This is an interesting and complicated question.
Typically, we do not recommend knee replacement surgery in patients unless they are significantly symptomatic and have failed multiple conservative measures. If someone fails these measures, but has severe arthritis with only minor deformity, then they might still be a candidate for surgery.
Another scenario is a patient who is relatively well controlled as far as symptoms go, but has significant contractures or deformity. That patient is the one who might "wait too long." If the deformity gets worse, the surgery becomes technically more difficult to perform and potentially has a chance for a poorer outcome. Additionally, as the arthritis progresses, the ROM of the knee worsens. We have discussed many times here that a patient's pre-op ROM is the best predictor of post-op ROM.
This particular patient may consider surgery before it "gets too bad." Additionally, there are patients who want to have surgery before they get "too old and have more medical problems." The counseling for these patients can be hard at times.
When I counsel these patients, I am always aware to make the following point: Not every patient has an excellent outcome from surgery. I explain that they might be in that small percentage of patients. If they were, they would be upset that they had proceeded with surgery and feel worse than they did before the operation. This can be a catch-22 so to speak.
The decision to move forward with surgery is such an individual process that there is no algorithm that fits everyone.
Orthodoc