Aim: The aim of our research is to study and compare physical and chemical phenomena on the surfaces of new and retrieved Ti6Al7Nb femoral components of cementless hip prostheses. Prostheses failures were due to three main causes: aseptic loosening, infection and latent infection. We wanted to assess whether differences in surface properties exist between prostheses with different failure cause. We wanted to know if the process of sterilization affects the surface properties. We investigated the impact of time since implantation affects the Ti6Al7Nb stem surface. Taper corrosion was also an object of interest, especially whether it affects the cause of premature prostheses failure.
Methods: In this retrospective study we analysed different surface properties of two new and thirty retrieved Ti6Al7Nb femoral components by several methods. Firstly, all the samples were cleaned and autoclaved. Wettability and roughness were measured. Scanning electron microscopy (SEM) was used to assess morphology, energy-dispersive X-ray spectroscopy (EDS), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) were used to analyse surface chemistry, electron back-scattered diffraction (EBSD) for phase analysis, and electrochemical measurements for the corrosion. Fluorescent microscopy was used to assess growth of bone marrow mesenchymal stem cells (BMSC) on grit-blasted Ti6Al7Nb stem surface. Taper corrosion was analysed with roughness and profile measurements as well as with potencio dynamic measurements.
Results: Our results showed wettability, roughness and the thickness and composition of oxide layer on the stem surface that were similar between all the investigated new stems and retrieved stems regardless of the cause of stem failure. We found corundum contamination in the surface and sub-surface of all the investigated new and retrieved stems. BMSC growth on grit-blasted Ti6Al7Nb femoral components is restricted, adhesion is limited, cells are porous and therefore more susceptible to infection. There was no relation between taper corrosion and the cause or time to premature stem failure.
Conclusion: Sterilization does not affect surface properties. Surface properties of the new and retrieved stems differ only slightly, regardless of the cause of stem failure. Type and time of premature stem failure is not affected by taper corrosion with the use of ceramic heads. We demonstrated that there is presence of retained corundum on stem surfaces and sub-surfaces for all the analysed new and retrieved implants. These particles are believed to cause inflammation in the tissue around the implanted stems which could cause osteolysis and aseptic loosening and failure of the stem.
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