• James Melrose, Sally Roberts, Susan Smith, Janis Menage, and Peter Ghosh.
• Institute of Bone and Joint Research, at the Royal North Shore Hospital, University of Sydney, Department of Surgery, NSW, Australia. jmelrose@mail.usyd.edu.au
• Spine. 2002 Jun 15; 27 (12): 1278-85.

Study DesignNerves and blood vessel distribution in discs were localized immunohistochemically and correlated with the proteoglycan contents of normal and degenerate disc tissues.ObjectiveThe aim of the present study was to systematically evaluate whether nerve and blood vessel ingrowth was associated with depletion of disc proteoglycans and degenerative changes in an established experimental model of disc degeneration.Summary Of Background DataAnimal models of disc degeneration, allowing longitudinal study of pathogenic mechanisms, are limited. The ovine model enables systematic monitoring of blood vessel and nerve ingrowth during the development of disc degeneration after injury to the anulus fibrosus.MethodsMerino sheep received a controlled left anterolateral surgical defect in the outer anulus fibrosus of the L1-L2 and L3-L4 discs (lesion group); sham-operated controls received the retroperitoneal anterolateral approach only. Animals were killed 3, 6, 12, and 26 months postoperation, and the discs were collected for histology and compositional and morphologic analyses. Sagittal tissue sections were stained with toluidine blue and hematoxylin and eosin; Type IV collagen immunolocalization visualized blood vessel ingrowth, and nerves were immunolocalized using monoclonal antibodies to growth-associated protein (GAP-43), protein gene product 9.5, and glial fibrillary acidic protein.ResultsCompositional and histologic results demonstrated early focal depletion 3-12 months postoperation of glycosaminoglycan associated with lesion development, increased blood vessel and nerve ingrowth, and infiltration of cells from the outer anulus fibrosus along the plane of the original defect. Blood vessel numbers in the outer to mid third of the anulus fibrosus were elevated in the lesion discs 3-6 months postoperation reaching a maximum at 12 months postoperation; nerves immunoreactive with protein gene product 9.5 (also maximal at 12 months postoperation) were often found associated (but not exclusively) with blood vessels, and some nerves were also reactive with GAP-43 and glial fibrillary acidic protein, but only at 12 months postoperation.ConclusionsNerve and blood vessel ingrowth into the anulus fibrosis were strongly associated with proteoglycan depletion. The ovine anular lesion model of disc degeneration is a useful experimental model for the systematic evaluation of nerve and blood vessel development after anular injury.

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