Biological changes in the annulus fibrosus in patients with low-back pain.

The anterior annulus from patients undergoing surgery for low-back pain was compared with the same region removed at autopsy. Collagen, proteoglycan, and water content were measured in different regions across the annulus. Water and proteoglycan contents increased from the outer to the inner annulus, whereas the collagen contents declined. Quantitative differences were found between agematched surgical and autopsy specimens. Discs from most patients showed lowered proteoglycan contents, and a few of these showed high water contents. Loss of collagen in isolated areas of the annulus was demonstrated in some patients. Collagen loss occurred most frequently in the lumbosacral disc, whereas changes in proteoglycan and water were more frequent higher in the lumbar region. No qualitative changes in collagen types were detected immunochemically. In many patients, the levels of proteoglycan which aggregated in vitro were extremely low. Changes in hexosamine molar ratio of disc proteoglycan and in the length of the chondroitin sulfate side chains were observed with aging in this group of patients.