title: Rotational malreduction of the syndesmosis: reliability and accuracy of computed tomography measurement methods.
abstract: BACKGROUND
  Computed tomography (CT)-based indices may be superior to plain radiographs in determining the adequacy of reduction following operative fixation of the syndesmosis in unstable ankle fractures. This study assessed the reliability and accuracy of four CT-based methods for measurement of rotational malreduction of the fibula.
  
  
  METHODS
  A simulated Weber C ankle fracture was created by performing an osteotomy in 9 cadaver ankles. The fibula was rotated and fixed in neutral (0 degrees) and 10 to 30 degrees of internal and external rotation. Fifty-two CT images at the level of the syndesmosis were obtained in neutral and rotated positions and presented in random order to 3 independent observers. Measurements were made using commercial imaging software and 4 methods for interpreting CT scans. Interobserver reliability and accuracy were assessed and compared.
  
  
  RESULTS
  Methods 1 and 4 showed high anatomic variability. Methods 1, 2, and 4 had a test-retest repeatability of about 15 degrees. Method 1 varied erratically with direction and degree of malrotation (R (2) = 0.15) and did not permit specification of a neutral range. Method 2 varied consistently and systematically with direction and degree of malrotation (R (2) = 0.88). Receiver operating characteristic curve analysis indicated that method 2 identified malrotation better than did the other methods. Methods 3 and 4 were somewhat more difficult to perform.
  
  
  CONCLUSIONS
  Method 2, the angle between the tangent of the anterior tibial surface and the bisection of the vertical midline of the fibula at the level of the incisura, was fairly reliable and accurate and had greater ease of measurement compared with the other methods that were tested.
  
  
  CONCLUSIONS
  This study demonstrated that assessment of malrotation of fibular fractures by CT scan can be difficult. We believe that of the 4 methods tested in this study, method 2, the angle between the tangent of the anterior tibial surface and the bisection of the vertical midline of the fibula at the level of the incisura, was the most useful.
authors.affiliation: Orthopaedic Trauma Institute, San Francisco General Hospital, University of California, San Francisco, CA, USA.
authors.forename: Simon P
authors.initials: SP
authors.lastname: Knops
authors.forename: Michael A
authors.initials: MA
authors.lastname: Kohn
authors.forename: Erik N
authors.initials: EN
authors.lastname: Hansen
authors.forename: Amir
authors.initials: A
authors.lastname: Matityahu
authors.forename: Meir
authors.initials: M
authors.lastname: Marmor
mesh_terms: D016512:Ankle Injuries / Q000601:surgery*; D000843:Ankle Joint / Q000601:surgery*; D005360:Fibula / Q000293:injuries*; D050723:Fractures, Bone / Q000000981:diagnostic imaging / Q000601:surgery*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D007091:Image Processing, Computer-Assisted; D010027:Osteotomy; D015203:Reproducibility of Results; D012399:Rotation; D014057:Tomography, X-Ray Computed
keywords: ankle fracture; computed tomography scan; fibular torsion; syndesmosis injury; trauma