Coronal Plane Alignment of the Knee Classification in Osteoarthritic Knees: Poor to Moderate Reliability and Implications for Imaging Choice
P. Bouché, Halah Kutaish, Xavier Gasparutto, Anne Lübbeke, Hermès H. Miozzari, Didier Hannouche
Abstract
Background The coronal plane alignment of the knee (CPAK) classification is increasingly used in daily practice and in scientific reports. The reliability of the angles measured has been estimated, but not that of the classification itself. The aim of this study was to assess the inter- and intra-observer reliability of the CPAK classification on hip-knee-ankle radiographs in osteoarthritic knees. Secondly, the use of full-length weight-bearing radiographs or a 2D electrons-optiques systemes (EOS) or a 3D EOS was compared to evaluate which was more effective in assessing the CPAK classification. Methods In this monocentric repeat cross-sectional study, 39 patients (78 knees) with all three types of images were included. There were two examiners who performed each planning run twice, with an interval of at least two weeks between the two planning runs for full weight-bearing radiographs, 2D EOS, and 3D EOS. The intraclass correlation coefficient (ICC) was used to evaluate the reliability of angles, and the Cohen's Kappa coefficient was used to evaluate the reliability of the CPAK classification. Results For CPAK classification, the intra-observer reliability (Kappa 1st = 0.39; Kappa 2nd = 0.48) and the inter-observer reliability (Kappa = 0.39) were poor. The intra-observer reliability of the lateral distal femoral angle (LDFA) was good (ICC 1st = 0.85) and excellent (ICC 2nd = 0.92). For medial proximal tibial angle (MPTA), the intra-observer reliability was moderate (ICC 1st = 0.72) and good (ICC 2nd = 0.75). The inter-observer reliability of the LDFA was excellent (0.91) and good (0.80) for MPTA. Comparing the three different long leg radiographs, the intra- and inter-observer reliability were better with full weight-bearing radiographs (Kappa 1st = 0.55, Kappa 2nd = 0.61, Kappa=0.57 ) than with 2D EOS (Kappa 1st = 0.35, Kappa 2nd = 0.35, Kappa inter-reliability = 0.25) and 3D EOS (Kappa 1st = 0.40, Kappa 2nd = 0.34, Cohen's Kappa inter-reliability = 0.22). Conclusion The reliability of the CPAK classification is poor to moderate, and full-length weight-bearing radiographs should be preferred over EOS.