My Zada had both knees operated on at the same time back in 06. She was not even limping or in any distress. The Vet who did the surgery didn't even deepen the grove the knee-cap sits on so they slipped out and I wasn't even aware they had until 3 months ago when she started limping. I then took her to an orthopedic surgeon who's the best in the country and teaches world wide. Anyway her limping was due to a torn ligament, but he did find she had a grade 4 in each knee. He did operate on the right leg to repair the torn ligament and patella. He left the left leg only because it isn't giving her problems. He did say she should not have been operated on the first time since she was not showing any signs of pain or stress.
He felt ligament knees and she too has a grade 4 in each knee, but no limping or in any discomfort and advises not to have her operated on unless she does.
Anyway, I would find a really good orthopedic surgeon and get an expert opinion.
