As a child I had Perthes disease (a rare, degenerative disease of the hip), and it has given me pain for 3 decades now. I've known that a joint replacement is in my future for essentially my entire life, and I was told as a kid to wait until the technology was better. There has long been talk about biological replacements, but nothing seems close to panning out, and the standard still seems to mean sawing off parts of your bones and replacing them with metal. The biggest change seems to be in the plastic parts and the addition of ceramics in places. My understanding is that both hip and knee replacements have benefited.