An Electrochemical Approach to Accelerate Mechanically Assisted Crevice Corrosion Damage on Modular Implant Interfaces

Corrosion within the crevice of modular tapers is one of the major mechanisms that leads to orthopedic device failures. However, the currently used fretting corrosion test methods involve extended test durations and are often burdensome. This study evaluates the feasibility of adding micromotion to crevices while being simultaneously subjected to cyclic polarization in order to accelerate corrosion damage. The addition of micromotion was intended to induce crevice and fretting corrosion between metals in a washer-rod combination geometry. Three commonly used orthopedic metals (316L stainless steel, SS316L; grade 5 titanium, Ti6Al4V; and cobalt-chromium-molybdenum per ASTM F1537-20, Standard Specification for Wrought Cobalt-28Chromium-6Molybdenum Alloys for Surgical Implants [UNS R31537, UNS R31538, and UNS R31539], CoCrMo) were used to form crevices in this study to evaluate the test method. A cyclic polarization control group in which no micromotion was present was used to determine the effect of the cyclic polarization alone. In addition, a fretting control group in which no cyclic polarization was conducted was used to assess the effect of micromotion without cyclic polarization. The results of this study showed that fretting corrosion damage can be achieved on Ti6Al4V and SS316L washer crevices when subjected to micromotion alone. The test method did not induce more corrosion on Ti6Al4V samples when crevices were tested with cyclic polarization alone. Furthermore, the results found that cyclic polarization in combination with micromotion did not achieve the same fretting corrosion damage on the CoCrMo samples as observed in explants. Still, electrochemical test methods have potential for accelerating corrosion damage within crevices when combined with existing fretting corrosion testing and therefore could potentially reduce test durations for fretting corrosion susceptibility evaluations for medical devices having modular taper connections.