PROXIMITY OF ILIOSACRAL SCREWS TO NEUROVASCULAR STRUCTURES AFTER INTERNAL-FIXATION

The placement of iliosacral screws for the stabilization of pelvic rin g lesions is technically demanding, The postoperative computed tomogra phy scans of 31 patients who had 57 iliosacral screws placed for vario us indications were studied to determine the proximity of these screws to neurovascular structures, The closest distance of the screws from the S1 foramen averaged 3 mm, (range, 0-10.5 mm); the average closest distance to the anterior cortex of the sacral ala was 4.8 mm (range, 0 -15.3 mm), The corridor for the insertion of the screws between the S1 foramen and the anterior cortex of the sacrum averaged 21.7 mm (range , 16.2-28.9 mm), Trigonometric analysis of these dimensions suggests t hat deviations of the surgeon's hand by as little as 4 degrees may dir ect iliosacral screws either into the 81 foramina or through the anter ior cortex of the sacrum.