Download Lumbar zygapophysial (facet) joint radiofrequency denervation

The Spine Journal 8 (2008) 498–504
Clinical Studies
Lumbar zygapophysial (facet) joint radiofrequency denervation
success as a function of pain relief during diagnostic medial
branch blocks: a multicenter analysis
Steven P. Cohen, MDa,b,*, Milan P. Stojanovic, MDc, Matthew Crooks, MDa,
Peter Kim, MDd, CPT Rolf K. Schmidt, MDb, LTC Cynthia H. Shields, MDb,
LTC Scott Croll, MDb, Robert W. Hurley, MD, PhDa
a
Pain Management Division, Department of Anesthesiology & Critical Care Medicine, Johns Hopkins School of Medicine,
550 North Broadway, Suite 301, Baltimore, MD 21029, USA
b
Department of Surgery, Walter Reed Army Medical Center, 6900 Georgia Avenue NW, Washington, DC, 20307 USA
c
Pain Management Division, Department of Anesthesiology & Critical Care, Massachusetts General Hospital, Harvard Medical School,
15 Parkman Street, WACC 324, Boston, MA, 02144 USA
d
Department of Anesthesiology, University of Southern California School of Medicine, Los Angeles, CA, 90033 USA
Received 8 February 2007; accepted 24 April 2007
Abstract
BACKGROUND CONTEXT: The publication of several recent studies showing minimal benefit
for radiofrequency (RF) lumbar zygapophysial (l-z) joint denervation have led many investigators
to reevaluate selection criteria. One controversial explanation for these findings is that the most
commonly used cutoff value for selecting patients for l-z (facet) joint RF denervation, greater
than 50% pain relief after diagnostic blocks, is too low and hence responsible for the high failure
rate.
PURPOSE: To compare l-z joint RF denervation success rates between the conventional greater
than or equal to 50% pain relief threshold and the more stringently proposed greater than or equal
to 80% cutoff for diagnostic medial branch blocks (MBB).
STUDY DESIGN/SETTING: Multicenter, retrospective clinical data analysis.
PATIENT SAMPLE: Two hundred and sixty-two patients with chronic low back pain who underwent l-z RF denervation at three pain clinics.
OUTCOME MEASURES: Outcome measures were greater than 50% pain relief based on visual
analog scale or numerical pain rating score after RF denervation persisting at least 6 months postprocedure, and global perceived effect (GPE), which considered pain relief, satisfaction and functional improvement.
METHODS: Data were garnered at three centers on 262 patients who underwent l-z RF denervation after obtaining greater than or equal to 50% pain relief after diagnostic MBB. Subjects were
separated into those who received partial (greater than or equal to 50% but less than 80%) and
near-complete (greater than or equal to 80%) pain relief from the MBB. Outcomes between groups
were compared with multivariate analysis after controlling for 14 demographic and clinical
variables.
RESULTS: One hundred and forty-five patients obtained greater than or equal to 50% but less than
80% pain relief after diagnostic MBB, and 117 patients obtained greater than or equal to 80% relief.
In the greater than or equal to 50% group, success rates were 52% and 67% based on pain relief and
GPE, respectively. Among patients who experienced greater than 80% relief from diagnostic
The opinions or assertions contained herein are the private views of the
authors and are not to be construed as official or as reflecting the views of
the Department of the Army or Department of Defense.
Funded in part by the John P. Murtha Neuroscience and Pain Institute,
Johnstown, PA and the Army Regional Anesthesia & Pain Medicine
Initiative, Washington, DC.
1529-9430/08/$ – see front matter Ó 2008 Elsevier Inc. All rights reserved.
doi:10.1016/j.spinee.2007.04.022
* Corresponding author. Steven P. Cohen, MD, Pain Management Division, Department of Anesthesiology & Critical Care Medicine, Johns
Hopkins School of Medicine, 550 North Broadway, Suite 301, Baltimore,
MD 21029, USA. Tel.: (410) 955-1818; fax: (410) 614-7597.
E-mail address: [email protected] (S.P. Cohen)
S.P. Cohen et al. / The Spine Journal 8 (2008) 498–504
499
blocks, 56% obtained greater than or equal to 50% relief from RF denervation and 66% had a
positive GPE.
