Exploring the Relationship Between Femoral Neck Torsion Angle and Anteversion Angle Through Three-Dimensional Reconstruction in a Fixed Coordinate System.

Background: The femoral neck torsion angle (FNTA), an important parameter for assessing femoral neck morphology, has long been underappreciated in clinical practice. This study aimed to explore the relationship between FNTA and femoral neck anteversion angle (FNAA) through a 3D reconstruction in a fixed coordinate system (3D-R-FCS). Methods: Fifty synthetic Sawbone femoral specimens were analyzed. A 3D-R-FCS was established using superimposing consecutive axial cross-sections after CT scanning and 3D reconstruction. Two independent evaluators measured FNAA via Reikeras, Murphy methods and 3D-R-FCS, and evaluated FNTA via 3D-R-FCS. Results: The FNAA measured by 3D-R-FCS significantly differed from those assessed by Reikeras and Murphy methods (p < 0.001). Intra- and inter-rater intraclass correlation coefficients (ICCs) for the 3D-R-FCS exceeded 0.96, markedly higher than those of the Reikeras (ICC = 0.72-0.73) and Murphy methods (ICC = 0.76-0.82). A strong positive correlation was found between the FNTA and the FNAA discrepancy values measured by the two 2D methods (r > 0.95, p < 0.001). Conclusion: The 3D-R-FCS provides a highly reproducible model for quantifying femoral neck anatomy. The study finds out a poor correlation between FNTA and FNAA under 3D-R-FCS, and a positive correlation between FNTA measured by 3D-R-FCS and the FNAA discrepancy values measured by the two 2D methods. The correlation analysis suggests that traditional 2D measurement errors primarily might result from the intrinsic 3D spatial configuration of the femoral neck. However, these results need further explorations and validations in clinical practice.