Department of Technique Modified Transthecal Digital Block Thomas P. Whetzel, MD, Shahriar Mabourakh, MD, Rob Barkhordar, BS, Sacramento,CA
The transthecal digital block was first introduced in 1990 by Chiu.~ That technique involved a single palmar percutaneous injection of lidocalne into the space of the flexor tendon sheath, resulting in centrifugal anesthesia diffusion and complete anesthesia of the digital nerves of the finger. This represented an improvement over conventional digital nerve block techniques because it involved a single injection for anesthesia of the entire digit. The transthecal block required a small (2-mL) volume of lidocaine, the onset of anesthesia was rapid (3--4 minutes), and there was little risk of direct mechanical trauma to the neurovascular bundle because the needle was not placed near the vascular structures. We have found that identification of the injection site at the flexor tendon sheath in the distal palm by palpation is more difficult to teach to medical staff than an injection site that is localized using visual landmarks. This led to the development of a simpler yet equally effective approach. In our technique, the center of the palmar digital crease on the volar surface of the digit is visually identified. Entry into the flexor tendon sheath with a needle at this point can easily be accurately performed, with little possibility of damaging neighboring neurovascular structures with lateral misplacement of the needle. Using this method, anesthesia
From the Division of Plastic Surgery, Department of Surgery, University of California, Davis, Medical Center, Sacramento, CA. Received for publication March 21, 1995; accepted in revised form Oct. 15, 1996. No benefits in any form have been received or will be received from a commerical party related directly or indirectly to the subject of this article. Reprint requests: Thomas P. Whetzel, MD, Division of Plastic Surgery, University of California, Davis, Medical Center, 4301 X Street, Room 2430, Sacramento, CA 95817-2282.
diffusion is rapid within the tendon sheath space, resulting in complete digital anesthesia.
Technique Preparation The hand on which the digit is to be anesthetized is prepared with Betadine and alcohol.
Localization of the Flexor Tendon Palpation or motion of the flexor tendon or skin marking, as with the palmar transthecal technique, is not necessary. The needle is inserted in the direct center of the volar surface of the finger at the palmar digital crease.
Injection of Anesthesia A 25-gauge needle is inserted at the palmar digital crease, penetrating both flexor tendons to bone (Fig. 1). The needle is withdrawn slowly away from the bone while gentle pressure is applied to the plunger on the syringe. While the needle tip lumen is against bone or within tendon proper, there is almost complete resistance to anesthetic flow through the needle. Immediately as the needle tip lumen clears the tendon proper on slow pull-back of the needle, lidocaine flows easily at low pressure into the tendon sheath (Fig. 2). If the needle is anywhere but within the tendon sheath space, the pressure required to inject local anesthesia is dramatically increased. We do not attempt to directly identify the potential space of the tendon sheath above the tendons with the needle tip or try to avoid entering the flexor tendon. Consistency and accuracy are excellent by going to bone and then drawing back the needle tip while maintaining low pressure on the The Journal of Hand Surgery 361
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Whetzel et al. / Modified Transthecal Digital Block Cadaver Stud ies
Figure 1. Technique of transthecal digital block to ring finger is demonstrated in a cadaver with ink substituted for lidocaine. A 25-gauge needle is inserted into the palmar digital crease, penetrating both flexors to bone. The needle is withdrawn slowly until injectant is passed easily.
Four digits from a fresh cadaver hand were injected as above at the palmar digital crease with 0.1-0.2 mL India ink. Although these volumes were only 5%-10% of the 2 mL used typically with patients, the digits in each case exhibited a dark discoloration in the volar skin well distal to the injection site over the distal middle phalanx immediately during injection. This demonstrates that even in the early phase of the injection, the ink has flowed along the length of the tendon sheath and that centrifugal diffusion out of the tendon sheath toward the skin, occurs resulting in cutaneous staining, (Fig. 3). The hand was then frozen in dry ice and sectioned transversely at 5-mm intervals straight across the hand. The cut across the hand demonstrated in Figure 4 is made within 3 mm of the palmar digital crease (injection site) of the long finger. Owing to
syringe plunger until anesthetic flows easily. Full block is obtained in less than 5 minutes with injection of 2 mL of lidocaine. We have successfully anesthetized 50 digits in 35 patients without complications. All finger procedures that could be performed using a classical digital block, such as finger tip completion amputations, nailbed repairs, and Kirschner wire pinning of middle and distal phalanx fractures, have been performed with the transthecal block.
