Hello - What causes your knee to hurt so much you just want to scream most times? My ACL, and MCL was recently replaced end of December. A few weeks ago I was sitting on a stool. Someone fell into my knee from the left side.. My knee hurt really bad when I tried walking. The next day I woke up as normal, stretched and there was such a super loud pop.. So loud my whole body froze, and I had this over whelming feeling something was wrong.. The pain and swelling has not gone away. There s swelling and lots of pain on the backside of my knee, inside of my knee, and my knee cap.. What could be causing such misery?