Volar Approach to the Ulnar Nerve

The volar approach is used for exploration of the ulnar nerve at the wrist. It is used primarily to decompress the canal of Guyon in cases of ulnar nerve compression. It also permits exploration of the ulnar nerve in cases of trauma. The approach is freely extensile proximally, allowing exposure of the nerve all the way up the forearm.

Position of the Patient

Place the patient supine on the operating table. Rest the hand on a hand table in the supinated position, so that the palm faces upward. Use an exsanguinating soft bandage, then inflate a tourniquet (see Fig. 5-15).

Landmarks and Incision

Landmarks

The hypothenar eminence is a readily palpable group of muscles on the ulnar border of the hand. The proximal transverse skin crease of the wrist overlies the wrist joint.

Incision

Make a curved incision, following the radial border of the hypothenar eminence and crossing the wrist joint obliquely at about 60 degrees. Extend the incision onto the volar aspect of the distal forearm. The incision should be about 5 to 6 cm long (Fig. 5-31).

Internervous Plane

There is no internervous plane. The approach is a true anatomic dissection in which the nerve and vessels are dissected out and preserved.

Superficial Surgical Dissection

Deepen the incision in the line of the skin incision and identify the tendon of the flexor carpi ulnaris in the proximal end of the wound (Fig. 5-32). Take care to identify and preserve the palmar cutaneous branch of the ulnar nerve which lies close to the plane of dissection in most patients. Mobilize the tendon by incising the fascia on its radial border, and retract the muscle and tendon in an ulnar direction to reveal the ulnar nerve and

artery (Fig. 5-33).

Figure 5-31 Incision for the exposure of the ulnar nerve in the canal of Guyon.

Figure 5-32 The volar carpal ligament is seen as a continuation of the deep palmar fascia and fibers of the flexor carpi ulnaris.

Figure 5-33 The volar carpal ligament is isolated and the nerve is protected in preparation for sectioning of the volar carpal ligament.

Deep Surgical Dissection

Trace the nerve and artery distally, incising overlying fibrous tissue, the volar carpal ligament. During this procedure, take great care to protect the nerve and vessel. The ulnar nerve now is exposed across the wrist joint; the canal of Guyon is decompressed (Fig. 5-34).

Dang

Nerves

The ulnar nerve is vulnerable during two phases of the dissection:

1. When the fascia on the radial side of the flexor carpi ulnaris is incised to allow retraction of the muscle, during superficial surgical dissection

2. When the volar carpal ligament is incised, during deep surgical dissection

If care is taken during these two phases of the procedure, the nerve should be safe.

How to Enlarge the Approach

Extensile Measures

Proximal Extension. Extend the skin incision proximally on the anterior aspect of the forearm, running it longitudinally up the middle of the forearm (Fig. 5-35). Incise the deep fascia in line with the incision and identify the radial border of the flexor carpi ulnaris. Develop a plane between the flexor carpi ulnaris muscle (which is supplied by the ulnar nerve) and the flexor digitorum superficialis muscle (which is supplied by the median nerve), retracting the flexor carpi ulnaris toward the ulna to reveal the ulnar nerve. This incision can expose the ulnar nerve almost to the level of the elbow joint (Fig. 5-36), where it passes between the two heads of the flexor carpi ulnaris muscle. If the nerve is exposed for a long distance, take care to preserve as many small vessels attaching to it as possible.

Figure 5-34 The roof of the canal has been incised, revealing the ulnar nerve and artery.

Figure 5-35 Explore the ulnar nerve proximally in the forearm.

Figure 5-36 Develop the plane between the flexor carpi ulnaris and the flexor digitorum superficialis. In the depth of the wound, the ulnar nerve is visualized running under the flexor carpi ulnaris.