My 67 years old mom has onfh (osteonecrosis of the femeral head) on both hip joints, what's success rate on surgery to replace total hip in her age?

Very high.: Most people who undergo total hip replacement for osteonecrosis do very well. She should ask her orthopedic surgeon though.

Depends: Your mother's current state of health and activity are two of the biggest predictors on how she would do with surgery. If her pain is disabling her and preventing her from having an otherwise active life, then there is a good chance she would benefit. Her primary care doctor and orthopedist would have the best perspective.

Very high: Rates depend on what you are defining as success. Hip replacement is more than 90% successful in reducing or eliminating pain. Depending on your mother's activity level and desired activities, some changes may need to be made but her orthopedic surgeon could talk to her about this before the surgery and be more specific.