Cranial Cruciate Ligament Disease in Dogs

What is cranial cruciate ligament disease?

Cranial cruciate ligament disease (CCLD) is a disease of the knee joint in which the cranial cruciate ligament gradually weakens. Over time, the ligament may partially tear or rupture, causing an unstable knee joint that creates pain, osteoarthritis, and limping.

What are the cruciate ligaments?

The cruciate ligaments are two strong bands of fibrous tissue inside each knee joint that connect the femur (thigh bone) and tibia (shin bone). They cross over each other in the center of the knee and help keep the stifle (knee) stable during movement, allowing it to move in only a hinge-like motion.

The cranial cruciate ligament (CCL) is attached to the front of the tibia and the back of the femur, while the caudal cruciate ligament is attached to the back of the tibia and the front of the femur. Since there are no interlocking bones in the knee joint, ligament strength is essential for preventing abnormal joint motion and damage. 

In dogs, the most common knee injury is a tear or rupture of the cranial cruciate ligament. The cranial cruciate ligament is similar to the anterior cruciate ligament (ACL) in humans and is the main stabilizing ligament in a dog’s knee. Its primary function is to prevent the tibia from sliding too far forward relative to the femur during movement.

What happens with cranial cruciate ligament disease?

With CCLD in dogs, the cranial cruciate ligament undergoes chronic degeneration, causing it to slowly and progressively weaken. Initially, the ligament may become stretched or partially torn, causing only slight or intermittent lameness. With continued use of the joint, the damage often worsens until the ligament ruptures completely.

As the ligament weakens or ruptures, the tibia can move too far forward relative to the femur. This abnormal movement makes the knee unstable, causing pain and lameness and contributing to the development of osteoarthritis. Dogs that rupture the cranial cruciate ligament in one knee are at increased risk of developing a cranial cruciate ligament rupture in the other knee.

A cranial cruciate ligament rupture can also damage the menisci, pieces of cartilage between the femur and tibia that act as shock absorbers in the knee. Meniscal damage can be quite painful and may cause a clicking noise as your dog walks.

What causes cranial cruciate ligament disease?

The exact cause of CCLD is unknown, but it is believed to be influenced by many factors. Factors that may contribute to degeneration of the ligament include:

• Obesity
• Abnormal bone or limb shape that places extra stress on the joint
• Immune-mediated disease
• Other knee problems, such as a luxating patella
• Sex: Female dogs are more likely than males to develop CCLD
• Breed: Boxers, Labrador retrievers, and Rottweilers appear to be at higher risk of developing CCLD earlier in life
• In some breeds, early spaying or neutering

Unlike in humans, a purely traumatic rupture of the cranial cruciate ligament is rare in dogs. A traumatic rupture may occur when the dog is running and suddenly changes direction, placing excessive twisting forces on the knee.

What are the signs of cranial cruciate ligament disease?

Because CCLD typically develops gradually, a dog may have subtle signs before the cranial cruciate ligament ruptures completely. Signs may include:

• Sitting with the back legs to one side (a “lazy sit”) instead of sitting squarely
• Difficulty getting up
• Hesitating before walking up stairs
• Muscle loss or wasting in the affected leg
• Shifting weight away from the affected leg when standing
• Slight or intermittent lameness (limping)

If the cranial cruciate ligament ruptures completely, a dog may suddenly become very lame and may be unable to bear weight on the affected leg. Some dogs “toe touch,” placing only a small amount of weight on the injured leg. A dog may also cry out when the ligament ruptures.

How is cranial cruciate ligament disease diagnosed?

Your veterinarian will examine your dog’s knee and check for abnormal movement using the drawer test or tibial compression (thrust) test. These tests check for abnormal forward movement of the tibia in relation to the femur, which indicates instability in the knee caused by damage to the cranial cruciate ligament. If your dog is in pain, has strong leg muscles, or is unable to relax, sedation may be needed to allow a thorough examination of the joint.

Other diagnostic tests, such as radiographs (X-rays), may also be necessary. Although ligaments are not generally visible on X-rays, your veterinarian may see evidence associated with ligament damage, such as inflammation within the stifle joint or abnormal positioning of the femur and tibia.

How is cranial cruciate ligament disease treated?

Treatment for CCLD may involve surgery or nonsurgical management. Surgery is often recommended to provide additional joint stability, slow the progression of arthritis, and reduce chronic pain. A surgeon can evaluate the joint, address complicating conditions like meniscal tears or patellar luxation, and stabilize the joint so it functions normally or nearly normally. After the operation, you must limit your dog’s exercise for several weeks and rehabilitation may be recommended.

What does surgery involve?

There are various surgical techniques to stabilize the knee joint following cranial cruciate ligament rupture. These techniques fall into two broad categories:

• Extracapsular techniques: These techniques use an artificial ligament, usually placed outside the joint capsule, to stabilize the joint and prevent abnormal motion.
• Bone cutting techniques: Procedures such as tibial plateau leveling osteotomy (TPLO), tibial tuberosity advancement (TTA), and CORA-based leveling osteotomy (CBLO) change the knee’s mechanics to improve joint stability. These techniques are particularly beneficial for larger, more athletic dogs.

During surgery, the surgeon will examine the joint, remove fragments of the ruptured ligament, and repair or remove damaged meniscal tissue. Dogs with concurrent patellar luxation may have that condition repaired at the same time to further stabilize the knee. Your veterinarian or surgeon will discuss the most appropriate surgical option for your dog.

Can cranial cruciate ligament disease be treated without surgery?

Some dogs with cranial cruciate ligament rupture may be managed without surgery. Dogs that weigh less than 33 lb (15 kg) have a better chance of doing well with conservative (nonsurgical) treatment, although there is limited evidence supporting this approach. Dogs that weigh more than 33 lb (15 kg), and dogs with other orthopedic conditions such as patellar luxation, generally have better outcomes with surgery.

Nonsurgical treatment typically involves strict rest followed by a gradual return to activity, along with pain medication, weight management, and veterinary rehabilitation. Laser therapy and acupuncture may also help control inflammation and relieve pain. If improvement does not occur, surgery is usually recommended.

All dogs with a cranial cruciate ligament rupture will develop arthritis in the affected knee. Your veterinarian can help determine the best treatment option for your dog.

What can I expect after surgery?

After surgery, your dog will need limited and controlled activity for at least six to eight weeks. The period of activity restriction may be shorter if a TPLO or TTA has been performed. Provided you can follow your veterinarian's instructions, good function should return to the limb within three months.

Many dogs receive physical therapy (rehabilitation) after surgery to improve recovery, help them return to function, and reduce complications. Your dog may also benefit from “prehab” — rehabilitation designed to improve your dog’s strength before surgery. Your veterinarian will discuss the recommended rehabilitation plan for your dog.

Surgery cannot prevent arthritis, but it can slow its progression and improve long-term comfort and function. Weight control and nutritional supplements may help delay the onset of arthritis.

Does obesity play a role in this condition?

Yes, obesity or excess weight can significantly increase the risk of cranial cruciate ligament injury or rupture. Carrying excess weight places additional strain on the ligament and may also cause changes that make it more likely to tear.

If your dog is overweight, recovery after surgery will often take longer. The other knee is also at greater risk of developing a cranial cruciate ligament injury or rupture, particularly during the recovery period. Weight loss is an important part of promoting a return to normal function and reducing stress on your dog’s joints. Your veterinarian can help develop an appropriate weight-loss plan for your dog.