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Patella luxation is a condition where the patella, or knee cap, slides out of its normal position. It is usually congenital (present at birth) but can also be caused by accident or trauma.
In a normal knee there are two ridges on the femur which comprise the patellar groove. It is in this groove that the knee cap rests and provides protection to the knee as well as helps control the quadriceps muscle. Because of deformities in the femur and tibia, this groove may be too shallow or the femur and/or tibia may be deformed and can allow the knee cap to dislocate, or luxate, over the ridges and out of normal position. Most of the time the patella will luxate medially, or towards the inside, of the knee.
Early detection and correction of patella luxation is the best way to prevent permanent damage including severe lameness and dysfunction. Breeding affected animals should be discouraged, however it is so prevalent in some toy breeds that this approach isn't practical.
Dogs that have intermittent or consistent lameness, an abnormally bowlegged stance, a disinclination to run and jump or a tendency to hold a rear leg out to the side when walking should be checked for patella luxation.
There are different grades of severity of the condition. Normally the cases are graded on a 1-4 scale with 1 being mild where the patella is able to be manually moved out of the normal position but returns quickly on its own and 4 being severe where the knee cap is out of position and unable to return to normal. Physical examination and radiographs are generally used to help determine just how severe the displacement of the knee cap is. The treatment recommended for patellar luxation varies depending on the specific case but usually includes surgery, especially with cases graded a 2 and above.
There are three main surgeries that are performed; trochlear modification, lateral imbrication, and tibial crest transposition. In trochlear modification the groove which the patella rests in is made deeper to help keep the knee cap from sliding out. When lateral imbrication is performed the knee cap is tightened to the outside of the knee preventing it from moving or slipping out of position. A tibial crest transposition requires that the bony projection where the quadriceps tendon attaches to the tibia is cut off and reattached more towards the outside of the knee to align the quadriceps mechanism. After surgery dogs generally will recover and can go back to living normal happy lives.
Most dogs with patellar luxation live a long happy life, with or without surgery. Be sure to watch for signs of lameness, and try to prevent too much activity that could cause the kneecap to become displaced (running, jumping off the bed, etc.).
CHF has funded one grant that looks for the genetic causes of patellar luxation.
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