• Koji Tamai, Phillip Grisdela, Joshua Romanu, Permsak Paholpak, Zorica Buser, and Jeffrey C Wang.
• Department of Orthopaedic Surgery, Keck School of Medicine, University of Southern California, Norris Research Tower, 1450 Biggy Street, Los Angeles, CA, 90033, USA.
• Eur Spine J. 2019 May 1; 28 (5): 1200-1208.

Study DesignIt is a retrospective analysis of 1806 consecutive cervical magnetic resonance images taken in weight-bearing flexion, neutral, and extension positions.ObjectiveThe aim was to identify the kinematic characteristics of patients with cervical imbalance. Additionally, factors were analysed in the neutral position that could predict the characteristics. Little is known about the kinematic characteristics during cervical flexion and extension positions of the patient with cervical imbalance (cervical sagittal vertical axis (cSVA) in neutral position ≥ 40 mm).MethodsAfter evaluating the whole images, cervical imbalance group (cSVA ≥ 40 mm, n = 43) and matched control group (< 40 mm, n = 43) were created using propensity score adjusting for age, gender, and cervical alignment. They were compared for cervical motion, changes in disc bulge, and ligamentum flavum (LF) bulge from flexion to extension. Multinomial logistic regression analysis and receiver operating characteristic curve analysis were calculated to verify the predictive factors and cut-off value of the identified characteristics.ResultsThere were no significant differences in range of motion and the change in bulged discs. There was significant difference in the presence of LF bulge from flexion to extension (p = 0.023); the incidence of LF bulge increased sharply from neutral to extension in imbalance group, while there was linear increase in control group. The canal diameter (odds ratio = 0.61, p = 0.002) and disc height (odds ratio = 1.60, p = 0.041) showed significant relationship with the segments with LF bulge observed in extension but not in neutral position in the imbalance group; the cut-off values were 10.7 mm for canal diameter (sensitivity 82.5%, specificity 66.7%) and 7.1 mm for disc height (70.8%, 58.5%).ConclusionPatients with cervical imbalance had a stark increase in LF bulge from the neutral to extension position. Canal diameter < 10.7 mm and disc height > 7.1 mm on neutral images may predict the segments with LF bulge observed in extension, but not in the neutral position.Level Of EvidenceII (Diagnostic: individual cross-sectional studies with consistently applied reference standard and blinding). These slides can be retrieved from Electronic Supplementary Material.

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