Effects of neck extension, coverage, and frequency on the fretting corrosion of modular THR bore and cone interface

Examination of retrieved modular total hip replacements (THR's) has identified fretting corrosion as one of the principal mechanisms of implant corrosion at the bore and cone interface. Increased instability due to increased neck extension has been attributed to one of the design factors affecting corrosion rates. A series of experiments was conducted on THR's with cobalt chromium molybdenum alloy heads and Ti 6Al 4V stems, which demonstrated higher fretting corrosion currents with longer neck extensions. Shortening the skirt reduced corrosion rates. In a second series, the effects of wave form and cycling frequency demonstrated higher currents with a ramp versus a sine wave, and higher currents with higher frequencies. Examination of the frequency components of the Paul curve for loads on the hip during gait demonstrated that higher frequencies may be appropriate for device testing.