[The pathogenesis of discogenic low back pain].

OBJECTIVE To study the pathogenesis of the pain of discography and the discogenic low back pain. METHODS 19 specimens of lumbar intervertebral discs from 17 patients with discogenic low back pain during posterior lumbar interbody fusion, and 12 physiologically aging discs and 10 normal control discs were collected to investigate the morphologic features and innervation containing neuropeptides substance P (SP), neural filament (NF), and vasoactive-intestinal peptide (VIP). RESULTS The distinct morphologic characteristic of the disc from the patient with discogenic low back pain was the formation of the strip zone of vascularized granulation tissue from the nucleus pulposus to the outer part of the annulus fibrosus in which there was one or several fissures. The structure of annulus fibrosus beyond the strip zone of granulation tissue was basically normal. The structures of the aging discs and the control discs showed the age-related changes. The innervation of SP, NF and VIP immunoreactive nerve fibers in the painful discs was more extensive compared with the aging discs and the control discs. The nerve in growth deep into annulus fibrosus and nucleus pulposus was observed mainly along the strip zone of granulation tissue in the painful discs. CONCLUSIONS Findings indicate that the strip zone of granulation tissue with extensive innervation in the posterior part of the painful disc is the original site of the pain of discography and the discogenic low back pain. The strip zone of granulation tissue might originate from the injury and subsequent reparation of the margin of annulus fibrosus. The difference of the aging disc and painful disc which can not be differed each other on MRI is the formation of the strip zone of granulation tissue along tear histologically in posterior part of the painful disc.