Ulnar Nerve: Course, Branches and Clinical Anatomy

By Dr Richard Miller, MBChB FRCS · Reviewed 1 October 2026

The ulnar nerve is the terminal branch of the medial cord of the brachial plexus that runs down the medial arm, behind the medial epicondyle and along the ulnar side of the forearm into the hand. It carries C8–T1 fibres, supplies most of the small muscles of the hand, and gives sensation to the medial one and a half digits.

Ulnar Nerve · key facts

Roots: C8–T1 from the medial cord, often with a C7 contribution
Course: Medial arm, through the medial intermuscular septum, behind the medial epicondyle, under FCU, through Guyon's canal
Motor supply: FCU and ulnar half of FDP; all intrinsic hand muscles except the LOAF muscles
Sensory supply: Medial palm and dorsum of hand; palmar and dorsal skin of the little finger and medial half of the ring finger
Branches: Muscular (forearm), palmar cutaneous, dorsal cutaneous, superficial and deep terminal branches
Key relations: Groove behind the medial epicondyle; medial to the ulnar artery at the wrist; lateral to the pisiform
Injury: Cubital tunnel syndrome, medial epicondyle fracture, Guyon's canal compression, wrist laceration

Course

The ulnar nerve runs down the medial side of the limb, changes compartment twice, and reaches the hand superficial to the flexor retinaculum.

In the axilla and arm

It arises from the medial cord and lies medial to the axillary artery, between the artery and the axillary vein. In the upper arm it stays medial to the brachial artery in the anterior compartment. Around the middle of the arm it pierces the medial intermuscular septum with the superior ulnar collateral artery and descends in the posterior compartment on the medial head of triceps. It gives no branches in the arm.

At the elbow

The nerve passes behind the medial epicondyle in the ulnar groove, where it can be rolled under a fingertip. It then enters the cubital tunnel: a fibrous roof (the cubital tunnel retinaculum, continuous with the aponeurosis joining the humeral and ulnar heads of flexor carpi ulnaris) over a floor of the ulnar collateral ligament and elbow capsule.

In the forearm

It enters the forearm between the two heads of flexor carpi ulnaris (FCU) and runs down on flexor digitorum profundus (FDP), covered by FCU. In the distal two-thirds of the forearm the ulnar artery joins it on its lateral side, and near the wrist the nerve lies lateral to the FCU tendon.

At the wrist and in the hand

The nerve crosses the wrist superficial to the flexor retinaculum through Guyon's canal (the ulnar canal), between the pisiform medially and the hook of the hamate laterally, roofed by the palmar carpal ligament. It divides there into a superficial and a deep branch.

Branches and supply

The ulnar nerve supplies two forearm muscles and nearly every intrinsic muscle of the hand, which makes it the nerve of fine finger movement.

Level	Branch	Supplies
Elbow	Articular and muscular branches	Elbow joint; FCU; ulnar half of FDP (ring and little fingers)
Mid-forearm	Palmar cutaneous branch	Skin over the hypothenar eminence and medial palm
Distal forearm	Dorsal cutaneous branch	Passes deep to the FCU tendon to the dorsum; medial dorsum of hand and dorsal skin of the medial one and a half digits
Hand	Superficial branch	Palmaris brevis; palmar skin of the little finger and medial half of the ring finger
Hand	Deep branch	Hypothenar muscles, third and fourth lumbricals, all seven interossei, adductor pollicis, deep head of flexor pollicis brevis

The deep branch runs with the deep branch of the ulnar artery between abductor digiti minimi and flexor digiti minimi, passes through opponens digiti minimi, hooks round the hook of the hamate and crosses the palm in the concavity of the deep palmar arch, ending in adductor pollicis and the first dorsal interosseous.

Relations

The ulnar nerve is easiest to find at three fixed points: between the axillary artery and vein, behind the medial epicondyle, and beside the pisiform.

Axilla: medial to the axillary artery and lateral to the axillary vein; the medial cutaneous nerve of the forearm lies more superficially.
Arm: medial to the brachial artery above the mid-arm, then behind the medial intermuscular septum with the superior ulnar collateral artery.
Elbow: directly on the back of the medial epicondyle, close to the ulnar collateral ligament.
Forearm: between FCU in front and FDP behind, with the ulnar artery lateral to it distally.
Wrist: lateral to the pisiform and the FCU tendon, medial to the ulnar artery.

Clinical relevance

Ulnar nerve lesions produce a claw hand and weak finger abduction, and the level of the lesion changes how severe the clawing looks.

