Fretting Corrosion of Plates and Screws: An In Vitro Test Method

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Abstract
A laboratory fretting corrosion simulator was constructed for studying the fretting corrosion of the contact areas between screw heads and plate hole countersinks of surgical implants used for fixation of broken bones. The system was constructed so that the tests could be done under sterile conditions, thus permitting the use of proteinaceous as well as conventional electrolyte solutions. Studies were done to investigate the effects of contact stress as controlled by screw torque, the effects of blood serum proteins, the effects of proteins at different solution pH values, and the effects of mixing metals. The alloys used were Type 316L stainless steel, MP35N, titanium, and titanium-6AI-4V. The results demonstrated that statistically significant data can be obtained with a small number of specimens. The rate of fretting corrosion was independent of load over a limited range. The presence of proteins significantly reduced the fretting corrosion of stainless steel and MP35N, had no effect of Ti-6AI-4V, but increased the fretting corrosion of titanium. In solution with pH values acidic to its isoelectric point, the protein albumin had a negligible effect; whereas at solution pH values basic to its isoelectric point, fretting corrosion was reduced. Mixing of metals had an effect on the fretting corrosion of MP35N and titanium, but no effect on stainless steel.

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