Ultrasound-guided lumbar medial branch block is utilized in a variety of clinical scenarios as a diagnostic and therapeutic maneuver in painful conditions involving the lumbar facet joint. As a diagnostic tool, ultrasound-guided lumbar medial branch block allows accurate placement of the needle tip to determine if a specific pair of medial branch nerves is in fact subserving the patient’s pain. In the acute pain setting, ultrasound-guided lumbar medial branch block with local anesthetics and/or steroids may be used to palliate acute low back pain emergencies while waiting for pharmacologic methods to become effective. This technique has great clinical utility when managing acute posttrauma pain. This technique is also useful in the treatment of arthritis-related facet joint pain (Fig. 105.1). Clinically, pain emanating from the lumbar facet joints is perceived in the paraspinous region and radiates in a nondermatomal pattern (Fig. 105.2).

The lumbar facet joints are formed by the articulations of the superior and inferior articular facets of adjacent lumbar vertebrae (Fig. 105.3). The lumbar facet joints are lined with synovium and possess a dense joint capsule. The joint capsule is richly innervated and explains why the facet joint can serve as a nidus for lumbar pain when it becomes damaged or inflamed. The lumbar joint is susceptible to degenerative arthritis and is frequently affected by the collagen vascular diseases. The joint is frequently injured in acceleration/deceleration injuries resulting in intra-articular hemorrhage with subsequent inflammation and development of adhesions.

Each lumbar facet joint receives innervation from two spinal levels, receiving fibers from the dorsal ramus at the same level as the vertebra as well as fibers from the dorsal ramus of the vertebra above (Fig. 105.4). This fact has clinical import in that it provides an explanation for the ill-defined nature of facet-mediated pain and explains why the dorsal nerve from the vertebra above the offending level must often also be blocked to provide the patient with complete pain relief.

Ultrasound-guided lumbar medial branch block can be carried out by placing the patient in the prone position with a thin pillow placed beneath the abdomen to slightly flex the lumbar spine (Fig. 105.5). A total of 1 mL of local anesthetic is drawn up in a 5-mL sterile syringe for each medial branch 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.

To perform ultrasound-guided lumbar medial branch block, a two-step process is used. This two-step process allows the clinician to quickly identify critical anatomic structures while at the same time maintaining a transducer position that allows a safe and easy placement of needles in proximity to the affected lumbar medial branch nerves.

Step One is to obtain a paramedian sagittal transverse process view by placing the 2- to 5-MHz low-frequency curvilinear probe in the longitudinal plane 3 to 4 cm lateral to the right side of the middle of the spinous processes at the level to be blocked for blockade of the right lumbar medial branch nerves and 3 to 4 cm lateral to the left side of the middle of the spinous processes at the level to be blocked for left-sided medial branch nerves (Figs. 105.6 and 105.7). An initial depth setting of 7 to 8 cm will work for most patients. An ultrasound survey is taken, and the transducer is slowly moved medially and laterally until successive transverse processes are visualized. The transverse processes of the lumbar spine will appear as hyperechoic domes with sausage-like acoustic shadows beneath them (Fig. 105.8). This classic appearance of successive transverse


processes viewed in the longitudinal plane has been named the “trident sign” after Neptune trident (Fig. 105.9).