Chapter 30. Digital Block

Strauss1 provided the first description of the digital block in 1889 for the condition of an ingrown toenail, using 20% cocaine at the base and under the nail. In 1905, Braun reported the synergistic advantage of adding epinephrine to local anesthetics.2,3 However, the use of epinephrine in digital block anesthesia has been avoided due to the theoretical risk of ischemia and possible gangrene. More recently, however, Wilhelmi and colleagues4 demonstrated the safety and efficacy of epinephrine-containing local anesthetic for digital block, which made its use only more controversial. Digital block is one of the most common nerve block techniques, frequently used in the emergency department and primary care settings for various procedures such as lacerations of the finger or toe, nail removal, nail bed repair, paronychia drainage, removal of foreign bodies, and any other painful procedures on digits.

In 1990, approximately a century after the first publication of traditional digital block, Chiu5 described a technique of digital block that produced complete finger anesthesia with a single injection into the flexor tendon sheath at the level of the distal palmar crease. In anatomic studies he showed that after injection of methylene blue into the flexor tendon sheath there was “complete staining of the entire flexor tendon sheath and centrifugal diffusion of the blue dye circumscribing the entire circumference of the proximal phalanx” (see section on Transthecal Digital Block). The advantages of this technique are (1) rapid onset of action, (2) only a small volume of anesthetic solution required, (3) only a single injection required, and (4) absence of risk of direct trauma to the neurovascular bundles.6–8 Although Chevaleraud and coworkers9 did not accomplish anesthesia of the dorsum of the finger in all cases, some authors consider the transthecal method to be as effective as a traditional digital nerve block.10 Others have found that it results in anesthesia comparable to the newer single-injection subcutaneous digital blocks,11 both in experimental and clinical situations.12,13 Transthecal anesthesia appears to be safe and effective without a risk of any long-term damage to the tendon sheath.

A digital block is the technique of blocking the nerves of the digits to achieve anesthesia of the finger(s). This technique is simple to perform and essentially devoid of systemic complications. It is a commonly used and effective method of anesthesia for a wide variety of minor surgical procedures on the digits. As such, this block should be in the armamentarium of every anesthesiologist. Several different techniques of digital block and their modifications are available; in this chapter, we chose to describe the one that is most commonly used in our institution.

The common digital nerves are branches of the median and ulnar nerves, which divide in the distal palm into the volar aspect, tip, and nail bed area (Figure 30–1). The main digital nerves, accompanied by digital vessels, run on the ventrolateral aspect of the finger immediately lateral to the flexor tendon sheath (Figure 30–2). Small dorsal digital nerves run on the dorsolateral aspect of the finger and supply innervation to the back of the fingers as far as the proximal joint.

A standard regional anesthesia tray is prepared with the following equipment:

• Sterile towels and 4-in. × 4-in. gauze pads
• A controlled, 10-mL syringe with local anesthetic
• One 1½-in., 25-gauge needle

Block of Volar & Dorsal Digital Nerves at the Base of the Finger

A 25-gauge, 1½-in. needle is inserted at a point on the dorsolateral aspect of the base of the finger, and a small skin wheal is raised. The needle is then directed anteriorly toward the base of the phalanx (Figures 30–3 and 30–4). The needle is advanced adjacent to the phalanx, while the operator observes for any protrusion from the palmar dermis directly opposite the needle path (Figure 30–5). Two to three milliliters of solution is injected. An additional 1 mL is injected continuously as the needle is withdrawn back to the skin. The same procedure is repeated on each side of the base of the finger to achieve anesthesia of the entire finger (Figure 30–6).

Transthecal Digital Block

The transthecal digital block is placed by using the flexor tendon sheath for local anesthetic injection. In this technique, the patient's hand is supinated and the flexor tendon is located. Using a 25- to 27-gauge, 1-in. needle, 2–3 mL of local anesthetic is injected into the flexor tendon sheath at the level of the distal palmar crease (Figure 30–7). The needle should puncture the skin at a 45-degree angle. Resistance to the injection suggests that the needle tip is against the flexor tendon. Careful withdrawal of the needle results in the free flow of medication as the potential space between tendon and sheath is entered. Proximal pressure is applied to the volar surface during injection to promote diffusion of the medication within the synovial sheath.

A skin wheal at the point of needle insertion significantly reduces the discomfort during the placement of the block. A digital block requires a small dose of a sedative or a narcotic during placement. Typical onset time for this block is approximately 5 min, depending on the concentration and volume of local anesthetic used.

The choice of the type and concentration of local anesthetic for a digital block is based on the desired duration of blockade (Table 30–1).

One specific complication of digital blocks is vascular insufficiency and gangrene. This catastrophe is a result of digital artery occlusion, together with collateral circulation insufficiency. A series of causative factors is often involved to produce this rare, but serious complication (Table 30–2).