The knee joint of the cat is one of the weakest in the body. Just as football players frequently suffer knee injuries, the cat also has knee injuries.
The knee joint is relatively unstable because there is no interlocking of bones in the joint. Instead, the two main bones, the femur, and tibia, are joined with several ligaments. When severe twisting of the joint occurs, the most common injury is a rupture of the anterior cruciate ligament. When it is torn, an instability occurs that allows the bones to move in an abnormal fashion in relation to each other. It is difficult for the cat to bear weight on the leg without it collapsing.
How is the diagnosis made?
The most reliable means of diagnosing this injury is to move the femur and tibia in a certain way to demonstrate the instability. This movement is called a "drawer sign." It can usually be demonstrated with the cat awake. If the cat is in pain, has very strong leg muscles, or is uncooperative, it may be necessary to use sedation in order to examine the joint thoroughly.
How is it treated?
Correction of this problem requires surgery. A skilled surgeon can fashion a replacement ligament and stabilize the joint so it functions normally or near normally. If surgery is not performed within a few days to a week, arthritic changes will begin that cannot be reversed, even with surgery.
What about torn cartilage?
Occasionally the injury that causes a ruptured anterior cruciate ligament will also result in tearing of one or both of the menisci or "cartilages." At the time of surgery, these are examined and removed if necessary.
Is there any non-surgical treatment?
Occasionally, the cat that has a ruptured cruciate ligament will become sound (will no longer limp) even if surgery is not performed. However, arthritis will usually begin and result in lameness a few months later. That cause of lameness cannot be corrected.
Does obesity play a role in this condition?
A special note is appropriate concerning the cat's weight. Obesity or excessive weight can be a strong contributing factor in cruciate rupture. The ligament may become weakened due to carrying too much weight; this causes it to tear easily. Obesity will make the recovery time much longer, and it will make the other knee very susceptible to cruciate rupture. If your cat has a weight problem, there are prescription diets that can be used to assist weight reduction.