CT Measurement of Anteversion in the Femoral Neck: The influence of femur positioning

Purpose: To evaluate CT methods of measuring anteversion in the femoral neck with respect to measurement accuracy and with respect to the influence exerted by different femoral shaft positions; and to describe a new CT measurement concept that introduces a mathematical adjustment for different femoral shaft positions. The new technique facilitates the taking of measurements in patients who cannot be correctly positioned in traditional methods. Material and Methods: CT examinations of previously measured anteversions in the femoral neck were reviewed in retrospect in 30 patients with fractures of the femoral neck. The position of the femoral shaft was assessed. A reference angle was compared with direct traditional measurements and with measurements adjusted for the actual position of the femoral shaft by means of a 3D mathematical reconstruction. Reproducibility and inter— and intraobserver variability were assessed in 10 cases. Results: All femurs varied in position within the gantry. The mean difference between the direct CT measurement and the adjusted CT measurement compared to the reference angle were -8.8° (range -35.0-16.3°) and -0.1° (range -1.4-1.4°), respectively. For the adjusted CT method, reproducibility and inter- and intraobserver variability were 1.4 intraobserver variability were 1.4, 1.6 intraobserver variability were 1.4 and 1.4° (SD of difference), respectively. Conclusion: CT measurement of femoral anteversion in clinical practice can only be accurate when corrected for variation in the position of the femoral shaft.