The Distal Ulnar Tunnel

Abstract

The distal ulnar tunnel was described by anatomist and urological surgeon Felix Guyon in 1861 based on his anatom-ical dissections investigating the unique and small protrusion of fatty tissue into the distal forearm noted when pressure was applied to the hypothenar eminence (" Ollier phenome-non "). 1 The triangular-shaped " loge " contained the ulnar nerve and artery with accompanying veins; Guyon postulated that this space may be a potential site of compression for the ulnar nerve, although this concept was presented more formally by others such as Hunt (1908), 2 Grantham (1966), 3 and, subsequently, by McFarlane et al through their considerations of the pisohamate tunnel. 4 The distal ulnar tunnel, or the Guyon canal, is 4–4.5 cm in length and begins at the proximal edge of the volar carpal ligament in the volar-ulnar forearm and ends at the fibrous arch of the hypothenar muscles. The distal ulnar tunnel is defined by the flexor carpi ulnaris, the pisiform, and the abductor digiti minimi as its medial wall and by the transverse carpal ligament and the hamate as its lateral margin. The floor of the tunnel consists of the flexor digitorum profundus tendons in the distal forearm, the transverse carpal ligament, the pisohamate and pisotriquetral ligaments, and the opponens digiti minimi. The roof of the tunnel includes the volar carpal ligament, palmaris brevis muscle, and hypothenar fat (►Figure 1). 5