Epidural Steroid Injections

Epidural steroid injections are one of the most commonly performed interventions for the management of painful spinal conditions. Approaches to the epidural space include interlaminar, transforaminal (or selective nerve root), catheter directed, and the caudal approach for the lower lumbar segments.

A recent systematic review of relevant ESI literature by Salahadin et al.⁴ highlights the variability in quality and relevance of studies looking at ESI efficacy. A common pitfall when studying invasive procedures is considering the efficacy of the comparator procedure. For instance, many studies evaluating ESI compare the procedure to epidural saline,⁵ epidural anesthetic without steroid,⁶ injections into nearby tissues,⁷ alternative injected medications (e.g., hyaluronic acid and Sarapin) or a combination of these strategies.^8,9 Many of these comparator procedures have demonstrated therapeutic efficacy and are therefore not truly placebo. Matthews et al.⁷ compared caudal ESIs to local anesthesia over the sacral hiatus (some were at “tender spots,” however). This may be most consistent with a true placebo comparator.

Considering the proposed mechanism of action of steroid injections (reducing inflammatory chemicals at the site of injury/pathology and possibly contributing to neuronal stability), the expectation that any type of steroid injection, done one time, will result in more than 6 months of relief or benefit is unrealistic.¹ Therefore the number and frequency of injections are other variables that must be considered when assessing the long-term efficacy of injections.^1,10 Consistency of outcome measures must also be considered: improvement in both reported pain and functional ability should be considered when judging the efficacy of any procedure, including ESI.

In their review, Salahadin and colleagues⁴ considered anything less than 6 weeks as “short term” and any time beyond 6 weeks as “long term.” Their analysis, using commonly accepted “evidence-based medicine” definitions for literature review, yielded ratings for each approach as outlined in Table 19-1. Interlaminar and transforaminal ESIs in the low back and neck had “indeterminate” evidence for use in axial spine pain, postlaminectomy syndrome, lumbar disc extrusions, and lumbar stenosis. Interestingly, caudal ESIs have “moderate” evidence for short- and long-term improvement for chronic, axial low back pain, and their “strong” and “moderate” short- and long-term ratings for radicular pain also include patients with postlaminectomy syndrome.⁴

TABLE 19-1 Summary of Literature Support for Various ESI Approaches for the Treatment of Lumbar and Cervical “Radicular Pain” as Outlined by Salahadin et al.⁴

From the surgeon’s standpoint, avoidance of surgery is an important outcome consideration. In this regard, at least transforaminal injections (lumbar and cervical) have shown efficacy.¹¹ This approach, in the lumbar spine, has also been shown to be more effective for radicular pain than interlaminar ESIs.

There is no significant evidence to suggest a specific, fixed timing regimen of injections. Current guideline recommendations (including Official Disability Guidelines and International Spine Intervention Society[ISIS]) suggest that repeated injections should be considered as symptoms recur, and the repeated injections should not be considered in patients who do not demonstrate significant (usually defined as >50% short-term relief) transient improvement following an initial injection. Similarly, the maximum number of injections that an individual may undergo during a specific amount of time (such as during 1 year) has not been adequately studied, but consensuses from various guidelines and societies suggest that no more than four injections should be considered over the course of a year and that repeated injections should be separated by at least one to two weeks. Riew et al.⁶ found that up to four lumbar transforaminal ESIs were required to optimize therapeutic benefit (in this case, avoidance of surgery) beyond 15 months, and the interval between injections ranged from 6 days to 10.5 months. This is also the only lumbar injection study¹² to require a failure of 6 weeks of other nonoperative interventions including physical therapy, nonsteroidal anti-inflammatory drugs (NSAIDs), bracing, or a combination of the three. The integration of these other treatments with injection therapies is therefore also poorly understood.

Complications of epidural injections include generic considerations for any invasive procedure (local tissue trauma, bruising, pain, infection) as well as those specific for trauma to the local spinal tissues, medication or steroid related side effects, and those associated with x-ray exposure during fluoroscopy. Minor complications including dural puncture with subsequent “spinal headache,” increased pain, elevated blood sugar level or blood pressure, sympathetic mediated symptoms such as flushing or vasovagal response and acute insomnia have been described and occur infrequently. Botwin et al reported an overall complication rate during fluoroscopically guided ESIs as occurring in less than 10% for lumbar injections¹³ and approaching 17% for cervical ESIs.¹⁴ Caudal injections had a rate of minor complications of 15.6%,¹⁵ and for the thoracic spine, a 20.5% rate was reported.¹⁶ Intravascular needle placement has been noted in about 10% to 20% of lumbar injections.¹⁷ Subarachnoid needle placement is also a concern, because it may cause spinal anesthesia or arachnoiditis.¹

Major or severe complications are fortunately very rare when injections are performed with fluoroscopy and by experienced interventionalists.¹ Potentially catastrophic injury can occur, however, including infarction of central nervous system tissues (causing paraplegia, tetraplegia, or stroke syndromes), compression of neural elements or spinal cord by hematoma, CNS infections, pneumocephalus, and chemical meningitis, to list a few. Transforaminal approaches, particularly in the cervical spine, likely carry the greatest risk of these rare yet serious complications.⁴

Predictors for negative outcome following ESI include poor education, unemployed status, smoking, chronic or constant pain, high medication usage, high number of previously attempted treatments, pain that is not increased with activity or coughing, psychological disturbances, and nonradicular diagnoses.¹⁸

Facet Joint Procedures

Approximately 20% of low back pain complaints can be attributed to the zygapophyseal joints in the lumbar spine^1,19–22 and likely account for even higher rates of pain in the cervical and thoracic spines.^19,20,22 Also known as facet or z-joints, these joints become arthritic and potentially painful as with any joint in the body, and consequently, older individuals may be expected to be more likely to respond to facet blocks than younger patients.^20,21,23 In fact, in a study of older Australians with non–injury-related chronic low back pain, 30% of individuals reported at least 90% relief following placebo-controlled facet blocks.²¹

Over the past 40 years, our understanding of the innervation of facet joints and their potential as pain generators has greatly expanded.² We now know that even referred leg pain and hamstring tightness can be associated with facet joint pain and thus mimic features of sciatica. Cervical facet joints may refer pain to the head, neck, and shoulder areas and have well- described referral pattern “maps,” whereas thoracic facet joints may produce mid back pain with accompanying neuropathic symptoms as well.²² Along with the evolution of this knowledge, so too have interventional approaches in dealing with facet-mediated pain.

The specific diagnosis of facet-mediated pain is difficult and controversial, however, because there are no reliable factors of patients’ history, physical exam, or imaging studies to otherwise effectively determine pain of facet origin. Several studies have evaluated the use of single photon emission CT (SPECT) to determine if abnormalities can predict facet joint disease and therefore predict favorable response to joint injections. One study example by Pneumaticos et al²⁴ determined that patients who had “hot” facet joints treated with steroid injection responded more favorably than patients who also had non–hot joints injected (joints were selected clinically by the attending physician as is done in typical practice). Despite this and other positive results, SPECT is not routinely used, perhaps because of limited availability and expense.

For diagnostic injections, there is a high false-positive rate for single sets of lumbar injections.¹⁹ Therefore two positive diagnostic injections are felt to be required before considering pain to be truly of facet origin, at least for the purposes of clinical research. These injections should be low volume and demonstrate a specific response based upon the expected duration of the anesthetic used.^23,25