The purpose of this experiment was to find out the three dimensional motion of lumbar spinal various conditions after multiple-segmental segimple total laminectomies and to answer some questions which have not been clear yet about lumbar spinal instability on biomechanics.We also want to get the reliable scientific data for selecting operations,improving surgical techniques,increasing the good outcome,reducing operative complications.Then we collected these data to esta blish the mathematical-biomechanical model of the lumbar spine.