Hi worried 25: it is a dilemma when you need a knee replacement but are too young. The reason for this is that they canonly give you 2 or at the outside, three replacements durng your lifeetime and a knee unit only lasts about 10 years on average. Each time you have a replacement done it means shaving off part of the bone so that the more ops you have the shorter the leg, that was how it as explained to me when I was 50 and told I had to wait until I was 55 at the least. HOWEVER. If the damage s not universal the is an op called a unicompartmental knee replacement and this just replaces teh damaged parts with metal. I had this done when I was 51 but it's not suitable for all. I looked up the info on the web and went armed with the nfo too my orthopod and he was honest enough to admt I could have the job done. Well worth looking at.