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Original Research |
1 Center for Spinal Surgery, University of Zurich, University Hospital Balgrist,
Zurich, Switzerland.
2 Department of Radiology, University Hospital Balgrist, Forchstrasse 340,
CH-8008 Zurich, Switzerland.
3 Department of Psychology, University of Berne, Berne, Switzerland.
Received June 30, 2004;
accepted after revision March 7, 2005.
Address correspondence to M. R. Schmid.
Abstract
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MATERIALS AND METHODS. Forty-two patients with chronic lower back pain who were undergoing facet joint blocks at one (n = 29) or two (n = 13) levels were analyzed. All patients underwent MRI or CT of the lumbar spine within 5 months before the facet joint blocks. The facet joint blocks were performed under fluoroscopic guidance. A small amount (< 0.3 mL) of iodinated contrast agent, 0.5 mL of local anesthetics and 0.5 mL of steroids, were injected. The initial pain response was prospectively assessed using a visual analogue scale. Additional data, including short-term effect (> 1 week) and medium-term effect (> 3 months), were collected by a structured telephone interview. CT and MRI were reviewed with regard to the extent of facet joint abnormalities. Multiple logistic regression analyses were conducted to identify outcome predictor for efficacy of facet joint blocks.
RESULTS. A positive immediate effect was seen in 31 patients (74%). A positive medium-term effect was found in 14 patients (33%). Pain alleviated by motion (p = 0.035) and the absence of joint-blocking sensation (p = 0.042) predicted pain relief. However, the extent of facet joint osteoarthritis on MRI and CT was not a significant predictor for outcome (p = 0.57-0.95).
CONCLUSION. Facet joint blocks appear to have a beneficial medium-term effect in one third of patients with chronic lower back pain and may therefore be a reasonable adjunct to nonoperative treatment. However, outcome appears to depend on clinical, not on morphologic, imaging findings.
Keywords: fluoroscopy • interventional radiology • musculoskeletal imaging • pain • spine
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The therapeutic efficacy of facet joint block in facet syndrome has not been as extensively evaluated as its diagnostic performance. Immediate pain reduction has been shown after injection of methylprednisolone and a placebo (saline) in 76% and 79% of injections, respectively [17]; however, after a follow-up period of 6 months, differences in pain relief (46% vs 15%, respectively) were found [17]. No outcome differences between intraarticular and periarticular injection of local anesthetics and methylprednisolone or saline injection were found [18, 19]. The authors of a literature review stated that there was no convincing evidence for the therapeutic efficacy of facet joint blocks in patients with lower back pain [20].
At our institution, facet joint blocks are routinely used to support nonoperative treatment for chronic lower back pain presumably due to symptomatic facet joint osteoarthritis. Our anecdotal perception is that a considerable proportion of patients report substantial pain relief after this procedure. However, there is a paucity of studies exploring the prediction of the therapeutic efficacy of a facet joint block. Selecting patients with chronic lower back pain who would benefit from a facet joint block would save health care costs.
The objective of this study was therefore to investigate outcome predictors of the short- and medium-term therapeutic efficacy of facet joint blocks.
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A total of 42 consecutive patients (32 women, 10 men; mean age, 61 years; age range, 39-88 years) who met these criteria were included in our investigation. Forty of the 42 patients presented with chronic lower back pain of more than 2 years' duration. The remaining two patients reported chronic (i.e., > 6 months' duration) lower back pain for a duration of less than 2 years. Twenty-nine patients had single-level facet joint blocks that were performed unilaterally in eight and bilaterally in 21 patients, respectively. In 13 patients, the facet joint block was performed bilaterally at two levels.
The target facet joints and sides were selected on the basis of clinical presentation and the presence of facet joint osteoarthritis according to previously published criteria that are valid for both CT and MRI [25].
The hospital's review board allows this type of retrospective study to be performed based on a general permit issued by the responsible state agency. Informed consent was obtained from all patients who fulfilled our inclusion and exclusion criteria.
Imaging Technique
All MR examinations were performed on a 1.0-T system (Expert, Siemens
Medical Solutions) with a dedicated receive-only spine coil. The imaging
protocol consisted of a sagittal T1-weighted spin-echo sequence (TR/TE,
700/12; section thickness, 4 mm; intersection gap, 0.8 mm; field of view, 300
mm; matrix, 512 x 512; 4 acquisitions), a T2-weighted turbo spin-echo
sequence (5,000/130; section thickness, 4 mm; intersection gap, 0.8 mm;
echo-train length, 15; 4 acquisitions), and an axial T2-weighted turbo
spin-echo sequence (4,000/96; section thickness, 4 mm; intersection gap, 0.8
mm; field of view, 300 mm; matrix, 512 x 512; echo-train length, 7; 2
acquisitions). CT scans were obtained using a single-detector helical CT unit
(Somatom Plus 4, Siemens Medical Solutions). The imaging parameters were 2-mm
slice thickness, 2.5-mm table feed, and a reconstruction increment of 2
mm.
