Location of the Ulnar Tunnel at the Wrist
The ulnar tunnel (Guyon's canal) is a fibroosseous tunnel located along the anteromedial (ulnar side) of the wrist, positioned radial to the pisiform bone and proximal to the carpal tunnel. 1
Anatomical Boundaries and Contents
The ulnar tunnel is situated on the flexor (volar) surface of the wrist on the medial side, where the ulnar artery pulse can be palpated. 2, 3 Specifically:
- The tunnel lies at the proximal part of the hand, radial to the pisiform bone and adjacent to the proximal portion of the carpal tunnel 1, 4
- It contains the ulnar nerve and ulnar artery as they pass from the forearm into the hand 5, 1
- The ulnar artery supplies the medial forearm, wrist, hand, superficial central palm structures, and most palmar and distal dorsal aspects of the fingers 2, 3
Clinical Landmarks for Localization
On physical examination, the ulnar tunnel can be located by palpating the ulnar pulse on the flexor surface of the wrist medially (on the ulnar/pinky finger side). 2, 3 This is in contrast to the radial pulse, which is palpable laterally on the flexor surface. 2
The acupuncture point HT 7 (Shenmen) is located at the ulnar end of the volar wrist crease, which corresponds to the region of the ulnar tunnel. 2
Clinical Significance
The ulnar tunnel is clinically important as a site of ulnar nerve compression (ulnar tunnel syndrome), which can occur from various causes including ganglion cysts, fractures, inflammatory conditions, neoplasms, vascular anomalies, or aberrant musculature. 5, 6
The boundaries and shape of the canal vary from proximal to distal, and anatomical variations are not uncommon, which can complicate clinical assessment. 5, 1 Anomalous muscles are present within the canal in approximately 25% of individuals, with two-thirds of these being bilateral. 1
Understanding the precise location is critical during endoscopic carpal tunnel release procedures, as damage to the ulnar nerve and artery has been reported during these procedures due to their close proximity to the medial part of the flexor retinaculum. 4