Occult contralateral sacroiliac joint injuries missed on single-energy CT of operative pelvis fractures.

OBJECTIVE

To determine the diagnostic performance of single-energy CT (SECT) scan for detecting contralateral posterior pelvic ring injuries in patients with an operative pelvis fracture.

METHODS

Retrospective cohort study.

SETTING

Level I Trauma Center PATIENT SELECTION CRITERIA: Consecutive adults with operatively-treated pelvic ring injuries and preoperative and postoperative pelvis CT scans. Exclusion criteria were incomplete or unreadable imaging, pelvis CT obtained on a spine board or with a pelvic binder in place, prior pelvic instrumentation, or sacroiliac joint fusion.

OUTCOME: Measures and Comparisons: An "occult" contralateral sacroiliac joint injury was defined as either (A) a positive change of ≥2.0 mm between preoperative and postoperative CT measurements at this level on the "uninjured" side or (B) an intraoperatively fluoroscopic finding of ≥2.0 mm of sacroiliac joint widening on either static or dynamic stress fluoroscopic imaging on the "uninjured" side not present on the initial, preoperative CT

RESULTS

One hundred forty-six adults, 62 % male sex, with a mean age of 42.5 years were included. A unilateral posterior pelvic ring injury was identified on the initial pelvis CT in ninety patients. An occult contralateral sacroiliac joint injury was identified in 11 patients (12.2 %), 5 by intraoperative fluoroscopic examination, none during instrumentation, and 6 by postoperative pelvis CT. One U-type sacral fracture was identified on postoperative CT. The diagnostic performance of pelvis SECT in the initial trauma evaluation for correctly classifying bilateral pelvic ring injuries was 84 % sensitivity with a 16 % false negative rate, 100 % specificity, 88 % negative predictive value, and 92 % accuracy.

CONCLUSIONS

In this cohort, 16 % of bilateral posterior ring injuries were incorrectly classified as unilateral from the initial pelvis CT. A complete unilateral posterior ring injury should raise suspicion for an occult contralateral injury and may warrant additional radiographic or fluoroscopic stress examination if clinically appropriate.