Shape description of three-dimensional images based on medial axis

3D-shape description requires the partition of objects in different parts. In this paper, we propose a new approach based on the analysis of a 3D skeleton. The skeleton is a representation of objects by their axis of symmetry. In 3D, it is composed of surfaces associated to plate-like parts of the objet and curves associated to cylindrical parts. Our method is two parts. First, 4 types of skeleton points are identified: boundary, branching, regular and arc points. A skeleton point is labeled according to the intersection of its maximal ball with the object. In order to add tolerance to the process, the radius of maximal balls is slightly increased. Second, the reversibility of the skeleton is used to deduce a labeling of the whole object. Finally, we present an application of the method to the identification of bone structures from 3D high-resolution tomographic images.