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Wrist Block - Detailed Guide with Diagrams

Overview

A wrist block is a peripheral nerve block technique that provides anaesthesia to the hand and all digits by blocking the three major terminal nerves of the upper limb at the level of the wrist. It is preferred over a nerve block at the elbow because it carries less risk of direct nerve injury and provides a more reliable field of anaesthesia for hand surgery.

Nerves blocked:

Ulnar nerve (+ its dorsal cutaneous branch)
Median nerve
Radial nerve (superficial branch - subcutaneous ring)

Sensory Innervation of the Hand

Before performing the block, understanding which nerve covers which territory is essential:

Surface	Nerve	Territory
Palmar	Median	Thumb, index, middle, and radial half of ring finger
Palmar	Ulnar	Little finger and ulnar half of ring finger
Dorsal	Radial (superficial)	Dorsum of thumb, index, middle, and radial ring finger (proximal phalanges)
Dorsal	Ulnar (dorsal cutaneous branch)	Dorsum of little and ulnar ring finger

Anatomy of the Nerves at the Wrist

Ulnar Nerve

Runs between the flexor carpi ulnaris (FCU) tendon (medially) and the ulnar artery (laterally)
Lies deep to the FCU at the wrist crease
Gives off the dorsal cutaneous branch about 5-7 cm proximal to the pisiform, which curves around the ulna to supply the dorsal-ulnar hand

Median Nerve

Lies between the tendons of palmaris longus (PL) and flexor carpi radialis (FCR)
If PL is absent (in ~15% of people), it lies just to the ulnar side of FCR
Passes under the flexor retinaculum through the carpal tunnel

Radial Nerve (Superficial Branch)

Purely sensory at the wrist
Divides into multiple small branches as it crosses the anatomical snuff box
No single injection point is reliable - requires a subcutaneous ring infiltration

Injection Level and Landmarks

All three injections are performed at the same level: the proximal wrist crease, approximately at the level of the distal end of the ulna.

Wrist block - palmar view showing ulnar nerve (4 ml) and median nerve (5 ml) injection sites

Figure 8.3 from Pye's Surgical Handicraft (22nd Ed.) - Wrist block, palmar (front) view. Upper needle (5 ml) = median nerve; lower needle (4 ml) = ulnar nerve.

Technique - Step by Step

Patient Position

Arm supinated, wrist extended slightly (a small roll under the wrist helps)
Identify key surface landmarks: FCU, FCR, palmaris longus, pisiform, ulnar styloid, radial styloid

1. Ulnar Nerve Block

Landmarks: FCU tendon at the level of the distal ulna, immediately radial (lateral) to it. The ulnar artery lies just radial to the nerve.

Technique:

Insert a 25 G needle to a depth of 1 cm, immediately to the radial side of FCU
Aspirate to confirm no vascular placement
Inject 4 ml of 1% lignocaine (or equivalent)

Dorsal branch of ulnar nerve: Also requires a separate subcutaneous injection - inject local anaesthetic between the proximal edge of the pisiform and the middle of the dorsum of the wrist, sweeping across the ulnar border subcutaneously.

Ulnar nerve block at the wrist - needle placement marked with landmarks

2. Median Nerve Block

Landmarks: Same level as the ulnar block, in the midline of the wrist between PL and FCR tendons.

Technique:

Insert a 25 G needle between the tendons of palmaris longus and flexor carpi radialis to a depth of 1 cm
If PL is absent, inject 3 mm to the ulnar side of FCR (this point sits close to the wrist midline or just slightly to the radial side)
Aspirate, then inject 5 ml of 1% lignocaine

Do NOT inject if strong paresthesia is felt - reposition the needle to avoid intraneural injection.

3. Radial Nerve Block (Subcutaneous Ring)

Because the superficial radial nerve divides into multiple small branches near the wrist with considerable anatomical variation, a single-injection technique is unreliable.

Technique:

Inject up to 10 ml of 1% lignocaine subcutaneously in a fan/ring around the entire radial border of the wrist
The injection arc extends from the middle of the dorsum, sweeping around the radial side, to the middle of the palmar surface - a semicircle that covers all branch points

Wrist block - dorsal (back) view showing radial nerve subcutaneous ring infiltration

Figure 8.4 from Pye's Surgical Handicraft - Wrist block (back). Dotted line represents the subcutaneous injection arc for the radial nerve.

Drugs and Doses Summary

Nerve	Volume	Drug	Depth
Ulnar	4 ml	1% lignocaine	1 cm deep to FCU
Median	5 ml	1% lignocaine	1 cm deep, between PL & FCR
Radial	Up to 10 ml	1% lignocaine	Subcutaneous ring, radial border
Dorsal ulnar	2-3 ml	1% lignocaine	Subcutaneous, pisiform to dorsal midline

Total volume: ~20-22 ml of 1% lignocaine. Bupivacaine 0.25-0.5% can be substituted for longer duration (4-8 hours).

Area of Anaesthesia

This triple block (with dorsal ulnar coverage) provides analgesia of:

All digits (fingers and thumb)
The whole hand

Exception: The proximal 1-2 cm of the palmar aspect of the hand immediately distal to the wrist joint may not be covered (this area is supplied by the palmar cutaneous branches of median and ulnar nerves, which arise proximal to the wrist crease).

Indications

Minor hand surgery (tendon repair, wound closure, foreign body removal)
Finger fracture reduction
Emergency hand procedures when a tourniquet will be applied at the forearm level
Carpal tunnel release (supplementary to local infiltration)
Burns/wound debridement of the hand

Contraindications

Infection at injection site
Patient refusal
Known allergy to local anaesthetic agent
Significant coagulopathy (relative)

Advantages over Elbow Block

Lower risk of direct nerve injury (ulnar nerve is superficial and at risk at the elbow)
More predictable block distribution
No motor block of forearm flexors
Suitable for outpatient/day-case procedures

Tips and Pitfalls

Always block the dorsal branch of the ulnar nerve separately - forgetting it leaves the dorsal-ulnar hand unsensate
Do NOT use vasoconstrictors (epinephrine) in the local anaesthetic for wrist blocks as there is some risk of digital ischemia through vascular reflex
Onset takes 10-20 minutes - allow adequate time before starting surgery
If paresthesia is elicited with needle placement, withdraw slightly before injecting to avoid intraneural injection

Source: Pye's Surgical Handicraft, 22nd Edition, Chapter 8 - Nerve block at the wrist; NYSORA Wrist Block Guidelines

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