*2.2. Radiographic Methods*

To assess the imaging parameters associated with the functional recovery, we used three radiographic methods and three functional outcome questionnaires in this study.

Three experienced orthopedic trauma surgeons collaborated on this measurement plan and independently measured radiographic features. For measurements using computerbased-reading methods, each observer was given an identical set of images (pre- and postoperative anteroposterior (AP), outlet, and inlet views). This study aimed to investigate the correlation between radiological measurements and the functional outcome. Three previously published radiographic measurement methods were chosen. Each observer was provided with a set of images (23 patients and six images per patient) and received the same instructions for measurement, including three radiographic measurement methods, which are described below (Table 1).

**Table 1.** Radiographic measurement methods for assessment of displacement and symmetry for pelvic fracture with spinopelvic dissociation.


**Figure 3.** The inlet and outlet ratio are calculated (DA/DU) with the pelvic inlet and outlet views. The solid lines refer the reference lines, and the dashed lines refer measured lines. The Abbreviations: DA = distance of affected side; DU = distance of unaffected side.

**Figure 4.** The cross−measurement method is illustrated with an example image.

**Figure 5.** (**A**,**B**) The absolute displacement method (ADM). The example image illustrated the measurement of vertical displacement in pelvis AP view pre- and post-operatively. (**A**) Pre-operative pelvis AP view. (**B**) Post-operative pelvis AP view. The reference lines are solid, and the measured lines are dashed. The Abbreviations: VDPRE = the pre-operative vertical displacement; VDPOST = the post-operative vertical displacement.
