Vertical shear pelvic ring injuries: do transsacral screws prevent fixation failure?

To determine the frequency of fixation failure after transsacral-transiliac (TS) screw fixation of vertical shear (VS) pelvic ring injuries (OTA/AO 61C1) and to describe the mechanism of failure of TS screws. Retrospective cohort study. Level 1 academic trauma center. Twenty skeletally mature patients with unilateral, displaced, unequivocal VS injuries were identified between May 1, 2009 and April 31, 2016. Mean age was 31 years and mean follow-up was 14 months. Twelve had sacroiliac dislocations (61C1.2) and eight had vertical sacral fractures (61C1.3). Operative treatment with at least one TS screw. Radiographic failure, defined as a change of >1 cm of combined displacement of the posterior pelvis compared with the intraoperative position on inlet and outlet radiographs. Radiographic failure occurred in 4 of 8 (50%) vertical sacral fractures. Posterior fixation was comprised of a single TS screw in 3 of these 4 failures. The dominant mechanism of screw failure was bending. All of these failures occurred early in the postoperative period. No fixation failures occurred among the sacroiliac dislocations. There were no deep infections or nonunions. This is the first study to describe the mechanism of failure of TS screws in a clinical setting after VS pelvic injuries. We caution surgeons from relying on single TS screw fixation for vertically unstable sacral fractures. Close radiographic monitoring in the first few weeks after surgery is advised. Level IV.