Ceramic-on-ceramic hip retrievals: SEM and fluorescence investigations.

Although polyethylene is a satisfactory bearing for many patients, total hip replacements are being performed in younger and more active patients, who challenge the limitations of the standard material. Polyethylene wear problem plays out as a biological disaster in the body. Any use of the joint, such as walking in the case of hips, results in a cyclic articulation of the polymer cup against the metal or ceramic ball. Ceramic-on-ceramic (COC) hip bearings (alumina & zirconia) were introduced to solve polyethylene problems such as osteolysis and wear. Ceramics appears to be ideally suited to joint prosthesis, because of their hardness and excellent biocompatibility. Alumina was introduced more than 40 years ago with good clinical results. Zirconia has become a very popular alternative to alumina because of its higher mechanical properties and higher toughness. Nevertheless, problems related to the steam sterilisation and the hydrothermal stability of zirconia in the body havae been reported. Zirconia needs an addition of yttria to be used at room temperature, but undergoes slow degradation as a consequence of progressive crystal transformation with time. To better understand the wear mechanism of ceramic bearings, in this study, we investigated several long-term retrivals of different materials developed during last decades; Biolox, Biolox-Forte and Delta components were studied through scanning electron miscroscope (SEM) amd fluorescence spectroscopy. The residual stress state in the worn specimens was evaluated by the frequency shift and broadening of the fluorescence bands due to the Cr3+ ions naturally present in alumina ceramics as trace impurities or expressly added by the manufacturer in Delta components. The analysed specimens were all wear failures without fracture, to avoid possible influences of other parameters on the failure mode. The study of worn ceramic retrievals is useful to very if damage patterns generated by hip jount wear simulation are comparable to those evident on explanted prostheses due to physiologic hip function.