Comparison of Visual Assessment Techniques for Wear and Corrosion in Modular Hip Replacement Systems

Wear and corrosion of implant metals have been associated with adverse tissue reactions and failures of total hips. However, the factors leading to component wear and corrosion, as well as the clinical effects of wear and corrosion, are not well understood. A visual inspection standard for taper corrosion and fretting, the Goldberg method, currently is used to quantify the amount of apparent corrosion damage present on an implant using a subjective score. We developed an approach to quantify the damage by creating digital microscopic images of the entire taper and trunnion surfaces, which enables an objective quantification of detailed wear and corrosion damage of the contacting surfaces, which we call the digital mosaic method (DMM). We compared the results of this new methodology to the Goldberg method and Anderson method (an expanded version of the Goldberg method). We examined the modular surfaces of ten retrieved metal-on-metal hip replacement systems. Each set of taper and trunnion surfaces were imaged and stitched into a composite image of the entire taper-trunnion surface. Three independent observers measured the surface area fraction of damage (wear or corrosion) for each surface, which in turn was compared with visual scores performed by independent observers on the same retrieved joints. To determine a measure of the intraobserver repeatability of the new method, a single reviewer measured the surface fraction of damage for the same set of explanted surfaces across different days, blinded to any previous specimen identification, with the image order randomized. The results of this study show that the DMM damage quantification correlates to the current visual scoring approaches (Goldberg and Anderson). The potential advantages to using this approach include better damage quantification, detailed analysis of specific locations, ability to identify matching damage locations on the two surfaces, and higher resolution of the contact area.