The Crux of the Matter: Cranial Cruciate Ligament Injuries

When your dog starts limping, it can be difficult to know how concerned to be. Does he have the canine equivalent of a sprained ankle? Or should you be preparing yourself for the long haul of treatment or even surgery? Sometimes, even when there is a clear diagnosis, you may have more questions. The most common cause of canine hind limb lameness is a torn cranial cruciate ligament. If your dog has been diagnosed with this, the information below may help to clear up some of these issues.

So what is a cruciate ligament?

To understand the role of the cruciate ligament, you need to have a basic understanding of the canine stifle. That is the dog equivalent of the knee, one of the major joints in the back leg. It connects the femur (the large bone at the top of the leg) to the tibia (the shin bone). Like any joint, there are several ligaments in it, or cordlike tissues that connect one bone to another.

The front of the knee contains the patella, also called the kneecap. This is a little bone white sits inside the patellar ligament. Essentially, it acts as a pulley for the patellar ligament, which connects the front of the femur to the front of the tibia. This is involved in the insertion of muscles on bone, and helps to actually move the stifle. Another set of important structures in the stifle are the menisci. These are crescent shaped wedges of cartilage between the two bones, and they act to cushion and absorb shock.

But other ligaments are needed to provide stability to the joint. Two of the most important are called the cranial (front) and caudal (back) cruciate ligaments. They are called cruciate ligaments because they cross inside the joint, as they connect the bottom of the femur to the top of the tibia. The main role of the cranial cruciate ligament (CrCL) is to keep the tibia from sliding forward when the stifle bends. It is analogous to the human ACL (anterior cruciate ligament).

Why does the cranial cruciate ligament tear in some dogs?

There are two major factors involved in cruciate ligament injuries — degenerative disease and trauma. In humans, we think of an ACL tear as a traumatic sports injury — common in basketball players or other athletes. This is not the case in dogs. The primary cause of injury in dogs is usually gradual degenerative change to the ligament, which causes it to lose its integrity. This is often accompanied by chronic inflammation of the joint. The ligament may then tear spontaneously, or after a minor trauma, such as turning while chasing a ball. In some dogs, of course, it is possible for the ligament to tear after a major trauma, like being hit by a car, even if the joint was healthy to start. However, this is a far less common presentation.

CrCL disease is more common in older, large breed dogs. It has a genetic component, and is especially common in Labradors, pitbulls, mastiffs, St Bernards, Newfoundlands, and Rottweilers. Poor joint conformation, like a very slanted tibial plateau (top of the tibia) or a luxating patella can also predispose to a cruciate tear. Spaying or neutering before six months has been associated with a greater risk of cruciate tears in some breeds. And importantly, obesity is also directly linked to CrCL disease. Greater weight places greater strain on the joint, and more fat also causes a body wide pro-inflammatory state.

Because of these underlying causes, bilateral disease is common. Fifty percent of dogs that tear one cruciate will tear the other one within two years.

What happens after the ligament tears?

A torn CrCL typically causes acute lameness. The dog may be running and then suddenly come up lame, potentially even refusing to put any weight on the affected leg. However, some dogs may develop signs gradually, especially if the ligament is frayed or partially torn. Many partial tears will eventually become complete given enough time.

If there was a sudden and complete tear, the initial pain and inflammation will be worst for the first few days. However, after two or three days, most dogs will start to put some weight on the leg, and may seem to temporarily improve. However, once the ligament is torn, the joint is unstable, and the tibia will slide forward with every step. That instability will lead to remodeling and chronic inflammation, and severe osteoarthritis will eventually occur. Over time, the lameness will recur and worsen, and be a cause of chronic pain. Additionally, the extra movement in the joint will often cause damage or tearing of the medial meniscus. This will worsen the instability and inflammation.

How can a torn cranial cruciate ligament be diagnosed?

This injury can typically be diagnosed by your vet on physical exam. The joint will be painful on manipulation, and there may be swelling and joint effusion with an acute injury. If it is a more chronic injury, there may be bony thickening on the medial (inside) of the stifle. Most importantly, the veterinarian will be assessing for “cranial tibial drawer,” or inappropriate forward movement of the tibia. Depending on the size and temperament of the dog, light sedation may be necessary. Cranial drawer is best assessed when the muscles of the leg are relaxed. Although radiographs are not always required for diagnosis, they may be suggested to rule out other causes of stifle pain, like bone cancer or arthritis. They are also required for some types of pre-surgical planning.

At some specialty centers, arthroscopy may be performed as well. This involves inserting a camera into the joint to assess the ligaments and menisci.

What does surgical treatment look like?

Ideally, treatment for a torn CrCl is surgical. Without surgery, the joint will always be unstable. Even with surgery, some amount of arthritis is expected to occur, but the joint should be less painful, and the rate of progression of arthritis much slower.

There are several different types of surgical correction. The most common type is a tibial plateau leveling osteotomy (TPLO). This is a procedure which changes the anatomy of the stifle so that there is no impetus for forward movement of the tibia. A cut is made into the tibia, the top part of the bone is rotated, and a bone plate is then used to hold it in the new position. Another procedure is called a tibial tuberosity transposition (TPA), which is also used to prevent the tibia from sliding forward. This technique moves the front piece of the tibia, the tibial tuberosity, forward to change the angle of the patellar ligament. The modified retinacular imbrication technique (MRIT) is a less invasive surgery, which essentially replaces the role of the cranial cruciate ligament with a very tough piece of suture outside of the joint. For all of these procedures, the joint may also be opened up to remove the torn sections of ligament, or all or part of the meniscus if is is damaged as well. There are too many specific procedures to describe them all thoroughly here, but many of them have equally successful outcomes.

The TPLO and TTA procedures are typically performed only by boarded surgical specialists. The MRIT can be a cheaper and equally effective option for some dogs, although it is not typically performed in very large dogs. At the Animal Clinic of Morris Plains, Dr. Sedlacek routinely performs MRIT surgeries. We can also bring in a surgical specialist for a TPLO procedure, and have that performed at our facility.

What about after surgery?

Most dogs will stay overnight for at least one night after surgery, in order to best control post-operative discomfort. Additional medication will also be sent home to control pain. It takes most dogs about three months to return to full function following a cruciate surgery. They will need to be strictly exercise restricted for at least eight weeks, meaning kept in a small room or crate if not directly supervised, and taken only for short leash walks outside. Repeat radiographs will be needed to assess bone healing if a TPLO or TTA is performed.

The gradual return to function can be hastened by a rehabilitation program. Laser therapy can be used immediately post-operatively and for several weeks afterwards to decrease inflammation. More intensive rehabilitation, such as underwater treadmill sessions, can also be useful. To promote long term joint health, many veterinarians will also suggest joint supplements. Maintaining a healthy weight and engaging in regular low-impact exercise are also important.

There are side effects and risks associated with any procedure. Possible complications include implant failure or infection, a meniscal tear after surgery, and delayed healing. However, most dogs which undergo surgery are able to return to their previous level of function, and are significantly more comfortable than before the procedure.

What if surgery is not an option?

For some dogs, whether because of finances or concurrent medical issues, surgical fixation is not feasible. And some evidence suggests that for small dogs (less than fifteen kg), medical management may lead to an acceptable outcome. For larger dogs, medical management is not ideal, but can be attempted. Medical treatment consists mainly of rest and anti-inflammatory medications. If the dog is overweight, weight loss can significantly improve symptoms. Some dogs may benefit from external braces, but they are often cumbersome, and do not significantly slow the progression of arthritis.


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