A recent report in the Lancet medical journal reports that in a survey of 3,982 Americans, 29% of men and 27% women reported feeling some pain. Those who have higher levels of pain are usually those with lower income and less education working in manual labor and other blue-collar jobs.
Pain can start as early as the teen years and increases to the mid-40s and then plateau to increase again after age 75. The degenerative changes seen in autopsies confirm the reason for these pain symptoms (see below).
The intervertebral discs lies between the vertebral bodies, linking them together. The components of the disc are nucleus pulposus, annulus fibrosus and cartilagenous end-plates. The blood supply to the disc is only to the cartilagenous end-plates. The nerve supply is basically through the sinovertebral nerve. The important components of the disc are collagen fibers, elastin fibers and aggrecan. As the disc ages, degeneration occurs, the nucleus dries up, and the disc flattens. During these changes, pain producing nuclear material tracks and leaks through the outer rim of the annulus. This is the main source of disc related pain. While this is occurring, the degenerative disc, having lost its height, effects the structures close by, such as ligamentum flavum, facet joints, and the shape of the neural foramina. This is the main cause of spinal stenosis and radicular pain due to the disc degeneration in the aged populations. (Raj PP. Intervertebral disc: anatomy-physiology-pathophysiology-treatment. Pain Practice. 8(1):18-44, 2008).
In a study of 248 sections of lumbar disc and vertebral bodies from 41 routine autopsies (range, 7 months to 88 years), these degenerative changes were noted: fibrous transformation starts in the nucleus, then annular disorganization, endplate, and vertebral body alterations progress. These changes occur predominantly in the first 2 decades and in the 5th to 7th decades. In the 3rd and 4th decades, little progression occurs. Nuclear clefts and annular tears appear later, mostly starting in the 2nd decade, with clefts preceding formation of tears. Radial and concentric tears develop similarly over time, whereas rim lesions mostly develop after the sixth decade. Significant differences are observed between upper and lower lumbar spine. Haefeli M. Kalberer F. Saegesser D. Nerlich AG. Boos N. Paesold G. The course of macroscopic degeneration in the human lumbar intervertebral disc. [Journal Article. Research Support, Non-U.S. Gov’t] Spine. 31(14):1522-31, 2006.