I wondered about that... my mom probably needs a new knee, but she won't even consider it, just limps around on the old one. Stubborn woman.
My mother was a lot like that, until the arthritis got REALLY bad this year. She was in a lot of pain, and the doctors did every non-surgical thing to help. Pain pills and arthritis meds lessened the pain, but she was ready to go with the surgery when she realized they had done all they could do.
One benefit is that the doctors said her left knee was the only significant area of arthritis in her. They made the case that she would enjoy significantly less pain, along with significantly more mobility, with the surgery, and she was ready to go. It would have been done in March, if she hadn't slipped and broke her back. Once she was healed up, she was ready to roll.
Older folks have to learn that putting up with constant pain is a source of depression. I rate depression as a major health problem with older people. So it's not just the pain that they're "putting up with", there is also a possible source of depression that they're fighting, without realizing it.