The cranial cruciate ligament (or CCL, see Figure 1.) is one of the most important stabilizers inside the knee (also called ‘stifle’) joint, the middle joint in the back leg. In humans the CCL is called the anterior cruciate ligament (or ACL).
The meniscus (Figure 1) is a ‘cartilage-like’ structure that sits in between the thigh and shin bones. It serves many important functions in the joint such as shock absorption, position-sensing, and load-bearing and is frequently damaged when the CCL is injured.
Rupture of the CCL is one of the most common reasons for hind limb lameness, pain and subsequent arthritis. Since the development of this problem in dogs is much more complex than in humans, and dogs suffer from different degrees of rupture (partial or complete), the condition is referred to as ‘cranial cruciate ligament disease’ (or CCLD). While the degree of lameness with CCLD varies, it invariably causes arthritis in the long-term.
Traumatic rupture can happen in dogs but it is extremely rare. Most commonly CCLD is caused by a combination of many factors, including aging of the ligament (degeneration), obesity, poor physical condition, conformation and breed. Ligament injury is a result of subtle, slow degeneration that has been taking place over a few months or even years rather than the result of acute (sudden) trauma to an otherwise healthy ligament. This difference between people and dogs explains two important features of canine CCLD:
- Half of the dogs that have a cruciate ligament problem in one knee will likely, at some future time, develop a similar problem in the other knee.
- Partial tearing of the CCL is common in dogs and frequently progresses to a full tear over time.
Cruciate disease affects dogs of all sizes and ages and rarely cats. Certain dog breeds are known to have a higher incidence of CCLD (such as Rottweiler, Newfoundland, Staffordshire Terrier, Mastiff, Akita, Saint Bernard, Chesapeake Bay Retriever, and Labrador Retriever) while others are less often affected (such as Greyhound, Dachshund, Basset Hound, and Old English Sheepdog).
Female and neutered dogs are at greater risk of developing CCLD. The exact reason for this finding is unknown and the benefits of neutering your pet (such as decreased risk of cancer) certainly outweigh this increased risk. A genetic mode of inheritance has been shown for Newfoundlands.
Poor physical condition and excessive body weight are risk factors for the development of CCLD. Both of these factors can be influenced by pet owners. A good fitness level of regular activity is advised and will also help avoid obesity.
As mentioned, progressive degeneration of the CCL from very mild partial tearing to a complete tear in the later stages of the disease is common in dogs. You may not notice a severe lameness initially, especially if both knees are affected. One common symptom is that dogs will not sit ‘square’ anymore but rather put their leg(s) out to the side when they sit down.
You may also observe that your dog has:
- difficulty rising
- trouble jumping into the car
- decreased activity level
- muscle atrophy (decreased muscle mass in the affected leg)
- decreased range of motion of the knee joint
- a popping noise (which may indicate a meniscal tear)
- swelling on the inside of the shin bone (fibrosis or scar tissue)
Many dogs will shift their weight away from the damaged leg when they stand but the lameness is less obvious during walking especially with partial tears of the CCL. When a partially damaged ligament ruptures completely or the meniscus becomes damaged your dog may also become non-weight bearing lame and may hop on three legs. This change in lameness may happen suddenly, usually without major trauma (a minor traumatic event may cause the partially torn ligament to rupture completely). Dogs with chronic (late stages) of CCLD usually show symptoms associated with arthritis, such as:
- decreased activity
- unwillingness to play
Diagnosing complete tears of the CCL is easily accomplished by a combination of observation of your pet’s gait, palpation of the knee, and radiographs (x-rays). Early partial tears can be a bit more complicated and may sometimes require advanced imaging such as MRI or surgical exploration to physically examine the ligament.
X-rays are usually taken to:
- confirm joint effusion (fluid accumulation in the joint which indicates that there is a problem within the joint)
- evaluate the degree of arthritis
- aid in surgical planning
- rule out concurrent disease conditions such as bone cancer
For certain treatments (TPLO, TTA) specific X-rays are required and hence your board-certified surgeon may need to repeat radiographs of the knee even if your primary care veterinarian has already taken some.
