I got into a accident about 1 year ago. Well I am now starting to have pains on the top of my knee. there is 3 scars and it is purple. Well if I stay in one spot to long my knee stiffens up and it hurts. Also, if i move around to much it starts to hurt. Um, it swells up then goes down and does it again and again. So what condition could this be?

Optional Information:
Male , Age: 20

Already Tried:
going to the doctors and the emergency room