Yes, I have had it ever since my ballet days. Best exercise: what they call short-arc extensions. I sit on the floor with a soccer ball under my knee to raise it up, and four pounds of weights on my ankle, and raise and lower my lower leg. They call them short-arc extensions because you are really only raising and lowering your lower leg the last 20 degrees or so of the 90 degree arc you have when your knee is completely bent (like when you're sitting upright in your chair).

Link to an excellent article: http://www.youtube.com/watch?v=_pGtY6e3fVI