Clean Run Magazine - April 2010 - 31

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Patellar Luxation

Congenital Conditions:

By Peter J. Lotsikas, DVM, DACVS and Faith M. Lotsikas, DVM, CCRT

Recently, we were invited to perform an orthopedic clinic for a national specialty show. Specifically, I was asked to evaluate and document patellar luxation in this particular breed for the Orthopedic Foundation for Animals (OFA) database. At first, the participants in the event were delighted to see me and thanked me for helping out. However, by the end of the day, I had documented patellar luxation in 8% of the dogs evaluated, which represented the best of the breed. Many handlers questioned how their dog could be competing in agility at the national level with a patellar luxation, having never exhibited lameness in their life. For this reason, I felt it would be appropriate to discuss the development and implications of this condition.
Patellar luxation is a common condition seen in toy, miniature, and large breed dogs and is characterized by the kneecap dislocating or “floating” out of the trochlear groove. The kneecap can float either to the inside of the knee (medial luxation) or to the outside of the knee (lateral luxation). Medial luxations account for 80%-90% of all cases, regardless of the size or type of dog. When lateral luxations occur, they are almost exclusively found in large and giant breed dogs. Patellar luxation is further classified as either congenital or traumatic in nature. Most cases are congenital, meaning the abnormalities leading to patellar luxation are present from birth. It is reported that both knees are affected in 25%-50% of congenital cases. Certain breeds are overrepresented for this abnormality, which would suggest that this is a heritable condition. (A complete breed ranking can be found at www.offa.org/patluxstatbreed.html.) Ideally, dogs affected with congenital patellar luxation should not be used for breeding.
April 10 | Clean Run

Anatomy
Anatomically, the patella is part of the pelvic limb extensor mechanism. This consists of the quadriceps muscle group (rectus femoris, vastus medialis, vastus intermedius, and vastus lateralis muscle) that conjoin to form a single tendon in which the kneecap is embedded. The quadriceps tendon courses over the end of the femur and inserts on the tibial crest. The normal femur is fairly straight, generally having less than 9° of medial to lateral deviation. At the distal end of the femur lies a groove, called the trochlea, which is covered with hyaline cartilage and articulates with the patella. The insertion point of the quadriceps tendon is called the tibial tuberosity and is located at the top portion of the tibia. The patella glides within the trochlear groove, which allows for fluid motion of the knee and maintains the normal tension needed to prevent collapse of the joint during forward motion.
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http://www.offa.org/patluxstatbreed.html
Clean Run Magazine - April 2010

Table of Contents for the Digital Edition of Clean Run Magazine - April 2010
