In this paper we present an elaborate and precise geometrical model of the spine structure based on spherical harmonics. We first describe the application of spherical harmonics to the modelling of the vertebra surface, then we study the behaviour of the model under particular deformations. The first results of this study show that we can obtain a realistic model of each vertebra of the spine and that it is possible to estimate particular deformations with a good accuracy from the spherical harmonics coefficients of the deformed surface. Furthermore, this model constitutes an a priori geometrical knowledge for the diagnosis of the spine scoliosis in a three-dimensional approach (reconstruction from 2D images).
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