Thirty old (1^st generation) Cobalt-Chromium metal-on-metal (Müller design) hip components and 83 new (2^nd generation) Cobalt-Chromium metal-on-metal (METASUL™ design) hip components were examined for their in-vivo wear behaviour. The in-vivo wear behaviour of these retrievals was compared with their in-vitro wear behaviour. A running-in period of about one year is observed where the in-vivo wear rate for the whole bearing is approximately 25 μm/year. After this running-in period, the measured in-vivo wear rate of the whole bearing decreases to about 5 μm/year. A very good consistency is found between the in-vitro and in-vivo wear rate. The examination of the wear pattern shows abrasive wear for all the prostheses and some adhesive-fatigue wear areas for 10 per cent of the prostheses. The observed wear rate is independent of the wear mechanisms.

The metal-on-metal bearing can be considered as a very low wear articulation system.