title: No adverse effects of submelt-annealed highly crosslinked polyethylene in cemented cups: an RSA study of 8 patients 10 yaers after surgery.
abstract: OBJECTIVE
  Highly crosslinked polyethylene (PE) is in standard use worldwide. Differences in the crosslinking procedure may affect the clinical performance. Experimenatal data from retrieved cups have shown free radicals and excessive wear of annealed highly crosslinked PE. We have previously reported low wear and good clinical performance after 6 years with this implant, and now report on the 10-year results.
  
  
  METHODS
  In 8 patients, we measured wear of annealed highly crosslinked PE prospectively with radiostereometry after 10 years. Activity was assessed by UCLA activity score and a specifically designed activity score. Conventional radiographs were evaluated for osteolysis and clinical outcome by the Harris hip score (HHS).
  
  
  RESULTS
  The mean (95% CI) proximal head penetration for highly crosslinked PE after 10 years was 0.07 (-0.015 to 0.153) mm, and the 3D wear was 0.2 (0.026 to 0.36) mm. Without creep, proximal head penetration was 0.02 (-0.026 to 0.066) mm and for 3D penetration was 0.016 (-0.47 to 0.08) mm. This represents an annual proximal wear of less than 2 µm. All cups were clinically and radiographically stable but showed a tendency of increased rotation after 5 years.
  
  
  CONCLUSIONS
  Wear for annealed highly crosslinked PE is extremely low up to 10 years. Free radicals do not affect mechanical performance or lead to clinically adverse effects. Creep stops after the first 6 months after implantation. Highly crosslinked PE is a true competitor of hard-on-hard bearings.
authors.affiliation: Department of Orthopaedics, Oslo University Hospital, CIRRO, Norway. s.m.rohrl@medisin.uio.no
authors.forename: Stephan M
authors.initials: SM
authors.lastname: Röhrl
authors.forename: Bo
authors.initials: B
authors.lastname: Nivbrant
authors.forename: Kjell G
authors.initials: KG
authors.lastname: Nilsson
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000295:instrumentation*; D001696:Biomechanical Phenomena; D001843:Bone Cements; D005260:Female; D005270:Femur Head / Q000000981:diagnostic imaging* / Q000601:surgery; D005500:Follow-Up Studies; D006621:Hip Joint / Q000000981:diagnostic imaging / Q000601:surgery; D006622:Hip Prosthesis; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D017063:Outcome Assessment, Health Care; D020959:Polyethylene / Q000009:adverse effects*; D011446:Prospective Studies; D011474:Prosthesis Design; D011475:Prosthesis Failure; D059869:Radiostereometric Analysis; D012189:Retrospective Studies; D013997:Time Factors
chemical_list: D001843:Bone Cements; D020959:Polyethylene