Faye, the link above tells you about ACL injury and what is done for it - brace and exercise to strengthen it even if surgery is down the path in the future. It's basically a tear in the ligament so a knee replacement would do nothing for it. I tore mine about 2 years ago - crutches and brace and I still use a brace for some of the stuff I do at the Y. It keeps it in place. My doctors know I am very proactive about my health and if I call, they call me back or know they will have an irate patient in the office the next day.
Jean, I take my car to the dealer (15% discount for seniors) and they have a lovely waiting room, too. Snacks, coffee, tea, cold drinks, tv and magazines and comfortable chairs. The time passes quickly.
Have a wonderful day, I'm off to the gym. Keep warm!