Specific palpation techniques that veterinarians use to confirm a problem with the CCL are the ‘cranial drawer test’ and the ‘tibial thrust test’. These tests confirm abnormal motion in the knee and hence a rupture of the CCL.
X-rays do NOT show the status (i.e. intact or damaged) of the CCL or the meniscus since those structures cannot be seen on X-rays. It is crucial that the surgeon evaluate both of these structures (meniscus and the cruciate ligament) when performing the selected surgical repair. This can be accomplished either via an arthrotomy (opening of the joint) or with the use of a minimally invasive camera (arthroscope) and is generally combined with the surgical stabilization procedure itself since both procedures require full anesthesia and clipping of the animal.
Postoperative care at home is critical. Premature, uncontrolled or excessive activity, risks complete or partial failure of the surgical repair. When choosing a suture repair, this failure may simply mean that the surgery has to be performed again but when choosing an osteotomy technique this failure may mean that a much more invasive approach is now needed. Proper postoperative care limits activity to leash walking for a minimum of 8 weeks and no running, jumping, rough-housing, or off-leash activity. While it is important to control activity it is also important to maintain muscle mass and joint function (range of motion).
Studies show that physical therapy can speed the recovery and improve final outcome regardless of the chosen surgical technique. This rehabilitation should start immediately after surgery and usually includes a regime of passive range of motion, balance exercises, controlled walks on leash and so forth. Discuss details with your board-certified surgeon and/or primary care veterinarian.
The long term prognosis for animals undergoing surgical repair of CCLD is good, with clinical reports of improvement in 85-90% of the cases. Unfortunately, arthritis progresses regardless of treatment, however much slower when surgery is performed. Therefore, medical arthritis management/prevention is recommended for any dog with CCLD regardless of the chosen surgical. It is important to realize that arthritis is a progressive disease and develops fairly quickly in an injured (or damaged) stifle joint.
The most common complication caused by CCLD is long-term impairment due to arthritis. Other complications associated with arthritis and CCLD include loss of range of motion in the joint, muscle atrophy, and loss of full function of the limb, as well as decreased activity. Unfortunately, neither human nor veterinary surgeons are able to completely restore normal joint anatomy and function. Even with surgery some progression of arthritis is expected. It is important to understand that arthritis is an irreversible disease and hence everything should be done to prevent its development or progression. Therefore, two steps are crucial when treating CCLD:
- surgical repair and
- medical management of arthritis
The second most common complication caused by CCLD is tearing of the meniscus. Due to the instability in the knee joint, the inside (medial) meniscus frequently gets damaged. This can happen during the initial injury or even later after surgical repair of the CCL. Meniscal damage in dogs is addressed by removing the damaged parts of the meniscus since it is too small to repair. A meniscal tear is very painful and if a damaged meniscus is left in place the animal will not regain full function. Removal of the damaged parts of the meniscus (if present) will be performed by your board-certified surgeon during the chosen procedure to address the knee instability.
As previously mentioned, rupture of the CCL in the opposite limb happens in more than half of the animals.
When choosing the best treatment for your dog, possible complications should be considered. Complications that can be observed with any technique include complications associated with:
- patellar (knee cap) luxation (dislocation)
- failure to return to normal function
- progressive arthritis
Complications specific to the osteotomy techniques include delayed healing of the bone, non-healing of the bone, healing in an incorrect position (i.e. with rotation of the limb), fracture of the bone, and failure/breaking of the screws/plates. These complications can be serious and may require multiple revision surgeries. Again, serious complications that require a second surgery are rare when the procedures are performed by an experienced surgeon and exercise-restriction guidelines are followed.
If your dog is overweight, a weight loss program might be advisable. Your veterinarian will gladly help you to determine the ideal weight of your pet. Regular, daily activity is another important component of CCLD prevention.