The role of surface pre-treatment on the microstructure, corrosion and fretting corrosion of cemented femoral stems

The use of cemented femoral stems is common practice worldwide with strong clinical data supporting their use. Over the years, different surface processing techniques have been employed to enhance the performance of the stem-cement interface. As a result different clinical outcomes and visual presentation at revision has been observed. Whilst research has focussed on increasing adhesion and better load bearing capacity, the effects of surface processing on the degradation of cemented femoral stems has not been investigated. The aims of this study was to investigate the effects of surface processing on the subsurface microstructure, surface chemistry and tribocorrosion degradation mechanisms of cemented tapered femoral stems subjected to polishing and blasting (Vaquasheen) processes. Cemented femoral stems were orientated and loaded according to ISO 7206-4 for 500,000 cycles in 0.9% NaCl at 37 °C. A three-electrode electrochemical cell was integrated into the mechanical test to facilitate in-situ corrosion measurements. The severity and mechanism of damaged were assessed scanning and transmission electron microscopy, X-ray photoelectron spectrometry, solution mass spectrometry and white light interferometry. Surface processing influenced the level of tribocorrosion at the interface with polished surfaces demonstrating higher levels of tribocorrosion and ion release when compared to the blasted surfaces. Surface analysis consistently demonstrated the presence of a SiO₂ layer on the vaquasheened stems thought to originate from the glass bead blast matrix. This resulted in lower levels of corrosion both under static and tribocorrosion assessment. In conclusion, blasted surfaces resulted in lower wear induced corrosion when compared to the polished surfaces. However the total metallic ion levels did not follow the same trend. This is thought to be due to the formation of metallic debris and dissolution of debris due to abrasion of the femoral stems.