My male Chi has it in both knees. He had the surgery on the one when he was just a couple of years old. It got so that it was causing him a lot of pain and kept slipping out often. In the first few days of recovery, he was miserable and in terrible pain. She shook and quivered and cried until his bladder let loose, even with pain meds. But after the first few days, he felt much, much better. That intense pain seemed to be gone. It was fine and his knee seemed intact for a couple of years, then it started slipping again. Apparently, this can happen where the repair just doesn't hold. However, he has been going along with this for quite some time now and it rarely gives him any problem. Occassionally, I'll see him stretch it out behind him as if trying to re-adjust it and then all is well. The patella on the other side has never been severe enough to cause him much trouble at all. He runs like the wind and can jump and play, so unless or untill it becomes really troublesome, I'm going to avoid the surgery.
With your dog, I also would avoid the surgery IF he is relatively functional, pain free and it doesn't bother him too much. How is it with your dog? If it's severe, I'd go with the surgery. There is just nothing else to do.
I wish you and your dog the best. It's an unpleasant defect with a lot of small dogs....such a shame.