Mother (90) has many feet issues. If she has knee replacement surgery, is it necessary for her to walk for therapy?

Who is going to these doctors who recommend elective surgery for 90-year-olds??

They remind me of what my own 91-year-old mother always said -- "Fifty percent of all doctors graduated in the bottom half of their class."

Aim for a doctor who was at least in the top half of his class.

I agree that if the feet issue isn't improved, knee surgery is moot. Also, you must consider the danger of anesthesia for someone at that age. My mom is 91, a retired nurse, and in no way is she willing to risk anesthesia. Do you have access to a pain clinic at the orthopedic center? If so, ask them about less invasive solutions for your mom. There is ablation (which deadens the nerve that carries the pain signal from the knee), and a newer technology is SPRint, which uses temporary (30-day max) tens-like impulses targeting pain receptors which reeducates how your brain perceives the pain, and has a 70% success rate. Both of those therapies have almost no downside and don't require anesthesia. Good luck!

This question is best addressed with the doctor who may allow you to visit with a Physical Therapist. You are correct that there is a lot of therapy that can be done in bed, indeed some are machines that are set to exercise the knee. THAT said, it is unlikely at this age to come out of this well, especially if the goal is walking. No matter what happens with the knee, the patient cannot walk because of the FEET, so what in the world is the point. If you are no familiar with what happens with elders post op, with the dementia that was never there suddenly there big time, with blood clots, and etc. I cannot imagine this being done in all truth. It may be time to accept being, for the most part, wheelchair bound.
Good luck. Have the doctor TAKE THE TIME to level with you, or don't consider this.

At 90, I am surprised ANY doc would consider surgery.

Yes, there are exercises that can be done sitting or in bed to strengthen muscles. At 90, that's probably the best way to go.

If she isn't walking now, she probably won't walk after knee surgery. I sound kind of mean and hopeless about her situation, but realistically, if she cannot walk, and the cortisone shots are helping at this point, I'd leave well enough alone.

Some gentle PT to possibly help her gain a little strength so she can walk a little more is probably the best you can hope for. I'd work with a registered PT first to make sure you know what kind of movements will help and not make her problems worse.