Change in Femoral Neck Anteversion Relative to the Retrocondylar Coordinate System and Computed Tomography Axial Plane

In the present study, we aimed to verify the discrepancies in the measured femoral neck anteversion (FNA) values relative to the retrocondylar plane and computed tomography plane by using computer simulation. We observed that the measured FNA values increased with an increase of each degree of extension and adduction. Moreover, in cases where the neck shaft angle was larger, the measured FNA values tended to increase more. The maximum discrepancy between the true value and measured value was 15.8, whereas the largest difference between the maximum discrepancy and minimum discrepancy of the fixed neck shaft angle and FNA was 25.8. In cases where the femur has a high neck shaft angle (valgus hip) and/or high anteversion, it is likely that the measured value is smaller than the actual value. Hence, it is essential to carefully consider the discrepancy of the measured value when the FNA is measured from the CT axial plane without any correction according to the retrocondylar plane.