Step 2: About ACL/CCL

The cranial cruciate ligament (CCL) is equivalent to the anterior cruciate ligament or ACL in people. This tissue is responsible for limiting hyperextension of the stifle and internal rotation of the tibia in relation to the femur. Moreover, it prevents forward sliding or drawer motion of the tibia. A CCL tear in dogs commonly causes hind limb lameness.

The underlying cause of CCL injury in dogs differs from ACL tears in most people. Whereas trauma is a common cause of ACL tears in people, CCLR in dogs is typically degenerative in nature. Some proposed predisposing factors for cruciate injuries in dogs include genetics, excessive tibial plateau slope (TPS), immune-mediated disease, and bacterial presence within the joint.

Other causes of CCL tears in dogs are obesity and poor fitness levels. Canines naturally walk with their knees bent at all times, and, the heavier they are, the more load is placed on their ligaments. Besides obese pets, those who undergo occasional strenuous exercise and follow a “weekend-warrior” lifestyle are also more likely to develop this injury. CCL injury in dogs is chronic and will gradually cause the limbs to be lame and damaged.

Early neutering has also been found to cause this injury, with females at higher risk than males. However, many owners still opt for the procedure as the benefits of neutering their pet outweigh the increased risk of a ruptured ligament.

Moreover, certain breeds are more susceptible to developing a CCL injury in dogs, such as Rottweilers, Newfoundlands, Mastiffs, and Akitas. You can also include Saint Bernards, Labrador Retrievers, and Staffordshire Terriers. Smaller dog breeds are less likely to be affected.

Though the underlying cause of CCL tears in dogs varies, the anatomy of the joint may play a role in the continued breakdown of the ligament. Due to the slope of the top of the tibia, or the tibial plateau, the cranial cruciate ligament of the dog is under stress during weight bearing as it attempts to keep the femur and the tibia in appropriate alignment. Once the integrity of the ligament is compromised, the tibia begins to move forward in relation to the femur during weight bearing.

Partial tearing of the ligament is common and frequently progresses to a full tear over time, especially when left untreated. When this condition develops with one knee, there is an increased chance that your dog will experience a similar problem with its other knee sometime in the future.

There is some evidence that the steeper the tibial plateau slope, the greater the likelihood of a CCL tear in dogs. The instability that develops is partly responsible for the pain. As the cruciate ligament tears, changes are also taking place in the joint, leading to a loss of cartilage health early on and a complete loss of cartilage in end-stage arthritis. In most patients, once the degenerative process of the CCL begins, the ligament will go on to a complete tear.

We recommend seeking veterinary help at the first sign of lameness that lasts longer than a day. If your pet experiences lameness of its legs, restrict any off-leash activities for a few days and see whether or not its weakness disappears. If symptoms persist, consult your vet as soon as possible to have your pet undergo physical exams, imaging, and other screening tests.