| An experimental apparatus has been designed and manufactured for the testing of in vitro performance of the interface between the femoral head and neck in modular artificial hip joints. The implants are subjected to a loading scheme and an environment resembling that found in vivo.;Commercial zirconia ceramic femoral heads and titanium alloy stems of a generic modular hip implant design were investigated to identify the quality of the methods used to inspect the finished components, including comparison with design specifications. Results from cone angle measurements of external versus internal cones obtained by the same machine show that for the internal cones there was an eight fold increase in the deviation of individual measurements from the sample average for each head. This increase indicates that it is more difficult to measure internally than externally. The analysis also shows that common methods used for obtaining conicity and circularity data on coordinate measuring machines may not be adequate.;The femoral head-neck interface of twelve sets of modular hip implants with zirconia ceramic femoral heads and titanium alloy stems were tested in vitro, on the custom built apparatus, for one million cycles each. A factorial experimental design was used, that involved short and long femoral neck lengths; proximal, uniform and distal cone fit; and varying and constant loading configuration. Uniform cone fit produced significantly more corrosion, in the form of titanium oxide removal and subsequent ceramic material deposition on the neck surface, than either proximal or distal cone fit. Variations in femoral neck length and loading configuration did not change cone performance. This study concludes that a deliberate distal gap between the femoral head and neck should be introduced when using ceramic heads. |
