Joint Replacement

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Biomaterials

Artificial joints such as shoulder implants are usually constructed from a plastic cup placed in the joint socket, made of ultrahigh molecular weight polyethylene (UHMWPE), and a metal or ceramic ball attached to a metal stem. The ball may be constructed out of metals such as titanium or cobalt chromium alloy or molded from ceramides such as aluminum oxide or zirconium oxide. (8)

For a more complete list of different types of polyethylene materials currently being used in implants, please refer to:

“Guide to Polyethylene in Joint Implants” http://www.slackinc.com/bone/ortoday/199910/chart.pdf

These materials are chosen in consideration towards the physiologic stress that the implant would have to endure, as well as its biocompatibility towards the surrounding tissue and the environment. Corrosion, friction, osseointegration (bone growth around the implant), and bone cement are also other major factors that must also be taken into account. (8)

Most of the problems that arise from joint replacements are because the materials get worn down. Excessive wear could cause millions of tiny polymer particles to be released in the surrounding tissues or fluid, which could stimulate the immune system and result in the necrosis of the cells in the area. This could cause the implant to become loose and hence would lead to replacement or revision surgery. (8)

A joint replacement usually lasts for about 8-12 years. This varies due to patient factors such as age and physical activity. (8)

Created by: Blair Smith, Connie Lee, Daniel Solomon, Matthew Whitson and Stephanie Chang
Date last modified: 5/2/2004