The ulnar tunnel is located at the proximal part of the hand
radial to the pisiform bone and to the proximal part of the
carpal tunnel. Inside it lie the ulnar nerve and artery.
Compression of the ulnar nerve in this tunnel is often
reported. Cysts, occupational trauma, fractures and muscle
variations are among the main causes (Schjelderup, 1964;
Kleinert & Hayes, 1971). Damage to the ulnar nerve and
artery during the endoscopic decompression of the carpal
tunnel has been reported recently (Agee et al. 1992; Nath et
al. 1993; De Smets & Fabry, 1995). The structures within
the ulnar tunnel are closely related to the medial part of the
flexor retinaculum, in particular the ulnar artery which is
located lateral to the ulnar nerve. During a study of this
region we found a rare disposition of the contents of this
tunnel. We believe that knowledge of this variation is
important for the surgical anatomy of this region.