Ultrasound-guided cervical 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 sinovertebral, 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 cervical nerve root block is also useful as a therapeutic maneuver when treating radiculitis involving a single nerve root.

The superior boundary of the cervical 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 cervical 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 cervical epidural space is 3 to 4 mm at the C7-T1 interspace with the cervical spine flexed. The cervical epidural space contains a small amount of fat, veins, arteries, lymphatics, and connective tissue. The eight cervical nerve roots exit their respective neural foramina and move anteriorly and inferiorly away from the cervical spine (Fig. 29.1). The cervical nerve roots C1-C7 exit above their corresponding vertebra. The C8 nerve root exits below the C7 vertebra. The vertebral artery lies ventral to the neural foramen at the level of the uncinate process. Care must be taken to avoid this structure when performing ultrasound-guided cervical selective nerve root block. The anterior and posterior tubercle of the transverse process serve as landmarks for ultrasound-guided cervical selective nerve root block as the exiting cervical nerve lies between these two bony landmarks (Fig. 29.2).

When performing selective nerve root block of the cervical 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 cervical selective nerve root block can be carried out by placing the patient in the lateral decubitus position. A total of 0.25 to 0.5 mL of local anesthetic is drawn up in a 10-mL sterile syringe for each cervical 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. The cricothyroid notch is then identified by palpation, which is at the C6 level. After preparation of the skin with antiseptic solution, a linear highfrequency ultrasound transducer is placed in a transverse plane at the level of C6 (Fig. 29.3). A transverse ultrasound view is obtained, and the anterior and posterior tubercles of the transverse process are identified. These tubercles have been described as a two-humped camel. The cervical nerve root lies between the two humps (Fig. 29.4). Because the C6 vertebral body can be easily identified by its characteristic camelhumped anterior tubercle (which is known as Chassaignac or the carotid tubercle), the ultrasound transducer is slowly moved in a cephalad or caudad direction until the C6 vertebral body is identified (Fig. 29.5). Once the position of the C6 vertebral body is confirmed, it can serve as a landmark to count from should the clinician desire to block the C5 or C7 nerve root. The C7 transverse process can be easily distinguished from the C6 transverse process by the lack of a taller and more pointed anterior tubercle on the C7 transverse process. At the C7 level, the C7 nerve root is located just anterior to the posterior tubercle. At each level, the anterior and posterior tubercle camel humps will appear as a hyperechoic twohumped camel with the hypoechoic nerve located between the two humps. Color Doppler can help identify the vertebral artery (Fig. 29.6). Once the correct level has been confirmed, a 22-gauge, 3½-inch blunt needle is inserted utilizing an inplane approach and is advanced until the needle tip is in proximity to the nerve root, which is resting between the anterior and posterior tubercle (Fig. 29.7). After gentle aspiration, 0.25 to 0.5 mL of solution is injected with care being taken to avoid the vertebral artery, which is located anteriorly in relation to the facet joints. The needle is removed and pressure is placed on the injection site to avoid hematoma formation.