Aims: To understand why during routine analyses of the physico-chemical properties of retrieved UHMWPE prosthetic components (Pes), it was noticed that some cups, which were directly in contact with bone, evidence a material loss in correspondence with the area adjacent to bone.

Methods: PEs retrieved during revision surgery and stored in formalin prior to observation, have been analysed by Fourier Transform InfraRed (FTIR) spectroscopy and Scanning Electron Microscopy (SEM).

Results: The results of the FTIR analyses did not display appreciable differences compared to those of the majority of the retrieved prostheses. Oxidation of UHMWPE was detected, but it is known to be due to sterilisation with high energy radiation in air, under uncontrolled conditions.

The SEM analyses indicated that the PEs surface which was directly in contact with bone shows an anomalous degradation. The surface looks as it has been corroded or “bitten” and its morphology is significantly different from that of surfaces abraded either in vivo or in vitro.

Conclusions: The results so far obtained seem to indicate that the surfaces, which have been in contact with bone during the implant time, undergo a selective biodegradation process, facilitated by gamma in air sterilisation, and influenced by the biological reactivity of the patient (such as osteclast activation).