Fig. 1

Planning mask for the posterior column screw. Planning mask for the posterior column screw resembling the anatomical bone corridor of the posterior column in regard to the optimal screw position. Fig. 1a shows a sagittal, Fig. 1b a coronal section. Fig. 1c shows nine axial sections which were planned according to Ebraheim et al. [5]. (8) axial section at the upper acetabular margin (6) axial section at the centre of acetabulum and (4) at the lower margin of acetabulum (9) axial section in the middle of the stretch between screw exit point and upper acetabular margin (7) axial section in the middle of the stretch between upper acetabular margin and centre of the acetabulum (5) axial section in the middle of the stretch between centre of acetabulum and lower acetabular margin (3) axial section at two thirds of the stretch between screw entry point and lower acetabular margin (2) axial section at one third of the stretch between screw entry point and lower acetabular margin (1) axial section at the screw entry point. In each of the axial sections, the maximum screw diameter is shown