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Chapter 17 Discography 303
TABLE 17.1 Suggested Criteria for Positive Provocative Discographic Injection
Test Criteria for Positive Result Positive Test Threshold Comments
Pain response (intensity)
Qualitative pain assessment (concordant pain) “Concordant pain” usually including “similar”
Anular disruption Dye must show ssure to or through outer
Control disc injections “Negative” injection (minimal or discordant
Demonstration of pain behavior Facial expressions of pain must be observed
Pressure-controlled injection Disc injections should be classied into low
Volume-controlled injections “Excessive volume” or speed to injection
Maximum one or two positive disc injections More than one or two positive disc injections
Quantify pain tolerance by response to
buered anesthetic injection
Needles should be inserted from
asymptomatic or least symptomatic side
Any positive disc injection must be repeated
with similar outcomes before accepting
result as “positive”
≥6/10 or 3/5
“Bad” pain or worse on pain thermometer
≥7/10
but not exact pain
anulus
pain) required adjacent to proposed
“positive” disc
“Normal” injection (i.e., no pain)
Some authors insist that adjacent “control
disc” must also have grade 3 anular ssure,
which is “relatively painless” at equal or
higher pressures than “positive disc”
to conrm verbal pain report
20 psi) or high (>50 psi) pressures
(<15 or <
at time of signicant pain response;
responses at pressures in between are
indeterminate
invalidates injection
invalidates study (all are indeterminate)
Subjects with poor pain tolerance may not
be “ideal” candidates for discography; needs
to be detected
Theoretically may decrease confusion
between injection and insertion pain
Intraprocedure reliability test No data available on whether this improved or decreased
Subjective and arbitrary scale. No data on reliability. Data
on validity in small groups of asymptomatic subjects
without psychosocial comorbidity are good (specicity
>90%). Data in several studies of subjects with increased
psychosocial or chronic pain comorbidity indicate
validity in these subgroups is poor (specicity 20–60%).
Subjective response. Data on reliability are unknown. Data
on validity in small study of experimental nondiscogenic
low back pain indicate that validity is questionable.“Exact” pain only
Tested only in clinical studies without follow-up to
conrm outcome or other gold standard. Radiologic
reliability best with computed tomography scan after
disc injection compared with radiograph alone. Validity
of additional criteria as conrming true-positive test
unknown; positive injection in discs without anular
disruption more common in psychologically disturbed
subjects.
Injections in morphologically normal discs seem to be
reliably negative even in subjects with serious
psychological distress and no back pain. Reliability in
other disc morphology unknown. Validity of this
additional criterion as conrming true-positive test
unknown.
Reliability and validity of this criterion as conrming
true-positive test unknown.
Small outcomes series suggest that low-pressure sensitive
discs are better treated with interbody fusion
techniques. Reliability and validity unknown.
Unvalidated concept based on anecdotal evidence.
Primary data unavailable to analyze.
Assumption is made that generalized hyperalgesic eect
may lead to multiple positive discs around single pain
generator.
It is unclear that pain tolerance to intradermal anesthetic
injection is valid test to determine “pain tolerance” in
patients with long-standing axial pain.
Some data suggest this is not an important technique.
No gold standard conrmation was applied.
test accuracy.
SECTION
II
these methods are not helpful in determining the true pain
generator among many degenerative structures.
Diagnostic Injections and Modulation of Pain Perception in Axial Pain Syndromes
Provocative discography relies on a patient’s subjective perception and report of pain aer a progressive pressurization
injection of a disc. Alternatively, a disc may be injected with
an anesthetic agent with subsequent documentation of the
patient’s subjective pain relief aer activities that usually
provoke pain. ese diagnostic injections seek to identify a
primary pain generator by provocative testing (stimulating a
potential site of pain, as in discography) or by temporary local
anesthetic relief. ese are subjective tests of pain perception
and are subject to the eects of volitional and neurophysiologic
modulation at multiple points along the neuraxis. Many
common factors are known to have potential dampening or
amplifying eects on the perception of back and neck pain.
ese factors must be considered when evaluating the validity
of diagnoses determined by diagnostic injections.
14–19
304 DIAGNOSIS
Adjacent Tissue Injury
Injury to adjacent tissues may increase the perception of pain
in surrounding structures by a local hyperalgesic eect. is is
a well-known phenomenon that occurs with any tissue
damage; it may amplify pain perception by increasing local
inammatory processes with secondary neurologic sensitization in areas not directly injured, such as the area surrounding
a burn or a fracture that is sensitive but without any thermal
or mechanical injury. is is an important phenomenon in
patients with low back pain and signicant disease at one or
more levels, which may sensitize the adjacent segments to
provocative testing (e.g., a spine that has undergone multiple
operations).
14,20
Local Anesthetic
Local anesthetic injections may decrease the perception of
pain at a local site. is is the specic, active eect used in
diagnostic blocks. is decrease in pain perception can also
be a source of confounding eects if the exact placement of
the agent is not well controlled. In addition to this direct local
eect, a nonspecic placebo eect and a neurophysiologic
modulation eect may occur. A relevant example is the eect
of local anesthetic blockade on the perception of painful
stimulus along the neuraxis proximal to the injection. A local
anesthetic injection in the lower extremity may be perceived
as relieving sciatica owing to disc herniation.21 is is not a
placebo eect (i.e., the phenomenon is seen only with an
active anesthetic agent) but rather an eect on neuromodulation. is eect is important in diagnostic anesthetic blockade
as a source of false-positive and false-negative ndings.
