Assessment of Medial Malpositioning during Thoracic Pedicle Screws Placement with a Contemporary Intraoperative Neurophysiological Monitoring Method

Introduction: Thoracic pedicle screws placement remains being a challenge despite modern technologies available. To assess neural integrity during these surgeries, intraoperative neurophysiological monitoring (IOM) is indicated. Motor-evoked potentials (MEP) and somatosensory-evoked potentials (SSEP) give valuable information regarding spinal cord function, and pedicle screws stimulation could evaluate medial malpositioning. However, the accuracy of thoracic pedicle screws stimulation is still controversial, using single-pulse stimulation, recording from intercostal and abdominal muscles, and with high false-positive rate. Objective: This article aims to demonstrate the superiority of a recently validated IOM method by Blair Calancie, and share our experience with it. Material and Methods: Prospective collected and reviewed study since March to October 2014. During T1–T12 level surgeries, we stimulated medial wall of pedicle track before screw placement with a ball-tipped probe using pulse-train stimulation, and recording from lower limbs muscles. MEP and SSEP were performed, and a postoperative computed tomography (CT) scans in all the cases. Results: In 21 patients, 240 thoracic pedicle screws were analyzed. In 36 screws of them (17.6%), a medial pedicle breach was informed, and 19 of 36 were redirected correctly more lateral; 8 of 36 pedicles were skipped; and 7 of 36 screws were placed regardless IOM warning criteria (3.4%), with a CT scan confirming medial misplacement > 2 mm. Fluoroscopy and manual pedicle palpation evinced a medial breach in 3 of 36 and 1 of 36 trajectories, respectively, but after pedicle track stimulation was done and informed. We did not observe any MEP or SSEP change during all these screws. Fortunately, no patients developed a new neurological deficit. CSF leak was not reported in this series. Our sensitivity with this method was 93.9%, specificity 97.6%, positive predictive value 86.1%, and negative predictive value was 99.0%. Conclusion: Pulse-train stimulation of pedicle track before screw placement has huge superiority over traditional IOM techniques, avoiding spinal cord encroachment and new neurological deficit. This IOM method is highly accurate during thoracic pedicle screws placement. Keywords: pulse-train, pedicle track stimulation, thoracic screw