Abstract
Ceramic-ceramic (C-C) bearings have 20 years clinical experience with alumina ceramics. This system is re-emerging because of its demonstrated excellent wear performance compared to metal-PE or ceramic-PE. However, alumina ceramic imposes a design limitation to reduce breakage risk: most of the implanted C-C systems present a head larger than 28 mm. Zirconia ceramic is three-times more mechanically resistant and has proven its efficiency in ceramic-PE couple. As a result, a new C-C bearing with zirconia head has been studied. Excellent wear performance of the zirconia-alumina (Z-A) combination system has already widely been proven through multilaboratory experiments on a hip simulator. The mechanical aspect is investigated here to analyse the benefit of a zirconia head in a C-C system. This aspect has been first studied by Finite Element Analysis (FEA) and then validated by experimental testing.
The first series of tests on the 28mm system confirmed the FEA predictions: the breakage loads were correctly estimated for each assembly, showing that FEA is an effective tool to predict breakage load and location. The second series of tests were performed on 22.22mm systems. FEA predicted that the Z-A system should pass the 46 kN contrary to the A-A system. Breakage of the A-A system is expected to be in the head.
In conclusion, Z-A combination offers higher mechanical security for the existing C-C designs but above all, larger design choice than A-A system. Considering that wear performances are equivalent, the Z-A system can be thought as the logical evolution of A-A system.
