Volar Approach to the Carpal Tunnel and Wrist
Volar Approach to the Carpal Tunnel and Wrist
Decompression of the median nerve within the carpal tunnel is one of the most common operations of the hand. Two anatomic structures, the motor and palmar cutaneous branches of the median nerve, determine how the tunnel is approached. Both structures vary considerably in the paths they take; they are so unpredictable that “blind” procedures, which are acceptable elsewhere, must be avoided. If treated by open surgery the tunnel must be decompressed through a full incision and under direct vision. The uses of the incision include the following:
1. Decompression of the median nerve12,13
2. Synovectomy of the flexor tendons of the wrist
3. Excision of tumors within the carpal tunnel
4. Repair of lacerations of nerves or tendons within the tunnel
5. Drainage of sepsis tracking up from the midpalmar space
6. Open reduction and internal fixation of certain fractures and dislocationsof the distal radius and carpus, including volar lip fractures of the radius and transscaphoid perilunate dislocations
Position of the Patient
Place the patient supine on an operating table. Rest the forearm on a hand table in the supinated position so that the palm faces upward. Use an exsanguinating bandage (see Fig. 5-15).
Landmarks and Incision
Landmarks
The thenar crease runs around the base of the thenar eminence. The proximal transverse skin crease of the wrist overlies the wrist joint. The tendon of the palmaris longus muscle bisects the anterior aspect of the wrist. Its distal end bisects the anterior surface of the carpal tunnel. It is easy to palpate in the distal forearm if the patient is instructed to pinch the fingers together and flex the wrist.
Incision
Begin the incision just to the ulnar side of the thenar crease, about onethird of the way into the hand. Curve it proximally, remaining just to the ulnar side of the thenar crease, until the flexion crease of the wrist is almost reached: To avoid problems in skin healing, do not wander into the thenar crease itself. Then, curve the incision toward the ulnar side of the forearm so that the flexion crease is not crossed transversely (Fig. 5-21).
Internervous Plane
There is no internervous plane. The approach is a true anatomic dissection in which the major nerves are identified, dissected out, and preserved. No muscles are transected except, on occasion, some fibers of the abductor pollicis brevis and palmaris brevis that cross the midline.
Superficial Surgical Dissection
Carefully incise the skin flaps. Remember that the palmar cutaneous branch of the median nerve, which usually presents on the ulnar side of the flexor carpi radialis, has a variable course. Dissection should be carried out meticulously, with particular attention paid to the location of the nerve (see Fig. 5-21). After the fat is incised, the fibers of the superficial palmar fascia come into view; divide them in line with the incision.
Retract the curved flaps medially, exposing the insertion of the palmaris longus muscle into the flexor retinaculum (the transverse carpal ligament; Fig. 5-22). Retract the tendon toward the ulna and identify the median nerve between the tendons of the palmaris longus muscle and the flexor carpi radialis muscle. The nerve lies closer to the palmaris longus than to the flexor carpi radialis (Fig. 5-23).
Pass a blunt, flat instrument (such as a McDonald dissector) down the carpal tunnel between the flexor retinaculum and the median nerve (Fig. 524). Carefully incise the retinaculum, cutting down on the dissector to protect the nerve. Make the incision on the ulnar side of the nerve to avoid possible damage to its motor branch to the thenar muscle. Divide the entire length of the retinaculum (Fig. 5-25).
Deep Surgical Dissection
Identify the motor branch of the median nerve. It usually arises from the anterolateral side of the median nerve just as the nerve emerges from the carpal tunnel. The motor branch then curves radially and upward to enter the thenar musculature between the abductor pollicis brevis and flexor pollicis brevis muscles. Sometimes, however, the motor branch arises within the tunnel and pierces the flexor retinaculum to reach the thenar musculature. In these rare cases, the motor nerve itself may have to be decompressed before the patient’s symptoms will be relieved fully (see Fig. 5-25).
