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Vascular and Interventional Radiology |
1 From the Departments of Radiology (C.W.A.P., P.A.O., M.Z., J.H.) and Orthopedic Surgery, Spinal Surgery Service (N.B.), University Hospital Balgrist, Forchstrasse 340, CH-8008 Zurich, Switzerland; and Department of Radiology, Veterans Administration Medical Center, San Diego, Calif (D.J.T., D.R.). From the 1999 RSNA scientific assembly. Received October 9, 2000; revision requested November 24; final revision received June 15, 2001; accepted June 20. Supported by the Swiss National Science Foundation. Address correspondence to C.W.A.P. (e-mail: christian@pfirrmann.ch).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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MATERIALS AND METHODS: The contrast material distributions of selective nerve root blocks (SNRBs) in 36 patients (13 women, 23 men; mean age, 52 years; age range, 22–88 years) were graded by two radiologists in conference as type 1 (tubular appearance), type 2 (nerve root visible as filling defect), or type 3 (nerve root not visible). These patterns were correlated with pain reduction after 15 minutes and 2 weeks (with a visual analogue scale of 100-mm length). In addition, 30 nerve roots were injected with iodine-containing contrast material and blue dye in three cadaveric specimens. Radiographs were compared with anatomic sections.
RESULTS: After 15 minutes and 2 weeks, 75% and 86% of the patients, respectively, reported pain relief. Mean pain relief length after 15 minutes for type 1 distribution was 60 mm; for type 2, 44 mm; and for type 3, 22 mm; and after 2 weeks, it was 34 mm for type 1, 31 mm for type 2, and 57 mm for type 3. There was no correlation between early and late response. Pain during intervention was less pronounced in type 2 injection, compared with type 1 (P = .002). On the basis of anatomic sections, type 1 injection was intraepineural; type 2, extraepineural; and type 3, paraneural.
CONCLUSION: Therapeutic SNRB is effective in sciatica, but early response does not predict the effect after 2 weeks. Type 1 injections are more painful than type 2 injections.
Index terms: Contrast media, comparative studies • Nerves, interventional procedures • Nerves, roots • Nerves, sciatic
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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Selective nerve root block (SNRB) was described by Macnab (6) in 1971 as a diagnostic test for the examination of patients with negative imaging study findings and with positive clinical findings of nerve root irritation. For therapeutic purposes, in cases in which nonoperative treatment of intractable sciatica has been chosen, epidural steroid injection (ESI) is most commonly performed. However, the usually dorsally or caudally introduced epidural steroids are mainly distributed in the dorsal epidural space, although the primary goal is to reach the dural disk interface (7). The transforaminal application performed with SNRB should be more accurate in this regard. Moreover, the amount of corticosteroid and local anesthetic can be reduced compared with the amount of these agents administered with ESI (8). Fluoroscopy-guided therapeutic SNRB is therefore a good procedure for nonoperative therapy of intractable sciatica (7).
Although a standardized SNRB technique is used, in our experience, different patterns of contrast material distribution and pain provocation have been observed. We hypothesize that different appearances of the distribution of contrast material correspond to different anatomic sites in relation to the nerve roots and could, therefore, have an effect on treatment success. Moreover, potential unfavorable effects of intrathecal application of corticosteroids, such as arachnoiditis, have been discussed controversially in the literature (9–11). Because of the potential damage to the nerve root by the sharp needle tip, the tip should be placed close to the nerve root rather than in the nerve root sleeve. To our knowledge, the effect of different anatomic injection sites on the treatment success of the therapeutic SNRB has not been formally evaluated.
The objectives of this study were to relate different types of radiographic contrast material distribution to anatomic compartments by using cadaveric specimens and to relate the injection site to treatment-induced discomfort and therapeutic effect.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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The indication and determination of the therapeutic SNRB level was established by the spinal surgeon after all diagnostic test results had been obtained and after a discussion with the patient.
During a 1-year period, 36 patients (13 women, 23 men; mean age, 52 years; age range, 22–88 years) who met all criteria were consecutively included in our study. The therapeutic SNRB was performed at the L2 and L3 spinal levels in one patient each, at the L4 level in three, L5 level in 19, and S1 level in 12 patients.
