Cranial Cruciate Ligament Disease

The cranial cruciate ligament (CrCL) is an important stabilizer within the knee joint (stifle) of dogs. It is analogous to the human anterior cruciate ligament (ACL). The CrCL is the ligament that helps the stifle function as a hinge joint, acting as a band of tough fibrous tissue connecting the femur (thigh bone) to the tibia (shin bone). The function of the CCL is to prevent the tibia from shifting forward relative to the femur. It also helps to prevent the stifle from over-extending and internally rotating. When standing, walking, and running, a dog’s stifle joint is reliant on the stability provided by an in-tact CrCL, making this structure of critical importance to sound function.

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What is cranial cruciate ligament disease?

Cranial cruciate ligament disease refers to the process that causes the CrCL to tear or rupture. The nature of CrCL disease is very different in dogs when compared to humans. In dogs, likely the result of a combination of factors, the CrCL degenerates or weakens over time (think of a woven rope fraying strand by strand). This process weakens the ligament, eventually leading to rupture with relatively minimal trauma. The underlying process is not entirely understood at this time. Research has found various links that can include factors such as genetics, obesity, individual differences in anatomy and conformation, poor physical condition, age, influence of hormones, and inflammatory conditions of the joint. Cruciate disease is often thought of as a disease of large breed dogs. While it is true that large-breed dogs are more prevalent, small and medium-breed dogs are often affected as well. Because this is a degenerative condition, approximately 50% of dogs that tear one cruciate ligament may tear the other side. This occurs, on average, within one to two years of the initial diagnosis.

What is happening inside a stifle with cranial cruciate ligament disease?

Osteoarthritis (OA) develops early in the disease, often presenting before the ligament tears. As the joint becomes more inflamed and as the CrCL loses mechanical function, the joint becomes more lame and eventually becomes unstable, resulting in a classic findings of cranial tibial thrust or caudal femoral subluxation. In many dogs, the instability can damage other structures in the joint, in particular the menisci (cartilage cups), which function as “shock absorbers” and stabilizers. The medial meniscus is particularly susceptible to crushing or tearing within unstable stifle joints.

How do I know if my dog has cranial cruciate ligament disease?

Stiffness and limping in one or both back legs is the most common signs of a cranial cruciate ligament tear. This may appear suddenly during or after exercise in some dogs or progressive and intermittent in others. The dog may show subtle changes in gait, a tendency to shift weight off the affected leg when standing in place, or the inability to sit straight. Many cruciate tears start as partial tears of the ligament but most often progress to complete tears unless surgical stabilization is performed before their progression. As the CrCL continues to tear further, clinical signs worsen. A full tear usually results in abrupt and severe lameness in the affected leg.

How is cranial cruciate ligament disease diagnosed?

While there are certainly other causes of lameness (limping) in the hind leg, CrCL tear is the most common. Age, breed, and history are all taken into consideration, in addition to a physical examination by your veterinarian and diagnostic imaging, when diagnosing a cruciate ligament tear. Radiographs (x-rays) are often used as a diagnostic tool to evaluate the degree of arthritis and the presence of effusion (fluid swelling) in the joint and to rule out other causes of lameness. Direct examination of the cruciate ligament is done at the time of surgery. The meniscus is also examined at that time to evaluate for any evidence of injury or tearing.

Repair options

Many repair options exist to provide stabilization following CrCL injury or tearing. These can be generally grouped into 3 categories

  1. Extra-capsular repair – these methods involve the use of synthetic materials placed near the joint to take over the function of the damaged cranial cruciate ligament, relying on eventual buildup of scar tissue (fibrosis) to permanently stabilize the joint over time. Examples of this technique include the lateral suture technique or the Tightrope repair technique. Other versions or variations of these options also exist
  2. Intra-capsular repairs – these methods involve the use of synthetic or natural grafts to directly replace the damaged cruciate ligament. Many options have been used historically. At this time, we are still in need of better studies to validate some of the existing techniques. Grafts are sometimes combined with extra-capsular repairs or geometry modifying procedures.
  3. Geometry modification – various techniques exist, including TPLO (tibial plateau leveling osteotomy), where the concept of surgery is to change the standing angle within the knee. By doing this, the new angle provides immediate stability during movement and makes it such that the CrCL is no longer necessary in most cases to provide stability during normal movement. These techniques are robust and have a proven track record of success in all sizes and breeds of dogs with some information now emerging for their application in cats. TPLO, CBLO, TTA, Modified Closing Wedge, are all examples of geometry modifying procedures. TPLO is perhaps the most commonly performed and well studied procedure and can be applied to the majority of patients with excellent outcomes. There are some select cases, where other techniques may be applied instead of or in combination with TPLO depending on the patient bone conformation and nature of their specific cruciate disease.