title: A new method to measure anatomic knee alignment for large studies of OA: data from the osteoarthritis initiative.
abstract: OBJECTIVE
  To develop and validate a new and improved software method to rapidly determine femur-tibia angle (FTA).
  
  
  METHODS
  Three readers, two skilled and one unskilled, without any formal medical training, measured FTA in 142 subjects from the Osteoarthritis Initiative (OAI). The reader reliability was assessed using the intra-class correlation coefficient (ICC), root mean square standard deviation (RMSSD), and Bland-Altman plots, comparing the existing and new FTA methods. Gender-specific linear regression assessed the relationship of FTA with the hip-knee-ankle angle (HKA).
  
  
  RESULTS
  The ICC (RMSSD) for intra- and inter-reader reproducibility of the existing FTA method was 0.96 (0.77°) and 0.92 (1.38°), respectively, and for the new technique was 0.98 (0.25°) and 0.98 (0.37°), with similar results for all three readers. Bland-Altman 95% limits of agreement were greater than ±2° for the existing, and ±1° for the new method. The r-value for the relation of FTA to HKA was 0.68 and 0.72 for the existing and new methods, respectively. Varus (HKA ≤ -2°)/neutral (-2° < HKA < 2°)/valgus (HKA ≥ 2°) alignment based on predicted HKA agreed moderately with measured HKA (weighted kappa = 0.53), and had moderate sensitivity (73%) and specificity (84%) for varus malalignment. The new FTA was related to HKA using a linear equation with a slope of 0.98 and an offset of 4.0°.
  
  
  CONCLUSIONS
  Since it is largely automated and uses unambiguous anatomical landmarks, the new method is highly reproducible and can be made on a standard posteroanterior (PA) knee radiograph by a relatively unskilled reader.
authors.affiliation: Brigham and Women's Hospital, Boston, MA, USA.
authors.forename: T
authors.initials: T
authors.lastname: Iranpour-Boroujeni
authors.affiliation: University of California San Francisco, San Francisco, CA, USA.
authors.forename: J
authors.initials: J
authors.lastname: Li
authors.affiliation: University of California San Francisco, San Francisco, CA, USA.
authors.forename: J A
authors.initials: JA
authors.lastname: Lynch
authors.affiliation: University of California San Francisco, San Francisco, CA, USA.
authors.forename: M
authors.initials: M
authors.lastname: Nevitt
authors.affiliation: Brigham and Women's Hospital, Boston, MA, USA. Electronic address: jduryea@bwh.harvard.edu.
authors.forename: J
authors.initials: J
authors.lastname: Duryea
mesh_terms: D000368:Aged; D017760:Bone Malalignment / Q000000981:diagnostic imaging*; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007719:Knee Joint / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000000981:diagnostic imaging*; D011859:Radiography; D015203:Reproducibility of Results; D012984:Software; D013977:Tibia / Q000000981:diagnostic imaging*
keywords: Knee alignment; Knee radiography; Quantitative imaging