Vacuum phenomenon in pelvic fractures

Background: Vacuum phenomenon (VP) in closed pelvic fracture is a rare disorder. This study aimed to examine the prevalence and clinical findings of VP in closed pelvic fracture. Methods: We retrospectively reviewed 197 patients with closed pelvic fracture who presented to our institution from January 2012 to December 2018. Pelvic fractures were diagnosed by plain radiography and computed tomography (CT). First, we investigated the prevalence and clinical findings of VP in pelvic fractures. Second, we compared the clinical findings between pelvic fracture with and without VP. Finally, VP in pelvic fracture was evaluated clinically and radiologically. Results: VP in pelvic fractures was detected by CT in 9 (3.6%) of the 197 patients with pelvic fractures. Patients with VP had a significantly greater proportion of fracture progression than those without VP (42.9% vs. 11.3%, P = 0.02). Patients with VP had a greater proportion of fragility fractures of the pelvis (FFP), and a lesser proportion of bone union than those without VP, although the differences were not significant. In nine pelvic fractures with VP, all sacral fractures were classified as type 1 according to the Denis classification, and all pubic fractures were classified as type 1 according to the Nakatani classification. Two (22.2%) nonunion in nine pelvic fractures with VP occurred at the pubic fracture site alone. Conclusions: Orthopedic clinicians should be aware of the potential of CT for detecting VP in pelvic fractures, especially in the course of FFP progression.