Had a knee problem for years but I had to learn how to ride out of the saddle many years ago. It was either that or walk the hills and I don't walk. But I was never an accomplished "Out of the saddle" Rider till I did some spinning classes. I did it but some knee pain was there. In the comfort of a nice warm gym and a bike that was not trying to throw me to the ground- I learnt the technique. Stay straight on the bike and go up a couple of gears as you rise out of the saddle.

But did a spinning class today and felt some pain. That's what I get for not getting enough rides in recently (For the past year or so if I think about it) that would push me to the limit and required that I exercise the whole body instead of just the straight legs and lungs.

Now you have learnt the technique- go and find plenty of hills so you can practise more and build up the knee joints and muscles.