We have learned on this site that some patients may suffer debilitating back pain and/or leg pain (sciatica) yet have no positive findings on MRI. For these unfortunate patients, the diagnosis of discogenic pain (i.e., the disc itself has become a pain generator) must be ruled out by a technique called provocative discography.
In a nutshell, this procedure calls for the examiner to place a needle (red arrow) into the center of the suspect disc and then inject it with contrast, which in turn will light-up the nucleus (make it white) on fluoroscopy (figure left) as well as any annular tears which are present (yellow arrows).
Just as important as the visual appearance of full thickness annular tears is the pain-response reported by the patient during pressurization of the nucleus.
Specifically, the examiner is supposed to pressurize the contrast-filled disc to 100 psi above the opening pressure and then carefully note whether or not that pressurization re-created the patient's exact (concordant) or typical low back and/or leg pain. If it does, then this is an indication that the disc and/or vertebral endplates are the source of the patient's chronic back pain.
To make test even more positive, the examiner will repeat the procedure on both adjacent, healthy discs and hopefully get no pain-response from the patient.
And to make the test super positive (i.e., very indicative that the disc is the cause of the low back pain), the examiner is supposed to anesthetize the painful disc with lidocaine and repeat the pressurization. This time, the patient should not feel pain since all the nerve endings in the outer annulus are numbed. This part of the test has recently become a little controversial, for we do know that there are pain-carrying nerve fibers within the subchondral region of the vertebral endplate which may not be affected by the lidocaine bath and still produce pain during the pressurization.
The figure above is a sagittal view (from the side) of the lumbar spine performed via fluoroscopy during discography. Note the needles (red arrow) have been placed in the center of the disc and contrast has been injected. Although the L3 and L4 nucleus are fairly normal (there is a small full thickness tear at L4 {green arrow}), the L5 disc is tore in half and the contrast is certainly not contained (yellow arrows).
The procedure is a true art form and should only be done by the most seasoned of physicians.
Although the procedure can be incredibly painful (anesthesia is not allowed because the patient-pain response is needed), it is a relatively safe procedure in the short run. However, there is pretty strong evidence that indicates sticking the disc with a needle is not good for the long-term health of the disc.
We know that disc-pokes resulting rapid degeneration of the disc, as well as the creation of full thickness annular tears and even herniations in animals. [5,27-30] In fact, if you want to study degenerative disc disease or annular tears in animals, all you have to do is prick the very outer portion of the annulus with the needle. Such A needle-stick will almost always result in the desired degenerative disc disease and full thickness annular tear within a few weeks.
However, does a needle-stick into a human disc result in the same train of degeneration? The short answer is it appears so, but deleterious effects takes a long time to manifest.
This important question was answered by the famous researcher in spine surgeon, Eugene Carragee of Stanford, who performed an ingenious and award-winning human experiment, which was published in 2009. [1]
In a nutshell, two groups of ~70 people were assembled and matched with regard to sex and age. Both groups underwent MRI to establish a baseline.Then, one group (the study group) underwent provocative discography with conservative techniques, while the other (the control group) did not. Both groups were followed for 10 years and new MRIs were obtained. Although only ~70% of the people in both groups were available at the 10-year follow-up, the results were shocking: there was a statistically significant increase in the frequency of disc herniations, annular tears, vertebral endplate defects, disc space narrowing, and a worsening of degenerative disc disease in the study group as compared to the control group. [1] These results led Dr. Carragee to conclude, "...careful consideration of the risk and benefit should be used in recommending procedures involving disc injection." In plain English, that means you should only poke a needle into the disc if absolutely necessary, for there are consequences to these types of procedures.
When it comes to diagnosing discogenic pain, provocative discography with fluoroscopic guidance is the proverbial gold standard. The Dallas Discogram Classification System was originally described in the late 1980s (126,118), but has since been modified twice. However, many examiners still use the original system; therefore, I believe it is useful describing it below in detail.
In a nutshell, the system rates the degree of annular tearing, as visualized on a CT axial view of the disc after dye has been injected. If no CT is available, the degree of tearing can be rated on sagittal fluoroscopy or radiograph.
Grade 0: A normal nucleus. As visualized on imaging, none of the contrast material has escaped the confines of the nucleus. A sagittal representation of a grade 0 can be seen on the very first image on this page at either of the top two discs. (Grade 0)
Grade 1: A small annular tear (black arrow) is visualized extending from the nucleus into the inner region of the annulus fibrosis. Fig. #1 demonstrates what this might look like on axial CT imagery (although the needle that delivered the contract material into the center of the disc would be long-gone by this time). Note the needle has injected a radio-opaque dye (pink) into the center of the disc (nucleus) which is used as a 'marker'. At about 5 O' Clock (black arrow) a 'tear' or 'fissure' has become visible from the leakage of some contrast material. It extends from the nucleus radially into the inner 1/3 of the annulus fibrosus. This fissure would probably not be painful since there are usually no pain fibers in this region. This could be described as a 'Grade 1 Radial Annular Tear', or Grade 1 Internal Disc Disruption (IDD).
