Causes of CCL Injuries

The stifle joint of the dog is especially vulnerable to injury, because it has no interlocking bones to provide structural support. Instead, a dog’s stifle, or knee joint (in its hind legs), depends upon a meshwork of ligaments and muscles for stability. The cranial cruciate ligament (CCL) provides most of this support for the stifle and, when partially torn or completely ruptured, leaves only the muscles and soft tissues surrounding the stifle to hold the stifle joint in place. The cranial cruciate ligament in dogs is called the anterior cruciate ligament in people. The CCL can be damaged from acute trauma or from chronic repetitive injury. Most acute (sudden) CCL injuries in dogs happen during strenuous or exuberant athletic activities, such as romping, roughhousing, running, hunting, playing, chasing, jumping or engaging in other enthusiastic antics. Owners often report that their dog suddenly stumbled, possibly yelped and then “came up lame,” or held its rear leg up at an exaggerated angle.

The affected ligament probably experienced excessive wear and tear well before observable signs of damage became apparent. Chronic damage develops slowly over time and can be caused by poor neuromuscular coordination, conformational abnormalities or poor muscle tone. Obesity certainly can contribute to chronic ligament damage as well, because it puts abnormal stress and weight on the stifle joint.

Prevention of CCL Injuries

Unfortunately, there is no fool-proof way to prevent stifle injuries in dogs, other than keeping them from playing and running around exuberantly, which is not a good option. Conditioning seems to be the best approach. Dogs that are in poor physical condition are at the greatest risk of injuring their CCL, while healthy, well-conditioned dogs are better able to avoid injuries, because their stifles are protected from outside stressors by strong surrounding musculature. Owners should keep their dogs on a high-quality diet and give them regular, moderate exercise. After a period of inactivity, a dog should not be asked to engage in rigorous physical activities all of a sudden. He should be allowed to gradually work up to a point where vigorous activities are enjoyable and not overly stressing. Finally, dogs with conformational abnormalities in their rear legs that predispose them to CCL injuries probably should be spayed or neutered and not bred. This is something best discussed with the dog’s breeder and its attending veterinarian.

Special Notes

Dogs that develop cruciate ligament injuries in both hind legs can look like they have a neurological disorder, because they typically rise and move with an unusual, exaggerated and uncoordinated gait. The cause of bilateral hind limb lameness can be difficult to diagnose. Most veterinarians will want to perform a thorough neurological examination in addition to an orthopedic examination when evaluating a dog that comes in with a sudden onset of abnormal rear end locomotion.

Dogs with cruciate ligament injuries often have a condition called “lymphoplasmacytic synovitis.” Many experts think that the dog’s immune system initiates an inflammatory reaction directed against the collagen of the torn ligament after a CCL injury. Another theory is that lymphoplasmacytic synovitis occurs first and causes the stifle joint laxity, weakness and instability, which in turn predisposes the dog to cranial cruciate ligament injury. The actual relationship between CCL damage and immune-mediated lymphoplasmacytic synovitis is still the subject of much debate in medical circles.