One day I was sitting in my recliner and was playing with my son. I went to get up real fast and as my leg was stretched out I got a sharp pain behind my knee. It was very sore for about a week and it was just a little sore for another week after that. My question is if I move my knee in a bending or twisting motion or even just move it to fast the pain comes back instantly and I have a hard time keeping it straight and putting weight on it but if I move it a certain way or walk on it for a bit the pain goes away instantly like it never happend and I can walk normal again. What causes this and what do I need to do to fix it.