Neurosurg Focus 13 (2):Article 14, 2002, Click here to return to Table of Contents

Black disc disease: a commentary

SETTI S. RENGACHARY, M.D., AND RAJU S. V. BALABHADRA, M.D. Department of Neurosurgery, Spine Service, Wayne State University School of Medicine, Detroit Medical Center, Detroit, Michigan

Internal disc disruption associated with axial back but not radicular pain is a disease entity that was recognized about two decades ago as a disorder that could potentially be treated by spinal fusion. In this article the authors describe the clinical syndrome, magnetic resonance imaging and discography findings of pathophysiological pain generation, and the available surgical options. Based on the current understanding of this disease entity, the optimum surgical procedure entails radical , anterior column support, adequate amounts of auto- or allograft bone, bone extenders and en- hancers, and rigid stabilization of the motion segment.

KEY WORDS • disc degeneration • internal disc disruption • magnetic resonance imaging • discography • discogenic pain • lumbar fusion

Lumbar DDD is manifest clinically by a spectrum of trauma-induced internal disc disruptions, black disc dis- disorders, including disc extrusion with or without mi- ease, isolated disc resorption, and segmented instability. grated fragment, disc protrusion, (central, paracentral, in- traforaminal, or far-lateral) disc bulge, and internal disc disruption. Of these, frank disc rupture causing mono- CLINICAL SYNDROME radiculopathy or cauda equina syndrome is a well-estab- Discogenic syndrome appears to be a disease lished entity. Very little, if any, controversy exists with of adulthood. Although disc disease is well recognized in regard to its clinical diagnosis or management, although teenagers and even younger children, the childhood syn- there may be minor differences of opinion about the drome is one of disc herniation at a single or multiple lev- choice of options for treatment. In the past two decades, els. The incidence of lumbosacral DDD is higher in young the syndrome of disc resorption without disc herniation athletes such as gymnasts or ballet dancers, but in our has been recognized as a definable entity amenable to experience, they present with disc herniation rather than surgical treatment.11,12 Historically, disc rupture with mo- black disc disease. This difference may be the result of noradiculopathy was thought to be a clinical syndrome age-related biochemical changes in the . amenable to surgery, originating with the initial descrip- The cardinal manifestation of internal disc disruption is tion of the syndrome by Mixter and Barr.30 Patients pre- back pain. Although a patient’s description may seeming- senting with axial back-dominant pain but with minimal ly suggest diffuse low-back pain, we have found that or absent radicular pain were not thought to be good when specifically questioned and asked to run a finger candidates for surgical intervention. There have been ad- horizontally across the back at the site of maximum pain, vances in several related fields, including a better under- the accuracy of this pain localization matches that defined standing of the anatomical, physiological, and biochemi- by MR imaging in approximately 80% of the cases. This cal features of pain generators in the intervertebral disc, observation may be related to the segmental nature of refinements in the technique of lumbar discography, im- innervation of the anulus, which is the most pain-sensitive proved resolution in MR imaging, development of newer structure.23 O’Brien35,36 has observed focal tenderness at anterior approaches to the lumbar disc (open or laparo- the anterior lumbosacral region with transabdominal pal- scopic), evolving concepts about the usefulness of bone pation. He attributed this to the rich innervation of the morphogenetic proteins, and critical evaluations of sur- anterior anulus, which is irritated with internal disc disrup- gery-related results following lumbosacral fusion. These tion. His observation has not been validated by others be- advances are contributing to the rapid contemporary evo- cause anterior abdominal palpation is not commonly prac- lution in the understanding of discogenic pain syndrome. Several terms have been applied to this discogenic pain ticed in the clinical setting in patients with low-back pain. syndrome and the differences are minor; these include The pain is characterized as mechanical, made worse with sitting, standing, pushing, pulling, bending, and twisting but relieved by recumbency. The pain may extend to the Abbreviations used in this paper: DDD = degenerative disc dis- sacroiliac area, buttock, and back of the thigh but general- ease; MR = magnetic resonance; PLIF = posterior lumbar interbody ly no farther. The pain may sometimes radiate to the groin fusion. or anterior thigh. Frank radicular pain is uncommon, but

