Defining a new three-dimensional method for determining femoral torsional pathology in children

The purpose of this study was to compare 2D femoral torsional values to measurements made from 3D reconstructions, in pediatric patients with torsional pathology. Seventeen patients were included in this study. Femoral torsion was measured in 2D and 3D and compared using interclass correlation and Bland-Altman plots. The 2D and 3D measurements had excellent correlation (r > 0.79, P < 0.001). However, we found a fixed bias of -5.1 ± 11.3°, with 3D being consistently lower than 2D. This bias persisted when looking at only subjects with normal neck shaft angles. A proportional bias of 1.2 ± 7.8° was found when comparing 2D and 3D MRI measurements indicating that as the magnitude of the torsion changed, the difference between the two measurement techniques also changed. Given the proven accuracy of 3D reconstructions in the measurement of femoral torsion, clinicians should consider this method in pediatric patients with torsional pathology. Although 2D and 3D computed tomography (CT)/MRI torsional measurements correlate well, the presence of fixed and proportional biases indicates that the two methods cannot be used interchangeably. We submit that 3D reconstructed CT/MRI imaging, aligned along the mechanical axis, should be considered to assess femoral torsion in pediatric patients. Level of evidence: III Diagnostic Study.