The radial, median, and ulna nerves may be blocked at the wrist, providing anesthesia to the hand. The anatomy and techniques of these three blocks are provided below.
While most injuries of the hand can be managed with either local infiltration or a digital block if an individual finger is involved, there are several circumstances where anesthesia of the entire hand may prove advantageous:
1. Diffuse or extensive injuries of the hand. Large lacerations of the hand, especially on the palmer aspect, may be quite difficult and painful to anesthetize with local infiltration, due to the often thick calloused skin and the extensive sensory nerve innervation.
2. Multiple finger lacerations where performing 4 - 5 individual digital blocks are required.
3. Extensive abrasions with debris embedded in the skin and subcutaneous tissues. This so called “road rash” is difficult and sometimes impossible to anesthetize with local infiltration or topical anesthesia prior to required debridement.
4. Burns, bites or envenomations. In cases of hydrofluoric acid burns where multiple subcutaneous calcium gluconate injections are required; In cases animal bites where rabies immune globulin is required. Stingray or sea urchin envenomation where foreign material removal may be required. Patients in all three situations may have a much less painful experience if total hand anesthesia is obtained prior to the required procedure.
Alternatives
Local anesthetic infiltration, procedural sedation, general anesthesia. Each case should be individualized, and patient preference, and a discussion of the alternative methods, risks and benefits should be initiated prior to any nerve block.
Radial Nerve Block
Distribution
Dorsal-radial aspect of the hand, the proximal dorsal regions of the index and middle finger, the radial half of the proximal dorsal ring finger.
Anatomy
The superficial branch of the radial nerve emerges from under the tendon of the brachioradialis muscle approximately 5-10 cm proximal to the wrist crease, and travels laterally toward the radial dorsal aspect of the wrist. At this region, the nerve branches into superficial rami and then more distally into the dorsal digital nerves which supply the sensory innervation of the radial side of the dorsum of the hand, as well as the proximal radial volar aspect of the thumb. It is important to realize that at the wrist crease the radial nerve had already divided into branches
Technique
Use the pulsatile radial nerve at the proximal palmar crease, and the radial stypoid as a landmarks. Just lateral to the artery, or at the region of the radial styloid and palmar crease, using a 25 gauge 2-4 cm depth needle, inject 2-5 cc of lidocaine 1% or buopivacaine 0.25 or 0.5% at the depth of the artery. Then using the same needle, perform a field block with 5 – 10 cc of additional anesthetic. This is done by infiltrating the subcutaneous region from the point of initial needle entry to the dorsal midline of the wrist, advancing the needle in the subcutaneous tissues in a dorsal and medial direction. This will require that the needle be withdrawn and repositioned with another injection at least once. Once can minimize the discomfort of the second or third injections by entering at a skin site already anesthetized by the previous injection. This technique should block the superficial radial nerve and its associated branches at the level of the wrist.
UlnaR Nerve Block
Distribution
Ulnar aspect of the hand, the little finger, and the ulnar half of the ring finger.
Anatomy
The ulnar nerve is adjacent and medial to the ulnar artery in the mid forearm as it travels toward the wrist. At this point both the nerve and artery are deep and just radial to the flexor carpi ulnaris tendon. This tendon can be palpated at the pisiform bone by having the patient flex the wrist against resistance. Approximately 5-7 cm proximal to the palmar crease, the nerve divides into the dorsal cutaneous branch and the palmar branch. The palmar branch continues on beneath the flexor Capri ulnaris tendon and then divides at the radial aspect near the pisiform bone into the superficial and deep branches. The dorsal cutaneous branch travels beneath the flexor carpi ulnaris tendon to reach the dorsal ulnar aspect of the hand.
Technique
Lateral Approach: Both the dorsal cutaneous and the palmar branches of the nerve must be anesthetized to achieve complete ulnar nerve region paresthesia.
To anesthetize the palmar branch, use the flexor carpi ulnaris tendon as your landmark. Insert a 2-4 cm 23-25 gauage needle, at the ulnar aspect of the flexor carpi ulnaris tendon, directing the needle under the tendon in a lateral/radial direct. Advance the needle 1 - 1.5 cm until paresthesia is elicited. Then deposit 2-5 cc of lidocaine or bupivacaine. If paresthesia is not elicited, then direct the needle toward the ulna bone, deep to the flexor carpi ulnaris tendon, and inject the anesthetic as the needle is withdrawn.
To anesthetize the dorsal cutaneous branch, insert the needle at the same site as above, and inject 5-10 cc of anesthetic from the lateral border just nder the flexor carpi ulnaris tendon to the dorsal midline, thus reaching and branches of the nerve. This lateral technique allows one to reach both nerve branches from the same initial injection point.
Median Nerve Block
Distribution
Radial half of the palmar surface of the hand; volar surface of the thumb, index, and middle finger; volar surface of the radial half of the ring finger; distal dorsal surface of the thumb, index, middle, and ring fingers.
Anatomy
The median nerve at the level of the wrist is located deep to the flexor retinaculum, although there may also be a cuteneous palmar branch that branches off before the wrist crease and lies superficial to the retinaculum. The median nerve lies deep to and just radial to the palmaris longus tendon, which can be found by having the patient oppose the thumb and 5 th finger while flexing the wrist against resistance. In patients, up to 20% of the population, who do not have a palmaris longus tendon, the best landmark is the flexor carpi radialis tendon, which can be found by having the patient make a fist and then flex the wrist against resistance. The medial nerve runs deep and approximately one cm parallel in the ulnar direction of the flexor carpi radialis. It innervates the palmar aspect of the distal thumb, 2 nd and 3 rd fingers , the radial volar aspect of the 4 th finger, and the radial two thirds of the palm. It also innervates the dorsal ulnar aspect of the thumb as well as the dorsal distal two fifths of the 2 nd and 3 rd fingers as well as the radial aspect of the dorsal distal two fifths of the 4 th finger.
Technique
Once the palmaris longus and or the flexor carpi radialis tendons area located, insert a 23 – 25 gauge needle at the palmar crease perpendicular to the skin, just radial to the palmaris longus (or one cm ulnar to the flexor carpi radialis) and advance the needle through the flexor retinaculum, noting its resistance and the sometimes felt pop after the sheath is penetrated. From that point, advance the needle approximately 0.5 cm further, at which point paresthesia in the hand may be obtained if the needle point is touching the nerve. If paresthesia is elicited, inject 2 cc of anesthetic. If no paresthesia is elicited, inject approximately 5 cc of anesthetic, being sure the needle is deep to the retinaculum, as the anesthetic would not infiltrate through the sheath if it were injected on its superficial side.
