Why Do Discs Herniate?

Why Do Discs Herniate?

A healthy disc is tough, resilient and resembles "gristle." As a disc degenerates it looses its toughness and assumes the consistency of soft "crab meat." This is the process of degeneration. As degeneration progresses the structural integrity of not just the disc but also that of the vertebral segment is compromised. This situation leads to segmental "dysfunction" much like "shimmy" in a car body. This "shimmy" directs stress to the zygoapophyseal joints (facet joints) causing them to also degenerate. Disc degeneration is easily recognized in post mortem tissue but the magnetic resonance imaging (MRI) technique is a particularly sensitive means of showing this. The reason for this is that "normal" discs are about 85% water. As discs degenerate they loose their water content. An MRI scan is actually a scan of hydrogen ions in the body. Since almost all hydrogen ions are found in body water (H₂O) a MRI is basically a very sensitive "water content" scan of all body tissues.

This lateral MRI scan shows a degenerated L4-5 level lumbar disc which has herniated (yellow dot). The radiologist has drawn the yellow lines to indicate the area of disc herniation. In this view the discs above and below have greater water content (less degeneration) and are shown to be lighter in color. A degenerated disc is more likely to herniate than one possessing a normal structure.

Intervertebral discs are one of only two body structures in adult life which do not have their own blood supply. The other one is the cornea of the eye. The cornea obtains its nutrition from tears while the disc obtains its nutrition from the diffusion of nutrient solutes across the porous endplates of the adjacent vertebrae.

The diffusion of nutrients across the endplate of the vertebrae can be enhanced by "pumping" activities (types of exercise) and by decreasing intradiscal tension (by segmental traction or distraction). In the case of individuals born with abnormal endplates (i.e. juvenile discogenic disease) the challenge to maintain healthy discs is greater and the liabilities of poisoning discal cells (i.e. smoking) is greater.

Courtesy of Wolfgang Rauschning

Courtesy of Wolfgang Rauschning

The spine model to the left is used for reference. In the middle image anatomically normal discs are shown. In the image to the right the upper disc shows degenerative change and a bulge in the annulus.

Disc Degeneration versus Degenerated Tires

Photo of an upside-down Ford Explorer following failure of the tire casing.

In many ways the simile between degenerated discs and degenerated tires is valid. In order for a human being to be successful for long-term (about 80 years) ambulation on a high gravity planet the individual has to have been careful in parenteral selection so that their spinal column genetic makeup will be adequate to deal with the insults and injuries along the way.

If initial fabrication of the spine is flawed incapacitation and disability will result. Tires, if sound, can be recapped. Spines only continue to be worn down by the daily insults of life and occupation, occasional traumas, and the process of aging. Genomic testing to determine spine liabilities early in life will be the future equivalent of tire testing before use. Its a shame we don't have this now because because valid self-administered spine health maintenance programs presently exist.

Tires are stressed when under inflated and run at high speeds in high temperature environments. In the same way human spines are stressed by labor intensive jobs as well as occupations such as trucking where compressional loading and vibratory factors conspire to injure discs. The simile with tires ends with the observation that humans can actually, on a daily basis, perform health maintenance programs capable of enhancing and improving spine nutrition and function whereas tires can only become more run down over the passage of time.

How Does Disc Herniation Start?

Unless due to acute trauma a typical disc herniation begins with an unhappy disc. The circumstances that promote this state of affairs is, as can be seen, are usually multiple leading to a loss of disc integrity. Once degeneration exists it usually doesn't take much for a disc herniation to start. Very often the first step in this process is a twist "injury" producing a tear in the disc annulus.

In this lateral MRI image the red dot is to the right of a degenerated disc showing the beginning of a herniating disc. At this stage the discal bulge is usually described as a "annular tear." In this case there is a small are of high intensity shown at the bottom of the tear. This is called a "high intensity zone" and refers to inflammatory fluid in a discal tear. This "HIZ" type of tear has been correlated with a high incidence of associated back pain and represents one of the very few MRI findings which can be directly related to back pain.

In this axial MRI scan from the same patient the red dot is exactly placed over the "high intensity zone" annular tear which, if seen from the side, appears as a white dot.

Disclaimer On Disc Degeneration

Mother Nature is the very best healer and, even though scientific data does not exist on this subject, it is clear that in the vast majority of cases degenerated discs are absorbed, the interspace narrows, osteophytes are formed, and a "restabilization" occurs spontaneously. Often the individual is aware only of a gradual reduction in body height, taking place over a period of years. A truism is: "if you are good to Mother Nature, she will be good to you."

The images above (courtesy Wolfgang Rauschning and William Kirkaldy-Willis) are actual anatomic examples of chronic degenerative changes in the intervertebral discs where the process of healing and re-stabilization is occurring. Patients such as this are frequently without low back pain or neurologic involvement. The ability of the spine to gradually acclimate to this process and maintain apparently "normal" function is truly amazing. The key is gradual acclimization. Superimposed injury or insult can readily convert a situation such as this into a disabled state.

Why Is There Back Pain?

In the September 2000 Issue of the Oprah Magazine an article "The Real Source of Your Back Pain" written by Emma F. Segal quotes physician Art Brownstein. His answer to the question "What causes most back problems?" was "Muscle strains and sprains." Another quote from Doctor was: "It is a common misconception that back pain starts with a disc problem." These statements are poor responses to the questions asked and are misleading to the public.

It is an anatomic fact the the surface of the brain given over to representing the back is remarkably small. This poor representation is the reason that back pain is non-specific and so poorly localized in comparison to large brain areas for fingers, tongue, etc., allowing more specific localization.

There is no question but that one can "strain or sprain" the ligamentous or muscular components of the spine but most back pain, spasm, and incapacitation are secondary to degenerative changes in the spinal column reflecting congenital abnormalities and well as acquired insults and injuries.

A complete MRI is an expensive proposition typically costing $1,000-1,2000 in the United States. A "screening MRI" costs a great deal less (usually $350-500). All adults in the population have some degree of disc degeneration and it is therefore essential that these studies be reported by experienced physicians. Most MRI reports, in the Burton Experience, only demonstrate how little is known regarding this radiologic diagnosis. Given that so little is really known regarding the differential diagnosis of disc degeneration and its role in initiating segmental disease it is not surprising that early identification and initiation of self-administered preventive programs, which may very well represent the very best investment which can be made in the future health and productivity of the population are presently rare phenomena.