It is necessary to provide complete anesthesia when treating
most fingertip injuries. Many techniques for performing a
digital nerve block have been described. The following is
one that is both effective and rapid in onset. This type of
digital block will only provide anesthesia distal to the
distal interphalangeal joint, but this is most often the
site that demands a nerve block.
What to do:
Cleanse the finger and paint the area with povidone-iodine
(Betadine) solution.
Using a 27 gauge needle, slowly inject 1% lidocaine midway
between the dorsal and palmar surfaces of the finger at the
midpoint of the middle phalanx.
Inject straight in along the side of the periosteum. Then
pull back without removing the needle from the skin and fan the
needle dorsally.
Advance the needle dorsally and inject again. Pull the
needle back a second time and, without removing it from the skin,
fan the needle in a palmar direction.
Advance the needle and inject the lidocaine in the vicinity
of the digital neurovascular bundle.
With each injection, instill enough lidocaine to produce
visible soft tissue swelling.
Repeat this procedure on the opposide side of the finger.
For anesthesia of the proximal finger as well, a similar block may be performed as far proximally as the middle of the metacarpal. There, the connective tissue is
looser, and the needle need not be fanned into digital septae as
described above. Be prepared to wait three to ten minutes for adequate anesthesia.
With painful crush injuries or when the pain will be prolonged, substitute bupivicaine for lidocaine.
What not to do:
Do not use lidocaine with epinephrine. The digital arteries
are end arteries that can spasm and provide prolonged anesthesia,
ischemia of the finger tip, and potentially, necrosis.
Discussion
Digital nerve blocks are often described as being injected at the base of the proximal phalynx, but it is not necessary to block the whole digit when only the distal tip is injured, and the first technique above provides anesthesia much faster. Toes are difficult to separate and it may be easier to perform a modified ring block at the base. Over the dorsum of the proximal interphalyngeal joint the connective tissue is loose enough for direct injection of anesthetic, and a digital block is not required. Some studies have demonstrated digital anesthesia by injecting 2 mL of buffered lidocaine directly into the flexor tendon sheath, using a 25 or 27 gauge needle at a 45 degree angle at the distal palmar crease.
