Ultrasound-guided lumbar selective nerve root block is utilized most frequently as a diagnostic maneuver to confirm that a specific nerve root is in fact subserving a patient’s pain symptomatology. In order for this technique to provide the clinician with accurate diagnostic information, the needle tip must be placed just outside the neural foramen adjacent to the target nerve root without entering the epidural, subdural, or subarachnoid space. If these conditions are met, selective spinal nerve root block is diagnostic to the specific targeted root. However, if the needle enters the neural foramen and local anesthetic is injected, then not only is the targeted nerve root blocked but there is also the potential for the sinuvertebral, medial branch, and ramus communicans nerves to be blocked. In this situation, if the local anesthetic does not enter the epidural, subdural, or subarachnoid space, the diagnostic block can be considered to be specific to that spinal segment and nerve root. However, if the local anesthetic also enters the epidural, subdural, or subarachnoid space, the diagnostic block cannot be said to be specific to a given nerve root or segment and may be simply called a diagnostic neuraxial block. Although these distinctions may seem minor, the implications of failing to distinguish these subtle differences relative to technique could lead to surgical interventions that fail to benefit the patient. Ultrasound-guided blockade of the lumbar nerve root block is also useful as a therapeutic maneuver when treating radiculitis or radiculopathy involving a single nerve root.

The superior boundary of the lumbar epidural space is the fusion of the periosteal and spinal layers of dura at the foramen magnum. The epidural space continues inferiorly to the sacrococcygeal membrane. The lumbar epidural space is bounded anteriorly by the posterior longitudinal ligament and posteriorly by the vertebral laminae and the ligamentum flavum. The vertebral pedicles and intervertebral foramina form the lateral limits of the epidural space. The lumbar epidural space is 5 to 6 mm at LS-3 and widens at the S-S1 level with the lumbar spine flexed. The lumbar epidural space contains a small amount of fat, veins, arteries, lymphatics, and connective tissue. The five lumbar nerve roots exit their respective neural foramina and move anteriorly and inferiorly away from the lumbar spine (Fig. 108.1). The lumbar roots then coalesce to form the lumbar plexus (Fig. 108.2).

When performing selective nerve root block of the lumbar nerve roots, the goal is to place the needle just outside the neural foramen of the affected nerve root with precise application of local anesthetic. As mentioned above, placement of the needle within the neural foramina may change how the information obtained from this diagnostic maneuver should be interpreted.

Ultrasound-guided lumbar selective nerve root block can be carried out by placing the patient in the prone position with a thin pillow placed under the abdomen to slightly flex the lumbar spine (Fig. 108.3). A total of 0.25 to 0.5 mL of local anesthetic is drawn up in a 10-mL sterile syringe for each lumbar nerve root to be blocked. If the painful condition being treated is thought to have an inflammatory component, 40 to 80 mg of depot steroid is added to the local anesthetic.

After preparation of the skin with antiseptic solution, a curvilinear low-frequency ultrasound transducer is placed in the longitudinal plane over the spinous processes to identify the affected spinal level, and an ultrasound survey scan is obtained (Figs. 108.4 and 108.5). Once the affected level is identified, the transducer is rotated 90 degrees and a transverse ultrasound view is obtained. The spinous process is reidentified, and its image is traced anteriorly to the lamina (Fig. 108.6). Once the lamina is identified, the ultrasound transducer is slowly moved inferiorly to identify the inferior border of the lamina (Figs. 108.7 and 108.8). The ultrasound transducer is then moved laterally until the facet joint is visualized (Fig. 108.9). Once the facet joint at the affected level is identified, a 3½-inch, 22-gauge blunt needle is inserted utilizing an in-plane approach and is advanced from a posterior to anterior trajectory until the needle tip is in proximity to the nerve root, which is resting just inferior and slightly lateral and anterior to the facet joint (Fig. 108.10). After gentle

aspiration, 0.25 to 0.5 mL of solution is injected. The needle is removed, and pressure is placed on the injection site to avoid hematoma formation.