Injection Technique
The technique we used is a modification of the one described by Bogduk et
al. [9]. All injections were
performed in our musculoskeletal radiology department either by an experienced
staff radiologist or by a radiology fellow. The facet joint blocks were
performed under fluoroscopic guidance with the patient lying prone. To
visualize the lumbar joints, either the patient was rotated appropriately and
supported in an oblique prone position or the image intensifier and tube were
tilted accordingly. Most commonly, a lateral-to-medial angulation of between
30° and 40° was necessary. In cases of L5-S1 facet joint block,
additional craniocaudal angulation was used to avoid a conflict of the needle
track with the iliac crest.
After appropriate disinfection, the skin over the target joint was anesthetized with 2-3 mL of mepivacaine 2% (Scandicain, AstraZeneca). A 22-gauge spinal needle was then inserted parallel to the X-ray beam, aiming at the joint space. In heavy patients, a coaxial needle technique was used, in which a 22-gauge needle was passed through a shorter 18-gauge needle. Depending on the specific situation (anatomic factors, presence or absence of osteophytes), either the midpoint or rather the cranial or caudal part of the joint was targeted. A minimal quantity of contrast medium (< 0.3 mL) was then injected under fluoroscopy to confirm the correct needle position (Fig. 1). Needle placement and contrast distribution were documented on standard radiographs.
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Measured Variables and Data Management
The patients were routinely followed up in the spine outpatient clinic,
typically 3-4 weeks after injection (mean, 23.7 days; range, 1-77 days). Based
on a chart review, five different domains were related to outcome—that
is, sociodemographic, general health indicators, clinical presentation,
technical aspects, and facet joint morphology. The initial (15-30 min) pain
response was prospectively collected using a visual analogue scale. For
immediate-term response analysis, we asked patients to score the degree of
pain reduction in relation to the pain level before the facet joint block. We
did not ask patients to provide a baseline visual analogue scale score before
injection.
Additional data were obtained by a structured telephone interview to complete the data from the chart review. Besides patient age, sex, and marital status, the following general health indicators were asked: general life satisfaction, general health, and whether the patient smokes. In addition, patients were asked about 17 clinical variables including the first episode and the number of episodes of lower back pain, maximum pain level, influence of different provocation movements, pain alleviation by motion, and joint-blocking sensation ("lumbar catch"). The interviewer of the structured telephone interview was aware of the facet joint block treatment without specific knowledge about the degree of facet joint degeneration. The following outcome variables were considered: pain reduction 15-30 min after injection (immediate effect); pain reduction for more than 1 week (short-term effect); and pain reduction for more than 3 months (medium-term effect). Responders were defined as those who reported a reduction in pain of more than 50%.
The imaging studies (CT and MRI) were reviewed by a musculoskeletal
radiologist with regard to the extent of facet joint abnormalities. The
following grading system was used (Figs.
2,
3,
4,
5): grade 0, normal width of
the facet joint space (2-4 mm); grade 1, narrowing of the facet joint space
(< 2 mm), small osteophytes, or mild hypertrophy of the articular process;
grade 2, narrowing of the facet joint space, moderate osteophytes, moderate
hypertrophy of the articular process, or mild subarticular bone erosions; and
grade 3, narrowing of the facet joint space, large osteophytes, severe
hypertrophy of the articular process, severe subarticular bone erosions, or
subchondral cysts. The grading of facet joint osteoarthritis was based on the
width of the facet joint space and the presence of osteophytes, articular
process hypertrophy, subchondral bone erosions, and subchondral cysts
[25]. Such assessment has been
reported to be reliable, with good interobserver agreement (
= 0.60)
[25]. Because there is good
agreement between MRI and CT with regard to facet joint osteoarthritis
[25], imaging findings were
not separately assessed for these two imaging methods.
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Statistical Analysis
For each outcome variable (i.e., immediate, short-term, and medium-term
effects) the population was divided into responders and nonresponders
(responders, > 50% pain reduction on the visual analogue scale). A
blockwise multiple logistic regression analysis, including a forward inclusion
criterion within each block of variables, was conducted to identify predictor
variables. All analyses were controlled for the effects of patient age and sex
(Table 1). The significance of
the differences between radiologic grades of osteoarthritis, immediate effect,
medium-term effect, and the duration of facet joint block were calculated
using Fisher's exact test (expected cell values were < 5 in more than 20%
of cells in most analyses, which prevented the use of the chi-square test and
analysis of variance). The statistical procedures were performed with SPSS
software (version 11.0, Statistical Package for the Social Sciences). Unless
stated otherwise, the level of statistical significance was set at 0.05
(two-tailed). Statistical tendencies (p < 0.10) were also reported
to identify all potential predictor variables that might prove to be
significant only in a larger patient population.