22
is eect may be regional or global and may be related to
neurophysiologic changes at multiple levels along the neuraxis.
Preexisting chronic pain syndromes are also associated with
depression, narcotic use, and habituation, which have independent pain perception eects. is eect has been shown to
have an impact on the pain intensity from discography in
experimental subjects.
14,23
Narcotic Analgesia and Habituation
Narcotic medications act at multiple levels to decrease pain
sensitivity thresholds, intensity, and aective response.
Administration of a narcotic medication may act as a common
confounder for diagnostic techniques that require accurate
feedback of pain perception from a patient.
14,24,25
Chronic
narcotic habituation may act to decrease pain tolerance in
the absence of increased narcotic intake. Narcotic habituation decreases endogenous abilities to modulate peripheral
nociceptive input. is eect is multifactorial. Chronic narcotic habituation is also associated with depression and sleep
disturbances.
Depression, Anxiety, and Somatic Distress
Clinical depression, anxiety disorders, and increased somatic
awareness may be seen as predisposing factors to chronic low
back pain syndromes or reactions to the pain and disability
of chronic low back pain illness, or both. In either event,
psychological distress usually decreases the pain threshold
perception and increases perceived pain intensity and aective
response.
chemical changes and systemic eects and have been shown
to aect pain responses in discographic evaluation.
5,24,26
ese eects are likely due to central neuro-
Tissue Injury and Nociception in Adjacent or Same Sclerotome
Tissue injury having the same or adjacent sclerotomal aerents
as lower spinal elements may increase pain sensitivity at any
given site. is eect is thought to be due to physiologic and
anatomic changes at the level of the dorsal root ganglion or
spinal cord ascending tracts. In animal models, single aerent
neurons from a dorsal root ganglion may innervate three
adjacent discs and a wide range of adjacent structures. is
eect is important in considering the specicity of discography
at sites of similar embryonic derivation to a known pathologic
structure (e.g., nonunion, spondylolisthesis, painful iliac crest
bone gra site). e confounding eect of this phenomenon
in discography has been experimentally and empirically
shown (discussed later).
14,23
Chronic Pain Syndromes
Chronic pain syndromes may complicate the evaluation of low
back pain. Chronic pain from regional sites that are near the
lumbar spine (chronic pelvic pain, irritable bowel syndrome,
failed hip arthroplasty) or distant to the lumbar spine (chronic
neck pain, chronic headache, temporomandibular joint syndrome) may increase pain sensitivity at lower spinal elements.
Social Imperatives
Overriding social imperatives may result in a decreased pain
perception or a dissociation of pain perception and functional
loss. A decreased pain perception or even an absence of pain
perception despite injury can be seen during some short-term
stressful events, such as in accident victims, soldiers in combat,
or individuals in certain training environments. Even over
long periods, social and cultural factors reinforce low painperception reporting and muted or absent pain behaviors.
Social Disincentive
Secondary gain issues may exaggerate pain responses of all
types. When the intensity of pain behavior and report is correlated with a real or perceived social benet or monetary
compensation, the reported pain perception and pain behavior may be increased. is situation can have direct eects
on provocative testing (e.g., discography) and the need for
a specic anatomic diagnosis to establish social validity of
an ongoing “sick role.” A real-world example of social disincentive exists in patients who have sustained a work-related
injury that requires an extended course of evaluation and
treatment.
Chapter 17 Discography 305
Summary
When considering the diagnostic certainty of a possible pain
habituation, depression, and compensation issues (social disincentives). In this case, a common mild backache pain generator is amplied to become a catastrophic illness.
generator in chronic axial pain illness, it is necessary to view
the aforementioned confounding factors for contribution to
the illness behavior observed (Table 17.2). An injured soldier
with facial trauma, aer narcotic administration and in the
Evidence for Validity and Usefulness of Provocative Discography
heat of combat, may mask the perception of a signicant low
back pain injury that otherwise could be clearly symptomatic.
