INTERPRETATION The guidelines have improved method ological reporting in RSA studies , but adherence to these guidelines is still relatively low .
BACKGROUND AND PURPOSE Guidelines for st and ardization of  radiostereometry ( RSA )  of implants were published in 2005 to facilitate comparison of outcomes between various research groups .
In this systematic review , we determined how well studies have adhered to these guidelines .
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
INTERPRETATION The guidelines have improved method ological reporting in RSA studies , but adherence to these guidelines is still relatively low .
BACKGROUND AND PURPOSE Guidelines for st and ardization of  radiostereometry ( RSA )  of implants were published in 2005 to facilitate comparison of outcomes between various research groups .
In this systematic review , we determined how well studies have adhered to these guidelines .