Introduction

Spine pain is the most common of all chronic pain disorders, with a lifetime prevalence reported to be from 54 to 80 % [1–6]. Epidural steroid injections are one of the most commonly performed interventions to treat spine pain, and their use continues to grow. Medicare expenditures for epidural steroid injections increased by 629 % from 1994 to 2001, with a steep rise from 1999 to 2001 [7]. From 2000 to 2008, the use of epidural steroid injections more than doubled in the United States [8–11]. These procedures have been used to treat radicular pain from disc herniations and spinal stenosis, as well as axial spinal pain.

Access to the epidural space is achieved through a caudal, interlaminar, or transforaminal route [12, 13•, 14–19, 20••]. While all three deliver medication to the epidural space, there are substantial differences between the approaches.

Caudal access involves needle insertion through the sacral hiatus into the dorsal epidural space. It is considered the safest and easiest approach, with minimal risk of inadvertent dural, vascular, or intervertebral disc penetration compared to other routes of entry [21–27]. Injectate spread is typically limited to the lowest lumbar levels at conventional volumes used, and it is non-specific to the site of pathology [10, 28].

In the interlaminar approach, a needle is inserted between two adjacent laminae, through the ligamentum flavum, and into the epidural space. Since a specific spinal level can be accessed through this approach, medication is delivered into the epidural space at a closer proximity to the presumed site of pathology compared to a caudal injection [29–31]. Consequently, compared to caudal epidural injections, smaller volumes of injectate are often used for interlaminar epidural injections.

With the transforaminal approach, the needle is inserted along an oblique path through a neuroforamen in order to access the epidural space. The transforaminal approach is considered the most target-specific modality, as medication is placed in the ventral epidural space at a specific spinal level in close proximity to the exiting spinal nerve root and intervertebral disc [32]. Smaller volumes are typically used for transforaminal ESIs compared to both caudal and interlaminar injections [10, 28].

The most effective route of administration for epidural steroids has been a topic of debate [32–34]. The purpose of this review is to evaluate the most recent 5 years of randomized controlled trials detailing the efficacy of caudal, interlaminar, and transforaminal epidural injections for managing various types of spinal pain. Additionally, we will review recent literature directly comparing the different injection approaches.

The Role of Imaging in Epidural Injections

Prior to assessing efficacy, it is first necessary to demonstrate that a procedure reliably achieves its intended goal from a technical standpoint, in this case, accurate needle placement in the epidural space. Historically, interlaminar and caudal epidural steroid injections (ESI) have been performed without the use of radiologic guidance and contrast dye to confirm needle position and injectate flow in the epidural space [35]. However, the blind (non-image guided) injection technique has been repeatedly shown to be inaccurate.

Levin et al. [34] reviewed the available literature on medication placement accuracy rates of non-image guided epidural injections. Seven studies on caudal injection accuracy rates and five studies on interlaminar injection accuracy rates were reviewed. In each of these studies, needle placement in the epidural space was attempted without image guidance, and then contrast dye was injected under fluoroscopic guidance to determine if the needle tip was truly positioned in the epidural space. These authors found that 9–52 % of caudal injections were inaccurately placed, and 7–30 % of interlaminar injections were inaccurately placed [35–44].

In addition to needle placement outside the epidural space, simultaneous epidural and vascular needle placement can contribute to medication not reaching the intended target. Smuck et al. [45] found a 32.8 % incidence of simultaneous epidural and vascular injection during cervical transforaminal epidural injections. Injections at higher spinal levels were significantly associated with a greater likelihood of vascular injection [45].

More recently, in an attempt to avoid intravascular injection, some clinicians have used digital subtraction technology (DS) to facilitate visualization of inadvertent vascular uptake of contrast dye after needle placement. However, although transforaminal epidural injections are typically performed with fluoroscopy or CT guidance with contrast dye confirmation of epidural needle placement, DS is not routinely used to assess for incidental vascular uptake.

In a comparison between DS and real-time fluoroscopy for lumbar transforaminal epidural steroid injections (TFESI), Hong et al [46]. found that DS was superior to real-time fluoroscopy for detecting intravascular uptake. In this study, 249 TFESI were performed, and the overall intravascular contrast flow rate was 12.4 %. Real-time fluoroscopy failed to detect 9 out of the 31 cases [46]. Nonetheless, real-time fluoroscopy was successful in confirming needle placement without vascular uptake greater than 96 % of the time.

