The lateral stress radiograph: an effective alternative to examination under anesthesia for identifying occult instability in minimally displaced lateral compression pelvic ring injuries.

Purpose: The purpose of this study was to review the practice of utilizing lateral stress radiographs (LSRs) to identify occult instability (≥ 10 mm of dynamic displacement on LSRs) of minimally displaced lateral compression type 1 (LC1) pelvic ring injuries and to evaluate for associations between instability and patient demographics, injury characteristics, and hospital course.

Methods: A retrospective review of a prospective registry from 2018 to 2022 identified 151 patients with LC1 injuries. LSRs were obtained in 86.8% (131/151) of patients. Three (2.2%) patients were excluded for malrotation of LSRs, leaving 128 patients for analysis.

Results: The median maximum dynamic displacement on LSRs was 12.2 mm (IQR: 5.9 to 17.3). Occult instability was present in 62.5% (80/128) of patients and was associated with older age (Median difference 11.0 years, 95% CI 3.0 to 20.0), Nakatani type 1 rami fractures (73.7% vs. 47.9%, p = 0.001), and rami fracture comminution (Proportional difference 58.7%, 95% CI 42.8 to 71.3%), but not gender, high-energy mechanism, bilateral rami fractures, Denis classification, sacral fracture completeness, or sacral comminution. Patients with occult instability took longer to ambulate 15 feet and clear physical therapy (PT), were more likely to be unable to clear PT by hospital day 3 or by time of discharge, had longer hospital stays, and were more likely to require rehabilitation facilities.

Conclusion: LSRs were obtained in a majority of patients. Occult instability was frequently present and associated with older age, comminuted distal pubic rami fractures, longer hospital stays, longer times to mobilize and clear PT, and an increased need for rehabilitation facilities.