Hello. Last night my son out of the blue said his leg hurt. He will not straighten is leg for anything. When he does he has pain in the knee . If his leg is bent he is fine. He can move around fine. What I find weird is that if the leg is bent he seems to have no pain. Not like with most pains, if something hurts you have pain from just moving the body around. What could this be? He said he did not fall or hit his knee or leg on anything. He sat on the couch and was sitting on his knees and now he can t unbend his knee without pain. I even tried while he slept to straighen it thinking he was just likeing the attenction but he started to cry in his sleep.