title: The seven-year wear of highly cross-linked polyethylene in total hip arthroplasty: a double-blind, randomized controlled trial using radiostereometric analysis.
abstract: 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 prospective, double-blind, randomized controlled trial with use of radiostereometric analysis.
  
  
  METHODS
  Fifty-four patients were randomized 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.
authors.affiliation: Biomedical Research Unit, Headington, Oxford OX3 7LD, United Kingdom.
authors.forename: Geraint E R
authors.initials: GE
authors.lastname: Thomas
authors.forename: David J
authors.initials: DJ
authors.lastname: Simpson
authors.forename: Shahid
authors.initials: S
authors.lastname: Mehmood
authors.forename: Adrian
authors.initials: A
authors.lastname: Taylor
authors.forename: Peter
authors.initials: P
authors.lastname: McLardy-Smith
authors.forename: Harinderjit Singh
authors.initials: HS
authors.lastname: Gill
authors.forename: David W
authors.initials: DW
authors.lastname: Murray
authors.forename: Siôn
authors.initials: S
authors.lastname: Glyn-Jones
mesh_terms: D000328:Adult; D019644:Arthroplasty, Replacement, Hip; D020099:Coated Materials, Biocompatible; D004311:Double-Blind Method; D019544:Equipment Failure Analysis; D005260:Female; D006622:Hip Prosthesis; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D015207:Osteoarthritis, Hip / Q000601:surgery*; D020959:Polyethylene / Q000737:chemistry; D011095:Polyethylenes; D011446:Prospective Studies; D011474:Prosthesis Design; D011475:Prosthesis Failure; D013499:Surface Properties; D016896:Treatment Outcome
chemical_list: D020099:Coated Materials, Biocompatible; D011095:Polyethylenes; C111601:ultra-high molecular weight polyethylene; D020959:Polyethylene