Rick has a similar problem with his right knee. An orthopedic surgeon recommended replacement, but after researching that, he found that if you plan to remain physically active, it is only temporary, and you have to keep replacing it again periodically, and each time the knee is replaced, your leg gets a little shorter. He finally learned that a custom-designed brace can accomplish the same thing. So that's what he did, and he has been using this brace for years. He used to use it for sailing, but now he just uses it for playing tennis. Without it, there is no way he would be able to play tennis. It's expensive and not very attractive, but it works for many situations.

I'm sure you have already looked into the brace option. Just mentioning it for the benefit of other people who might have knee problems and want to remain physically active for the rest of their lives.