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 ) .
The seven-year wear of highly cross-linked polyethylene in total hip arthroplasty: a double-blind, randomized controlled trial using radiostereometric analysis.
BACKGROUND The use of highly cross-linked polyethylene is now commonplace in total hip arthroplasty . Hip simulator studies and short-term in vivo measurements have suggested that the wear rate of highly cross-linked polyethylene is significantly less than that of conventional ultra-high molecular weight polyethylene . However , long-term data to support its use are limited . The aim of this study was to compare the intermediate-term steady-state wear of highly cross-linked polyethylene compared with that of conventional ultra-high molecular weight polyethylene acetabular liners in a prospect i ve , double-blind , r and omized controlled trial with use of radiostereometric analysis . METHODS Fifty-four patients were r and omized to receive hip replacements with either conventional ultra-high molecular weight polyethylene acetabular liners ( Zimmer ) or highly cross-linked polyethylene liners ( Longevity ; Zimmer ) . All patients received a cemented , collarless , polished , tapered femoral component ( CPT ; Zimmer ) and an uncemented acetabular component ( Trilogy ; Zimmer ) . Clinical outcomes were assessed and the three-dimensional penetration of the head into the socket was determined for a minimum of seven years . Linear regression was used to calculate the steady-state wear rate following the creep-dominated penetration seen during the first year . RESULTS At a minimum of seven years postoperatively , the mean total femoral head penetration was significantly lower in the highly cross-linked polyethylene group ( 0.33 mm ; 95 % confidence interval [ CI ] , ±0.10 mm ) than it was in the ultra-high molecular weight polyethylene group ( 0.55 mm ; 95 % CI , ±0.10 mm ) ( p = 0.005 ) . The mean steady-state wear rate  of highly cross-linked polyethylene was 0.005 mm/yr ( 95 % CI , ±0.015 mm/yr ) , compared with 0.037 mm/yr ( 95 % CI , ±0.019 mm/yr ) for conventional ultra-high molecular weight polyethylene ( p = 0.007 ) . No patient in the highly cross-linked polyethylene group had a wear rate above the osteolysis threshold of 0.1 mm/yr , compared with 9 % of patients in the ultra-high molecular weight polyethylene group . CONCLUSIONS This study demonstrates that highly cross-linked polyethylene has a significantly lower steady-state wear rate compared with that of conventional ultra-high molecular weight polyethylene . Longer-term follow-up is required to determine if this will translate into improved clinical performance and longevity of these implants
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 ) .