• Paul Hobeika, MD
• Douglas Unis, MD
• Jerry D. Vloka, MD

I.	INTRODUCTION
II.	INDICATIONS & CONTRAINDICATIONS
III.	FUNCTIONAL ANATOMY OF WRIST BLOCK
IV.	ANATOMIC LANDMARKS
V.	EQUIPMENT
VI.	TECHNIQUE Block of the Radial Nerve Block of the Dorsal Sensory Branch of the Radial Nerve Block of the Ulnar Nerve Block of the Dorsal Sensory Branch of the Ulnar Nerve Block of the Median Nerve Nerve Stimulation Technique
VII.	CHOICE OF LOCAL ANESTHETIC
VIII.	BLOCK DYNAMICS & PERIOPERATIVE MANAGEMENT
IX.	COMPLICATIONS & HOW TO AVOID THEM

INTRODUCTION

The wrist block is a technique for blocking branches of the ulnar, medial, and radial nerves at the level of the wrist. The wrist block is a basic peripheral nerve block technique that involves anesthesia of the median, ulnar, and radial nerves, as well as the dorsal sensory branch of the ulnar nerve. The wrist block is simple to perform, essentially devoid of systemic complications, and highly effective for a variety of procedures on the hand and fingers. As such, skill in performing a wrist block should be in the armamentarium of every anesthesiologist. Wrist blocks can be used in the outpatient setting and office setting along with the standard operating room setting, resulting in safe, effective, and cost-effective anesthesia that is well accepted by both surgeons and patients.^1–8 Wrist blocks are also useful in the emergency setting to provide anesthesia for repair of hand injuries in the emergency room because there is adequate anesthesia of the hand without motor blockade of the extrinsic hand muscles.⁹

INDICATIONS & CONTRAINDICATIONS

A wrist block is most commonly used for carpal tunnel and hand and finger surgery.^10,11 The most common hand surgery in the United States is carpal tunnel release. Paget described carpal tunnel syndrome in 1853.^{1, 12} Although Learmonth reported release of the carpal tunnel at the wrist in 1933, it was not until the 1950s that the surgery became popular through the efforts of Phalen.^13–15 Because of the ease of performing a wrist block, wrist blocks are used in a variety of settings including the emergency room, outpatient surgery centers, and office-based anesthesia practices. Hand surgeons also make use of the wrist block to perform minor procedures in their offices. A wrist block can be used in a patient with a full stomach requiring emergeny surgery, thereby obviating the need for general anesthesia and reducing the risk of aspiration.

Figure 29-1. Innervation of the hand: Territorial distribution of nerves.

The contraindications to wrist blocks are few, but include local infection at the sites of needle insertion, preexisting central or peripheral nervous systems disorders, and allergy to local anesthesia. Patients are usually able to tolerate a tourniquet on the arm without anesthesia for 20 min; a wrist tourniquet can be tolerated for about 120 min.

Figure 29-2. Innervation of the hand: The course of the terminal nerves.

FUNCTIONAL ANATOMY OF WRIST BLOCK

Innervation of the hand is shared by the ulnar, median, and radial nerves (Figure 29-1). The ulnar nerve innervates more intrinsic muscles than the median nerve, which in turn innervates digital branches to the skin of the medial one and a half digits (Figure 29-2). A corresponding area of the palm is innervated by palmar branches that arise from the ulnar nerve in the forearm. The deep branch of the ulnar nerve accompanies the deep palmar arch and supplies innervation to the three hypothenar muscles, the medial two lumbrical muscles, all the interossei, and the adductor pollicis. The ulnar nerve also innervates the palmaris brevis muscle.

Figure 29-3. Position and course of the radial nerve at the wrist.

The median nerve traverses the carpal tunnel and terminates as digital and recurrent branches. The digital branches innervate the skin of the lateral three and a half digits and, usually, the lateral two lumbrical muscles. A corresponding area of the palm is innervated by palmar branches that arise from the median nerve in the forearm. The recurrent branch of the median nerve supplies the three thenar muscles. In the palm, the digital branches of the ulnar and median nerves lie deep in the superficial palmar arch, but in the fingers, they lie anterior to the digital arteries that arise from the superficial arch. Although the innervation of the ring and middle fingers may vary, the skin on the anterior surface of the thumb is always supplied by the median nerve and that of the little finger by the ulnar nerve. The palmar digital branches of the median and ulnar nerves also innervate the nail beds of their respective digits.

The radial nerve passes along the front of the radial side of the forearm. It arises first from the lateral side of the radial artery and beneath the supinator muscle. About 3 inches above the wrist, it leaves the artery, pierces the deep fascia, and divides into two branches (Figure 29-3). The superficial branch, the smaller of the two branches, supplies the skin of the radial side and base of the thumb, and joins the anterior branch of the musculocutaneous nerve. The deep branch of the radial nerve communicates with the posterior branch of the musculocutaneous nerve. On the dorsum of the hand, the deep branch of the radial nerve forms an arch with the dorsal cutaneous branch of the ulnar nerve.

Figure 29-4. Cross-sectional anatomy of the wrist as shown on an MRI scan just above the carpal tunnel. A = anterior, FCR = flexor carpi radialis, FCU = tendon of the flexor carpi ulnaris, FPL = tendon ofthe flexor palmaris longus, M = medial, PL = tendon of the palmaris longus, SRN = superficial radial nerve.

ANATOMIC LANDMARKS

The superficial branch of the radial nerve runs along the medial aspect of the brachioradialis muscle (see Figure 29-3). It then passes between the tendon of the brachioradialis and radius to pierce the fascia on the dorsal aspect. Just above the styloid process of the radius (circle), it gives off digital branches for the dorsal skin of the thumb, index finger, and lateral half of the middle finger. Several of its branches pass superficially over the anatomic “snuffbox.”

The median nerve is located between the tendons of the palmaris longus and the flexor carpi radialis (see Figures 29–2 and 29–4). The palmaris longus tendon is usually the more prominent of the two tendons, and the median nerve passes just lateral to it.

The ulnar nerve passes between the ulnar artery and tendon of the flexor carpi ulnaris (see Figures 29–2 and 29–4. The tendon of the flexor carpi ulnaris is superficial to the ulnar nerve.