Suggest Treatment For Knee Joint Pain

I am consulting you on behalf of my mother who is 57 years old and is having knee pains in the joints. She is also having swelling in her lower part of the legs (both the legs). She was operated for Uterus around 10 years back and she is having this knee pain since 7 years. Thou we consulted many consulted many doctors but they suggested for operation only as they say that there is a gap in her knee joints and the lubricant is also reduced. What do you suggest?