Coronal Plane Alignment of the Knee Classification in Osteoarthritic Knees: Poor to Moderate Reliability and
Pierre-Alban Bouché1, Halah Stern2, Xavier Gasparutto2
1Division of Orthopaedic Surgery and Musculoskeletal Trauma Care, Geneva University Hospitals, Geneva, Switzerland; University of Paris Cite, Faculty of Medecine, Paris, France.
Background:
The coronal plane alignment of the knee (CPAK) classification is increasingly used in daily practice and in research. The reliability of the angles measured has been estimated, but not that of the classification itself. This study aimed to assess the inter- and intra-observer reliability of the CPAK classification using different imaging modalities: full-length weight-bearing radiographs, two-dimensional (2D) electrons-optiques systemes (EOS), and three-dimensional (3D) EOS in osteoarthritic knees.
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 intraobserver reliability (Kappa 1st = 0.39; Kappa 2nd = 0.48) and the interobserver reliability (Kappa = 0.39) were poor. The intraobserver reliability of the lateral distal femoral angle (LDFA) was good (ICC1st = 0.85) and excellent (ICC2nd = 0.92). For medial proximal tibial angle (MPTA), the intraobserver reliability was moderate (ICC1st = 0.72) and good (ICC2nd = 0.75). The interobserver reliability of the LDFA was excellent (0.91) and good (0.80) for MPTA. Comparing the three different long leg radiographs, the intraobserver and interobserver reliability were better with full weight-bearing radiographs (Kappa1st = 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).
Conclusions:
The reliability of the CPAK classification is poor to moderate, and full-length weight-bearing radiographs should be preferred over EOS.
Level Of Evidence:
IV, retrospective cohort.
Related Concept Videos
01:09Functional Classification of Joints
The functional classification of joints is determined by the amount of mobility between the adjacent bones. Joints are functionally classified as a synarthrosis or immobile joint, an amphiarthrosis or slightly moveable joint, or as a diarthrosis, a freely moveable joint. Fibrous and cartilaginous joints can be functionally classified as either synarthroses or amphiarthroses, whereas all synovial joints are classified as diarthroses.
Synarthrosis
An...
01:23Knee Joint
A total of seven ligaments support the knee joint. The patellar ligament, which is also attached to the quadriceps femoris...
01:20Structural Classification of Joints
A fibrous joint is where the adjacent bones are united by fibrous connective...
01:18Classification of Bones
Long and Short Bones
The appendicular skeleton, particularly the upper and lower limbs, is primarily made of long and short bones. The...
01:16Eccentric Axial Loading in a Plane of Symmetry
01:16Bones of the Lower Limb: Femur and Patella