Dogs sometimes develop a problem with a ligament on the inside of the knee joint that keeps the knee tight and functioning smoothly. This ligament is called the anterior cruciate ligament. A ruptured cranial cruciate ligament (RCCL) refers to a tear or a rupture; in humans, this is known as a ruptured anterior cruciate ligament (RACL). The knee joint has a posterior cruciate ligament that can also tear or rupture. The cranial cruciate ligament rupture is far more common.

The black line represents what the cranial cruciate ligament would look like on a radiograph. The white arrow is the patella (kneecap). Photos courtesy of Long Beach Animal Hospital.

Large-breed dogs are prone to this problem. It usually results from a traumatic episode like running or jumping. Overweight dogs and those with Cushing’s disease, a pituitary gland condition, are even more susceptible. It occurs in cats as well.

The primary symptom is a limp on one of an animal’s rear legs. A physical exam is a big part of the diagnosis. During the exam, the veterinarian will gently stress the joint to see if there is laxity when moving it backward and forward. This laxity is known as drawer movement and is an indication of a rupture of the ligament.

A recent trauma may show swelling in the joint due to the rupture, and the drawer movement might not be apparent for several days until the swelling subsides. Sometimes, pets experiencing pain or anxiety will need to be sedated so that the veterinarian can assess the movement of the limb.

The white arrow points to a swollen joint that could be due to a cranial cruciate ligament rupture. Photos courtesy of Long Beach Animal Hospital.

Radiographs are utilized to confirm the diagnosis and check for other problems like fractures and dislocations from the initial trauma. Dogs need to be sedated for proper positioning because the ruptured ligament cannot be directly observed; only secondary joint swelling can be observed, and it can be subtle. We always radiograph both knees as a comparison.

To prevent long-term arthritis, surgery in dogs is called for. Cats may be able to get by without surgery. There are several different techniques that have been developed over the decades to surgically correct this problem. The technique used depends on the training and skill of the surgeon and the size of the dog.

The oldest technique uses a special suture to stabilize the joint. Other techniques involve cutting the bone and rotating the bottom of the knee to prevent it from sliding back and forth. Several months of confinement with very controlled walks are needed so that the dog can completely heal after surgery. Unfortunately, when one cranial cruciate ligament ruptures, the leg on the other side can get the same problem because of the added stress of weight bearing.

This is a postoperative radiograph of a tibial plateau leveling osteotomy (TPLO) surgery. This is a common surgery for larger dogs.

The best way to prevent this problem is to keep your pet’s weight at an optimum level, let it play in a field or area that is level and has no holes to stumble into, and, if possible, let your pet warm up and not jump or run with excessive vigor.