McLean et al. [47] used DS to study the rate of detection of intravascular injection in cervical TFESI. Subjects (n = 134) were randomized to receive an injection under real-time fluoroscopy with or without DS. Intravascular injection was detected in 17.9 % of cervical TFESI performed without DS [47]. By adding DS technology to the real-time fluoroscopic imaging procedure, the detection of vascular injection nearly doubled to 32.8 %, which was statistically significant (P = 0.0471) [47]. Interestingly, this was the same percentage of vascular injections that were found in Smuck’s study without the use of DS [45].

Given the high inaccuracy rates of non-radiologic guided injections with caudal and interlaminar approaches, as well as the sparse literature comparing DS with fluoroscopy or CT-guided ESI, the studies in this review were selected with the presumption that image-guided injections, regardless of approach, represent the most accurate methods for injecting into the epidural space. Therefore, assuming equivalent accuracy for needle placement during caudal, interlaminar, and transforaminal approaches, the relative efficacy of each method can be appropriately compared.

Methods

A comprehensive literature search of Medline (PubMed)® and Cochrane Central Register of Controlled Trials (CENTRAL) was conducted in order to identify randomized controlled trials evaluating the efficacy of caudal, interlaminar, and transforaminal ESIs published between January 1st 2009 and August 31st 2014. Search terms included, “Transforaminal Epidural Steroid injection”; “Interlaminar Epidural Steroid Injection”; “Caudal Epidural Steroid Injection”; and “Efficacy of Epidural Steroid Injection”. Works cited lists were then searched and cross referenced in order to identify additional appropriate articles.

Study Inclusion Criteria

  1. (1)

    Randomized Controlled Trial study design

  2. (2)

    Publication from January 1st, 2009–August 31st, 2014

  3. (3)

    Adult men and women (≥18 years)

  4. (4)

    Caudal, interlaminar, or transforaminal approach used to enter the epidural space

  5. (5)

    Image guidance used during injections

  6. (6)

    Follow-up a minimum of >3 months

  7. (7)

    Pain and Functional outcome measures used*

  8. (8)

    Categorical outcome measures of pain and function used (“responder analysis”)*

  9. (9)

    Publication in English

*7 + 8 recommended in NIH guidelines for low back pain clinical outcome research [48].

Results

Caudal RCTs

The trials of caudal ESIs published from 2009 to 2014 are summarized in Table 1 [13•, 14, 49–54]. The trial designs included randomized, double-blind, active-control trials (RDBACT), and randomized, double-blind, control trials (RDBCT). These studies were designed primarily for management of chronic low back pain with or without radicular symptoms related to lumbar disc herniation or central spinal stenosis. The efficacy of this procedure for the persistence of these symptoms post lumbar surgery was also evaluated in two trials.

Table 1 Summary of clinical trials published during 2009–2014 to evaluate effectiveness of caudal epidural injections in pain management
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In all studies assessed, primary outcomes included pain relief as measured by the Numeric Rating Scale (NRS) or Visual Analogue Scale (VAS), and functional improvement in pain measured with the Oswestry Disability Index 2.0 (ODI). Clinically significant pain relief was defined as ≥50 % reduction NRS or VAS score. A significant functional improvement was defined as ≥50 % reduction in ODI score.

The duration of follow-up was 12 months in five studies and 24 months in 4 studies. In all studies, subjects who received caudal epidural injection, regardless of whether the injectate included steroid or not, experienced a significant improvement in pain and function at both short- and long-term follow-up compared to pre-injection baseline. However, there were no statistically significant differences between the two groups at any follow-up interval. This was true for both comparison of group means and for categorical analysis of the proportion of responders in each group. Two studies that included only subjects with radicular pain due to a lumbar disc herniation showed significantly greater reduction in mean pain score reduction per procedure, as well as a significant reduction in the number of procedures required over the 2-year study period in favour of the steroid group [52, 53].

Only one study in the last 5 years compared caudal epidural injection to a true placebo (sham needle placement). In this study by Iversen et al., no significant improvement in pain, function, surgical rate, or use of physiotherapy was observed at 6, 12, and 52 weeks follow-up when comparing both epidural steroid and local anaesthetic alone groups to the sham needle placement group [13•].

