Selective Epidural Injection: Section 2

Precision Injection Techniques for Diagnosis and Treatment of Lumbar Disc Disease: Part 8

Spinal injectionThere are two major advantages of a selective epidural technique over a selective nerve root technique. First, with a selective epidural injection a foraminal approach is used and contact with the nerve is avoided, minimizing the potential for neural injury. Rather than relying on leg pain provocation from needle contact, needle localization is confirmed with contrast enhanced images demonstrating an outline of the nerve.

Derby, et al. Precision percutaneous blocking procedures for localizing spinal pain. Part 2: The lumbar neuraxial compartment. Pain Digest 1993;3:175-88.

Secondly, a selective epidural approach ensures that the injection incorporates all the sites where pathology can affect the nerve, from the disc level in the subarticular zone out lateral to the extraforaminal zone. If the pathology causing a patients symptoms is a paramedian disc herniation, but the nerve is injected in the extraforaminal zone, as with a classic selective nerve root injection, the portion of the nerve where the pain is coming from may not be anesthetized, potentially leading to a false negative result.

A selective epidural injection anesthetizes not only the spinal nerve itself but also all it’s branches. Two important branches of the spinal nerve are the sinuvertebral nerve and the medial branch of the dorsal primary ramus. The sinuvertebral nerve forms just lateral to the foramen from the ventral ramus and the grey ramus communicans.

Bogduk, N. Clinical Anatomy of the Lumbar Spine and Sacrum. Third edition. Churchill Livingstone, 1997.

Once formed, the nerve re-enters the foramen, where it runs across the back of the vertebral body just below the upper pedicle. Two branches arise from the nerve, one ascending branch supplying the PLL and the next higher disc, and one descending, innervating the disc and and PLL at the level of entry of the parent nerve (Bogduk). Each svn is also distributed to the dura mater, with descending branches up to two segments caudally and an ascending branch up to one segment.

The dorsal primary ramus from each spinal nerve divides into three branches, the medial, lateral, and intermediate (except at L5, which has only a medial and lateral branch).

Bogduk, N. Clinical Anatomy of the Lumbar Spine and Sacrum. Third edition. Churchill Livingstone, 1997.

The most important of these branches is the medial branch, which hooks medially around the base of the SAP at the inferior most aspect of the intervertebral foramen, supplying the z-joints just above and below it’s course.

Thus, a selective epidural injection will partially anesthetize the dura (including the dural nerve root sleeves) up to two segments caudally and one segment rostrally, the PLL and intervertebral disc at the same level as the nerve and one segment rostrally, and the z-joints at the same level of the nerve and one segment below.

Updated on: 01/28/16
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