title: Calibration Marker Position in Digital Templating of Total Hip Arthroplasty.
abstract: BACKGROUND
  We report a mathematical method to assess the vertical and horizontal positions of spherical radiopaque objects of known size in conventional radiographs.
  
  
  METHODS
  The reliability and validity of the method were tested in an experimental setting and applied to 100 anteroposterior pelvic radiographs with external calibration markers and unilateral total hip arthroplasty (THA).
  
  
  RESULTS
  We found excellent reliabilities; intraclass correlation coefficients for interobserver and intraobserver reliabilities were 0.999-1.000 (P = .000). The mean normal height of THA was 198 mm (range: 142-243 mm, standard deviation: 18 mm) above the detector. Vertical and horizontal external marker positions differed significantly from the true hip center (THA; P < .001 and P = .017).
  
  
  CONCLUSIONS
  This method could enhance patient safety by enabling automated detection of malpositioned calibration markers by templating software.
authors.affiliation: Department of Orthopaedic and Trauma Surgery, University Hospital of Cologne, Cologne, Germany.
authors.forename: Christoph K
authors.initials: CK
authors.lastname: Boese
authors.affiliation: Department of Orthopaedic and Trauma Surgery, University Hospital of Cologne, Cologne, Germany.
authors.forename: Jan
authors.initials: J
authors.lastname: Bredow
authors.affiliation: Department of Orthopaedic and Trauma Surgery, University Hospital of Cologne, Cologne, Germany.
authors.forename: Jens
authors.initials: J
authors.lastname: Dargel
authors.affiliation: Department of Orthopaedic and Trauma Surgery, University Hospital of Cologne, Cologne, Germany.
authors.forename: Peer
authors.initials: P
authors.lastname: Eysel
authors.affiliation: Mathematical Institute, University of Cologne, Cologne, Germany.
authors.forename: Hansjörg
authors.initials: H
authors.lastname: Geiges
authors.affiliation: Centre for Orthopedic and Trauma Surgery, University of Giessen and Marburg, Marburg, Germany.
authors.forename: Philipp
authors.initials: P
authors.lastname: Lechler
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging / Q000601:surgery; D019644:Arthroplasty, Replacement, Hip; D002138:Calibration; D005269:Femur / Q000000981:diagnostic imaging / Q000601:surgery; D006621:Hip Joint / Q000000981:diagnostic imaging* / Q000601:surgery; D006801:Humans; D008297:Male; D008962:Models, Theoretical; D010384:Pelvic Bones / Q000000981:diagnostic imaging*; D011859:Radiography; D015203:Reproducibility of Results; D012984:Software
keywords: calibration; digital radiography; hip anatomy; templating; total hip arthroplasty