The patella, or kneecap, is attached at the top and bottom by ligaments, and it slides in a groove in the bone of the femur, or thigh bone. Luxation refers too slipping out of place. In medial patellar luxation, the groove the patella rides in is shallow, which allows the patella to slip off towards the inner, or medial, side of the leg.

An animal with MPL will usually show signs of an abnormal walk or run. They may limp or run/walk with a skipping step in one or both rear legs. They may even run on three legs, holding one hind leg up, and then walk on four legs again as if nothing was wrong. In severe cases, the animal may have one or both rear paws pointing inward towards the other, and they may have difficulty walking at all or they may walk primarily on the front legs and hop in the rear.

MPL is an inherited condition. Although it occurs most often in small dogs and in some cats, it may also occur in larger breed. When present in larger dogs it is more common to see the patella luxate laterally (away from the opposite leg) instead of medially.

MPLs are usually diagnosed upon palpation during a physical examination. Some veterinarians may suggest x-rays to interpret the severity of the condition.

Treatments vary depending upon the severity of the MPL. A mild luxation (Grade 1) requires no surgical treatment, although over time the weigh-bearing stress of the rear leg may be altered, and the animal may become more and more bow-legged. This is more of a concern with Grade 2 – 4 luxations. Surgical repair is recommended for those animals that have the kneecap out of place all or most of the time to help prevent changes in the hips and legs leading to arthritis. Some animals may be prescribed medication to control pain and inflammation, or to help increase cartilage or joint fluid production.

Do not allow your pet to become overweight. Excess weight will compound the problem. Occasional limping or lameness may occur with mild MPL, but it is usually not a constant issue and should not be a major concern. Helping pets up and down stairs or providing ramps to get on and off furniture alleviates stress and strain on the knees. Give any recommended medications as directed.

If the limping or lameness worsens, the MPL may require surgery to correct it. Ligaments within the knee can be more easily torn in an MPL knee due to the change in weight-bearing. Any evidence of increasing pain or lameness is a reason to call your regular veterinarian. DO NOT give medications such as ibuprofen (Advil/Motrin), acetaminophen (Tylenol), or aspirin unless you have been specifically advised to do so by your veterinarian.