CONCLUSIONS: Using more stringent pain relief criteria when selecting patients for l-z joint
RF denervation is unlikely to improve success rates, and may lead to misdiagnosis and withholding a potentially valuable treatment from good candidates. Ó 2008 Elsevier Inc. All rights
reserved.
Keywords:
Denervation; Facet joint; Low back pain; Medical branch block; Predictive value; Radiofrequency; Zygapophysial joint
Introduction
Lumbar zygapophysial (l-z) joint pain is a challenging
condition affecting approximately 15% of patients with
chronic, axial low back pain (LBP) [1]. One of the biggest
challenges in managing l-z (facet) joint pain is the lack of
any standard, reliable treatment. Until recently, radiofrequency (RF) denervation of the nerves innervating the
l-z joints was widely considered to be the gold standard
for treating lumbar facet arthropathy, having been shown
to provide intermediate to long-term relief in patients
who positively respond to diagnostic blocks [2–4]. However, the publication of three consecutive negative trials
evaluating RF denervation for lumbar and cervical z-joint
pain has cast doubts as to the efficacy of RF lesioning [5–
7]. Whereas this has led some clinicians to question the
concept of RF lesioning for z-joint pain, others have implicated flaws in technique and selection criteria as the
likely causes for treatment failure [8–11]. One variable
yet to be examined for its relationship to RF treatment
outcome is the pain relief cutoff for designating a diagnostic block as ‘‘positive.’’ Several authors have claimed that
the identification of z-joints as pain generators is best accomplished only after complete or near-total relief of back
pain after low-volume diagnostic injections [12–15]. In
addition to the logic behind this assertion, this claim
seems to be borne out by an examination of prospective
studies evaluating medial branch RF denervation. Among
six prospective studies evaluating lumbar or cervical medial branch RF denervation that used near-total pain relief
after diagnostic blocks as an inclusion criterion, all reported excellent outcomes [14–19]. In similar studies using 50% pain relief as the threshold for lesioning, about
half reported positive outcomes [3–7,20]. Yet despite the
surface validity of this comparison, any conclusions that
can be drawn regarding the superiority of choosing a higher analgesic threshold for RF lesioning is limited by
a plethora of confounding variables including a lack of
direct comparison between outcomes based on the degree
of pain relief experienced after diagnostic blocks, publication bias, variations in RF technique and other selection
criteria, multiple publications by the same groups of authors, and the fact that most studies that used complete
or near-complete pain relief as an inclusion criterion evaluated cervical (rather than lumbar) z-joint denervation.
As a source of spinal pain, cervical z-joints have consistently been found to account for a higher percentage of
chronic neck pain than lumbar z-joints do in LBP
sufferers [1,21,22].
Perhaps most significant is that in almost all of the prospective studies using greater than or equal to 80% pain
relief as a cutoff value, either placebo-controlled or comparative local anesthetic blocks were used to minimize
the high false-positive rate of uncontrolled z-blocks, estimated at between 25% and 40% [23–26]. In a busy clinical
practice, the recommendation to use double blocks is often
disregarded on the bases that the definitive RF neurotomy
procedure carries a serious complication (eg, epidural abscess, meningitis) rate comparable to that of each diagnostic injection [1]; each diagnostic injection is associated with
a small but quantifiable false-negative rate [27]; and the use
of controlled diagnostic blocks is not cost effective [28].
This is the case in many academic pain clinics and military
treatment facilities, including our own. Even in the positive
studies whereby 50% pain relief was designated as the RF
threshold, because no subgroup analyses were performed, it
is possible that the beneficial effects were realized mostly
in patients who obtained nearly complete pain relief from
diagnostic blocks.
