Design-related fretting wear in modular neck hip prosthesis

An accelerated cyclic loading corrosion test was used to determine the corrosion behavior of a commercial (GSP) and a prototype titanium hip prosthesis each with a modular neck. Four GSP and four prototype stems were subjected to a 2-Hz cyclic load ranging between 200 and 2,100 N for 1,000,000 cycles. Three stems were tested in an environment of FeCl3 solution, three stems were tested in Ringer's solution, and two stems were tested in air. After cyclic loading, the specimens were carefully examined with optical and scanning electron microscopy (SEM). None of them showed macroscopic or microscopic signs of corrosion, regardless of the environment to which the specimens were subjected. However, macroscopic evidence of mechanical fretting was present at the neck-stem modular junction, primarily concentrated at the medial contact point between stem and neck, especially for the prototype stems. SEM analysis confirmed these observations. The appreciable differences observed between the two designs suggest that the problem can be minimized or eliminated with an accurately designed taper fitting.