Metal-on-metal bearings for total hip arthroplasties have an 80-year long clinical history with a first implantation done in England in 1938. With a few early exceptions, the alloy used for these metal-on-metal bearings was always a cobalt-chromium-molybdenum alloy, which is a very common alloy in modern orthopaedic technology.
Based on the good clinical results seen in the early 80’s with some patients with a metal-on-metal bearing implanted in the 60’s, a research development was conducted by Sulzer Medizinaltechnik in Switzerland to better understand the tribology of these bearings. Two major improvements were made: (1) development of a wrought high carbon cobalt-chromium-molybdenum alloy and (2) optimization of the bearing clearance. These two improvements allow Allo Pro and Protek to re-introduce small diameter metal-on-metal bearings in the early 90’s under the tradename Metasul™. As the clinical results of these small diameter metal-on-metal bearings were excellent, they were used as a basis for the development of large diameter metal-on-metal bearings, especially for resurfacing prostheses. The research conducted in the late 90’s demonstrated that large diameter metal-on-metal bearings have definitively an excellent in-vitro tribological behaviour based on partial or full film lubrication. These good in-vitro results lead to the market introduction of these large diameter metal-on-metal bearings, not only for resurfacing prostheses, but also for total hip arthroplasties. These bearings were rapidly “adopted” by orthopaedic surgeons for their multiple advantages (stability and range of motion). Their early clinical results were promising, but a small number of patients developed some adverse biological reactions with these bearings.
This plenary talk will analyse the reasons for these adverse biological reactions and investigate the patients’ consequences, the media and legal implications of these large diameter metal-on-metal bearings.