The lumbar spine consists of individual motion segments which comprise the vertebral body, intervertebral disc and facet joints. The spinal canal is made up of a bony-ligamentous ring which consists of the posterior aspect of the vertebral body and intervertebral disc anteriorly, pedicles and intervertebral foramina laterally together with the laminae and liga-mentum flavum posteriorly. The articular processes of the facet joints are posterolaterally. The facet joints are enclosed within the facet joint capsules. Along the posterior aspect of the vertebral bodies, extending down the posterior fibres of the annulus fibrosis, is the posterior longitudinal ligament.
This bony-ligamentous ring of each motion segment completes the spinal canal posterior to the vertebral body. Contained within the canal are the thecal contents. The spinal cord ends at the lower border of the L1 vertebral body. Below this the cauda equina trails down from the conus medullaris, the individual nerve roots exiting through the intervertebral foramina at their appropriate levels and extending of the dural sleeve of the intervertebral foramen.
The anatomy of the intervertebral foramina, through which the individual nerve roots exit, consists of the pedicle of the corresponding body superiorly, posterolateral aspect of the vertebral body and intervertebral disc anteriorly, adjacent superior and inferior articular processes of the corresponding facet joint posteriorly and pedicle of the vertebral body below inferiorly.
As the nerve root exits through the foramen, it can be subjected to compression from a disc herniation medially, facet joint capsule hypertrophy and osteophytes on the facet joints laterally and also from the stenosis of the exit foramen due to collapse of the intervertebral disc with resultant loss of height of the intervertebral disc space, thus narrowing the exit foramen. A combination of all three pathological processes may occur simultaneously also resulting in circumferential stenosis of the exit foramen. All these processes can impinge extradurally on the exiting nerve root resulting in a radicu-lopathy. The symptoms and signs of this are generally referred to as sciatica but the overall clinical picture is determined by which individual nerve roots are compromised, their myotomal and dermatomal distribution.
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