Elbow block (median, radial and ulnar nerves)

Basic. The nerves are shallow, sit next to clear landmarks (the brachial artery and the groove between brachioradialis and brachialis), and there are no vital structures nearby. Avoid injecting the ulnar nerve inside the cubital tunnel.

Median nerve. At the elbow crease the median nerve lies just medial to the brachial artery, on brachialis, under the bicipital aponeurosis. Below the crease it passes between the two heads of pronator teres.

Radial nerve. After piercing the lateral intermuscular septum, the radial nerve runs on the front of the lateral elbow in the groove between brachioradialis (lateral) and brachialis (medial). Just above or at the level of the lateral epicondyle it divides into the superficial (sensory) branch and the deep (posterior interosseous, motor) branch.

Ulnar nerve. The ulnar nerve passes behind the medial epicondyle in the cubital tunnel, then enters the forearm between the two heads of flexor carpi ulnaris. Inside the tunnel it is tightly packed, so it is better blocked 3–5 cm above the epicondyle or a few centimetres below it in the forearm.

The lateral cutaneous nerve of the forearm (end of the musculocutaneous nerve) emerges lateral to the biceps tendon at the elbow crease, and the medial cutaneous nerve of the forearm runs near the basilic vein. Both supply forearm skin and are not covered by the three main nerve blocks.

• Elbow crease (intercondylar line) and the biceps tendon.
• Brachial artery pulse medial to the biceps tendon.
• Lateral and medial epicondyles; olecranon.
• The groove between brachioradialis and biceps on the lateral side of the elbow.

• Surgery on the hand and wrist, alone (with forearm tourniquet) or with a proximal block.
• Rescue of a missed nerve after an axillary or infraclavicular block.
• Long-acting analgesia for the hand while the proximal block is short-acting (selective distal blocks).
• Emergency department analgesia for hand injuries.

• Median nerve: forearm flexors and the radial side of the palm and fingers.
• Radial nerve: wrist and finger extensors (if the deep branch is reached) and the back of the radial hand.
• Ulnar nerve: flexor carpi ulnaris, small hand muscles, and the ulnar side of the hand.
• The lateral and medial cutaneous nerves of the forearm need separate injections for forearm skin.

Surface anatomy, relevant structures and landmarks

Median: just medial to the brachial artery at the elbow crease. Radial: 1–2 cm lateral to the biceps tendon at the crease, in the groove next to brachioradialis. Ulnar: 3–5 cm above the medial epicondyle, behind the medial intermuscular septum.

Positioning

Supine, arm abducted, elbow extended and forearm supinated. For the ulnar nerve, bend the elbow and rotate the arm outwards.

Block technique

Insert the needle perpendicular to the skin at each point until a motor response or a fascial click is felt, then inject. Avoid deliberate injection into the cubital tunnel.

Needle choice

22–25 G, 25–50 mm needle; insulated if using a nerve stimulator.

Neurostimulation technique

• Median: wrist and finger flexion, forearm pronation
• Radial: wrist and finger extension
• Ulnar: ring and little finger flexion, thumb adduction
• Accept at 0.3–0.5 mA

Choice of local anaesthetic (including volume)

5 mL per nerve.

Show scan

Ba Brachial arteryMn Median nervePT.m Pronator teres muscleHumerus Distal humerus

Show scan

Ba Brachial arteryPTm Pronator teres muscleMn Median nerveBRa.m Brachioradialis muscleBrm Brachialis muscleHumerus Distal humerus

Positioning

Supine, arm on an arm board, elbow straight and forearm supinated. For the ulnar nerve, flex the elbow and abduct and externally rotate the shoulder, or ask the patient to lie the arm across the chest.

Scanning technique

• Median: probe across the elbow crease. Find the brachial artery; the median nerve is the honeycomb oval just medial to it, on brachialis.
• Radial: probe across the front of the lateral elbow, 3–5 cm above the crease. Find the groove between brachioradialis and brachialis; the nerve sits in it, on or just above the humerus. Slide down to see the split into superficial and deep branches; block above the split.
• Ulnar: probe across the medial arm 3–5 cm above the medial epicondyle, or in the proximal forearm under flexor carpi ulnaris. Avoid the cubital tunnel itself.

Structures to identify

• Brachial artery
• Biceps tendon
• Brachialis
• Pronator teres
• Brachioradialis
• Humerus and epicondyles
• Median, radial and ulnar nerves

Position / ergonomics

Sit beside the outstretched arm with the screen beyond the hand.

Probe

High-frequency linear probe; a small-footprint probe helps over the epicondyle.

Settings

Small-parts or nerve preset, depth 2–3 cm, colour Doppler for the brachial and radial recurrent arteries.

Depth

1–3 cm.

Needle size

22–25 G, 50 mm.

Needling technique

In-plane or out-of-plane. For the median nerve, an in-plane needle from medial keeps away from the artery. For the radial nerve, in-plane from lateral through brachioradialis.

Optimal needle-tip position

Next to each nerve, so that the solution spreads round it. For the median nerve, on the side away from the artery.

Drug choice

For surgery: 1.5–2% lidocaine or 1.5% mepivacaine. For long analgesia: 0.5% ropivacaine or 0.25–0.5% levobupivacaine.

Volume

3–5 mL per nerve.

Optimal current if nerve stimulation is used

0.3–0.5 mA.

Muscle responses acceptable

• Median: wrist flexion, pronation
• Radial: wrist and finger extension
• Ulnar: little finger flexion, thumb adduction

Testing block success

• Median: pad of the index finger
• Radial: back of the first web space
• Ulnar: pad of the little finger

Indication

Seldom used; a single nerve catheter can be placed for chronic pain or ischaemic digits, but brachial plexus catheters are more common.

Kit

Small catheter-over-needle set if used.

Catheter

Next to the target nerve.

Regime

0.2% ropivacaine at 2–4 mL/h.

• Block the radial nerve above its split, otherwise the deep (motor) branch may be missed or the superficial branch alone blocked.
• Do not inject the ulnar nerve inside the cubital tunnel; go 3–5 cm higher or into the forearm.
• Distal blocks do not cover an upper-arm tourniquet.
• Use long-acting drug at the elbow and a short-acting proximal block to give hand analgesia without a numb arm (selective distal analgesia).

• McCartney and colleagues (2007) traced the median, radial and ulnar nerves from the elbow to the wrist with ultrasound and found their positions consistent; the radial nerve was easiest to see at the elbow.
• Dufeu and colleagues (2014) described a short-acting axillary block combined with long-acting ultrasound-guided distal blocks; 96% of distal blocks worked, lasting about 12 hours, with no prolonged motor block.

• McCartney CJ, Xu D, Constantinescu C, Abbas S, Chan VW. Ultrasound examination of peripheral nerves in the forearm. Reg Anesth Pain Med 2007;32:434–439. PubMed
• Dufeu N, Marchand-Maillet F, Atchabahian A, et al. Efficacy and safety of ultrasound-guided distal blocks for analgesia without motor blockade after ambulatory hand surgery. J Hand Surg Am 2014;39:737–743. PubMed