My Dog Has Torn Their Cruciate Ligament. What Does That Mean?
It’s finally stopped raining. You head outside to play fetch with your dog. Fido sits excitedly at your feet, waiting for you to throw the ball. You chuck it as far as you can. He takes off after it, picks it up and turns. As he does so you see him slip on the wet grass. You hear him yelp, and then back he comes limping on three legs, holding his back leg in the air. Your face crumples because you know exactly what’s just happened … Fido has torn his cruciate ligament. So, what is the cruciate ligament and how is it injured?
There are actually two cruciate ligaments, the cranial and caudal. The word cruciate means ‘cross shaped’, and these two ligaments cross over each other within the dog’s stifle (knee) joint. The cranial ligament passes from the inner aspect of the knee at the front, to the outer aspect of the knee at the back (this ligament is red in the picture below). The caudal ligament passes from the inner aspect of the knee at the back, to the outer aspect of the knee at the front (this ligament is blue in the picture below). It is more common to injure the cranial cruciate than the caudal, and so we are going to focus on this ligament.
The stifle is a hinge joint, which means that it only allows motion in one plane. It can move back and forth, but not side to side. The joint is relatively unstable as there are no interlocking bones, and so its stability relies on a number of ligaments, including the cruciates. As well as helping prevent rotation of the stifle, the cranial cruciate ligament stops hyperextension (which is where the shin bone moves forward on the thigh bone).
The anatomy and function of the cruciate ligaments in dogs is similar to that in humans, but with slightly different names.The cranial is known as the anterior cruciate ligament, and the caudal the posterior cruciate ligament. Again, the anterior cruciate is the most frequently injured; however, the most common mechanism of injury does differ between the two species.
In humans, the anterior cruciate ligament is most likely to be torn or ruptured due to a traumatic event. Recently Sam Kerr, the captain of the Matilda’s, ruptured her ACL while performing a drill at training when she was turned to shoot the ball. In this instance her foot was planted on the ground while her body rotated over the top. Another common way an athlete injures the ligament is to land from a height, causing the knee to hyperextend. And while a dog can tear their cranial cruciate ligament in the same traumatic ways, it is more likely that the ligament has been progressively weakening over time secondary to repeated micro trauma or arthritic disease, to the point where it then tears or ruptures.
So, what is the difference between a tear and rupture?
A tear can be either partial or complete. A partial tear means some of the ligament fibres have been torn, but not all. You may have heard someone grade a tear as either Grade I, Grade II or Grade III. This simply refers to the severity of the tear. The lower the grade, the less fibres involved. A grade IV tear is a complete tear. This means the ligament fibres have completely torn away from each other. A grade IV tear is the same as a rupture.
Can any other structures in the stifle be involved?
While difficult to determine on a physical assessment, it will often be discovered during surgery that a dog’s meniscus has also torn. The meniscus (yellow in the picture above) is a cartilage-like structure that sits within the knee joint. It’s main functions are shock-absorption, proprioception (awareness of the position of each part of the body) and load bearing. There are two menisci - the medial and lateral - and it is the medial meniscus that is most likely to be involved when a dog tears their cranial cruciate ligament.
What are the risk factors for Cranial Cruciate Ligament Disease (CCLD)?
CCLD can affect dogs of any size and age; however, there are risk factors that predispose a dog to its development. These include:
Age - the older the dog, the more likely there is to be degeneration of the ligament (think of this like a fraying rope).
Obesity.
Poor physical condition.
Poor conformation.
Breed - including, but not limited to, Retrievers, Labrador Retrievers, Newfoundlands, German Shepherds, Boxers and Staffordshire Terriers.
Weekend Warriors - for example, dogs (and humans) that do no exercise during the week and then tear around an agility course on a weekend.
It is also important to note that at least half of dogs that have CCLD in one knee will likely develop it in the other at some stage.
What are the signs of CCLD?
Many of the sigs are similar to those of a dog who presents with osteoarthritis in the stifle. However, a dog with arthritis in the knee joint is also likely to have a weakened cranial cruciate ligament. Signs of CCLD include:
The dog does not sit square, or the stifle is at an angle when the dog sits. Keep in mind though that a number of dogs do not sit square, simply because they have a ‘lazy sit’.
Difficulty rising from a lying or sitting position.
Difficulty getting up onto furniture or into a car.
Muscle atrophy (loss of muscle mass), particularly in the quadriceps muscles on the front of the thigh.
Decreased range of movement of the stifle.
Abnormal gait - from a slight limp, to toe-touching, to not weight bearing through the limb at all. If a dog has CCLD in both knees an abnormal gait may not be so evident as both sides may look even.
How is a cruciate ligament tear or rupture diagnosed?
Subjective History: this is where you, the owner, give the veterinarian as much information as you can regarding what you have observed. This will include how your dog injured their knee and any of the signs mentioned above. If you have a dog that is still able to weight bear, keep in mind that dogs are fantastic at hiding signs of pain. Have you ever taken your dog to the vet because they were limping at home, just for the limp to miraculously disappear when they walked through the clinic door? To counter this I would take videos of what you are observing at home to show to your vet.
Objective Assessment: this is where the vet will perform a physical examination of your dog. One test they may perform is the anterior (or cranial) draw test. This is where the shin bone is drawn forward on the thigh bone. Abnormal movement indicates laxity of the ligament. This can be difficult to perform in larger dogs, or whose thigh muscles are strong, so it may need to be done under sedation or anaesthesia to ensure the dog is fully relaxed.
The vet may, or may not, do a radiograph (usually an x-ray). A radiograph is done to look for joint effusion (fluid accumulation or swelling), the degree of arthritis in the stifle, to establish the best surgical plan and to rule out concurrent conditions such as bone cancer.
So, your dog has been diagnosed with a cranial cruciate ligament tear. What happens now?
This is going to be dependent on a number of factors such as the size of your dog, their age, the degree of the tear, whether they are weight bearing or not, how well the dog is able to carry out every day activities, and how active the dog is normally. The two main management options are either conservative treatment (non-surgical) or surgery.
In my next blog post I am going to explain the two main surgical options and the post-surgical rehabilitation for these. Then in the third blog post of this series, I will discuss conservative management.
I hope today’s post has given you a greater understanding of cranial cruciate ligament disease. And, if your dog has had a cranial cruciate ligament tear I would love for you to share with how they injured their knee in the comments below. Two of my dogs have had partial tears of their cruciate ligaments. One tore theirs slipping on wet concrete whilst being an idiot, while the other tore theirs while chasing a wallaby. If you know my dogs, this will not surprise you in the least!
And, as always, if you have any questions please feel free to drop them into the comment section or flick me an email by clicking here.
If you are concerned your dog may be experiencing pain then my eBook, ‘How to Tell if Your Canine Companion is in Pain’ is a helpful resource full of advice & tips that help you monitor them. You can purchase a copy for only $19.95 (AUS) by clicking here.
