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Original Research |
1 Department of Radiology, Seoul National University, Bundang Hospital, 300
Gumi-dong, Bundang-gu, Seong Nam, Gyeongi-Do 463-707, South Korea.
2 Department of Radiology and Institute of Radiation Medicine, Seoul National
University Hospital, Chongno-gu, South Korea.
Received September 29, 2005;
accepted after revision November 3, 2005.
Address correspondence to S. H. Kim.
Abstract
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MATERIALS AND METHODS. Transforaminal epidural steroid injections were performed in 248 patients from June 2003 to May 2004. Fifty-six patients (33 women, 23 men; mean age, 53.3 years; age range, 30-83 years) were included. Therapeutic effects were evaluated 2 weeks after injection. The possible outcome predictors were as follows: intraepineural or extraepineural injection, saddle-type distribution pattern (contrast material distributed rostrally to the epidural portion of the preganglionic nerve root) or not saddle type, cause of sciatica (spinal stenosis vs herniated disk), patient age, patient sex, and duration of sciatica (acute or subacute [< 6 months] vs chronic [> 6 months]). The relationships between possible outcome predictors and therapeutic effects were analyzed. Statistical analysis was performed using Fisher's exact test, the chi-squire test, and multiple logistic regression analysis.
RESULTS. Forty-three (76.8%) of the 56 patients achieved a satisfactory result 2 weeks after transforaminal epidural steroid injection. Nineteen (65.5%) of the 29 patients treated by intraepineural injection and 24 (88.9%) of the 27 patients treated by extraepineural injection achieved a satisfactory result, and this difference was significantly different (p < 0.05). Other possible predictors of a better outcome were identified—that is, saddle-type pattern of contrast distribution, a herniated disk, and sciatica of less than 6 months' duration. Multiple regression analysis showed that the only factor significantly associated with outcome was the type of injection (p = 0.04, odds ratio: 5.01).
CONCLUSION. Transforaminal epidural steroid is an effective tool for managing sciatica, and an extraepineural injection may be a predictor of a better outcome for sciatica treated using transforaminal epidural steroid.
Keywords: CNS • interventional radiology • musculoskeletal imaging • sciatica • spine
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Many reports have been issued about the use of transforaminal epidural steroid in patients with sciatica; however, to the best of our knowledge, few reports are available about the outcome predictors of treatment with transforaminal epidural steroid, especially in terms of contrast distribution. In a cadaveric study, Pfirrmann et al. [6] classified the different types of contrast material distributions caused by intraepineural or extraepineural injection. We have also observed another pattern of contrast distribution that we refer to as the "saddle type"; this distribution pattern is defined as being present when contrast material is distributed rostrally with respect to the epidural portion of the preganglionic nerve root.
Our hypothesis was that because drug distributions differ in accord with observed contrast distributions, differences in contrast distribution influence the therapeutic efficacy of transforaminal epidural steroid. The objectives of our study were to assess the therapeutic effect of transforaminal epidural steroid for sciatica and to identify outcome predictors.
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During a 1-year period (from June 2003 to May 2004), 56 patients (33 women, 23 men; mean age, 53.3 years; age range, 30-83 years) who met all inclusion criteria were consecutively included in this study. Transforaminal epidural steroid injection was performed at the level of L2 in two, L3 in three, L4 in 16, L5 in 31, and S1 in four.
Technique
All therapeutic transforaminal epidural steroid injections were conducted
under biplane fluoroscopic guidance by two musculoskeletal radiologists
experienced in performing spinal interventions. All the injections were
performed as outpatient procedures, and informed consent was obtained from
each patient. With a patient lying prone, the tube was rotated obliquely to
ensure injection at the neural foramen site. The goal of positioning was to
allow a perpendicular needle track toward the classic injection site
underneath the pedicle in the so-called "safe triangle"
[6,
13]. The safe triangle is
defined by the pedicle superiorly, the lateral border of the vertebral body
laterally, and the outer margin of the spinal nerve medially. After the
patient's skin was disinfected, a local anesthetic was administered using a
25-gauge needle. With fluoroscopic guidance, a 12-cm, 22-gauge spinal needle
was then advanced into the safety triangle.
