Standing Up to the Test

This article analyzes changes in sterilization techniques that can substantially increase the life of implants. A result of the work on sterilization methods has led to a related development—crosslinking—that greatly increases the wear resistance of the joints’ polyethylene mating surfaces. The vast majority of the prostheses used in a half-million hip replacement procedures performed worldwide each year are a combination of metal and ultrahigh molecular weight polyethylene. Some experts believe that the overall effects of gamma radiation in air have been misrepresented. Howmedica recently developed a highly crosslinked polyethylene, called Crossfire, which achieves a 90 percent reduction in wear compared to standard polyethylene. The crosslinking is achieved with an elevated dose of gamma radiation, followed by heating the material close to its melting point. The polyethylene is then machined and packaged in a nitrogen atmosphere, and sterilized with gamma radiation.