Indications

Contraindications

Clinical anatomy

The three major nerves of the forearm can be blocked at the elbow (Fig. 21.1), and also the three cutaneous nerves of the forearm.

Figure 21.1 Axial T1-weighted MR image showing anatomy of relevant structures at the elbow. 1: radial nerve with profunda brachii artery and vein; 2: biceps tendon; 3: brachial artery; 4: brachioradialis; 5: site of median nerve; 6: extensor carpi radialis longus; 7: ulnar nerve.

The median nerve, which lies anteromedially to the brachial artery near the axilla, crosses medial to the artery in the arm. At the elbow it lies between the tendons of brachialis and pronator teres, and deep to the bicipital aponeurosis. It passes between both heads of pronator teres to enter the forearm (Fig. 21.2). The median nerve provides sensory innervation to the lateral half of the palm, flexor aspect of the thumb, index finger, middle finger, and radial side of the ring finger.

Figure 21.2 Cadaver structures illustrating anatomy pertinent to median and radial nerve block at the elbow. 1: biceps muscle and aponeurosis; 2: brachioradialis; 3: brachialis; 4: radial nerve; 5: lateral cutaneous nerve of forearm; 6: brachial artery; 7: median nerve; 8: brachial vein; 9: pronator teres; 10: medial cutaneous nerve of forearm.

The radial nerve passes between the long and medial head of the triceps to travel around the humerus and emerges on the anterior aspect of the arm above the brachioradialis. It passes deep to the brachioradialis over the lateral epicondyle, where it divides into a deep and a superficial branch (Fig. 21.2). The radial nerve provides sensation for the radial half of the dorsum of the hand, the back of the thumb, and part of the dorsum of the index finger.

The ulnar nerve leaves the brachial artery halfway down the arm and passes behind the medial epicondyle in a fibrous tunnel. It passes between the two heads of flexor carpi ulnaris to enter the forearm (Fig. 21.3). The ulnar nerve provides sensation for the ulnar half of the dorsum of the hand, little finger, and ulnar side of the ring finger.

Figure 21.3 Cadaver structures illustrating anatomy pertinent to ulnar nerve block at the elbow. 1: Olecranon process; 2: medial epicondyle; 3: triceps muscle; 4: ulnar nerve.

Surface anatomy

Important structures include the medial and lateral epicondyles of the humerus, olecranon process, intercondylar skin crease, biceps tendon, brachioradialis muscle, and brachial artery (Fig. 21.4). The biceps tendon can be palpated with elbow flexion beneath the intercondylar crease, and it runs laterally to the head of the radius. The brachioradialis muscle can be palpated lateral to the biceps tendon. The brachial artery is palpated medial to the biceps muscle.

Figure 21.4 Landmarks for nerve blocks at the elbow. Landmarks include the medial and lateral epicondyles of the humerus, intercondylar skin crease, biceps tendon, brachioradialis muscle, and brachial pulse. The biceps tendon can be palpated with elbow flexion beneath the intercondylar crease and it runs laterally to the head of the radius. The brachioradialis muscle can be palpated lateral to the biceps tendon. The brachial artery is palpated medial to the biceps muscle.

Sonoanatomy

The examination begins with the patient supine, the arm abducted, the forearm supinated, and the wrist halfway between pronation and supination (Fig. 21.5). A systematic survey should be performed from superficial to deep and medial to lateral. A high frequency ultrasound transducer is used. With a transverse orientation, the median nerve is found medial to the brachial artery at the elbow as a hyperechoic structure (Fig. 21.6). This is on the medial side of the antecubital fossa. The radial nerve, after winding around the humerus, descends in the intermuscular septum between the brachialis and brachoradialis initially, and then the extensor carpi radialis. The radial nerve is easily seen with ultrasound, as the deep and superficial branches between the brachioradialis and brachialis muscles at the elbow. This nerve appears as a hyperechoic oval structure on the radial side of the antecubital fossa. The two key structures to identify include the hypoechoic brachioradialis and brachialis muscles. The radial nerve lies in the fascial thickening between these (Fig. 21.7). The ulnar nerve is seen posterior to the medial epicondyle at the elbow level in the condylar groove (Fig. 21.8).

Figure 21.5 Arm position for ultrasound-guided nerve blocks at the elbow.

Figure 21.6 Sonosatomy relevant to median nerve block at the elbow. MN: median nerve; BA: brachial artery; B: bone.

Figure 21.7 Sonosatomy relevant to radial nerve block at the elbow. RN: radial nerve; BM: brachialis muscle; BRM: brachoradialis muscle.

