Torn Anterior Cruciate Ligament (ACL), also referred to as rapture of the Cranial Cruciate Ligament (CCL), is the most common form of knee injury in dogs. This injury can happen to any breed at any age, but studies indicate that middle-aged, overweight, medium to large breeds are more prone to ACL injuries. These include Poodles, Golden Retrievers, Labrador Retrievers, Rottweilers, Bichon Frises, and German Shepherd Dogs. While not a life-threatening condition, torn ACL in dogs is often a painful and immobilizing injury that must be promptly addressed for the sake of your pet. As a dog owner, understanding the signs and treatments of torn ACL, as well as knowing how to prevent it, is important.
A Brief Overview of the Anatomy of the Canine Knee
The stifle is made up of three bones: Femur (the long bone between the hip and knee), Tibia (the bone extending down from the knee to the ankle, and Patella (or the kneecap). These three bones are connected together by a number of tough fibrous bands of tissue, which are referred to as ligaments. Two ligaments crisscross within the joint and connect femur to the tibia. These ligaments are referred to as cruciate ligaments. The one located towards the front of the joint is the anterior cruciate ligament (ACL), and its function is to stabilize the joint by preventing the ends of both the femur and tibia from moving back and forth. When the ACL is torn (or ruptures), the tibia and the femur start to move back and forth across each other, making the joint unstable.
Causes of ACL Injuries in Dogs
There are many factors that lead to torn ACL in dogs. Simple or fun activities, such as running, jumping and walking, can cause ligament tears. The ACL is commonly torn when the animal twists on his/her hind leg. This may occur when the dog makes a sudden turn when running, or if the pet slips on a slippery surface. The tension caused by the twisting motion often causes the ACL to tear.
Obesity is another causative factor for torn ACL in dogs. The huge weight of the obese dog puts pressure on the knees, resulting in the rapture of the cruciate ligaments. In this case, the dog doesn’t necessarily have to suffer from a sudden injury. The cruciate ligaments slowly degenerate and become weaker until they rapture. Certain breeds are more prone to cruciate ligaments degeneration. They include Bichon Frise, Rottweiler, Labrador Retriever, Newfoundland, and others.
Some smaller breeds of dogs are particularly predisposed to rapture of the ACL due to a luxating patella. Other predispositions to ACL injuries include dogs that have had previous CCL rapture, animals with conformational abnormalities, and male dogs neutered at 5 months old or below.
Signs of Torn ACL in Dogs
A rupture of the ACL can be extremely painful and affected animals often experience pain simply walking. The injury may cause instability and swelling in the knee joint. If left untreated, torn ACL can lead to lameness and, ultimately, a degenerative joint condition in the affected rear leg.
Some of the warning signs of an ACL injury include:
- Weakness or lameness in one or both back legs
- Wasting away of muscle (atrophy) in the affected rear limb
- Swelling around the affected joint
- An abnormal sitting posture
- Stiffness or difficulty getting up
- Reluctance to get up, walk, jump, go up and down stairs, or run.
- Reluctance to use one or both back legs
Treatment Options for ACL Injuries in Dogs
The most preferred treatment method for torn ACL in dogs is surgery. Conservative therapy, including cage rest, anti-inflammatory medications and supplements, may help provide relief in some cases. Small breeds may even achieve full recovery with non-surgical ACL injury treatment solutions.
But in cases where the ligament is completely torn, and especially in large dogs, surgery may be the only option. The two most commonly used surgical techniques for repairing torn ACL in dogs are Tibial Tuberosity Advancement (TTA) and Tibial Plateau Leveling Osteotomy (TPLO) surgery.
This procedure involves advancing the tibial tuberosity to change the angle of the patellar ligament – which neutralizes the shear force between the femur and the tibia during weight bearing.
In this procedure, the top of the tibia bone is cut and rotated so that its slope changes to a predetermined position (approximately five degrees from the horizontal plane), which stabilizes the joint by preventing the femur from sliding down the slope of the tibial plateau.