When your doctor tells you that your Prosthetic knees is titanium he's not technically accurate. The prosthetic is an alloy that contains titanium. Titanium by itself would be too soft causing the implant to fail prematurely. I couldn't answer your question whether there is iron in it so I googled it as follows "a combination of materials, including titanium alloys, cobalt-chromium alloys, and medical-grade plastic (polyethylene)."
My problem was that my last doctor said "we can't do an MRI because your knee is magnetic," which is a total falsehood. My present doctor will schedule me for an MRI following a bone scan. Have a good day Ouchy.