- Indications: hand and wrist surgery
- Transducer position: transverse on the elbow and/or forearm
- Goal: injection of local anesthetic in the vicinity of individual nerves (radial, median, ulnar)
- Local anesthetic: 4–5 mL per nerve
(A) Radial nerve block above the elbow. The needle is inserted in-plane from lateral to medial direction. (B) Median nerve block at the level of the midforearm. (C) Ulnar nerve block at the level of the midforearm.
Ultrasound imaging of individual nerves in the distal upper limb allows for reliable nerve blockade. The two main indications for these blocks are a stand-alone technique for hand and/or wrist surgery and as a means of rescuing or supplementing a patchy or failed proximal brachial plexus block. The main advantages of the ultrasound-guided technique over the surface-based or nerve stimulator–based techniques are the avoidance of unnecessary proximal motor and sensory blockade, that is, greater specificity. Additional advantages are avoidance of the risk of vascular puncture and a reduction in the overall volume of local anesthetic used. There are a variety of locations where a practitioner could approach each of these nerves, most of which are similar in efficacy. In this chapter, we present the approach for each nerve that we favor in our practice.
The radial nerve is best visualized above the lateral aspect of the elbow, lying in the fascia between the brachioradialis and the brachialis muscles (Figure 33-2). The transducer is placed transversely on the anterolateral aspect of the distal arm, 3–4 cm above the elbow crease (Figure 33-1A). The nerve appears as a hyperechoic, triangular, or oval structure with the characteristic stippled appearance of a distal peri-pheral nerve. The nerve divides just above the elbow crease into superficial (sensory) and deep (motor) branches. These smaller divisions of the radial nerve are more challenging to identify in the forearm; therefore, a single injection above the elbow is favored because it ensures blockade of both. The transducer can be slid up and down the axis of the arm to better appreciate the nerve within the musculature surrounding it. As the transducer is moved proximally, the nerve will be seen to travel posteriorly and closer to the humerus, to lie deep to the triceps muscles in the spiral groove (Figure 33-3).
(A) Radial nerve anatomy at the distal third of the humerus. (B) Sonoanatomy of the radial nerve at the distal humerus. Radial nerve (RN) is shown between the biceps and triceps muscles at a depth of approximately 2 cm.