title: Correlation of the cross-over ratio of the cross-over sign on conventional pelvic radiographs with computed tomography retroversion measurements.
abstract: OBJECTIVE
  To find a correlation between the cross-over ratio of the cross-over sign on conventional anteroposterior (AP) pelvic radiographs and retroversion measurements ('roof-edge angle' and 'equatorial-edge angle) on computed tomography (CT) scans. This would facilitate the interpretation of the cross-over sign regarding the amount of acetabular retroversion.
  
  
  METHODS
  Correctly projected AP pelvic radiographs (2,925 hips) were examined for the presence of the cross-over sign (COS), and the overlap ratio of the COS was measured. On CT scans of the same patients the 'roof-edge angle' (RE angle) and the 'equatorial-edge angle' (EE angle) were also calculated.
  
  
  RESULTS
  A statistically significant but only weak relationship could be found between the overlap ratio of the COS and the 'roof-edge angle' (P < 0.0001; correlation coefficient -0.486) and between this ratio and the 'equatorial-edge angle' (P < 0.0001; correlation coefficient -0.395).
  
  
  CONCLUSIONS
  A relationship between the overlap ratio and orientation measurements on CT scans could be found, but it was less strong than expected.
authors.affiliation: Department of Orthopaedics, Uniklinik Balgrist, University of Zurich, Zurich, Switzerland. cwerner@gmx.ch
authors.forename: Clément M L
authors.initials: CM
authors.lastname: Werner
authors.forename: Carol E
authors.initials: CE
authors.lastname: Copeland
authors.forename: Jeff
authors.initials: J
authors.lastname: Stromberg
authors.forename: Thomas
authors.initials: T
authors.lastname: Ruckstuhl
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010388:Pelvis / Q000000981:diagnostic imaging*; D011856:Radiographic Image Enhancement / Q000379:methods*; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013223:Statistics as Topic; D014057:Tomography, X-Ray Computed / Q000379:methods*; D055815:Young Adult