Radial Nerve Block

Radial nerve block is a simple procedure that can be performed at various levels along the course of the radial nerve. Surgical anesthesia, postoperative analgesia, and palliative measures for acute painful conditions are all indications for radial nerve block.

Radial nerve anatomy

The radial nerve is 1 of the 4 important branches of the posterior cord of the brachial plexus and has the root values of C5, C6, C7, C8, and T1. The mnemonic STAR (Subscapular, Thoracodorsal, Axillary, Radial) is an easy way to remember the 4 branches.

A brachial plexus schematic, radial nerve sensory distribution, and radial nerve course are shown in the images below.

In the axilla, the radial nerve descends behind the axillary and brachial arteries, passes between the long and medial heads of the triceps muscle, and enters the posterior compartment of the arm. It then winds in the spiral groove of the humerus with the profunda brachii vessels. Just above the elbow, it pierces the lateral intermuscular septum and continues downward into the cubital fossa between the brachialis and brachioradialis muscles. At the level of the elbow (lateral epicondyle), it divides into superficial and deep branches.

• Branches of the radial nerve in the axilla

  • Cutaneous branch - Posterior brachial cutaneous nerve

  • Muscular branches - Long and medial heads of triceps

• Branches of the radial nerve in the spiral groove

  • Cutaneous branches - Lower lateral brachial cutaneous nerve, posterior antebrachial cutaneous nerve

  • Muscular branches - Lateral and medial heads of the triceps, anconeus

• Branches of the radial nerve in the arm

  • Articular branch - Elbow joint

  • Muscular branches - Brachialis, brachioradialis, extensor carpi radialis longus

The superficial branch of the radial nerve descends lateral to the radial artery and passes backward under the tendon of the brachioradialis muscle. It then continues distally between the brachioradialis and supinator muscles before descending onto the dorsum of the hand. ^[1] It provides cutaneous innervation to the lateral two thirds of the dorsum of the hand and the lateral two and one half proximal phalanxes.

The deep branch of the radial nerve winds around the lateral part of the neck of the radius and enters the posterior compartment of the forearm. It descends between the superficial and deep layers of the supinator muscle and reaches the dorsal aspect of the interosseous membrane. It innervates the extensor carpi radialis brevis, supinator, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, abductor pollicis longus, extensor pollicis longus, extensor pollicis brevis, and extensor indicis. It also provides articular branches to the wrist and carpal joints.

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• Surgical anesthesia along the course of the radial nerve

• Supplement to brachial plexus block

• Postoperative analgesia

• Acute pain emergencies in the course of the radial nerve

• Radial tunnel syndrome: ^[2] This is a painful condition of the radial nerve. To distinguish radial tunnel syndrome from tennis elbow, palpate the lateral epicondyle. In tennis elbow, this palpation reveals tenderness over the lateral epicondyle that is absent in radial tunnel syndrome.

• Cheiralgia paresthetica or Wartenberg syndrome: ^[3] This syndrome is secondary to compression of the radial nerve distal to the musculospiral grove. Compression occurs because of the brachioradialis muscle during forearm pronation. The syndrome is manifested by painful paresthesias and decreased sensation over the dorsum of the hand.

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• Patient refusal

• Infection at the site

• Coagulopathy

• Allergy to available local anesthetic

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• In adults, the radial nerve block is well tolerated with reassurance from the practitioner. Skin infiltration with lidocaine 1% 0.5-1 mL suffices to facilitate needle entry. For more information, see Local Anesthetic Agents, Infiltrative Administration.

• Extremely anxious patients may benefit from oral diazepam 10 mg the night before or intravenous midazolam (1-2 mg, titrated to sedation) prior to the block.

• General anesthesia may be needed for pediatric patients.

