A digital block is a form of regional anesthesia designed to numb a finger or toe (digit) for medical procedures. This technique involves injecting a local anesthetic near the nerves at the base of the digit, effectively interrupting pain signals to the brain. Because it offers profound, localized pain relief, it is a common and effective procedure in emergency departments and primary care settings. This localized approach is generally considered advantageous over direct infiltration into an injury, which can cause wound distortion and may not provide complete pain control.
When a Digital Block Is Needed
A digital block is appropriate for a variety of minor surgical interventions and painful injuries affecting the fingers or toes. Common situations include the repair of lacerations, the reduction of dislocations or fractures, and the removal of foreign bodies embedded in the digit. It is also routinely used for procedures involving the nail and nail bed, such as the drainage of abscesses like a felon or paronychia, or the removal of an ingrown nail. The goal is to provide a pain-free field for the practitioner to work and to alleviate the patient’s discomfort.
There are, however, certain conditions under which a digital block must not be performed. An absolute contraindication is a known allergy to the local anesthetic agent being used, which necessitates finding an alternative form of anesthesia. The presence of an active infection, such as cellulitis, directly at the intended injection site is another absolute contraindication, as inserting a needle risks spreading the infection deeper into the tissue. Compromised circulation in the digit, often caused by severe vascular injury or certain pre-existing conditions, is also a contraindication because the volume of injected fluid could further impair blood flow.
Essential Supplies and Patient Preparation
The successful execution of a digital block requires careful preparation and the right tools to ensure a sterile and effective procedure. Essential materials include a local anesthetic agent, typically 1% or 2% Lidocaine, often without epinephrine. The anesthetic is drawn up using a larger gauge needle (18 to 22 gauge) into a small syringe (5 or 10 mL), but is injected using a finer 25- to 30-gauge needle to minimize patient discomfort.
Patient preparation begins with obtaining informed consent and positioning the patient comfortably, typically with the hand or foot supported under adequate lighting. Before the first puncture, the injection site must be thoroughly cleansed with an antiseptic solution, such as chlorhexidine or povidone-iodine, to reduce the risk of infection. The practitioner must wear appropriate personal protective equipment, including sterile gloves, to maintain an aseptic environment throughout the injection.
Detailed Steps for Digital Block Techniques
The digital nerves run along both the palmar (or plantar) and dorsal sides, meaning anesthesia must be delivered to both sides of the digit’s base. The traditional web-space block targets these nerves as they pass through the web space just distal to the metacarpal-phalangeal joint. The procedure begins by inserting the fine needle perpendicularly into the dorsal aspect of the web space, just lateral to the digit.
The practitioner slowly advances the needle toward the palmar side, injecting about 1 mL of anesthetic as it passes through the subcutaneous tissue to block the dorsal nerve. Before reaching the palmar skin, the needle is repositioned slightly to ensure the anesthetic reaches the deeper palmar digital nerve. It is crucial to aspirate—pull back on the syringe plunger—before injecting any medication to confirm the needle tip is not inside a blood vessel, preventing intravascular injection and potential toxicity. This process is then repeated on the opposite side of the digit to achieve complete anesthesia.
A distinct alternative is the transthecal block, which uses a single injection site and targets the flexor tendon sheath running along the palmar side of the finger. The patient’s hand is positioned palm up, and the flexor tendon is located by palpating it near the distal palmar crease.
The needle is inserted at the distal palmar crease, often at a 45-degree angle, to enter the flexor tendon sheath. The goal is to inject the anesthetic into the sheath, not the tendon itself; therefore, a slow, resistance-free injection is sought. The anesthetic (typically 2 to 3 mL) then diffuses out of the sheath, blocking the palmar nerves and providing sufficient spread for the dorsal nerves. The advantage of this method is a single, less painful injection, though it requires precise placement and is generally used for fingers, less so for toes.
Recognizing and Avoiding Complications
Although a digital block is generally safe, practitioners must be aware of potential complications, the most serious being systemic toxicity from intravascular injection. Signs of systemic toxicity include lightheadedness, ringing in the ears (tinnitus), or a metallic taste, which occur when the anesthetic enters the bloodstream rapidly. The primary method to prevent this is the consistent practice of aspirating the syringe before injecting any anesthetic, confirming the needle is not inside a vessel.
Other complications include nerve injury and compartment syndrome. Nerve injury can occur if the needle directly strikes the nerve or if the anesthetic is injected under high pressure, which the patient may report as sudden, sharp pain or an electric-shock sensation. The risk of compartment syndrome, caused by excessive pressure from fluid buildup, is mitigated by using the lowest effective volume of anesthetic (no more than 3 to 4 mL total per digit). Patients should be warned that the protective reflexes of the digit will be lost, making the digit susceptible to accidental thermal injury or trauma until sensation returns.