Cranial Cruciate Ligament Disease

Brief overview:

The cranial cruciate ligament is inside the dog knee and prevents the femur (thigh bone) from sliding off the back of the tibia (shin bone) and is therefore important to stability of the knee. This ligament deteriorates over time in dogs and often culminates with complete rupture (break/tear) of the ligament and an unstable knee. The diagnosis is made by a combination of physical examination, radiographs (X-rays), and by arthroscopy. Once the diagnosis is confirmed, we address this problem by cutting the tibia (shin bone) and re-aligning it so that the knee is stable and the femur (thigh bone) does not slide off the back of the tibia (shin bone). Once the tibia is healed from this procedure, usually 10-12 weeks following surgery, most dogs (95%) can go back to running, jumping, playing and doing the things they love to do.

Signs of CCL disease

Dogs may show different signs of CCL disease such as limping, difficulty rising from lying down, difficulty going up stairs, or difficulty jumping. However, one other thing that is easy for owners to assess is how their dog sits. This is called the sit test. A normal dog should sit squarely on his/her rump with his or her knees directly under her body. Dogs with CCL disease have discomfort bending their knees fully so they roll over onto their rump and place their legs out to the side. If a dog sits like this they are said to “fail the sit test”. There are different explanations for failing a sit test, but the most common is CCL disease.

Terminology

The appropriate terminology for this ligament in veterinary medicine is the cranial cruciate ligament (or CCL). However, both veterinarians and the public often refer to this as the anterior cruciate ligament (or ACL). Technically, the term ACL is appropriate for people but not dogs. However, the terms CCL, ACL, and “cruciate” are often used interchangeably in veterinary medicine so do not be confused when these different terms are used.

Degeneration versus Traumatic Injury

Cranial cruciate ligament disease is the most common orthopedic abnormality in dogs. The term “disease” is used because in most dogs the ligament deteriorates over time, rather than tearing abruptly. In many dogs this process culminates with complete rupture of the ligament that appears to be a sudden injury, but it really is a culmination of the degenerative process. In a very small percentage of dogs (<1%) the ligament does rupture (tear) abruptly with trauma when it was completely normal just moments before. What this means is that there are many different scenarios or histories for dogs with CCL disease or injury that include:

1. Sporadic lameness/limping that improves and gets worse in cycles. This process corresponds with the degeneration of the ligament, the associated inflammation in the knee that coincides with this degeneration, and the soreness that results from the inflammation and degeneration. At this stage the dog is often referred to as having a “partial tear”.
2. In many patients the aforementioned history then culminates with some dogs becoming abruptly lame and remaining lame. The sudden onset of abrupt and severe lameness often corresponds with complete CCL rupture.
3. Acute onset of lameness that is truly the result of trauma and that corresponds with rupture of the ligament without any preceding deterioration. This scenario is rare.

Anatomy

Dog Ankle Scan First, we need to understand some basic anatomy. The cranial cruciate ligament is in the knee (stifle) of dogs.

To the left, please see a Great Dane showing where the knee is located and an X-ray (radiograph) showing where the knee (stifle) is located.

The knee in the dog basically comprises two bones with the femur resting on top of the shin bone (tibia). There is a smaller third bone (fibula), but the fibula is not relevant to this topic.

In the radiographs to the right, we are looking at the dog knee from the front and in the figure on the right we are looking at the knee from the side. The femur (thigh bone) is on top of the tibia (shin bone).

femur In the dog, the top of the tibia (referred to as the tibial plateau) is sloped downhill and backwards, typically at about 30 degrees. Because of this 30-degree slope of the proximal tibia, the femur wants to slide off the back of the femur. These characteristics are shown in the next figure.

The image to the far left shows a normal knee and the tibial plateau, which is typically sloped down-hill and backwards at about 30 degrees. In that dog the cranial cruciate ligament is intact and so the femur remains perched on top of the tibia. However, the mechanical impetus is for the femur to slide off the back of the tibia (think of a ball on a hill) and this is what happens if the cranial cruciate ligament is ruptured, as in the second radiograph.

The femur does not normally slide off the back of the tibia because the CCL holds it in place. The CCL is inside the knee and is a stout ligament that is oriented specifically to prevent the femur from sliding off the back of the tibia (or from the tibia from sliding forward out from under the femur). See next.

The cranial cruciate ligament is in the dog’s knee. The image on the left shows how the CCL is oriented in order to prevent the femur from sliding off the back of the tibia. The image in the middle shows where the CCL is located inside the knee as you look at the knee from the front. The image on the R is an arthroscopic image looking inside a dog’s knee and showing an intact (ie normal) CCL. It is big, strong, smooth, white structure providing knee stability.

arthroscopic When the CCL ruptures, the femur can then slide off the back of the femur.

The image above is an arthroscopic image looking at a ruptured (torn) cranial cruciate ligament. It looks like the ends of a mop. On the right we can see that the femur is sliding off the back of the tibia.

Diagnosis

When the ligament is completely ruptured it is easy to make a diagnosis of complete rupture based on physical examination because the knee is palpably unstable. However, when there is only a “partial” tear, the degree of instability can be subtle and subjective and it is not possible to make a definitive diagnosis based on the physical exam alone.

Radiographs (X-rays) provide additional information that can be helpful. It allows the veterinarian to see effusion (fluid) in the knee and bone spurs (osteophytes) around the knee, both of which indicate there is a problem in the knee. In some cases, one can also see that the femur (thigh bone) has slid backward on top of the tibia (shin bone), which does indicate CCL rupture. However, in cases of “partial rupture” there are times when both the physical exam and the radiographs are subtly abnormal. Since the CCL cannot be seen on an X-ray, the diagnosis is considered presumptive, or tentative, at this point.

