Stereotactic navigation for placement of pedicle screws in the thoracic spine

OBJECTIVE: Pedicle screw fixation in the lumbar spine has become the standa rd of care for various causes of spinal instability. However, because of th e smaller size and more complex morphology of the thoracic pedicle, screw p lacement in the thoracic spine can be extremely challenging. In several pub lished series, cortical violations have been reported in up to 50% of screw s placed with standard fluoroscopic techniques. The goal of this study is t o evaluate the accuracy of thoracic pedicle screw placement by use of image -guided techniques. METHODS: During the past 4 years, 266 image-guided thoracic pedicle screws were placed in 65 patients at the University of Michigan Medical Center. Po stoperative thin-cut computed tomographic scans were obtained in 52 of thes e patients who were available to enroll in the study. An impartial neurorad iologist evaluated 224 screws by use of a standardized grading scheme. All levels of the thoracic spine were included in the study. RESULTS: Chart review revealed no incidence of neurological, cardiovascular , or pulmonary injury. Of the 224 screws reviewed, there were 19 cortical v iolations (8.5%). Eleven (4.9%) were Grade 11 (less than or equal to2 mm), and eight (3.6%) were Grade III (>2 mm) violations. Only five screws (2.2%) , however, were thought to exhibit unintentional, structurally significant violations. Statistical analysis revealed a significantly higher rate of co rtical perforation in the midthoracic spine (T4-T8, 16.7%; T1-T4, 8.8%; and T9-T12, 5.6%). CONCLUSION: The low rate of cortical perforations (8.5%) and structurally s ignificant violations (2.2%) in this retrospective series compares favorabl y with previously published results that used anatomic landmarks and intrao perative fluoroscopy. This study provides further evidence that stereotacti c placement of pedicle screws can be performed safely and effectively at al l levels of the thoracic spine.