Choice of local anesthetic for the block

The choice of the type and concentration of local anesthetic for radial nerve blockade is based on the desired duration. Alkalinization of mepivacaine and lidocaine with sodium bicarbonate results in faster time to onset of anesthesia. Table 1 provides onset times and duration for some commonly used local anesthetics mixtures. ^[4]

Table 1. Local Anesthetic for Radial Nerve Block (Open Table in a new window)

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• Alcohol, povidone-iodine solution (Betadine), or chlorhexidine (Hibiclens) preparatory solution

• Syringe, 1 mL, for local anesthetic

• Syringe, 5 mL, for the block

• Needle, 1 in, 25-27 gauge (ga), for the block

• Lidocaine 1%, bupivacaine 0.5%, or ropivacaine 0.5%; 5 mL

• Depot corticosteroid (eg, methylprednisolone acetate [DepoMedrol] 40 mg, triamcinolone acetonide [Kenalog] 40 mg)

• Gauze, 2 X 2

• Adhesive bandage

• Sterile gloves

• All resuscitative equipment

• Standard monitoring equipment

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• Position the patient comfortably with the affected arm well supported.

• Usually, the supine position is preferred, with the arm supported on the side.

Block at the humerus level

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• Position the patient supine with the arm abducted 45º and the hand resting comfortably on the abdomen. Radial nerve block land marks are shown in the image below. ^[2]

  Radial nerve block at the humerus level.

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• Palpate deeply between the heads of the triceps muscle and the brachialis muscle to identify the musculospiral groove.

• Prepare the skin with an antiseptic solution.

• To facilitate needle entry, infiltrate the injection site with lidocaine 1% 0.5-1 mL.

• Insert the 25-ga 1-in needle perpendicularly toward the musculospiral groove.

• Identify the nerve by paresthesia or nerve stimulator technique. If no response is elicited, redirect the needle slightly more anteriorly or posteriorly until the response is elicited.

• Aspirate gently to identify intravascular location of the needle.

• If the aspiration is negative, slowly inject 7-10 mL of the local anesthetic in slow increments, with intermittent aspiration. The image below shows landmarks for a radial nerve block at the humerus level.

  Radial nerve block at the humerus level.

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Block at the elbow level

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• Position the patient as described above.

• Identify the lateral margin of the biceps tendon at the elbow crease by flexing the elbow.

• Prepare the skin with an antiseptic solution.

• Insert the needle just lateral to the tendon and advance it in a slightly medial and cephalad direction toward the humerus. Landmarks for a radial nerve block at the elbow are shown in the image below.

  Radial nerve block at the elbow. The bicipital aponeurosis is visible. Needle entry is just lateral to the bicipital aponeurosis.

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• Identify the nerve with paresthesia, nerve stimulation, ultrasonographic guidance, or a combination thereof. ^[5]

• After negative aspiration, slowly inject 7-10 mL of the local anesthetic. Landmarks for a radial nerve block at the elbow are shown below.

  Radial nerve block at the elbow.

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Block at the wrist level

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• The radial nerve block at the wrist level (landmarks shown below) is essentially a field block and requires a more extensive infiltration because of its less predictable anatomic location and division into multiple, smaller, cutaneous branches. ^{[4, 6]}

  Radial nerve block at the wrist level.

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• Inject 5 mL of local anesthetic subcutaneously, just above the radial styloid, aiming medially. Additional landmarks for a radial nerve block at the wrist are shown below.

  Radial nerve block at the wrist.

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• Extend the infiltration laterally, using an additional 5 mL of local anesthetic.

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• The radial nerve block may be performed solely or in combination with ulnar and median nerve blocks.

• The radial nerve block may supplement the brachial plexus block. If performing a brachial plexus block at the humeral canal, block the radial nerve before blocking the ulnar nerve. ^[7]

• This block can be performed at the humerus, elbow, and wrist levels.

• Lidocaine, bupivacaine, ropivacaine are the local anesthetics typically used for this procedure.

• Surface landmarks, paresthesia, nerve stimulation, and ultrasonographic guidance are all helpful in performing the radial nerve block.

• Take care to avoid intraneural or intravascular injection of the local anesthetic.

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• Complications after wrist block are typically limited to residual paresthesia due to an inadvertent intraneuronal injection. Systemic toxicity is rare because of the distal location of the blockade.

• Complications may be avoided by taking preventive measures (see Table 2). ^[4]

Table 2. Prevention of Complications in Radial Nerve Block* (Open Table in a new window)