Patient Reported Outcome Measures ( PROMs ) at six months have been investigated but have not been vali date d against long-term outcomes .
EBRA can be used to investigate acetabular wear but not femoral migration .
OBJECTIVES High failure rates of metal-on-metal hip arthroplasty implants  have highlighted the need for more careful introduction and monitoring of new implants and for the evaluation of the safety of medical devices .
The National Joint Registry and other regulatory services are unable to detect failing implants at an early enough stage .
We aim ed to identify vali date d surrogate markers of long-term outcome in patients undergoing primary total hip arthroplasty ( THA ) .
Early migration predicts late aseptic failure of hip sockets.
We report a prospect i ve , stratified study of 60 PCA-cups and 60 RM-polyethylene cups which have been followed for a median time of 90 months , with annual radiography .  The radiological migration of cups was measured by the computer-assisted EBRA method . A number of threshold migration rates from 1 mm in the first year to 1 mm in five years have been assessed and related to clinical ly determined revision rates . A total 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 migration were considerably different from those without early migration . For cups with a migration of less than 1 mm within the first two years the 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 sockets
Patient Reported Outcome Measures ( PROMs ) at six months have been investigated but have not been vali date d against long-term outcomes .
EBRA can be used to investigate acetabular wear but not femoral migration .
OBJECTIVES High failure rates of metal-on-metal hip arthroplasty implants  have highlighted the need for more careful introduction and monitoring of new implants and for the evaluation of the safety of medical devices .
The National Joint Registry and other regulatory services are unable to detect failing implants at an early enough stage .
We aim ed to identify vali date d surrogate markers of long-term outcome in patients undergoing primary total hip arthroplasty ( THA ) .