To confirm a diagnosis an MRI can be performed, and is frequently performed in people. However, in dogs MRI is rarely performed to assess the CCL. Rather, in most cases the diagnosis of CCL disease or rupture is made at the time of surgery as this is when the surgeon can see the CCL and confirm the diagnosis. There are two ways to do this. One way is to do an arthrotomy. This is where the surgeon incises and “opens” the knee to look inside with his/her naked eye. Conversely, the more advanced way to do this is to make a small incision and insert a camera (and arthroscope) and evaluate the interior of the knee, including the CCL, on a video screen. Arthroscopy provides a more thorough and less invasive way of evaluating the interior of the knee than does cutting the knee open to inspect it. One of the important points to take away is that the diagnosis of CCL disease or rupture is not confirmed until visualization of the CCL is performed. In rare cases of suspect “partial tear”, the CCL is found to be normal on inspection and some other problem is identified, such as an isolated meniscal tear, posterior cruciate ligament rupture, or cartilage injury. These other causes of lameness are far less common than CCL disease, but they can occur.

Treatment

Once the CCL is ruptured and the femur is sliding off the back of the tibia we need to try and stabilize the knee. In humans they would replace your ACL. In dogs we have not had good or consistent success doing this even though veterinary surgeons have been trying to do so for many decades. It is likely that the substantial (30 degree) slope of the dog tiibal plateau causes breakdown and rupture of any material we use to replace the CCL. In addition, dogs are not very good about resting and doing rehab for 6 months. As a result, veterinary surgeons need to treat these patients differently. The most consistently successful and most commonly performed surgery by board-certified surgeons is the tibial plateau leveling osteotomy.

Tibial Plateau Leveling Osteotomy (TPLO)

We have already discussed above how the tibial plateau is sloped downhill and backwards by about 30 degrees in the average dog. In order to prevent the femur from sliding off the back of the tibia we level the top of the tibia. We do this by making a semi-circular cut in the top of the tibia and rotating that portion of the tibia until the plateau is now leveled. We then have to secure the tibia with a bone plate and screws (similar to how we treat a fracture). The femur then sits back on top of the tibia instead of sliding off the back of the tibia. Please see the next images.

The image above shows a tibial plateau that is sloped backwards at about 30 degrees and the femur has slid off the back. A semi-circular cut (ie osteotomy) is made in the tibia and is shown by a black line in the image on the R. The top segment is rotated until the tibial plateau is now between 0-5 degrees (as shown on the right). A bone plate with 6 screws is then applied to hold the tibia in this position. Now the femur sits back on top of the tibia again as is shown in the image on the right.

Once the surgery is performed the bone (tibia) needs to heal. This takes time, typically about 10 weeks, and is shown below by a montage of X-rays. Note that we usually do not take X-rays at multiple time points following surgery, but this patient was part of one of Dr. Franklin’s published research project closely evaluating bone healing and so multiple radiographs (X-rays) were taken for those patients.

Figure. The images above show a patient immediately prior to surgery, immediately following surgery, and then at 4, 7, and 10 weeks following surgery. What we can see is that where the bone was cut was still visible at 4 and 7 weeks following surgery but that this had filled in with new bone (ie was healed), at 10 weeks following surgery.

Following surgery

The following is a broad overview of the timeline of recovery and does not serve as a set of specific discharge instructions. Detailed discharge instructions are provided to pet owners separately.

Since the tibia (shin bone) has been cut and stabilized, the first major objective following surgery is to have the tibia (shin bone) heal without complication. It usually takes bone 8-12 weeks to heal with most dogs having substantial healing by 8 weeks post-operatively. Additional time is needed for the dog to reach their full potential. A brief review of post-op timelines includes:

1. 2 weeks post-op: The incision is healed. The dog should be bearing weight (with a limp) on the limb at this point most of the time when walking.
2. During month 1: The patient is allowed to walk about 15-30 minutes per day (on leash) and should use the limb >90% of the time when doing so by the end of the first month.
3. During month 2: The patient is allowed to walk 30-45 minutes per day (on leash) and should use the limb the vast majority of the time, although not normally.
4. 8 weeks: Radiographs (X-rays) are usually checked at about this time to make sure that the bone is healing appropriately and most dogs have about 85% healing of their bone at this point in time.
5. During month 3: Most dogs can have extensive leashed walking, jogging, and hiking during this month. Brief, moderated, and supervised periods of off leash running can be started during this month.
6. End of month 3: Dogs are usually released to unlimited activity at the end of month 3.

Prognosis

The prognosis with TPLO is excellent. Approximately 94% of owners of dogs treated with TPLO ultimately report a good or excellent outcome.

Potential Complications

Major complications with TPLO are infrequent. Dr Franklin has performed thousands of TPLOs dating back to 2009 and his re-operation rate is currently less than 1%. However, numerous complications are possible and include infection (most common), tearing of the meniscus weeks or months following TPLO, incisional complications like bruising or fluid accumulation, fracture of the tibia, inflammation of the patella tendon, anesthesia-related complications including death, and others.

Summary Points

- CCL disease is the most orthopedic abnormality in dogs
- Physical exam, radiographs (X-rays), and visualization of the CCL, preferably with arthroscopy, are all important in confirming a diagnosis of CCL disease.
- TPLO is the most thoroughly researched and supported treatment of CCL disease in dogs.
- Prognosis with TPLO is excellent and major complications are infrequent but all owners should be aware of the possibility of complications.
- Recovery period is 3 months with the dog having minimal, moderate, and substantial activity in months 1, 2, and 3 respectively.

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