Observational Study
Copyright ©The Author(s) 2015. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Orthop. Dec 18, 2015; 6(11): 983-990
Published online Dec 18, 2015. doi: 10.5312/wjo.v6.i11.983
Postural spinal balance defined by net intersegmental moments: Results of a biomechanical approach and experimental errors measurement
Benjamin Blondel, Elke Viehweger, Bertrand Moal, Patrick Tropiano, Jean-Luc Jouve, Virginie Lafage, Raphael Dumas, Stéphane Fuentes, Gérard Bollini, Vincent Pomero
Benjamin Blondel, Elke Viehweger, Patrick Tropiano, Jean-Luc Jouve, Stéphane Fuentes, Gérard Bollini, Laboratoire d’analyse du mouvement, Spine Unit, Université Aix-Marseille, CHU Timone, 13005 Marseille, France
Benjamin Blondel, Elke Viehweger, Jean-Luc Jouve, Vincent Pomero, Ecole Doctorale 463, Sciences du Mouvement Humain, Université Aix-Marseille, 13005 Marseille, France
Benjamin Blondel, Bertrand Moal, Virginie Lafage, Department of Spine Surgery, Hospital for Joint Diseases, New-York University, New York, NY 10002, United States
Raphael Dumas, Université de Lyon, F-69622 Lyon, France
Raphael Dumas, IFSTTAR, LBMC, F-69675 Bron, France
Raphael Dumas, Université Lyon 1, LBMC, F-69373 Lyon, France
Author contributions: Viehweger E, Jouve JL and Bollini G designed research; Blondel B, Viehweger E, Moal B, Tropiano P and Fuentes S performed research; Moal B and Lafage V contributed new reagents or analytic tools; Moal B, Lafage V and Pomero V analyzed data; Blondel B wrote the paper.
Supported by The Association pour le Développement des Recherches biologiques et Médicales and the French Society of Orthopaedics and trauma surgery (Blondel B).
Institutional review board statement: The study was reviewed and approved by the Spine Unit Institutional Review Board.
Informed consent statement: All study participants, or their legal guardian, provided informed written consent prior to study enrollment.
Conflict-of-interest statement: There are no conflicts of interest to report.
Data sharing statement: No additional data are available.
Open-Access: This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/
Correspondence to: Benjamin Blondel, MD, PhD, Laboratoire d’analyse du mouvement, Spine Unit, Université Aix-Marseille, avenue Jean-Moulin, CHU Timone, 13005 Marseille, France. benjamin.blondel@ap-hm.fr
Telephone: +33-4-91384430 Fax: +33-4-91384247
Received: May 29, 2015
Peer-review started: May 30, 2015
First decision: July 30, 2015
Revised: August 4, 2015
Accepted: September 29, 2015
Article in press: September 30, 2015
Published online: December 18, 2015

AIM: To describe initial results and experimental error measurement of a protocol analyzing Human posture through sagittal intersegmental moments.

METHODS: Postural analysis has been recently improved by development of three-dimensional radiographic imaging systems. However, in various situations such as global sagittal anterior malalignment interpretation of radiographs may not represent the real alignment of the subject. The aim of this study was to present initial results of a 3D biomechanical protocol. This protocol is obtained in a free standing position and characterizes postural balance by measurement of sagittal intersegmental net moments. After elaboration of a specific marker-set, 4 successive recordings were done on two volunteers by three different operators during three sessions in order to evaluate the experimental error measurement. A supplementary acquisition in a “radiographic” posture was also obtained. Once the data acquired, joint center, length, anatomical frame and the center of mass of each body segment was calculated and a mass affected. Sagittal net intersegmental moments were computed in an ascending manner from ground reaction forces at the ankles, knees, hips and the lumbo-sacral and thoraco-lumbar spinal junctions. Cervico-thoracic net intersegmental moment was calculated in a descending manner.

RESULTS: Based on average recordings, clinical interpretation of net intersegmental moments (in N.m) showed a dorsal flexion on the ankles (8.6 N.m), a flexion on the knees (7.5 N.m) and an extension on the hips (8.5 N.m). On the spinal junctions, it was flexion moments: 0.34 N.m on the cervico-thoracic; 6.7 N.m on the thoraco-lumbar and 0.65 N.m on the lumbo-sacral. Evaluation of experimental error measurement showed a small inter-trial error (intrinsic variability), with higher inter-session and inter-therapist errors but without important variation between them. For one volunteer the “radiographic” posture was associated to significant changes compared to the free standing position.

CONCLUSION: These initial results confirm the technical feasibility of the protocol. The low intrinsic error and the small differences between inter-session and inter-therapist errors seem to traduce postural variability over time, more than a failure of the protocol. Characterization of sagittal intersegmental net moments can have clinical applications such as evaluation of an unfused segment after a spinal arthrodesis.

Keywords: Posture, Sagittal alignement, Biomechanical evaluation, Intersegmental net moments

Core tip: Postural evaluation is commonly performed using full-spine radiographs. However, a biomechanical approach using a dedicated protocol is possible in order to evaluate sagittal intersegmental net moments. Results from this study confirmed the technical feasibility of the protocol. Furthermore, these results revealed postural variability over time. Such evaluation may have various clinical applications such as evaluation of an unfused segment after a spinal arthrodesis.