This coronal image from a post-operative MRI scan shows how femoral axis angular deviation as seen in the coronal plane was measured in this study. Hilgenreiner’s line is first drawn, followed by a sagittal line perpendicular to it. The coronal projection angle is then measured between the femoral shaft axis and the sagittal line. Using this measurement along with that shown in Figure 4, one can calculate the true angle of hip abduction using Equation 3.