Imaging Case of the Week 522 Answer

The pelvic x-ray shows right inferior pubic ramus fracture as well as right acetabular fracture. There is buckling of arcuate line of S1 vertebra suggestive of fracture.

Sacral fractures can be difficult to diagnose on plain x-rays due to overlap from bowel gas. Tracing the arcuate lines on both sides is a useful tip. Arcuate lines are bow shaped, short, curved lines seen on the sacrum on the right & left side. Buckling or step defect involving these lines indicates fracture.

Reference: Fundamentals of Diagnostic Radiology by Brant & Helms.