Lots of thoughts and prayers for Smokey and that trick knee.
I don't think any of us would have made a different choice then you did...seeing him run around the dog park for the last 5 years, I would have never said he needed to have that knee checked out.
I remeber maybe the first time you came, he favored it once or twice toward the end of the day...but he hasn't shown a sign of pain out there since. Dogs are so good at hiding their pain it is often to the extreme point before we humans ever know. Doesn't make you a neglectful parents...just makes him a strong dog!