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Joint Replacement Implant Materials

Jan 20, 2018

Joint Replacement Implant Materials

The replacement knee joint is comprised of a flat metal plate and stem implanted in your tibia, a polyethylene bearing surface and a contoured metal implant fit around the end of the femur. The use of components made from metals and polyethylene allow for optimum articulation (or joint mobility) between the joint surfaces with little wear. Because the knee implant has a flatter bearing, wear is less of a problem than in a hip implant which has a very deep bearing.


Materials which can be used in knee implants are:


Titanium and Titanium Alloys

Pure titanium is generally used in implants where high strength is not necessary. For example, pure titanium is sometimes used to create fiber metal, a layer of metal fibers bonded to the surface of an implant which allows bone to grow into the implant or allows cement to better bond to the implant for stronger fixation.

Titanium alloys are bio-compatible in nature. They commonly contain amounts of vanadium and aluminum in addition to titanium. The most used titanium alloy in knee implants is Ti6Al4V. Titanium and titanium alloys have great corrosion resistance, making them inert biomaterial (which means they will not change after being implanted in the body).

Titanium and its alloys have a lower density compared to other metals used in knee implants. Additionally, the elastic nature of titanium and titanium alloys is lower than that of the other metals used in knee implants. Because of this, the titanium implant acts more like the natural joint, and as a result, the risk of some complications like bone resorption and atrophy are reduced.

For this, surface of the titanium is modified by coating the implant with hydroxyapatite, a bioactive surfacing agent that will ultimately bond as the bone grows into it.


Tantalum

Tantalum is a type of pure metal, which has excellent biological and physical properties, namely flexibility, corrosion resistant, and biocompatibility. Recently, a new porous substance has been made of tantalum named Trabecular Metal. It contains pores, the size of which makes this material very good for bone in-growth. In addition, Trabecular Metal has an elastic nature which aids bone remodeling.


Zirconium alloy and all plastic tibial component:

Zirconium alloy is used in a new ceramic knee implant. The zirconium alloy is combined with an all-plastic tibial component, replacing the metal tray and plastic insert used in other knee replacements. It is believed that this new knee could last for 20-25 years, substantially more than the 15-20 years that cobalt chromium alloy and polyethylene implants are effective. The new combination can be lubricated, which results in a smoother and easier articulation through plastic.


Another important characteristic of this material is that it is biocompatible, meaning that people who have nickel allergies and cannot have knee implants made of cobalt chromium alloy (because nickel is an ingredient of cobalt chromium alloy). Zirconium alloy implants eliminate the risk to nickel-allergic patients because this new material contains no nickel.

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