Title: Guyon's Canal Release of the Ulnar Nerve and Decompression of the Deep Motor Branch. Published: 4/11/2011, Updated: 4/11/2011.

Author(s): Susan E. Mackinnon MD, Andrew Yee BS. Division of Plastic and Reconstructive Surgery, Washington University School of Medicine, St. Louis, MO.

The decompression of the ulnar nerve through Guyon’s canal is a well-known procedure; however the decompression of the deep motor branch of the ulnar nerve is not. Lister, G.D. has stated to the senior author that the decompression of the deep motor branch of the ulnar nerve in Guyon’s canal was a procedure that even challenged trained hand surgeons. The senior author has agreed to this statement and has had the opportunity to “redo” Guyon’s canal releases and found in every case that the deep motor branch has not been decompressed. The reason that hand surgeons are challenged with decompression of the deep motor branch is that the branch is not visualized until after it has been completely decompressed. Typically, the sensory component of the ulnar nerve is easily visualized through Guyon’s canal for decompression, but in many circumstances, the compression point of the deep motor branch by the hypothenar muscles is not addressed. This will result in relief of ulnar nerve-related pain, but weakness will persist in intrinsic muscles of the ulnar nerve. In the face of incorrect depiction of the anatomical course of the deep motor branch by reputable literature sources, the deep motor branch requires correct knowledge of its anatomical course in order to achieve a successful decompression.

Besides the deep motor branch, there exist other surgical nuances that are important to a successful Guyon’s canal release. An additional main entrapment on the ulnar nerve, besides the palmar carpal ligament that composes the roof of Guyon’s canal, is the antebrachial fascia proximal to Guyon’s canal in the distal forearm. This fascia can be thick and compressive for a distance of approximately a centimeter in many patients. In terms of other surgical nuances, there is a small cutaneous nerve that branches from the sensory component of the ulnar nerve that innervates a small cutaneous area of the palm. This cutaneous nerve branch is typically found 2.5cm distal to the wrist crease and 1cm ulnar to the thenar crease. This cutaneous branch must be protected during the Guyon’s canal release. In the past decade, the senior author has found increasingly that patients with cubital tunnel and motor complaints of clumsiness, loss of dexterity, and certainly anyone with ulnar intrinsic weakness will benefit not only from an ulnar nerve transposition at the elbow, but also a Guyon’s canal release. With the ability to utilize the scratch collapse test with ethyl chloride, a hierarchy of entrapment points in the ulnar nerve can determine the benefit of the Guyon’s canal release addition to patients with ulnar nerve motor problems and cubital tunnel benefit from Guyon’s canal release.

 
Surgical Tutorial – Guyon's Canal Release and Carpal Tunnel Release. 
The ulnar nerve is decompressed in the wrist through Guyon's canal and in the hand, specifically the deep motor branch of ulnar nerve. The deep motor branch of ulnar nerve is released by dividing the tendonious arch of the hypothenar muscles. In addition, a carpal tunnel release is performed by transecting the transverse carpal ligament.
 Surgical Techniques
 PROCEDURE: Guyon's Canal Release of the Ulnar Nerve and Decompression of the Deep Motor Branch.
Incision Description: 
Incision is marked ulnar to the thenar crease and comes across the wrist in a Brunner’s fashion.
Sugical Steps:
Guyon's Canal Release and Decompression of Deep Motor Branch:
1. Open Guyon’s canal.
2. Release the thickened antebrachial fascia just proximal to Guyon’s canal.
3. Sweep the neurovascular bundle medially.
4. Palpate the hook of the hamate.
5. Look at the hypothenar muscle and fascia and identify the proximal free border of the hypothenar fascia.
6. Decompress the deep motor branch by dividing the attachment of the hypothenar muscles, staying close to the hook of the hamate.