Radial Nerve Block

Published on 06/02/2015 by admin

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Last modified 22/04/2025

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35 Radial Nerve Block

The radial nerve is a branch of the posterior cord of the brachial plexus. It provides motor innervation to the extensor-supinator group of muscles. Of the three nerves that surround the axillary artery in the axilla (median, radial, and ulnar), the radial nerve is the most difficult to visualize and access with the block needle.¹

The radial nerve has branches all along its course, including the posterior cutaneous branch of the forearm (sensory), deep radial nerve (motor), and superficial radial nerve (sensory).

The posterior cutaneous branch of the forearm diverges from the radial nerve about 16 cm proximal to the lateral epicondyle of the humerus.² This branch provides sensation to both the elbow joint and posterior forearm.

The radial nerve divides into its superficial and deep branches in the antecubital fossa over the lateral epicondyle of the humerus. The radial nerve often has a snake-eyes appearance before this separation. The superficial radial nerve is slightly medial to the deep radial nerve within a fascial plane in this location. The deep radial nerve can be easily viewed crossing through the supinator muscle by sliding the transducer back and forth just distal to the lateral epicondyle with the arm pronated. This is a useful starting point to help find the common radial nerve and its superficial branch, which can be more difficult to visualize.

The superficial radial nerve joins the lateral side of the radial artery in the middle third of the forearm. The superficial radial nerve travels the lateral forearm just deep to the brachioradialis muscle. Most patients have radial dominance of sensation of the dorsal aspect of the hand, as primarily supplied by the superficial branch of the radial nerve.³

Suggested Technique

The superficial radial nerve can be blocked in the proximal third of the forearm before it joins the lateral side of the radial artery and divides into smaller branches.^4,⁵ In this location the superficial radial nerve is covered by the brachioradialis as it travels over the supinator muscle. An in-plane approach from the lateral side of the forearm works well with the block needle tip placed under the nerve. The arm is pronated to facilitate placement of the needle. Similarly, the radial nerve can be blocked slightly more proximally in the antecubital fossa before the nerve divides into superficial (sensory) and deep (motor) branches.

The radial nerve also can be blocked in the distal arm after the nerve emerges from the spiral groove of the humerus. The radial nerve lies within the fascia that divides the brachioradialis from the underlying brachialis muscle. The arm is pronated and elevated to facilitate imaging of the nerve in the posterolateral arm for the block procedure. The radial nerve is round or oval in this location. The injection targets the fascial plane between the brachialis (deep) and brachioradialis (superficial). The posterior cutaneous nerve of the forearm lies superficial and posterior to the radial nerve above the elbow, so injection on pullback of the needle is advised to ensure complete block.

The radial nerve emerges from the spiral groove where the lateral intermuscular septum inserts on the humerus. This insertion creates the lateral supracondylar ridge along the bone. Because the lateral intermuscular septum separates the brachioradialis from the triceps, the ridge will point behind to the radial nerve. The radial nerve travels anteriorly after emerging from the spiral groove of the humerus. The nerve travels within the fascia between the brachialis and brachioradialis muscles.

Neurologic Assessment

Sensory block of the radial nerve can be tested at the dorsal web between the index finger and thumb. Motor block of the deep radial nerve results in wrist drop.

Key Points

Superficial Radial Nerve Block	The Essentials
Anatomy	The brachioradialis muscle covers the SRN in the forearm.
Image orientation	The SRN lies lateral to the RA.
Positioning	Arm pronated
Operator	Standing on the lateral (cephalad) side of the armboard
Display	Across the armboard
Transducer	High-frequency linear, 23- to 38-mm footprint
Initial depth setting	25 mm
Needle	25 gauge, 38 mm in length
Anatomic location	Proximal third of the forearm
Approach	SAX view of SRN, in-plane from lateral to medial
	Place the needle tip through BR adjacent to the SRN.
	Local anesthetic should layer under the BR and around the SRN.
Sonographic assessment	The injection should track along the SRN.
Anatomic variation	Proximal branching of SRN is possible.

BR, Brachioradialis muscle; RA, radial artery; SAX, short axis; SRN, superficial radial nerve.

FIGURE 35-1 External photograph showing the approach to superficial radial nerve block in the proximal forearm. An in-plane approach from the lateral aspect of the forearm is shown.

FIGURE 35-2 Image sequence showing superficial radial nerve block in the forearm. An in-plane approach is demonstrated where the needle tip is placed under the superficial radial nerve (A). After injection, local anesthetic is distributed around the superficial radial nerve, resulting in sensory block of the dorsum of the hand (B).

FIGURE 35-3 Snake-eyes appearance to the radial nerve in the antecubital fossa (A). The snake-eyes appearance consists of both the superficial (sensory) and deep (motor) branches before the deep branch dives through the supinator muscle. In-plane approach to radial nerve block from the lateral aspect of the arm (B). If the radial nerve is blocked in this location, the motor block will result in wrist drop.

FIGURE 35-4 Short-axis view of the radial nerve in the distal arm between the spiral groove and the lateral epicondyle of the humerus showing the block needle in place (A). The brachialis muscle separates the radial nerve from the underlying bone. The brachioradialis muscle covers the radial nerve. After injection, local anesthetic is seen to surround the radial nerve (B). Radial nerve block in this location results in both sensory and motor block.

1 Chan VW, Perlas A, McCartney CJ, et al. Ultrasound guidance improves success rate of axillary brachial plexus block. Can J Anaesth. 2007;54:176–182.

2 MacAvoy MC, Rust SS, Green DP. Anatomy of the posterior antebrachial cutaneous nerve: practical information for the surgeon operating on the lateral aspect of the elbow. J Hand Surg (Am). 2006;31:908–911.

3 Auerbach DM, Collins ED, Kunkle KL, et al. The radial sensory nerve. An anatomic study. Clin Orthop Relat Res. 1994;308:241–249.

4 Ikiz ZA, Ucerler H. Anatomic characteristics and clinical importance of the superficial branch of the radial nerve. Surg Radiol Anat. 2004;26:453–458.

5 Visser LH. High-resolution sonography of the superficial radial nerve with two case reports. Muscle Nerve. 2009;39(3):392–395.

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