• Eaman Balouch, Aonnicha Burapachaisri, Dainn Woo, Zoe Norris, Anand Segar, Ethan W Ayres, Dennis Vasquez-Montes, Aaron J Buckland, Afshin Razi, Michael L Smith, Themistocles S Protopsaltis, and Yong H Kim.
• Department of Orthopaedic Surgery, NYU Langone Orthopedic Hospital, New York, NY.
• Spine. 2022 Aug 15; 47 (16): 115111561151-1156.

Study DesignA retrospective review of operative patients at a single institution.ObjectiveThe aim was to validate a novel method of detecting pseudarthrosis on dynamic radiographs.Summary Of Background DataA common complication after anterior cervical discectomy and fusion is pseudarthrosis. A previously published method for detecting pseudarthrosis identifies a 1 mm difference in interspinous motion (ISM), which requires calibration of images and relies on anatomic landmarks difficult to visualize. An alternative is to use angles between spinous processes, which does not require calibration and relies on more visible landmarks.Materials And MethodsISM was measured on dynamic radiographs using the previously published linear method and new angular method. Angles were defined by lines from screw heads to dorsal points of spinous processes. Angular cutoff for fusion was calculated using a regression equation correlating linear and angular measures, based on the 1 mm linear cutoff. Pseudarthrosis was assessed with both cutoffs. Sensitivity, specificity, inter-reliability and intrareliability of angular and linear measures used postoperative computed tomography (CT) as the reference.ResultsA total of 242 fused levels (81 allograft, 84 polyetheretherketone, 40 titanium, 37 standalone cages) were measured in 143 patients (mean age 52.0±11.5, 42%F). 36 patients (66 levels) had 1-year postoperative CTs; 13 patients (13 levels) had confirmed pseudarthrosis. Linear and angular measurements closely correlated ( R =0.872), with 2.3° corresponding to 1 mm linear ISM. Potential pseudarthroses was found in 28.0% and 18.5% levels using linear and angular cutoffs, respectively. Linear cutoff had 85% sensitivity, 87% specificity; angular cutoff had 85% sensitivity, 96% specificity for detecting CT-validated pseudarthrosis. Interclass correlation coefficients were 0.974 and 0.986 (both P <0.001); intrarater reliability averaged 0.953 and 0.974 ( P <0.001 for all) for linear and angular methods, respectively.ConclusionsThe angular measure for assessing potential pseudarthrosis is as sensitive as and more specific than published linear methods, has high interobserver reliability, and can be used without image calibration.Level Of Evidence3.Copyright © 2022 Wolters Kluwer Health, Inc. All rights reserved.

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