

The ACL keeps the knee stable. Stability is important to keep the joint healthy.  Tears of the ACL cause the knee to become unstable, which in turn causes damage to structures in the joint.  Arthritis results in loss of cartilage and damage to the joint capsule.  If the damage becomes severe, it can not be reversed. Meniscal tears (cartilage tears) occur in half the dogs having ACL injury.

Early treatment is the key!

If stability can be restored to the knee, arthritis and pain can be avoided.   The ACL can even be saved if the injury is diagnosed in its early stages.  Many dogs and cats can be returned to normal function – running and jumping for the rest of their lives.  Early treatment is also recommended to decrease the time the pet is placing excessive weight on the opposite “good” leg.  Increased force on this leg may increase the odds of a 2nd ACL tear.  If signs of hind limb problems are noticed, consult your veterinarian as soon as possible.

How will your veterinarian determine if the ACL is injured?

The diagnosis of and ACL tear is simple in most dogs and cats.  A physical exam is often all that is needed.  Radiographs (x-rays) are also helpful.  It may be necessary to visit an orthopedic specialist to diagnose difficult cases.

What is the best treatment?

Surgical treatment is the best option because the knee is mechanically unstable. Medical therapy may make the dog or cat feel better, but instability persists and arthritis progresses silently.  Drug therapy only masks the clinical signs and side effects can occur in some patients receiving medications.  Surgical treatment immediately restores stability to the knee and eliminates the cause of arthritis and cartilage tears.

How can the knee be surgically stabilized?

There are several options to stabilize the injured knee and your veterinarian or veterinary orthopedic specialist can determine the best course of action for your dog or cat.  The torn ligament can be replaced with an artificial ligament.  It is critical to replace the ligament at the optimal position to lessen the chance of breaking the replacement ligament and to ensure the best outcome.  Many dogs have an underlying factor that increases the chance of tearing the ACL.  A force known as “cranial tibial thrust” can cause pressure on the ACL every time the pet takes a step.  Over time, excessive force on the ACL can cause it to tear.  This is common and explains why so many dogs eventually tear the ACL on the opposite leg.  This force can be eliminated with a TPLO (tibial plateau leveling osteotomy) or TTA (tibial tuberosity advancement).  These procedures often give the best chance of a permanent repair and less arthritis.  These procedures have a success rate that exceeds 95%.

Is surgery painful?

Fortunately, the ACL can now be repaired with minimally-invasive techniques.  Arthroscopy is extremely beneficial because it minimizes pain and returns the patient to normal activity sooner.  That means less time trying to keep them quiet following surgery!  Arthroscopy is performed by inserting a small scope into the knee through a tiny incision.  The scope is attached to a large video monitor, creating a close-up view of all of the structures inside the knee.  Arthroscopy is not only less invasive, but the magnification provided by the scope allows the surgeon to see the damage more clearly and treat the condition with greater precision.  Arthroscopy has been the gold standard for treatment of joint problems in man for many years, and now the same can be said of pets.