[Lumbar intervertebral disk disease and its sequelae: segmental instability, intervertebral disk displacement, lumbar spinal stenosis--change in a common disease].

Clinical, radiological, surgical and experimental experiences allow to construct a theory of degeneration of the lumbar spine, which explains the pathogenesis of spondylosis, stenosis and disc displacement as well. The centre of the whole process is the segmental instability due to disc derangement. Several partially new criteria for a rational surgical and conservative therapy follow from such theory, which we try to explain by some exemplaric cases. Finally, we describe shortly own surgical procedure for combined operation of decompression and lumbar fusion.