Figure 21.8 Sonosatomy relevant to ulnar nerve block at the elbow. UN: ulnar nerve, B: bone.

Technique

Landmark-based approach

As for all regional anesthetic procedures, after checking that the emergency equipment is complete and in working order, intravenous access, ECG, pulse oximetry, and blood pressure monitoring are established. Asepsis is observed.

The patient is placed in the supine position, with the arm to be blocked abducted 30° with the elbow extended on an arm board. The operator sits at the side to be blocked below the patient’s elbow. The needle insertion point is infiltrated with local anesthetic using a 25-G needle. For block at the elbow, a 25-mm insulated needle is used.

Median nerve block

Needle insertion for median nerve block is medial to the brachial pulse at the level of the intercondylar crease (Fig. 21.9). Needle orientation is cephalad and toward the humerus. The stimulating current is set at 1.0 mA, 2 Hz, and 0.1 ms. The needle is advanced slowly until the appropriate muscle response is obtained: finger rather than wrist flexion. A loss of resistance is felt as the bicipital aponeurosis is punctured. The needle position is adjusted while decreasing the current to 0.35 mA with maintenance of the muscle response. Wrist flexion may be due to direct muscle stimulation. Incremental injections of local anesthetic (4–6 mL) are made with repeated aspiration. If no twitch is found, ‘walk’ the needle in a medial to lateral plane.

Figure 21.9 Median nerve block technique. Needle insertion for median nerve block is medial to the brachial pulse at the level of the intercondylar crease. Needle orientation is cephalad and toward the humerus.

Radial nerve block

Needle insertion for radial nerve block is halfway between the biceps tendon and lateral border of the arm (or 1 cm lateral to the biceps tendon), in the gutter between the biceps tendon and brachioradialis at the level of the intercondylar skin crease (Fig. 21.10). Needle orientation is cephalad and aimed toward the humerus (toward the lateral epicondyle). At a depth of 2–3 cm, the radial nerve will be encountered. Finger and thumb extension, rather than wrist extension due to possible direct stimulation of extensor carpi radialis, results in greatest block success. Incremental injections of local anesthetic (4–6 mL) are made with repeated aspiration.

Figure 21.10 Radial nerve block technique. Needle insertion for radial nerve block is halfway between the biceps tendon and lateral border of the arm (or 1 cm lateral to the biceps tendon), in the gutter between the biceps tendon and brachioradialis at the level of the intercondylar skin crease. Needle orientation is cephalad and toward the humerus.

If direct brachioradialis contraction is elicited, move the needle slightly more medially. Failure to elicit an appropriate muscle response should be followed by walking the needle in a medial to lateral orientation.

Ulnar nerve block

The elbow is flexed 90° and the arm internally rotated across the upper body for ulnar nerve block. Needle orientation is 45° to the skin in a cephalad direction (Fig. 21.11). The ulnar nerve is very superficial and contacted within 0.5–1 cm. Little finger flexion and ulnar deviation of the hand, rather than wrist flexion due to possible direct flexor carpi ulnaris stimulation, results in greatest block success. Incremental injections of local anesthetic (4 mL) are made with repeated aspiration. The needle is walked in a medial to lateral direction if the ulnar nerve is not stimulated. With elbow flexion, the ulnar nerve may slip over the medial epicondyle.

Figure 21.11 Ulnar nerve block technique. The elbow is flexed 90° and the arm internally rotated across the upper body for ulnar nerve block. Needle orientation is 45° to the skin in a cephalad direction.

Cutaneous nerves of forearm blocks

Because the branches of the sensory nerves of the forearm have already ramified extensively and cross the joint superficially in a diffuse subcutaneous network, good anesthesia of the forearm itself is difficult to obtain. The lateral cutaneous nerve of the forearm can be blocked by injection deep to the fascia in the muscular groove between the biceps and brachioradialis. The medial cutaneous nerve of the forearm can be blocked by subcutaneous injection in the intermuscular groove between the biceps and pronator teres. The posterior cutaneous nerve of the forearm can be blocked by subcutaneous injection from the lateral epicondyle to the olecranon.

Ultrasound-guided approach

Intravenous access, electrocardiogram (ECG), pulse oximetry and blood pressure monitoring are established. Maximized comfort for the operator and patient is an important step in pre-procedure preparation. For ultrasound-guided nerve blocks at the elbow, the patient is placed in the supine position, the arm abducted, the forearm supinated, and the wrist halfway between pronation and supination. The operator sits adjacent to the side to be blocked. The ultrasound screen, transducer, needle, and plane of imaging should all be placed in one view for the operator. For ultrasound-guided nerve blocks at the elbow, the ultrasound screen is placed above the elbow on the side to be blocked (Fig. 21.12). Room lights may be turned down to enhance image viewing. The operating lights can be used to maintain some working lighting in the background.