The question as to what the optimal cutoff should be before proceeding to RF lesioning is both clinically and academically relevant. To illustrate, withholding a definitive
treatment from someone who experiences only partial pain
relief from z-blocks but is nevertheless likely to benefit may
potentially lead to misdiagnosis, increased disability, unnecessary interventions, and amplified costs. On the other
hand, performing RF lesioning on patients who experience
partial pain relief from diagnostic blocks and are consequently predisposed to treatment failure exposes them to
unnecessary risks, wastes valuable resources, and threatens
the viability of the RF denervation because it undermines
the very concept of the procedure. To help determine the
optimal pain threshold to guide treatment in patients being
considered for RF denervation, we conducted a retrospective analysis of large, multicenter databases comparing outcomes between patients experiencing partial but significant
pain relief (greater than or equal to 50% but less than 80%) after diagnostic medial branch blocks (MBB) and those
who experience near-total relief (greater than or equal to
80%) after diagnostic injections.
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S.P. Cohen et al. / The Spine Journal 8 (2008) 498–504
Patients and methods
Permission to conduct this study was granted by the Internal Review Boards at three different institutions and all
patients who provided informed consent for the procedures.
The institutions participating in this study were Johns Hopkins Medical Institutions, Walter Reed Army Medical Center (WRAMC), and Massachusetts General Hospital. The
data collected for this study were garnered from the medical records of 298 consecutive patients who underwent
lumbar medial branch and L5 dorsal rami RF denervation
between July 2003 and July 2006 for suspected l-z joint
pain. Thirty-six subjects with ambiguous records or inadequate follow-up were excluded, leaving 262 patients
eligible for inclusion.
Patients were selected for diagnostic MBB based on presenting symptoms and physical examination. Inclusion criteria for MBB were age greater than 18 years, chronic LBP
greater than 3 months duration, and absence of focal neurological signs or symptoms. Excluded from consideration
were patients with Grade II or higher spondylolisthesis,
symptomatic spinal stenosis, vertebral fractures, untreated
coagulopathy, or concomitant medical or psychiatric illness
likely to compromise evaluation or treatment.
Lumbar medial branch and L5 dorsal ramus blocks
Diagnostic MBB were performed using our previously described single [29,30] and conventional multiple needle techniques [4,8,9,17]. Before needle placement, the skin at each
entry point was anesthetized using less than 1 mL of 1% lidocaine. Patient with unilateral pain underwent unilateral
blocks; those with bilateral or central pain received bilateral
blocks. The number of levels blocked varied according to the
patient’s symptoms. Correct needle placement was confirmed in both anteroposterior and oblique fluoroscopic
views after negative aspiration and contrast injection. At each
level, 0.5 mL of bupivacaine or ropivacaine was administered. No patient received intravenous sedation. Consistent
with most outcome studies [4,6,8,9,20,31,32], greater than
or equal to 80% pain relief during normal activities was used
as the criterion for a positive response to account for concurrent sources of back pain. All patients who obtained significant pain relief after MBB proceeded to RF denervation at
their next visit.
the diagnostic block was determined retrospectively by an
attending physician.
Radiofrequency denervation
RF denervation was performed as an ambulatory procedure using superficial local anesthesia and if necessary, intravenous sedation. With the C-arm intensifier positioned to
confer a slightly oblique or anteroposterior view, 22-gauge
SMK-C10 cannulas with 5-mm active tips (Radionics, Burlington, MA) were inserted parallel to the course of the
nerve until bone was contacted at the junction between
the superior border of the transverse process and superior
articular process for all medial branch lesions, and at the
junction of the ala and articular process of the sacrum for
all L5 dorsal ramus lesions. At each site, correct placement
was confirmed using electrostimulation at 50 Hz, with
concordant sensation achieved at less than 0.5 V. Before lesioning, multifidus stimulation and the absence of leg contractions were verified with electrostimulation at 2 Hz.
After satisfactory electrode placement, 0.5 mL of 1% lidocaine was injected through each cannula to reduce thermal
pain. The RF probe was then reinserted and a 90 second,
80 C lesion was made using an RF generator (Electrothermal 20S Spine System; Smith and Nephew, Andover, MA
or Radionics RF Lesion Generator System, Model RFG3C; Radionics, Valleylab, Boulder, CO).