Technique
All therapeutic SNRBs were performed as outpatient procedures without premedication. Informed consent was obtained. The procedure was performed by three musculoskeletal radiologists (C.W.A.P, M.Z., J.H.) experienced in spinal interventions in accordance with the standard protocol of the Orthopedic University Hospital Balgrist. The patients were lying prone, with the injected side elevated approximately at a 30° angle. The final degree of rotation was determined with fluoroscopy. The goal of positioning was to allow for a perpendicular needle tract toward the classic injection site underneath the pedicle, in the so-called safe triangle (7). 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 (7) (Fig 1). After skin disinfection, a local anesthetic was administered by using a 25-gauge needle. With fluoroscopic guidance, a 12-cm 22-gauge needle was then advanced through a short 4-cm 18-gauge needle to the region of the safe triangle.
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After the procedure, the patients usually experienced numbness in the dermatome, which is supplied by the injected spinal nerve. Sometimes muscle weakness occurred in accordance with the innervation pattern. All patients underwent a standardized program of intensive physical therapy, which included procedures for local pain relief and reconditioning exercises for the spinal muscle, for at least 6 weeks after the procedure.
Image Analysis and Monitoring of Effectiveness
All patients were monitored by means of a questionnaire that was completed 15 minutes and 2 weeks after the procedure. This monitoring is part of the institution’s quality control management. The use of the collected data is covered by an institutional review board waiver. Pain was assessed by using a visual analogue scale, which was presented as a line of defined length (commonly 100 mm) with anchors on either end. The patients were instructed to grade the sensation by placing a mark between the two anchors without being told about the precise distance between them. The left anchor was defined as no pain at all, and the right anchor was defined as unbearable pain. The distance between one of the anchors and the patient’s mark was then measured, and the patient’s sensation was expressed in millimeters of the maximum sensation (100 mm) (12).
For this investigation, the visual analogue scale was used in two ways: First, the amount of pain reduction was measured 15 minutes and 2 weeks after the therapeutic SNRB in comparison with the pain sensation before the procedure (left anchor, no change; right anchor, pain completely relieved). Second, pain provocation during the intervention was measured. The left anchor was defined as no pain provocation by the intervention. The right anchor represented the worst pain imaginable.
The radiographs obtained during intervention were analyzed at the end of the inclusion period. Contrast material distribution was graded in consensus by two musculoskeletal radiologists (C.W.A.P., J.H.) who were experienced in interventional procedures and who were blinded to the outcome of the procedure. The following are definitions of the types of contrast material distribution:
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Cadaveric Study
Three lumbar spines were harvested from three nonembalmed human cadavers (one woman, two men; ages at death, 72, 76, 81 years, respectively). The specimens were deep frozen at -40°C (Bio-Freezer; Forma Scientific, Marietta, Ohio) immediately after harvesting. In two specimens, the whole lumbosacral spine from T12 to the sacrum, and in one specimen, the lumbosacral spine from L4 to the sacrum, were available. The skin and the surrounding soft issues were left intact. All specimens were allowed to thaw for 24 hours at room temperature prior to the injections.
All available lumbar (n = 24) and sacral (n = 6) nerve roots were injected in the same fashion as that described for the patients. In addition, the iodinated contrast material (Omnipaque [iohexol, 300 mg of iodine per milliliter]; Nycomed, Princeton, NJ) was mixed with a blue dye to mark the injected area and with 1 mL of a 15% concentrated solution of gelatin to prevent further diffusion after the injection. The injections were performed randomly by one of two musculoskeletal radiologists (C.W.A.P, J.H.) experienced in spinal injections. For each injection, one of three target points in the safe triangle underneath the pedicle was targeted, as depicted in Figure 1 (site 1 at the medial border, site 2 in the middle, and site 3 at the lateral border of the safe triangle). The injection site and the radiologist performing the injection were randomly selected according to a table of random numbers. The correct position of the needle tip, according to the site defined in the protocol, was verified and recorded by the two radiologists in consensus.