Grade 2: A full-thickness annular tear has completely disrupted the disc but has NOT affected the outer contour of the annulus. Specifically, no leakage, bulging, or herniation is visualized.
Figure #2 demonstrates that there has been a progression or worsening of the annular tear/fissure previously visualized in figure 1.
Now the entire annulus has been disrupted (torn through), except for the very outer fibers and the PLL (blue) as denoted by the pink contrast material that has now moved from the nucleus through the annulus. Note that there is no leakage of dye from the disc, nor is there any bulging or protrusion of the disc. This would be classified as Grade 2 IDD or a Grade 2 radial annular tear.
Although the most patients with this condition would suffer principally from low back pain, some may also suffer from a "referred" pain down the lower extremity, notwithstanding the fact that none of the sciatic nerve rootlets have been mechanically compressed. I have termed this phenomenon discogenic sciatica.
Grade 3: The annular tear has now completely disrupted the annulus and posterior longitudinal ligament (PLL) (Blue), as well as deformed (pushed out) a small posterior region of the disc. Such an "outpouching is termed a disc protrusion (a.k.a. herniation).
Note in figure 3 that nuclear material (pink) has escaped into the anterior epidural space and onto the adjacent nerve tissue (i.e., the anterior dura of the thecal sac, the traversing nerve root and potentially the exiting nerve).
Such a scenario may result in real (non-discogenic referred) lower extremity radicular pain secondary to the development of an inflammatory process within the sciatic nerve roots.
More specifically, it is well known that the evil biochemicals that live within the degenerated disc (i.e., cytokines) can result in true radicular pain without mechanical compression of the nerve roots if exposure occurs. These cytokines are pro-inflammatory, which means they are capable of starting a vicious cycle of inflammation, which in turn results in lower extremity pain and even findings of true radiculopathy has confirmed by EMG/NCV.
The 'Modified Dallas Discogram Description' was finalized in the 1990's and is the 'Gold Standard' for the classification of annular tears. It was initially developed by a group of researchers from Texas (as described above in detail) (126), 'modified' by Bogduk et al. (7) in 1992, and then finally modified by Schellhas et al. in 1996(15). Below is a brief look at what that system looks like: (Sorry for getting off topic here!)
The chart on the left demonstrates the five possible severities of the radial angular tear, as seen on an axial CT image. (In reality things are not always so 'nice and need' on discography but often they are.) The grade 0 is a normal disc, where no contrast material (red stuff that was injected into the center of the disc) has leaked from the confines of the nucleus. The grade 1 tear has leaked contrast material but only into the inner 1/3 of the annulus. The grade 2 tear has leaked contrast from the nucleus into the outer 2/3s of the annulus. The grade 3 tear has leaked contrast completely through all three zones of the annulus. This tear is now believed to be painful since the outer 1/3 of the disc has many tiny nerve fibers that may now be irritated. The grade 4 tear further describes the grade 3 tear, in that, now the contract has spread circumferentially around the disc, often resembling a ships anchor. To qualify as a grade 4 tear tear, the circumferential spread must be greater than 30 degrees. (Pathologically, this represents the merging of a full thickness radial tear with a concentric annular tear.) The 'evil' grade 5 tear describes either a grade 3 or grade 4 radial tear that has completely ruptured that outer layers of disc and is 'leaking' contract material from the disc into the epidural space. This type of tear is thought to have the ability to induce a severe inflammatory reaction in 'some' peoples posterior neural structures. In some cases this inflammatory process is so severe is causes a painful 'chemical radiculopathy' and sciatica 'without' even the presents of nerve root compression.
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1) Carragee EJ, et al. 2009 ISSLS Prize Winner: Does discography cause accelerated progression of degeneration changes in the lumbar disc. A 10-year matched cohort study. Spine 2009; 34:2338-45.
5) Osti OL, et al. Volvo Award - "Anulus Tears & Intervertebral Disc Degeneration: an Animal Model" - Spine 1990; 15(8):762-766
27) Moore RJ, et al. "Remodeling of Vertebral Bone after Outer Anular Injury in Sheep." – Spine 1996;21(8):936-940
28) Key JA, Ford LT "Experimental intervertebral disc lesions" – J Bone Joint Surg 30A:621, 1948
29) Moore RJ et al "Changes in Endplate Vascularity After an Outer Anulus Tear in the Sheep" – Spine 1992; 17(8):874-877
30) Kim KS, Yoon ST, Li J, Park JS, Hutton WC. 'Disc degeneration in the rabbit: a biochemical and radiological comparison between four disc injury model s. Spine. 2005 Jan 1;30(1):33-7.
118) Moneta GB, et al. "Reported pain during lumbar discography as a function of annular disruption and disc degeneration." Spine 1994; 19:1968-74
126) Sach BL, et al. " Dallas discogram description: A new classification of CT/discography in low back disorders. Spine 1987 ;12:287 -94
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