Outcome measures
All pain scores were measured using a 0 to 10 visual analog scale or numerical pain rating score. A successful
treatment was defined as a greater than 50% or equal to average reduction in preprocedure pain score that persisted at
least 6 months after the procedure. For the WRAMC patient
subset, a secondary outcome measure, global perceived effect (GPE), was recorded based on the response to three
questions routinely administered to all patients in the pain
clinic. These questions were 1) My pain is better now than
before treatment; 2) The treatment I received improved my
ability to perform daily activities; and 3) I am satisfied with
the treatment I received and would recommend it to others.
An affirmative response to all three of these questions at the
6-month follow-up visit was considered a positive GPE.
A negative response to any of these questions constituted
a negative GPE outcome.
Grading of pain relief after medial branch blocks
Statistical analysis
Before the procedure and again in the recovery area, patients were instructed to engage in their normal daily activities and to maintain a written 0 to 10 numerical pain diary
every 30 minutes for 6 to 8 hours. In addition to pain
scores, diaries were used to monitor postblock activities.
The classification as to whether patients experienced partial
(greater than or equal to 50%, but less than 80%) or nearcomplete (greater than or equal to 80%) pain relief from
In addition to the aforementioned outcome measures,
other demographic and clinical variables recorded for analysis were age, sex, duration of pain, opioid usage, pain
referral pattern(s), presence of paraspinal tenderness,
presence of pain worsened by extension and/or rotation
(ie, ‘‘facet loading’’), magnetic resonance imaging evidence of l-z joint hypertrophy or degeneration, smoking
history, trauma history, presence of diabetes, obesity
S.P. Cohen et al. / The Spine Journal 8 (2008) 498–504
(defined as body mass index greater than 30), previous neck
surgery, laterality, and number of levels treated.
Statistical analyses were performed using STATA version 9.2 (Statacorp, College Station, TX) as in a previous
study [9]. The distribution of categorical variables in each
group was compared using Pearson’s chi-square. Continuous variables were compared with analysis of variance.
Categorical data are reported both by number of patients
and percentage. Continuous data are reported as mean
and standard deviation unless otherwise indicated. A p
value less than .05 was considered statistically significant.
Bonferroni correction was used for post hoc analysis. Data
were combined across institutions. Regression analysis was
used to quantify the association between the many possible
predictive variables and clinical outcome. Because the outcome variable was binary (either positive or negative), a logistic statistical model was chosen. Unadjusted univariate
analyses were performed, followed by multivariate logistic
regression. Variables found to be significant in multivariate
logistic regression in a previous publication [9] were
included in the multivariate model.
Results
Data were analyzed on 262 patients. Morphometric, demographic, and clinical characteristics were somewhat heterogeneous among the three treatment centers. WRAMC
patients were younger, more often male, and less likely to
smoke cigarettes, use opioids, or have a BMI greater than
30. Massachusetts General Hospital patients had a higher
incidence of paraspinal tenderness, ‘‘facet loading,’’ and
pain radiation below the knee. Johns Hopkins Medical Institutions patients had a higher prevalence of diabetes (Table 1). Because no statistically significant difference with
regard to treatment outcome between study centers was
found in either univariate or multivariate logistic analysis,
all data were combined.
The mean age of the subjects was 54.2 years (SD515.4,
range 17–89). Their average duration of LBP was 5.7 years
(SD55.9, range 0.5–40), and a slight majority (53%) were
female. Fifty-five percent of all subjects received greater
than or equal to 50% but less than 80% pain relief from
the diagnostic block. On average, subjects had three levels
treated with denervation (SD50.5, range 2–7). Overall,
54% of the subjects reported greater than or equal to 50%
pain relief persisting at least 6 months postprocedure, and
66% of the subjects reported a positive GPE.
