Hey, I broke my patella about two years ago now in an accident with martial arts... It healed up okay without surgery as it was a clean split straight down the centre of the bone, and the doctor said there was no need to pin it as it wasn't displaced. When I had the cast removed, I could get about 50 degrees of motion within the first two minuets, so the doctor decided I did't need any physio to help with my recovery, but now, two years on, my knee is starting  to give me a lot of trouble with my Ninjutsu.
 It's a Japanese art, so there is fair bit of sitting on your knee's, and that's what's causing the problems (only started about two months ago, after the break it was fine. But now it's starting to hurt), when I stand up, my knee feels like it's about to give out, and I have to wait almost twenty minutes for it to feel normal again, and while I'm sat, it hurts like hell to put any weight on it. Also, I have to stretch it pretty well again before I can straighten it fully after standing up, and it stiffens up a lot more than it used to after I train as well.
 I was wondering if this is normal, and also if there is anything I can do about it, as it's becoming really annoying to have to spend so much time pandering to my knee before I can train, and the pain while sat isn't great either. Also, is this likely to get worse or ware off after some time?