Internal Disc Disruption

Internal Disc Disruption is a pathological process only understood over the last half of a century. Physical examination of these patients only tends to reveal pain and guarding, without clear objective signs. Often patients suffering from this condition were thought to be psychologically impaired and were used as examples of psychogenic pain disorders, hypochondriasis, factitious disorders and malingering. Nothing could be further from the truth and even today the idea of Internal Disc Disruptions has its detractors, especially in medical legal cases.

Until 1946 medical practitioners believed that the only painful disorders of the intervertebral discs themselves were those of herniation of the nucleus pulposis, with impingement of a nerve root. The argument was that the intervertebral discs lacked innervation and injury to the discs themselves could not be painful. When discograms were developed in the late 1940's, the idea was to replace myelography as a means of diagnosing herniations. Discographers injected radio-opaque dye into the nucleus pulposis of lumbar discs and found that they could trace the contour of the herniation from the inside of the disc, rather than view the impression the disc made, as was possible with oil based mylelograms. The advantage of discograms was thought to be one of replacing the relatively high side effect risk with myelography, while providing a more direct structural view of the herniation. To the surprise of early discographers, it was often determined that pain occurred in non-herniated discs, which showed a disrupted pattern of the nucleus pulposis outside of its boundaries, but contained within the walls of the disc. Contrary papers were published with reports of massive false positive test results, and these remained the cornerstone of discrediting discograms. Interestingly, they never addressed the issue of internally disrupted discs, and instead focussed upon pain provocation without frank herniation. The controversy raged into the 1980's, when anatomists were able to show clear innervation of the external 1/3 of the intervertebral disc anulus fibrosis, with a rich supply of nerves feeding three separate pain pathways into the dorsal horn of the spinal cord.

The mechanisms of pain are both inflammatory and mechanical. The nucleus pulposis of the intervertebral disc is kept isolated from the body's immune system. When the disc is disrupted this isolation is broken and the proteoglycans in the nucleus cause the body to mount an inflammatory response to seal off what it sees as a foreign invader. When the nuclear material reaches the outer third of the anulus the inflammatory response causes pain to be transmitted from the pain nerves in this area. The mechanical problem occurs when the functional capabilities of the disc anulus are lost. The anulus fibrosis is made up of tough connective tissue that must withstand the incredible forces of compression and rotation found in the spine. Much of the disc is weakened by a marauding nucleus pulposis destroying collagen fibers. The mechanical forces translate to the remaining fibers and overwhelm the disc's ability to function normally. The excessive strain transmitted to the highly innervated outer 1/3 of the disc wall results in a mechanical signal of pain, with normal disc compression and rotation.