Diagnosis: Trick Knee Or Luxating Patella In Dogs

Every year, thousands of small dogs and less frequently, large dogs are diagnosed with luxating patella or trick knee. The reason for the dog's trick knee is that the knee cap (patella), usually held in place by a ligament, slides or pops out of its track or grove.

The Mechanics
There are several reasons why the knee cap dislocates or luxates. The bony track that the knee cap slides in may be too shallow. The dog may have a twisted lower leg bone. Or the point where the ligament connects to the lower leg bone may be off-center. In any case, the medical community points the finger at genetics for the cause of canine luxating patella.

Note that the lameness usually associated with this condition may not show up until the dog is older and heavier and more pressure is applied to the knee joint as the dog walks or runs. This is the case with Simon, a poodle and cocker spaniel mix.

At about a year old, Simon was diagnosed with medial luxating patella, the most common type. His knee cap dislocated toward the inside of his right knee. Vet examinations at various times during his first year did not uncover a trick knee. But, during his second summer, he showed the typical symptoms.

Arriving At The Diagnosis
Here's what normally happens to arrive at a diagnosis for trick knee in dogs:

1. The owner notices limping or lameness that persists.

2. During a trip to the vet, the medical personnel ask question about the dog's gait and frequency of the problem and the vet examines the knee to see if it dislocates easily.

3. The vet may confirm initial diagnosis with X-rays.

4. The vet (you may have to ask) explains why the dog's knee is dislocating or is dislocated. (Simon's vet used a model of a dog's knee to explain the reason for his trick knee).

5. The vet may assign a grade indicating the severity of the luxation/dislocation. For example, because Simon's diagnosis was Grade I Luxating Patella.

The Owner's Responsibility

If your dog limps frequently and the condition does not resolve itself in a few days, take the dog to a vet. In Simon's case, he could relocate his knee cap quite easily, so he did not limp all the time. But, over time, the frequency of dislocation/relocation increased as evidenced by a distinct limp and stiff-legged hop.