|[What the patella is and what it does] [Medial Patellar Luxation] [Grade I] [Grade II] [Grade III] [Grade IV] [Lateral Patellar Luxation] [Ethical Considerations] [Recognizing the problem] [Three Steps to Sound Stifles]|
Attached to the patella is the quadriceps tendon and the patellar tendon. The quadriceps tendon runs from the patella up to the muscle mass on the front of the thigh and to a lesser extent downover the patella to the patella tendon. The patella tendon runs from the patella down to a protuberance on the front of the tibia.
When the muscles contract, they pull the quadriceps tendon up which pulls the patella up, which, in turn pulls on the tibia via the patella tendon. The result of all this pulling is to straighten or extend the leg.
As the leg is extended and flexed, the patella rides up and down in the trochlear groove. Ideally, the groove should be deep enough for the patella to fit snugly into it. If the tendons, muscles and bones are all aligned properly, the result is a stable, sound stifle joint. Improper alignment means instability and this not only leads to degenerative joint disease, but also places increased stress on other ligaments and supporting structures.Back to index
Proper joint function relies on a perpendicular alignment of the quadriceps tendon, patella and patellar tendon, one right above the other when viewed from the front. If the upper end of the tibia is rotated inward, for example, it takes the attachment of the patellar tendon with it. The alignment is no longer perpendicular and patella is pulled to the inside (medially).
Medial patellar luxations (dislocations) can occur in varying degrees of severity and they have been classified into four grades:
The veterinarian will not usually recommend surgery for Grade I cases, but surgery becomes more advisable with the increasing severity.Back to index
The conscientious breeder is aware - aware of the problem in the breed, aware of the stifle status of all breeding stock, aware of the consequences of not breeding the problem out, aware that soundness and health are just as important as breed type.Back to index
If we are to ever eliminate patellar luxation, everyone who breeds Chihuahuas must know about the problem and be able to recognize it in their dogs. As the patella moves in and out of the trochlear groove, there is a "clicking" feeling. All you have to do in some dogs is take hold of the back legs, one in either hand, and raise and lower the back feet off the ground to feel the clicking. Judges do this while checking for rear leg straightness, and they should discover patellar luxation more often this way than trying to feel a loose patella with the leg on the ground.
If your dog passes this test, try holding one hind leg in the hock area and stretching the leg out straight behind. While the leg is fully extended, twist the hock outwards, turning the toes inward and holding it in this position, push the leg so as to bend it. If you feel a "click", it is the patella popping back into the groove.
Detecting very slight luxations is more difficult and it would be a good idea to have your veterinarian show you how to push the patella with your thumb while holding the leg extended.Back to index
2. Learn to recognize it in your dogs.
3. Conduct a breeding program to eliminate it.