Neurovascular risks of sacral screws with bicortical purchase: an anatomical study

Abstract

The aim of this cadaver study is to define the anatomic structures on anterior sacrum, which are under the risk of injury during bicortical screw application to the S1 and S2 pedicles. Thirty formaldehyde-preserved human male cadavers were studied. Posterior midline incision was performed, and soft tissues and muscles were dissected from the posterior part of the lumbosacral region. A 6 mm pedicle screw was inserted between the superior facet of S1 and the S1 foramen. The entry point of the S2 pedicle screw was located between S1 and S2 foramina. S1 and S2 screws were placed on both right and the left sides of all cadavers. Then, all cadavers were turned into supine position. All abdominal and pelvic organs were moved away and carefully observed for any injury. The tips of the sacral screws were marked and the relations with the anatomic structures were defined. The position of the sacral screws relative to the middle and lateral sacral arteries and veins, and the sacral sympathetic trunk were measured. There was no injury to the visceral organs. In four cases, S1 screw tip was in direct contact with middle sacral artery. In two cases, S1 screw tip was in direct contact with middle sacral vein. It was observed that the S1 screw tips were in close proximity to sacral sympathetic trunk on both right and the left sides. The tip of the S2 screw was in contact with middle sacral artery on the left side only in one case. It is found that the tip of the S2 screw was closely located with the middle sacral vein in two cases. The tip of the S2 pedicle screw was in contact with the sacral sympathetic trunk in eight cases on the right side and seven cases on the left side. Lateral sacral vein was also observed to be disturbed by the S1 and S2 screws. As a conclusion, anterior cortical penetration during sacral screw insertion carries a risk of neurovascular injury. The risk of sacral sympathetic trunk and minor vascular structures together with the major neurovascular structures and viscera should be kept in mind.

Morphometry of the Iliolumbar Artery and the Iliolumbar Veins and Their Correlations with the Lumbosacral Trunk and the Obturator Nerve

“…This theory may be adapted to other cancellous bones such as the pelvis and the sacroiliac joint. The tips of the screws or pins may penetrate the inner cortex of the pelvic bones and they may damage the vascular structures [26]. Therefore, the iliolumbar artery variations and the related neurovascular structures are important.…”

Multiple recurrent postoperative spinal infections due to an unrecognized presacral abscess following placement of bicortical sacral screws: case report

“…1,14,19,20 Bicortical screws are a good example of this: by breaching 2 segments of cortical bone, these screws offer a greater degree of stability than do monocortical screws. 5,13,21 This is especially important at the lumbosacral junction when a long fusion lever arm is present. 13 On the other hand, our patient's case shows that as a screw passes through the anterior surface of the vertebrae it opens the potential for reinfection through recurrent seeding of the sacral tract.…”

May dubel be a solution for pullout problem of the pedicle screws at osteoporotic spine?

“…However, various anterior intra and extra abdominal organs and vascular structures may be injured (13,14,22). The use of hydroxyapatite-coated pedicle screws can improve pedicle-screw contact, bone fusion and mineralization that may increase the screw pullout strength (33).…”