The replacement knee joint consists of a flat metal plate and stem implanted in your tibia, a bearing surface of polyethylene and a contoured metal implant that fits around the end of the femur.The use of metal and polyethylene components enables optimum articulation (or joint mobility) between low-wear joint surfaces. Due to the flatter bearing of the knee implant, wear is less of a problem than in a hip implant with a very deep bearing.
In the long term, stainless steel is not often used in knee replacement implants due to the limited ability to withstand corrosion in the human body. It is more suitable for use as temporary implants such as plates and screws for fractures.
Cobalt-chrome alloys are metals that are hard, tough, resistant to corrosion, bio-compatible. Cobalt chromium is one of the most widely used metals in knee implants, along with titanium. There is no consensus on which material is better and more appropriate. While the percentage of patients with allergic reactions associated with the use of cobalt-chromium alloys is very low, one area of concern is the issue of small particles (metal ions) that may be released into the body as a result of joint movement. Sometimes these particles can cause reactions in the human body, especially in patients with allergies to special metals such as nickel.
Titanium and titanium alloys
In implants where high strength is not required, pure titanium is generally used. Pure titanium, for example, is sometimes used to create fiber metal, a layer of metal fibers bonded to an implant’s surface that allows bone to grow into the implant or allows cement to bond better to the implant for stronger fixation.Titanium alloys are naturally bio-compatible. In addition to titanium, they usually contain amounts of vanadium and aluminum. Ti6Al4V is the most commonly used titanium alloy in knee implants. Titanium and titanium alloys are highly resistant to corrosion, making them inert bio-material (which means that after being implanted in the body they will not change).