title: Accuracy and Reliability of Computed Tomography and Magnetic Resonance Imaging Compared With True Anatomic Femoral Version.
abstract: BACKGROUND
  Abnormal torsion of the femur is correlated to lower extremity pathologies. Although computed tomography (CT) scan is the gold standard torsional measurement, magnetic resonance imaging (MRI) is proposed as a viable alternative. Our aim was to determine the accuracy and consistency of MRI and CT femur rotational studies based on 4 described protocols.
  
  
  METHODS
  Twelve cadaveric femora were stripped of soft tissue before imaging and physical assessment of torsion. Four advanced imaging series were obtained for each specimen: CT with axial cuts of the femoral neck (CT-axial); CT with oblique cuts of the femoral neck (CT-oblique); MRI with axial cuts of the femoral neck (MR-axial); MRI with oblique cuts of the femoral neck (MR-oblique). Anatomic specimens were placed with the posterior femoral condyles flat on a dissection table for assessment of true torsion with digital images. Three independent reviewers performed all measurements, including true torsion, using imaging software. Bland-Altman analysis was repeated with the data from each reviewer.
  
  
  RESULTS
  Interobserver repeatability for all groups was high at 0.95, 0.87, 0.90, 0.97, and 0.92 for CT-axial, CT-oblique, MR-axial, MR-oblique, and true torsion, respectively. CT-axial had the lowest mean difference from clinical imaging for all three observers (all <1 degree) and held the tightest 95% limits of agreement for 2/3 observers. As torsion increases from neutral, MR-oblique linearly overestimates the rotation compared with true torsion. CT-oblique and MR-axial showed slightly greater differences from true torsion compared with CT-axial, but did not reach clinical significance.
  
  
  CONCLUSIONS
  CT-axial was both most accurate and reproducible when compared with true torsion of the femur and should be the gold standard imaging modality; however, both MR-axial and CT-oblique were accurate to a level that is likely less than clinical significance. MR-axial images should be used in clinical situations where radiation exposure needs to be limited. MR-oblique images can overestimate true antetorsion and should not be used.
  CT-axial followed by MRI-axial is the most accurate and consistent in measuring true torsion of the femur.
authors.affiliation: *Department of Orthopaedics, University of Utah Hospitals and Clinics, Salt Lake City, UT †Department of Orthopaedic Surgery and Biomedical Engineering, University of Tennessee-Campbell Clinic, Memphis, TN ‡Department of Orthopaedics, University of Colorado, Boulder, CO.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Beebe
authors.forename: James D
authors.initials: JD
authors.lastname: Wylie
authors.forename: Bill G
authors.initials: BG
authors.lastname: Bodine
authors.forename: Ashley L
authors.initials: AL
authors.lastname: Kapron
authors.forename: Travis G
authors.initials: TG
authors.lastname: Maak
authors.forename: Omer
authors.initials: O
authors.lastname: Mei-Dan
authors.forename: Stephen K
authors.initials: SK
authors.lastname: Aoki
mesh_terms: D005269:Femur / Q000000981:diagnostic imaging; D005272:Femur Neck / Q000000981:diagnostic imaging*; D006801:Humans; D007719:Knee Joint; D008279:Magnetic Resonance Imaging; D015203:Reproducibility of Results; D012399:Rotation; D014057:Tomography, X-Ray Computed; D014102:Torsion Abnormality / Q000000981:diagnostic imaging* / Q000473:pathology