in real life matthew gray gubler dislocated his kneecap while he was out with some of his castmates from 500 days of summer. this all happened before the new season of criminal minds aired so in the very first episode of the new season his character was shot in the leg so that would explain the crutches and eventually the cane.
yeah he had to get three surgeries just to fix his kneecap. he said recently that he was finally able to walk without his cane or a friend's shoulder for the first time in six months so he's finally getting better