by John Andersen, DVM
As I drive to work each day, I pass by one particular house with a dog who is always in the yard at the time I drive by. He runs the property line, protecting his territory with a bark and energetic sprinting about. And although I don’t know him or his owners and have never examined him, I’d bet the farm that he’s got a torn ACL in his right rear leg.
The ACL, or anterior cruciate ligament (or more properly in dog anatomy the CCL or cranial cruciate ligament), is an extremely important ligament located inside of the knee joint. It is one of many important structures that give the knee stability, yet flexibility.
Unfortunately, it is also very susceptible to injury, and for unknown reasons the incidence of ACL tears in dogs is on the rise.
Hip dysplasia and hip arthritis in dogs used to get all the press. There are special foundations that assess dogs’ hips for breeding purposes, and clients are often asking questions about the quality of their dog’s hips. Well, move over hips, the canine knee is the new problem of today’s era. ACL tears in the knee cause considerably more pain and lameness and require expensive surgery to repair.
Hip dysplasia is a term used to describe a hip joint that was not quite formed properly, typically a hip joint that is too “loose” and unstable. This leads to painful arthritis over time and is often worsened by obesity.
As stated before, ACL injuries are a much worse problem. While hip arthritis is commonly associated with stiffness and soreness, ACL injuries are commonly associated with non-weight bearing on the leg, more arthritis and pain, and more muscle loss and debility over time.
Many people think of ACL injuries in humans occurring during physical activity like football or soccer, essentially getting the knee turned the wrong way. In dogs, this does occur, however the consensus these days is that most dogs with ACL tears have a slight deformity in the shape of the knee which leads to excessive strain on the ACL. Eventually, after thousands upon thousands of steps, the ACL finally breaks. This is especially evident in younger dogs who have torn one ACL and the next year tear the other. And once the ACL has torn, it is gone and will not heal back together on its own.
Interestingly, we don’t see a lot of minor sprains and strains in veterinary medicine. I think this is because dogs have four legs and if they stumble they’ve got three other legs to catch themselves. So when a dog pulls up completely lame on one of its rear legs, the likelihood is that it either got a cut on its foot or has a torn ACL.
ACL injuries are diagnosed based on history and physical exam. Sudden, non-weight bearing lameness on a hind leg that lasts for more than a day is very likely to be an ACL injury. A chronic, on-and-off history of significant lameness in one leg is also very likely an ACL tear. Some dogs have no obvious lameness because they’ve managed to tear both ACL’s, so their left rear leg is equally as painful as the right and neither is held up off the ground.
The diagnosis is confirmed by being able to move the tibia (shin bone) forward relative to the femur (thigh bone). The ACL normally prevents this movement and we should never be able to feel this type of instability. Some dogs are too tense or in too much pain to tolerate an accurate physical exam. These dogs need to be sedated so we can feel the leg with no tension or muscle tone present.
Lastly, x-rays of the knees and hips are needed to rule out other diseases and also to be aware of the dog’s entire orthopedic situation prior to having discussions about surgery.
Ideally, every dog with an ACL tear should have surgery to stabilize the knee. Without surgery, the knee will be forever unstable and will not only develop arthritis at a fast and debilitating rate, but also these dogs will continue to injure other ligaments in the knee as well as the meniscus.
There are a few different techniques to repair an ACL tear, all of which have been shown to stabilize the knee and slow the progression of arthritis. No technique has been proven substantially better than the others. I have repaired knees on dogs ranging from 10 to 100 pounds, and all of them have benefitted greatly from surgery. Unfortunately, no matter how successful the repair, the dog’s knee will never be the same. I think of it this way: A football player tears his ACL during his sophomore year in college. He gets surgery, works hard on rehab, and comes back the following year and has a successful junior and senior season, even a few years in the NFL. But talk to that guy at 50 and he may be getting ready to have a knee replacement. If he doesn’t get surgery, his sports days are over and his knee replacement happens earlier (knee replacements aren’t going to happen anytime soon in dogs).
ACL surgery is expensive, ranging from $1500-$3000 per knee, depending on the type of surgery performed and where it is done. That is a hard pill to swallow for most of us, and to me is the worst thing about ACL injuries.
That dog I see every morning clearly has an ACL tear and it may be that surgery is cost-prohibitive for his owners, or maybe they think their dog is fine ’cause he keeps barking at me every morning. Either way, get your dog checked out if he’s lame in the rear and pray for bad hips!