Figure 5-21 The incision for the volar approach to the wrist. The incision should be made on the ulnar side of the palmaris longus tendon to protect the palmar cutaneous branch of the median nerve.
Figure 5-22 The skin is retracted, and the deep fascia and tendon of the palmaris longus are inspected.
Figure 5-23 The deep fascia is incised. The palmaris longus is retracted toward the ulna, revealing the median nerve as it enters the carpal tunnel.
Figure 5-24 A spatula is placed under the transverse carpal ligament to protect the median nerve as the ligament is incised.
Figure 5-25 The transverse carpal ligament is released on the ulnar side of the nerve to avoid damage to the motor branch of the thenar muscle.
It rarely is necessary to gain access to the volar aspect of the wrist joint. If this is required, mobilize the median nerve in the carpal tunnel and retract it radially to avoid stretching its motor branch. Next, mobilize and retract the flexor tendons in the carpal tunnel (Fig. 5-26). Incising the base of the tunnel longitudinally exposes the volar aspect of the carpus. Extending the incision proximally provides access to the volar aspect of the wrist joint and the distal radius (Fig. 5-27). The most convenient approach for access to the volar aspect of the distal radius is the volar approach to the distal radius or the distal portion of the anterior approach to the radius (see Chapter 4).
Dangers
Nerves
The palmar cutaneous branch of the median nerve arises 5 cm proximal to the wrist joint and runs down along the ulnar side of the tendon of the flexor carpi radialis muscle before crossing the flexor retinaculum. The greatest threat to this nerve occurs if the skin incision is not angled to the ulnar side of the forearm (see Fig. 5-21).
The motor branch of the median nerve to the thenar muscles exhibits considerable anatomic variation. The risk to the nerve is minimized if the incision is made into the carpal tunnel on the ulnar side of the median nerve (see Applied Surgical Anatomy of the Volar Aspect of the Wrist and Fig. 5-39).
Vessels
The superficial palmar arch crosses the palm at the level of the distal end of the outstretched thumb. Blind slitting of the flexor retinaculum may damage this arterial arcade if the instrument passes too far distally. The arch is in no danger if the flexor retinaculum is cut carefully under direct observation for its entire length (see Figs. 5-21 and 5-39). Minimally invasive approaches to divide the flexor retinaculum rely on arthroscopic visualization of the anatomical structures to ensure their preservation.
How to Enlarge the Approach
Extensile Measures
Proximal Extension. The approach can be extended to expose the median nerve. To accomplish this, extend the skin incision proximally, running it up the middle of the anterior surface of the forearm (Fig. 5-28). Incise the deep fascia of the forearm between the palmaris longus and flexor carpi radialis muscles. Retract the flexor carpi radialis in a radial direction and the palmaris longus in an ulnar direction, exposing the muscle belly of the flexor digitorum superficialis muscle in the distal two-thirds of the forearm (Fig. 5-29). The median nerve adheres to the deep surface of the flexor digitorum superficialis, held there by fascia. Thus, if the flexor digitorum superficialis is reflected, the nerve goes with it (Fig. 5-30).
Figure 5-26 The median nerve is retracted radially and the flexor tendons are retracted toward the ulna, revealing the distal radius and joint capsule. An incision then is made into the capsule to expose the carpus.
Figure 5-27 Incise the joint capsule to expose the carpus.
Figure 5-28 Extend the wrist incision proximally to expose the distal forearm and median nerve.
Figure 5-29 Incise the fascia on the forearm between the palmaris longus and the flexor carpi radialis to expose the tendons and muscles of the flexor digitorum superficialis.
Figure 5-30 Reflect the flexor digitorum superficialis and note that the median nerve moves with it, because it is attached to the muscle via the posterior fascia of the muscle.
Distal Extension. The skin incision can be extended into a volar zigzag approach for any of the fingers, providing complete exposure of all the palmar structures (see Volar Approach to the Flexor Tendons and Fig. 545).