Rationale and Basic Science

James C. Y. Chow published his dual-portal technique in 1989¹ 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

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.

The distal portal is established approximately 4 to 5mm distal to the distal edge of the transverse carpal ligament along the long axis of the ring finger. This effectively allows the cannula system to pass between the common digital nerves of the third and fourth web spaces, distal and palmar to the superficial palmar arch and palmar to the communicating branch sensory branch between the median and ulnar nerves.³ Once the cannula system passes out through this distal portal, the system is fixed in position. The elastic band is placed across the fingers to hold the hand in position. The assistant extends the thumb, thus placing tension on the TCL (Figure 31.3).

FIGURE 31.3 Chow dual-portal endoscopic carpal tunnel release setup. Cannular in position while assistant palmarly adducts the thumb.

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