Lumbar Spinal Stenosis

Collectively, the spine has an anterior and a posterior region (see . Lumbar Vertebral Anatomy). The cylindrical vertebral bodies comprise the anterior spine, separated by intervertebral (IV) disks and held in place by the anterior and posterior longitudinal ligaments. The IV disks have the gelatinous nucleus pulposus in the middle, surrounded by the cartilaginous annulus fibrosus (see . Intervertebral Disk). The cervical and lumbar spinal segments have the largest IV disks, owing to these regions' mobility. The anterior spine is a shock absorber of bodily movements. The vertebral arches and processes constitute the posterior spine. Each vertebral arch has an anterior pair of cylindrical pedicles and a posterior pair of laminae (see . Lumbar Vertebra, Superoposterior View). Other structures emanating from the vertebral arch include 2 lateral transverse processes, 1 posterior process, and 2 superior and 2 inferior articular facets. Facet joints form from superior and inferior facet apposition. The spinal canal, which houses the spinal cord, is formed by the vertebral bodies and IV disks anteriorly and vertebral arches posteriorly. The nerve roots exit superior to their corresponding vertebral body through the intervertebral canal. The ligamentum flavum (yellow ligament) is a thick, fibrous structure passing between adjacent laminae. The lateral recess is an anatomic space in the posterior spine bounded anteriorly by the vertebral body and disk, posteriorly by the ligamentum flavum and vertebral arch, laterally by the pedicle, and medially by the thecal sac. This region is narrow and is a potential area of nerve root compression. The posterior spine has various functions, including spinal cord and nerve root protection and muscle and ligament support.   Lumbar spinal stenosis (LSS) is the narrowing of the lumbar vertebra in the central canal, lateral recess, or neural foraminal areas. Central canal stenosis may compress the thecal sac and bilateral spinal segments and thus, in the severe form, may produce bilateral symptoms. Lateral recess and neural foraminal stenosis may compress the nerve roots and produce unilateral lumbar radiculopathy symptoms.  Central stenosis arises from anterior ligamentum flavum hypertrophy compounded by posterior disk bulging. This condition is more prevalent at the L4 to L5 level than other spinal segments. Meanwhile, lateral recess stenosis results from facet arthropathy and osteophyte formation, compressing the nerve before it passes the intervertebral foramen. Foraminal stenosis is due to disk height loss, foraminal disk protrusion, or osteophyte formation. These changes impinge on the nerve root inside the intervertebral foramen. Extraforaminal stenosis is usually due to far lateral disk herniation. This condition compresses the nerve root after exiting the intervertebral foramen laterally.  LSS is a significant cause of disability in older individuals and a common spinal surgery indication in patients older than 65 years. Henk Verbiest first described relative and absolute spinal stenosis as lumbar canal midsagittal diameter of less than 12 mm and 10 mm, respectively. However, LSS clinical and radiologic diagnostic criteria have not been established despite this condition's global prevalence. Thus, this clinical entity has no universally accepted definition.