Fig. 3

The 3D lower extremity alignment assessment system under WB conditions based on biplanar long lower extremity radiographs, applying the 3D-to-2D image registration techniques. 3D bone models and the anatomic coordinate system of the femur and tibia were reconstructed. The 3D bone model included the definitions of the parameters in the bony morphology and whole lower extremity alignment. To assess the 3D parameters “in the standing position” under WB conditions, biplanar long lower extremity radiographs were obtained in the standing position. Applying the 3D-to-2D image registration technique, projected outline points of each 3D model were the finite edge points of the 2D shadow created from the projections of all visible triangular surfaces of the 3D model. To precisely assess the position and angle to the ground, the world coordinate system was reconstructed