2017 Volume 36 Issue 2 Pages 147-154
Objective: Improving wear and oxidation resistance has been recognized as the key task to achieve longer-term implant survival in vivo. Beta-sterilization is a unique sterilization method of B. Braun Aesculap and it has the potential to prevent oxidation because the process is completed in short time as compared to gamma-sterilization. In this study, we investigated the oxidative degradation of retrieved conventional tibial inserts using Fourier Transform Infra-red Spectroscopy (FT-IR) and Raman spectroscopy (RS).
Materials and Methods: We analyzed 12 retrieved and three unused tibial inserts made of beta-sterilized conventional ultra-high-molecular-weight polyethylene. The average in vivo time was 33.6 months (0.7-94.6). We obtained microtomed sections from three locations: medial, lateral and non-load zones. We calculated in each section the maximum values and the profiles of oxidation index, lipid and crystallinity along the thickness by FT-IR and RS.
Results: Increases of maximum oxidation index, lipid and crystallinity were observed in all the retrieved samples as compared with the unused samples; each parameter correlated with in vivo time in both load zones. Furthermore, the maximum oxidation index showed strong correlation with maximum crystallinity and maximum lipid. We observed the white band at the depth of 2-3 mm from the bearing surface in most of the slices obtained from the mid-term retrievals.
Conclusion: Our results show that oxidative degradation occurred in beta-sterilized polyethylene after in vivo exposure and the crystallinity increased along with the extent of oxidation. Lipid absorption was promoted in the contact area by the mechanical action of the femoral counterpart combined with mechanical stress, which exacerbated oxidative degradation. The free radicals generated during the process might trigger oxidative degradation close to the bearing surface in beta-sterilization, where a reduction of mechanical properties could cause delamination and wear damage.
