Introduction

An epidural steroid injection (ESI) is a minimally invasive and effective procedure frequently used for several conditions such as lumbar disc herniation, radiculopathy, spinal stenosis and postlaminectomy syndrome. ESI has been in use since 1952 [1].

Activity of epidural local anesthetic and steroid administration is not well understood. Different mechanisms have been introduced. Local anesthetics are thought to interrupt pain spasm link and nociceptor transmission. Corticosteroids diminish inflammation, suppress neuronal discharge and desensitize dorsal horn neurons [2].

ESI is performed via a caudal, interlaminar (IL) or transforaminal (TF) approach. Although the IL approach is commonly used, its efficacy has been reported to be limited. The anesthetic injected via the IL approach spreads into the posterior epidural space rather than the ventrolateral epidural space. It may not reach the desired target region. However, recent studies and systematic reviews have demonstrated that the IL injections performed under fluoroscopy are as effective as TF and caudal injections [3].

Indications

• Spinal stenosis
  
• Disc herniations with or without radicular pain
  
• Non-specific radiculitis
  
• Vertebral bone spurs impinging spinal nerve roots
  
• Postlaminectomy syndrome
  
• Facet or nerve root cyst with radicular pain
  
• Postherpetic or posttraumatic neuralgia
  
• Compression fracture with radicular pain
  
• Spondylolysis
  
• Spondylolisthesis.

Contraindications

• Systemic infection or local infection at the site of injection
  
• Bleeding diathesis or use of anticoagulants
  
• Allergic reaction to contrast, anesthetic or corticosteroid
  
• Local malignancy
  
• Patient refusal
  
• Uncontrolled diabetes mellitus (relative contraindications) [4].

Anatomy of the Epidural Space

The spinal cord extends down to the level of L1–L2 in adults while the dural sac extends to the level of the 2nd sacral foramen. The epidural space extends from the foramen magnum to the sacrococcygeal hiatus. The width of the posterior epidural region is 1.0–1.5 mm in the cervical region, 2.5–3 mm in the upper thoracic region, 4.0–5.0 mm in the lower thoracic region and 5.0–6.0 mm in the lumbar region. The epidural space is limited by ligamentum flavum and periosteum in its posterior side, posterior longitudinal ligament and vertebral body in its anterior side and pedicle and intervertebral foramen in its lateral side [1] (Figure 32.1).

The posterior epidural space involves the connective tissue and the ligamentum flavum. The main content in the epidural space is adipose tissue. Moreover, the epidural space contains the spinal branches of the segmental arteries, the internal vertebral venus plexus, lymphatics and the dura arachnoid projections that enclose the spinal nerve roots [1].

Ligamentum flavum is suggested to be separately located on the right and left sides and join in the midline. However, fusion defects at varying degrees on the ligamentum flavum in the midline were demonstrated in the thin cross-sections of the epidural space [5].

The medulla spinalis is supplied by an anterior spinal artery (ASA) and two posterior spinal arteries (PSA). The largest of the anterior radicular arteries supplying blood to the lower thoracic and lumbar parts of the medulla spinalis is named the “Adamkiewicz Artery”. Although this artery has several anatomic variations, it often arises from the level of T9–T12 and usually from the left side in most people [6, 7].

Technique

Lumbar Interlaminar Block

The patient is placed in prone position (Figure 32.2). For the lumbar interlaminar blockade, a pillow is put under the upper abdomen to decrease physiologic lumbar lordotic curve. The lumbar region is prepared and draped in sterile condition. After checking the level on the true AP view (spinous processes should be on the midline), the C-arm is rotated in the cephalad or caudad direction to open up the interlaminar space. The paramedian or median approach can be used for interlaminar injection. The appropriate interlaminar spacing is determined. The procedure is performed by squaring the lower end plate of the target level vertebra. Target needle entry point is 1 or 1.5 vertebral body height inferior and approximately 1–2 cm lateral to the midline for the paramedian approach; middle of the interlaminar space for the median approach. After infiltration of local anesthetic to the skin, the needle is advanced toward the midline of the interlaminar space in the paramedian approach. The needle entry angle is around 45–60 degrees between the needle and skin on the coronal plan. The needle is advanced perpendicularly by using the tunnel of vision technique in the median approach. Then the C-arm is rotated laterally. When the top of the needle reaches the spinolaminar line, the needle should be advanced slowly until the loss of resistance and bounce feeling is obtained (Figure 32.3). The loss of resistance and bounce technique can be used and an air- and fluid-filled injector that contains a small bubble of air to allow compression. The needle tip should be seen just ventral to the spinolaminar line (the base of the spinous process) on the lateral view. The AP view must be rechecked to confirm the needle’s direction (Figure 32.4a,b). Then, the contrast agent is injected to verify the needle position. When the needle tip arrives at the posterior epidural space just ventral to the spinolaminar line, the contrast agent flows dorsally along the spinolaminar line (Figure 32.5a,b). After confirming correct placement of the needle, a mixture of local anesthetic and steroid is injected.