March 15, 2009 "Ask Seth"

My dog was recently diagnosed with an MPL. What does this mean and does it require surgery?

Dear Seth,

My pug, Thor, has just been diagnosed with an MPL. What does that mean and does it require surgery?


MPL stands for Medial Patellar Luxation. MPL can be either hereditary or a result of trauma. The hereditary form is more common and is generally found in small breeds. It usually appears in dogs less than one year old.

The patella is the knee-cap. When the patella is in its normal position, it slides smoothly and painlessly in a groove in the femur, the upper bone of the leg. The groove is lined with cartilage so the bones move smoothly. A luxation is when the patella pops out of place, causing the bones to rub against each other. This can be extremely painful. A patellar luxation may occur intermittently or constantly. If your dog displays occasional lameness, he or she may have MPL.

Thor may try to straighten his leg to pop the patella back into place. Some dogs will hold their leg up until the kneecap repositions itself in the groove. He may appear lame or bow-legged and walk with an unusual gate until the luxation corrects itself.

Considering the severity of the luxation, this can occur over and over again and even erode the cartilage away. Some luxations are only occasional. Your veterinarian will grade the luxation on a scale of 1 to 4. 1 means the patella is in the normal position; 4 is when the patella is completely misaligned and never in place. Each case is unique and your vet will tell you how best to treat your pet.

Surgery is often recommended, especially for severe luxations, and usually corrects the problem. Your vet may recommend an orthopedic specialist to perform the surgery. After surgery, most pets will be back to normal in about 6 weeks.

Seth Mayersohn, CVT

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