Tuesday, May 10, 2011

Repairing the Anterior Cruciate Ligament

One of the more common injuries we see in small animal practice is rupture or tear of the anterior cruciate ligament of the knee. Perhaps some of you reading this blog have had your dog or cat (yes I said cat) diagnosed with this injury.

The knee is a complicated joint. It consists of the femur above, the tibia below, the kneecap (or “patella”) in front, and the bean-like fabellae behind. Pillows of cartilage called the medial and lateral menisci fit between the femur and tibia like cushions and there are assortments of ligaments holding everything together allowing the knee to bend the way it should.

There are two cruciate ligaments which cross inside the knee joint: the anterior  cruciate and the posterior cruciate. They are named for the side of the knee (front or back) where their lower attachment is found. The anterior cruciate ligament prevents the tibia from slipping forward out from under the femur.

Diagnosing the Tear

The ruptured cruciate ligament is the most common knee injury of the dog; in fact, chances are that any dog with sudden rear leg lameness has a ruptured anterior cruciate ligament rather than something else. The history usually involves a rear leg suddenly so sore that the dog can hardly bear weight on it. If left alone, it will appear to improve over the course of a 5 to 10 days but the knee will be notably swollen and arthritis will set in quickly. The key to the diagnosis of the ruptured cruciate ligament is the demonstration of an abnormal knee motion called a “draw sign.” It is not possible for a normal knee to show this sign.

Draw Sign

The veterinarian stabilizes the position of the femur with one hand and manipulates the tibia with the other hand. If the tibia moves forward (like a drawer being opened), the cruciate ligament is ruptured.
It is not unusual for your pet to be tense or frightened at the vet’s office. Tense muscles can temporarily stabilize the knee preventing demonstration of the drawer sign during examination. Often sedation is needed to get a good evaluation of the knee. This is especially true with larger dogs.

Since arthritis can set in relatively quickly after a cruciate ligament rupture, radiographs to assess arthritis are helpful. Another reason for radiographs is that occasionally when the cruciate ligament tears, a piece of bone where the ligament attaches to the tibia breaks off as well. This will require repair and the surgeon will need to know about it before beginning surgery. Arthritis present prior to surgery limits the extent of the recovery after surgery though surgery is still needed to slow or even curtail further arthritis development.

Consequence of Not Repairing the Injury


Without an intact cruciate ligament, the knee is unstable. Wear between the bones and meniscal cartilage becomes abnormal and the joint begins to develop degenerative changes.

                                                                                               Damaged Knee

The Surgical Repair
There are many different “repairs” of the anterior cruciate ligament. There are more than a dozen published descriptions. Since there are that many or more, you may conclude that no one has the absolute correct answer to the injury.
The procedure that I have currently favored (about 150 times) can be described more as a clean out of all damaged or torn tissue rather than a “repair”. The word repair suggested I have somehow fixed the anterior cruciate ligament and left it to heal inside the joint. The ligament does not heal.

The knee joint is opened and completely inspected. The torn or partly torn cruciate ligament is removed. If the posterior cruciate is damaged, it too is removed.  Any bone spurs of significant size are bitten away with an instrument called a “rongeur.” If the meniscus is torn, the damaged portion is removed. The joint capsule is closed in a “pants over vest” pattern which adds stability to the knee as it heals. This suture technique is called imbrications of the joint capsule.

Typically, the dog may carry the leg up for 10-14 days after surgery but will increase knee use over the next 2-3 months eventually returning to normal. Cats heal faster. They are usually more gentle and careful.
Typically, your dog will require 12 weeks of exercise restriction after surgery (no running, outside on a leash only including the backyard)
  • Your dog should increase weight bearing about 5 to 10 % per week.
  • The hardest part of healing is when your dog feels better and walks and wants to run and the 12 weeks of healing are not over yet.. This is where intellect rules over emotion. Keep your dog on a leash and limit his or her exercise as directed.
  • Remember that 12 weeks will heal the knee to 90% of normal strength under normal circumstance. Your dog will appear perfectly sound.  It will take a full year to achieve 100% maturity.
  • Listening to your vet’s discharge instructions is probably the most important thing you can do to be successful.
Unsolicited Feedback from a Client:

Our Shepherd Lab Mix Prince had been suffering for over 2 years with a bad limp.  We had taken him to 2 other Vets and received conservative treatments and just began medicating our Prince with pain meds.  He was only about 2 when this began and just turned 4.  It was breaking our hearts the way he was limping around and in constant pain. 

We took Prince to Doctor Herman.  Dr Herman was very thorough with the examination.  He suggested that Prince be sedated for an x-ray to allow him to properly check range of motion since he would tense up.  This made perfect sense but the other 2 vets we had taken him to didn't do this.  With he examination Dr Herman diagnosed him with an ACL tear (knee) and arthritis forming.  The knee needed surgery and the joint had to be cleaned up. We had the surgery done and within 2 days Prince was putting weight on the joint, his appetite had returned and he is a much happier boy, all around!  Prince is making an amazing recovery. I would recommend Dr Herman to anyone who has a pet with similar issues. We also found the cost for the procedure to be quite reasonable. 


Dennis and Joyce C

    The Providence Veterinary Hospital Blog is a publication of Peter Herman, VMD, at the Providence Veterinary Hospital, 2400 Providence Ave. in Chester, PA. Contact Dr. Herman at 610-872-4000 or visit us at http://www.providencevet.com/.