Patellar luxation is a condition where the kneecap (patella) is able to move out of its normal position.  Luxating patella is one of the most common knee joint abnormalities of dogs, but it is only occasionally seen in cats.  It may affect one or both of the knees.   In some cases the patella moves (luxates) towards the inside of the knee (medial luxating patella), and in other cases it luxates towards the outside of the knee (lateral luxating patella).

Medial luxation is the most common form we see—it is seen most frequently in small or miniature breeds of dogs such as Poodles, Maltese, Yorkies, and Chihuahuas.  Lateral luxation is seen less frequently—it can be present in many breeds, but especially in Newfoundlands.

There are four grades of patellar luxation:

1. Grade I: The patella can be manually luxated but the kneecap returns to its normal position when pressure is released.
2. Grade II: The kneecap can spontaneously luxate out of position with just normal movement of the knee.
3. Grade III: The kneecap remains luxated most of the time but can be manually reduced into the normal position.
4. Grade IV: The patella is permanently luxated and can not be manually repositioned

Dogs frequently start with a Grade I or II and worsen over time to a Grade III or IV. Dogs with patella luxation must not be allowed to become overweight!  A lighter pet just might not develop a worse luxation. 

Many people are not aware their pet is affected by patellar luxation.  Owners may see their pet run and suddenly not use the affected leg for a few steps as the knee pops out and them pops in again.

The only correction for patellar luxation is done surgically.