Interlaminar RCTs

The trials of interlaminar epidural injections from 2009 to 2014 are summarized in Table 2 [56–70]. All study designs were either randomized, double-blind, active-control trials (RDBACT) or randomized, double-blind, controlled trials (RDBCT), and all were conducted by the same author. These studies were designed to address the management of various spinal pathologies of the cervical, lumbar, or thoracic spine.

Table 2 Summary of randomized controlled trials published during 2009–2014 to evaluate effectiveness of interlaminar epidural injections in pain management
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In all studies, patients were randomly assigned into two groups, group I or group II. Group I patients were treated with LA only, and Group II patients were treated with LA/Steroids. No study during the past 5 years compared interlaminar ESI to interlaminar sham needle placement.

Primary outcomes included pain relief as measured by the NRS and functional improvement measured by the ODI or the Neck Disability Index (NDI) if the study focus was on the cervical spine. Clinically significant pain relief was defined as ≥50 % reduction in NRS. A significant functional improvement was defined as ≥50 % reduction in ODI or NDI score.

All studies demonstrated that patients who received interlaminar epidural injections either with or without steroids showed a significant improvement in pain and function in both short- and long-term follow-up when compared to pre-injection baseline levels. However, only three studies showed statistically significant differences between treatment groups. All three evaluated the procedure for patients with chronic pain from a lumbar disc herniation and/or radiculitis [57, 63, 69].

In the 2010 study by Manchikanti that evaluated the effectiveness of lumbar interlaminar epidural injections in managing chronic pain of lumbar disc herniation with or without radiculitis the steroid group showed a significantly greater reduction in mean pain score at 6 months compared to the LA group (P = 0.001). Patients in the steroid group also had significant improvements in ODI scores at 6 and 12 months compared to the LA group (P = 0.019 and P = 0.045, respectively) [56].

Similar studies by Manchikanti in 2013 and 2014 also evaluated the efficacy of lumbar interlaminar ESI for the treatment of chronic low back pain with radicular symptoms due to lumbar disc herniation. The 2013 study showed significantly greater improvements in the steroid group for both mean pain reduction (P = 0.020) and mean functional improvement at 3, 6, and 12 months (P < 0.05) [63]. In the 2014 study, the steroid group was again found to have overall significantly greater improvement in mean pain reduction at 6 months and in ODI score at 6 and 12 months (P < 0.05) compared to the LA group [69]. None of the studies on interlaminar epidural steroid injections included a true placebo (such as the sham needle placement that was performed in the Iversen study [13•]).

Transforaminal RCTs

The trials of transforaminal epidural injections from 2009 to 2014 are summarized in Table 3 [20••, 71, 72]. All three trials focused on transforaminal epidural injections for lumbar disc herniation with radicular pain; however, they were performed using different methods and varying group comparisons. The primary outcome measure of >50 % pain relief from patient baseline was common among the three studies. Two measured functional improvement [71, 72], and one measured the number of injections required during the study period [71].

Table 3 Summary of randomized controlled trials published during 2009–2014 to evaluate effectiveness of transforaminal epidural injections in pain management of lumbar disc herniation
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The study by Ghahreman et al. [20••] investigated five different interventional groups: transforaminal steroids, transforaminal normal saline, transforaminal local anaesthetic, intramuscular steroids, and intramuscular normal saline. Notably, this is the only study in the last 5 years to compare transforaminal epidural steroid to a true placebo (intramuscular normal saline). A total of 150 patients were enrolled in the study and randomly assigned to one of the five treatments. Patients treated with transforaminal local anaesthetic showed the least improvement, with only 2 patients having 50 % pain relief at 1 month after treatment [20••]. The group treated with transforaminal ESI demonstrated the most robust improvement, where 15 patients experienced at least 50 % pain relief [20••]. This response rate was statistically significantly higher when compared to all other groups. Irrespective of the treatment, all patients who reported relief of pain also reported substantial improvements in physical functioning, social functioning, and disability [20••].

Kennedy et al. [71] performed a study that directly compared the efficacy of dexamethasone (a non-particulate steroid) with triamcinolone (a particulate steroid) for treating lumbar radicular pain due to acute disc herniation. Seventy-eight subjects were enrolled and randomized into one of the two groups. Although there was no placebo control, both treatment methods showed significant reduction in pain from pre-injection baseline; however, there was no significant difference in pain improvement between the two groups themselves [71]. A greater proportion of patients treated with dexamethasone underwent three injections, which was significantly higher than those treated with triamcinolone [71].

