Fig. 1.

Illustration demonstrating the postoperative displacement measurements measured on postoperative radiographs in different views. A This demonstrates displacement evaluation in the anterior posterior (AP) direction. On postoperative inlet plain films, a straight line connecting anterior midline to posterior midline was drawn. A line perpendicular to this midline line was drawn out to each ischial spine. The distance between these two lines, represented by a two headed arrow, is taken as the AP displacement. B This demonstrates evaluation of pelvic symmetry which was performed on AP radiographs according to method described by Lefaivre et al. [17]. On an AP radiographs, a line is drawn from the inferior aspect of the sacroiliac joint to the contralateral teardrop inferior aspect. The length of the two lines is represented by the letters X and Y. The longer line (X) is subtracted from the second line (Y), yielding a pelvic asymmetry value (X-Y). C This demonstrates the vertical displacement measurements we applied technique which was described by Henderson et al. [16]. A straight midline was drawn through the lower lumber and upper sacral area. Horizontal lines perpendicular to this center line is drawn across the superior most point of each iliac wing. The distance between these two horizontal lines, illustrated by a two-headed arrow, is taken as the posterior displacement