History and Background

Discography has become a valuable diagnostic tool since its introduction in the 1940s to diagnose lumbar disc herniation.^1–3 Since discography was introduced, computed tomography (CT) and magnetic resonance imaging (MRI) scanning have also added to our knowledge of the lumbar discs; however, because structural abnormalities such as degenerative disc changes, herniations, and annular tears occur in patients asymptomatic of low back pain,^4,5 discography is the only direct method to asses if a disc is painful or not. Discography has also been shown to reveal abnormalities in symptomatic patients with normal MRI scans.^6,7

Today, discography is used most often to identify painful internally disrupted discs.³ Discography is unique in that it is the only diagnostic technique that directly correlates a patient’s symptoms with disc morphology.⁴ This is analogous to palpation, which is fundamental to physical diagnosis.⁵ Tenderness elicited on palpation is analogous to pain provocation on discography.

When evaluating a suspected spinal origin of pain, it is critically important to assess the significance of pathological findings on imaging studies and to determine whether those findings correlate with a patient’s symptoms. Discography is distinctive in its ability to make this determination. Discography is used in the lumbar,^6–19 thoracic,^20–25 and cervical^26–35 regions to assess pain that is suspected to be of discogenic origin. Discogenic pain is mechanical in nature (exacerbated with activity and relieved by rest) and is felt primarily in an axial distribution. Performing discography involves the injection of radiographic contrast into the nucleus of the intervertebral disc to visualize disc morphology (Fig. 17-1).⁴

Fig. 17-1 The circumferential area of the surface area of the disc. Both sides come in contact with surface above and below that endplate adhering itself to the vertebral body.

The prevalence of discogenic low back pain is 39% in those with low back pain persisting for at least 6 months and who have an unremarkable diagnostic workup and 26% of patients without radicular pain after facet joint pain was eliminated by either performing a diagnostic median branch nerve block or an intraarticular facet joint injection.³⁶ The advent of new technology such as MRI, CT, and CT myelography has improved anatomical visualization of spine structures. However, these diagnostic modalities have not reliably identified the anatomical location of symptomatic spinal structures. This is evident in the individual who does not have radicular symptoms. Discs that appear normal or abnormal on MRI can either reproduce clinical symptoms during discography or be painless. The lumbar discs are innervated by branches from the lumbar ventral rami, the grey rami communicans, and the sinuvertebral nerve (Figs. 17-2 and 17-3). Lumbar discography has been postulated as a diagnostic test to elucidate the specific disc that requires disc excision and fusion with subsequent pain relief. The North American Spine Society (NASS) released its Position Statement on Discography in 1988³⁷ and again in 1995, summarizing the indications for discography. Both the International Spine Injection Society and NASS agree on the criteria for functional discography. Each organization indicates that a “chemically” sensitive disc is one that a patient feels pain at a low pressure stimulus (basically <15 psi). Between 15 and 50 psi, if a patient experiences pain that is concordant with the pathology of the painful disc, then it is deemed a pressure-sensitive disc. Pressures greater than 51 psi to 90 psi above the opening pressure are noted to be determined. A pressure above 90 psi is stated as being normal. The most common indication for lumbar discography is the need to determine whether one or more lumbar discs are responsible (i.e., the pain generator) for chronic ongoing low back pain. The study by Walsh et al³⁸ refuted the findings by Holt¹⁹ demonstrating a 0% false-positive rate. Recent literature has demonstrated that compared with present imaging modalities, lumbar discography and lumbar CT discography are superior to MRI in determining abnormal annular pathology.^39–43

Fig. 17-2 The cross-sectional area denotes how the surface area is viewed and adherent to the vertebral body. The figure demonstrates that relationship of the foramen and the nerve root.

Fig. 17-3 The endoperoxides of the disc, a disc bulge, and annular tear in relation to the nerve root proximity.

(Netter illustration from www.netterimages.com © Elsevier Inc. All rights reserved.)