In this case, a bona de local pain generator results in little
pain perception. Conversely, a very minor nociceptive input
(common backache) from a disc can be amplied in the case
of a patient with multiple chronic pain syndromes, narcotic
TABLE 17.2 Neurophysiologic Factors Inuencing Result of Diagnostic Injections
Modulator of Diagnostic
Injection Eect Type of Eect on Pain Perception at Site of Injection Diagnostic Eect
Adjacent tissue injury Increased regional pain perception Decreased specicity in provocative injection
Local anesthetic Decreased pain perception at depot site and sometimes in
sclerotomal or referral pattern
Tissue injury in adjacent or same
sclerotome
Chronic pain syndrome Increased generalized pain perception Decreased specicity in provocative injection
Narcotic analgesia Decreased generalized pain perception and aective response Decreased sensitivity and increased specicity
Narcotic habituation Increased pain perception and exaggerated aective response Decreased specicity in provocative injection
Depression, anxiety, and somatic
distress
Social imperatives Decreased pain perception, suppressed aective response Decreased sensitivity and increased specicity
Social disincentives Specic increased pain reporting and demonstration of pain
Increased regional pain perception Decreased specicity in provocative injection
Decreased generalized pain perception and unpredictable
aective response
behavior
Sackett and Haynes have described the criteria for an evidencebased evaluation of diagnostic test validity.27 Four phases of
scientic scrutiny and evidence in discography research are
shown in Table 17.3. ese phases of evidence progress from
the simple comparison of testing in subjects known to have
Decreased specicity in provocative injection
of provocative injections
Decreased specicity in provocative injection
of provocative injections
Decreased specicity in provocative injection
SECTION
II
TABLE 17.3 Four Phases of Evidence-Based Criteria for Evaluation Diagnostic Tests
Phase of Study Strategy Discography Evidence
Phase I Diagnostic test compared in subjects with index
disease vs. results in complete normals
(experimental setting)
Phase II Evaluation of range of test results in subjects with
disease (establishes positive result guidelines)
compared with known normals
Phase III Diagnostic test applied in clinical subjects likely to
have disease (clinical setting of test application in
subjects with similar presentation, signs,
symptoms, and risk factors)
Phase IV Does having the diagnostic test result improve
outcomes compared with management without
test result (controlled trial)?
Data from Sackett D, Haynes R. Evidence base of clinical diagnosis: The architecture of diagnostic research. BMJ. 2002;324:539–541.
PPV, positive predictive value.
Few painful disc injections in completely normal asymptomatic subjects (e.g.,
normal psychometric testing, normal disc morphology, no chronic pain
issues, no compensation issues)
Examples: Walsh et al., 19903; Carragee et al., 2000
Wide range of pain reactions to injections in asymptomatic subjects
depending on psychological status, disc morphology, chronic pain issues,
compensation issues. Wide overlap between asymptomatic subjects and
patients with presumed discogenic pain.
Examples: Carragee et al., 200016; O’Neill and Kurgansky, 200423; Carragee
et al., 2006
Poor validity testing subjects with persistent low back pain with known
nondiscogenic pain syndromes (e.g., iliac crest pain) or asymptomatic disc
pathology (i.e., previous disc surgery). PPV approximately 50% in ideal
patient, PPV <50% in typical discography patient (outcome ndings).
Examples: Carragee et al., 199915; Carragee et al., 200035; Derby et al., 200536;
Carragee et al., 200237; Carragee et al., 2006
Little to no evidence of provocative discography improving outcomes
compared with modern diagnostic techniques.40 Substantial evidence
provocative discography is worse than anesthetic injection alone.42
Substantial evidence discography may worsen outcomes in certain at-risk
groups.
38
44–46
16
43
306 DIAGNOSIS
a disease with subjects who are completely normal without
any signs, symptoms, or morbidity associated with the disease
(phase I) to the blinded study of a diagnostic test in determining outcomes in actual clinical therapeutic intervention
(phase IV).
An example of a phase I diagnostic study is the classic study
of discography by Walsh and colleagues3 in asymptomatic
healthy young men without signicant degenerative disease
or comorbidities associated with chronic low back pain illness
(e.g., depression, chronic pain behavior, compensation issues).
Discography seemed to perform well in this phase I study, with
little pain provocation in the subjects with a lack of disease (one
of 10 subjects [10%; 95% condence interval, 0–40%] had pain
intensity rated “bad”). In phase II and III studies, comparing
subjects without low back pain illness but with signicant
comorbidities, discography did not perform as well.
15,16
Generally, there has been limited high-quality evidence
supporting provocative disc injections. Despite the limited
evidence, some authors believe that primary discogenic pain
is the most common cause of chronic low back pain
12,13,28,29
illness.
As is shown subsequently, a major constraint in
this research has been a failure to use a bona de gold standard
for primary discogenic pain causing low back pain illness
against which investigators document that the diagnosis suggested by discography is correct.
Validity of Discography
Discography purports to diagnose the presence or absence of
a disc lesion responsible for the syndrome of chronic low back
pain illness caused by primary discogenic pain. ere is no
commonly used gold standard or criterion to determine who
actually has chronic low back pain illness from primary discogenic pain. ere are well-accepted standards, however, for
who does not—someone with no evidence of signicant low
back pain. Similarly, someone with new pain resulting from
another process (pelvic fracture) does not have “chronic low
back pain illness caused by primary discogenic pain.” Provocative discography can be assessed by the results of disc injections in subjects who denitively do not have chronic low back
pain illness caused by primary discogenic pain.
Alternatively, a patient’s response to treatment may be
considered a surrogate gold standard if the treatment denitively removes the pain generator (the disc) and adjustments
can be made for surgical and nonspecic limitations of the
treatment. e following section describes a series of clinical
and experimental studies that have attempted to dene the
specicity of discography in dierent at-risk subgroups.
Specicity of Positive Discography: Testing on
Subjects With No Axial Pain History
Careful technique and the standardization of discography
were believed by many discographers to have reduced the
false-positive rate to a negligible level in experienced hands. In
1990, Walsh and colleagues3 performed a carefully controlled
set of discographic lumbar injections in 10 paid volunteers,
all asymptomatic young men (mean age, 22 years) with little
disc degeneration. Of 30 discs injected in this asymptomatic
group, ve produced “minimum” pain (16.7%), two produced
“moderate” pain (6.7%), and one produced “bad” pain (3.3%).
