Q: Last week, our kitten starting favoring her left rear leg. After taking her to the vet, I found that she has a medial patellar luxation. She doesn’t seem to be in pain, but every once in a while her leg just gives out on her. The vet said she might grow out of it. What would be the best course of action, and how will we handle her care in the future?
A: The patella is the knee-cap. In order for the rear legs to flex and extend properly, the patella needs to glide within the natural groove that is present at the end of the femur (thigh bone). In some cats, the patella does not glide properly in the groove. It slips out of the groove, usually toward the inside (medial) part of the leg (as opposed to the outside or lateral part). Cats with this problem are said to have a medial patellar luxation (MPL). It is much more common in dogs, however, compared to cats.
The most common cause of MPL in cats is developmental; cats are born with a tendency to develop the problem, usually within the first year of life. Severe cases may lead to lameness problems early in the cat’s life, but this is rare. Most cases show no symptoms at all. As the cat ages, mild cases of MPL may progress in severity, eventually leading to persistent lameness. Again, this is uncommon. Cats with MPL are rarely bothered by it. Trauma is the second most likely cause of MPL in cats, usually as a result of being hit by a car.
The main clinical sign of MPL is lameness. This can vary from a very mild limp to a complete lameness with the cat being unable to bear weight on the affected limb. Diagnosis is based mainly on physical exam findings. On orthopedic examination, the patella will be manipulated by your veterinarian to see if it is firmly in its groove or if it can easily be displaced out of the groove. Both knees will be evaluated. In many cases, the luxation is bilateral, although there may be differing degrees of severity between knees. X-rays may be useful in confirming the diagnosis.
Treatment varies, depending on the severity of the MPL and the cat’s clinical signs. Mild cases may not require treatment, or may be managed with a short course of pain medication. More severe cases may require surgery. Because your cat is just a kitten, I think its fine to wait and see if she does outgrow it. If she shows signs of lameness when she gets older, then you’ll have to consider surgery. The most common surgery for MPL involves deepening the groove that the patella glides in, making the knee-cap less likely to pop out of place. Most cats respond well to surgery and walk normally several weeks later, however, arthritis is likely to develop in the joint later in life.