Because of the complex 3 dimensional structure of the femur, the conventional methods that use cross sectional computerized tomograph (CT) images to measure anteversion have several problems. These are 1) the ambiguity of defining the femoral neck axis and condylar line, 2) the dependence of patient positioning. Especially, the femoral neck axis which is known as a major source of error is hard to determine from single or several 2 dimensional transverse CT images. The present study has devised a new method for the measurement of anteversion utilizing the 3 dimensional imaging technique. First, the CT scan was taken into two parts include from the head to lesser trochanter (proximal part) and the condylar part (distal part) of femur. The two parts of cross-sectional images were position-corrected by adjusting the centroid of the neck base and the supra-condylar cross-sections. Then the slice images of proximal part are rearranged to antero-posterior view parallel to the condylar axis and bisected obliquely along the line of the inclination of the neck for a better definition of the neck axis. Then the bisected proximal part and the distal part of femur were 3 dimensionally reconstructed and rotated to make a cranio-caudal view for a final measurement. The direct measurement was performed on computer screen with the aide of specially designed caliper tool software. This method provides the most accurate measurement of anteversion because it is virtually equivalent to the direct measurement of bisected dried femur in vitro.
