This paper describes a new segmentation approach for detecting the location and the orientation of the cervical vertebrae in medical X-ray images. A first pre-processing step consists on determining a global polygonal region for each vertebra. After this, we propose a new approach of vertebrae localization based on the four faces detection of each vertebra contour. A specific goal of the proposed application is to create an efficient semi-automated method of identifying the overall angle of curvature of the spine and the angles between vertebrae. The final goal is to determine the motion of the vertebrae induced by their movement between two or several positions.