title: Analysis of acetabular version in the native hip: comparison between 2D axial CT and 3D CT measurements.
abstract: OBJECTIVE
  To compare two-dimensional (2D) axial with three-dimensional (3D) computerized tomography (CT) measurements of acetabular version in native hips.
  
  
  METHODS
  CT scans of 34 hips in 17 consecutive patients being investigated for femoroacetabular impingement were analyzed. Acetabular version was measured using 2D CT at two different axial levels, one cranial (slice 2) and the other at the equator (slice 3). The measurements were repeated after correction for pelvic tilt. The results were compared to the measurements of anatomical version obtained using a 3D CT method that automatically corrects for pelvic tilt.
  
  
  RESULTS
  The mean acetabular version using the 3D CT method was 15.7° (SD 6.9°). The mean version using slice 2 was 9.3° (SD 6.5°) before correction for pelvic tilt and 15.7° (SD 8.0°) after the correction. The mean version using slice 3 was 16.4° (SD 4.2°) before tilt correction and 19.0° (SD 5.0°) after the correction. In relation to the 3D method, the intraclass correlation coefficient (ICC) was 0.58 for the uncorrected and 0.93 for the corrected slice 2 method. For the uncorrected and corrected slice 3 methods, the ICC was 0.64 and 0.89, respectively.
  
  
  CONCLUSIONS
  The 2D axial methods produced variable results. The results that correlated best with the 3D method were those of the cranial slice (slice 2) after correction for pelvic tilt. Interpretation of 2D axial CT measurements of acetabular version should be done with caution. The level at which the measurement is done and the presence of pelvic tilt appear to be significant factors.
authors.affiliation: Department of Orthopaedic Surgery, Imperial College London Hospitals, 7th Floor, East Wing, Fulham Palace Road, London, W6 8RF, UK. w.dandachli@imperial.ac.uk
authors.forename: Wael
authors.initials: W
authors.lastname: Dandachli
authors.forename: Saif
authors.initials: S
authors.lastname: Ul Islam
authors.forename: Richard
authors.initials: R
authors.lastname: Tippett
authors.forename: Margaret A
authors.initials: MA
authors.lastname: Hall-Craggs
authors.forename: Johan D
authors.initials: JD
authors.lastname: Witt
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods*; D055815:Young Adult