title: New radiographic index for evaluating acetabular version.
abstract: BACKGROUND
  Several qualitative radiographic signs have been described to assess acetabular retroversion. However, quantitative assessment of acetabular version would be useful for more rigorous research purposes and perhaps to diagnose and treat hip disorders.
  
  
  OBJECTIVE
  We developed a new quantitative index for acetabular version (p/a ratio). We determined the average p/a, compared it with previous radiographic signs for acetabular retroversion, and evaluated its relationship with anatomic acetabular version.
  
  
  METHODS
  We calculated the p/a ratio by measuring p (distance from acetabular articular surface to posterior wall) and a (distance from acetabular articular surface to anterior wall) on plain hip AP radiographs and dividing p by a. P and a were assessed on the perpendicular bisector of the line between the teardrop and the lateral edge of the acetabulum. Using 185 hip radiographs from patients with suspected idiopathic osteonecrosis, we measured p/a and compared it with previous qualitative signs for acetabular retroversion. Using 62 hip CT images from patients with no osteoarthritis, we measured the anatomic anteversion at the height of the central femoral head and investigated its relationship with p/a.
  
  
  RESULTS
  The average p/a was 2.05 in 185 hips, and most patients with a p/a greater than 2.05 had a negative qualitative retroversion sign. A correlation was observed between central anteversion and p/a (r = 0.84).
  
  
  CONCLUSIONS
  We believe this ratio can be considered a simple quantitative parameter to assess acetabular version using plain AP radiographs.
authors.affiliation: Department of Orthopaedic Surgery, Hamamatsu University School of Medicine, 1-20-1 Handayama, Higashi-Ku, Hamamatsu, 431-3192, Japan. hiromania27@hotmail.com
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Koyama
authors.forename: Hironobu
authors.initials: H
authors.lastname: Hoshino
authors.forename: Daisuke
authors.initials: D
authors.lastname: Suzuki
authors.forename: Shoichi
authors.initials: S
authors.lastname: Nishikino
authors.forename: Yukihiro
authors.initials: Y
authors.lastname: Matsuyama
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging* / Q000601:surgery; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip; D016022:Case-Control Studies; D005260:Female; D005271:Femur Head Necrosis / Q000000981:diagnostic imaging* / Q000601:surgery; D006618:Hip Dislocation, Congenital / Q000000981:diagnostic imaging* / Q000601:surgery; D006801:Humans; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D011237:Predictive Value of Tests; D011857:Radiographic Image Interpretation, Computer-Assisted; D015203:Reproducibility of Results; D014057:Tomography, X-Ray Computed; D055815:Young Adult