Manchikanti et al. [72] compared LA alone to LA/Steroid in subjects with unilateral radicular pain. One hundred twenty patients were enrolled and randomly assigned to one of the two groups. Similar to the results from their caudal and interlaminar studies, Manchikanti et al. again found no statistical difference in pain relief or functional improvement between the groups. The success rate of the subjects in the LA only group—72 % of subjects with greater than 50 % pain relief at 12 months—was vastly different compared to the same group in the Ghahreman study that showed only 4 % of patients as having 50 % pain relief at 12 months [20••, 72].

Looking at all three studies, transforaminal epidural steroid injections were shown to be an effective treatment for lumbar radicular pain in 32–76 % of patients at 6 months time [20••, 71, 72]. Of the successfully treated patients in each group, all showed significant improvement in function as well [20••, 71, 72].

Comparing Injection Methods

During the past 5 years, five randomized control trials directly compared the efficacy of an interlaminar and a transforaminal approach for lumbar ESI for low back pain with radicular symptoms. Depending on the study, the aetiology of symptoms included disc herniation [73–75], spinal stenosis [76], or both [77]. Three studies were reviewed (Table 4) and two studies were not included because of short-term follow-up that did not meet the criteria for this review [74, 76].

Table 4 Summary of randomized controlled trials published during 2009–2014 to evaluate effiectiveness of interlaminar compared to transforaminal injections
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A 2009 study by Lee et al. [77] compared the effectiveness of interlaminar and bilateral transforaminal epidural steroid injections for pain reduction in patients with axial back pain from herniated intervertebral disks (HIVD) and spinal stenosis (SS). While both the transforaminal and interlaminar epidural steroid injections provided significant pain reduction in subjects with HIVD and SS from 2 weeks to 4 months after treatment, in subjects with SS, the bilateral TFESI group showed a greater mean reduction in NRS score compared to the interlaminar group [77]. It is worth noting, however, that a successful outcome was measured as only a 2-point or greater decrease from baseline NRS. Also, there was no functional outcome measure and no categorical “responder” analysis reported in this study.

Two randomized control trials compared interlaminar and transforaminal ESIs specifically for lumbar radicular pain from disc herniations [73, 75]. In 2011, Rados et al. [75] randomized 64 patients with chronic unilateral radicular pain to receive a series of three interlaminar or transforaminal lumbar ESIs spaced 2 weeks apart. Pain and function were assessed at 3 and 6 months following the first injection using the visual analogue scale (VAS) and the ODI. Successful outcomes were defined as >50 % improvement in VAS or greater than 10-point change in the Oswestry scale. Mean improvements were seen in both groups through 6-month follow-up (P < 0.001). However, there was no statistically significant difference between the two groups with respect to the proportion of those with a successful pain and functional outcome (P = 0.774) [75].

In 2014, Ghai et al. [73] studied 62 subjects with chronic low back and unilateral radicular pain who were randomized to receive a lumbar ESI either through a parasagittal interlaminar (PIL) or a transforaminal approach. Outcomes included >50 % pain relief from baseline on the VAS and functional improvement by Modified Oswestry Disability Questionnaire (MODQ). These outcomes were measured at 2 weeks, 1, 2, 3, 6, 9, and 12 months, though the primary endpoint was effective relief at 3 months [73]. If pain returned, a maximum of 3 injections were given. Significant reduction in mean VAS and MODQ was observed at all intervals compared to baseline in both groups (P < 0.001) [73] with no differences between approaches at 3 months with regard to pain (P = 1.00) and functional outcomes (P = 0.60) [73].

Discussion

ESIs are used to treat several types of spinal pathologies, with caudal, interlaminar, and transforaminal injections as potential approaches for therapeutic treatment. As this review shows, epidural injections can be successful short-term and long-term treatments for a subset of patients with disc herniation with radicular pain, spinal stenosis, and postsurgery syndrome. However, this review also highlights the need for more direct comparison trials between injection types.

