Simultaneous Hip Head-Stem Taper Junction Measurements of Electrochemical Corrosion and Micromotion: A Comparison of Taper Geometry and Stem Material

Fretting corrosion or mechanically assisted crevice corrosion is a current topic of research in total hip arthroplasty highlighted by the modularity of the head-neck taper junction. The extent of corrosion may be influenced by a multitude of factors, and in this study, we examined two specific variables: material combination and taper geometry. Corrosion performance was quantitatively assessed by measuring fretting corrosion at the taper junction as well as relative micromotion between the head and stem components. To examine the effect of material combinations, stems composed of either Ti-6AI-4V or TMZF (R) were tested with CoCrMo femoral heads. To study taper geometry, a V40 (TM) taper design was compared with a C-taper design. Cyclic fatigue loading was applied to the test specimens, increasing load from 100 to 3200 N and then continuing loading to 1 million cycles. All tests were performed in phosphate-buffered saline solution at room temperature and electrochemical data analysis included determination of onset load, average current, average open-circuit potential, peak-to-peak current, and absolute change in potential. Micromotion fixtures were attached rigidly to the head and proximal stem. The micromotion output was used to calculate pistoning of the head along the stem, rocking of the head about the stem, and subsidence (or seating or slipping) of the head against the stem. The electrochemical data showed that the mean onset load for different groups was in the range of 1075 to 1194 N and average currents up to 2 mu A were recorded for different sample groups during cyclic loading. Fretting corrosion and micromotion measurements in this study showed that the variation produced by material combination and taper design within the range of test groups tested were less than the variation that existed in each test group.