42 years old, 5 5 , 203 lbs, I do have Lupus ( in remission) OA, Osteopina. I was walking down the stairs at home and my knee gave out, popped and felt like it was on fire. Then when I straightened up it popped very loudly again. Now it is locking up with stabbing pain and something can physically be felts moving in my knee when I bend it.