Well, when I was coming off an injury that kept me out of the game for a month, I did great with three full's a week. Rep range really didn't matter nor did exercises. It's really meant to re-establish your mind muscle connection as well as to regain your confidence without destroying you. I shy away from low reps mainly because it's a real blow to your confidence marching in after a long layoff and hoping for the best. In the case of your knee, I'd stay away from free squatting, leg extensions, ect. Perhaps some low weighed sets of 15-20 on the leg press. Low weight!
PM me if you'd like.