Epidural steroid injections have been used to treat low back and radicular pain since the early 1900s. The epidural space is a potential space within the spinal canal and outside the dura mater. A mixture of local anesthetic and corticosteroid is injected into the epidural space via various approaches: interlaminar, transforaminal, or caudal.
The interlaminar approach is the most commonly used approach for cervical, thoracic, and lumbar epidural injections (Fig. 16-1). Epidural needles (Crawford or Tuohy type) are directed between the lamina via a midline or paramedian approach. As the needle penetrates the ligamentum flavum, the epidural space is identified by the loss-of-resistance method. Typically 5 to 10 mL of corticosteroid and local anesthetic solution is injected in the lumbar and thoracic spine. In the cervical spine, 3 to 5 mL is injected. The injectate is delivered to the posterior epidural space, and indirect spread to the anterior epidural space is anticipated.
The transforaminal approach is used to inject the medication directly into the neuroforamen. The injectate is delivered to the anterior epidural space in the region of the targeted pathology (Fig. 16-2). Transforaminal injection should be performed only under fluoroscopic guidance for accuracy and safety. The needle is directed obliquely to a specific target area in the neuroforamen. Because the needle is placed directly at the target nerve root, less volume is required to achieve pain relief. In the lumbar spine, 3 to 5 mL of corticosteroid and local anesthetic solution is injected. In the cervical spine, 1 to 1.5 mL is required to adequately block the target nerve root.
The caudal approach is the safest approach for injection into the lumbar epidural space and has the least risk of dural puncture. The needle is inserted between the sacral cornu into the sacral hiatus, which leads to the caudal epidural space. The drawback of this approach is the large volume of the injection required to reach the target area in the lumbar spine. Frequently, 10 to 15 mL of corticosteroid and local anesthetic solution is needed to achieve pain relief.
Use of an epidural catheter to deliver the medication to the lumbar spine is helpful in patients with prior history of spine surgery (Fig. 16-3). Various manufacturers offer epidural catheters specifically designed for pain procedures. An introducer needle is placed caudally, and the flexible epidural catheter is advanced cephalad to the target. These catheters can also be steered to the left or right to reach the target area. With the use of a catheter, less volume is necessary to achieve pain relief if the catheter tip is in close proximity to the target area.
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