Vibrational spectroscopy study of the oxidation of Hylamer UHMWPE explanted acetabular cups sterilized differently.

Ultra-high-molecular-weight polyethylene (UHMWPE) has been used for over 40 years for acetabular cups in total hip joint prosthesis. Hylamer is a hot isostatically pressed material with high crystallinity. Early loosening due to extensive oxidation and phase transformation has been observed for this material. To analyze the reasons for its high tendency to oxidize, we have examined by FT-IR spectroscopy explanted acetabular cups γ-sterilized in different ways. The oxidation and wear rate observed were: Hylamer cups γ-sterilized in air with a long shelf life > Hylamer cups γ-sterilized in air with short shelf life Hylamer cups γ-sterilized in nitrogen. Our data indicate the important role of the shelf life on the oxidation of the cups: the samples γ-sterilized in air characterized by a shelf life greater than 3 years showed severe oxidation, a high wear rate, and marked debris production with delamination and the formation of a brittle zone in the more oxidated regions. In these regions we observed an increase in crystallinity, which was probably due to the decrease in the molecular weight of PE. The high oxidation was probably due to the modifications induced by the material treatment.