The cranial cruciate ligament (CCL) is a band of connective tissue that connects the femur (thigh bone) and the tibia (shin bone). The CCL stabilizes the stifle (knee) joint in the hind leg. The CCL in dogs is comparable to the anterior cruciate ligament (ACL) in people. A tear in the CCL, called a rupture, is the most common stifle injury in dogs.
CCL rupture is usually due to a combination of factors that weaken the ligament, but a rupture can also be caused by a sudden injury, even if the ligament is healthy. Some of the most common factors contributing to ligament rupture include obesity, poor physical condition, genetics, breed, and degenerative or aging changes to the ligament. CCL ruptures can occur in dogs of any size, breed, and age, but Newfoundlands, Rottweilers, St. Bernards, Chesapeake Bay Retrievers, and Labrador Retrievers are commonly affected breeds. Partial or incomplete tears are common and will progress to full or complete tears of the ligament. Up to 60% of dogs with a ruptured CCL will eventually rupture the CCL in the other stifle.
The most common clinical sign of a ruptured CCL is sudden hind leg lameness. The limping can be mild or severe, up to the point of not bearing any weight on the affected hind leg. Other signs include pain, difficulty jumping, difficulty getting up, decreased activity, muscle atrophy (loss), and stiffness. Your pet may also have a firm swelling on the knee. The clinical signs are the same for both complete and partial tears of the ligament, but may differ in severity.
Your veterinarian will diagnose a ruptured CCL by observing how your pet walks and bears weight, by performing a physical examination, and by evaluating radiographs or x-rays of your pet’s stifle. Your veterinarian may also perform specialized tests as part of the physical examination - such as the drawer test or the tibial compression test - to look for instability in the stifle. In a normal stifle, the CCL prevents any forward or sliding movement of the tibia relative to the femur. Forward movement of the tibia detected with either of these tests typically indicates CCL rupture.
Surgery is the best option for the treatment of a ruptured CCL, as it is the only way to prevent the forward movement in the stifle and correct the instability that results from the torn ligament. In cases where surgery is not an option, medical management (anti-inflammatory medication, pain medication, and exercise restriction) can make the pet more comfortable in the short term. Ligaments cannot repair themselves. This means a ruptured CCL will not heal on its own. Failure to treat a ruptured CCL surgically will result in further degenerative changes, such as arthritis, which will develop quickly in the joint.
If your dog is limping or showing any other changes in her behavior, see your veterinarian right away for proper diagnosis and treatment.