Well, you can always depend upon this forum to find out all sorts of tidbits of information like this!! I just dug out some old hip and knee prostheses and weighed them and found that, metal on metal or metal on plastic, they all weigh in at around 250-300gms (9-10½ ozs). The two I weighed were stainless steel and cobalt chrome. Titanium is a very much lighter material but I don't have a specimen in that so can't exactly say what it would weigh. And btw, this is generally about the same weight as the bone that's been removed!