Medial patella luxation (MPL) is a condition in which the patella (knee-cap) no longer glides within its natural groove (sulcus) in the femur, the upper bone of the knee joint. It becomes displaced to the inside of the joint and can be partial or complete, intermittent or permanent.

MPL can occur as a result of trauma or develop during the first year of an animal's life. Congenital or developmental MPL is more common. It is most commonly found in a wide variety of small dogs such as poodles, Yorkshire terriers, Maltese and bichon frise, but it also occurs in larger breeds. Animals may present when they are young, during the first year of life, particularly if the abnormality is severe, or any time later in their life if the problem is lower grade and leads to a more progressive, chronic lameness. Traumatic patella luxation can of course occur at any age and is usually secondary to being hit by a car.

Lameness can vary from an occasional hitch of the leg, like an intermittent skipping, to a persistent weight bearing lameness. Traumatic luxations are more likely to result in a non-weight bearing lameness.

Diagnosis

Physical examination is a crucial part of diagnosis. Your veterinarian will observe your dog both walking and trotting. In a standing position, the knee joint of the affected leg is compared to the opposite side.

Your veterinarian will put the knee joint through a normal range of motion to feel the tracking of the patella during flexion and extension of the joint. Dependent on the severity of the problem the patella may move only slightly toward the inner aspect of the joint or may pop completely and audibly out of position.

X-rays of the knee can be helpful in documenting the luxation.

Treatment

Low grade MPL may be managed conservatively with restricted exercise and non-steroidal anti-inflammatory medication.

More severe grades of MPL should be addressed surgically. There are a variety of surgical options dependent on which factors within and around the knee joint that are contributing to the luxation.

Home Care and Prevention

Following surgery many small dogs are sent home with the leg in a soft padded bandage. This should be kept clean and dry at all times and the toes at the bottom of the bandage checked twice daily for swelling and/or pain.

Most animals require exercise restriction for the first four to six weeks following surgery. The bandage and stitches are removed at 10 to 14 days. Passive flexion and extension of the knee can be helpful to reduce joint stiffness.

Congenital luxation is commonly a bilateral problem, that is it affects both hind legs, though not necessarily to the same degree. When selecting a dog, ask the breeder about the history of patella problems in the bloodline.