Objectives: To compare the accuracy and reliability of 2D and 3D methods for measuring femoral version against an anatomic reference standard using 3D-printed femoral phantoms.
Methods: CT data from three skeletally mature pediatric patients (2 females, 1 male; age 17.8 ± 0.1 years) were used as digital templates for 3D-printed haptic femur models. The anatomic reference standard for femoral version was determined by an established drilling technique. Models underwent CT scanning in neutral position and variations of flexion, internal/external rotation, and abduction/adduction (in increments of 15°, 30°, 45°). Two radiologists measured femoral version on axial datasets using 2D techniques (Murphy, Lee, Reikerås) and a 3D-reconstructed model in a blinded fashion. Mean absolute error (MAE) between measurements and the reference standard and mean absolute differences (MAD) between readers were calculated.
Results: Across all positions in all femurs, MAE was 22.9° ± 23.7° for the Murphy technique, 12.1° ± 8.5° for the Lee technique, 12.2° ± 9.6° for the Reikerås technique, and 2.3° ± 1.3° for the 3D method. For all 2D methods, MAE was greatest with adduction, flexion, and combinations of both. For the 3D method, femur position had no impact on MAE. MAD between readers was 9.7° for the Murphy technique, 4.7° for the Lee technique, 4.4° for the Reikerås technique, and 2.9° for the 3D method.
Conclusions: Femoral version measurements based on 3D reconstructions are more accurate than traditional 2D techniques, more robust to femur positioning, and more consistent between readers. Accurate measurement of femoral version is important for understanding and treating lower extremity deformities in the skeletally mature pediatric population.
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