My little dog also has Luxating Patella in both back knees since I got her almost 4 years ago. Her back right knee progressed from a 2 on the scale of 4 that the vets use to categorize the severity of the luxating patella to a 3. Then last Spring it got worse. She needed the surgery so she didn’t end up with a damaged ACL, too. I had the bad knee operated on, but the left knee was only at a 2 (has been the whole time). The surgeon said it can be that way for the rest of her life, never changing condition and did not recommend operating. Where I’m going with this is: it might never be an issue. If the shelter is addressing the one bad knee, you are in a great spot. The dog needs to be kept relatively immobile during recovery, but should be fine after it. The other knees may never be a problem.