CCL Injury - What Happens When a Dog's Knee Ligament Ruptures?

An analogy for CCL (cranial cruciate ligament) ruptures is like having a door break a hinge. Then the door won't open or close very well - usually causing a lot of scraping on the floor. Something similar happens in the stifle joint (the knee joint of a dog). The bones are no longer properly aligned, and the joint doesn't work well, causing inflammation, pain, and damage to the cartilage.

Most clients bringing in a pet with a CCL rupture say that it occurred during running, fetching, or playing with another dog. To the owner, it may appear as an acute (or quick onset) injury, but that is not so. This is a chronic disease in dogs, unlike humans. Human ACL (anterior cruciate ligament) traumas are almost always the result of athletic injuries.

Typically, when the CCL (cranial cruciate ligament) ruptures, the femur rides backwards on the tibia, and the tibia wants to come forward. The medical term for this phenomenon is cranial tibial subluxation. The end-effect is that it can be excruciatingly painful for your dog.

It's often asked, "What's the difference between canine knee ligament injuries and human knee ligament injuries?"

Primarily, the stance of the human knee is different than the stance of the dog's knee. People stand straight up, with the joint at an angle of 180 degrees, with their femur directly on top of their tibia. Dogs, on the other hand, stand with the stifle joint at angle of 135 degrees.

Because of the angle, every time that a dog stands, the bone alignment is dependent upon an intact CCL to hold the bones in place in the stifle (knee) joint. Chronic wear and tear on the CCL causes it to ultimately fail.

Using another analogy, you could say that the CCL is like a rope made up of many fibers. With time and stress, the fibers of the rope slowly break down until it is so weak that it can't do its job anymore and breaks.

Most dogs are brought to a vet when the CCL finally breaks and the dog is so lame that it either can't bear any weight, or can only touch its toes to the ground.

There can certainly be a partial tear, which can be just as painful, and can leave the CCL just as incapacitated. This is important because CCL injury is always accompanied by some form of osteoarthritis or degenerative joint disease. This arthritis is irreversible.

Most surgeries slow the progression of arthritis, but it cannot prevent the arthritis that has already set in, therefore the stifle joint is never the same as if it had an intact CCL. (The world is not perfect!)