Peripheral Blocks at the Midhumeral Level, Elbow, and Wrist

Clinical Applications

As techniques for brachial plexus blockade have gained popularity, indications for peripheral nerve blockade at the wrist and elbow have diminished. However, these techniques can be useful when limited anesthesia is required, when contraindications to brachial plexus block (e.g., infection, bilateral surgery, coagulation abnormalities, bleeding diathesis, difficult anatomy) exist, or when brachial plexus blockade is incomplete. Only the midhumeral approach provides anesthesia for the use of a tourniquet.

1693

Midhumeral Block

A midhumeral approach to the brachial plexus has been described. This novel approach involves blocking each of the four nerves of the brachial plexus separately in the humeral canal at the level of the proximal one third and distal two thirds of the humerus. At this level, the median and ulnar nerves are located on the lateral and medial aspects of the brachial artery, respectively. The musculocutaneous nerve is identified within the body of the biceps muscle, and the radial nerve lies adjacent to the humerus. A volume of 8 to 10 mL of local anesthetic is injected after localization of each nerve with a nerve stimulator. Midhumeral block has been reported to have a higher success rate than traditional (defined as stimulation of two nerves) axillary brachial plexus block.^[33] In this study,^[33] time to complete the block was not different between the two techniques; however, the onset of complete sensory block was shorter in the axillary approach, whereas the success rate of blockade of all four major nerves was higher in the midhumeral group. This technique may have applications when anatomic difficulties preclude a traditional approach or when the surgical procedure requires a dense block of all four major nerves. The safety and clinical practicality of the midhumeral approach remain to be proved.

Median Nerve Block

Block of the median nerve provides anesthesia of the palmar aspects of the thumb and index finger, the middle finger and radial half of the ring finger, and the nail beds of the same digits. Motor block includes the muscles of the thenar eminence, lumbrical muscles of the first and second digits, and in the case of the block at the elbow, median-innervated wrist flexor muscles of the forearm.

Technique at the Elbow

With the patient's arm placed in the anatomic position (i.e., palm up), a line is drawn connecting the medial and lateral epicondyles of the humerus. The major landmark for this technique is the brachial artery, which is found medial to the biceps tendon at the intercondylar line. The median nerve lies medial to the artery ( Fig. 44-8 ) and can be blocked with 3 to 5 mL of solution after eliciting a paresthesia. If no paresthesia is obtained, the solution can be injected in a fanlike pattern medial to the palpated artery.

Technique at the Wrist

The median nerve is located between the flexor carpi radialis and palmaris longus tendons and can be blocked at a point 2 to 3 cm proximal to the wrist crease ( Fig. 44-9 ). (The palmaris longus tendon is congenitally or postsurgically absent from some patients.) A loss of resistance is felt as the needle passes through the flexor retinaculum, at which point 2 to 4 mL of solution should be injected. A superficial palmar branch supplying the skin of the thenar eminence can be blocked by injecting 0.5 to 1 mL of solution subcutaneously above the retinaculum. Paresthesias should not be sought because of the confinement of this nerve within the carpal tunnel.

Figure 44-8 Anatomic landmarks for median and radial nerve blocks at the elbow.

Radial Nerve Block

Block of the radial nerve provides anesthesia to the lateral aspect of the dorsum of the hand (i.e., thumb side) and the proximal portion of the thumb, index, middle, and lateral half of the ring fingers.

Technique at the Elbow

The radial nerve can be blocked at the elbow as it passes over the anterior aspect of the lateral epicondyle. The intercondylar line and lateral edge of the biceps tendon are marked. A 22-gauge, 3- to 4-cm needle is inserted at a point 2 cm lateral to the biceps tendon and is advanced until bone is encountered (see Fig. 44-8 ). A fanlike injection is made using 3 to 5 mL of solution.

Technique at the Wrist

The radial nerve block at the wrist is a field block of the multiple peripheral branches descending along the dorsum and radial side of the wrist. The extensor pollicis longus tendon can be identified when the patient extends the thumb. The needle insertion is over this tendon at the base of the first metacarpal; the injection is superficial to the tendon. A volume of 2 mL of local anesthetic is injected proximally along the tendon, and an additional 1 mL is injected as the needle passes at a right angle across the anatomic snuffbox ( Fig. 44-10 ).

Ulnar Nerve Block

Blockade of the ulnar nerve provides anesthesia of the ulnar side of the hand, the little finger, and the ring finger and all the small muscles of the hand, except those of the thenar eminence and the first and second lumbrical muscles.

1694

Figure 44-9 Anatomic landmarks for median and ulnar nerve blocks at the wrist. An alternative method for ulnar nerve block, from the ulnar side of the wrist, is shown.

Technique at the Elbow

Although the ulnar nerve is easily accessible at its subcutaneous position posterior to the medial epicondyle, blockade at this site is associated with a high incidence of neuritis. The nerve is surrounded by fibrous tissue at this point, requiring an intraneural injection for successful blockade. Use of a very fine needle along with a small volume of solution (1 mL) diminishes the risk; however, the nerve can be satisfactorily blocked with 5 to 10 mL of solution at a site 3 to 5 cm proximal to the elbow. The local anesthetic should be injected in a fanlike fashion without elicitation of a paresthesia.

Technique at the Wrist

At the wrist, the ulnar nerve lies beneath the flexor carpi ulnaris tendon between the ulnar artery and the

Figure 44-10 Anatomic landmarks and method of needle insertion for a radial nerve block at the wrist.

Musculocutaneous Nerve Block

The musculocutaneous nerve terminates as the lateral cutaneous nerve of the forearm. This nerve provides sensory innervation to the skin on the radial side of the forearm up to the radiocarpal joint. This block is usually performed to supplement the axillary approach to brachial plexus anesthesia.

Technique at the Elbow

The lateral cutaneous nerve of the forearm can be blocked 1 cm proximal to the intercondylar line immediately lateral to the biceps tendon. Fanlike infiltration of 3 to 5 mL of solution subcutaneously at this site provides excellent anesthesia of this nerve.

Peripheral Blockade at the Elbow Versus the Wrist

The forearm cutaneous nerves arise in the upper arm and are not anesthetized by block of the peripheral nerves at the elbow. There is no advantage of block of the peripheral nerves of the upper extremity when comparing elbow with wrist techniques; both provide sensory anesthesia of the hand.

1695

Side Effects and Complications

In general, distal peripheral blocks are associated with a lower risk of complications. However, intravascular injection can occur, and the usual precautions of incremental injection after aspiration are recommended. The risk of nerve injury is theorized to be higher when more distal peripheral blocks are performed, possibly because of superficial nerve placement between bony and ligamentous structures, thereby offering ready access to the probing needle point.