title: Determination of digitised radiograph magnification factors for pre-operative templating in hip prosthesis surgery.
abstract: OBJECTIVE
  With digital radiography development, information technology (IT) companies have developed specific software for templating procedures, requiring individual magnification assessments for each patient. The aim of this study was to determine the mean magnification factor of digital radiographs and to evaluate the possibility of using the mean magnification factor or clinical information in templating.
  
  
  METHODS
  We retrospectively evaluated 100 primary total hip arthroplasty digital radiographs using the femoral head prosthesis as a calliper to determinate the mean magnification factor. Working on the assumption that altitude of the hip during radiograph is decisive in modification of magnification factors, we also looked for a correlation between weight, body mass index (BMI), altitude and magnification factor.
  
  
  RESULTS
  The magnification factor was 126% (121-130%). A relationship was found between magnification factor (Mf) and weight (Mf = 7.10(-4)x weight (kg) + 1.21), but not BMI. In 98% of cases, if the weight-correlated formula is used, the sizing is correct or the error is +/- 1 mm. With the mean method the sizing is correct or within 1 mm in only 78.2% of cases.
  
  
  CONCLUSIONS
  Levels of accuracy for the mean magnification factor and the weight-correlated formula are not as high as individual assessments using a calliper; however, they could be used in everyday practice where individual magnification factors have not been calculated.
authors.affiliation: Service de Chirurgie Orthopédique et Traumatologique, Hôpital Gabriel Montpied, CHU de Clermont Ferrand, BP 69, 63003, Clermont Ferrand Cedex 01, France. s_descamps@chu-clermontferrand.fr
authors.forename: Stephane
authors.initials: S
authors.lastname: Descamps
authors.forename: Christine
authors.initials: C
authors.lastname: Livesey
authors.forename: Ian Douglas
authors.initials: ID
authors.lastname: Learmonth
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000379:methods*; D005260:Female; D006621:Hip Joint / Q000000981:diagnostic imaging* / Q000601:surgery*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011300:Preoperative Care / Q000379:methods; D011379:Prognosis; D011856:Radiographic Image Enhancement / Q000379:methods*; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D055815:Young Adult