Visiting Vet: Tearing the cranial cruciate ligament

It’s tough on retrievers. And receivers.

A large, athletic dog may be at risk for tearing a ligament. — Trac Vu

By the time you read this, the Super Bowl will be over. We will know which team triumphed and, I imagine, at least one more NFL player will have torn their cranial cruciate ligament.

I did not grow up watching football. My parents were typical first-generation Jewish Americans, born to immigrant parents, raised in urban poverty. Their entire focus was on education and hard work. Sports were something “those other people” were interested in. Not us. We went to college and read books and watched PBS. Nonetheless, when I was in veterinary school, learning about common orthopedic injuries in large, athletic dogs, I heard professors and other veterinarians tell owners that a torn cranial cruciate ligament in the knee was also a common injury in skiers and football players. I repeated that phrase for almost 40 years without ever having watched a football game.

The knee in dogs is in the hind leg, and is also called the stifle. It is a complicated joint, anatomically similar to the human knee, having a patella (kneecap) and similar ligaments connecting all the moving parts. This can be endlessly confusing to laypeople since in horses (and many other farm animals), the hind leg stifle joint is just called the stifle, and the term “knee” is used to describe a joint in the front leg that is actually equivalent to the human wrist. This “knee” bends in a way that allows the horse to “kneel down.” But let’s stick to dogs today, and agree that when I say “knee,” I am referring to the stifle joint in the hind leg that is structurally more-or-less the same as Patrick Mahomes’ knee.

Here’s a quick review of the anatomy of the knee. The big thigh bone is the femur. The main lower leg bone is the tibia. These bones meet at the knee, a very complex joint. All you need to know today is that there are two ligaments, the cranial (or anterior) cruciate ligament (CCL) and the caudal cruciate ligament. These run from the end of the femur to the top of the tibia, forming an X inside the knee, hence the name “cruciate,” meaning crossed. One ligament goes from the back of the femur to the front of the tibia, and the other goes the opposite way. These ligaments stabilize the stifle, so when weight is put on the leg, they prevent hyperextension and excessive rotation.

Except when too much pressure is applied, especially pressure with torque. Like that slo-mo NFL replay of some huge guy being taken down by two other huge guys and the commentator says, “Wow, Troy. See how his knee got caught and twisted as he went down.” Then the guy is helped to his feet and limps off, praying he hasn’t torn his CCL. Big dogs do the same thing. Say your dog, Eagle, is a 60-pound Labrador who loves to chase the ball. One day he goes tearing around the yard, leaps into the air, spins sideways to grab the tennis ball in his mouth, then lands with a twist and a sudden yelp. He then limps over to you, clearly hurt.

When you get to your veterinarian, Eagle’s size, age, and breed, and the history of how the injury occurred, will suggest a CCL tear, but the most definitive diagnostic tool is palpating the knee, the “drawer sign.” With one hand above and one below the knee, your vet will manipulate Eagle’s lower leg. There shouldn’t be much “give.” If the lower leg can slide forward, like opening a drawer, that’s a torn CCL. Sometimes the knee will be palpably swollen, warm, and sore. Other times, not. Sometimes if Eagle is particularly muscular or anxious, just the muscle tension may be enough to mask the “drawer sign.” So a positive drawer sign definitely diagnoses a CCL rupture, but a negative result does not necessarily rule it out. Anesthesia may be required for definitive diagnosis. Radiographs may or may not help. CCL rupture is most common in larger, young, athletic dogs. Breeds predisposed include Labrador, golden, and Chesapeake retrievers, Rottweilers, and American Staffordshire terriers. Older, overweight dogs are also at higher risk. Dogs who tear one CCL often tear the other sometime later.

Of course, not every knee injury is a CCL tear. Dogs can strain and sprain things without tearing ligaments. If Eagle comes up suddenly lame, you can try resting him for a few days, but don’t wait too long. Smaller dogs (under 30 pounds) may sometimes heal well enough with just several months of strict exercise confinement, but most dogs require surgical repair. If the knee is left unstable, significant, irreversible arthritic changes are sure to happen, leading to chronic pain and lameness.

In the old days, general practitioners routinely did CCL surgical repairs, using one or two simple techniques. Over the past few decades, however, new and probably better methods of repair have been developed. These techniques should be done by specialists. They are more expensive and more invasive, but likely provide faster recovery, better stability, and better long-term results, especially in larger dogs. Eagle will need dedicated postoperative care, including strict confinement, pain medication, and weight management, followed by gradual reintroduction of exercise and rehabilitation.

As far as football goes, I will admit, I used to be a bit of a snob. Then two things happened. My husband bought a large ( I mean large) flat-screen television, and my (then) teenage daughter made me watch the Patriots play in the 2019 Super Bowl, patiently explaining to me how it all worked. By the end of the game, I was hooting and hollering along with everyone else. I was hooked. I hope I haven’t jinxed anyone with my talk of knee injuries.and even though I went to vet school in Philadelphia at the University of Pennsylvania, and I agree the Chiefs should change their name and logo. I’m rooting for my favorite QB, Patrick Mahomes. Time to go make the nachos.