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Thirty-one patients (74%) experienced immediate pain reduction of more than 50%, eight of whom (19%) had complete disappearance of pain. After 1 week, 24 patients (57%) were still experiencing a pain reduction of more than 50%. The eight initially pain-free patients remained asymptomatic after 1 week. After 3 months (medium-term effect), pain relief of more than 50% persisted in 14 patients (33%). Eleven patients (26%) experienced no relevant immediate, short-term, or medium-term pain relief. After 7 days, three subjects who initially experienced no decrease in pain at all reported pain relief of between 20% and 45% that lasted up to 30 days.
There was no significant relationship between sociodemographic factors and positive response to a facet joint block (Table 1). Patients who were smokers were somewhat less likely to respond immediately to a facet joint block (p = 0.06). This tendency was more pronounced at short-term follow-up (p = 0.039). Patients in good general health were more likely to respond well after short-term follow-up (p = 0.054). Pain that was alleviated by motion was a positive predictor for a good immediate response (p = 0.035). Such pain was associated with higher grades of osteoarthritis (odds ratio = 9.27, p = 0.01, confidence interval = 1.70-50.60). Patients without joint-blocking sensations had a higher chance to respond at medium-term follow-up (p = 0.042).
If only the patients without the symptom of pain decreasing with motion had been injected, 52% (16 of 31) of patients instead of 67% (whole study group) would have been responders in the immediate term. This group showed no difference in medium-term outcome. If only the patients with the symptom of absence of joint-blocking sensation had been injected, 45% (9 of 20) of patients instead of 33% (whole study group) would have been responders in the medium term. When patients with absence of joint-blocking sensation and without pain decreasing with motion were selected (only four patients fulfilled these criteria), 75% and 100% would have been responders in the immediate and medium terms, respectively.
There was no significant immediate and medium-term difference between maximum and average grades of facet joint osteoarthritis (Table 2 and Figs. 6A, 6B, 7A, and 7B). Although patients with radiologic grade 1 facet joint osteoarthritis showed a shorter mean duration of pain decrease (86 days) compared with those with grades 2 (120 days) and 3 (117 days), this difference was not statistically significant (p = 0.69). In 28 cases, all injections were intraarticular, and in four cases only a periarticular injection was possible. In the remaining patients, a mixed intraarticular-periarticular injection of the selected joint was performed.
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To limit the facet joint blocks to a population with a positive medium-term therapeutic effect, outcome predictors after facet joint block are important. Interestingly, facet joint degeneration as diagnosed on either CT or MR images was not a predictor. No statistically significant difference in the medium-term effect between low- and high-grade facet joint osteoarthritis could be found in our investigation. However, patients with pain alleviation on motion and higher grades of osteoarthritis were more likely to respond immediately, indicating a correlation to symptomatic facet joint osteoarthritis. We also noted that patients without joint-blocking sensations had a higher chance to respond at medium-term follow-up (p = 0.042). A joint-blocking sensation is reported by the patient as a sudden catch in the back that resolves again after a few movements. Joint-blocking sensations can be interpreted as a clinical sign of instability. In this context, patients with that finding appear to respond less consistently to facet joint blocks because pain is not originating only from the facet joints.
If only patients with pain decreasing with motion and without joint-blocking sensation were injected, immediate and medium-term success (> 50% pain decrease) would have been achieved in 75% and 100% of patients, respectively. Only four patients in our study group fulfilled both criteria, and this combined evaluation of symptoms was statistically not significant.
Our study and previously published investigations have attempted to relate several clinical signs to the outcome of facet joint block. Jackson [26] and Jackson et al. [27] concluded that there were no such findings predicting injection response. Revel et al. [28] reported several predictor variables (i.e., age > 65 years, pain not exacerbated by coughing, not worsened by hyperextension, not worsened by forward flexion, not worsened when rising from flexion, not worsened by extension-rotation, and well relieved by recumbency) for a positive effect to lidocaine facet joint blocks. Our results showed different clinical predictor variables— decreasing pain during motion and absence of joint-blocking sensation—that seem to be related to a good facet joint block response. These results have a fairly high sensitivity (94%) but a low specificity (55%). Furthermore, there is a statistical trend for good general health (p = 0.054) to be predictive for a positive response and for smoking (p = 0.060) to be predictive for a negative response to a facet joint block.
We acknowledge the following study limitations. The retrospective pain assessment may decrease the reproducibility and validity of our results. Moreover, there was no control group receiving a placebo treatment. However, the presence and extent of the placebo effect have to be taken into account when discussing the efficacy of facet joint blocks [29]. In addition, it is unlikely that the natural history of lower back pain would positively influence the course in our patient group because of the fact that all but two patients had lower back pain for more than 2 years. In patients with chronic lower back pain [30, 31], natural history is unlikely to have a positive influence anymore.
This study shows a beneficial medium-term effect (> 3 months) in one third of patients with chronic lower back pain and facet joint blocks may therefore be a reasonable adjunct to nonoperative treatment. However, outcome appears to depend on clinical, not on morphologic imaging, findings. Further exploration of the therapeutic efficacy—particularly with regard to cost-effectiveness—is required to determine more conclusively the value of facet joint blocks in patients with lower back pain.
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