Edge loading does not increase wear rates of ceramic-on-ceramic and metal-on-polyethylene articulations

The mal-positioning of total hip arthroplasty components can result in edge loading conditions. Purpose of this study was to determine if the wear rate of ceramic-on-ceramic and metal-on-polyethylene increases under edge loading conditions. The literature was reviewed to determine which of the commonly used hip bearings is the most forgiving to implant mal-orientation. Two 28-mm ceramic-on-ceramic articulations were tested in vitro: pure alumina (PAL) ceramic versus the new alumina-toughened zirconia (ATZ). Two 28-mm metal-on-polyethylene articulations were tested in vitro: conventional ultrahigh molecular weight polyethylene (UHMWPE) versus highly crosslinked polyethylene (HXLPE) stabilized with vitamin E. All bearings were tested at standard and at highest possible inclination angles. Hip simulator tests were run for five million cycles based on N = 3 tests per condition. The average wear rate of ATZ-on-ATZ is 0.024 mm(3) /Mcycles at 45° and 0.018 mm(3) /Mcycles at 65°. Wear rate of PAL-on-PAL is between 0.02 and 0.03 mm(3) /Mcycles at 45°, as well as 65°. The wear rate of UHMWPE was 31 ± 1 mm(3) /Mcycles at an inclination angle of 45° and 26 ± 1 mm(3) /Mcycles at 80°. The wear rate of vitamin E stabilized HXLPE was 5.9 ± 0.2 mm(3) /Mcycles at 45° and 5.8 ± 0.2 mm(3) /Mcycles at 80°. Edge loading does not increase the wear rate of ceramic-on-ceramic and metal-on-polyethylene articulations. The newest biomaterials showed markedly lower wear rates compared with their conventional counterparts. ATZ-on-ATZ showed the lowest wear rate of all tested pairings, but the vitamin E stabilized HXLPE seems to be the most forgiving material when it comes to implant mal-orientation.