On Friday, I twisted the heck out of my knee again--just trying to sit down in a confined space. My foot got caught on something so when I put my weight on my right leg, the foot wasn't under the knee--and so my missing ACL wasn't there to keep my knee from twisting. Very painful. Rest, ice, compression, elevation.
I took a couple of days off from PT at home, and have since resumed. I haven't trained at my school, though I've done the elliptical machine at the gym (and some of the PT is real strength training for my legs).
It's worrisome to me that I could re-injure my leg just trying to sit down.
On Friday the 13th, I'm going back to the doctor, following a month of PT, to see what he says and, I suspect, order a brace. Then I have to decide what I will do.