Have you ever heard of a ‘torn ACL’, or also known as ‘skier’s knee’? The ‘ACL’ stands for ‘anterior crutiate ligament’, which can be found within our knees. The ligament’s job is to stabilize the femur (thigh bone) against the tibia (shin bone). A torn ACL is a common knee injury among human athletes that allows the femur and tibia to move independently of each other, resulting in an abnormal rubbing of the cartilage within the knee. However, humans are not the only species that get this injury. In fact, an ACL tear in dogs is even more common than in humans!
In a dog, we call it the CCL, or cranial crutiate ligament. Although the names are different, the ligament’s job is the same in dogs as it is in humans.
Which Dogs Get Torn CCLs?
CCL tears are most common in medium to large, athletic dogs. A few breeds, such as Labrador Retrievers, Rottweilers, St. Bernard's, Mastiffs, and Pit Bulls are more prone than others. These breeds are muscular, heavy-set dogs that often have inherent knee abnormalities that predispose them to tearing their CCLs.
The most common story behind a tear goes like this:
My dog was running around with another dog/chasing a ball/chasing a squirrel and suddenly came back limping on one of the back legs.
With strict rest and dog safe NSAID medications, these limps can sometimes resolve. Unfortunately, most of these limps return again and again. Most dogs are never able to recover full use of their back legs without surgical intervention.
This is because many CCLs only partially tear at first, and can heal with some rest and pain medications. However, the healed tissue isn’t made of the same fibers as the original ligament, and is instead made of a weaker scar tissue. This scar tissue is prone to tearing easily, and that is why we see many of these dogs alternate between periods of limping and walking normally.
Inherent Knee Abnormalities
The inherent issue with these dogs has to do with the anatomy of their knees. Instead of breeding for dogs with femurs that sit squarely on top of their tibias, we bred for dogs with femurs that sit slightly behind the tibia. Dogs with this inherited conformation are born with CCLs that are constantly strained, like slightly over-stretched rubber bands. And just like an over-stretch rubber band is more easily torn over time or with enough force, the CCL can tear as well.
Less commonly, trauma in which the knee is overly hyper-extended can also cause a tear in a dog’s CCL. However, this type of trauma requires a lot of force and is usually only seen with severe injuries, such as those sustained falling from a high distance or getting hit by a car.
Previous Tear of An Opposite Knee
Over 50% of dogs who tear their CCL in one knee will also tear the same ligament in the other knee. This is because when one knee is injured, more weight is put on the other knee. The more strain the good knee takes on, the more that knee’s CCL is stretched and likely torn.
How Do We Prevent Tears?
- Maintaining a healthy weight: There’s no doubt about it that heavier dogs are more likely to tear their CCLs. This is because increased weights also put increased strain on ligaments.
- Staying fit: It’s not just about weight, but about muscle tone and strength. Stronger muscles from regular exercise help to hold up the femur and tibial bones, respectively, and prevent over-stretching of the ligament.
- Joint supplements: Joint supplements with glucosamine, chondroitin, and methylsulfonylmethane (MSM) have been proven to keep joints lubricated. Lubrication helps to decrease the damage that can result from over-stretching of ligaments. Even after there is already damage to the knee, these joint supplements help to delay the onset of arthritis.
How Do We Diagnose CCL Tears?
A veterinarian will want to examine a dog if there is suspicion that the CCL is torn. He or she will perform a few key tests:
Cranial Drawer: This is where the veterinarian will grab hold of the femur with one hand and the tibia with the other. If the bones are able to move independently of each other, then a CCL tear is likely.
Tibial thrust test: The veterinarian will put one hand over the femur and knee joint and use the other hand to extend, flex, and rotate the tibia. If a ‘click’ is felt within the knee, then this means that there is a torn meniscus, which is a piece of cartilage that sits between the two bones — the meniscus is often torn after a CCL tear occurs due to the abnormal rubbing between the femur and tibia.
Sit test: When sitting, dogs with torn CCLs will no longer sit squarely on his or her haunches. Instead, the leg with the torn CCL will be extended off to the side.
- X-rays: X-rays of the knees are very useful in helping to diagnose a torn CCL. While we can’t see ligaments on x-ray images, when there is a CCL tear, we will see swelling within the knee joint. With old CCL tears, we may even see arthritic changes due to the constant swelling and pressure within the knee.
- MRI or CT scan: Both MRI and CT scan are types of non-invasive advanced imaging that can allow images to be taken of the CCL. Both procedures require general anesthesia.
- Arthroscopy: This is a surgical procedure where a tiny opening is made in the knee and an arthroscope, or tiny camera (sometimes with tiny pliers or blade) is inserted. This allows direct visualization of the CCL. This procedure requires general anesthesia.
How Do We Treat Tears?
As mentioned above, strict rest and NSAID medications can help in some cases of extremely mild injuries. However, most tears never heal and end up causing long-term pain. The only treatment that ensures full healing is surgery.
There are different surgical options for dogs of different ages, sizes, weights, and lifestyles. All options require general anesthesia and an approximately 8–12 week healing process. The most commonly performed surgical procedures are the lateral suture and the TPLO (tibial plateau leveling osteotomy).
The earlier a tear is recognized and treated, the more likely a dog will be able to recover. The recovery rate is extremely high for dogs who receive early treatment and most move on to regain over 95% usage of their knees.
Maintenance on joint supplements for life (with or without surgery) is key to providing comfort for your pet with a CCL injury. Joint supplements that include glucosamine, MSM, and chondroitin are key to providing increased joint lubrication and cartilage regrowth in these cases. I personally recommend Wellnergy Pets hip and joint products for pets suffering from these issues:
If you suspect your dog may be prone to tearing their CCL or you think he or she may have injured it, please feel free to reach out to our team on Facebook, Instagram, e-mail, or in the comments section, or make an appointment with your regular veterinarian.
About the Author:
Dr. Debra Chen, D.V.M. has been a practicing companion animal veterinarian for over three years in the San Francisco Bay Area. Prior to moving to the Bay, she received both her veterinary and undergraduate degrees at the University of Minnesota. After spending a third of her life in Taiwan, she is also fluent in Mandarin Chinese. Her veterinary interests include preventative medicine, animal behavior, and surgery. When not practicing medicine, Dr. Chen can be found camping, hiking, eating, or traveling with her husband and Formosan Mountain Dog, Tuna. They also share a home with their two feline overlords, brown tabby cats Cairo and Khaleesi.