The knee joint of the cat is one of the weakest joints of the body. Just as football players frequently suffer knee injuries, the cat also has knee injuries. Fortunately, cruciate ligament injuries are relatively uncommon in the cat. The doctors at the Animal Hospital at Thorndale recommend that if your cat is limping, it is important that it be examined by a veterinarian. Our pets limp because they are in pain. Because cats are especially good at hiding illnesses and injuries, it is safe to assume that a limping cat is a very uncomfortable cat.
Cruciate Ligament Rupture in the Cat
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, 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.
Contributing Factors
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.
Overgrown toe tails that catch in objects can lead to a tear as the cat jumps off, twisting the leg. Other traumatic injuries can be involved in tearing the cruciate ligament in cats.
Prevalence
This type of injury is relatively uncommon in the cat, although it can and does occur. It is the most common orthopedic injury in the dog.
Clinical Signs
Most owners report the sudden onset of moderate to severe lameness in the cat. If the lameness is not addressed with medical attention, there is usually improvement after 4-5 weeks.
Causes
Trauma can be responsible for cruciate injuries, although the trauma may not always be observed by the owner. As noted above, obesity can predispose the cat to this type of injury, also.
Diagnosis
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. Torn ligaments do not show up clearly as such on x-rays. It may, however be important to rule out fracture, or other bone disease. The position of the femur relative to the tibia, and inflammatory changes in the knee fat pad may indicate a cruciate ligament tear.
Treatment
Many cats that have a ruptured cruciate ligament will become sound (will no longer limp) even if surgery is not performed. However, arthritis is likely later on. Pain relief medications are usually prescribed during the acute phase after the injury. It is very important to control the weight of the cat as added stress on the joint will perpetuate the instability. Over time, the body works to thicken the other ligaments around the knee.
Definitive correction of this problem requires surgery. A skilled surgeon can 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. 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.
Prognosis
The prognosis is dependent upon successful management, either surgical or medical. As noted above, cats that do not receive surgery will often develop irreversible arthritis in the joint even though their lameness may go away for a few weeks or months.