Figure 21.12 Global view of the block field for ultrasound-guided nerve blocks at the elbow.

The skin is disinfected with antiseptic solution and draped. A sterile sheath (CIVCO Medical Instruments, Kalona, IA, USA) is applied over the ultrasound transducer with sterile ultrasound gel (Aquasonic, Parker Laboratories, Fairfield, NJ, USA). Another layer of sterile gel is placed between the sterile sheath and the skin. The ultrasound screen should be made to look like the scanning field. That is, the right side of the screen represents the right side of the field. Adjustable ultrasound variables such as scanning mode, depth of field, and gain are optimized.

Developing and maintaining a predetermined basic scanning routine is of enormous help in improving operator confidence and success. On the medial side of the antecubital fossa, the median nerve is identified on the medial side of the brachial artery. A 21-GA × 50-mm insulated needle is inserted parallel to the axis of the beam of the ultrasound transducer (Fig. 21.13). The operator can slide and tilt the transducer to maintain the needle tip within the plane of imaging as much as possible. The needle is slowly advanced under ‘real-time’ imaging to bring the needle tip to rest adjacent to the median nerve. Once the needle tip has been confirmed by ultrasonography to lie in close proximity to the median nerve, this can be confirmed by using a nerve stimulator. Characteristic motor activity in the hand is seen. Test injections for assessment of local anesthetic spread should be small (0.5–2 mL). If the local anesthetic spread is not seen on the ultrasound screen, the injection should be stopped. The needle is readjusted to allow complete encirclement of the nerve with local anesthetic (5 mL). Local anesthetic appears as a hypoechoic image (Fig 21.14).

Figure 21.13 Ultrasound transducer and needle positioning during ultrasound-guided median nerve block at the elbow. Note the needle orientation in the same plane as the ultrasound beam.

Figure 21.14 Real-time imaging of needle insertion for ultrasound-guided median nerve block at the elbow. Needle insertion is on the medial aspect of the transducer. Notice the needle shaft and the needle tip (N) in close proximity to the median nerve. N: needle tip; MN: median nerve; LA: local anesthetic; BA: brachial artery; B: bone.

On the lateral side of the antecubital fossa, the radial nerve is identified as deep and superficial branches between the brachioradialis and brachialis muscles. A 21-GA × 50-mm insulated needle is inserted parallel to the axis of the beam of the ultrasound transducer (Fig. 21.15). The needle is slowly advanced under ‘real-time’ imaging to bring the needle tip to rest adjacent to the radial nerve. The needle is readjusted to allow complete encirclement of the nerve with local anesthetic (5 mL). Local anesthetic appears as a hypoechoic image (Fig. 21.16).

Figure 21.15 Ultrasound transducer and needle positioning during ultrasound-guided radial block at the elbow. Note the needle orientation in the same plane as the ultrasound beam.

Figure 21.16 Real-time imaging of needle insertion for ultrasound-guided radial nerve block at the elbow. Needle insertion is on the medial aspect of the transducer. Notice the needle shaft and the needle tip (N) in close proximity to the radial nerve. N: needle tip; RN: radial nerve; LA: local anesthetic; BM: brachialis muscle; BRM: brachoradialis muscle, B: bone.

The ulnar nerve is seen posterior to the medial epicondyle at the elbow level in the condylar groove (Fig. 21.8). A 21-GA × 50-mm insulated needle is inserted parallel to the axis of the beam of the ultrasound transducer (Fig. 21.17). The needle is slowly advanced under ‘real-time’ imaging to bring the needle tip to rest adjacent to the ulnar nerve. The needle is readjusted to allow complete encirclement of the nerve with local anesthetic (5 mL). Local anesthetic appears as a hypoechoic image (Fig. 21.18).

Figure 21.17 Ultrasound transducer and needle positioning during ultrasound-guided ulnar nerve block at the elbow. Note the needle orientation in the same plane as the ultrasound beam.

Figure 21.18 Real-time imaging of needle insertion during ultrasound-guided ulnar nerve block at the elbow. Notice the needle shaft marked with arrows and the needle tip (N) in close proximity to the ulnar nerve. N: needle tip; UN: ulnar nerve; LA: local anesthetic.

Adverse effects