I was back in the saddle 2 months after my accident, with my brace on. Doing speed events such as barrels and pole, even. Still couldn't bend my knee or walk without the brace and needed the crutches most of the time.
It can be done, but each person should know their own limitations. I probably should have taken things easier, but I know my horse and completely trust her not to do anything dirty. Not that an accident still couldnt occur.
How is your knee now?