(13,14) Apart from this branch, the bulk of the ulnar nerve passes through the ulnar canal
(Guyon's canal) at the wrist and divides into a superficial branch which provides motor innervation to the palmaris brevis and skin sensation to the palmar surface of D5 and medial half of D4.1314 The deep motor branch of the ulnar nerve then innervates the hypothenar muscles (abductor digiti minimi, flexor digiti minimi, and opponens digiti minimi), lumbricale muscles to D4 and D5, and the ulnar intrinsics including the dorsal and palmar interassei and adductor pollicis.
Accessory muscles may compress underlying structures in the carpal tunnel region or ulnar canal, causing pain and paresthesias (Morrison, 1916; Ryu & Watson, 1987; Sanudo et al., 1993; Server et al, 1995; Sanchez Lorenzo et al, 1996; Depuydt et al., 1998; Santoro et al, 2000; Schuurman & van Gils, 2000; Soldado-Carrera et al., 2000; Bozkurt et al., 2005; Jones, 2006, Acikel et al., 2007; Ogun et al., 2007).
The muscle was located over flexor carpi ulnaris muscle, ulnar side of flexor digitorum superficialis tendons and crossed over the proximal third of ulnar canal, in close contact with the ulnar nerve and vessels.
The muscle was excised in order to decompress ulnar canal.
The anomalous branch, known as Kaplan anastomosis, was originally described by Kaplan in 1963, as a communication which was originated from the DBUN, crossing from the posterior to the anterior side, close to the pisiform bone, anastomosing with the superficial branch of the ulnar nerve (SBUN), close to the ulnar canal (Kaplan, 1963).
It continues by crossing deep at the pisohamate ligament and communicating with the ulnar nerve, near to ulnar canal (Fig.
During routine dissection of an old male cadaver we observed an anomalous muscle was found to take it's origin from the antebrachial fascia and flexor retinaculum, traversed ulnar canal (Guyon's) superficial to ulnar vessels and nerves to reach the proximal part of abductor digiti minimi.
Guyon's canal syndrome also called as the ulnar tunnel syndrome, caused due to compression of the ulnar nerve as it passes through the ulnar canal (Guyon's) is a well recognized entity (Cem Bozkurt, 2005).
Since, the aforesaid muscle is taking origin partly from the roof (antebrachial fascia) and partly from the floor (flexor retinaculum) of ulnar canal. And therefore every time it contracts the tunnel will be squeezed, thereby the likelihood of compression of the contents of the ulnar canal is very high.