Knee replaced 11-13-09. Finally felt I've been making some progress until yesterday. During therapy, performing lateral steps over 6" hurdles, I felt a sudden pain and kind of a pop on the interior medial aspect, a little toward the back of the knee. During the course of the day, I would experience sudden pain causing me to yell out, even when non-weight bearing. My wife appreciates this. Increased pain yesterday, last night, and this morning when I turn, walk with a cane, and just sit. Increased lateral motion and popping and clicking. Difficult to walk without pain again. What's up???