Abstract
A first introduction of a successful metal-on-metal (m-o-m) articulation was made by G.K. McKee in 1956 using a cast CoCrMo alloy for the head and cup. Long-term clinical investigations of m-o-m and polyethylene-on-metal articulation showed similar 20 years follow-up survival rates. This and very good wear results obtained with some of the first generation m-o-m articulation led to a re-introduction of the m-o-m articulation in 1988. A healthy hip joint has a very low friction coefficient and almost no wear due to the optimal lubrication, which, under normal conditions, completely separates the two articulation surfaces. On the other hand all artificial hip prostheses are unable to produce or maintain a permanent lubrication film. Therefore, the surfaces of the prostheses are always subject to wear. Compared to polyethylene liners, wearing at an average linear rate of 0,1 to 0,2mm per year, m-o-m articulations showed generally very little wear. In vitro simulations of the second generation m-o-m articulation on a Stanmore hip simulator showed a steady wear rate of 5.6±7.3μm per million cycles, with a higher wear rate during the running-in phase of about one million cycles. The analysis of over 200 second-generation m-o-m retrieved hip implants showed an average linear wear rate of approximately 5μm per year after the running-in period, with a follow up time of up to ten years. There’s a great concern about the incidence of cancer after a total m-o-m hip replacement. It is very difficult to find a causal relationship between THR and cancer occurrence, as in some studies many cancers were detected within two years after THR, which indicate rather an associative relationship. However, the summarized results do not indicate an increased cancer risk after m-o-m total hip replacements. Over 130,000 m-o-m articulations have been implanted since 1988 and the clinical results have been excellent matching or surpassing current gold standards for hip replacement.
The abstracts were prepared by Nico Verdonschot. Correspondence should be addressed to him at Orthopaedic Research Laboratory, University Medical Centre, PO Box 9101, 6500 HB Nijmegen, The Netherlands.
