Aging changes in the macromolecular organization of the intervertebral disc: an X-ray diffraction and electron microscopic study.

The macromolecular organization, in particular the collagen fibril network, of annulus fibrosus has been investigated, in humans and a strain of mice reared for aging research, by X-ray diffraction and electron microscopy. Collagen fibrils are arranged into fibers which are tilted so that the disc can perform its mechanical function. In neither mice nor humans did the tilt change with age, despite abnormal spinal curvature observed in aging mice. The spread of fibrils appears to decrease with age in anterior human annulus, but this is unlikely to affect function. Elastic fibers are associated with the collagen in mouse and human material of all ages. Aging is associated with the appearance of larger collagen fibrils, especially in human annulus. Increased radius and the biochemical changes which occur during aging may increase the likelihood of an overstressed region of annulus tearing.