Endoscopic Carpal Tunnel Release: The Chow Dual-Portal Technique

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CHAPTER 31 Endoscopic Carpal Tunnel Release: The Chow Dual-Portal Technique

Daniel J. Nagle

Rationale and Basic Science

James C. Y. Chow published his dual-portal technique in 1989 ¹ and reported his clinical results in 1990.² The rationale for developing an endoscopic carpal tunnel release is similar to that used in the development of other endoscopic techniques such as laparoscopic cholecystectomy and arthroscopy. A minimal incision approach to carpal tunnel release leads to a decrease in postoperative pain and an earlier return to daily activities. The dual-portal system has the advantage of creating a fixed space in which to operate. The cannula is fixed at the proximal and distal portals. The cannula creates an operative field into which instruments can be easily moved (Figure 31.1).

FIGURE 31.1 Palpation and marking of distal edge of transverse carpal ligament.

Indications and Contraindications

The indications for endoscopic and open carpal tunnel release are similar. There are, however, certain situations in which endoscopic carpal tunnel release may not be helpful. One such situation is that of the patient who has undergone a previous carpal tunnel release. The patient’s history must be carefully reviewed. If the patient had a successful carpal tunnel release and presents with a recurrent carpal tunnel syndrome some years later without intervening trauma, an endoscopic carpal tunnel release could be considered. If, however, only transient relief after an ECTR is noted it would make sense to perform an open exploration of the carpal tunnel—assuming that a structure not seen during the ECTR continues to compress the median nerve.

A fused wrist constitutes a contraindication for ECTR. The inability to extend the wrist on the hand holder precludes the safe placement of the cannula. In addition, if one suspects the presence of proliferative tenosynovitis an open carpal tunnel release would be preferable. Of course, any suspicion of the presence of a mass within the carpal tunnel would be an indication for an open carpal tunnel release rather than an endoscopic carpal tunnel release.

Technique

Anesthesia

The anesthetic used is a matter of personal preference. Chow feels very strongly that local anesthesia be used because this allows instant feedback from the patient if the median or ulnar nerve is touched. Local anesthetic also allows the surgeon to assess the neurovascular status of the patient immediately after completion of the carpal tunnel release while the patient’s hand is still prepped. Should there be signs of a nerve, tendon, or arterial injury, immediate exploration could be carried out. It should be understood that the “local” anesthetic is supplemented with IV fentanyl and midazolam just prior to the cannula being passed into the carpal tunnel. Local anesthesia is particularly well suited to performing bilateral ECTR in one sitting.

IV regional anesthesia (Bier block) can also be used. It does not allow the instant feedback of local anesthesia, but once the tourniquet is released the patient’s neurological status returns quickly to preoperative levels such that a complete neuromuscular exam can be performed prior to breaking the sterile field. The Bier block eliminates the need to give fentanyl and midazolam in the doses needed during the “pure” local anesthesia as the patient does not feel the cannula pass into the carpal tunnel. Axillary block and general anesthesia have been used but eliminate the patient feedback noted with the local techniques.

Surgical technique

The dual-portal endoscopic carpal tunnel release, as described by Chow and modified by others, uses a proximal portal that is established 1 cm proximal to the wrist flexion crease just ulnar to the palmaris longus. The distal portal is established just distal to the distal edge of the transverse carpal ligament along the long axis of the ring finger. The volar antebrachial fascia is carefully entered, and a curved dissector is passed into the carpal tunnel—taking care to hug the hook of the hamate.

A “washboard” sensation is felt as the tip of the dissector passes over the ridges in the dorsal surface of the transverse carpal ligament (TCL). If this washboard sensation is not felt, the dissector is either palmar to the TCL or in Guyon’s canal. The distal edge of the transverse carpal ligament is able to be palpated using the curved dissector and the position of the distal edge of the transverse carpal ligament is marked on the overlying palmar skin (Figure 31.1).

The curved dissector is removed and the slotted cannula/obturator is placed into the carpal tunnel. The operator’s hand is placed on the palmar aspect of the hand between the thenar and hypothenar eminences and the cannula system is lifted (the lift test). The examiner’s palpating fingers should not be able to feel the cannula. If the cannula is palpable, it is either palmar to the TCL or in Guyon’s canal and must be removed and repositioned. Once the cannula is safely placed, taking care to stay close to the hook of the hamate and keeping the cannula system parallel to the long axis of the arm, the wrist and fingers are extended and the hand is placed on the hand holder. The tip of the cannula system is palpated just distal to the distal edge of the TCL. The cannula system is then passed through the distal portal while pushing the superficial palmar arch dorsally with the palmar arch depressor (Figure 31.2).

FIGURE 31.2 Passage of the cannula system out the distal portal while applying dorsally directed pressure with the arch depressor to displace the superficial palmar arch dorsal to the cannular system.

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