Electrical stimulation of the rat lumbar spine induces reflex action potentials in the nerves to the lower abdomen

Insight into neural mechanisms underlying discogenic back pain

Back pain is a common clinical symptom. Degeneration of intervertebral discs is one of the most important factors leading to back pain, namely, discogenic back pain. However, at present, the understanding of lumbar intervertebral discs causing back pain is confined to biomechanical and histological studies. The neuropathological mechanism related to discogenic back pain is still not well understood. Many studies have found that as an intervertebral disc degenerates, the peripheral nerve tissues have corresponding structural reorganization, and a series of nerve cells become involved in progression of discogenic back pain. Therefore, study of neural mechanisms that are involved in progression of discogenic back pain will provide additional assistance for treatment of its symptoms. We review the anatomical structure of intervertebral discs and the related neural mechanisms involved in discogenic back pain. We also discuss the current view of neural mechanisms underlying discogenic back pain.

Projection field of primary afferent fibers innervating the ventral portion of the lumbar intervertebral disc in the spinal cord dorsal horn

In the present study, we investigated the central projection of afferent fibers innervating the lumbar intervertebral disc using the fluorescent neurotracer 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (Dil). The tracer Dil was applied to the ventrolateral portion of the L5-L6 intervertebral disc in 11 adult rats. Fluorescent sites were observed microscopically on spinal cord transverse sections. Fluorescent spots in laminae I-III were plotted on the central projection map of cutaneous afferents. In six of 11 rats, Dil was restricted to the application site. Of these six rats, three showed no evident fluorescent sites. In the remaining three rats, small fluorescent spots were scattered in the dorsal horn. Fluorescent spots in dorsal horn lamina I were located in the central projection fields of the low back and groin skin. Fluorescent spots were observed, also sporadically, in Clarke's column in T12-L1 segments. The central projection of afferent fibers innervating the rat lumbar intervertebral disc was indistinct with Dil labeling. We presumed this was due to the scarcity of central terminal arbors of disc afferent fibers. Spotty projections in laminae I-IllIIere present near the central projection fields of the loin and groin, indicating that pain would be perceived in the groin.

Stereoscopic structure of sensory nerve fibers in the lumbar spine and related tissues

STUDY DESIGN

Neurotracer was applied to various sites in the rat lumbar spine and related tissues. The segmental distribution of labeled neurons in dorsal root ganglia (DRG) was investigated.

OBJECTIVES

To clarify the stereoscopic structure of afferent fibers innervating the lumbar spine and related tissues.

SUMMARY OF BACKGROUND DATA

Afferent fibers in the rat L5-L6 lumbar intervertebral disc are reported to originate from neurons in L1 and L2 DRG. However, anatomic studies determined that each dorsal ramus of the spinal nerve sends nerves to dorsal elements of the corresponding lumbar vertebra.

METHODS

Fluorescent neurotracer DiI (1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate) was applied to various sites of the lumbar spine and related tissues in the L2, L5, and L6 levels in rats. DRG were sectioned 3 weeks after DiI application. Rostrocaudal distribution of DiI-labeled neurons was investigated.

RESULTS

At L5, DiI-labeled neurons were prominent in DRG L3 for the lamina, L2 for the spinous process, L2 for the back muscle fascia, and L1 for the skin. Dorsal elements are therefore innervated by neurons in more rostral DRG. In the transverse plane, the more distant from the DRG a site was, the more rostral the DRG innervating the site. This structure suggested a concentric innervation pattern in the transverse plane.

CONCLUSION

Stereoscopically, the peripheral innervation territory of a lumbar DRG is conical, with the apex at the ganglion and the base circumference located on the dermatome. The lumbar spine itself is involved in the conical innervation territories of DRG.

Lumbar discography

STUDY DESIGN

A comprehensive review of the literature dealing with lumbar discography was conducted.

OBJECTIVE

The purpose of the review is to update the North American Spine Society position statement published in 1994 that addressed criticisms of lumbar discography, to identify indications for

SUMMARY OF BACKGROUND DATA

Lumbar discography remains a controversial diagnostic procedure. There are concerns about its safety and clinical value, although many support its use in specific applications.

METHODS

Articles dealing with lumbar discography were reviewed and are summarized in this report.

RESULTS

Most of the recent literature supports the use of discography in selected patients. Although not to be taken lightly, many of the serious complications and high complication rates reported before 1970 have decreased since then because of improvement in injection technique, imaging and contrast materials.

CONCLUSIONS

Most of the current literature supports the use of discography in select situations. Indications for discography include, but are not limited to: (1) Further evaluation of demonstrably abnormal discs to help assess the extent of abnormality or correlation of the abnormality with the clinical symptoms. Such symptoms may include recurrent pain from a previously operated disc and lateral disc herniation. (2) Patients with persistent, severe symptoms in whom other diagnostic tests have failed to reveal clear confirmation of a suspected disc as the source of pain. (3) Assessment of patients who have failed to respond to surgical intervention to determine if there is painful pseudarthrosis or a symptomatic disc in a posteriorly fused segment and to help evaluate possible recurrent disc herniation. (4) Assessment of discs before fusion to determine if the discs within the proposed fusion segment are symptomatic and to determine if discs adjacent to this segment are normal. (5) Assessment of candidates for minimally invasive surgical intervention to confirm a contained disc herniation or to investigate dye distribution pattern before chemonucleolysis or percutaneous procedures. Lumbar discography should be performed by those well experienced with the procedure and in sterile conditions with a double-needle technique and fluoroscopic imaging for proper needle placement. Information assessed and recorded should include the volume of contrast injected, pain response, with particular emphasis on its locations and similarity to clinical symptoms, and the pattern of dye distribution. Frequently, discography is followed by axial computed tomography scanning to obtain more information about the condition of the disc.