Several studies have demonstrated the limitations of MRI compared with lumbar discography in identifying symptomatic versus asymptomatic discs.^39–42 In 2000, Carragee et al⁴⁴ challenged the concept of zero false-positive discography results on the grounds that abnormal psychometrics lead to misleading abnormal results. Manchikanti et al,⁴⁵ in 2001, to the contrary, did not find any impact on discography results in those with or without a somatization disorder. Crock⁴⁶ was the first to use the term internal disc disruption in 1970 to describe the clinical syndrome of axial low back pain secondary to pathological changes within the disc in the absence of a disc herniation. Radial fissures into the outer innervated annulus can cause pain because of mechanical or chemical irritation. This is the salient pathologic feature of internal disc disruption that cannot be detected on plain radiography, CT, or myelography because these studies are unable to detect internal disc abnormalities.

CT combined with discography allows the detection of annular pathology and determines if it is symptomatic or not. MRI can reveal annular pathology but cannot determine whether or not the disc is the pain generator (Fig. 17-2).^38–41 Although the presence of a high intensity zone (HIZ) on T2-weighted MRI sagittal images in the posterior annulus (representative of a radial annular fissure) has a near 90% positive predictive value with concordant discography,^{34–36,38,39} this is not absolute, and the absence of an HIZ does not exclude annular pathology or discogenic low back pain.^38–42 HIZ lesions are also found in patients without low back pain symptoms.^47–49 Lumbar discography is not only important in identifying discs that are pain generators but also serves a key role in detecting whether abnormal or normal discs (based on imaging studies) are painful.

Pathophysiology

Two of the most common problems associated with the intervertebral disc are intervertebral disc degeneration and intervertebral disc protrusion or herniation; however, the two processes are not mutually exclusive. Extruded nucleus pulposus spontaneously produces increased amounts of matrix metalloproteinases, nitric oxide, interleukin-6, prostaglandin E2, and other chemical mediators (Fig. 17-3). These products may be intimately involved in both the biochemistry of disc degeneration and the pathophysiology of radiculopathy.

Intervertebral disc degeneration is difficult to define and is also difficult to separate from the normal aging process of the intervertebral disc. However, there is a wide variation in the aging and degenerative process of the disc, and some septuagenarians have the intervertebral discs of 30-year-old adults and vice versa. The hallmarks of disc degeneration are loss of fluid and fluid pressure, disruption or breakdown of collagen (including tearing of the annulus fibrosus) and proteoglycans, and sclerosis of the cartilaginous endplate and adjacent subchondral bone. The normal aging and degeneration of the intervertebral disc is closely related to the number of vessels that reach the intervertebral disc, especially the cartilaginous endplate. As the number of vessels decreases and the nutrition provided and waste removed by these vessels decrease, the changes associated with intervertebral disc aging and degeneration increase.⁴⁶ The first significant degenerative changes in the intervertebral disc appear around 11 to 12 years of age.

The number of clefts and radial tears increases from 17 to 20 years of age, and the overall number of chondrocytes decreases as cell death, mucoid degeneration, and granular changes begin to appear.⁴⁵ The number of clefts and radial fissures continues to increase until late in life (>70 years of age).

Functional Discography

Functional anesthetic discography (FAD)⁵⁰ is an additional test that can be carried out after provocation discography. It is based on analgesic discography, in which local anesthetic is injected into a painful disc and pain relief is assessed. The theory is similar to diagnostic injections of facet joints or sacroiliac joints. A 17-gauge introducer needle is used for disc access. After the provocation discogram, a balloon-tipped catheter is placed into the center of the disc through the needle (Fig. 17-4).⁵⁰ The balloon is inflated with contrast, and a stopcock is closed to secure the catheter in the nucleus.

Fig. 17-4 The intradiscal catheter is placed through the needle and has a distal balloon that is inflated with contrast to maintain placement.

(Courtesy of Kyphon Medtronic.)

