title: Quantification of clearance and creep in acetabular wear measurements.
abstract: BACKGROUND
  This study aimed to measure femoral head penetration before occurrence of real wear, and to quantify the portions attributable respectively to clearance and plastic deformations in various acetabular designs.
  
  
  METHODS
  We analyzed CT scans from 15 patients at 'day five' after total hip arthroplasty (THA). All patients received Exafit(®) femoral stems and 28 mm heads: 5 patients had cemented Durasul(®) all-PE cups, 5 patients had un-cemented Allofit(®) metal-backed cups, and 5 patients had un-cemented Stafit(®) dual-mobility cups. We also analyzed CT scans of samples of the three head-cup combinations to compare in vivo and in vitro measurements.
  
  
  RESULTS
  The mean femoral head penetration measured on 'day five' was lower for all-PE cups (0.196 mm) than for metal-backed cups (0.551 mm) and dual-mobility cups (0.634 mm).
  
  
  CONCLUSIONS
  The present study indicates that isolated measurements of femoral head penetration include 0.15-0.46 mm of radial clearance and 0.05-0.27 mm of creep, and confirms that the majority of so-called bedding-in observed in the first post-operative months is not entirely due to wear.
authors.affiliation: 1 Accelerate Innovation Management, Geneva, Switzerland ; 2 Department of Orthopaedic Surgery, Hôpital Européen Georges Pompidou, University René Descartes, Faculty of Medicine, Paris, France ; 3 Department of Mechanical Engineering, Imperial College London, London, UK.
authors.forename: Mo
authors.initials: M
authors.lastname: Saffarini
authors.affiliation: 1 Accelerate Innovation Management, Geneva, Switzerland ; 2 Department of Orthopaedic Surgery, Hôpital Européen Georges Pompidou, University René Descartes, Faculty of Medicine, Paris, France ; 3 Department of Mechanical Engineering, Imperial College London, London, UK.
authors.forename: Thomas
authors.initials: T
authors.lastname: Gregory
authors.affiliation: 1 Accelerate Innovation Management, Geneva, Switzerland ; 2 Department of Orthopaedic Surgery, Hôpital Européen Georges Pompidou, University René Descartes, Faculty of Medicine, Paris, France ; 3 Department of Mechanical Engineering, Imperial College London, London, UK.
authors.forename: Eric
authors.initials: E
authors.lastname: Vandenbussche
keywords: Total hip arthroplasty (THA); femoral head penetration; polyethylene wear