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Polyethylene in Knee Replacements: Brace Yourself

The knee joint endures more stress than any other joint in the human body. Thus, it is not surprising that it is often the first joint to fail. Knee injuries and normal aging can limit a person's mobility, motivating one to acquire a knee replacement. Such a manufactured joint has to react well within the human body, and endure the day-to-day strain sustained by such a heavily used joint. Most modern knee replacements are composed of a round metal plate attached to the femur that sits in a plastic bearing allowing the metal "ball and socket" joint to pivot. Titanium, cobalt, and nickel alloys are often used for the metal plates and femoral components, while ultra-high-molecular-weight polyethylene. This type of polyethylene is a high strength plastic making it relatively resistant to wear, but is compressible enough to cushion the impact exerted on the knee joint. These designs are still fairly new, and they have been relatively difficult to perfect. For example, one limitation of using polyethylene is that it wears down over time, often because of contact with the femoral components, causing gradual discomfort and limited mobility. Over time, the micro-motion between the femoral component and the polyethylene can wear down the plastic to such an extent that a total replacement is needed. Advancements have been made and research is underway to greatly extend the longevity of these devices, and with the implementation of ultra-high-molecular-weight polyethylene, this lifespan has already doubled. Engineers are perpetually striving to improve knee replacements by enhancing the quality of the materials used and the general mechanisms in which they used.

Resources
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