How bad does a knee have to be before replacement? These are the factors that needed to be diagnosed before having a knee surgery: • When you suffering from pain and awkwardness problems it is difficult you to walk, stair-climbing, or quit out of a chair. • When aching knee pain problems you while sleeping, possibly keeping you from resting well. • When your knee is frequently swollen. • When your knee is bowed or has other defects. • When Physical treatment and medicine haven’t helped, you need a knee replacement operation.