LOCATION OF THE SACRAL PEDICLE, FORAMINA, AND ALA ON THE LATERAL ASPECT OF THE SACRUM - A RADIOGRAPHIC STUDY

Twenty-one adult dry-bone sacral specimens were used to quantitatively determine the location of the sacral pedicle, foramina, and ala on th e lateral radiographic view of the sacrum. The anterior and posterior sacral foramina from S1 to S3, the midlines of the anterior sacrum and cephalad border of the S1 vertebral body, and the lateral limit of th e lateral sacral mass were outlined with wires. A lateral radiograph w as taken, and measurements were made directly from the radiograph. The average sacral pedicle height for both male and female specimens was approximately 20 mm for S1, 12 mm for S2, and 7 mm for S3. The sacral foramina height averaged approximately 13 mm for S1 and S2, and 10 mm for S3. The average ala and S1 body-ala angles were 88 degrees and 35 degrees. The distance from the ala tip to the anterior aspect of the s acrum averaged 12 mm, and the average anterior height of the S1 verteb ral body above the ala was 11 mm. These measurements, in conjunction w ith inlet and outlet radiographs, may aid in the recognition of the vi tal structures of the sacrum on the lateral radiographic view and enha nce the safety of dorsal sacral screw placement.