Quantification of global intervertebral torques during gait: comparison between two subjects with different scoliosis severities.

The internal forces in the human body in motion could provide valuable information for the evaluation and follow-up of subjects with musculo-skeletal pathologies, such as scoliosis, but are still difficult to accurately measure. In this context, the objective of this study is to quantify the global intervertebral torques along the spine during walking, in order to compare the dynamical behavior between two subjects with different scoliosis severities. Practically, two patients, both with left lumbar adolescent idiopathic scoliosis (lumbar Cobb angles: 40 degrees), but with different apical axial rotations (20 degrees and 30 degrees) and different thoracic Cobb angles (20 degrees and 30 degrees), walked on a treadmill at 4 km/h. The acquisition system included optokinetic sensors (reflective markers), recording the 3D-joint coordinates, and a treadmill equipped with strain gauges, measuring the external forces independently applied to both feet. The global intervertebral torques were computed using an inverse dynamic model of the human body in 3D. As results, significant differences of the subject kinematics and ground reaction forces were recorded, which lead to different internal torque behavior in magnitude, maxima and minima when normalized to the subject mass. In conclusion in this preliminary study, different dynamical behavior was found between two subjects with different scoliosis severities, suggesting that the scoliosis severity could be affected by abnormal internal torques along the spine during gait (different than in the standing posture), which could lead to a supplementary asymmetric growth modulation of the vertebrae and the further progression of the scoliotic deformities in the framework of the Hueter-Volkman principle. Finally, this is a pilot study and the results will inform future studies and biomechanical modeling.