title: Analysis of polyethylene wear in plain radiographs.
abstract: OBJECTIVE
  Two-dimensional computerized radiographic techniques are frequently used to measure in vivo polyethylene (PE) wear after total hip arthroplasty (THA), and several variables in the clinical set-up may influence the amount of wear that is measured. We compared the repeatability and concurrent validity of linear PE wear on plain radiographs using the same software but a different number of radiographs.
  
  
  METHODS
  We used either 1, 2, or 6 anteroposterior (AP) hip radiographs of 11 patients from a clinical THA series with 12 years of follow-up, and measured the PE wear with the software PolyWare 3D Pro. Repeatability within and concurrent validity between the different numbers of radiograph strategies were assessed using limits of agreement (LOAs) and bias.
  
  
  RESULTS
  Observed median wear (range) in mm was 3.4 (1.6-4.6), 2.3 (0.7-4.9), and 4.0 (2.6-6.2) for the 1-, 2-, and 6-radiograph strategies. For repeatability, no bias (p > 0.41) was observed. LOAs around the bias were + or - 0.6, + or - 0.4, and + or - 1.2 mm for the 1-, 2-, and 6-radiograph strategies. For concurrent validity, a bias (+ or - LOA) between all pairwise comparisons was observed (p < 0.02) with 0.8 mm (+ or - 2.5) between the 1- and 2-radiograph strategies, 1.0 mm (+ or - 2.2) between the 1- and 6-radiograph strategies, and 1.8 mm (+ or - 1.2) between the 2- and 6-radiograph strategies.
  
  
  CONCLUSIONS
  The number of radiographs used for wear measurement with a shadow-casting analysis method on plain AP radiographs influences the amount of linear wear measured. Results of PE wear obtained with PolyWare in studies using a different number of radiographs are not comparable.
authors.affiliation: Department of Orthopaedics, Aarhus University Hospital, Holstebro, Denmark. maiken.stilling@ki.au.dk
authors.forename: Maiken
authors.initials: M
authors.lastname: Stilling
authors.forename: Kjeld
authors.initials: K
authors.lastname: Søballe
authors.forename: Niels Trolle
authors.initials: NT
authors.lastname: Andersen
authors.forename: Kristian
authors.initials: K
authors.lastname: Larsen
authors.forename: Ole
authors.initials: O
authors.lastname: Rahbek
mesh_terms: D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects; D019245:Compressive Strength; D019544:Equipment Failure Analysis; D005270:Femur Head / Q000000981:diagnostic imaging*; D005500:Follow-Up Studies; D006621:Hip Joint / Q000000981:diagnostic imaging; D006622:Hip Prosthesis / Q000009:adverse effects; D006801:Humans; D021621:Imaging, Three-Dimensional; D015588:Observer Variation; D020959:Polyethylene; D011474:Prosthesis Design; D011475:Prosthesis Failure; D011859:Radiography; D012086:Reoperation; D015203:Reproducibility of Results; D012984:Software; D013314:Stress, Mechanical
chemical_list: D020959:Polyethylene