Claw hand and the ulnar paradox

Paralysis of the interossei and the medial two lumbricals leaves the long extensors unopposed at the metacarpophalangeal joints and the long flexors unopposed at the interphalangeal joints. The ring and little fingers hyperextend at the knuckles and flex at the interphalangeal joints. The index and middle fingers are spared because their lumbricals are median-supplied. A lesion at the wrist gives a more obvious claw than one at the elbow, because an elbow lesion also paralyses the ulnar half of FDP, so the fingertips no longer flex: this is the ulnar paradox.

Sites of injury

Cubital tunnel syndrome: the second commonest entrapment neuropathy of the upper limb, worse with prolonged elbow flexion. Old valgus deformity after a childhood lateral condyle fracture causes a late (tardy) ulnar palsy.
Medial epicondyle fracture or elbow dislocation: the nerve can be stretched or trapped in the joint.
Guyon's canal: compression by a ganglion, a hamate hook fracture or cycling. Sensation on the dorsum is spared because the dorsal cutaneous branch leaves above the wrist.
Wrist laceration: often divides the ulnar artery and FCU tendon too.

Clinical tests

Froment's sign is flexion of the thumb interphalangeal joint when gripping paper between thumb and index, as flexor pollicis longus substitutes for a weak adductor pollicis. The card test checks palmar interossei, resisted index abduction checks the first dorsal interosseous, and Wartenberg's sign is a little finger that drifts into abduction from unopposed extensor digiti minimi.

How it is examined

On a cadaveric spotter, in an OSPE and in MRCS Part B anatomy.

In the axilla, the nerve pinned between the axillary artery and axillary vein is the ulnar; the thinner, more superficial nerve running with the basilic vein is the medial cutaneous nerve of the forearm, its usual look-alike.
On an elbow prosection, a nerve behind the medial epicondyle is the ulnar; a nerve passing between the heads of pronator teres at the front is the median.
At the wrist the ulnar nerve lies medial to the ulnar artery and lateral to the pisiform, superficial to the flexor retinaculum; candidates who put it inside the carpal tunnel lose the mark.
Expect the viva question on why a wrist lesion claws more than an elbow lesion (the ulnar paradox), and on which intrinsic muscles the ulnar nerve does not supply (the LOAF muscles).
Be ready to perform Froment's sign and the card test and to name the muscle each one tests.

Key points

The ulnar nerve arises from the medial cord (C8–T1) and has no branches in the arm.
It passes behind the medial epicondyle and enters the forearm between the heads of FCU.
It supplies FCU, the ulnar half of FDP and every intrinsic hand muscle except the LOAF muscles.
It crosses the wrist in Guyon's canal, superficial to the flexor retinaculum, medial to the ulnar artery.
Its lesion claws the ring and little fingers, more obviously when the lesion is at the wrist.
The dorsal cutaneous branch leaves above the wrist, so Guyon's canal lesions spare dorsal sensation.

Common questions

What does the ulnar nerve supply?

The ulnar nerve supplies flexor carpi ulnaris and the ulnar half of flexor digitorum profundus in the forearm. In the hand it supplies the hypothenar muscles, the third and fourth lumbricals, all the interossei, adductor pollicis and the deep head of flexor pollicis brevis. Its skin territory is the medial palm and dorsum of the hand and both surfaces of the little finger and medial half of the ring finger.

Why does hitting the funny bone cause tingling in the little finger?

The funny bone is the ulnar nerve lying directly on the back of the medial epicondyle of the humerus, covered only by skin and fascia. A knock compresses the nerve against the bone and fires its sensory fibres, which are felt in the nerve's skin territory: the little finger, the medial half of the ring finger and the ulnar border of the hand.

What is Guyon's canal?

Guyon's canal is the fibro-osseous tunnel at the base of the hypothenar eminence through which the ulnar nerve and artery enter the hand. It lies between the pisiform medially and the hook of the hamate laterally, over the flexor retinaculum and under the palmar carpal ligament. Compression there weakens the intrinsic muscles and may numb the little finger, but spares sensation on the back of the hand.

What is cubital tunnel syndrome?

Cubital tunnel syndrome is compression of the ulnar nerve at the elbow, where it runs behind the medial epicondyle under the fibrous band joining the two heads of flexor carpi ulnaris. It causes numbness of the little and ring fingers, worse with the elbow bent, and later weakness and wasting of the intrinsic muscles. Treatment ranges from splinting at night to decompression or anterior transposition of the nerve.

References

Gray's Anatomy: The Anatomical Basis of Clinical Practice. Standring S (ed). Elsevier, 2020.
Moore's Clinically Oriented Anatomy. Moore KL, Dalley AF, Agur AMR. Wolters Kluwer, 2022.
Last's Anatomy: Regional and Applied. Elsevier.