A luxatating Patellais the term used for a slipping knee cap. may be a result from a traumatic injury or congenital deformities. The Patella protects the large tendon of the thigh muscle as it rides over the front of the femur while the quadriceps is straighten.

is caused by a congenital abnormality usually located at the hip joint. During a Chihuahua's growth and development the quadriceps muscles in front of the thigh tends to pull the kneecap to the inside of the leg rather than pulling the kneecap up and down. Over time the inside ridge of the trochlear groove erodes and the groove fails to deepen because of the absence of normal wear. The actual luxation may not be present at birth, but the structural changes which lead to luxation are present.

Patella luxation may develop soon after birth or will generally be seen after four months of age. Sometimes only one knee is involved, but the disease can become bilateral. Dislocation can occur on either the inside surface or outside surface of the knee.

Lameness occurs because the kneecap does not have a normal groove to slide in. It is much more common for the kneecap to ride on the inside than on the outside surface of the knee. With mild forms of luxation, the Chihuahua may occasionally pick up the affected leg when they run. As the disease progresses, the Chihuahua may develop increased lameness with a decreased ability
to jump. With time this constant rubbing will result in arthritis. When the patella is luxated, the quadriceps will also put a rotational force on the tibia, which over time will increase the rotation of the tibia, which again will increase the severity of the problem. The
additional strain caused by the malformation of the bones may also lead to later ligament ruptures

Signs of Patella Luxation:

Some Chihuahuas show only a single sign, where others will show many signs of the condition. There are varying degrees of patella luxation that are graded depending on whether the patella is intermittently or constantly luxated.

Most Chihuahuas that are affected with Patella luxation have Grade I or Grade II. The best time for testing in most cases will be at 4 to 6 months of age. This will allow for the joints to be tight enough to allow reliable palpation.

Grading of Patella Luxation

Testing for a

• Hold the fingers lightly over the knee-cap and bend and stretch the leg. If while doing this, the patella bone can be moved sideways in and out of position with ease, and these movements are accompanied by a "click", then the dog is exhibiting a Luxating Patella.
• Stand the dog on a table or a firm and non-slippery surface. Lift up them from the front so that the dog is standing almost upright and its weight on its hind legs. Gently press the hind- quarters just above the root of the tail with the palm of your hand. If there is any degree of luxation, the hock joint becomes straight and the joint just above the foot will compensate for this by becoming over flexed.
• Another method is to stand the dog on a hard surface on all four legs. Press on the rump. The joint will go straight easily if there is any Patella Luxation.

Treatment