title: What are the bias, imprecision, and limits of agreement for finding the flexion-extension plane of the knee with five tibial reference lines?
abstract: BACKGROUND
  Internal-external (I-E) malrotation of the tibial component is associated with poor function after total knee arthroplasty (TKA). Kinematically aligned (KA) TKA uses a functionally defined flexion-extension (F-E) tibial reference line, which is parallel to the F-E plane of the extended knee, to set I-E rotation of the tibial component.
  
  
  METHODS
  Sixty-two, three-dimensional bone models of normal knees were analyzed. We computed the bias (mean), imprecision (±standard deviation), and limits of agreement (mean±2 standard deviations) of the angle between five anatomically defined tibial reference lines used in mechanically aligned (MA) TKA and the F-E tibial reference line (+external).
  
  
  RESULTS
  The following are the bias, imprecision, and limits of agreement of the angle between the F-E tibial reference line and 1) the tibial reference lines connecting the medial border (-2°±6°, -14° to 10°), medial 1/3 (6°±6°, -6° to 18°), and the most anterior point of the tibial tubercle (9°±4°, -1° to 17°) with the center of the posterior cruciate ligament, and 2) the tibial reference lines perpendicular to the posterior condylar axis of the tibia (-3°±4°, -11° to 5°), and a line connecting the centers of the tibial condyles (1°±4°, -7° to 9°).
  
  
  CONCLUSIONS
  Based on these in vitro findings, it might be prudent to reconsider setting the I-E rotation of the tibial component to tibial reference lines that have bias, imprecision, and limits of agreement that fall outside the -7° to 10° range associated with high function after KA TKA.
authors.affiliation: Biomedical Engineering Graduate Group, University of California, Davis, 1 Shields Ave, Davis, CA 95616, USA. Electronic address: asbrar@ucdavis.edu.
authors.forename: Abheetinder S
authors.initials: AS
authors.lastname: Brar
authors.affiliation: Biomedical Engineering Graduate Group, University of California, Davis, 1 Shields Ave, Davis, CA 95616, USA; Department of Biomedical Engineering, University of California, Davis, 1 Shields Ave, Davis, CA 95616, USA. Electronic address: sebhowell@mac.com.
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Howell
authors.affiliation: Biomedical Engineering Graduate Group, University of California, Davis, 1 Shields Ave, Davis, CA 95616, USA; Department of Biomedical Engineering, University of California, Davis, 1 Shields Ave, Davis, CA 95616, USA; Department of Mechanical Engineering, University of California, Davis, 1 Shields Ave, Davis, CA 95616, USA. Electronic address: mlhull@ucdavis.edu.
authors.forename: Maury L
authors.initials: ML
authors.lastname: Hull
mesh_terms: D001696:Biomechanical Phenomena; D017760:Bone Malalignment / Q000000981:diagnostic imaging; D005269:Femur / Q000000981:diagnostic imaging* / Q000601:surgery; D006801:Humans; D021621:Imaging, Three-Dimensional; D007719:Knee Joint / Q000000981:diagnostic imaging*; D008279:Magnetic Resonance Imaging; D008954:Models, Biological; D015203:Reproducibility of Results; D012399:Rotation; D013977:Tibia / Q000000981:diagnostic imaging*
keywords: Internal and external rotation; Kinematic alignment; Knee arthroplasty; Malrotation of tibial component