MIGRATION AND WEAR OF LONG-TERM SUCCESSFUL CHARNLEY TOTAL HIP REPLACEMENTS

We analysed in-vivo migration and wear over a long period of all-polye thylene acetabular cups which had not been affected by mechanical loos ening. The selection criteria of regular radiological follow-up, good clinical outcome (Charnley score of 5 or 6), continued walking without crutches and no radiological signs of loosening of the acetabular cup s were fulfilled by 25 Charnley total hip arthroplasties. Mean migrati on, measured by the Nunn method, was 0.6 mm in the medial and 0.2 mm i n the cranial direction. The mean yearly rate of wear was 0.05 mm and 0.04 mm, with six and two cups having no detectable wear, as measured by the Livermore and Charnley-Cupic methods, respectively. The maximal detected wear was 3.7 mm, There were no changes in the rate of wear w ith time. Computerised Ein Bild Rontgen Analyse (single-image radiolog ical analysis) measurements of 20 hips indicated plastic deformation o f the cups. We conclude that long-term successful cups do not migrate and have a very low rate of wear which was not affected by ageing of t he polyethylene. There was no evidence that polyethylene wear alone ca used mechanical loosening of the cup but high rates of wear seem to ha ve an adverse prognostic value in terms of the long-term survival of t he prosthesis.