Medially Luxating Patella (MLP)

What is a medially luxating patella (MLP)?

A medially luxating patella (MLP) happens when the patella (the kneecap) moves out of the stifle (the knee) and moves to the side of the stifle. An animal with a mild MLP will just move around in and out of its normal place.

This can lead to the cartilage under the patella and femur wearing down, which can cause pain and lameness in the animal. When the luxating patellae move over time, if left untreated, most of them stay that way for good.

Every now and then, people notice their pet skip or hop a little; this behaviour can be a sign they are trying to get their patella back in the right place. Your pet won't feel pain until cartilage loss results in bone to bone contact. The animal will be lame by that point, not just hop a little. Knee palpation will show whether the kneecap is in the right place or if it moves quickly into and out of the correct position. Crepitus, which is the loss of cartilage and bone-on-bone contact, may also be taking place at the same time.

Treatment options

In some cases where the dog hops a little but isn't yet lame, weight loss, no more rotational activities like fetching, and medications like Cartrophen or Zydax may head off the need for surgery. However, if cartilage loss is causing pain and lameness, surgery will be the best course of action. Animals with MLP are treated by cutting away part of the bone on the tibial crest. Then, they move the bone to the side and attach it with a pin again. This moves the patella tendon, which keeps the patella in the right place. When we do surgery, we will deepen the femur groove to make it more difficult for the patella to move in and out of its normal place. When we do this, we separate the medial adductor muscles from the thigh muscles so that they don't pull on the thigh muscles. This allows the patella to move more naturally at the femur.

Chihuahua, Boo, 3 year old, during surgery