At the same time, a lateral view was obtained to verify that the anteroposterior position of the needle tip was appropriate. The needle position was checked using biplanar fluoroscopy, and this was followed by an injection of approximately 1 mL of contrast material (iohexol, 300 mg I/mL [Omnipaque 300, Amersham Health]). Posteroanterior and lateral spot radiographs were obtained to document contrast material distribution. Bupivacaine hydrochloride (0.5 mL/0.5% [Marcaine Spinal 0.5% Heavy, AstraZeneca]) and 40 mg (1 mL) of triamcinolone acetonide suspension (Tamcelon, Hanall) were slowly injected.
Two weeks after transforaminal epidural steroid injection, follow-up was conducted at our department. Follow-up at this time has been proposed in the literature and is based on the duration of the therapeutic effect of corticosteroids [6, 14]. To check the effect of the transforaminal epidural steroid, all patients were asked to refrain from drug or physical therapy for sciatica over the 2-week period after transforaminal epidural steroid injection.
Image Analysis
Radiographs obtained during transforaminal epidural steroid injection were
retrospectively analyzed. Contrast material distribution was graded by
consensus among three musculoskeletal radiologists, all of whom were
experienced in performing spinal interventions and were blinded to procedure
outcome. We classified contrast material distribution types, as described by
Pfirrmann et al. [6], as intra-
or extraepineural (Figs. 1A,
1B,
2A, and
2B). In cases of intraepineural
distribution, a tubular outline of the nerve root was seen. The contrast
material was well demarcated from the outer border of the nerve root.
Centrally, a feathery appearance was noted. The width of the area of
opacification was uniform. For cases of extraepineural distribution, the
contrast material outlined the nerve root as a tubular filling defect. There
was a sharp interface between the contrast material and the nerve root. The
contrast material tended to be less well demarcated in the periphery than
centrally. The width of the area of opacification was usually not uniform.
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Three musculoskeletal radiologists blinded to clinical outcomes retrospectively reviewed cross-sectional imaging studies by consensus. After reviewing cross-sectional images, the cause of the source of the sciatica was classified as spinal stenosis or disk herniation.
Review of Clinical Data
Retrospective reviews of patients' charts were performed by two other
radiologists who were not involved in image analysis. The effectiveness of the
transforaminal epidural steroid injection was determined using documented
patient satisfaction and visual analog scale (VAS) scores. Outcome measures
were collected before and 2 weeks after the injection. Treatment outcome was
measured using a 5-point patient satisfaction scale—that is, 0 for poor
satisfaction; 1, fair; 2, good; 3, very good; and 4, excellent. On the other
hand, the VAS scores ranged from 0 to 100. A successful outcome required a
patient satisfaction score of 3 (very good) or 4 (excellent) and a reduction
in the VAS score of more than 50% 2 weeks after transforaminal epidural
steroid injection. The patients with a successful outcome were described as
having experienced effective treatment.
Demographic variables, such as patient age and sex, were documented at an
initial clinical evaluation before treatment. For statistical analysis,
patient age was classified in one of six groups: < 29, 30-39, 40-49, 50-59,
60-69, or 
70 years. The duration of sciatica was classified as less than
6 months or as more than 6 months
[16].
Statistical Analysis
Potential predictors of the effectiveness of treatment with transforaminal
epidural steroid were intra- versus extraepineural injection, saddle-type
versus non-saddle type contrast distribution pattern, cause of sciatica
(spinal stenosis vs herniated disk), patient age, patient sex, and duration of
sciatica (< 6 months vs > 6 months). The Fisher's exact test was used to
examine associations except for age group, for which the chi-squire test was
used. Using the six variables mentioned, we also performed multiple logistic
regression analysis to rule out confounder effect. The analysis was performed
using SPSS software (version 10.0, Statistical Package for the Social
Sciences). A p value of less than 0.05 was considered statistically
significant.
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Several other marginal predictors of a better outcome were identified—namely, a saddle-type contrast distribution, a herniated disk, and less than 6 months' duration of sciatica. Forty-seven patients had a saddle-type appearance and nine, a non-saddle type. Thirty-seven patients with the saddle-type distribution pattern achieved a satisfactory result (78.7%) and six with the non-saddle type (66.7%) (p = 0.35). Spinal stenosis was considered the cause of sciatica in 34 patients and a herniated disk, in 22. Of those with spinal stenoses, 25 (73.5%) achieved a good outcome, whereas 18 (81.8%) of those with a herniated disk achieved a good outcome (p = 0.35). Transforaminal epidural steroid injection was least effective in patients in the age subgroup of 70 years old or older (42.9%) (p =0.2). Twenty-five (75.8%) of 33 women and 18 (78.3%) of 23 men achieved a good outcome (p = 0.55). In patients with acute or subacute sciatica, 26 (81.3%) of 32 achieved a satisfactory result; in those with chronic disease, 17 (70.8%) of 24 achieved a satisfactory result (p =0.28).
