How to know if your Dog has a Torn ACL (Anterior Cruciate Ligament)

How to know if your Dog has a Torn ACL
(Anterior Cruciate Ligament)

A tear of the ACL ligament in the knee or stifle joint is the most common orthopedic injury in dogs. There are two Cruciate ligaments in the knee or stifle joint of the dog. The reason these two ligaments are called Cruciates is that they cross over each other like a cross, actually more like an X. The Anterior or Cranial Cruciate ligament runs from the bottom rear portion of the Femur or upper leg bone to the top front of the Tibia or lower leg bone within the joint itself. The Anterior Cruciate prevents the lower portion of the joint from slipping forward and the upper portion of the joint from slipping backward. This injury can be due to trauma to the knee joint or wear and tear over time.
How to know if your dog has a torn ACL Cruciate Diagram

Your dog will limp on his affected leg intermittently or bare weight by toe touching or not bear weight at all. This injury is more complicated and more varied than its name would indicate. The diagnosis of this injury is more complicated than your Veterinarian can fully appreciate because of the lack of diagnostic equipment such as an MRI which would allow visibility of the Cruciate ligaments as well as all soft tissue structures in the stifle or knee joint. Your Veterinarian should take an x-ray but only to eliminate other possible problems such as various types of cancers that can replicate your dog’s symptoms. A medical problem that can replicate these symptoms is arthritis, as well as others. The Anterior Drawer Sign is the exam that confirms or eliminates the diagnosis of a Cruciate injury determined by the lack of motion or excessive forward movement of the lower leg from the upper leg at the knee or stifle joint. The way this test is performed by your Vet is to bend the dog’s leg at the knee joint and then pull the Tibia or lower leg bone of the stifle or knee joint forward to determine if movement is present at the joint. This maneuver can be painful with your dog tightening his muscles around the joint to avoid the pain. Sometimes this exam can demonstrate movement at the knee joint with the dog awake and not sedated. In other dogs, sedation of the dog is necessary to relax the dog’s muscles around the knee joint to allow for abnormal movement at the joint when present.

The diagnosis of the degree of injury to the Anterior Cruciate Ligament such as “partial tear” or “full tear” is not always clear and is based on this clinical diagnostic test. Once this diagnosis is made, the decision to choose surgery or conservative treatment should be made. If the Anterior Drawer is negative for movement at the joint and the dog is at least partially bearing weight on his leg this could indicate a “Strain” as opposed to a tear. If this is the case then a limited time period (perhaps one week) of anti-inflammatories, rest and leash walking should be attempted. If this is unsuccessful a Cruciate Brace should be attempted prior to surgery. When possible–in humans or dogs, conservative treatment should always be attempted prior to a surgical option due to the risks, potential failures and complications. In addition, studies tracking Cruciate surgeries demonstrate a 40 to 60% incidence of the opposite leg acquiring a Cruciate tear within one year of the procedure. This is most likely do to the additional stress on the opposite leg during the long post-operative time period.


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