11: Endoscopic Carpal Tunnel Release

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Procedure 11 Endoscopic Carpal Tunnel Release

Shimpei Ono, Sandeep J. Sebastin, Kevin C. Chung

Indications

Failure of conservative treatment for idiopathic carpal tunnel syndrome (CTS).

Patient prefers the endoscopic procedure.

The authors’ preferred technique is the limited incision open carpal tunnel release (LOCTR) (see Procedure 12). Studies have not demonstrated significant differences in outcomes between endoscopic carpal tunnel release (ECTR) and LOCTR. ECTR has a steep learning curve, needs a sizeable initial capital investment in video equipment, and incurs the recurring cost of the single-use disposable blade. Although the time taken to perform ECTR is less than for LOCTR, the time expended to set up the equipment mitigates this advantage.

Occasionally, patients request the endoscopic procedure. They are counseled with regard to the cost and complications. We prefer the single-portal Agee technique to the double-portal Chow technique because the Agee technique avoids a scar in the palm.

Surgical Anatomy

The carpal tunnel is a fibro-osseous tunnel that contains the median nerve and the nine flexor tendons to the thumb and the fingers. The roof of the carpal tunnel is formed by the flexor retinaculum, which extends between four bony prominences (proximally: pisiform and tubercle of scaphoid, distally: hook of the hamate and tubercle of trapezium) (Fig. 11-1).

The flexor retinaculum can be divided into three components (see Fig. 11-1).

• Proximal: Direct continuation of the deep antebrachial fascia

• Middle: Transverse carpal ligament (TCL)

• Distal: Aponeurosis between the thenar and hypothenar muscles

Some authors consider the flexor retinaculum and the TCL to be synonymous.

The carpal tunnel is narrowest in both palmar-dorsal and ulnar-radial planes at the level of the hook of the hamate. The other narrow portion of the carpal tunnel is at the proximal edge of the TCL (see Fig. 11-1).

The important surface landmarks and surrounding neurovascular structures related to the carpal tunnel are as follows (Fig. 11-2):

• The hook of the hamate is palpable 1 cm distal and radial to the pisiform and is in line with the ulnar border of the ring finger.

• The Kaplan cardinal line (KCL) connects the apex of the first web with the thumb in abduction to the hook of hamate. This line is usually parallel to the proximal palmar crease.

• The distal aspect of the flexor retinaculum lies 1 cm distal to the hook of the hamate.

• The superficial palmar arch (SPA) lies about 2.5 cm distal to the hook of the hamate.

• The origin of the recurrent motor branch is surface-marked at the intersection of a vertical line from the radial border of the long finger and KCL. The recurrent motor branch arises from the palmar and ulnar aspect of the median nerve (Fig. 11-3), and three courses of this branch have been described (Fig. 11-4).

♦ Extraligamentous (46%)

♦ Subligamentous (31%)

♦ Transligamentous (23%)

• The third common digital nerve is surface-marked by an oblique line joining the midpoint of the palmar digital crease of the ring finger to the scaphoid tubercle. This nerve is always located distal to the KCL at an average distance of 0.5 cm.

• The palmar cutaneous branch of the median nerve arises from the radial aspect of the median nerve about 5 cm proximal to the wrist crease (see Fig. 11-2). It runs parallel to the median nerve for 1.6 to 2.5 cm and then passes under the antebrachial fascia between the palmaris longus (PL) and the flexor carpi radialis (FCR). About 0.8 cm proximal to the wrist crease, it pierces the antebrachial fascia, becoming superficial to the flexor retinaculum.

The ulnar nerve and artery overlie the ulnar border of the flexor retinaculum and may be at risk during ECTR. The nerve is generally anterior or ulnar to the hook of the hamate, but the artery is often immediately superficial to the flexor retinaculum lying within a fat-filled space (Fig. 11-5).

FIGURE 11-1

FIGURE 11-2

FIGURE 11-3

FIGURE 11-4

FIGURE 11-5

Positioning

The procedure is performed under tourniquet control with the patient in supine position and the affected extremity on a hand table. The positioning of surgeon, patient, and anesthesiologist is shown in Figure 11-6.

It can be done under general regional anesthesia, intravenous regional (Bier block) anesthesia, or local anesthesia.

FIGURE 11-6

Pearls

The infiltration of local anesthetic within the carpal tunnel can obscure endoscopic viewing and cause fogging of the lens. Care should be taken to infiltrate only the skin and to block the median nerve in the distal forearm rather than under the carpal tunnel.

Exposures

We use the 3M Agee Carpal Tunnel Release System for ECTR (Fig. 11-7).

A 1- to 1.5-cm transverse skin incision is made over the proximal wrist crease, ulnar to the PL tendon and radial to the flexor carpi ulnaris (FCU) tendon (Figs. 11-8 and 11-9).

Once the incision is made, the underlying loose tissue is dissected by spreading longitudinally to identify and preserve any palmar cutaneous nerves.

The antebrachial fascia is exposed, and a U-shaped, distally based fascial flap is raised (Fig. 11-10). Elevation of the flap ensures that the endoscope enters the right plane deep to the fascia and not superficial to it.

The fascial flap is held up using a hemostat to expose the underlying median nerve (Fig. 11-11).

FIGURE 11-7

FIGURE 11-8

FIGURE 11-9

FIGURE 11-10

FIGURE 11-11

Pearls

If more than one wrist flexion crease exists, the most proximal crease is selected because there is less subcutaneous fat.

Pitfalls

Care should be taken not to injure the palmar cutaneous branch of the median nerve and the palmar cutaneous branch of the ulnar nerve.

The median nerve is directly below this flap, so care must be taken during the initial flap incision and elevation, especially in patients who do not have a PL tendon.

Procedure

Step 1: Release the Forearm Fascia

Using tenotomy scissors, the antebrachial fascia is released proximally for 1 to 2 cm (Fig. 11-12).

FIGURE 11-12

Step 1 Pitfalls

Care is taken not to injure the palmar cutaneous branch of the median nerve, which is located on the radial aspect of the PL.

Step 2: Dilate the Carpal Tunnel

The smallest probe (hamate finder) is inserted under the previously elevated fascial flap. The wrist is held in slight extension, and the probe is gradually advanced in line with the ring finger. The tip of the probe is automatically directed radially by the hamate and should be palpable subcutaneously as it exits the distal free edge of the TCL. The probe is then removed.

The next-sized probe is inserted (Fig. 11-13), and finally the largest probe is inserted (Fig. 11-14). These probes function both as dilator and to confirm that the probe is within the carpal tunnel and not the Guyon canal.

FIGURE 11-13

FIGURE 11-14

Step 2 Pearls

It is good to mark the most proximal point where the tip of the probe can be palpated subcutaneously. This indicates the end of the TCL and provides a visual clue to how far the blade assembly can be advanced safely.

Step 3: Clear the Synovium

The synovial separator is then passed into the dilated carpal tunnel. The synovial separator is used to sweep any adherent synovial membranes off the undersurface of the TCL. Adequate clearing of the synovial membrane is indicated by the roughness (“washboard effect”) of the transverse fibers of the TCL.

Step 6: Incise the TCL

Once the distal end of the TCL has been identified, the blade is elevated (Fig. 11-18), and slight pressure is applied on the palmar aspect of the carpal tunnel. The blade is then gradually withdrawn under visual guidance on the monitor to divide the TCL (Fig. 11-19).