Examination under anesthesia in anterior posterior compression pelvic ring injuries; additional assessment of the posterior pelvic ring reveals occult sacroiliac joint instability.

PURPOSE: To investigate the added value of directly observing sacroiliac (SI) diastasis with a modified examination under anaesthesia (EUA) protocol, including obturator inlet SI joint projections, in patients with anterior-posterior compression (APC) pelvic ring injuries. METHODS: This prospective cohort study, conducted in a level-1 trauma centre in 2017–2024, included patients > 18 years old with an APC injury, who underwent the modified EUA protocol. The modified protocol includes anterior-posterior projections of the anterior pelvis (as in the original EUA protocol), with additional obturator inlet projections of the SI joints. The primary outcomes were reclassification and detection of occult SI joint diastasis, either anterior or complete, following the modified EUA protocol. RESULTS: Thirty-five patients, with a mean age of 53, were included, 80% sustaining high-energy trauma. Following modified EUA, 23 (65.7%) of injuries were reclassified compared to classifications from CTs: 9 of 12 (75%) APC1s to APC2, 1 of 12 (8.3%) APC1s to APC3, and 13 of 23 (56.5%) APC2s to APC3. In 16 cases (45.7%), examining the SI joint during EUA enabled localisation of SI diastasis. Eleven patients of 13 (84.6%) with symphyseal diastasis less than the standard cut-off value of 2.5 cm had occult SI diastasis visible on the obturator inlet images. Four of 14 (28.5%) patients with rotational instability less than the standard cut-off value of 1.0 cm had complete SI diastasis visible on obturator inlet images. CONCLUSIONS: A modified EUA protocol, including obturator inlet projections of the SI joints, in patients with APC pelvic ring injuries has been proposed. This protocol allows for direct detection of SI joint diastasis that was not visible on the CT scans, allows for localization of SI joint diastasis, and reveals SI joint diastasis that would remain undetected if only the anterior ring was visualized.