• Kosei Nagata, Steven D Glassman, Morgan E Brown, Christy L Daniels, Grant O Schmidt, Leah Y Carreon, Bren Hines, and Jeffrey L Gum.
• Department of Orthopedic Surgery, University of Louisville School of Medicine, Louisville, KY.
• Spine. 2024 Jun 1; 49 (11): 780787780-787.

Study DesignRetrospective single-center study using prospectively collected data.ObjectiveTo describe the incidence of and identify risk factors for intraoperative screw malposition secondary to skive or shift during robot-assisted cortical bone trajectory (RA-CBT) insertion.Summary Of Background DataRA-CBT screw malposition occurs through 2 distinct modes, skive or shift. Skive occurs when a downward force applied to the cannula, drill, tap, or screw, causes the instrument to deflect relative to its bony landmark. Shift is a change in the position of the RA system relative to the patient after registration.Patients And MethodsA consecutive series of patients older than 18 years who underwent RA-CBT screw placement between January 2019 and July 2022 were enrolled. Baseline demographic and surgical data, Hounsfield Units (HUs) at L1, and vertebral shape related to screw planning were collected. Skive or shift was recorded in the operating room on a data collection form.ResultsOf 1344 CBT screws in 256 patients, malposition was recognized intraoperatively in 33 screws (2.4%) in 27 patients (10.5%); 19 through skive in 17 and 14 through shift in 10 patients. These patients had higher body mass index than patients without malposition (33.0 vs. 30.5 kg/m 2 , P = 0.037). Patients with skive had higher HU (178.2 vs . 145.2, P = 0.035), compared with patients with shift (139.2 vs . 145.2, P = 0.935) and patients without screw malposition. More than half of the screw malposition was observed at the upper instrumented vertebra. At the upper instrumented vertebra, if the screw's overlap to the bone surface at the insertion point was decreased, skive was more likely (57% vs . 87%, P < 0.001). No patients were returned to the operating room for screw revision.ConclusionsIntraoperative screw malposition occurred in 2.4% of RA-CBT. High body mass index was associated with screw malposition, regardless of etiology. Skive was associated with high HU and decreased screw overlap to the bone surface at the insertion point.Copyright © 2023 Wolters Kluwer Health, Inc. All rights reserved.

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