There has not been a direct comparison of the three injection routes published in the literature in the last 5 years. In fact, only one study to date by Ackerman and Ahmad [78] has directly compared the three routes for the treatment of lumbar disc herniation. In this study, 90 subjects were randomly assigned to a caudal, interlaminar or transforaminal treatment group and all received the same dose of triamcinolone and saline. At 2 weeks post-injection, all three groups had reduced pain scores, but the transforaminal group had a significantly greater reduction. Functional improvement was seen in all three groups without any significance between them. On average, subjects in the transforaminal group received fewer injections.

Although this is the only study comparing all three injection methods, slight favorability for transforaminal epidural steroid injections exists in the more recent studies mentioned in this review. Compared to the interlaminar approach for lumbar radicular pain, the transforaminal approach required a smaller steroid dose volume per injection [75]. This might be preferable for patients at risk of steroid side effects, such as the elderly, diabetics, and others receiving chronic steroids.

When interpreting data from the studies of each particular injection method individually, it is more difficult to discern which type of injection might be preferable. Most caudal studies and all interlaminar studies were completed by the same author, using the same methods, with relatively similar results throughout. More importantly, only the caudal study by Iversen [13•], and the transforaminal study by Ghahreman [20••], used placebo groups as a comparison. Interestingly, although the Ghahreman study did show that transforaminal epidural steroid injections are efficacious compared to placebo, these two placebo-controlled studies showed the lowest efficacy rates for the particular epidural injection tested.

It is also difficult to compare one injection type to another based on pathology, again, because many of the studies were completed by the same author with largely the same results, regardless of pain aetiology. However, by evaluating and comparing outcomes between studies that had similar inclusion criteria of a lumbar disc herniation, comparisons can be inferred. There were three caudal studies [13•, 14, 52, 53] (two by the same author looking at patients at 1 year from starting treatment, and then at 2 years from treatment), three interlaminar studies [57, 63, 69] (all by the same author revisiting patients at varied time intervals), and three transforaminal studies [20••, 71, 72] (each from a different author).

The caudal study by Manchikanti et al. found a significant decrease in pain from baseline in 70 % of patients receiving local anaesthetic, and 77 % of patients receiving local anaesthetic and steroids at 1-year follow-up [52]. On the other hand, Iversen et al. found no difference in pain reduction between the epidural group and the sham group at 6 , 12 weeks, and 1 year [13•]. The interlaminar studies for lumbar disc herniation all showed significant improvement in pain from baseline at 1 year, with 72–74 % of patients in the local anaesthetic group and 85–86 % of patients in the local anaesthetic/steroid group having success [57, 63]. Notably, the group receiving interlaminar epidural injections with steroids had a significantly greater percentage of patients with improvement when compared to the group who only received local anaesthetic [57, 63]. The three transforaminal studies each found significant pain reduction with epidural steroid injection as well, but the groups to which the epidural injections were compared varied. Simply focusing on the common element among these studies, we see that transforaminal epidural steroid injections can produce successful pain reduction in 25–63 % of patients at 1-year follow-up [20••, 72]. Kennedy et al. [71] showed the steroid injections to significantly reduce pain in up to 75.7 % of patients at 6 months, regardless of whether particulate or non-particulate steroid is used.

Taken as a whole, we may be able to interpret these results as favouring transforaminal epidural steroid injections for lumbar radicular pain over caudal or interlaminar injections. The caudal studies have conflicting outcomes: one proclaiming success with the injection, and another discounting it entirely [13•, 52]. The interlaminar studies, despite showing the highest percentage of patients with successful pain reduction [57, 63], lack a true placebo group to properly compare the results. The transforaminal epidural injection studies are the only group of studies where all reported significant improvement in pain reduction from baseline, even in those studies with a true placebo group [20••, 71, 72]. Nonetheless, there is still room for debate.

The interlaminar approach can also be more affected by epidural ligaments or fibrotic scarring which may prevent flow of posteriorly administered injectate to the ventral epidural space [77]. It is generally believed that increased deposition of medication into the ventral space results in greater efficacy and reduction in pain scores [33]. Although only one head-to-head study supports this conclusion, Lee et al. see this as an explanation for why transforaminal injections were found to be superior to interlaminar injections for treatment of spinal stenosis [77]. Despite these favourable advantages to TFESIs, the transforaminal approach is associated with a higher incidence of complications due to the anatomical relation of the radicular artery accompanying the nerve root [79]. However, these complications have not been reported when dexamethasone was the steroid that was used.

