Mathematical modelling and parameters extraction for the lateral bending movement analysis in patients affected by ankylosing spondylitis

A study was carried out using the ELITE system on 10 patients affected by ankylosing spondylitis and on 8 healthy people. The ELITE system provides the complete kinematic analysis of the movements, allowing the quantitative study of 3D-trajectories, displacements, velocities and accelerations. A two-poles dynamical model was introduced to describe the angular net displacement versus time θ(t) of the vertebral column during the lateral bending movement [θ(t) = angle between the vertical axis and the line connecting the 7-th cervical and 5-th lumbar vertebra]. This model links the increase in the pathological disease to the variation in the viscoelastic properties of the vertebral column. Moreover this work introduces dynamical measures in the ankylosing spondylitis. In previous works, only static indexes of the pathology was used (Forester index, Fingers-to-floor index, ...). We introduce diagnostic indexes of the ankylosing spondylitis, which take into account the trajectories described in the frontal plane by selected reference points of the spine, during the lateral bending movement.