Posterior iliac crescent fracture-dislocations: Evaluation of morphological aspects and mechanisms in unstable pelvic ring injuries.

Abstract

Posterior iliac crescent fracture-dislocations (PICFDs) were originally considered rotationally unstable and vertically stable injuries, strongly associated with lateral compression (LC) mechanism. However, it is currently recognized that PICFDs may exhibit variable injury patterns and result from different mechanisms. The purpose of this study was to evaluate relevant morphological aspects and the mechanism of injury of PICFDs in a cohort of patients presenting unstable pelvic ring injuries (PRIs) PATIENTS AND METHODS: Patients presenting unstable PRIs that underwent surgical treatment at two level 1 trauma centers from January 2019 to December 2024 were retrospectively reviewed. Individuals presenting PICFDs were recorded, and relevant morphological aspects scrutinized. 363 unstable PRIs were identified and a PICFD was present in 29 (8.0%) individuals. Among these, 23 (79.3%) were attributed to LC, 4 (13.8%) to APC (anteroposterior compression) and 2 (6.9%) to CCM (complex/combined mechanism). According to Day's classification, PICFDs were categorized as type I (n=8, 27.6%), type II (n=16, 55.2%), and type III (n=5, 17.2%). Most PICFDs (n=26, 89.6%) were displaced, 72.4% (n=21) exhibited posterior dislocation and 96,5% (n=28) presented associated ipsilateral anterior pelvic ring disruption. Comminution of the crescent-shaped fragment was seen in 13.8% (n=4) patients and vertical instability was observed in 34.5% (n=10) PICFDs. This investigation reinforced modern concepts regarding PICFDs, suggesting that the understanding of this infrequent injury pattern warrants constant refinement. Morphological aspects of PRIs presenting with PICFDs were detailed, exhibiting variable deformity, displacement and comminution. Furthermore, PICFDs can be caused by different injury mechanisms and carry the potential to cause vertical instability.