Therapeutic Epidural Injections

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Chapter 11 Therapeutic Epidural Injections

Interlaminar and Transforaminal

Chapter Overview

Chapter Synopsis: Similar to many spinal injection therapies, epidural injections for the treatment of sciatica have evolved in recent years because of a better understanding of the underlying condition. Initially, injections consisted of a simple anesthetic and later of corticosteroids. This chapter covers more recent findings that have led to refinement of the technique. Radiculopathy is the loss of sensory or motor conduction that can arise from a herniated intervertebral disc. These poorly vascularized structures can be damaged by mechanical impingement, which then may lead to an inflammatory response raised by spinal glia. This inflammatory soup, which contains cytokines and tumor necrosis factor-α, likely mediates the painful component known as radicular pain. When a patient complains of low back pain without leg pain, discogenic pain may be a more likely candidate, which may also be treated with epidural injection. Spinal stenosis can also cause similar radicular pain. These spinal disorders require a combination of imaging results, electrodiagnostic studies, and physical examination for proper diagnosis and treatment. Recent reviews of the literature suggest that some injection procedures can provide short-term relief from radicular pain caused by these conditions. This chapter also describes the technical aspects of the procedures and avoiding risks of complications.

Important Points:

Clinical Pearls:

Clinical Pitfalls:

Introduction

The use of therapeutic epidural injections for the treatment of sciatica with back and leg pain dates back approximately 80 years. Initially, therapeutic epidurals were predominately transsacral (caudal) injections of local anesthetics such as procaine.1 After the introduction of corticosteroids into clinical practice,2 researchers in Europe were the first to inject corticosteroids into the epidural space.3,4 The techniques of administration have gradually been modified, with early use of higher volume caudal epidural injections eventually being largely replaced, first by level-specific interlaminar epidural injections and second by transforaminal epidurals performed with fluoroscopic guidance. Despite the increasing sophistication and advances in the techniques of steroid injection, a number of authors still question the role of these injections for the therapy of sciatica. In particular, two physician specialties (neurology and occupational medicine) have published guidelines or reviews suggesting that these injections are performed too often with uncertain results.5,6 Other authors are beginning to examine the role of alternate compounds such as etanercept for the treatment of sciatica based on the underlying pathophysiology.7 Finally, a recent head-to-head trial of several conservative treatments (including injections in some) compared with surgical therapies was performed demonstrating the superiority of surgery, at least in the first year.8 This trial augmented the previous large-scale trials comparing surgical with nonsurgical therapies.9,10 This chapter discusses the current role of therapeutic epidural injections.

Basic Science

Radiculopathy is most commonly associated with intervertebral disc herniation and likely includes two distinct pathways: mechanical compression and cytokine-mediated radiculitis.11 Mechanical impingement may induce poor tissue oxygen delivery to the spinal (radicular) nerve, resulting in an inadequate nutritional supply and decreasing the vascular perfusion to critical levels. Interestingly, however, mechanical compression alone may not result in pain.12,13 Radiculopathy describes neurological conduction loss (sensory or motor) occurring secondary to mechanical impingement or compression (e.g., disc protrusion, herniation, or extrusion) pressing on the spinal nerve in the foramina. Other common causes of radiculopathy include spondylosis, vertebral subluxation, and ligamentum flavum hypertrophy or thickening.14 Abnormal nerve conduction may manifest as sensory loss, depressed spinal reflexes, or motor deficits. Radicular pain may occur concomitantly with radiculopathy or separately. The pain is thought to be an inflammatory phenomenon induced by neurochemical products such as cytokines. Cytokines are produced by spinal glia. They include tumor necrosis factor-α (TNF-α) and several interleukins. Herniated nucleus pulposus may induce the release of such inflammatory mediators, leading to a chemical radiculitis. Olmarker et al15 found that the application of a homogenate of disc material onto porcine cauda equina induced functional and morphologic changes in those nerves. Then Igarashi and colleagues16 reported that in a rat model, TNF-α applied to the dorsal root ganglia produced functional and morphological changes that were identical to that seen with nucleus pulposus material. Burke et al17 found increased levels of the inflammatory cytokines interleukin-6 (IL-6) and IL-8 in disc material taken from patients with known disc disease. Finally, further study produced compelling evidence that TNF-α inhibitors could reduce the histological and functional changes caused by nucleus pulposus material. These studies cemented the concept that TNF-α and other cytokines were causative agents in the development of radiculitis and further suggested an entirely new pharmacological treatment strategy for patients with sciatica.18

Discogenic pain is another pathological condition for which epidural therapies are occasionally tried. Discogenic pain is unlike radicular pain in that the patient will predominately complain of low back pain without significant leg involvement that is exacerbated by the sitting position, spinal flexion, heavy lifting, or other stresses. The intervertebral disc is a very poorly vascularized structure that receives nutrients primarily by diffusion. Intervertebral disc innervation is complex, arising primarily from nerve ingrowth through the vertebral endplate into the outer third of the disc annulus. Nerve fiber types in the annulus fibrosis are peptidergic, using neurotransmitter substances such as calcitonin gene-related peptide. Nerve fibers are small and follow new blood vessels.19

Indications and Contraindications

Therapeutic epidurals are generally used in three major instances: (1) for the symptomatic treatment of radicular pain secondary to an intervertebral disc herniation, protrusion, or extrusion causing a combination of back and leg pain in a characteristic dermatomal pattern (Fig. 11-1); (2) spinal stenosis presenting with symptoms of neurogenic claudication, radicular pain, or mixed pain (Fig. 11-2); and (3) postoperative back and leg pain caused by recurrent disc material, granulation tissue or scarring, or other causes (Fig. 11-3). In some cases, therapeutic epidural injections may also be performed in cases of discogenic pain or for tumor-related nerve pain when a radicular syndrome is manifested by the tumor growth into the foramen or around the exiting spinal nerve (Fig. 11-1). How these therapeutic procedures are applied is also somewhat variable depending on regional variations in the use of initial conservative therapies, the specialty of origin of the managing clinician, and the availability of clinicians capable to do therapeutic epidurals. However, population-based examinations of therapeutic epidural injections have not demonstrated any long-term advantage to their use in terms of reduced surgical volumes or enhanced functionality.20

Spinal stenosis is most commonly acquired but can be congenital. Large studies are lacking for results of therapeutic epidural injections. The natural history of spinal stenosis is reassuring, however. Johnsson and colleagues21 demonstrated that older patients with spinal stenosis commonly presented with low back pain (100%), claudication (75%), radicular pain (12.5%), and mixed symptoms (12.5%). Interestingly, the patients with spinal stenosis did not appear to worsen significantly over a 4-year period, with equal numbers showing improvement as progression.

Patients with worse clinical and functional symptoms most often had surgical laminectomy without fusion. At 8 to 10 years, the patients treated with either surgical or nonsurgical approaches had similar rates of satisfaction with current state, back pain incidence, and symptom improvement. Patients with initial surgical treatment had better leg pain and functional status. Overall, the results suggested that patients may be optimally managed in a shared decision model.22