Titanium knee joint replacement possible?

Yes: Most knee replacements are made of cobalt alloys because they are harder. The titanium is generally too soft to work as a knee surface. There is, however, one total knee replacement made of titanium where they have hardened the end of the titanium (making it a ceramic compound).

Yes: Titanium is commonly used in orthopaedic implants. In knee replacement, titanium can be used for the tibial prosthesis (part on top of your shin bone). Because titanium is a soft metal, it is not generally used for the femoral prosthesis (on the end of your thigh bone) however. The femoral proshtesis is usually made of an alloy of chrome and cobalt, or an oxidized zirconium (known as oxinium).