No single demographic, physical symptom or sign was
associated with patient-reported differential pain relief after
diagnostic MBB in either univariate analysis, or when all
covariates were controlled for using multivariate logistic regression (Table 2). Greater pain relief from diagnostic
MBB (80% vs. 50%) was not associated with greater success as defined by greater than or equal to 50% relief of
pain persisting for 6 months after RF denervation
501
Table 1
Patient characteristics by study center
WRAMC
(n5155)
JHMI
(n567)
MGH
(n540)
p
Value*
Age in years, mean (SD) 51.2 (15.6) 57.1 (13.6) 61.2 (14.6) 0.002
Sex
0.09
Male
82 (53%)
27 (40%)
15 (38%)
Female
73 (47%)
40 (60%)
25 (62%)
Success
89 (57%)
36 (54%)
17 (43%) 0.24
Smoking
28 (19%)
21 (32%)
15 (38%) 0.02
Diabetes
14 (10%)
18 (27%)
3 (8%) 0.001
Scoliosis
16 (11%)
12 (20%)
11 (28%) 0.03
Location of symptoms
0.22
Axial
96 (62%)
31 (46%)
18 (45%)
Above knee/groin
37 (24%)
22 (33%)
8 (20%)
Below knee
22 (14%)
14 (21%)
14 (35%)
% Relief from
0.22
diagnostic block
50%
92 (59%)
35 (52%)
18 (45%)
80%
63 (41%)
32 (48%)
22 (55%)
Obesity
54 (36%)
36 (54%)
17 (50%) 0.03
Opioid use
35 (23%)
33 (49%)
15 (38%) 0.001
Failed back surgery
30 (19%)
11 (16%)
13 (33%) 0.11
syndrome
6 (6)
5.6 (6.5)
4.8 (4.4) 0.44
Duration of symptoms
in years, mean (SD)
Facet pathology on MRI
90 (68%)
40 (65%)
27 (68%) 0.86
Pain exacerbation by
88 (58%)
42 (68%)
31 (79%) 0.04
extension/rotation
(facet loading)
Paraspinal tenderness
78 (54%)
41 (66%)
35 (88%) 0.001
Number of levels
3.1 (0.5)
3.2 (0.6)
3 (0.3) 0.12
treated, mean (SD)
WRAMC5Walter Reed Army Medical Center; JHMI5Johns Hopkins
Medical Institutions; MGH5Massachusetts General Hospital; SD5standard deviation; MRI5magnetic resonance imaging; RF5radiofrequency;
ANOVA5analysis of variance.
Success defined as $50% pain relief persisting at least 6 months after
RF denervation.
Data are presented as number (%) unless otherwise specified.
* Age, duration of symptoms, and number of levels treated were
compared with ANOVA; categorical data were compared with Pearson’s
chi-square.
(p5.52). Additionally, greater pain relief from diagnostic
blocks was not associated with improved patient satisfaction as measured by GPE (p5.89). The lack of association
with either pain reduction by numerical pain rating score or
GPE persisted in multivariate analysis (p5.84 and p5.54,
respectively; Table 3).
Discussion
The principal finding in this study is that the degree of
pain relief obtained after diagnostic screening blocks does
not correlate with l-z joint denervation outcomes. It suggests that using 50% pain relief as the benchmark for a positive diagnostic procedure, which based on the current
literature is the most commonly used cutoff, leads to comparable success rates and superior overall outcomes (because it is more inclusive) than using more stringent
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Table 2
Patient characteristics by response to diagnostic block
Age in years, mean (SD)
Sex
Male (n5124)
Female (n5138)
Institution
WRAMC (n5155)
JHMI (n567)
MGH (n540)
Success (n5142)
GPE improvement (n5100)
Smoking (n564)
Diabetes (n535)
Scoliosis (n539)
Location of symptoms
Axial back pain only
(n5145)
Above knee/groin (n567)
Below knee (n550)
Obesity (n5107)
Opioid use (n583)
Failed back surgery syndrome
(n554)
Duration of symptoms,
mean (SD)
Facet pathology seen on
MRI (n5157)
Pain exacerbated
by extension/rotation
(facet loading) (n5161)
Paraspinal tenderness
(n5154)
Table 3
Factors associated with successful outcome*
Greater than
50% relief
(n5145)
Greater than
80% relief
(n5117)
53.1 (16)
55.5 (14.7)
63 (43.4%)
82 (56.6%)
61 (52.1%)
56 (47.9%)
92
35
18
76
60
31
21
25
63
32
22
66
40
33
14
14
p
Value
0.21
0.16
0.22
(63.4%)
(24.1%)
(12.4%)
(52.4%)
(66.7%)
(22.8%)
(15.2%)
(19.2%)
(53.8%)
(27.3%)
(18.8%)
(56.4%)
(65.6%)
(29.2%)
(12.3%)
(12.6%)
78 (53.8%)
67 (57.3%)
40
27
53
50
31
27
23
54
33
23
(27.6%)
(18.6%)
(38.4%)
(34.5%)
(21.4%)
(23.1%)
(19.7%)
(47.8%)
(28.2%)
(19.7%)
0.52
0.89
0.25
0.50
0.16
0.71
0.14
0.28
0.73
5.99 (6.6)
5.44 (5.0)
0.46
87 (67.4%)
70 (66.7%)
0.90
92 (67.6%)
69 (59.5%)
0.18
80 (58.4%)
74 (68.5%)
0.10
WRAMC5Walter Reed Army Medical Center; JHMI5Johns Hopkins
Medical Institutions; MGH5Massachusetts General Hospital; SD5standard
deviation; MRI5magnetic resonance imaging; GPE5global perceived
effect; RF5radiofrequency; ANOVA5analysis of variance.
