Feline Medial Patella Luxation 

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. MPL is uncommon in cats. 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 of Medial Patella Luxation in Cats

Physical examination is a crucial part of diagnosis. Your veterinarian will observe your cat 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 of Medial Patella Luxation in Cats

Cats with low grade MPL should be managed conservatively with a period of rest and a short course of non-steroidal anti-inflammatory agents. If the lameness persists or worsens they should be re-evaluated.

Some cats will fall into a gray zone, with grade 2 or even 3 MPL but minimal clinical signs. If the lameness is occasional and not progressive then surgery is probably not indicated. But where this grade is associated with a more marked lameness or serial X-rays show significant progression of arthritis, surgery would be appropriate.

A variety of available surgical techniques aim to restore the patella to tracking permanently in its correct plane within the groove of the femur. To achieve this goal the groove may be artificially deepened either by abrading the existing surface or cutting a v-shaped wedge into the bone. The joint capsule surrounding the knee may be too tight on the inside, pulling the patella in that direction, and so may need to be loosened while the opposite side of the capsule is tightened. Finally, the attachment of the patella itself may deviate to the medial or inner aspect of the tibia, and therefore need to be restored to a straight attachment. This is usually achieved by cutting the tendon at its bony interface, and fixing this with pins and wire into a new straighter location on the tibia.

Home Care and Prevention

Following surgery many small cats 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. To prevent traumatic MPL, keep your cat indoors.