Based on these data, the authors believed that the risk of
false-positive injections was very low. is study is frequently,
and incorrectly, cited to conrm a 0% false-positive rate.
In 1997, a review of one discography practice26 found cases
that seemed to be clinically apparent false-positive cases. ese
injections were believed to meet full criteria for discogenic
pain, with concordant, painful injections and negative control
injections. Clinical follow-up revealed other causes of the
patients’ back pain illness, however, including spinal tumor,
sacroiliac joint disease, and emotional problems. Block and
colleagues30 related abnormal Minnesota Multiphasic Personality Inventory (MMPI) testing and Ohnmeiss and colleagues31
related abnormal pain drawings with “nonorganic” features,
suggesting possible false-positive discographic injections.
Other authors performed thoracic32 and cervical33 injections
in subjects asymptomatic for pain in those areas. Signicantly
painful injections were found to occur in approximately 30%
of these volunteers.
Following the Walsh protocol, Carragee and colleagues16
examined 30 volunteer subjects with no history of low back
pain who were recruited to undergo a physical examination,
magnetic resonance imaging (MRI), psychometric testing,
and provocative discography. e results showed that little
pain was elicited by injection of any anatomically normal disc.
Discs with advanced degenerative anular ssuring with dye
leakage to the outer (innervated) anular margins were more
commonly painful aer discography than less degenerative or
normal discs. e intensity of the pain reported by the subjects
with anular disruption was predicted by the presence of
chronic nonlumbar pain and abnormal psychological scores.
Only 10% of subjects without any other pain processes had a
positive disc injection by the Walsh criteria, but 50% of subjects with nonlumbar chronic pain had at least one positive
disc injection.
e interaction between pending compensation claims and
discographic pain was also signicant in this select group of
volunteers. Of the 10 subjects with positive injections, 8 had
contested workers’ compensation or personal injury claims,
with resulting litigation. Conversely, of 9 subjects with disputed litigation claims, 8 had positive injections (P < .0001).16
It was not found, however, that all subjects involved in previous work injury claims had similar rates of positive disc
injection. A history of an uncontested claim from a past
compensation injury and no pending legal action did not
predict signicant pain on disc injection. Given that no subject
in this study stood to have any secondary gain from positive
discography, the increased pain reporting in subjects with
unrelated but contested compensation claims is intriguing. It
is possible that the eect of the prolonged social turmoil
associated with a litigation dispute has the eect of diminishing one’s resilience to irritative stimuli. Another explanation
could be that persons with abnormally low pain tolerance are
more likely to have a legal dispute regarding the signicance
and damages associated with previous minor injury.
Chapter 17 Discography 307
Discographic Injections in Previously Operated Discs
Provocative discography is frequently used to evaluate persistent or recurrent low back pain syndromes in patients who
have had a posterior discectomy. e validity of interpreting
painful injections aer herniation is unknown despite its
common usage. Heggeness and colleagues34 reported on 83
postdiscectomy patients and found that 72% had a positive
concordant pain response on injection of the previously operated disc. is study did not address the possibility of false-
positive injections. All positive injections were assumed to be
true-positive injections for identifying the source of the
patient’s pain.
Using the same methodology developed by Walsh and
colleagues,3 a large study of discography in asymptomatic
patients aer discectomy for sciatica was performed.35 Painful
disc injections were frequently seen in the asymptomatic
postdiscectomy group. As in previous studies, a higher rate of
painful injections was seen in patients with abnormal psychological proles.
Validity of Concordance Report
Provocative discography is considered positive only when the
injection elicits the patient’s usual pain in quality and in location. e reliability of the test would be substantially supported
if patients could identify the quality of pain coming from a
particular disc and dierentially compare that sensation with
their usual pain. It is unclear to what extent similar neurologic
and behavioral factors may inuence the results in provocative
discography. It is possible that the disc stimulation in discography may also provoke a “concordant” pain response without
actually having located a true pain source. As discussed earlier,
there have been reported cases of individuals undergoing
discography who were diagnosed as having discogenic pain as
the source of their illness on the basis of positive concordant
disc injections, but who were subsequently shown to have
nonspinal sources for their pain.
is issue was investigated using an experimental model
to determine the response to disc injection in patients known
to have nonspinal back pain.15 Subjects were recruited to
participate in this study if they had no history of back pain
and were scheduled to undergo posterior iliac crest bone gra
harvesting for nonspinal problems, including appendicular
fracture nonunions or bone tumors. Most of these patients
experienced low back and buttock pain from bone graing
for several months postoperatively; this pain was in a similar
distribution to what is normally considered discogenic lumbar
pain. Discography was performed several months aer bone
gra harvesting; subjects were asked to compare the quality
and location of the disc injection pain with their usual iliac
crest pain.