25ga needle Fibrous flexor sheath Skin
Flexor dlgltorum superliclalis
Palmar digital nerve Synovial sheath _ _ Digital artery
Flexor digitorum profundus Dorsal digital nerve
Proximal phalanx
Figure 2. Schematic diagram demonstrating site of needle tip during instillation of anesthetic fluid. Potential space between tendons proper and synovial sheath has been illustrated to clarify the technique. Needle tip is immediately inserted against proximal phalanx bone and then is slowly pulled out of finger to the position in the distal space (shown in the illustration) where anesthesia flows readily out of needle tip with gentle pressure.
Figure 3. Same cadaver hand as in Figure 1 has had 0.15 mL of black ink injected into the ring finger and 0.1 mL of ink injected into small finger at palmar digital crease. Injection site at midvolar position at palmar digital crease is identified as a black dot (single pair of arrowheads). A dark discoloration representing superficial staining of skin from ink diffusing out of the flexor tendon sheath is seen distributing distally in the finger immediately after injection (multiple arrowheads).
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within the tendon sheath for the small finger 12 mm distal to the injection point; (2) ink in the early phase of leaving the tendon sheath in the ring finger diffuses centrifugally outward 8 m m distal to the injection point; (3) ink stains further out from the tendon sheath, which surrounds the digital nerves with some additional component of subcutaneous infiltration for the long finger within 3 m m of the injection point; and (4) ink centrifugally diffuses out of the tendon sheath primarily toward the radial digital nerve of the index finger at 8 mm distal to the injection site.
Discussion Figure 4. Same cadaver hand as in Figure 1 has been frozen in dry ice after ink injection of all 4 digits at palmar digital creases into the spaces of the flexor tendon sheaths. Cross-section of the small finger demonstrates ink confined almost entirely within the tendon sheath at 0.1 mL injectant, 12 mm distal to the injection point. Cross-section of the ring finger shows ink diffusing centrifugally out of the tendon sheath space at 0.15 mL injectant, 8 mm distal to the injection point. Cross-section of the long finger demonstrates that ink has diffused out past the digital nerves at 0.2 mL injectant within 3 mm of the injection point. There is also some evidence of subcutaneous infiltration by staining of the skin on the volar surface of the palmar digital crease. Cross-section of the index finger shows ink diffusing centrifugally out of the tendon sheath primarily toward the radial digital nerve at 0.1 mL injectant at 8 mm distal to the injection site.
the curvature of the distal arch of the metacarpal heads, a straight cut results in the ring and index fingers' being observed on cross-section 8 m m distal to their volar palmar digital creases; the small finger cross-section is 12 mm distal to its palmar digital crease. As observed on the digital cross-sections of the hand in Figure 4, (1) ink is confined almost entirely
We present a simplified technique of digital block to obtain complete anesthesia with a single injection of 1% lidocaine. Localization of the single injection point is simple using visual landmarks and easily taught to other medical personnel. Full block is obtained rapidly in less than 5 minutes, and partial digit amputations have been performed without patient discomfort. In our experience, there have been no complications with the transthecal digital block. The cadaver study has demonstrated the early phase of centrifugal diffusion of ink from the tendon sheath space at very low volumes. Some subcutaneous infiltration appears to occur as higher volumes of injectant are used, particularly near the injection site. Whether the digital anesthetic effect is the result of pure flexor sheath space diffusion or of a combination of centrifugal diffusion and subcutaneous infiltration is not known. In clinical usage, however, the modified transthecal block provides a simple, accurate, safe, and effective technique for providing a one-injection digital block.
Reference 1. Chiu DTW. Transthecal digital block: flexor tendon sheath used for anesthetic infusion. J Hand Surg 1990;15A: 471-473.