Digital Nerve Block

 Digital Nerve Block

Digital nerve blocks are important tools for the emergency medicine clinician. Injuries or infections of the digits are extremely common.  Adequate analgesia is essential to properly address the presenting condition and to minimize the patient's discomfort. Digital blocks are useful in many scenarios in which local infiltration of an anesthetic would require several injections into the already painful site of injury.

Each digit is innervated by 4 digital nerves. In the upper extremity, the digital nerves arise from the median, ulnar, and radial nerves. The 2 palmar digital nerves innervate the palmar aspect of the digit and the nail bed, whereas the dorsal nerves innervate the dorsum of the digit

Indications

Digital blocks are indicated for any minor surgery or procedure of the digits. These include, but are not limited to, the following:

• Large irregular lacerations
• Felon or paronychia
• Lacerations involving the nail or the nail bed
• Ingrown nails
• Digit dislocations or fractures
• Trephination of subungual hematoma

Contraindications

See the list below:

• Compromised digit circulation
• Infected injection site
• Known allergy to anesthetic

Equipment

The equipment necessary includes the following:

• Sterile gloves, drapes, and gauze pads
• Povidone-iodine (Betadine) solution
• Syringe, 5-10 mL, with an 18-gauge needle for drawing up the anesthetic and a 25- to 30-gauge needle for injection
• Local anesthetic of choice

Local anesthetic agents

Table 1. Commonly Used Local Anesthetics and Their Properties

Agent	Maximum Adult Dose (mg)/Procedure*	Onset (min)	Duration
Lidocaine	300	2-5	1-2 h
Procaine	500	2-5	15-45 min
Bupivacaine	175	2-5	4-8 h

Technique

1. Web-Space Block

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

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

 2. 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).

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

 4. 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.

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

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

2. Transthecal Block

     This technique is also known as the flexor tendon sheath digital block. Originally described by Chiu in 1990, 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.

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

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

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

d. 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.

• 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).

 

3. Three-Sided Digital Block

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

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

b. Insert the needle at a 90-degree angle at the medial aspect of the digit, just distal to the metatarsal-phalangeal joint 

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

d. Slowly withdraw the needle and redirect it medially.

e. Advance the needle slowly from medial to lateral side while the anesthetic is injected 

 

f. Withdraw the needle.

g.  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

4. Four-Sided Ring Block

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.

5. Wing Block Procedure

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.

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

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

  c. 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).

  d.    Inject the anesthetic along the proximal nail fold.

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

  f. This may be performed on the opposite side of the nail as necessary.

References

1. Agur A. Grant's Atlas of Anatomy. 10th ed. Lippincott Williams & Wilkins; 2003.

2. Simpson PM, McCabe B, Bendall JC, Cone DC, Middleton PM. Paramedic-performed digital nerve block to facilitate field reduction of a dislocated finger. Prehosp Emerg Care. 2012 Jul-Sep. 16(3):415-7. [Medline].

3. Mulroy MF, Bernards CM, McDonald SB, Salinas FV. Local anesthetics. A Practical Approach to Regional Anesthesia. 4th ed. Lippincott Williams and Wilkins; May 2008. 1.

4. Roberts JR, Hedges JR, Chanmugam AS. Clinical Procedures in Emergency Medicine. 4th ed. Elsevier Health Sciences; October 2004.

5. Denkler K. A comprehensive review of epinephrine in the finger: to do or not to do. Plast Reconstr Surg. 2001 Jul. 108(1):114-24. [Medline].

6. Motoki Sonohata, Satomi Nagamine, Kazumasa Maeda, Kenji Ogawa, Hideki Ishii, Kenji Tsunoda, et al. Subcutaneous Single Injection Digital Block with Epinephrine. Anesthesiology Research and Practice. 2012. 2012:4. [Medline].

7. Chiu DT. Transthecal digital block: flexor tendon sheath used for anesthetic infusion. J Hand Surg [Am]. 1990 May. 15(3):471-7. [Medline].

8. Hill RG Jr, Patterson JW, Parker JC, Bauer J, Wright E, Heller MB. Comparison of transthecal digital block and traditional digital block for anesthesia of the finger. Ann Emerg Med. 1995 May. 25(5):604-7. [Medline].

9. Low CK, Wong HP, Low YP. Comparison between single injection transthecal and subcutaneous digital blocks. J Hand Surg [Br]. 1997 Oct. 22(5):582-4. [Medline].

10.         Dehghani M, Mahmoodian A. A revisit of transthecal digital block and traditional digital block for anesthesia of the finger. Journal of Research in Medical Sciences. Nov/Dec 2007. 12(6):

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12.         Salasche SJ. Scher RK, Daniels CR, eds. Surgery In Nails: Treatment; Diagnosis; Surgery. 2nd ed. WB Saunders; 1997. 329.

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14.         Schmidt RM, Rosenkranz HS. Antimicrobial activity of local anesthetics: lidocaine and procaine. J Infect Dis. 1970 Jun. 121(6):597-607. [Medline].

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17.         http://emedicine.medscape.com/article/80887-technique#c3