Pedicle Guide for Thoracic Pedicle Screw Placement Kingsley O. Abode-Iyamah MD; Luke Stemper BS; Shane Rachman BS; Kelly Schneider BS; Kathryn Sick BS; Patrick W. Hitchon MD University of Iowa Hospitals and Clinics, Iowa City IA Pedicle guide Pedicle screw guide Introduction The placement of thoracic pedicle screws is challenging requiring intra-operative imaging. While increasing accuracy, these modalities increase intra-operative time, radiation to patient, surgeon, and cost. We have designed a pedicle screw guide (PSG) for placement of thoracic pedicle screws to potentially provide increased accuracy compared to free hand screw placement. Methods Two spines were imaged to measure the angle between the long axis of the pedicle and the sagittal plane from T1-T12. The cortex at the junction of the transverse process and the superior facet was penetrated using an awl. The PSG was used to make a 20 mm pilot hole into the pedicle along the trajectory calculated from the CT scans. On one side from T1- T12, pedicle screws were placed freehand based on clinical experience. On the other, pedicle screws were placed using the PSG. After placement of the screws, CT scans were obtained and grading of medial violation was recorded. The degree of violation was recorded for each pedicle (1: no violation, 2: <2mm violation, 3: >2mm violation). Pedicle angles measured with axial CT for spine 1 and 2. L1 and L2 representsangle of left pedicle (L1=spine 1, L2=spine 2). R1 and R2 represents angle of Rightpedicle (R1= spine 1, R2=spine 2). The mean of the pedicle angles are also displayed. Results Two specimens were used with a total of 48 pedicles. Of the total 48-pedicle screw there were a total of 11 pedicle violations. Of these violations, 3(12.5%) were with the use of PSG, all of which were grade 2. There were 8 violations (33%) with the free hand technique. The percent error from the pre-instrumentation CT trajectory angle was 62.3%(+/-39.5) and 34.3%(+/-23.3) (p=0.002) for freehand and guide assisted respectively. Conclusions Free hand placement of thoracic pedicle screw is challenging due to the unique anatomy of the thoracic spine. While intra-operative imaging techniques increase accuracy there is radiation risk to the surgeon. The use of the PSG increases accuracy while decreasing the duration of radiation. Learning Objectives 1.Thoracic spine anatomy 2. cortical violation with thoracic pedicle screw placement 2. New method for thoracic pedicle screw placement The average pedicle diameter from T1 to T12 Right (freehand) pedicle screw with >2mm (Grade 3) cortical violation and left(PSG) without cortical violation. Post instrumentation angle measuring angle of the pedicle screw placement (indegrees) References 1.Boucher HH. A method of spinal fusion. 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