Digital Nerve Block Technique

Several different techniques can be used to anesthetize the digits: the web-space block, the transthecal block, the 3-sided digital block, and the 4-sided ring block. Standard sterile precautions should be followed for all of the described procedures.

This method is very effective in achieving adequate anesthesia and is probably the least painful.

• Place the patient’s hand on a sterile field with the palm down.

• Hold the syringe perpendicular to the digit and insert the needle into the web space, just distal to the metacarpal-phalangeal (MP) joint (see image below).

  Needle position for web-space block.

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• Slowly inject the anesthetic in the dorsal aspect of the web space.

• Slowly advance the needle straight down toward the volar aspect of the web space, slowly infiltrating the surrounding tissues of the web space (see video below). The needle should not pierce the volar aspect of the web space.

  Web-space block technique.

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• Withdraw the needle and repeat the procedure on the other web space of the involved digit.

• The toes (except the great toe) can be effectively anesthetized in the same manner.

Originally described by Chiu in 1990, ^[12] this technique is also known as the flexor tendon sheath digital block. While treating trigger finger by injecting steroids and lidocaine into the tendon sheath, Chiu noted that anesthesia of the entire digit was achieved. Although adequate anesthesia is achieved with a single injection, this injection is painful because the needle pierces the very sensitive skin of the palm. Studies have shown that this type of block is as effective as traditional ring blocks in achieving adequate anesthesia. ^{[13, 14, 15]}

• Place the patient’s hand on the sterile field with the palm up.

• Locate the flexor tendon sheath by palpating it at the distal palmar crease.

• Insert the needle at a 45-degree angle just distal to the distal palmar crease (see image below).

  Needle position for transthecal block.

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• Inject the anesthetic, it should flow freely. If resistance is met, reposition the needle by slowly withdrawing it.

A modified version of this technique can also be used effectively. ^[16]

• Position the patient’s hand with the palm facing up.

• Insert the needle at a 90-degree angle at the metacarpal crease until bone is hit.

• Withdraw the needle slightly and inject the anesthetic.

• During the injection, use the nondominant hand to apply pressure just proximal to the injection site, to direct the flow distally (see image below).

  Modified transthecal block.

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This type of digital block is effective in anesthetizing the great toe, but it can be used for any digit.

• Place the patient’s extremity volar/plantar side down.

• Insert the needle at a 90-degree angle at the medial aspect of the digit, just distal to the metatarsal-phalangeal joint (see image below).

  Medial injection for 3-sided digital block.

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• Slowly inject the anesthetic as the needle is advanced toward the volar/plantar side, without piercing the volar skin.

• Slowly withdraw the needle and redirect it medially.

• Advance the needle slowly from medial to lateral side while the anesthetic is injected (see image below).

  Medial to lateral injection for 3-sided digital block.

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• Withdraw the needle.

• Make another injection over the already anesthetized skin at the lateral aspect of the digit, with the needle at 90 degrees, advancing it from the dorsal to ventral aspect, as was done medially (see image below).

  Lateral injection for 3-sided digital block.

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This method is an extension of the 3-sided block. After the 3-sided block is performed, a third injection is performed. Insert the needle at the lateral aspect of the digit on the volar/plantar side and advance it medially as the anesthetic is slowly injected. This technique is less favored because of the potential for ischemic complications.

When only the distal part of the digit is involved (eg, nail injury), a wing block procedure can be used instead of a digital block.

• Position the extremity with the volar/plantar side down.

• Hold the needle perpendicular to the long axis of the digit and at 45 degrees to the plane of the sterile field.

• Insert the needle 3 mm proximal to an imaginary point where a linear extension of the lateral and proximal nail folds would intersect (see image below).

  Wing block technique.

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• Inject the anesthetic along the proximal nail fold.

• Slowly withdraw the needle and redirect it toward the lateral nail fold.

• This may be performed on the opposite side of the nail as necessary. ^[17]