Sagittal rotation determination

A computer-implemented method for determining a pelvic sagittal rotation of a pelvis from a radiation distorted image of the pelvis, wherein the image was made in an anterior-posterior direction, the method comprising:

• determining, based on the image, a position of each of a plurality of pelvic landmarks;
• determining a calibration plane with respect to the pelvis, wherein the calibration plane is perpendicular to the anterior-posterior direction;
• projecting in parallel the plurality of pelvic landmarks onto the calibration plane to generate a calibrated two-dimensional projection;
• determining a distance between two or more of the plurality of pelvic landmarks in the calibrated two-dimensional projection, wherein the distance is in a direction perpendicular to the anterior-posterior direction;
• and
• determining the pelvic sagittal rotation of the pelvis based on a predetermined correspondence and the determined distance, wherein the predetermined correspondence comprises statistical data based on distances between the plurality of pelvic landmarks within the calibration plane and a corresponding sagittal rotation of the pelvis for a plurality of reference patients.