Abstract
Study Design
Retrospective observational study.
Objectives
To determine the mass distribution along the scoliotic trunk using barycentremetry and its relationship with vertebral axial rotation and torque.
Summary of the Background Data
Deformity progression in adolescent idiopathic scoliosis (AIS) is not yet fully understood, but gravity load on the spine could play a role. Barycentremetry allows to characterize body mass distribution in standing position, which could provide a better understanding the mechanisms of progression.
Methods
81 subjects (27 healthy adolescents and 53 AIS patients) underwent biplanar radiography and 3D reconstruction of the spine and body envelope. Position of the gravity line was estimated, as well as trunk segmental centers of mass COMs at each vertebral level and resulting axial torques to each vertebra.
Results
The COM of all trunk segments was less than 1 cm from the gravity line in the frontal plane for healthy subjects, and less than 1.5 cm for AIS patients. Vertebral axial torque was 0.7 ± 0.5 Nm in healthy subjects, 2.9 ± 2.1 Nm at the junctional vertebrae of AIS patients and 0.5 ± 0.5 at the apex. A strong association was found between high torque and high intervertebral rotation at junctions, with low torque and low intervertebral axial rotation at the apex.
Conclusion
Results suggest that AIS patients can maintain the COM of each body segment close to their gravity line, irrespective of the severity and asymmetry of their deformity. Moreover, torque analysis shed some light on the importance of junctional vertebrae in the spinal deformity and, potentially, in the vicious cycle determining scoliosis progression.
Level of Evidence
Level III.
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Author disclosures: TT (none), CV (none), TH (none), RV (grants from Eos Imaging, other from Spineguard, other from Stryker Spine, other from NuVasive, outside the submitted work), WS (coinventor of the EOS system, without personal financial benefit [royalties rewarded for nonprofit research and education institutions]).
IRB approval: Subject inclusion was approved by the ethical committee (6001 CPP Ile de France VI and local hospital ethical committee).
Funding: The authors are grateful to the ParisTech BiomecAM chair program on subject-specific musculoskeletal modelling (with the support of ParisTech and Yves Cotrel Foundations, Société Générale, Proteor and Covea)
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Thenard, T., Vergari, C., Hernandez, T. et al. Analysis of Center of Mass and Gravity-Induced Vertebral Axial Torque on the Scoliotic Spine by Barycentremetry. Spine Deform 7, 525–532 (2019). https://doi.org/10.1016/j.jspd.2018.11.007
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DOI: https://doi.org/10.1016/j.jspd.2018.11.007