Biochemical aspects of development and ageing of human lumbar intervertebral discs

Nucleus pulposus and annulus fibrosus from individual normal discs of different ages have been separately examined, and the topographical distribution of constituents across the annulus fibrosus has been determined. Collagen content, including the molecular species, and proteoglycans have been estimated. Type I collagen was found in the outermost regions of the annulus and type II in the innermost, whereas the nucleus contained type II collagen. In older spines the collagen content of the annuli increased both outwards in the disc, and downwards along the spinal levels. Proteoglycan content was higher in the nucleus, and the proportion of keratan to chondroitin sulphate increased with age, as did the hyaluronate content. It is concluded that differences in mechanical function may be reflected by differences in chemical composition of the discs, and that mechanical failure could result from local variations in chemical composition.