The lifespan of a knee prosthesis primarily depends on the durability of its wear-prone components, especially the special compressed plastic (polyethylene) interface surfaces. Modern knee prostheses can function for up to 25 years under suitable conditions. However, this duration varies significantly based on how the patient uses the prosthesis and their adherence to doctor's recommendations. Regular exercise and maintaining an ideal weight can significantly extend the lifespan of a knee prosthesis.