Approach to the Ulnar Nerve (Guyon’s Canal)

APPROACH TO THE ULNAR NERVE (GUYON’S CANAL)

USES

This approach provides exposure of the ulnar nerve at the wrist for decompression or repair of the nerve at the wrist and palm, treatment of tumors or masses affecting the ulnar nerve, treatment of ulnar artery injury or thrombosis, treatment of hamate fractures, or for motor neurectomy for spastic contracture of the hand.

ADVANTAGES

The approach provides direct exposure of the nerve at the wrist and is easily extensile along the course of the ulnar nerve in the forearm. The deep dissection can be performed through the same incision as for a carpal tunnel release, and both the median and ulnar nerves can be simultaneously decompressed through the same incision.

DISADVANTAGES

The incision leaves a palmar scar near the hypothenar eminence, which can be very sensitive. Incisions made over the hypothenar eminence are more likely to injure the palmar cutaneous branch of the ulnar nerve. It is sometimes better to use the same skin incision as would be used for a carpal tunnel release, and then mobilize the medial flap to gain access to Guyon’s canal.

STRUCTURES AT RISK

There are many structures at risk in this approach, most importantly the ulnar nerve and artery and their branches. The motor branches of the ulnar nerve to the hypothenar muscles are at risk in this approach. They are often thin filamentous branches that can easily be mistaken for fascial bands. The palmar cutaneous branch of the ulnar nerve can also be injured.

TECHNIQUE

The skin incision borders the radial side of the flexor carpi ulnaris (FCU) tendon, diagonally crosses the proximal wrist crease, then follows longitudinally in the palm in line with the ring finger. The fascia on the radial side of the FCU is opened, and the ulnar nerve and artery are identified just below the radial edge of the FCU. The nerve is traced from proximal to distal. The roof of Guyon’s canal, the volar carpal ligament, is divided in line with the skin incision. The nerve and artery are carefully mobilized and explored.

TRICKS

Identify the ulnar nerve proximal to Guyon’s canal in the distal forearm. Remember that the wrist is “framed by nerves,” that is, the ulnar nerve lies medial (ulnar) to the artery. Trace the nerve distally as it enters Guyon’s canal. The canal is triangular in shape. The boundaries of the canal are the volar carpal ligament (roof), the pisiform and the fibrous attachments of the pisohamate ligament (medial wall), and the hook of the hamate (lateral wall). The pisiform marks the level of the division of the ulnar nerve into superficial and deep branches.

HOW TO TELL IF YOU ARE LOST

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