A new method to measure anatomic knee alignment for large studies of OA: Data from the Osteoarthritis Initiative

T. Iranpour-Boroujeni, J. Li, J. A. Lynch, M. Nevitt, J. Duryea

Research output: Contribution to journalArticlepeer-review

32 Scopus citations


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 (HKAρ2°) 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.

Original languageEnglish (US)
Pages (from-to)1668-1674
Number of pages7
JournalOsteoarthritis and Cartilage
Issue number10
StatePublished - Oct 1 2014
Externally publishedYes


  • Knee alignment
  • Knee radiography
  • Quantitative imaging

ASJC Scopus subject areas

  • Rheumatology
  • Biomedical Engineering
  • Orthopedics and Sports Medicine


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