Learning Objectives
By the end of this topic, the learner will be able to:
- Identify the spinal roots of the ulnar nerve.
- Trace its anatomical course from the axilla to the hand.
- Describe its motor and sensory functions.
- Recognize the clinical features of ulnar nerve injury at the elbow and wrist.
The ulnar nerve is a major peripheral nerve of the upper limb that supplies key intrinsic hand muscles and provides sensation to the medial hand.
- Roots: C8–T1
- Motor:
- Forearm: Flexor carpi ulnaris, medial half of flexor digitorum profundus
- Hand: All intrinsic hand muscles except the thenar muscles and the lateral two lumbricals
- Sensory: Medial one and a half fingers and the corresponding palm and dorsal hand area
Anatomical Course
The ulnar nerve arises from the medial cord of the brachial plexus in the axilla and contains fibres from C8–T1.
- In the axilla, it lies between the axillary artery (lateral) and the axillary vein (medial).
- It descends along the medial side of the arm, initially in the anterior compartment.
- At the mid-arm, it pierces the medial intermuscular septum and enters the posterior compartment.
- It passes posterior to the elbow through the ulnar tunnel between the medial epicondyle and olecranon (the “funny bone”).
- In the forearm, it passes between the two heads of flexor carpi ulnaris and travels deep to this muscle alongside the ulna.
Branches in the Forearm
- Muscular branch – to FCU and medial FDP
- Palmar cutaneous branch – medial palm
- Dorsal cutaneous branch – dorsal medial hand and digits
At the wrist, the ulnar nerve passes superficial to the flexor retinaculum, medial to the ulnar artery, and enters the hand through Guyon’s canal, where it divides into:
- Superficial branch (sensory)
- Deep branch (motor)
Motor Functions
Forearm
- Flexor carpi ulnaris – wrist flexion and adduction
- Flexor digitorum profundus (medial half) – flexion of ring and little fingers
Hand (Deep Branch)
- Hypothenar muscles
- Medial two lumbricals
- Interossei (palmar and dorsal)
- Adductor pollicis
Exception: Palmaris brevis is innervated by the superficial branch.
Sensory Functions
- Palmar cutaneous branch: Medial half of palm
- Dorsal cutaneous branch: Dorsal medial 1½ digits
- Superficial branch: Palmar surface of medial 1½ digits
Clinical Relevance
Froment’s Sign
Tests for ulnar nerve palsy (adductor pollicis):
- Patient holds paper between thumb and index finger
- Positive test: Thumb flexes at IP joint instead of adducting
Ulnar Nerve Palsy
At the Elbow
Cause: Medial epicondyle fracture, cubital tunnel compression
- Motor:
- Loss of finger abduction/adduction
- Weak wrist flexion with radial deviation
- Clawing of 4th and 5th digits
- Positive Froment’s sign
- Sensory: Loss over the medial palm and digits
- Signs: Hypothenar wasting, poor grip
At the Wrist
Cause: Laceration at the anterior wrist
- Motor: Only intrinsic hand muscles affected
- Sensory: Loss over the palmar medial 1½ digits
- Dorsal hand sensation preserved
