Experimental intervertebral disc degeneration: morphologic and proteoglycan changes over time.

An animal model of intervertebral disc degeneration produced by surgical ventral disc herniation in the rabbit is described. Histologic studies showed proliferation of cells on the inner third of the annular wound, with metaplasia into fibrocartilage in the first 2 weeks following injury. Progressive fibrocartilaginous change occurred, reproducing the morphologic changes of disc degeneration over the first 6 weeks involving nearly the entire disc. Proteoglycans (total and newly synthesized) were studied qualitatively and quantitatively for periods of 1 to 200 days after herniation. There were two periods of time during the early course of degeneration when the ability of the proteoglycans to aggregate by interaction with hyaluronic acid was recovered, but this decreases progressively after 6-7 weeks. There was an immediate loss of water content from the injured disc which was restored only transiently during the first 2 days after herniation. Thereafter the water content progressively decreased. The uronic acid content of the disc changed in parallel with the changes in water content. The hyaluronic acid content decreased rapidly after herniation. However, the size of the proteoglycan monomers did not change with degeneration. The biochemical and morphologic changes are correlated, and an early repair mechanism is postulated to exist after injury.