Occult bladder injury in low displacement anterior–posterior compression pelvic fractures type I: a retrospective analysis of incidence and predictors

BACKGROUND: Pelvic ring injuries are frequently associated with genitourinary trauma, particularly bladder injury, traditionally considered proportional to fracture displacement. Minimally displaced anterior-posterior compression (APC I) fractures are often regarded as low risk. However, high-energy trauma may cause significant soft-tissue injury even when skeletal displacement is minimal. This study evaluated the incidence, characteristics, and outcomes of bladder injury in minimally displaced APC I fractures and identified associated risk factors, including dynamic instability. METHODS: We retrospectively reviewed 180 adult patients with APC I fractures undergoing operative fixation after dynamic stress examination under anesthesia confirmed instability, at a high-volume pelvic trauma center (2020-2024). Data included demographics, mechanism of injury, intraoperative findings, bladder injury type, operative parameters, and functional outcomes. Bladder integrity was assessed intraoperatively and repaired primarily by urology. Associations between bladder injury and clinical, radiographic, and biomechanical factors, including pubic diastasis, sacroiliac widening, and pubic rami configuration, were analyzed. RESULTS: Bladder injury occurred in 27 patients (15%), involving the dome (41%), body (37%), or neck (22%). High-energy mechanisms accounted for 95% of injuries, including motor vehicle (47%) and motorcycle (26%) collisions, falls from height (15%), and pedestrian accidents (7%). Female patients had a higher relative incidence (18% vs. 13%, p = 0.04). Bladder injury correlated with longer operative time, increased blood loss, greater dynamic pubic symphyseal diastasis, sacroiliac widening, and high-energy trauma. Pubic rami separation or rotation also signaled increased soft-tissue risk. All injuries were repaired successfully, and functional outcomes were comparable between groups. CONCLUSION: Even minimally displaced APC I fractures may conceal clinically significant bladder trauma, particularly after high-energy mechanisms. Reliance on radiographic displacement alone may underestimate soft-tissue injury risk. Intraoperative vigilance, direct bladder inspection, and timely urologic repair are essential for optimal outcomes. Recognition of this phenomenon can guide risk stratification and improve perioperative management in pelvic trauma. TRIAL REGISTRATION: This study was performed in line with the principles of the Declaration of Helsinki. Approval was granted by the Ethics Committee of orthopaedic department of Cairo University (Approval No. [N3032025]).