Nerve roots and root ganglia

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Both exiting and traversing roots that form the lateral and medial boundaries of the triangular working zone are in the path of dorsolaterally inserted instruments and may be subject to insult during intradiscal or extraannular approaches to the lumbar spine. At the onset of arthroscopic disc surgery, the final and proper positioning of the instruments is best determined by accurate placement and documentation of the tip of the inserted instruments (18-gage needle or guide wire) on the annular surface in the triangular working zone. The fibers of the posterior longitudinal ligament extend laterally into the triangular working zone and extraforaminal region (4-8) (Fig. 8). These fibers are innervated by branches of sinu-vertebral nerve and are highly sensitive to palpation by the inserted instruments. The superficial layer of the annulus and the expansion of the posterior longitudinal ligament must be adequately anesthetized during the operative procedure and annular fenestration. The exiting root is well protected in the triangular working zone, where it lays under the pedicle in the pedicular notch and is accompanied by the radicular artery, radicular vein, and branches of the sinu-vertebral nerve. The posterior sensory nerve fibers and the anterior motor fibers usually join one another prior to their departure from the dural sac. However, at times they part individually from the dura. The posterior sensory root is larger than the anterior motor root, and it continues into the fusiform root ganglia and then joins the anterior motor root. Usually the L4 and L5 dorsal root ganglia are intraforaminal and must be protected during foraminal access to the intervertebral disc or the spinal canal. The S1 root ganglion is likely to be intraspinal.

Fig. 4. (A,B) Arthroscopic view of annular surface in triangular working zone. Note the loose/woven adipose tissue on the surface of annulus.

The mobility of the traversing and exiting roots at the lower lumbar region allows the operative surgeon to retract these structures during both arthroscopic and open spinal surgery. However, limited mobility of the nerve roots in the upper lumbar spine and at the thoracolumbar junction, combined with the bulk of the cauda equina and conus medullaris in the subarachnoid space, demands protection of neural tissue by accurate positioning of the instruments, clear visualization, and careful handling of the resecting instruments.

Fig. 5. Interoperative photo demonstrating presence of superficial veins on surface of annulus.

In a series of T1 imaging studies of the thoracolumbar junction, the end of the conus was identified at the L1 level in 50% of individuals but at the L2 segment in 20% of patients. Therefore, great care must be exercised while performing arthroscopic or endoscopic surgery adjacent to these two segments. The nerve roots appear as pale yellow, multifiber structures under arthroscopic illumination and magnification. Fine vessels are present on the surfaces of the nerve root and root ganglia (Fig. 9A-D). The inflamed nerve roots are highly sensitive to palpation and compression. The traversing root may be

Fig. 6. Interoperative photos showing (A) annular surface following removal of adipose tissue and (b) magnified view of avascular fibers of annulus following extraction of superficial adipose tissue.

Fig. 7. A thin layer of psoas muscle that covers the triangular working zone is observed and is being removed with the aid of laser light.
Fig. 8. Cadaveric dissection showing fibers of posterior longitudinal ligamentum, which extends to dorsolateral aspect of annulus, foraminal, and extraforaminal region.

observed adjacent to the dural sac in the medial pedicular line region and is usually surrounded by epidural veins and adipose tissue.

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