Metal on metal hip replacements have been one of worst failures in recent years in terms of orthopaedic implants. Some of these devices have had catastrophic failure rates, with reports of 48% failure at 6 years. The failure of these devices has led to considerable suffering, pain and reduction in quality of life; consequently, they have given rise to high costs and multi-million-dollar legal cases. This talk will describe the history of the current metal on metal failure and discuss some of the reasons why might have occurred. It will also consider the reasons that wear debris arising from the trunnion is worse in terms of biological activity then that arising from the bearing surfaces.