Radiographic Quantification and Analysis of Dysmorphic Upper Sacral Osseous Anatomy and Associated Iliosacral Screw Insertions

Objective: To quantify upper sacral dysmorphic osseous anatomy and assess its impact on second sacral segment iliosacral screw insertion. Design: Retrospective evaluation of a prospective trauma database. Setting: Regional Level I trauma center. Patients: Twenty-four patients with unstable posterior pelvic ring disruptions and sacral dysmorphism were evaluated radiographically and second segment (S2) screws were placed using a standard technique. Main Outcome Measurements: The sacral osseous pathway limits were measured using preoperative pelvic computed tomography at the upper and second sacral segments. The S2 screw location relative to the sacral nerve root tunnels and the maximum possible screw lengths for both S1 and S2 screws were evaluated with postoperative pelvic computed tomography. The S2 screw positions were graded as intraosseous, juxtaforaminal, or extruded. Preoperative and postoperative peripheral neurologic examinations were documented. Results: The dysmorphic S1 width available for screw insertion averaged 13.2 mm. The S2 pathway width averaged 15.2 mm. The maximum potential screw length for the dysmorphic S1 averaged 100.8 mm and for S2 measured 151.9 mm. Twenty of 24 patients with S2 screws were intraosseous and in four patients were juxtaforaminal. There were no extruded screws. There were no neurologic injuries. Conclusions: Dysmorphic S1 segments are anatomically competent for routine screw fixation. The S2 segment provides a larger osseous site for screw insertion than S1 in dysmorphic sacrums. Significantly longer screws are possible in S2 compared with the dysmorphic S1 segment. S2 iliosacral screws can be safely and accurately accomplished using a standard technique in patients with unstable posterior pelvic ring disruptions and sacral dysmorphism. Safe screw insertions avoid iatrogenic nerve root injuries.