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Dynamic Fluctuation of Truncal Shift Parameters During Quiet Standing in Healthy Young Individuals

Kato, So, MD∗,†; Fok, Kai Lon; Lee, Jae W.‡,§; Masani, Kei, PhD‡,§

doi: 10.1097/BRS.0000000000002521
BIOMECHANICS
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Study Design. Retrospective analysis.

Objective. To describe the dynamic fluctuation of truncal shift parameters during quiet standing in healthy young individuals using biomechanical analyses.

Summary of Background Data. Coronal decompensation (CD) and sagittal vertical axis (SVA) are the key radiographic parameters to assess static truncal stability, with the known cut-off value of 4 cm for SVA in determining severity of spinal deformity. These values are obtained at a specific moment during quiet standing, when the posture innately changes. Thus, unassessed truncal sway could potentially compromise the reliability of these measurements.

Methods. Previously obtained biomechanical data with 11 male, healthy participants aged 16 to 29 were used to quantify the dynamic sway of standing posture. The participants were instructed to quietly stand with surface reflective markers for 130 seconds. The midpoint of bilateral acromia was used as a surrogate for C7 vertebral body. The time series of coronal and sagittal shifts of C7 to sacrum were measured as quasi-coronal decompensation (CD) and quasi-sagittal vertical axis (SVA) to simulate CD and SVA on radiographs. A force platform was also used to measure the center of pressure (COP) displacement.

Results. The group averages of the dynamic sway range were 20.2 ± 4.1 mm (range: 15.1–28.6) in the sagittal plane (quasi-SVA) and 9.8 ± 3.2 mm (range: 5.5–15.2) in the coronal plane (quasi-CD). There were significant correlations between quasi-CD sway and medial-lateral COP velocity (Pearson r = 0.65, P = 0.03), as well as between quasi-SVA sway and COP sway area (r = 0.65, P = 0.03).

Conclusion. Given the considerable fluctuation of quasi-SVA and quasi-CD during quiet standing, the reliability of radiographic measurement using CD and SVA at a specific moment can be substantially compromised. The assessment based on the currently proposed cut-off values should be interpreted with caution, and repeat examinations are warranted.

Level of Evidence: 4

The Department of Orthopaedic Surgery, University of Tokyo, Tokyo, Japan

Toronto Western Hospital, University Health Network, Toronto, Ontario, Canada

Toronto Rehabilitation Institute – University Health Network, Toronto, Ontario, Canada

§Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, Ontario, Canada.

Address correspondence and reprint requests to Kei Masani, PhD, Lyndhurst Centre, Toronto Rehabilitation Institute - University Health Network, 520 Sutherland Drive, Toronto, Ontario, Canada, M4G 3V9; E-mail: k.masani@utoronto.ca

Received 24 October, 2017

Accepted 16 November, 2017

The manuscript submitted does not contain information about medical device(s)/drug(s).

No funds were received in support of this work.

No relevant financial activities outside the submitted work.

Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.