The median nerve lies between the flexor carpi radialis and palmaris longus tendons at the wrist.

Except in rare cases, it does not have an associated vascular structure.

It provides sensory innervation to the thumb, index finger, third finger, lateral aspect of the ring finger, and palm.

It provides motor innervation to the thenar muscles and first and second lumbricals.

The radial nerve is located lateral to the radial artery at the wrist.

The superficial branch of the radial nerve passes over the styloid process of the radius, and other branches pass over the anatomic snuffbox.

The radial nerve provides sensory innervation to the dorsal lateral half of the hand and dorsal aspect of the thumb.

It provides motor innervation to the extensor muscles in the dorsal forearm.

The ulnar nerve lies medial to the ulnar vessels and travels deep to the flexor carpi ulnaris.

Dorsal and palmar cutaneous branches of the ulnar nerve arise approximately 5 to 10 cm proximal to the wrist.

The ulnar nerve provides sensory innervation to the fifth finger, medial aspect of the ring finger, and the medial hand and wrist.

It provides motor innervation to the hypothenar muscles, interossei, adductor pollicis, deep head of the flexor pollicis brevis, and the medial two lumbricals.

Have the patient sit or lie supine with the arm resting on a hard surface, with the hand supinated.

Put the ultrasound machine at the head of the bed.

Stand at the patient’s waist looking at the ultrasound machine.

Use a high-frequency (5 to 10 MHz) linear ultrasound probe to identify the forearm nerves.

• The forearm nerves become easier to identify as you move from the wrist to the mid forearm.

Place the probe in transverse orientation over the palmar aspect of the wrist with the middle of the transducer overlying the middle of the wrist crease. Figure 1

Move the probe proximally to the mid forearm to visualize the median nerve, which is located between the fascial planes of the flexor digitorum superficialis and profundus.

• As you move proximally, the tendon structures disappear, and the median nerve becomes more obvious.
• Except in rare cases, there is no vascular structure associated with the median nerve.

Place the probe in transverse orientation over the radial, palmar aspect of the patient’s wrist to identify the distal radial artery in cross-section. Figure 2

• Color Doppler mode can be used to help identify the artery.

Move the probe proximally to the mid forearm to visualize the radial nerve, which lies lateral to the radial artery.

• The radial nerve appears as hypoechoic fascicles surrounded by hyperechoic connective tissue.

Have the patient extend the arm and supinate the elbow, facing away from you. Figure 3

• Alternatively, have the patient flex the arm and supinates the elbow, facing toward you.

Place the probe in transverse orientation over the ulnar, palmar aspect of the patient’s wrist to identify the distal ulnar artery in cross-section.

• Color Doppler mode can be used to help identify the artery.

Move the probe proximally to the mid forearm to visualize the ulnar nerve, which lies medial to the ulnar artery.

• The ulnar nerve appears as hypoechoic fascicles surrounded by hyperechoic connective tissue.

Disinfect the skin.

Place a local skin wheal of anesthetic just adjacent to the probe in transverse orientation.

• For a median nerve block, place the skin wheal on either side of the probe, depending on hand dominance.
• For a radial nerve block, place the skin wheal on the lateral (radial) side of the probe to avoid puncture of the radial artery.
• For an ulnar nerve block, place the skin wheal on the medial (ulnar) side of the probe to avoid puncture of the ulnar artery.

Place a sterile cover over the ultrasound probe and apply sterile gel.

With a spinal needle attached to the anesthetic syringe, enter the skin 1 cm adjacent to the probe with the needle bevel up. Entry of the needle should generally be at a 45-degree angle.

To best visualize the needle tip, keep the probe in a transverse orientation and use an in-plane technique.

Advance the needle slowly, and aim toward the dorsal aspect of the hyperechoic (bright) nerve. Stay at least 1 cm from the nerve to avoid puncture.

Slowly inject 2 to 3 mL of anesthetic to confirm location. Anesthetic will have a hypoechoic (dark) appearance. If patient feels a sharp electric type pain with injection remove needle slightly and re-inject. Patient should feel pressure but not electric shooting pain.

Using V-shaped redirections of the needle, inject 2 to 5 mL of anesthetic per each nerve over the palmar and dorsal aspects of the nerve. The needle should not penetrate the nerve at any point.

• Full circumferential spread of anesthetic around the nerve is ideal but not required.

Visualize injection of the anesthetic at all times.

• If the injection cannot be visualized, stop the procedure.

The patient should start to experience pain relief within 15 minutes and full blockade after 30 minutes. The duration of the block should be 3 to 8 hours, depending on the anesthetic used.