I know your original post was older but....
Do you have a good running shoe and insoles? I tore my ACL completely in June of last year and had it replaced September of last year. I'm only "allowed" to do the Insanity workout if I'm very careful and behave. That being said, I invested in a good pair of shoes with a HIGH IMPACT insole. I've also invested in a brand new knee brace. So far my knee (well, the bad one plus the good one) seems to be holding up pretty well. I also ice down for about 10 minutes after the workout and that seems to have stopped any swelling that may be occurring.