Eight volunteer subjects were studied using the same
protocol as the Walsh and colleagues study.3 All subjects had
some disc degeneration on MRI, and 24 of the discs were
injected. Of the 14 disc injections causing some pain response,
ve were believed to be “dierent” (nonconcordant) pains
26
(35.7%), seven were “similar” (50%), and two were “exact” pain
reproductions (14.3%). e presence of anular disruption was
correlated with concordant pain reproduction (P < .05). Of
10 discs with anular tears, injection of seven elicited “similar”
or “exact” pain reproduction to the pain at iliac crest bone
gra harvest sites. By the strict criteria for positive discogra-
phy, four of the eight patients (50%) had positive injections:
e pain on a single disc injection was “bad” or “very bad,”
and the pain quality was noted to be exact or similar to the
usual discomfort. All subjects had a negative control disc. All
positive disc injections had anular ssures. Half of the positive
disc injections occurred at low pressures (< 20 psi).
15
Discography in Subjects With Minimal Low Back Symptoms
e ability of a test such as discography to discriminate a true
pain generator disc responsible for causing serious disabling
low back pain illness from another disc that causes only trivial
or clinically inconsequential backache is critical to the test’s
validity in clinical practice. Derby and colleagues36 performed
discography in a group of 16 subjects with occasional or
minimal low back pain, none of whom required current
medical care or were experiencing disability because of low
back pain. Of the 16 subjects, ve (31%) had a pain response of
5 out of 10 or greater, and two (12.5%) had a pain response of
6 out of 10 or greater. e subjects with more frequent benign
low back pain had more painful injections. None of these
subjects had abnormal psychological proles, compensation
issues, or chronic pain syndromes or had signicant secondary gain motivation to underreport pain. In this study, there
were signicant confounding methodologic issues that made
the results open to criticism. ese issues include using the
investigators’ employees and sta as the subjects of the study.
In another study, the Stanford group performed experimental discography on 25 volunteer subjects with no clinical
back pain illness; these volunteers had persistent low backache
unassociated with any physical restrictions that was not bad
enough to seek medical care.37 All subjects had normal psychological proles, but half had other chronic pain syndromes
that are risk factors for positive injections. In 36% of these
subjects with common backache, discographic injection of
one or more discs was signicantly painful and concordant.
All positive discs had anular disruption, and all had negative
control discs. By the usual proposed criteria, these were positive disc injections for clinically signicant discogenic pain
illness. Discs sensitive to low-pressure injections were found
in 28% of subjects.
Pressure-Sensitive Injections and Discography Validity
In some cases, dye injected at low pressures may cause signicant pain. Derby and colleagues9 labeled these “chemically”
sensitive discs as opposed to discs that are painful only on
injection with high pressures. ese authors theorized that
“chemically” sensitive discs are painful because of the exposure
of anular nerve endings or nearby neural structures to the
SECTION
II
308 DIAGNOSIS
Pain
somatization
Increasing risk factors
SUBJECTS WITHOUT LBP SUMMARY
80
60
40
20
Increasing injection pressure
Hypersensitive
Chronic pain syndrome
Psychological distress
Secondary gain issues
Narcotic habituation
FIG. 17.1 Hypothetical responses to pressurization of degenerative disc
depending on pain sensitivity and reporting biases of the patient.
“Normal”
Reduced
Social imperatives
Psychological reserve
Cultural norms
Low pressure number
Medium pressure number
Psychometric testing, chronic pain, litigation/contested
and anular disruption strongly predict painful injections.
0
Young
men
FIG. 17.2 Discography testing in asymptomatic subjects with varying risk
factors. Proportion of painful disc injections and painful injections at low
pressures seems to increase with increasing risk factors. DDD, degenerative
disc disease; LBP, low back pain; Post-op, postoperative. (Data from
references 15, 20, 29, and 36.)
Older +
DDD
Spine
Society
Chronic
pain
Post-op Disc
leakage of irritating substances. It is postulated that this pain
is incited by chemical leakage from the disc during daily
activities. Some theorize that the disc injections simulate this
chemical leakage. Low-pressure–positive discs are arbitrarily
dened as discs found to be painful at pressures less than 15
or 22 psi greater than opening pressures.
9,23
Derby and colleagues9 postulated further that disc injections eliciting pain
at higher pressures (> 50 psi), called “mechanically” sensitive
discs, physically distend the anulus and simulate mechanical
loading. In these discs, it is presumed that a mechanical
deformation of the anulus is the inciting painful event.
e use of pressure measurements has been postulated as
a means to decrease the risk of false-positive injections. is
assertion would be true if injections were rarely, if ever, positive at low pressures in subjects without true low back pain
illness. Previous neurophysiologic considerations suggest that
a pain and pressure prole for a given disc lesion may depend
on individual pain sensitivity and local pain processes not
related to the disc. Hypothetically, the pain and pressure
prole may be depicted as shown in Fig. 17.1. e presence of
the factors enumerated in Table 17.2 thought to have a desen-
sitizing eect would move the curve down and to the right,
whereas factors that increase pain sensitivity may move the
pain and pressure curve up and to the le.
Experimental work has corroborated this hypothetical
pain response. Discographic injections have been performed
with pressure measurements in asymptomatic or minimally
symptomatic volunteers.
3,16,35–37
Fig. 17.2 shows the proportion of painful injections at low pressures in volunteers with
varying risk factors for increased pain sensitization. It seems
from these and other data38 that low-pressure injections are
more likely positive in subjects with some type of chronic
pain state, psychological distress, and, presumably, a generalized sensitization to irritable stimuli. An increased perception
of pain at low-pressure injections seems to aect the pain
response even when the chronic pain state is not in the low
back region.
