ACL Injuries in Dogs

If your dog goes lame in one of his hind legs, he may have torn or ruptured his anterior cruciate ligament, or ACL. This ligament, which also is called the cranial cruciate ligament in animals, connects the back of the femur (the bone above the knee) with the front of the tibia (the bone below the knee). The ACL is responsible for keeping the tibia in place beneath the femur and stabilizing the knee joint.

There are multiple causes of dog ACL injuries, including activity, breed, age, and obesity.

Symptoms of dog ACL injuries

ACL injuries in dogs are one of the most commonly seen orthopedic problems.

Depending on the severity of the ACL injury, a dog's symptoms might range from having a hint of lameness to being unable to bear weight on the injured leg. A dog with an ACL injury may also have swelling on the inside of the knee.

One definitive indication of a torn ACL in dogs is the presence of the "drawer sign." This means that when the veterinarian holds the dog's femur in place, the tibia can be pulled forward in a manner similar to a drawer sliding open. However, the lack of the drawer sign does not mean there is not damage to the ACL.

In addition to a complete physical exam, your veterinarian will probably take X-rays of your dog's knee to investigate the extent of damage and rule out other possible causes of lameness. X-rays will allow your veterinarian to determine the presence of fluid or arthritis in the joint, and also whether any small pieces of bone broke off with the ligament when it ruptured.

Dogs at risk for torn ACLs

Certain breeds are more prone to dog ACL injuries, including Labrador retrievers, poodles, bichon frises, German shepherds, rottweilers, and golden retrievers.

Obese animals and those that get occasional strenuous exercise – so-called "weekend warriors" – may also be more likely to develop ACL injuries. Often, these chronic conditions persist for long periods of time, with the dog gradually becoming more lame as the ligament becomes more and more damaged. Sometimes, however, a dog will have no obvious symptoms until the ligament finally ruptures, often with something as simple as a slight misstep.

Additionally, male dogs neutered at younger than five months old may be more likely to develop ACL injuries later in life.

Studies have shown that about one-third of the dogs that rupture the ACL on one leg will develop the condition in the opposite leg.