The Prevalence of Open and Closed Posterior Superior Iliac Spine.

To determine the prevalence of open and closed posterior superior iliac spine (PSIS) using lower abdominal computed tomography (CT) examinations. Eight hundred and fifty (M/F:464/386) adult patients who underwent lower abdominal CT between January 2018 and December 2018 were evaluated retrospectively. One radiologist reviewed CT images of patient pelvises to assess the presence of open and closed PSIS. The mean age of all patients was 52.7 ± 18 years. Of the 850 patients, 522 (61.5%) had open PSIS, while 328 (38.5%) had closed PSIS. The distribution of open and closed PSIS by gender was 57.5% and 42.5% in males and 66% and 34% in females, respectively. Overall, open PSIS is more common than closed PSIS. The closed PSIS is seen more often in males than in females. If an anteromedial sacral (S)-1 screw direction is chosen for posterior fusion with rod-screw fixation, it is essential to obtain CT images for evaluation of PSIS.