51315-5599-The Effect of Microseparation on Corrosion Rates of Metal-on-Metal Total Hip Replacements

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Product Number: 51315-5599-SG

ISBN: 5599 2015 CP

Author: Andrew Beadling

Publication Date: 2015

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IntroductionMost metallic biomaterials owe their corrosion resistance to a protective passive oxide film which can become damaged during articulation. Exposure of the reactive bulk alloy to the synovial fluid results in corrosive material loss. The degradation of Metal-on-Metal (MoM) Total Hip Replacements (THRs) is a complex mix of mechanical wear and corrosive phenomena as well as synergistic effects [1]. The ability to predict the performance of a MoM device therefore needs a greater understanding of the interaction between the tribology and electrochemistry during sliding.Methods28 mm HC Cobalt-Chromium (CoCr) alloy hip bearings were tested to one million cycles in a ProSim Deep Flexion Hip Simulator. The simulator was instrumented with a three-electrode electrochemical cell. The free corrosion potential (Ecorr) was monitored throughout each test. In order to determine the corrosion current (Icorr) and quantify the mass loss due to corrosion the resistance to polarisation (Rp) was periodically determined.A twin-peak loading cycle was used in part reference to ISO 14242-1 [2]. MoM bearings were tested either under a standard walking cycle or subjected to 0.8 mm microseparation. Both tests were performed with Foetal Bovine Serum as the lubricant diluted to 17 gL-1 total protein content using PBS. 0.03% Sodium Azide was also added to retard bacterial growth. Total material loss was determined using gravimetric and CMM volumetric assessment.ResultsUpon cyclic motion the Ecorr and Rp were seen to decrease and a corresponding increase in Icorr was noted. This indicates an increase in corrosion during sliding due to removal of the oxide layer. On average Icorr was higher for bearings subjected to microseparation.DiscussionThe corrosion currents measured under microseparation were often an order of magnitude higher than under a normal walking cycle suggesting more severe material loss as a result of corrosion during adverse loading conditions.References[1] Watson et al 1995 “Methods of measuring wear-corrosion synergism” Wear 181-183(2) pp 476-84[2] International Standards Organisation BS ISO 14242-1 2012 “Implants for surgery - Wear of total hip-joint prostheses - Part 1: Loading and displacement parameters for wear-testing”