Correlating fretting corrosion and micromotions in modular tapers: Test method development and assessment

Mechanically assisted crevice corrosion (MACC) has become a significant problem in the orthopaedic device industry, particularly in modular devices with metal-on-metal tapered interfaces. Fretting corrosion in the presence of a crevice accelerates corrosion processes and in some instances may lead to failure of the implant. To date, no device test method can systematically assess and correlate corrosion and micromotions at modular interfaces. Hence, the goal of this study is to develop a short-term incremental fretting corrosion test method that can evaluate the combined effects of mechanics and electrochemistry on the performance of modular tapers. Two modular taper groups, representing design, material and seating combinations thought to yield a high sensitivity and low sensitivity to fretting corrosion, were tested. These experiments used a custom-built test fixture to hold the neck component of the taper and an electrochemical setup for monitoring corrosion. For micromotion measurements, two submersible noncontact differential variable reluctance transducers were mounted to the neck component (superior and inferior head-neck junction) positioned closely to the head component to detect any micromotions that may arise during loading. Seating displacements were studied by measuring head displacement during seating. The developed test method can measure both fretting corrosion currents and micromotions at the head-neck junction. Significant differences were seen in terms of corrosion currents and micromotions for the two groups and demonstrated the ability of the test to link corrosion currents and micromotions. This short duration test method can be used to evaluate performance of modular implants with different taper geometries, materials, and other conditions to assess the relative effects of fretting corrosion in the early cyclic loading of the junctions.