I feel like most folks know someone whose dog has needed its knee repaired. Most of the time, the cranial cruciate ligament is the culprit for the failing knee. It is the same ligament as the anterior cruciate ligament (or ACL…) in humans. So, for ease of client conversations, most general practice veterinarians use the terms interchangeably. Despite this, ACL tears are fairly uncommon in humans compared to the rate in dogs. You may hear about it a lot in human athletes, but most of the dogs blowing their knees are not getting tackled by heavy-weight linemen like a human does. So why is this so common?
The main reason is anatomy. With humans, we are meant to straighten our legs and lock our knees when we are standing. In dogs, the legs are meant to hold the body weight on the ligaments while maintaining a bend in the knee. So, when the knee is straightened, this is actually considered a hyperextension. Without much force on the leg, this straightening is possible without causing any damage… just some slight extra tension in the ligaments. However, if there is any kind of forward momentum when the leg gets caught, the leg will straighten with enough force that the ligaments can pop. Around here, the two most common ways this can happen is having a running dog’s leg get caught on underbrush in the forest or down a clam hole on the beach. You will hear the dog yelp loudly, then hobble around on three legs with one of the hind limbs held up.
Some dogs are more prone than others for ACL injury. The first factor in this is genetics. Some dogs have been bred to have a certain stance, especially when being shown at competitions. German shepherds are a good example. If you look up pictures of this breed at a dog show, you will likely see them with their legs positioned far behind them compared to most other dogs. This is an orthopedic nightmare that puts strain on the wrong parts of the knee and wears them down over time. Other breeds have similar characteristics bred into them that increase risk as well.
The other big factor for increased prevalence is being overweight. Just like in humans, dogs’ joints are only meant to hold a certain amount of body weight. When that weight increases, the cartilage and ligaments are put under chronic strain. This will lead to arthritis that weakens the ligaments. When that happens, it won’t take much force to push those ligaments over the edge. So, keeping your dogs trim and avoiding high-risk breeds are the two key factors in decreasing the chances of an ACL tear. If you have a high-risk breed, we also usually recommend over-the-counter joint supplements to keep the knees as healthy as possible Ask you vet which brand they recommend.
Next month, keep an eye out for our next article where we will dive into the common repairs for ACL tears.