title: Wear of a 5 megarad cross-linked polyethylene liner: a 6-year RSA study.
abstract: BACKGROUND
  One cross-linked polyethylene (XLPE) liner is manufactured using a lower dose of radiation, 5 Mrad, which may result in less cross-linking. The reported in vivo wear rate of this XLPE liner in patients undergoing THA has varied, and has included some patients in each reported cohort who had greater than 0.1 mm/year of wear, which is an historical threshold for osteolysis. Previous studies have measured wear on plain radiographs, an approach that has limited sensitivity.
  
  
  OBJECTIVE
  We therefore measured the amount and direction of wear at 6 years using Radiostereometric analysis (RSA) in patients who had THAs that included a cross-linked polyethylene liner manufactured using 5 Mrad radiation.
  
  
  METHODS
  We prospectively reviewed wear in 30 patients who underwent primary THAs with the same design of cross-linked acetabular liner and a 28-mm articulation. Tantalum markers were inserted during surgery and all patients had RSA radiographic examinations at 1 week, 6 months, 1, 2, and 6 years postoperatively.
  
  
  RESULTS
  The mean proximal, two-dimensional (2-D) and three-dimensional (3-D) wear rates calculated between 1 year and 6 years were 0.014, 0.014, and 0.018 mm/per year, respectively. The direction of the head penetration recorded between 1 week and 6 years was in a proximal direction for all patients, proximolateral for 16 of 24 patients, and proximomedial for eight of 24 patients.
  
  
  CONCLUSIONS
  The proximal, 2-D and 3-D wear of a XLPE liner produced using 5 Mrad of radiation was low but measurable by RSA after 6 years. No patients had proximal 2-D or 3-D wear rates exceeding 0.1 mm/year. Further followup is needed to evaluate the effect of XLPE wear particles on the development of long-term osteolysis.
authors: Discipline of Orthopaedics and Trauma, University of Adelaide, Adelaide, SA, Australia. stuart.callary@health.sa.gov.au
authors: Stuart A
authors: SA
authors: Callary
authors: David G
authors: DG
authors: Campbell
authors: Graham
authors: G
authors: Mercer
authors: Kjell G
authors: KG
authors: Nilsson
authors: John R
authors: JR
authors: Field
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects / Q000295:instrumentation*; D005260:Female; D057918:Fiducial Markers; D006621:Hip Joint / Q000000981:diagnostic imaging / Q000601:surgery*; D006622:Hip Prosthesis; D006801:Humans; D008297:Male; D008875:Middle Aged; D010014:Osteolysis / Q000209:etiology; D020959:Polyethylene / Q000528:radiation effects*; D011446:Prospective Studies; D011474:Prosthesis Design; D011475:Prosthesis Failure; D059869:Radiostereometric Analysis; D013314:Stress, Mechanical; D013635:Tantalum; D013997:Time Factors; D016896:Treatment Outcome
chemical_list: D013635:Tantalum; D020959:Polyethylene