Patellar Luxation: Naughty Kneecaps

The patella, or kneecap, is a small round bone at the front of the knee.  It is embedded in a major ligament that attaches the huge quadriceps muscle group of the upper hind leg to the tibia, or shin bone.  The patella may seem like a small, cute and innocent little bone, but it can be a trouble-maker if it doesn’t do what it’s supposed to!  You see, the patella’s rightful place is the trochlear groove at the front of the femur bone.  Its position is very important to the mechanics of the knee joint, and it should track nicely in the trochlear groove when the knee flexes and extends. In some dogs and cats, the patella does not sit properly in the groove, and pops in and out of it sideways as the knee moves. This condition is called ‘patellar luxation’ and is most common in toy breed dogs and miniature breed dogs.

It is usually a developmental condition which occurs due to the confirmation of the skeleton, but can also be a result of trauma.  The condition is classified into different grades, with grade 1 being a mild version which usually doesn’t cause any problems, and grade 4 or 5 being the most severe.  The condition causes lameness which is either constant or intermittent (hopping every now and then), as well as instability of the knee.  The instability can lead to tears of other ligaments within the joint, especially the Cranial Cruciate Ligament.  In the higher grades, the patella can be permanently located outside the groove.

Correction of this condition involves surgery and this is usually recommended for higher grades as well as for lower grades that are experiencing lameness.  Patellar Luxation surgery may include soft tissue procedures as well as cutting and re-positioning of bone.  A period of rest and rehabilitation for around 6 to 8 weeks is usually required.

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