Abstract
The Exeter totally collarless, double-tapered femoral component was developed in 1969 jointly at the School of Engineering at the University of Exeter and the old Princess Elizabeth Orthopaedic Hospital. At the time, in common with a number of implants in contemporary use, the new Exeter stem was manufactured from the rather ductile stainless steel EN58J. The original version of the Exeter stem had a polished surface. This feature was not part of the original design specification, but was demanded by the current British standard governing the use of EN58J in orthopaedic implants. At that time, no thought was given to the possibility that the surface finish of the stem might influence outcome.
Used from 1970 to 1975, the original stems rarely came to need replacement because of loosening. The major complication was the incidence of stem fracture, first seen in 1973, which has reached 4% over a 25 to 30 year follow-up. A stronger stem was introduced at the beginning of 1976. This was manufactured from 316L. As there was no standard demanding a polished surface, this stem was manufactured with a surface two orders of magnitude rougher than the surface of the original polished Exeter stems. While the introduction of this stem almost completely solved the problem of stem fracture, with it appeared notable problems of femoral endosteal bone lysis and aseptic stem loosening, hardly seen with the original polished stems. The study of retrieved prostheses showed the matt surface stem to be prone to abrasive wear against the inside of the cement mantle, and that this phenomenon could lead both directly and indirectly to stem loosening.
Unfortunately, a decade passed before the polished stem was re-introduced in 1986. A monobloc version was used until the beginning of 1988, when the modular Exeter Universal stem was introduced. With both the monobloc and modular versions of the polished Exeter stem, both aseptic loosening and localised endosteal bone lysis have become rare.
Further retrieval studies have shown that in polished and matt Exeter stems the wear processes between stem and cement are fundamentally different. This difference may explain the substantial clinical difference in outcome between these two types of stem. These considerations lead to the view that abrasive stem wear in matt stems is probably a major cause of failure, and more important than failure of cement.
The abstracts were prepared by Professor M. B. E. Sweet. Correspondence should be addressed to him at The Department of Orthopaedic Surgery, Medical School, University of Witwatersrand, 7 York Road, Parktown, Johannesburg, 2193 South Africa
