The pathogenesis of discogenic low back pain

This was a cross-sectional analytic study of patients with chronic low back pain. To investigate whether the criteria for internal disc disruption, as adopted by the International Association for the Study of Pain, could be satisfied in patients with chronic low back pain and to test whether there were any conventional clinical features that could identify this condition. Internal disc disruption has been postulated as an important cause of low back pain. To diagnose this condition, the International Association for the Study of Pain taxonomy requires that pain be reproduced on provocation discography and that computed tomography discography reveal internal disc disruption, provided that as a control, stimulation of at least one other disc fails to reproduce pain. Ninety-two consecutive patients with chronic low back pain and no history of previous lumbar surgery were studied. Each patient underwent a standard physical examination. Computed tomography discography was performed at a minimum of two levels. The diagnostic criteria for internal disc disruption were fully satisfied in 39% of patients, most commonly at L5-S1 and L4-L5. None of the clinical tests used could differentiate between those patients with internal disc disruption and other patients. A diagnosis of internal disc disruption can be made in a significant proportion of patients with chronic low back pain, but no conventional clinical test can discriminate patients with internal disc disruption from patients with other conditions.

The authors investigated the innervation of discographically confirmed degenerated and "painful" human intervertebral discs. To determine the type and distribution patterns of nerve fibers present in degenerated human intervertebral discs. The innervation of intervertebral discs has previously been extensively described in fetal and adult animals as well as humans. However, little is yet known about the innervation of severely degenerated human lumbar discs. The question may be posed whether a disc that has been removed for low back pain possesses an increased innervation compared with normal discs. The presence of nerve fibers was investigated using acetylcholinesterase enzyme histochemistry, as well as neurofilament and substance P immunocytochemistry. From 10 degenerated and 2 control discs, the anterior segments were excised and their nerve distribution studied by examining sequential sections. In all specimens, nerve fibers of different diameters were found in the anterior longitudinal ligament and in the outer region of the disc. In 8 of 10 degenerated discs, fibers were also found in the inner parts of the disc. Substance P-immunoreactive nerve fibers were sporadically observed in the anterior longitudinal ligament and the outer zone of the anulus fibrosus. Findings indicate a more extensive disc innervation in the severely degenerated human lumbar disc compared with normal discs. The nociceptive properties of at least some of these nerves are highly suggested by their substance P immunoreactivity, which provides further evidence for the existence of a morphologic substrate of discogenic pain.