Success defined as $50% pain relief persisting at least 6 months after
RF denervation.
GPE percentages calculated from a denominator of 151 patients ($50%
n590, $80% n561).
Data are presented as number (%) unless otherwise specified. Age,
duration of symptoms, and number of levels treated were analyzed with
ANOVA. Categorical data were compared with Pearson’s chi-square.
criteria for identifying RF candidates. Whether lower
thresholds might result in similar outcomes remains unknown because most previous studies used 50% pain relief
as the threshold for proceeding to denervation.
The rationale for using 50% pain relief as the criteria for
RF treatment has been elegantly outlined by Schwarzer
et al. [23], who cite the high incidence of concurrent spinal
pathology occurring with l-z joint degeneration as the primary reason. This is perhaps best illustrated by the work
of Fujiwara et al. [33], who found that whereas lumbar degenerative disc disease frequently occurs in the absence of
z-joint degeneration, the reverse is almost never true (ie, patients with severe l-z joint osteoarthritis virtually always
have radiologic evidence of degenerative disc disease
and/or other spinal pathology).
% Relief from diagnostic block
Failed back surgery syndrome
Duration of symptoms
Pain exacerbated by
extension/rotation
(facet loading)
Paraspinal tenderness
Successful
outcome
p Valuey
GPE
p Valuey
0.95
0.59
0.98
0.48
0.84
0.11
0.33
0.01
0.78
0.40
0.93
0.5
0.54
0.04
0.04
0.09
2.25
0.005
2.25
0.04
GPE5global perceived effect; RF5radiofrequency.
Success defined as $50% pain relief persisting at least 6 months after
RF denervation.
Failed back surgery syndrome, ‘‘facet loading’’ and duration of symptoms were significantly associated with negative outcome.
Paraspinal tenderness was significantly associated with positive
outcome.
* Data are presented as Odds Ratio (95% Confidence Limits).
y
p Values determined from adjusted multivariate logistic regression
analysis.
The impetus behind choosing more stringent denervation criteria seems equally compelling. MBB are inherently
nonspecific, even when low volumes are injected under
fluoroscopic guidance [1,34]. In a cadaveric study conducted by Kellegren [35] in the 1930s, the injection of as
little as 0.5 cc of contrast was found to encompass an area
of 6 cm2 of tissue. A later study by Dreyfuss et al. [36]
found that performing low-volume (0.5 mL) MBB using
conventional landmarks resulted in contrast spread into
the epidural space or intervertebral foramen in 16% of
cases, and between the cleavage plane of the multifidus
and longissimus muscles in all injections. In addition, the
excessive use of superficial anesthesia, intravenous or oral
sedation, and a host of other factors may contribute to analgesia unrelated to nerve blocks [1,37,38]. Thus, even
when RF denervation is flawlessly performed, the degree
of long-term pain relief achieved is unlikely to match that
which follows diagnostic MBB.
