Pathoanatomy of lumbar disc degeneration and stenosis

This paper details the characteristic pathoanatomical features of the normal lumbar spine and of degenerative changes of the lumbar motion segment that cause both central and lateral canal stenosis.Since the pathoanatomical changes are degenerative derangements of the normal motion segment, the normal anatomy is briefly outlined.The terminology adheres to the Glossary on Spinal Terminology published by the American Academy of Orthopedic Surgeons' Committee on the Spine with the exception of the term "spine" which is replaced by "spinous process" and "vertebral canal" which is used synonymously with the established term "spinal canal" (1).Conventional dissection, by definition, inevitably destroys and distorts potentially crucial topographicanatomical relationships.By contrast, sectional images from in situ frozen specimens show the unequivocal relationships of the musculoskeletal spinal column to the delicate neurovascular spinal elements.Moreover, freezing specimens in functional postures also allows to study functional topographic relationships and the effect of extension, rotation and bending (and combinations of the above) on the neurovascular spinal elements in both normal and degenerated specimens because these relationships are "frozen" (2, 20).Plain radiography and high resolution CT-scanning of the specimens prior to to sectioning on the cryomicrotome also facilitates accurate and direct point-to-point radioanatomical correlations.A distinction should be made between the vertebral column and the spine.The mobility and motion pattern greatly varies between the different storeys of the spine.Every spinal motion segment has a typical range and pattern of motion that is determined by the shape and three-dimensional arrangement of bony and articular surfaces, intervening discs, ligaments and joint capsules (24).Mobility is also determined and controlled by the insertion and origin of the muscles that attach to the spine, their mass, fiber composition and orientation in space.