Evidence That Discography in Clinical Practice May Improve Outcomes
Many case series report that provocative discography is helpful
in management of patients with chronic low back pain illness.
ese are uncontrolled studies, however, and the relationship
of discography ndings to clinical outcome aer surgery is
speculative. When encountered, good outcomes may be the
result of nonspecic eects, natural history of the condition
independent of diagnosis or treatment, scrupulous patient
selection, or confounding ndings on standard imaging
studies. In a retrospective literature review, Cohen and Hurley39
compared outcomes of spinal fusions in studies that included
patients who had preoperative discography versus those who
did not have preoperative discography. e outcomes were not
signicantly dierent.
In the era before routine MRI use, Colhoun and colleagues40
retrospectively compared a series of fusions planned with and
without preoperative discography. In this study on patients
having surgery in the 1970s and early 1980s, there were no preoperative dynamic radiographs, MRI, or computed tomography
(CT). e authors reported better results in the discography
group. e two groups were not similar at baseline, however,
and the authors did not examine or account for potential biases.
One important bias in the study population is the fact that some
patients had preoperative discography, whereas some did not.
In the era before contemporary imaging techniques, this study
suggested that discography might assist in the evaluation of
patients before surgery. Even if this conclusion was true, this
paradigm is currently unusual given the widespread availability
of advanced imaging modalities in modern medicine.
Madan and colleagues41 did a retrospective review of consecutive patients undergoing spinal fusion performed by the
same surgeons, with and without preoperative discography.
e two groups seemed well matched for demographic, psychometric, and radiographic features. At a minimum of 2-year
Chapter 17 Discography 309
Percent
80
70
60
50
40
30
20
10
0
Final ODI <20 Final VAS <2
Clinical judgment plus provocative discography
Clinical judgment plus anesthetic disc injection
FIG. 17.3 Randomized clinical trial by Ohtori and colleagues comparing
the proportion of good outcomes for pain and function after single-level
spinal fusion in patients selected by best clinical judgment and provocative
discography with best clinical judgment plus anesthetic disc injection.
These were best-case scenario subjects in many respects: no worker’s
compensation cases, no road trac accident litigation cases, no high
somatic distress cases, no depression cases, all selected by very experienced
spinal surgeons in Japan. Outcomes are clearly inferior when discography is
used to select patients for fusion. ODI, Oswestry Disability Index, VAS, visual
analog scale. (Data from Ohtori S, Kinoshita T, Yamashita M, et al: Results of
surgery for discogenic low back pain: a randomized study using
discography versus discoblock for diagnosis. Spine. 2009;34:1345–1348.)
follow-up, there was no signicant dierence in outcome
between the two groups. e addition of discography to
radiographs and MRI did not improve outcomes compared
with radiographs and MRI alone.
A more recent randomized clinical trial compared outcomes of subjects having single-level fusion based on preoperative evaluation using provocative discography with subjects
having an anesthetic disc injection.42 In many ways, these
subjects were the best-case scenarios given the lack of psychological distress, depression, workers’ compensation cases, or
trac accident litigants. e discography was performed
using low-pressure injections. e outcomes in the discography group were uniformly worse than the group using an
anesthetic block to diagnose discogenic pain (Fig. 17.3).
Despite the number of dierent studies on provocative discog-
raphy, a phase IV evaluation (based on evidence-based criteria
as described by Sackett and Haynes27) of discography has not
been performed to date (see Table 17.3).
Clinical Outcome as a Gold Standard in Provocative Discography
From the evidence reviewed in this chapter, discography has
been shown to be frequently positive in asymptomatic subjects
and in subjects with pelvic pain owing to iliac crest harvesting.
It has also been shown to be frequently fully concordant in
subjects with clinically insignicant backache. ese ndings
suggest that there is limited experimental evidence to support
the premise that discography can accurately identify clinically
signicant lesions responsible for a patient’s chronic low back
pain illness. Direct assessment of a positive test against an
accepted gold standard, conrming a true-positive result, has
not been performed.
A common empirical gold standard would involve comparing
the test results with clinical surgical outcomes, assuming that
an excellent clinical outcome would conrm a true-positive
test. ere is concern, however, that an excellent clinical result
may overestimate the number of true-positive results because
of a placebo or nonspecic eect of spinal fusion or other
intervention. ere is also concern that clinical outcomes may
underestimate the number of true-positive tests because the
ability to achieve outstanding results is limited by patient-specic
variables (psychological distress or social issues preventing
recovery despite surgical cure of the lesion). Other concerns
include results tempered by operative morbidity or technical
limitations, which, in the best of cases, cannot achieve 100%
success in the ideal situation of an accurate diagnosis.
An attempt was made to control these variables (patientspecic variables and operative comorbidities) in a prospective
controlled study of spinal fusion for presumed diagnoses of
unstable spondylolisthesis versus discogenic pain diagnosed
by discography. Identical operative techniques were used, and
patients had no psychosocial comorbidities.43 Both groups
included only highly selected patients with 6 to 18 months of
severe low back pain, normal psychological testing, no previous
or concomitant pain syndromes, and no workers’ compensation or personal injury claims. All patients had either positive
discography at one level only and at low pressures (< 20 psi) or
unstable spondylolisthesis by strict radiographic criteria. All
patients were working full time before their low back problem,
and no patient was taking daily narcotic medications.
