• Yoichi Tani, Takanori Saito, Shinichiro Taniguchi, Masayuki Ishihara, Masaaki Paku, Takashi Adachi, Muneharu Ando, Nobuo Kohara, and Jun Kimura.
• Department of Orthopaedic Surgery, Kansai Medical University, Osaka, Japan.
• Spine. 2022 Jul 15; 47 (14): 100310101003-1010.

Study DesignA prospective analysis.ObjectiveTo test if threshold-based monitoring of compound muscle action potentials (CMAPs) by stimulating the screw loaded to uninsulated extender sleeve provides a valid safety warning for percutaneous pedicle screw (PPS) placements in the lumbosacral spine.Summary Of Background DataUtility of the CMAP monitoring to PPS procedures remains controversial.MethodsA series of 202 patients underwent a total of 1664 lumbosacral PPS placements under CMAP monitoring without fluoroscopic guidance. The monitoring consisted of stimulating the PPS assembled to uninsulated extender sleeve and recording CMAPs from the vastus medialis, biceps femoris, tibialis anterior, and medial gastrocnemius. Automated steps of a threshold hunting algorithm using 0.2-ms duration pulses of increasing intensities delivered at 2/s allowed quick determination of a minimum stimulation current to evoke >100-μV amplitude CMAPs.ResultsAt L2 through S1 spines, postoperative CT scans identified 51 medial or inferior pedicle wall breaches of 1536 screws (3.3%) without neurologic complications. The receiver operating characteristic curve analysis determined the critical cutoff threshold value of 27 mA (74% sensitivity and 95% specificity) for predicting 35 breaches of 627 screws (5.6%) at L2 and L3, and of 17 mA (100% sensitivity and 98% specificity) for 16 of 909 (1.8%) at L4 through S1. While advancing the screw, three breaches (5.9%) showed a particularly low threshold of ≤6-mA, allowing the surgeon to immediately redirect the screw and retest the new trajectory as safe.ConclusionScrew stimulation with threshold hunting algorithm has a distinct advantage over the time-consuming insulated pilot hole stimulation, allowing an uninterrupted flow of the surgery. The present findings have documented practical usefulness and reliability of CMAP monitoring using direct stimulation of the PPS assembled to uninsulated extender sleeve.Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.

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