ESIs for spinal stenosis have also been studied using all three injection methods. Manchikanti et al. looked at the efficacy of caudal injections to treat spinal stenosis [14, 50], and interlaminar injections to treat cervical and lumbar spinal stenosis [62, 65]. Also, Lee et al. compared interlaminar and transforaminal injections for treating lumbar stenosis [77]. All of these studies found a significant improvement in patient pain scores compared to baseline. This is in marked contrast to a recent multi-centred study by Friedly et al. [76]. This study was not included in this review because it did not meet the 3-month follow-up requirement, but it is certainly worth noting because of the large number of patients studied. In this randomized, double-blind, multisite trial, 400 patients who had lumbar central spinal stenosis and moderate to severe leg pain and disability received epidural injections (either interlaminar or transforaminal) of glucocorticoids plus lidocaine or lidocaine alone. The patients received one or two injections before the primary outcome evaluation, performed 6 weeks after randomization and the first injection. At 6 weeks, there were no significant between-group differences in the Roland–Morris Disability Questionnaire score (adjusted difference in the average treatment effect between the glucocorticoid–lidocaine group and the lidocaine-alone group, −1.0 points; 95 % confidence interval [CI] −2.1 to 0.1; P = 0.07) or the intensity of leg pain (adjusted difference in the average treatment effect, −0.2 points; 95 % CI −0.8 to 0.4; P = 0.48) [76]. A prespecified secondary subgroup analysis with stratification according to type of injection (interlaminar vs. transforaminal) likewise showed no significant differences at 6 weeks. Given the results of this study, it is difficult to reach a definitive conclusion on the superiority of a particular route of injection for those with spinal stenosis.

When viewing the literature on epidurals for axial spine pain, it is not clear that the addition of a corticosteroid offers any benefit, regardless of route. No study to date on ESI for the treatment of axial pain without radicular symptoms has shown superiority of ESI over epidural local anaesthetic alone. Therefore, there is dubious benefit for the majority of epidural injections that are done for axial pain. This is in contrast to the general trend of the literature in the past 5 years demonstrating that radicular pain responds better to ESI than axial pain alone when using an interlaminar or transforaminal approach. There is no evidence that caudal ESI is effective for axial or radicular pain.

Limitations

It must be noted when attempting to compare the efficacy of the three types of epidural injections based on their individual trials, that there is lack of standardization between them. Aside from the interlaminar studies (completed by the same author using the same methods, medications, doses, and outcome measures), there is no consistency between studies on patient inclusion or exclusion criteria. Moreover, the number of injections per patient was not consistent among all studies. Some studies provided a second or third injection only if a patient’s pain returned within the follow-up period; others provided all patients with three injections regardless of pain relief or resumption. It also important to note that the same steroid was not used across all studies, and follow-up periods varied as well. Although all studies had pain relief as a primary outcome, the methods for quantifying the change before and after treatment differed. Additionally, duration of pain prior to treatment was also not standardized between studies. Better powered studies would improve the ability to detect statistical significance between injection types not seen in smaller randomized clinical trials, however, because of these variations in methodology and data collection, results between studies cannot be combined for meta-analyses [80]. Lastly, by mandating that studies had a minimum follow-up period of 3 months, a recent high-profile study by Friedly et al. was excluded [76]. This multi-centre study did offer insights into the treatment outcomes from ESI in spinal stenosis and they did stratify the results based on injection type. However, subjects were not randomized to injection type, thus the injection type was at the discretion of the treating physician, thus significantly limiting the ability to draw conclusions on their relative efficacy due to selection bias.

Conclusions

ESIs are the most commonly performed interventions in medicine for spine pain, with their utilization continuing to increase. The last 5 years of data suggest that epidural injections provide effective pain relief and function improvement particularly when using the transforaminal approach for radicular pain related to disc herniation. Interlaminar epidural steroid injections also appear to be efficacious for radicular pain from a disc herniation; however, the data are not as strong. It is unclear if ESI provides significant benefit for pain and functional improvement with the caudal approach regardless of the diagnosis. For spinal stenosis, the data are not nearly as robust as it is for disc herniations. Additionally, no significant conclusions can be made regarding the ideal approach for those with spinal stenosis. For axial back pain, there are no data showing that an injection of a corticosteroid offers any benefit regardless of route of injection.