P37. The screw-aorta dilemma: changing patient position in CT scan is critical in documenting aortic mobility

Abstract

BACKGROUND CONTEXT PS misplacement rate is reported between 6-15%. Studies looking at misplacements on a per patient basis show up to 14% of patients have screws at risk (impinging vital structures). A screw abutting the aorta is a management challenge and often requires vascular surgery intervention. However, CT scans routinely done in supine position may overestimate screw-aorta relationship. Change in patient position may allow the aorta to roll away and, in most cases, reveal an uncompromised aorta. This will allow safe removal of pedicle screws without any vascular intervention. PURPOSE To assess whether prone CT helps delineate the aorta-pedicle screw relationship. STUDY DESIGN/SETTING Retrospective chart review. PATIENT SAMPLE A total of 111 patients with post-op CT, who underwent PSF for spinal deformity, from 2004-2009. OUTCOME MEASURES Distance of pedicle screw from posterior margin of Aorta. METHODS A total of 111 patients with post-op CT, who underwent PSF for spinal deformity, from 2004-2009, were evaluated. Patients with concerning screw-aorta relationship underwent a prone CT scan. Mobility of the aorta was determined by measuring between a line drawn from the posterior margin of the aorta, perpendicular to the long axis of the screw, and a parallel line passing through the anterior margin of the body of the vertebra (in mm). This distance was compared using prone and supine CT scans. Paired t-test and signed rank tests were utilized. RESULTS There were 2,295 screws were reviewed, 45 screws in 27 patients were in proximity to the aorta. Thirty-six of these were in close proximity, but not impinging (>1cm aorta-screw distance). Fourteen screws (7 patients) were impinging ( CONCLUSIONS Supine CT-scan alone is not entirely accurate in determining screw-aorta relationship. Prone-CT scan provides additional information for better delineation. This additional diagnostic step can change the treatment option by limiting the need for vascular intervention. When in doubt, the additional use of an arteriogram can allow for improved visualization. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.