Ulnar Nerve Block Technique
- Author: Bassem Asaad, MD; Chief Editor: Meda Raghavendra (Raghu), MD more...
The clinical indication of the block is the main factor in choosing the approach level of completing the block. Blockade distal to the take-off of the branches may lead to failure or incomplete effect of the desired blockade. The nerve can be blocked in the axilla, mid-humeral, above or below the elbow, and at the wrist. The authors will describe the 2 most commonly used techniques (above the elbow and at the wrist approaches) to block the ulnar nerve, whether for rescue purposes or for cases that require blockade of the ulnar nerve solely.
Above the Elbow
A block of the nerve should be attained at this site if elbow coverage is desired and also for forearm arteriovenous fistula creation.
The nerve can be approached 2-3 inches above the elbow joint. Block at this level results in coverage distal to the block point, including the articular branches to the elbow, the muscular branches to flexor carpi ulnaris, and half of flexor digitorum profundus (the other half is supplied by the median nerve), the palmar cutaneous branch, the dorsal branch as well as the supply of the terminal branches to the hypothenar muscles, adductor pollicis and flexor pollicis brevis, all interosseous muscles, and the last 2 lumbrical muscles.
Place the patient in the supine position with the arm extended and externally rotated at the shoulder; the forearm should be slightly flexed and supinated. ASA standard monitors should be applied and supplemental oxygen should be given. The elbow joint should then be prepared in the usual surgical fashion. Sterilizing the whole upper arm is highly recommended, and tracing the nerve up and down the arm is recommended for confirmation and identification of the different anatomical structures. The area distal to the wrist should not be covered to allow observing twitches in case neurostimulation is used.
The high-frequency ultrasound linear probe is placed transversely at the level of the elbow joint, over the medial epicondyle of the humerus; a short axis view of the ulnar nerve will be easily identified inside the sulcus ulnaris groove. The ulnar nerve should not be blocked at this site due to the potential buildup of pressure by the injectate as well as the potential for needle injury to the nerve itself against the bone. The nerve is scanned proximally for 2-3 inches, where it can be safely blocked by injecting about 7 ml of local anesthetic (see video below).
A continuous infusion catheter may also be inserted, especially in cases in which a staged surgical procedure is planned.
If combined with ultrasound, neurostimulation of the nerve at this site causes ulnar deviation and flexion of the wrist, flexion and opposition of the little and ring fingers, and adduction and flexion of the thumb.
Above the Wrist
The choice of this approach is mainly indicated for providing anesthesia and analgesia to the little finger. An advantage to blockade at this level is that the block includes the dorsal cutaneous branch, especially if the block is done 15 cm above the wrist crease. The ulnar nerve can also be blocked at this level in conjugation with median and radial nerve blocks (wrist block) to provide anesthesia and analgesia to the hand.
Place the patient in the supine position with the arm extended and externally rotated at the shoulder and the forearm extended and supinated. ASA-standard monitors should be applied, and supplemental oxygen should be given. The forearm and wrist should then be prepared in the usual surgical fashion. Sterilization should include a wide area starting below the wrist distally to the upper one third of the arm, as tracing the nerve up and down the forearm and arm is recommended for confirmation and identification of the different anatomical structures.
Blockade at this level results mainly in dermatomal block to the lateral third of the palm and palmar surface of both the little finger and medial half of the ring finger, dorsal medial half of the hand as well as the dorsal surface of the little finger and proximal phalanges of the ring and middle finger. It also results in motor block of the 3 hypothenar muscles, adductor pollicis and flexor pollicis brevis, all interosseous muscles, and the last 2 lumbrical muscles, and articular block to intercarpal, carpometacarpal, and intermetacarpal joints for the little and ring fingers.
A high-frequency ultrasound probe is placed transversely about 5-15 cm above the wrist (see the image below).
After local infiltration of the skin, a blunt 1.5-inch needle is advanced toward the nerve using in-plane or out-of-plane technique. Special care should be given to avoid puncturing the ulnar artery. Then 5 mL of local anesthetic may be injected around the nerve. If neurostimulation is used in conjugation with the ultrasound guidance, stimulation of the nerve at this level mainly results in flexion and opposition of the little and ring fingers and adduction and flexion of the thumb.
Under ultrasound guidance, the needle can be placed on the medial side of the forearm and advanced laterally under the flexor carpi ulnaris toward the ulnar nerve. This approach is more favorable if a continuous infusion catheter will be left in place.
See the list below:
Infection - Uncommon if proper sterile technique is used
Hematoma - If the ulnar artery is inadvertently punctured
Neuropathy - Mostly occurs if the nerve is blocked inside the sulcus ulnaris, where a significant chance exists for nerve injury by the needle or for ischemia as a result of high pressure by the local anesthetic injectate
Ulnar nerve blocks are used to rescue an incomplete brachial plexus block and can result in a faster onset of analgesia and better outcome when done concomitantly with infraclavicular blocks. The block can provide complete anesthesia and analgesia to the fifth digit finger and is a practical and easy approach for anesthesia for such cases in the emergency room. In the chronic pain field, a diagnostic block may be considered before implanting a peripheral nerve stimulator, especially for cases of ulnar nerve neuropathy and failed ulnar nerve transposition.
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