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Unauthenticated | Downloaded 10/02/21 05:22 AM UTC S. S. Rengachary and R. S. V. Balabhadra we have encountered patients reporting radiating pain in younger age. Elfering, et al.,14 noted a high incidence of the nerve root distribution but have found no evidence of disc degeneration in individuals working night shifts be- objective root deficit; even if a deficit is present, it is a cause of the relative dessication of the disc at night. blunting to pinprick sensation, but invariably there is no Occupation is a very important determinant. Workers motor weakness. Straight leg raising tests or -relat- performing typical repetitive work in an assembly line ed stretch tests consistently show no signs of abnormality. setting are prone to back problems, especially if the work When the aching pain extends to the posterior thigh, it involves repetitive bending, turning, and lifting. Jobs ne- may be difficult to differentiate from facet joint origin. cessitating lifting and carrying heavy loads are associated The use of differential blocks of the disc and facets in with a high incidence of lumbar degenerative disease; ex- patients with back pain syndrome, however, have shown a amples include furniture movers, landscapers, and med- low incidence of facet disorder with discogenic pain.44 ical assistants working in nursing homes. Authors of epi- The onset of pain is generally gradual and insidious. demiological studies point to whole-body vibratory forces Patients generally are not able to relate a specific event or such as driving trucks, earthmovers, or tractors as con- determine a specific date of onset. The exception to this tributing to low-back pain.18,40 rule is a forceful fall in which the individual lands on the Vigorous and compulsive athletic activities in a com- buttocks. We have observed graphic instances of this in petitive setting predispose to accelerated degeneration of cases of occupational injury (for example, with one leg discs.1 Examples include weightlifting and gymnastics. dropping into a manhole not protected by a cover and the Cigarette smoking is implicated in DDD, but a direct pelvis striking the ground). These cases may initially be link has not been proven. treated as back sprains or back contusions, only to present years later with typical syndrome of internal disc disrup- tion. Although direct loading injuries to the lumbar spine PAIN GENERATION can explain the onset of internal disc disruption biome- It is crucial to understand and localize the DDD-related chanically, victims of motor vehicle accidents in whom pain generator to tailor the surgical treatment and elimi- this disorder is diagnosed have had a preexisting problem nate the source of pain. As stated previously, O’Brien35,36 that is only aggravated by the accident. Loading injuries has noted pain in the anterior anulus on direct palpation of do not occur even in high-velocity accidents with the indi- the area transabdominally. In pioneering studies in per- vidual in the seated position. forming lumbar laminectomy after injection of a local anesthetic Kuslich, et al.,23 and others49 noted that anular CAUSATIVE FACTORS fibrosis is the most pain-sensitive structure. Histopath- Unquestionably, repetitive or continuous axial over- ological studies of cadaveric discs and those removed loading is the key determinant in the pathogenesis of lum- surgically have shown rich innervation of the anulus. The nerve terminals involved may be either somatic or auto- bosacral degenerative disease. Morbid obesity continues 19,37,45 to be a major public health issue in the United States and, nomic. It is intriguing to observe that in the patho- logical disc there is more active sprouting of the nerve to a lesser extent, in other Western nations. The clinical 10 2 triad in the obese individual is intractable low-back pain, terminals than in a normal disc. Ashton and associates bilateral knee pain, and flat feet with bilateral ankle pain. identified substance P in the vascular endothelium of the The primary pathological process is cartilaginous degen- anulus fibrosus in excised discs. All of these observations eration in the intervertebral discs and the cartilage in the indicate that total disc excision to eliminate all anular pain knee joint. Although axial loading is the obvious factor nerve endings should be part of a well-designed surgical implicated, accelerated degeneration due to fatty infiltra- procedure. This observation is also corroborated by the tion of cartilage may not be ruled out. It is unwise in this fact that patients who have undergone nondiscectomy setting to consider surgical intervention until serious mea- posterior spinal fusion may continue to experience disco- sures are undertaken for weight reduction. These may genic back pain despite demonstration of solid posterior include sustained, systematic reduction in caloric intake fusion on neuroimaging studies. An ideal operation should under medical supervision, increased physical activity with eliminate the disc (the pain source) as well as motion. a tailored exercise program, pharmacological therapy for appetite suppression and enhanced fat excretion, and, as a MAGNETIC RESONANCE IMAGING FINDINGS final resort, gastric bypass surgery. If the patient fails to participate in a weight-reduction program, it will be futile There are certain consistent MR imaging changes indic- in most instances to consider back surgery. ative of DDD,15,17,29,38,39 but the findings should always be Genetic factors have an influence in the incidence of the interpreted in light of clinical presentation because it is DDD.3 Defects in the DNA for collagen have been identi- impossible to differentiate symptomatic from incidental fied in family clusters predisposed to degenerative disc syndromes based on MR imaging studies alone.32 A defin- disease. Other genetic defects resulting in impaired pro- ing characteristic is the decrease in signal intensity on T2- teoglycon synthesis are being explored. Videman, et al.,46 weighted sequences obtained in the nucleus pulposus noted that polymorphism associated with the vitamin D compared with the adjacent disc (Fig. 1). The outline of receptor gene correlated with intervertebral disc degener- the nucleus pulposus becomes irregular and the disc height ation. Richardson, et al.,41 confirmed, through an epidemi- decreases. An intense dotlike high-intensity signal in the ological survey, the presence of a familial disposition for posterior anulus signifies an anular tear.43 The cortical back pain. Degenerative disorders involving family clus- endplate and the adjacent marrow show changes in three ters tend to manifest as multilevel disc herniations at a steps, well described by Modic.31

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Unauthenticated | Downloaded 10/02/21 05:22 AM UTC Black disc disease

TABLE 1 Surgical options in black disc disease*

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