Ultrasound-guided medial brachial cutaneous nerve block is used primarily as an adjunct to brachial plexus block rather than as a stand-alone regional anesthesia and pain management procedure. The medial brachial cutaneous nerve is the smallest branch of the brachial plexus and is often not adequately blocked when performing standard brachial plexus block techniques. This means that the medial and posterior aspect of the arm just below the axilla remains unanesthetized making prolonged use of a pneumatic tourniquet or the performance of surgical procedures in this region problematic. The medial brachial cutaneous nerve may be injured during cubital tunnel surgery.

The medial brachial cutaneous nerve is composed of fibers from the eighth cervical and first thoracic nerves. It is the smallest branch of the brachial plexus and arises from the medial cord of the brachial plexus. While passing through the axilla on its downward path, it provides communicating branches with the intercostobrachial cutaneous nerve. After leaving the axilla, it passes downward along with the brachial artery to provide cutaneous sensory innervation to medial and posterior aspect of the upper extremity just below the area innervated by the intercostobrachial cutaneous nerve (Figs. 45.1 and 45.2). This nerve can be damaged by surgical procedures, and there are case reports describing damage to the medial brachial cutaneous nerve during placement of long-acting contraceptive implants. The superficial location of this nerve makes it easily accessible for ultrasound-guided nerve block.

The benefits, risks, and alternative treatments are explained to the patient and informed consent is obtained. The patient is then placed in the supine position with the affected upper extremity abducted 90 degrees and the palm facing upward (Fig. 45.3). With the patient in the above position, the medial epicondyle is identified, and at a point ˜1 inch above the superomedial margin of the epicondyle, a high-frequency linear ultrasound transducer is placed in the transverse position (Fig. 45.4).

An ultrasound survey image is obtained, and the basilic vein and branches of the medial brachial cutaneous nerve are identified (Fig. 45.5). Color Doppler can aid in the identifications of the basilica vein and any other vasculature in proximity to the medial brachial cutaneous nerve (Fig. 45.6). The ultrasound transducer is then slowly moved proximally to follow the branches of the medial brachial cutaneous nerve until they coalesce into a single ovoid hyperechoic nerve (Fig. 45.7). As the ultrasound transducer is moved more proximally, the medial brachial cutaneous nerve moves from its 6:00 o’clock position in front of the basilic vein to the 9:00 o’clock position next to the vein (Fig. 45.8). It is at this point that ultrasound-guided medial brachial cutaneous nerve block is easiest to perform. Ultimately, as the nerve is followed more proximally, it will move from the 9:00 o’clock to the 12:00 o’clock position making more difficult to block without traversing the basilica vein (Fig. 45.9). Once the medial brachial cutaneous nerve is clearly identified and is felt to be in satisfactory position for ultrasoundguided nerve block, the skin overlying the area beneath the ultrasound transducer is prepped with antiseptic solution. A sterile syringe containing 3.0 mL of 0.25% preservative-free bupivacaine and 40 mg of methylprednisolone is attached to a 1½-inch, 22-gauge needle using strict aseptic technique. The needle is placed through the skin just below the center of the transducer and is then advanced using an out-of-plane approach with the needle trajectory adjusted under realtime ultrasound guidance so that the needle tip ultimately rests in proximity to the medial brachial cutaneous nerve (Fig. 45.10). When the tip of needle is thought to be in satisfactory position, after careful aspiration, a small amount of local anesthetic and steroid is injected under real-time ultrasound guidance to confirm that the needle tip is in the proper position. After proper needle tip placement is confirmed, the
remainder of the contents of the syringe is slowly injected. There should be minimal resistance to injection.