[Sphericity measurements on the McKee-Farrar and Weber-Huggler total hip prostheses]

Long-term results of a contemporary metal-on-metal total hip arthroplasty: a 10-year follow-up study

The goal of the study was to evaluate the long-term results of a metal-on-metal articulation. We evaluated the results and histologic findings in patients who had undergone revision. One hundred total hip arthroplasties with a Lubrimet metal-on-metal articulation (Smith and Nephew, Rotkreuz, Switzerland) were implanted in 99 consecutive unselected patients in 1995 and 1996, and the results were prospectively analyzed up to a mean of 126 months postoperatively. Periprosthetic tissues of all 6 hips that had undergone revision because of aseptic loosening, mechanical failure, or periprosthetic fracture showed metallosis and extensive lymphocytic and plasma cell infiltration around the metal debris. With removal of the component because of aseptic loosening as the end point, survivorship was 98% for the stem and 96% for the cup.

Die Metall-Metall-Gleitpaarung in der Hüftendoprothetik

It was about 1966 that the metal/metal coupling was introduced into clinical use by McKee and Watson-Farrar. The main arguments for the introduction of this hard/hard coupling were the low wear rates compared to polyethylene couplings and the long-term stability of the metal components. The metal/metal couplings of McKee and Watson-Farrar could not meet the requirements of corresponding long-term results (loosening rates of more than 50% in part). The reason was the inadequate manufacturing quality, but also the random combination of components of different manufacturers. Nevertheless, remarkable long-term results could be reported and they were the reason for introducing a modified metal/metal coupling into clinical use in 1999. This metal/metal coupling of the second generation is characterised by modified CoCrMo materials, but also by definitely excellent manufacturing technologies. The clinical results seem to be better due to improved material quality and manufacturing technique. However, the question remains whether the high Co and Cr level, which is often noticed, has any pathological relevance.

Experience with the Metasul total hip bearing system

The author and Sulzer Medical Technology Ltd, Switzerland, have developed a new generation of metal on metal bearing total hip joints. The design is different than the McKee type prostheses in that the cobalt chrome alloy heads and cups (Metasul) are of the highest precision with controlled loose fitting. These allow low friction and low wear of approximately 5 micrometers per year. It is anticipated that debris related late loosening will be avoided by the use of this design. Approximately 30,000 Metasul hearings have been produced. The first 110 Weber metal on metal hip implants have been analyzed. No adverse effects from the wear of the new metal on metal components have been noted in this series.

[Studies on the surface and new joint capsule of McKee-Farrar prosthesis implanted for several years (author's transl)]

These studies are intended as a critical contribution to the question, wether the McKee-Farrar (MF) prosthesis, on account of its stronger friction and the consequences of this, as compared to other models, still has its justification or wether these "secundary" manifestations indicate that this prosthesis should be abandoned. Studies on primary and secundary alteration of the surface were carried out on exchanged MF prosthesis with the aid of the grid electron microscope. The signs of wear are clearly visible and can be differenciated from production artefacts. The movement and deposit of abraded particles into the new joint capsule was studied qualitatively and quantitatively with the aid of radioisotopes. All samples showed an increased accumulation of chrome in the tissues as compared to cobalt. There is no indication of significant damage. On the basis of the results of these studies and on account of the favourable personal experience from a surgical and clinical point of view -- particulary with reference to minimal preparation of the acetabulum and ready replacement, the MF prosthesis will continue to hold its place as the standard model for total prosthetic hip joint replacement.