I have no idea what I did to it! Well, that's not entirely true, I have a theory that when I went for a run a week or so a go, my hormones were a little out of whack and my joint stability (or just general stability/co-ordination) was shot and the uneven terrain I was running over irritated the ligaments a little. I'm icing the knee and avoiding certain exercises that might cause trouble and it does seem to be settling down. Of course if I was being sensible, I'd just stop doing lower body stuff for a couple of weeks, however, I'm not being that sensible!