The purpose of this study is to assist the optimal placement of sacroiliac screw by evaluating the anatomic and radiologic features of upper sacrum.

Fourteen fresh-frozen cadaveric pelvises and 13 normal adults were studied for the evaluation of morphology of first sacrum and dysplastic patterns. Measurement of anatomic parameters and CT imaging of pelvis were performed. Thirty-two patients with complicated pelvic fracture were evaluated for detection of variations in the sacral alar anatomy and slope found in upper sacral segmentation.

The mean distance between midpoint of sacrum and sacroiliac joint was 52.75 mm. The height of first sacral body was 21.71 mm. The longest antero-posterior distance in sacral alar was 52.36 mm. The mean angle between the coronal plane of S1 vertebra and anterior aspect of the alar was 29.3 degree. The mean angle between the superior aspect of S1 vertebral body and superior edge of the alar was 34.8 degree. The mean angle between the superior aspect of S1 vertebral body and supero-posterior edge of the alar was 12.5 degree. The studies revealed about 28 to 33% of cases as dysplastic sacrum.

We studied anatomic and radiologic features of upper sacrum in cadaveric and clinical cases to gain information on the optimal placement of sacroiliac screw.