THE KNEE: A BIG OR SMALL PROBLEM?
Janet was clearly concerned when she brought Adidas in to see me. Adidas was normally a happy, bounding 6-year-old Labrador Retriever that ran to greet everyone. But, three days ago, that had abruptly stopped. She had watched Adidas trot around the yard when suddenly he yelped and held his right rear leg up. She ran out to him and checked where he had been to make sure there were no holes he had stepped in or things on the ground. When she was satisfied that he hadn't injured himself in an obvious was, she took him in and let him rest. Unfortunately, things did not improve. He still wasn't using that right rear leg when he walked in to see me except for occasionally trying to touch his toes to the ground. You could tell he hurt. She was worried that something was broken and, in truth, she was right. Something did break. It just wasn't a bone.
You may have heard of the injury we uncovered in Adidas by a different name in people, especially if you are a sports fan. The anterior cruciate ligament (ACL) is a crucial ligament in the knee that keeps it stable, especially from drawer motion - i.e. moving inappropriately forwards and backwards. Because dogs stand on four legs and not upright on two, it gets a slightly different directional name in dogs compared to us, but it's the same ligament: the cranial cruciate ligament (CCL). This is what Adidas had broken.
In medium to large breed dogs, especially those that are overweight and middle-aged to older, this is a fairly common orthopedic injury (it happens in small dogs, just not often). In people, this is very often traumatic. Sports fans probably think about a football player getting clipped running downfield who then ends up with an ACL tear. In dogs, though, this is usually a 'wear-and-tear' injury. The ligament just gets strained over time until, usually during relatively normal activity, it just can't do its job anymore and gives way, tearing partially or completely. (This is why overweight dogs, who have more 'wear-and-tear', suffer from this more). This is definitely a painful injury and can lead to many short and long-term changes in the knee, especially if not addressed appropriately.
Generally, this is a surgical fix. There are many variations of the surgery, and a big factor in which options are available is the size of the dog. We recommend surgery early for two primary reasons. First, if not done, even if the dog retains some use of the leg, those chronic changes can easily lead to a chronic pain state that is not healthy for the dog. Second, we know that statistically within two years of the one side rupturing, there is a 50% chance of the other side also rupturing. If the first side is not stabilized and healthy by that time, this can become very difficult for the dog, since they do not have any truly good, stable knees to stand on.
Adidas got surgery and did well. Unfortunately, almost one year to the day of the first injury, Adidas' other knee gave way and he needed surgery on that one as well. But, as a result of the early intervention, successful surgery and post-op rehab, Adidas is thriving today.
In small dogs, we see another common knee problem far more than we do in big dogs. Just as CCL injuries are far more likely in big dogs, a medial luxation of the patella (MLP) is far more common in small dogs. We can notice it at almost any age.
The patella is the "kneecap". It sits in a small 'valley' at the end of the femur (the thigh bone) and is held in place by four tendons that branch out from it like a giant "plus" sign. Many small dogs are born with a 'valley' that is too shallow and/or tendons that are not as stable or strong. Because of this, the knee-cap may start to fall out of place, or dislocate (this is called luxation). While it can go to the outside of the leg (called a lateral luxation), it most commonly goes towards the inside (or, the medial direction), which is where it gets its name.
This disease has four grades depending on how easily the patella can be luxated. Any degree of MLP predisposes that knee to developing arthritis more than if it did not have an MLP. This will usually happen years down the road. Some dogs will develop regular lameness issues from this disease. That is why dogs with somewhat regular lameness or high-grade disease may need surgery to repair this problem as well (typically, this involves deepening the 'valley' to give the patella a better place to sit.)
Next month, Dr. Hendrickson will join us again to discuss another common feline problem. After that, I'll be back to discuss the single most common orthopedic problem in dogs: arthritis.
I hope you have a good summer, and I'll be back in July.
Dr. Brandon Stapleton
Managing Doctor/Medical Director
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