title: Inter-observer reliability of measurements performed on digital long-leg standing radiographs and assessment of validity compared to 3D CT-scan.
abstract: BACKGROUND
  Long-leg radiographs (LLR) are often used in orthopaedics to assess limb alignment in patients undergoing total knee arthroplasty (TKA). However, there are still concerns about the adequacy of measurements performed on LLR. We assessed the reliability and validity of measurements on LLR using three-dimensional computed tomography (3D CT)-scan as a gold standard.
  
  
  METHODS
  Six different surgeons measured the mechanical axis and position of the femoral and tibial components individually on 24 LLR. Intraclass correlation coefficients (ICC) were calculated to obtain reliability and Bland-Altman plots were constructed to assess agreement between measurements on LLR and measurements on 3D CT-scan.
  
  
  RESULTS
  ICC agreement for the six observer measurements on LLR was 0.70 for the femoral component and 0.80 for the tibial component. The mean difference between measurements performed on LLR and 3D CT-scan was 0.3° for the femoral component and -1.1° for the tibial component. Variation of the difference between LLR and 3D CT-scan for the femoral component was 1.1° and 0.9° for the tibial component. 95% of the differences between measurements performed on LLR and 3D CT-scan were between -1.9 and 2.4° (femoral component) and between -2.9 and 0.7 (tibial component).
  
  
  CONCLUSIONS
  Measurements on LLR show moderate to good reliability and, when compared to 3D CT-scan, show good validity.
  
  
  BACKGROUND
  institutional review board Atrium-Orbis-Zuyd, number: 11-T-15.
  
  
  METHODS
  Prospective cohort study, Level II.
authors.affiliation: Zuyderland Medisch Centrum, Dr. H. vd Hoffplein 1, 6162 BG Sittard-Geleen, The Netherlands. Electronic address: boonenbert@gmail.com.
authors.forename: B
authors.initials: B
authors.lastname: Boonen
authors.affiliation: AZ Sint-Maarten, Leopoldstraat 2, 2800 Mechelen, Belgium. Electronic address: bartkerens@hotmail.com.
authors.forename: B
authors.initials: B
authors.lastname: Kerens
authors.affiliation: Zuyderland Medisch Centrum, Dr. H. vd Hoffplein 1, 6162 BG Sittard-Geleen, The Netherlands. Electronic address: m.schotanus@orbisconcern.nl.
authors.forename: M G M
authors.initials: MG
authors.lastname: Schotanus
authors.affiliation: Maastricht Universitair Medisch Centrum, P. Debyelaan 25, 6229 HX Maastricht, The Netherlands. Electronic address: p.emans@mumc.nl.
authors.forename: P
authors.initials: P
authors.lastname: Emans
authors.affiliation: Zuyderland Medisch Centrum, Dr. H. vd Hoffplein 1, 6162 BG Sittard-Geleen, The Netherlands. Electronic address: b.jong@orbisconcern.nl.
authors.forename: B
authors.initials: B
authors.lastname: Jong
authors.affiliation: Zuyderland Medisch Centrum, Dr. H. vd Hoffplein 1, 6162 BG Sittard-Geleen, The Netherlands. Electronic address: n.kort@orbisconcern.nl.
authors.forename: N P
authors.initials: NP
authors.lastname: Kort
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging* / Q000601:surgery; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000601:surgery*; D007866:Leg / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012372:ROC Curve; D015203:Reproducibility of Results; D013977:Tibia / Q000000981:diagnostic imaging* / Q000601:surgery; D014057:Tomography, X-Ray Computed / Q000379:methods*
keywords: 3D CT-scan; Long-leg radiographs; Reliability; Total knee arthroplasty; Validity