Cruciate Ligament Rupture in Cats

By Malcolm Weir, DVM, MSc, MPH; Ernest Ward, DVM


What are the cruciate ligaments?

The word cruciate means 'to cross over' or 'form a cross'. The cruciate ligaments are two bands of fibrous tissue located in each knee joint. They connect the femur and tibia (the bones above and below the knee joint). One ligament runs from the inside to the outside of the knee joint and the other from the outside to the inside, crossing over each other in the middle. The two cruciate ligaments are called the cranial cruciate ligament and the caudal cruciate ligament.

The cranial cruciate ligament (CCL) is like the anterior cruciate ligament (ACL) in humans. The cranial ligament is anchored on the front part of the lower leg bone (the tibia) and runs up and to the back of the upper leg bone (the femur).

cruciateligamentcolour_updated2017-02The caudal cruciate ligament is anchored in the back of the tibia and connects to the front of the femur. The CCL is the main supporting ligament in a cat’s knee. Their primary function is to prevent the lower leg from moving forward of the femur during movement. When the ligament is torn or unstable, the lower leg slides forward.

Cruciate ligament injuries are common in dogs and relatively uncommon in cats.

"Cruciate ligament injuries are common in dogs and relatively uncommon in cats."

How does a cruciate injury occur?

The knee joint of the cat is one of the weakest in its body. It is relatively unstable because the knee joint has no interlocking bones. Instead, it is held together by several ligaments, including the cruciate ligaments, which allow it to move back and forth like a hinge but restrict its front-to-back and side-to-side motion.

When severe twisting of the knee joint occurs, the anterior or cranial cruciate ligament most commonly tears or breaks. When the cranial cruciate ligament is torn, instability occurs that allows the bones to move abnormally in relation to each other. It is difficult for the cat to bear weight on the leg without it collapsing. This condition is painful and, if untreated, can lead to permanent joint complications.

How is a cranial cruciate ligament rupture diagnosed?

An acute cruciate injury often has a history of trauma, such as an automobile accident or a fall from a height. In some cats, cruciate injury is secondary to another knee problem, such as a luxating patella (a kneecap that slips out of place). The most reliable means of diagnosing that a cruciate injury is torn can often be demonstrated with the cat awake. If the lower part of the leg can be pulled forward, a 'positive drawer sign' is said to occur and is highly suggestive of a torn CCL. If the cat is in severe pain, has strong leg muscles, or is uncooperative, it may be necessary to use sedation to examine and palpate the joint thoroughly.

Is other joint damage common?

Occasionally the injury that causes the cruciate injury also results in the tearing of one or both of the menisci or cartilages between the bones in the knee joint. These menisci may be viewed as 'shock absorbers' for the joint. At the time of surgery, these are examined and repaired as necessary. The collateral ligaments (the two fibrous bands running along the sides of the knee) or the patellar ligament (running along the front of the knee joint with the patella or 'kneecap’) may also be injured.

How is a cruciate ligament tear treated?

Correction of a torn CCL often requires surgery. A skilled surgeon can create a replacement ligament and stabilize the joint, so it functions normally or nearly normally. Post-operatively, you will need to limit your cat's exercise for several weeks; this is not a difficult proposition for the average housecat.

"Correction of a torn CCL often requires surgery."

Is there a non-surgical treatment for cruciate ligament rupture?

Surgery may not be advised in certain cases for various reasons. If surgery is not an option for some reason, the cat's activity must be severely curtailed, with no jumping or running allowed for up to six weeks. Unfortunately, when left untreated, the cruciate damage will result in a rapid onset of arthritis in the affected joint. If surgery is performed, the cat may still develop arthritic changes in the joint, but this will occur much more slowly and to a lesser degree than if surgery is not performed.

Does obesity play a role in this condition?

Obesity or excessive weight can significantly contribute to cruciate ligament rupture. The ligament may become weakened due to the strain of carrying too much weight, or other factors associated with obesity may cause ligament changes, causing it to tear more easily. Obesity will make the recovery time much longer and the other knee more susceptible to future ligament injury or rupture. Weight loss is as critical as surgery in ensuring rapid return to normal function and is a preventive measure to help protect against this debilitating injury.

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