This video reviews three techniques for digital nerve blocks: dorsal, volar (also known as transthecal or flexor tendon sheath block), and web-space. First let’s do some anatomy review.
Each finger has two digital nerves on each side: the dorsal digital nerves are at 10:00 and 2:00, and the volar digital nerves are at 4:00 and 8:00. Remember that volar and palmar are synonyms, used interchangeably.
Closely review the innervation of the dorsal and volar nerves. You have to block both nerves on each side to get complete anesthesia of the entire finger. Note the different nerve distributions of the thumb and small finger over the dorsal aspect of the distal phalanx. For these fingers you have to anesthetize the dorsal nerves to numb up the distal phalanx. In contrast, the distal phalanx of the 2nd through 4th fingers are innervated by the volar nerves. When in doubt, anesthetize both to get full anesthesia of the finger.
For each of these techniques always prep the skin, use a small gauge needle (25-27 gauge), and aspirate before you inject.
Prep the skin. With the patient’s hand resting palm down insert the needle at the dorsal web space and advance it until it reaches the palmar aspect of the hand but does not exit the palmar skin. Aspirate, and inject up to 3 ml of anesthetic as the needle is withdrawn. This allows you to reach both the volar and dorsal nerves. Repeat the same process on the other side of the finger.
Volar Approach (Transthecal / Flexor Tendon Sheath Block):
The volar approach is also called a transthecal block or flexor tendon sheath block, since the anesthetic is injected into and spreads along the flexor tendon sheath. With the patient’s hand resting palm up, insert the needle at the midpoint of the crease where the finger meets the palm, or just proximal to this over the metacarpal head. Advance the needle until you touch bone and then slightly withdraw the needle. Aspirate, and inject 3 ml of anesthetic. This should anesthetize all 4 digital nerves. A nice adjunct is to slightly withdraw and reangle the needle tip towards each webspace, delivering a little more anesthetic on each side.
The webspace approach to a digital nerve block is quite simple, shown here on a toe instead of a finger. Once the skin is prepped, introduce the needle into the webpace with the needle tip aiming right down the middle. Aspirate, then inject 2-3 ml of anesthetic on each side. Ideally this should anesthetize both the dorsal and volar digital nerve.