Goal
Wrist Block
|
|
A wrist block is the technique of 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 terminal branches of the respective nerves.
The technique 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.
Several different techniques of wrist blockade and their modifications have been
suggested; in this chapter, we chose to describe the one that is most commonly used
in our institution. A wrist block is most commonly used for carpal tunnel and hand
and finger surgery.
Innervation of the hand is shared by the ulnar, median, and radial nerves.
The ulnar nerve supplies more intrinsic muscles than the median nerve, which supplies digital branches to the skin of the medial 1½ digits. A corresponding area of the palm is supplied 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 lumbricals, all the interossei, and adductor pollicis. The ulnar nerve also innervates the palmar brevis.
The median nerve traverses the carpal tunnel and terminates as digital and recurrent branches. The digital branches supply the skin of lateral 3½ digits and, usually, the lateral two lumbricals. 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 mus-cles. 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 super-ficial arch. Although there may be variability of innervation of the ring and middle fingers, 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 supply innervation to 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 outer side the radial artery and beneath the supinator longus. About 3 inches above the wrist, it leaves the artery, pierces the deep fascia, and divides into two branches. The external branch, the smaller of the two, supplies the skin of the radial side and base of the thumb, and joins he anterior branch of the musculocutaneous nerve. The internal branch communicates with the posterior branch of the musculocutaneous nerve. On the back of the hand, it forms an arch with the dorsal cutaneous branch of the ulnar nerve.
| As previously mentioned, blockade of the ulnar, median, and radial nerves results in anesthesia of the entire hand. The nerve contribution to the innervation of the hand considerably varies; the illustrations show the most common arrangement. |
|
|
| The patient is in the supine position with the arm abducted. The wrist is best kept in a slight dorsiflexion. |
|
A standard regional anesthesia tray is prepared with the following equipment:
|
|
The superficial branch of the radial nerve runs along the medial aspect of the brachioradialis muscle. 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 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 "snuff box". |
|
TIP: The position of the radial nerve is often confusing to trainees as to its relationship to the radial artery. The illustration clarifies the course of the radial nerve branches at the wrist. |
|
| The medial nerve is located between the tendons of the palmaris longus (white arrow) and the flexor carpi radialis (red arrow). The palmaris longus tendon is usually the more prominent of the two; the median nerve passes just lateral to it. |
|
| The ulnar nerve passes between the ulnar artery and tendon of the flexor carpi ulnaris. The tendon of the flexor carpi ulnaris is superficial to the ulnar nerve. |
|
The entire wrist area should cleaned with a disinfectant solution.
Block of the radial nerveThe radial nerve 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. Local anesthetic should be injected subcutaneously, with 5 mL of local anesthetic just above the radial styloid, aiming medially. The infiltration is then extended laterally, using an additional 5 mL of local anesthetic. |
Block of the ulnar nerveThe ulnar nerve is anesthetized by inserting the needle under the tendon of the flexor carpi ulnaris muscle close to its distal attachment just above the styloid process of the ulna. The needle is advanced 5-10 mm to just past the tendon of the flexor carpi ulnaris. Three to 5 mL of local anesthetic solution is injected. A subcutaneous injection of 2-3 ml of local anesthesia just above the tendon of the flexor carpi ulnaris is also advisable in blocking the cutaneous branches of the ulnar nerve which often extend to the hypothenar area. |
The median nerve is blocked by inserting the needle between the tendons of the palmaris longus and flexor carpi radialis. The needle is inserted until it pierces the deep fascia. Three to 5 mL of local anesthetic is injected. Although the piercing of the deep fascia has been described to result in a fascial "click", it is more reliable to simply insert the needle until it contacts the bone. The needle is then withdrawn 2-3 mm and the local anesthetic is injected.
TIP: A "fan" technique is recommended to increase the success rate of the medianus block. After the initial injection, the needle is withdrawn back to the skin level, redirected 30o laterally, and advanced again to contact the bone. After pulling back 1-2 mm off the bone, an additional 2 mL of local anesthetic is injected. A similar procedure is repeated with a medial redirection of the needle.
The choice of the type and concentration of local anesthetic for wrist blockade is based on the desired duration. Table provides onset times and duration for some commonly used local anes-thetics mixtures.
| Onset (min) |
Anesthesia (hrs) | Analgesia (hrs) | |
| 1.5% Mepivacaine (+ HCO3) | 15-20 | 2-3 | 3-5 |
| 2% Lidocaine (+ HCO3) | 10-20 | 2-5 | 3-8 |
| 0.5% Ropivacaine | 15-30 | 4-8 | 5-2 |
| 0.75% Ropivacaine | 10-15 | 5-10 | 6-24 |
| 0.5% Bupivacaine (or l-bupivacaine) | 15-30 | 5-15 | 6-30 |
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.
| Infection | - This should be very rare with the use of an aseptic technique |
| Hematoma |
- Avoid multiple needle insertions for superficial blocks - Most superficial blocks can be accomplished with one or two needle insertions - Use 25-gauge needle and avoid puncturing superficial veins |
| Vascular Puncture | - Do not use epinephrine with wrist and finger blocks |
| Nerve Injury |
- Do not inject when patient complains of pain or high pressure on injection is detected - Do not reinject the medianus and ulnaris nerves |
| Others | - Instruct the patient on the care of the insensate extremity |
- Brown DL, Bridenbaugh LD: The Upper Extremity. Somatic Block. In Cousins, M.J., and Bridenbaugh PO (eds): Neuronal Blockade in Clinical Anesthesia and Management of Pain. Philadelphia, J.B. Lippincott-Raven Publishers, 1988, pp 345-71.
- Delaunay L, Chelly JE: Blocks at the wrist provide effective anesthesia for carpal tunnel release. Can J Anaesth 2001; 48:656-60.
- Derkash RS, Weaver JK, Berkeley ME, Dawson D: Office carpal tunnel release with wrist block and wrist tourniquet. Orthopedics. 1996; 19:589-90.
- Gebhard RE, Al-Samsam T, Greger J, Khan A, Chelly JE: Distal nerve blocks at the wrist for outpatient carpal tunnel surgery offer intraoperative cardiovascular stability and reduce discharge time. Anesth Analg 2002; 95:351-5.
- Hahn MB, McQuillan PM, Sheplock GJ: Regional Anesthesia: An Atlas of Anatomy and Techniques. St. Luis, Mosby, 1996.
- Mulroy MF: Regional Anesthesia: An Illustrated Procedural Guide (3rd ed). Philadelphia, Lippincot, 2002.
- Ramamurthy S., Hickey R.: Anesthesia . In Green DP and Hotchkiss RN (eds): Operative Hand Surgery. New York, Churchill Livingstone, 1993, pp 25-52.
