A new measurement method of femoral anteversion based on the 3D modeling

Three dimensional (3D) modeling of the femur is a very useful method of measuring femoral anteversion. Conventional methods based on cross-sectional computed tomography (CT) images have difficulty in determining the major axes: femoral neck axis, condylar line and longitudinal axis. The authors modeled the femur and defined three parameters: neck axis, long axis and knee axis. First, the neck axis consists of centers of femoral head and neck. The femoral head is modeled as a sphere. The authors define the center of femoral head from the center of fitted sphere. The center of femoral neck is the mid-point of the two dimensional (2D) reconstructed oblique image in the part of femoral neck. The neck axis is a line connecting these two centers. Second, the authors model the longitude of the femur as a cylinder, and the long axis is defined from the fitted cylinder. Third, the knee axis which is tangent to the back of the femoral condyles is easily determined by table-top method. According to the definition of the femoral anteversion, the femoral anteversion is efficiently measured from this model. The method provides accurate, fast and human factor free measurement for femoral anteversion.