4 types of knee implants

Published: June, 2019

Thinking about a total knee replacement? There are a few different kinds of knee implants that are used in this procedure. The different types are categorized by the materials that rub against each other when you flex your knee:

Metal on plastic. This is the most common type of implant. It features a metal femoral component that rides on a polyethylene plastic spacer attached to the tibial component. The metals commonly used include cobalt-chromium, titanium, zirconium, and nickel. Metal-on-plastic is the least expensive type of implant and has the longest track record for safety and implant life span. However, one problem that can happen with plastic implants is an immune reaction triggered by tiny particles that wear away from the spacer. This can cause bone to break down, leading to loosening and failure of the implant. Advances in manufacturing have greatly reduced the rate of wear in the plastic.

Ceramic on plastic. This type uses a ceramic femoral component instead of metal (or a metal component with a ceramic coating). It also rides on a plastic spacer. People who are sensitive to the nickel used in metal implants might get the ceramic type. Plastic particles from this type of implant also can lead to an immune reaction.

Ceramic on ceramic. The femoral and tibial components are both made of ceramic. Ceramic parts are the least likely to react with the body. However, ceramic joint prostheses can make a squeaking noise when you walk. In rare cases, they can shatter under heavy pressure into pieces that must be removed by surgery.

Metal on metal. The femoral and tibial components are both made of metal. Metal-on-metal implants have been used much less often in recent years because of concerns over traces of metal leaking into the bloodstream. The metal comes from the chemical breakdown of the implant hardware. All metal implants originally were developed to provide longer-lasting joint replacements for younger people.But the traces of metal can cause inflammation, pain, and possibly organ damage. Metal-on-metal implants may be considered only for young, active men, because they may last longer than other materials. Women of childbearing age can't receive these implants because the effects on a fetus are not known.

To learn more about your options for knee replacement surgery, read the Harvard Medical School guide Total Knee Replacement.

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