EARLY MIGRATION PREDICTS LATE ASEPTIC FAILURE OF HIP SOCKETS

We report a prospective, stratified study of 60 PCA-cups and 60 RM-pol yethylene cups which have been followed for a median time of 90 months , with annual radiography. The radiological migration of cups was meas ured by the computer-assisted EBRA method. A number of threshold migra tion rates from 1 nun in the first year to 1 mm in five years have bee n assessed and related to clinically determined revision rates. A tota l of 28 cups showed a total migration of 1 mm or more within the first two years; 13 of these cups have required revision and been exchanged . The survival curves of cups which had previously shown early migrati on were considerably different from those without early migration, For cups with a migration of less than 1 mm within the first two years th e mean survival at 96 months was 0.96 +/- 0.02; for migrating cups, it was 0.63 +/- 0.11 (log-rank test, p = 0.0001; chi-square value = 39.4 ). Early migration is a good predictor for late loosening of hip socke ts.