Metal-on-metal hip prostheses: where are we now?

In the late 1950s John Charnley, working in the north of England, introduced Teflon as a joint bearing surface material in his then visionary “low friction” hip joint replacement. Initial clinical success was soon followed by catastrophic mechanical failure and local tissue destruction owing to foreign body soft tissue reactions, and the use of Teflon in prostheses was abandoned by 1962.1 Fifty years later this cycle of promising innovation followed by unforeseen complications seems to be repeating itself with metal-on-metal hip prostheses that use large diameter (≥36 mm) bearings.

Charnley’s solution was to use high density polyethylene, and this is still a good choice of bearing material for older patients. However, in young patients with high physical demands, polyethylene prostheses wear out too quickly and often need to be revised. The introduction of hard wearing contemporary metal-on-metal bearings in the 1990s promised an end to prosthesis failure related to wear debris and better biomechanical function owing to the larger more natural diameter of the replaced joint. Initial enthusiasm led to about a million of these bearings being inserted worldwide during the past decade. However, reports of poor …