Figure 1.

Measurement of cephalad residual displacement (CRD) of the right hemipelvis and sacrum illustrated on a pelvic outlet image. A midline vertical line is drawn along the axis of the central portion of the sacrum. A horizontal line, perpendicular to the vertical line, is drawn on the highest of the 2 measurement points—in this case, the lateral top points of the sacral transverse process elements (STPE). The difference in height between the horizontal line and the lowest of the 2 measurement points is the CRD.