Both groups underwent an anterior spinal fusion with
posterior instrumentation and fusion. Two years aer surgery,
only 27% of patients in the discography group met stringent
criteria for clinical success compared with 71% of the spondylolisthesis group. Success was dened as full return to work
and recreational activities, pain scores on a visual analog pain
scale less than 2, Oswestry Disability Index score less than
15, and no daily medications for back pain. Even using less
rigorous outcome measures, 43% of the discography group
compared with 91% of the spondylolisthesis group reported at
least moderate improvement. Even aer controlling for operative
morbidity, the maximum proportion of true-positive discograms
in a best-case scenario (i.e., assuming normal psychometric
testing, no other chronic pain history, no compensation issues
or litigation, and single-level degeneration) was 40% to 60%,
with a false-positive rate of approximately 50%.
For less “ideal” patients, provocative discography may be
an extremely poor tool to select appropriate operative candidates. Freeman and colleagues,44 used CT and provocative
discography to select a wide range of typical low back pain
subjects for an intradiscal electrothermal therapy trial, including patients with psychometric distress and compensation
claims. ese investigators found no improvement compared
with control subjects. In a similarly designed trial, Pauza and
colleagues45 reported only slightly better outcomes even
though they excluded patients with psychological abnormality, workers’ compensation claims, or litigation claims.
SECTION
II
Abnormal MCS Normal MCS
18
16
14
12
10
310 DIAGNOSIS
PCS improvement (1 year)
PCS improvement (2 year)
Minimum clinically important
8
6
4
2
0
FIG. 17.4 Outcomes of spinal fusion when discography was used in
patient selection. Subjects with a positive discogram in the setting of
abnormal mental component scores (MCS) in the 36-Item Short Form
Health Survey were highly unlikely to improve or reach even minimum
clinically important change in physical outcomes. In contrast, subjects with
more normalized mental component scores had signicantly better
improvement in outcomes (P < .005). In this study, positive provocative
discography result in clinical subset of psychologically distressed patients
seems to select patients unlikely to improve with surgical treatment. PCS,
pain catastrophizing scale.
difference for PCS
Even more striking, Derby and colleagues46 found such
poor outcomes for spinal fusion aer provocative discography
in patients with abnormal mental component scores on the
36-Item Short Form Health Survey that the discography
seemed to preselect patients who were extremely unlikely to
have a satisfactory outcome. ese results, illustrated in Fig.
17.4, may be substantially worse than using alternative patient
selection strategies without discography (e.g., radiographs,
MRI, patient interview, or psychological screening).
Complications
Although there are many potential complications of any
invasive procedure, several potential complications of discography warrant specic discussion:
1. Infection: ere is a small but denite risk of discitis aer
percutaneous puncture and injection. e absolute risk is
dicult to calculate, but modern methods likely limit this
risk to much less than 1%. Double-needle techniques for
insertion, less irritating dye, and intravenous or injectable
antibiotics all have been postulated to decrease the infection risk.
2. Prolonged pain episode: Occasionally, patients may experience a prolonged episode of pain aer a disc injection. One
reason given for this phenomenon is the hypothetical displacement of brous repair over anular ssures owing to
disc pressurization.2 Other work has shown that 40% of
subjects with psychological distress at the time of injection
can have markedly increased back pain for 1 year aer
discography. is eect was not seen in subjects with
normal psychological proles.
3. Misleading diagnosis resulting in inappropriate or ineective
invasive treatments: As discussed previously, subjects with
one or more risk factors for false-positive testing may be
47
misdiagnosed as having primary discogenic pain as the
cause of their persistent low back pain illness. Patients
with abnormal psychometric testing undergoing surgery
based on this test are extremely unlikely to have substantial
benet from disc-directed interventions (see Fig. 17.4)
and are exposed to the hazards and morbidity of these
procedures.
46
4. Accelerated disc degeneration: In animal models, disc
puncture with a needle has provided a reliable model to
initiate rapid disc injury with structural changes similar
in some respects to naturally occurring disc degeneration.
Working with a large animal model, Korecki and colleagues48 showed that relatively minor disruption in the
disc from even a 25-gauge needle puncture injury had
“immediate and progressive mechanical and biologic
consequences with important implications for the use of
discography….” Similarly, Nassr and colleagues49 showed
that needle puncture in cervical discs during cervical spinal
surgery localization radiographs was apparently associated
with a threefold risk of rapid disc degeneration. Carragee
and colleagues50 performed a prospective, matched-cohort
study of disc degeneration progression over 10 years
with and without baseline discography. e investigators
performed a protocol MRI and L3–L4, L4–L5, and L5–S1
provocative discography at baseline in 75 subjects without
serious low back pain illness. e investigators enrolled a
matched group at the same time and performed the same
protocol MRI examination. Subjects were followed for 10
years. At 7 to 10 years aer baseline assessment, eligible
discography and control subjects underwent another protocol MRI examination. MRI examinations were scored
for qualitative ndings (Prrmann grade, herniations,
endplate changes, and high-intensity zone). Loss of disc
height and loss of disc signal were measured by quantitative
methods (Fig. 17.5). e investigators found that modern
discography techniques with small-gauge needle and
limited pressurization resulted in accelerated disc degeneration, disc herniation, loss of disc height and signal, and
development of reactive endplate changes compared with
matched controls. e clinical follow-up of these patients
demonstrated even more concerning ndings in the study
subjects through 10 years.51 Despite some attrition related
to a 10-year study, 110 of 150 subjects were available for
all interval assessments. In these subjects, there was a
statistically signicant increase in the number of medical
visits, lumbar CT/MRI tests, and lumbar spine surgery in
the cohort exposed to provocative discography compared
to the control cohort (Fig. 17.6). ese data suggest that
lumbar provocative discography leads to an increased risk
of harm to exposed subjects.
