The natural history of age-related disc degeneration: the influence of age and pathology on cell populations in the L4-L5 disc.

Study Design. A study of the density of cells in the L4-L5 disc during aging and in the presence of major pathology. Objective. To quantify the density of cells throughout well-preserved adult L4-L5 discs and in discs containing major pathology. of Background Data. The few and limited studies of disc have largely been part of biochemical studies having a major focus on disc nutrition. Excluding the cartilage end plate, the density of healthy cells in the disc is much lower than that of most body tissues. Method. The nucleus zone and 18 annulus zones were demarcated by inking the coverslips of hematoxylin-eosin-stained 5-μm thick sagittal sections of the L4-L5 disc. In each of the 19 zones, the healthy disc cells were enumerated in 10 randomly selected nonoverlapping high-power microscope fields. Results. Assessment of the spatial cellularity in a disc divided into 7 parasagittal sections showed that the average density in the posterior annulus was significantly greater than that in the anterior annulus; the average density in the right half of the disc, including the nucleus, was significantly higher than that in the left and lowest in the left anterior quadrant. Studies of midsagittal sections from the spines of 10 men and 10 women, aged 13 to 78 years, showed that nuclear cellularity declined progressively throughout life, whereas that of the annulus ceased to decline after the age of 50 years. Some tears were associated with low cellularity close to the tear but not elsewhere, whereas extensive end-plate separations showed global reductions in cellularity. Conclusion. Disc cellularity declines as age advances and is reduced in the vicinity of major tears. Extensive end-plate abnormalities reduce cellularity by impeding disc nutrition.