A question came through on our blog recently regarding the composition of the specific materials used in the ConforMIS Knee Prosthesis. That’s a great question and one that I’m happy to address.
Today, most of the knee implants that are on the market are made from chrome cobalt molybdenum. Most of us have heard of chrome, seen, and touched it. Chrome is the shiny metal that makes cars gleam and is used to coat many other metals because of its low friction ratio.
Cobalt is probably less familiar but is a heavy metal ore that is relatively rare. In its polished state, it is silver with a blue tint (cobalt blue). It is usually collected as a byproduct from mining other ores, such as nickel, silver, copper, or manganese. It can be magnetized, is very strong and heat-resistant, which makes it useful for industry. When mixed with chrome, it has a very high specific strength.
Molybdenum might be the material that gives you pause unless you are a chemistry major. In the periodic table, Molybdenum’s symbol is MO, atomic number is 42, and is in period 5, group 6. Known for its strength, weldability, as an anti-corrosive, and as a solid lubricant (anti-friction properties), it is the perfect addition to an alloy that is going to be used for a joint replacement prosthesis.
This metal alloy has been tested over and over in the laboratory for wear and tear (put through millions of repetitive motions), safety in the human body and for use in contact with human bone, soft tissue, synovial fluid, blood and other bodily fluids. Of course, there is a very rare chance that someone could have an allergy to the metals contained in the alloy. In a informal poll of the surgeons in my practice while writing this article, not a single surgeon could say that a patient had a proven allergy to the metals in an implant that required its removal. I’m sure if you Googled it, you may find a case, but in the many years of combined practice here at OSC, I feel it is safe to say these metal alloys are quite safe.
I would be remiss if I didn’t also address the “plastic” in the knee prosthesis, which is actually a sterilized polyethylene which has a coating infused with vitamin E. This polyethylene is also wear-and-tear, strength and human tested. Today, it seems almost impossible to wear this out during a patient’s lifetime!