It is time to do a knee replacement when conservative Physiotherapy treatment has not allowed you to regain your normal function. I would suggest that you try a Custom unloader knee brace first before doing a knee replacement as this can ‘buy you a few extra years of comfort’. When you have done all of these things and you still cannot walk comfortably, it is time to do the surgery. Wait as long as you can but dont allow it to significantly affect your ability to get on with your life.