Distal Ulnar Nerve Anatomy
Also see Ulnar nerve compression
Guyons Canal
 interaponeurotic space about 4 cm in length with discrete anatomical limits and
boundaries.
 It extends from the proximal edge of the palmar carpal ligament, which is the
distal extent of the antebrachial fascia, to the fibrous edge of the hypothenar
muscles
 Ulnar artery lies radial and volar to the nerve
 Boundaries
o Radial: hook of hamate, junction of the roof, including the palmaris brevis
muscle, to the flexor retinaculum
o Ulnar: Flexor carpi ulnaris, the pisiform, and the abductor digiti minimi
constitute the ulnar wall
o Roof: proximally is composed of the palmar carpal ligament which
blends with the tendinous insertion of the flexor carpi ulnaris into the
pisiform bone. Distally, the palmaris brevis muscle, hypothenar fat and
fibrous tissue form the roof
o Floor: floor is made up of the pisohamate ligament centrally, fibres of the
transverse carpal ligament and the opponens digiti minimi radially, and
fibres of the pisometacarpal ligament distally and ulnarly
Muscles
 abductor digiti minimi (ADM) muscle
1. originates from the pisiform, the tendon of the flexor carpi ulnaris, and the
pisohamate ligament.
2. 2 insertions - one slip inserted into the ulnar side of the proximal phalanx base
of the small finger and the other slip inserted into the extensor apparatus of the
LF
3. in 75% of cases, ADM is supplied by 1 branch
4. In 45%, motor branch to the ADM originates from the deep branch distal to
the hiatus.
5. In 30%, the main motor branch to the ADM originates from the main trunk of
the ulnar nerve proximal to the hiatus in Guyon's canal
 Flexor digiti minimi brevis
1. absent in up to 40%
2. originates from the hook of the hamate, the adjacent ulnar portion of the flexor
retinaculum, and/or the radial portion of the pisiform
3. often fused distally with the ADM
4. inserts onto the volar aspect of the head of the fifth metacarpal but if fused
with ADM, shares common insertion with ADM.
5. a fascial arch exists between ADM and FDM origins
 Opponens Digiti Minimi
1. has deep and superficial parts
2. superficial layer originates from the distal part of the hook of the hamate and
inserts into the distal ulnar side of the fifth metacarpal shaft.
3. deep layer originates from the part of the ulnar flexor compartment wall that is
adjacent to the hook of the hamate and it inserts into the proximal ulnar side of
the small finger metacarpal shaft
4. deep branch of the ulnar nerve passes between the superficial and the deep
layers of the ODM
 Abberant Muscles
1. Accessory ADM
 Most common variation – present in 25% of hands
 fuses with ADM distally
 May arise from flexor retinaculum, antebrachial fascia or pisiform
 lie volar to the ulnar neurovascular bundle in Guyon's canal
 Inserts with ADM
Ulnar Nerve Path
 ulnar nerve usually bifurcates (occasionally trifurcates) into a deep branch and a
superficial trunk just distal to the distal edge of the pisiform

3 zones. (Gross and Gelberman)
1. Zone 1 is in the most proximal portion of the canal, where the nerve is a single
structure consisting of motor and sensory fascicles
o Boundaries
1. Dorsal –TCL
2. Volar/radial – palmar carpal ligament
3. Medial – pisiform and FCU
2. Zones 2 - motor branch
o Boundaries
1. Dorsal –pisometacarpal and pisohamate ligaments. Triquetrohamate
joint, opponens digiti minimi
2. Volar – palmaris brevis, fibrous arch insertion of flexor digiti minimi
over hook of hamate
3. Radial - TCL, flexor digiti minimi, hook of hamate
4. Ulnar – abductor digiti minimi, Sensory branch
o Path – leaves the tunnel between abductor and flexor digiti minimi
(pisohamate tunnel), pierces opponens digiti minimi and then curves
radially and dorsally around the hook of hamate within the concavity of
the deep palmar arch
3. Zone 3 - superficial branch
o Boundaries
1. Dorsal – hypothenar fascia
2. Volar – Palmaris brevis and ulnar artery
3. Radial – motor branch
4. Ulnar – abductor digiti minimi
o superficial trunk bifurcates distally into 2 sensory branches: the fourth
common digital nerve and the ulnar proper digital nerve of the small
finger.
Interossei
 palmar interossei along with the first and second dorsal interossei were all
innervated within the middle third of their corresponding metacarpal.
 The third and fourth dorsal interossei were innervated within the proximal third
of their corresponding metacarpals
 the third lumbrical was innervated within the middle third whereas the fourth
lumbrical was innervated along its distal third.
Nerve of Henle
 nerve of Henle, a branch of the ulnar nerve in the forearm, is thought to deliver
sympathetic innervation to the ulnar artery.
 Two distinct patterns of the nerve were found. In the typical pattern (45%), the
nerve originates 16 cm proximal to the ulnar styloid, travels distally with the
ulnar artery, and frequently, branches to pierce the superficial fascia 6 cm
proximal to the ulnar styloid and innervate the skin of the distal ulnar forearm. In
the atypical pattern (12%), the nerve originates in the distal 8 cm of the forearm
and travels briefly with the ulnar artery before branching to the skin.
 The palmar cutaneous branch of the ulnar nerve was absent in cadavers with the
nerve of Henle and may be a distal variant of that nerve.