After the injections, anteroposterior spot radiographs were obtained. All cadaveric specimens were immediately frozen at -40°C for at least 24 hours and subsequently sectioned with a band saw into 3-mm–thick sagittal sections. Two low-kilovoltage high-spatial-resolution contact radiographs of each section were obtained with a radiographic unit (X-ray System 43805 N; Faxitron X-ray, a division of Hewlett-Packard, Palo Alto, Calif) to precisely locate the contrast material, and each nerve root in all sections was photographed for the analysis of the distribution of the dye in relation to the nerve root. The radiographs obtained during the cadaver interventions were graded in consensus by the two musculoskeletal radiologists, who were blinded to the results of the analysis of the cadaver sections, in accordance with the same definitions as those described for the patients.
On all consecutive slab contact radiographs and anatomic sections, the distribution of the contrast material and dye in relation to the nerve root was recorded according to the following categories: intraepineural, contrast material or dye located inside the nerve root sleeve (Fig 6); extraepineural, contrast material or dye located around the nerve root with contact with the nerve root (Fig 7); and paraneural, contrast material or dye without any contact with the nerve root.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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Pain provocation length during intervention was 52 mm ± 41 with type 1 contrast material distribution, 14 mm ± 28 with type 2, and 31 mm ± 29 with type 3 (P = .021, ANOVA) (Table 2). Pain provocation was significantly more pronounced with intraepineural contrast material distribution, as compared with the pain provocation with nonintraepineural contrast material distribution (P = .002, Tukey multiple comparison procedure).
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In 77% (23 of 30 cases) of injections, the injected substances were in contact with or within the nerve root. In the remainder of the cases, the contrast material was in close proximity to the nerve root but did not contact it. Injection in the safe triangle resulted in 23% (n = 7) of intraepineural injections (Table 4). Four of these (57%) injections were related to the injection into the medial part of the safe triangle (site one, Fig 1). Injection into the middle and lateral parts (in sites two and three) resulted in an intraepineural contrast distribution in only three (15%) of 20 injections.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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The antiinflammatory properties of corticosteroids are also well known (17). Their local application is considered to relieve reversible inflammatory changes or processes, such as vascular congestion related to mechanical obstruction (17,18). There has also been evidence that methylprednisolone has a local anesthetic effect (19). In an experimental animal study, it was reported that the effect of an ESI relates to the inhibition of phospholipase A2 activity (20). Moreover, it has been shown that most disk herniations gradually resorb on their own (21). Therefore, in the treatment of patients with intractable sciatica, nonoperative measures can be considered, and the use of a therapeutic SNRB to deliver corticosteroid locally appears to be rational (22). The object of the therapeutic SNRB is not to "cure" the patient by interfering with pathogenetic factors that are responsible for sciatica but rather to provide temporary relief from peak pain during the time required for spontaneous resolution of radiculopathy.
The ESI is the classic procedure for conservative treatment of sciatic pain. To reach an affected nerve root with a conventional epidural injection, a large amount of solution is necessary (8); up to 64 mL of total injection volumes have been described (7). Because the tissue surrounding the spinal nerve is considered to be an extension of the epidural space, the therapeutic SNRB may be considered to be a selective ESI (23), providing the same mechanism of pain relief with a much smaller amount of therapeutic agent. The smaller amount of fluid and the smaller dose of steroids that are used in the therapeutic SNRB reduce the risk of hypercorticism, hyperglycemia, and fluid retention. Moreover, ESI has a reported risk of 5% with the interlaminar approach and of 0.6% with the caudal approach for intradural injections; this procedure is also associated with the risk of an intravascular injection, a possibility that can be diminished, however, by using fluoroscopic guidance (24).
In our experience, therapeutic SNRB in the lumbar spine can be performed most conveniently with fluoroscopic guidance. Fluoroscopy-guided injections have been proven to be safe and fast injections in the axial skeleton (24–26). Our data suggest that the lateral part of the safe triangle is the best target point for the needle tip. The primary goal of using contrast material is to document the correct needle position and prevent inadvertent paraspinal, intravascular, intrathecal, or intraarticular injections (27). However, the diagnostic benefit of contrast material injection in the identification of the site of the nerve root compression is doubtful (6,28). Pain provocation has also been used for diagnostic purposes. Typical pain reproduced by needle positioning and relieved by nerve root infiltration can aid in the confirmation of local root disease (29). However, this diagnostic test is not as reliable as pain relief with infiltration of a local anesthetic (23). Our data suggest that pronounced pain provocation can be a sign of intraepineural injection. For therapeutic purposes, pain provocation is unnecessary.
