Risk of vertebral artery injury associated with subaxial cervical pedicle screw malposition: cadaveric evidence and clinical relevance.

Abstract

Experimental cadaveric anatomical study. This study aims to test the safe zone hypothesis for preventing vertebral artery injury as a notable complication of subaxial cervical spine pedicle screw malpositioning and determine the critical threshold at which screw malposition causes vertebral artery injury. The pedicle screw fixation is the strongest biomechanical stabilization approach in the posterior cervical region. Although it is associated with potential complications like vertebral artery injury, these complications are rarer than anticipated. Accordingly, several authors have proposed a "safe zone" within which even a malpositioned screw may displace and not injure the artery. Five human cadavers were subjected to transpedicular screw fixation for creating lateral pedicle violation. Pre- and post-procedural anatomical measurements were obtained using computed tomography scans. Postoperatively, vertebral arteries were dissected to assess damage macroscopically and histopathologically. A significant correlation was observed between the safety margin (the combined distance of the vertebral artery from the lateral and medial walls of the transverse foramen) and the intraforaminal area occupied by screws for causing vertebral artery damage (p <0.001). The critical threshold for causing vertebral artery damage is exceeding this safety margin. This study experimentally validated the "safe zone" hypothesis, confirming its presence and effectiveness. In cases of screw breach, the decision for revision surgery should be based on the patient's clinical condition and breach status (vessel displaced or injured), rather than the screw position alone. However, if a vertebral artery injury is suspected, acute intervention should be initiated promptly.