Radiographic displacement in pelvic ring disruption: reliability of 3 previously described measurement techniques.

BACKGROUND: The literature on pelvic ring disruptions is based largely on nonstandardized and nonvalidated radiographic outcomes. A thorough review of the literature revealed only 3 described methods for measuring radiographic displacement and 1 frequently used grading system for displacement. We aimed to test the reliability of these previously published radiographic measurement methods and grading system.
METHODS: Five separate observers measured radiographic displacement on the standardized pre- and postoperative anteroposterior, inlet, and outlet views of 25 patients with surgically treated Tile B and C pelvic fractures. The readers measured their initial impression based on the Tornetta and Matta grading system (excellent, good, fair, and poor). Next, they measured displacement using the inlet and outlet ratio as described by Sagi, the cross measurement technique as described by Keshishyan, and the absolute displacement method (ADM) as described by Lefaivre. The millimeter measurement obtained by the ADM was converted using the Tornetta and Matta grading system. Each continuous measure was compared for interobserver reliability using intraclass correlations (ICCs), and the categorical outcomes were compared using a kappa statistic. Finally, the relationship of the initial impression to the grade as determined by the ADM was compared using kappa agreement.
RESULTS: The agreement among observers based on initial impression was poor (kappa statistic, 0.306) but was fair among those reductions that were excellent (κ = 0.495). Using the Sagi method, the reliability ICC was moderate for the postoperative inlet [0.515, 95% confidence interval (CI), 0.338-0.702] and outlet ratio (0.594, 95% CI, 0.423-0.760) but almost perfect in preoperative radiographs (inlet: 0.814, 95% CI, 0.703-0.901; outlet: 0.863, 95% CI, 0.775-0.929). The ICCs for all interpretations of the Keshishyan technique were excellent but were highest when considered as a ratio (preoperative: 0.938, 95% CI, 0.894-0.969; postoperative: 0.912, 95% CI, 0.850-0.955). Using the ADM, the location and film used for measurement had poor agreement, and the ICC for the measurement in millimeters was moderate (preoperative: 0.522, 95% CI, 0.342-0.708; postoperative: 0.432, 95% CI, 0.255-0.634) and the kappa agreement poor when converted using the Tornetta and Matta scale (κ = 0.2190). The agreement between the impression and the converted grade from the ADM was poor (κ = 0.2520).
CONCLUSIONS: Radiographic measurement in pelvic x-rays to date has been nonvalidated, and we found the interobserver reliability on common methods, including overall impression and absolute displacement in millimeters, to be poor. The inlet/outlet ratio as described by Sagi was reliable only with wide displacement. The cross measurement technique allows least observer choice and had excellent reliability but does not give a measurement that we can easily interpret based on convention in pelvic fracture description.