Multiple regression analysis identified only the type of injection—that is, intra- versus extraepineural injection—as being significantly associated with outcome (p = 0.04, odds ratio: 5.01).
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Several studies have isolated chemotoxic pain mediators, such as matrix metalloproteinase, the c-fos gene, phospholipase A2, and cytokines, that are overexpressed after disk herniation [20-23]. A study by Roberts et al. [24] showed a positive relation between disk degeneration and matrix metalloproteinase expression. In addition, in vitro studies simulating lumbar stenosis have shown that venous congestion, intraneural edema, and impaired axonal transport are present secondary to chronic compression [25-27].
Corticosteroids have been shown to be able to block nociceptive C-fiber conduction and to inhibit prostaglandin synthesis [28, 29]. Spinal stenosis is a condition that is usually associated with intermittent compression of nerve roots, which can lead to hyperemia; venous congestion; and, perhaps, the leakage of neurotoxic substances. Therefore, the rationale for corticosteroid use in epidural injections for the treatment of spinal stenosis is to impair prostaglandin synthesis, block nociceptive C-fiber conduction, and possibly alter nerve root blood and chemotoxic mediator flow [20-29].
In a prospective study, Weiner and Fraser [30] investigated the success of nerve root blocks in 28 patients with foraminal or extraforaminal disk herniation. In total, 22 (79%) of the 28 patients experienced a substantial, permanent reduction in pain. Narozny et al. [31] reported that transforaminal epidural steroid injection was effective initially in 26 (87%) of 30 patients with either disk herniation or spinal stenosis. In our study, we found that it was effective in 76.8% of patients with disk herniation or spinal stenosis. Although Narozny et al. reported that the therapeutic effect of a nerve root block was more pronounced in patients with discogenic nerve root compression than in those with foraminal (bone) stenosis, they found no statistical difference between the two groups. The patients with disk herniation in our study achieved slightly better outcomes than did those with spinal stenosis, but we found that this difference in outcome was not statistically significant.
In a cadaveric study, Pfirrmann et al. [6] revealed that a type 1 contrast material injection has intraepineural distribution and that a type 2 injection has extraepineural distribution. In that study, 13 (81%) of 16 patients who received a type 1 injection and 12 (86%) of 14 patients who received a type 2 injection experienced pain relief 2 weeks after treatment with transforaminal epidural steroid, which was not significantly different. However, those results contrast with ours, although Pfirrmann et al. enrolled a smaller number of patients and possible confounders were not considered. No other report, to our knowledge, about the clinical meaning of these different types of injection, as classified by Pfirrmann et al. [6], has been issued.
Why is an extraepineural injection more effective that an intraepineural injection? One explanation is that inflammation outside the epineurium of the nerve root causes radiculopathy and that drugs are delivered closer to the region of inflammation by an extraepineural injection. Another possible explanation is that an intraepineural injection may cause mechanical neuritis in the injected nerve root and thus cause persistent radiculopathy.
According to our results, saddle-type contrast distribution (rostral spread of injectate to contact the preganglionic portion of nerve root) might predict a good outcome. However, we found no statistical significance difference in outcome between patients with saddle-type contrast distribution and those with non-saddle type distribution to support this conclusion. We believe that this is because of the small number of patients with the non-saddle type distribution. In many cases of lumbosacral radiculopathy, the site of impingement lies rostral to the injection site. Lew et al. [15] recommended that because one cannot always guarantee a rostral spread of injectate to bathe the epidural and preganglionic portions of a nerve root, a preganglionic approach to the transforaminal injection at the level of the supraadjacent intervertebral disk should be taken (for example, L4-L5 disk level for L5 nerve root).
The present study is a retrospective analysis of patients with sciatica treated using transforaminal epidural steroid injection and is limited by its retrospective design.
In conclusion, the results of our study confirm that transforaminal epidural steroid is an effective tool for managing sciatica. Extraepineural injection may predict a better outcome in cases of sciatica treated using transforaminal epidural steroid.
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