There are several explanations for our findings. First, the
group of patients who experienced near-total pain relief
may have contained a higher percentage of placebo responders than their counterparts who obtained only partial
pain relief. Whereas placebo responders might also be expected to positively respond to the definitive treatment,
the benefit is unlikely to be sustained for a prolonged time
period [4,39]. One method advocated to screen out placebo
(or false-positive) responders is to exclude patients who obtain prolonged, discordant pain relief after their diagnostic
block. Whereas some patients may experience prolonged
relief after MBB with local anesthetic secondary to a resetting of pain thresholds, most should not [24,40,41].
A second possible reason no difference was found in
outcomes is because once a certain analgesic threshold is
exceeded, a host of different confounding factors diminish
the relationship between the degree of pain relief experienced after blocks and the extent l-z joint arthropathy
S.P. Cohen et al. / The Spine Journal 8 (2008) 498–504
contributes to back pain. Secondary factors that may contribute to pain relief or the lack thereof after diagnostic
MBB include the use of sedation and/or supplemental analgesics, excessive use of superficial anesthesia, a patient’s
motivation to adhere to normal activities and maintain
a pain diary after the procedure, accuracy of needle placement, the aptitude of the injector, and a patient’s ability to
distinguish between their typical symptoms and procedurerelated pain [1,37,38]. Because the role each of these
factors plays varies on a case-to-case basis (ie, an anxious
patient might be more likely to increase their pain medications the morning of the procedure or require higher dosages of local anesthesia), it is difficult to control for one,
let alone all of these variables. Whether the same factors
that account for the high false-positive rate of uncontrolled
l-z blocks are also responsible for the imprecise correlation
between short-term pain relief after diagnostic MBB and
denervation outcomes has yet to be determined.
There are several flaws in this study that need to be addressed. First and foremost is its retrospective nature, which
fails to control for the plethora of potential confounding
factors. Yet controlling for these confounding variables
would not simulate realistic conditions, whereby anxious
patients do often preemptively self-medicate with sedatives
and/or analgesics, and patients who experience severe
procedure-related pain usually are administered larger
quantities of local anesthetic. Collecting data retrospectively also tend to result in more excluded subjects than
prospective analyses and less accurate measurements. However, the large size of this study and multiple sources of
data might conceivably serve to mitigate these effects.
Another shortcoming is that pain relief was classified
categorically instead of as a continuous variable. This
was deemed appropriate because of slight variations in
the way pain relief was assessed and diaries interpreted
(ie, in some cases patient comments were used to qualify
numerical pain scores) by the responsible attending physician. For obvious reasons, we also did not perform RF on
patients who experienced less than 50% pain relief after
the diagnostic blocks, although some of these patients
would have likely responded to treatment. Whereas classifying the response categorically may be more accurate in
some cases, it prevents the use of a receivers operating
characteristic curve to determine an optimal cutoff value
for RF lesioning. Future studies should attempt to address
this deficiency.
Finally, some may criticize the lack of controlled blocks
as a major flaw in this study. Whereas the use of double
blocks may have eliminated some placebo responders and
consequently resulted in a higher success rate, the total
number of successful outcomes would have also probably
been less. However, the presence of a purer target population may obviate the need to establish an optimal cutoff
point for definitive treatment. The goal of establishing an
ideal threshold is only relevant because of the low success
rates reported when single diagnostic blocks are used.
503
Thus, the 50% cutoff advocated here cannot be extrapolated
when the more stringent diagnostic criterion of a concordant
response to controlled or comparative local anesthetic
blocks is used.
In conclusion, the results of this study suggest that using
more stringent pain relief criteria when selecting candidates
for l-z joint RF denervation is unlikely to improve outcomes, but may lead misdiagnosis and the withholding of
a potentially beneficial treatment. Although our findings revealed 50% pain relief to be a better cutoff point than 80%
pain relief, the optimal threshold cannot be determined
from this study. Moreover, the results of this study should
not be misconstrued as evidence to support the efficacy
of facet joint RF denervation, for which better-designed,
controlled studies are needed. Prospective studies classifying the response to MBB as a continuous rather than a categorical variable, and that subject a wide range of
responders to RF treatment, are necessary to best determine
the ideal cutoff point for facet joint denervation.
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