Otani et al (30) observed that the inflammatory effect of nucleus pulposus is only temporary. The inflammatory effect is most pronounced after 7 days and diminishes within 2 months. This could explain the relative benign and self-limiting course of sciatica in the majority of cases. Olmarker et al (17) also found, in an experimental pig model, that the nucleus pulposus–induced effects on nerve function may be reduced dramatically by high-dose methylprednisolone administration within 24–48 hours after epidural application of autologous nucleus pulposus.
The follow-up of 2 weeks chosen for our investigation has been proposed previously in the literature and relates to the duration of the therapeutic effect of the corticosteroids (31). After 3 weeks, the substance used in our investigation was completely metabolized. Most previous investigations of the duration of pain relief after spinal steroid injections had a short- or mid-term follow-up of as long as 3 months. Although most study findings indicate a markedly declining effect after 3 months (32), there is also evidence of a potential long-term effect (33), which was not investigated in patients in our study. When the therapeutic effect of therapeutic SNRB is assessed, confounding factors such as oral medication and intensive physical therapy have to be kept in mind. These factors, however, should not have influenced our results because they were standardized.
Seventy-five percent of patients in our study experienced pain relief 15 minutes after the procedure, and 86% reported a benefit after 2 weeks. Our results indicate that there is no need to inject corticosteroids and local anesthetics into the nerve root sleeve. Besides a potential mechanical impairment of the neural structure due to puncturing of the nerve with a sharp needle tip, an injection into the nerve root produces substantial pain, which can be avoided at least in part by peri- and paraneural injections. The effectiveness of extradural steroid injections, especially with regard to long-term success, has been discussed in the literature, although not without controversy (32,34,35). Nevertheless, the use of steroids for conservative treatment with short- and mid-term effectiveness is generally accepted (33,36). In our series, the mean pain reduction length 15 minutes and 2 weeks after the procedure was 47 mm versus 37 mm. Eighty-six percent of patients in our study had at least some pain relief after 2 weeks, which compares favorably to the results in a study in which ESI was used, which demonstrated that 62% of patients felt better 2 weeks after the procedure (31).
To our knowledge, major reversible complications or persistent structural damage to the nerve root has not been reported with SNRBs. In a prospective series of 139 diagnostic SNRB procedures, no major complications were recorded (37). In a series of 888 fluoroscopically guided spinal injection procedures (including EBI, SNRB, facet joint blocks, sacroiliac blocks, and lumbar sympathetic blocks), eight reversible complications occurred: three cases of subarachnoid needle placement, two allergic reactions to contrast material, one allergic reaction to local anesthetics, one vasovagal response with severe bradycardia, and one case of pain exacerbation (38). There is a potential risk of infection with spinal injections. To our knowledge, no case of infection with SNRB was reported. In our series, no complications occurred. In general, spinal injections are safe and accurate when performed with imaging guidance (24). Contraindications to the procedure are bleeding diathesis, suspected local infection (which could be unmasked by the steroids), and adrenal function that may be suppressed for 2–3 weeks (7).
In conclusion, the therapeutic SNRB is an effective tool for the treatment of pain in patients with sciatica. The early response of the procedure does not predict the effect after 2 weeks. Type 1 injections are intraepineural and are more painful than type 2 (extraepineural) injections.
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FOOTNOTES |
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Author contributions: Guarantors of integrity of entire study, C.W.A.P., J.H.; study concepts, C.W.A.P., J.H., D.R.; study design, C.W.A.P., J.H., N.B.; literature research, C.W.A.P., P.A.O.; clinical studies, C.W.A.P., J.H., M.Z.; experimental studies, D.J.T., C.W.A.P., J.H.; data acquisition, P.A.O.; data analysis/interpretation, C.W.A.P., P.A.O.; statistical analysis, C.W.A.P.; manuscript preparation, C.W.A.P., D.J.T.; manuscript definition of intellectual content, C.W.A.P., N.B., J.H.; manuscript editing, D.R., J.H.; manuscript revision/review, J.H., M.Z., D.R.; manuscript final version approval, J.H., D.R.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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