Re: Knee Surgery
I will add that there are professional soccer players out there who continue to play having blown out their acl's. They are highly conditioned athletes, with more muscle strength and dynamic coordination than most aikidoka, so that even though they don't have actual acl's, they are functionally stable.
It is not unheard of for people who dance or do aikido to be able to achieve this stability without surgery. I have trained with one such person.
So if a person really is opposed to surgery, is functionally stable enough to do sedentary "activities of daily living" for a while, and is really motivated, it is theoretically an option to defer surgery and give all-out athletic training aimed at acheiving a functional knee a chance to work. I would NOT recommend going this route without the solid ongoing support of a properly trained and certified rehab person/athletic trainer.