Chapter 80G: Digital Block

INTRODUCTION

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, Heinrich 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. However, Bradon Wilhelmi and colleagues⁴ demonstrated the safety and efficacy of epinephrine-containing local anesthetic for digital block. Digital block is one of the most common nerve block techniques. It is 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, almost a century after the first publication regarding traditional digital block, David 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 investigations 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 Transthecal Digital Block). The advantages of this technique are (1) rapid onset of action, (2) only a small volume of anesthetic solution is required, (3) only a single injection is required, and (4) absence of risk of direct trauma to the neurovascular bundles.^6,7,8 Although Chevaleraud and coworkers⁹ did not find anesthesia of the dorsum of the finger in all cases, some investigators 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 causing any long-term damage to the tendon sheath.

Several different techniques of digital block and their modifications are available: In this chapter, we describe the two that are most commonly used in our institution.

REGIONAL ANESTHESIA ANATOMY

The common digital nerves are derived from the median and ulnar nerves and divide in the distal palm into the volar aspect, tip, and nail bed area (Figure 80G–1). The main digital nerves, accompanied by digital vessels, run on the ventro-lateral aspect of the finger immediately lateral to the flexor tendon sheath (Figure 80G–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.