My Boston also has a patella that goes out of whack from time to time..(We call it his "bad wheel") LOL. Doc gave me previcox, an anti-inflammatory that usually works quite well. We were told when the patella actually moves out of place there is pain, but once it is out it is not painful for the dog, only he cannot bear weight.
The 1st doctor also quoted $1400 to fix. He didn't have a surgery date available for 4 days. Thank God! The "miracle pill" worked just fine. Then another doctor in the same practice told us that fixing the kneecap doesn't guarantee it will stay that way. And also that our dog was too arthritic to even consider such a surgery! And yes, I have changed vets..
Hope your little guy gets better