In the recovery area, the patient is instructed to perform specific activities and positions that typically elicit pain, and the visual analog scale (VAS) scores are recorded. In the author’s practice, 1 mL of 4% lidocaine is injected into the painful disc through the balloon-tipped catheter after baseline pain scores have been recorded. The same measurements are carried out 8 to 10 minutes later, and the change in VAS is recorded. Provocation discography facilitates diagnosis by eliciting pain, and FAD helps clarify the diagnosis by relieving pain and improving mobility during testing. Each painful disc can be studied sequentially and individually. The results of the provocation discography are compared with the FAD results to produce a final report. After the FAD is completed, the balloon on each catheter is deflated, and the catheter is removed.

Alamin and coworkers⁵¹ reported that 50% of patients (n = 32) had confirmatory findings on FAD after a positive discogram result. The patients with confirmatory FAD underwent fusion and were followed for at least 3 months. The mean preoperative Oswestry Disability Index score was 58.5, and the mean postoperative score was 26.5. The mean preoperative VAS score for back pain was 7.2, and the mean postoperative VAS score was 3.1.

Intradiscal Procedures

Disc biacuplasty is a procedure for treating discogenic pain through neuron ablation by heating intervertebral disc tissue using cooled, bipolar radiofrequency (RF) technology. One study⁵² has demonstrated temperature profiles created by disc biacuplasty in human cadavers.

Many practitioners have used various injection formulas to help patients with discogenic pain (Table 17-1). From the Saal brothers using intradiscal electrothermal therapy⁵³ to the use of catheters, medications, and now a “super glue” to help seal off annular tears, these techniques enable us to stop pain emitting from the intradiscal areas of the nucleus (Fig. 17-5).

Table 17-1 Intradiscal Procedures

IDET, intradiscal electrothermal therapy.

Fig. 17-5 Intradiscal electrothermal therapy catheter.

DiscTRODE from Radionics did show some promise by using a catheter spiraled in the posterior portion of the disc wall. Allowing heat to be generated helped to seal off the posterior annular tear that may have been provoking the leakage of caustic irritants.

Nucleoplasty from Arthrocare Spine allowed the knowledge and technique to be capitalized on by the use of RF energy to heat up channels within the disc, allowing a coblation and coagulation to occur simultaneously inside the nucleus. By the use of the technique, one could vaporize material and create a negative vacuum in the nucleus, thereby allowing the outer rim to retract back into the disc. Stryker developed the very well-known and proven Dekompressor. This device actually removes intradiscal material and creates a negative vacuum in the disc, allowing the out-bulge defect to retract and lessen the contact on the nerve root (Fig. 17-6). The use of a sealant to stop annular stimulation in addition to helping the disc to actually rehydrate is another novel concept. Spinal Restoration in Austin, Texas, is in a third-phase clinical trial analyzing the concept at the present time.

Fig. 17-6 A, Dekompressor device. B, Dekompressor removing intradiscal material.

Conclusion

Discography has become an indispensable assessment tool in the evaluation of patients with spinal pain. Current imaging techniques are insufficient to determine if a suspected disc is the source of pain. Discography is the only test of the intervertebral disc that is able to stimulate the disc and recreate a patient’s pain. This is analogous to palpation, which is fundamental to physical diagnosis. Disc stimulation and pain reproduction can be correlated with analgesia and function if local anesthetic is introduced into the disc. There is both historical and current controversy surrounding the use of discography. This has promoted healthy discussion and advanced the standards for performance of this examination. The use of manometry, FAD, “sham” injection, and strict criteria for identifying positive discs are all intended to limit the likelihood of false-positive results. It is acknowledged that discography has to be interpreted with caution in patients with significant behavioral pathology.

With the continuous evolution of spinal interventions come many new and promising treatments for painful intervertebral discs. These include a host of emerging biological therapies and surgical treatments. All of these require the ability to safely access the intervertebral disc for both diagnosis and treatment. The demand for this procedure is certain to increase. When discography is performed with appropriate clinical indications by skilled, knowledgeable, and experienced proceduralists, it leads to improved clinical outcomes.