The patella is the knee cap in people and in pets. A Luxating Patella or Dislocated Knee Cap occurs when the knee cap pops in and out as the affected joint is flexed, extended, or bears weight. This is a congenital condition. It is more common in toy and small breed dogs but it can affect large dogs as well. It is rare in cats. Yorkies, Pomeranians, Pekingese, and Chihuahua are the most commonly affected breeds.
The Luxating Patella generally occurs when the groove of the femur that the patella sits in is too shallow which allows the patella to move out of place. It can be caused by trauma but that is rare. It usually presents between four to six months of age. Both knees are affected in 50% of the dogs that have this condition.
Luxating Patella is graded as follows:
- Grade I—The patella can be luxated manually but won’t move by itself
- Grade II—The patella can luxate on its own but can return to normal position manually or when the pet straightens the joint
- Grade III—The patella remains luxated most of the time but can be moved back into the correct position manually
- Grade IV—The patella is permanently luxated and cannot be repositioned
- Rear legs having a “bow-legged” appearance
- Not bearing weight on a hind limb
- Holding up a hind limb
- Skipping or bunny hopping when attempting to run
- Pain when the patella pops out of the proper position
This condition is diagnosed by a physical exam during which the veterinarian palpates the knee joints and does x-rays to screen for arthritis, hip dysplasia, or other abnormalities of the bones.
Surgical repair should be performed as soon as possible on Grade II and Grade III Luxating Patellas to prevent the formation of arthritis and keep the condition from progressing to Grade IV. Surgical repair for Grade IV Luxating Patella may be worse than the condition itself so careful consideration should be taken to prevent progression to Grade IV. Surgery involves repositioning and stabilizing the patella so that it sits properly in the groove. The groove may need to be deepened to do so.
Post-surgical recovery includes involves exercise restrictions and leash walking. Full recovery takes eight weeks. There are no known preventive measures for this condition to date. Dogs with Luxating Patella should not be bred as there is a genetic component to the condition.