What is the prognosis? In many ways, a total knee replacement is similar to changing a set of car tyres. How long the tyres lasts depends on how much the car is used, on what types of roads the car is driven, how heavy the car is, and whether or not the car is properly serviced and maintained. Similarly, how long a total knee lasts depends on how much it is used, what types of activities it is used for and whether you have regular follow-ups. Average life of Total Knee replacement is 12-15years.