Influence of surface topography on junction strength of modular hip endoprostheses

The improved adaption of a modular hip endoprosthesis to patient-specific anatomy by means of a neck adapter is accompanied by the risk of a higher revision rate. This is due to micromotions leading to friction wear and corrosion of the additional taper interface. This results in the need to manufacture a load-adapted interface of modular hip endoprostheses. In this study, the influence of the machining processes turning and deep rolling on the surface topography of outer tapers of TiAl6V4 ELI and CoCrMo28 was investigated. In order to gain knowledge about the junction strength in dependence of the surface topography, tapers were joined and the separation force was investigated during push out tests. Results indicate that the adjustment of surface topographies of the outer taper is associated with a higher reproducibility in deep rolling than in turning. In addition, for the turning process inner tapers have a higher scattering of the investigated roughness parameters of the surface topography than the outer tapers. For the investigated taper angle of 5.665°, the influence of the surface topography on the separation forces is not significant. However, there is a little scatter of the taper angles of the samples depending on the machining process which leads to a difference between the inner and outer taper angle. This could significantly reduce the contact area of the junction and could be an explanation for the lack of significance of the separation forces we observed. Furthermore, no significant dependence of the separation forces on material properties was observed.