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 degrees (range -35.0-16.3 degrees) and -0.1 degrees (range -1.4-1.4 degrees), respectively. For the adjusted CT method, reproducibility and inter- and intraobserver variability were 1.4 degrees, 1.6 degrees and 1.4 degrees (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.