When someone has severe pain in the ankle from a disease like arthritis, like your mother, it can cause a lot of problems, particularly pain and difficulty moving around. Some orthopedic surgeons are doing ankle replacements for patients who are in situations like this. The other, older and more common surgery is called arthrodesis, or bone fusion.
The research is showing, right now, that patients who have a total ankle replacement have a higher rate of having to have a revision surgery within five years of the initial surgery. For a fusion, the surgeon grafts some bone to the ankle joint and joins them together so they do not move, therefore eliminating the pain from the joint. The drawbacks from this surgery include the future fusion of the other joint in the ankle and the limited range of motion in the ankle after it has been fused.
Your mother should speak to her doctor about the type of surgery he or she is offering and ask questions about why one is preferred over the other.