The Effect of Implant Size on Fretting Currents of Acetabular Cup-Liner Tapers During in Vitro Cyclic Loading

As dual mobility hips become more popular, there is a clinical need to investigate design features that will impact tribocorrosion of these devices. While previous studies have investigated both corrosion and wear damage, the effect of device size on fretting corrosion response has yet to be evaluated. In this study, we compare two implants of the same design (EMPHASYS Hip Solution) but with different-sized acetabular cups (66 mm vs 44 mm) representing the range of sizes typically used. We hypothesized that the smaller implant would perform better due to the smaller taper engagement area and the smaller moments imparted during normal activities. Each device underwent a physiologically representative intermittent cyclic load between 400 N and 4000 N in 50,000 cycle increments with pauses in between, up to a total of 3,000,000 cycles and 110 h at 9 Hz in phosphate-buffered saline (PBS). Under potentiostatic control (-50 mV vs Ag/AgCl), fretting corrosion currents were generated and monitored with intermittent measurement of baseline currents. Post-testing, solution ion levels were measured using inductively coupled mass spectrometry (ICP-MS). Results showed there was no difference between devices when comparing average current, average cumulative charge, average decay constant (s-), total volume lost and solution ion levels. We report a total volume loss of 0.0028 ± 0.0015 mm³ and 0.0052 ± 0.0035 mm³ for the 66 mm and 44 mm implants, respectively. The devices had only minor evidence of fretting or corrosion damage. These results suggest there is no difference in fretting corrosion performance based on implant size.