title: Postural spinal balance defined by net intersegmental moments: Results of a biomechanical approach and experimental errors measurement.
abstract: OBJECTIVE
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: 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.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Blondel
authors.affiliation: 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.
authors.forename: Elke
authors.initials: E
authors.lastname: Viehweger
authors.affiliation: 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.
authors.forename: Bertrand
authors.initials: B
authors.lastname: Moal
authors.affiliation: 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.
authors.forename: Patrick
authors.initials: P
authors.lastname: Tropiano
authors.affiliation: 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.
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Jouve
authors.affiliation: 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.
authors.forename: Virginie
authors.initials: V
authors.lastname: Lafage
authors.affiliation: 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.
authors.forename: Raphael
authors.initials: R
authors.lastname: Dumas
authors.affiliation: 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.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Fuentes
authors.affiliation: 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.
authors.forename: Gérard
authors.initials: G
authors.lastname: Bollini
authors.affiliation: 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.
authors.forename: Vincent
authors.initials: V
authors.lastname: Pomero
keywords: Biomechanical evaluation; Intersegmental net moments; Posture; Sagittal alignement