Conclusions Regarding Provocative Discography
As for most diagnostic tests, the usefulness of discography is
aected by the characteristics of the population being studied.
As a provocative test depending on the subjective reporting of
A
40%
35%
30%
25%
20%
15%
10%
5%
60
10 mm
C
Chapter 17 Discography 311
SECTION
B
50
40
30
20
10
Disco
Control
II
0
New herniation
Disco
Control
P = 0.03
0
Progressed 1 or more grade
16
14
12
10
8
6
4
2
0
Disc height x
FIG. 17.5 Progression of disc degeneration in matched cohorts of subjects, discography (Disco) versus
nondiscography controls. Baseline versus 10-year follow-up magnetic resonance imaging studies were
compared for (A) progression of Prrmann grade, (B) development of new disc herniations, (C) loss of disc
height and nuclear signal, and (D) development of new Modic ndings or high-intensity zones (HIZ). In all
parameters, degeneration was greater in discography group. (Data from Carragee EJ, Don AS, Hurwitz EL, et al:
Does discography cause accelerated progression of degeneration changes in the lumbar disc: a ten-year
matched cohort study. Spine. 2009;34:2338–2345.)
Disco
Control
P = 0.05
P =
0.001
Signal loss
pain with injection, the central factors inuencing reliability
and validity of discography have to do with the neurophysiologic, psychological, and social factors that aect pain per-
ception and expression. In the subset of patients without
signicant confounding factors, the test may be more likely to
identify accurately a local pain generator as a primary cause
of disabling axial pain illness. In subjects with signicant
psychosocial risk factors or confounding neurophysiologic
factors, even the theoretical basis of the test is in doubt. Finally,
the ability of the test to improve clinical outcomes has not
been proven, and studies so far have been disappointing.
Serious risks of accelerated disc degeneration are also suspected aer disc puncture/injection and more recent clinical
data have corroborated this concern. e risk and benets of
this procedure must be carefully weighed.
PEARLS
Patient selection for discography is of primary importance in
1.
determining the accuracy and utility of the test.
2.
Results need to be interpreted in the context of the patient’s
entire medical history, including other chronic pain issues.
3.
It is extremely unlikely that a disc with a negative injection,
normal morphology, and no pain with the injection would be a
primary cause of serious low back pain illness.
35
D
30
25
20
15
10
P = 0.04
5
0
New Modic New HIZ
Disco
Control
P = 0.1
4. In the best-case scenario of a patient with no known risk factors
for a false-positive test, the positive predictive value of the test
is not greater than 50%.
5.
Most low back pain syndromes are multifactorial.
PITFALLS
During injection, it is important to avoid high-pressure injections
1.
(> 100 psi) because these may cause gross mechanical motion
of the segment or injure the endplate directly.
2.
In patients with psychological distress, disputed compensation
claims, or multiple chronic pain syndromes, the reported pain
responses to disc injection have not been shown to be reliable
or valid.
3.
There is clear risk of accelerated disc degeneration with
discographic injections and this disc degeneration may lead to
clinically signicant sequelae.
4.
Disc injections in patients with psychological distress may result
in an increase in back pain for weeks or months.
KEY POINTS
1. Provocative discography is a diagnostic test that may identify
primary “discogenic” pain if present in psychologically normal
patients without confounding pain or compensation issues.
2.
Patient responses to disc injection are subjective and strongly
inuenced by pain sensitivity and reporting variables, including
312 DIAGNOSIS
Untreated fraction (no lumbar surgery)
A
Incidence of > 5 one-week episodes
C
51
Year
Incidence of medical visits due to
E
1.0
0.9
0.8
0
0123 4
200
150
100
Discography
Control
Discography
Control
5678910
Year
*
1.0
0.9
0.8
0.7
*
Untreated fraction (no MRI or CT scan)
0.6
0
01234
B
250
200
150
Discography
Control
Discography
Control
*
5678910
Year
**
of LBP per 100 person-years
50
0
01 2
250
200
150
100
LBP - per 100 person-years
50
0
01 2
**
Discography
Control
Year
510
**
510
100
Incidence of work loss due to
50
LBP in days per 100 person-years
0
01 2
D
0
Year
FIG. 17.6 The comparative incidence of clinical variables in patients exposed to lumbar provocative
discography and controls over 10 years. Asterisks indicate statistically signicant dierence. (A) Surgery-free
survivorship (P = .016). (B) Imaging-free survivorship (P = .044). (C) Serious low back pain episodes (**P = .008
and *P = .016). (D) Work loss (P =.009). (E) Medical visits for low back pain (P = .002). CT, computed tomography;
LBP, low back pain; MRI, magnetic resonance imaging.