RESUMEN
OBJECTIVES: Morphologic measurements of the lateral sacral mass (LSM) and adjacent bone structures were made on dried sacrum specimens, together with radiologic evaluations on computed tomography (CT) scans in order to assess the appropriateness of this area in iliosacral screw applications. METHODS: On thirty dried human sacral bone specimens, morphologic measurements of the LSM were made by a compass sensitive to millimeters. Computed tomographic views of S1 and S2 pedicle-bodies and intervertebral foramina were obtained to make radiologic measurements by a millimeter-sensitive ruler to examine the relationship between LSM and the neural canal and intervertebral foramina. RESULTS: The average widths of the LSM on the posterior and anterior surfaces of the sacrum were as follows. Posterior aspect: 24.1 mm on S1, 18.4 mm on S2 levels on the right; 24.5 mm on S1 and 18.8 mm on S2 levels on the left. Anterior aspect: 28.9 mm on S1, 22.6 mm on S2 levels on the right; 29.1 mm on S1 and 23 mm on S2 levels on the left. The average (oblique) heights of LSM on the postero-lateral surface were 39 mm on S1, 28.6 mm on S2 levels on the right; 37.4 mm on S1, 27.6 mm on S2 levels on the left. The average depth of the sacral ala was 50.6 mm on the right, 50.7 mm on the left. The average posterior alar height was 26 mm on both sides. On CT scans, the average widths of pedicle+sacral ala were measured as 37.6 mm (right) and 36.3 mm (left) at the S1 pedicle-body level. The average widths of LSM were 22 mm (right) and 22.3 mm (left) at the S1 intervertebral foramina level. The average widths of pedicle+LSM were 27.8 mm (right) and 26.4 mm (left) at the S2 pedicle-body level. The average widths of LSM at the S2 intervertebral foramina level were 15.9 mm (right) and 16.3 mm (left). CONCLUSION: Our results suggest that iliosacral screw fixation may be more safely performed, especially at the S1 pedicle-body level and lateral to the sacral neural canal and intervertebral foramina. Injury to the neural tissues and surrounding structures is more unlikely if preoperative measurements of LSM are made on CT scans.
