[Plain X-rays of the spine: dynamics and elements of semiology].

Man is standing up and he moves himself in a world subject to the gravity's laws. His spine reflects these constraints. Each bivertebral unit that composes the long supple stem of the spine has an anatomic cohesion with some mobility. The mobility of the spine is the sum of the motilities of its elementary units. Despite the criticisms, all deserved, the dynamic radiographies in flexion (seating position) and in extension (standing position, lower limbs straight and buttocks wedged) give major informations with important clinical consequences. Some semiologic points of the radiographic study of the vertebra are perfectly explained by its specific architecture: a radiolucent lesion is difficult to see whereas a sclerotic one is much more easy to individualize; the sclerotic line of the vertebral endplate must be continuous and any interruption is pathologic; the corners of the vertebra must be sharp; the foramen's shape reflects the size of the spinal canal.