Fluoroscopic images of the sacroiliac joint alone are unable to identify simulated flexion or extension malreduction of the anterior pelvic ring in AO/OTA 61-B2.3 pelvic injuries

Purpose: Reduction of AO/OTA 61-B2.3 (APC2) pelvic fractures is challenging in the setting of anterior ring comminution. The anterior ring is visually much simpler to evaluate for flexion or extension hemipelvis deformity than the posterior ring, except in the setting of comminution, necessitating some other visual reference to judge hemipelvis reduction. We sought to test whether pelvic inlet and outlet fluoroscopy of the contours of the sacroiliac joint could be used in isolation to judge hemipelvis flexion or extension. Methods: Symphyseal and anterior SIJ ligaments were cut (6 cadaveric pelvis). The symphysis was held malreduced to produce one centimeter flexion and extension deformity: 1 cm was selected to mimic a maximum clinical scenario. The SIJ was assessed using inlet and outlet fluoroscopy. The scaled width of the SIJ was assessed at the joint apertures and midjoint on both inlet and outlet views. Joint widths in flexion and extension were compared against joint widths measured on the reduced SIJ using paired t-tests. Results: There was no statistical difference in the superior (p = 0.227, 0.675), middle (p = 0.203, 0.693), and inferior (p = 0.232, 0.961) SIJ widths between hemipelvis flexion or extension models against reduced SIJ on outlet views. There was no statistical difference in the anterior (p = 0.731, 0.662), middle (p = 0.257, 0.655), and posterior (p = 0.657, 0.363) SIJ widths between flexion or extension models against reduced SIJ on inlet views. Conclusion: Inspection of SIJ width on inlet and outlet fluoroscopy cannot detect up to one centimeter of hemipelvis flexion or extension malreduction in the setting of AO/OTA 61-B2.3 (APC2) pelvic fractures with complex anterior injuries.