My knee routinely collapses when I am doing physical activities. It pops out of place, and back in immediately, and hurts pretty bad, and ceases after a few minutes. It is primarily on the inner right knee, and never with my left knee. I can feel when it is about to pop out of place, but cannot avoid it. It usually happens when I turn my leg to the inside, or put a lot of pressure on my knee (kicking a soccer ball, for example). I have no other symptoms whatsoever. My doctor says I have "patella instability." Is this a correct diagnosis? Is it due to having weakened muscles and ligaments? And what kind of therapy should I go through?