Origin

• Medial cord of brachial plexus (C8, T1; C7 also contributes — supplies FCU)
• No branches in axilla or arm

Course in Forearm

• Enters forearm between two heads of FCU
• Upper 1/3: under FCU, above FDP
• Lower 2/3: superficial; lateral to FCU, medial to ulnar artery

Forearm Branches

Course in Hand

• Enters superficial to flexor retinaculum, lateral to pisiform, through ulnar tunnel (Guyon’s canal)
• Divides into superficial and deep terminal branches just distal to pisiform

Terminal Branches

Superficial (Sensory + Small Motor)

• Motor: palmaris brevis
• Sensory: palmar digital branches → palmar skin of medial 1½ digits

Deep (Purely Motor)

• Passes between ADM + FDM, pierces opponens digiti minimi
• Turns laterally within concavity of deep palmar arch
• Ends within adductor pollicis

Muscles supplied by deep branch:

Ulnar nerve = all intrinsic hand muscles except LOAF (Lumbricals 1+2, Opponens pollicis, APB, FPB superficial head — median nerve)

Applied Anatomy

A. Injury at Elbow

Causes: medial epicondyle fracture-dislocation, cubital tunnel syndrome, cubitus valgus (tardy ulnar palsy)

Features:

• Wasting + flattening of hypothenar eminence
• Ulnar claw hand (ring + little: MCP hyperextension, IP flexion); index + middle less affected (lumbricals 1+2 intact via median)
• Loss of finger abduction/adduction (interossei)
• Froment’s sign positive (adductor pollicis paralysed → thumb IP flexion by FPL)
• Sensory loss: medial 1/3 palm + dorsum; medial 1½ fingers
• Clawing less pronounced — medial ½ FDP also paralysed → less DIP flexion

B. Injury at Wrist (Guyon’s Canal Syndrome)

Causes: cuts/lacerations, ganglion, hook of hamate fracture, repetitive compression

Features:

• Ulnar claw — more pronounced (FDP intact → maximal IP flexion)
• Weakness of all ulnar intrinsics
• Hypoaesthesia: palmar medial 1½ digits
• Dorsal hand sensation SPARED (dorsal cutaneous branch arises 5 cm above wrist)
• Hypothenar eminence sensation SPARED (palmar cutaneous branch arises proximal to canal)

Ulnar Paradox

• Wrist injury → worse claw than elbow injury
• Elbow: FDP also paralysed → less IP flexion → less deformity; Wrist: FDP intact → maximal IP flexion → worse claw
• Paradox: more proximal lesion = less deformity; more distal lesion = more deformity

Froment’s Sign

• Patient grasps card between thumb + index; adductor pollicis paralysed → compensates with FPL → distal thumb phalanx flexes = positive

Complete Claw Hand

• Median + ulnar nerve combined injury → all 4 lumbricals paralysed → all 4 fingers clawed

Origin

Arises from the medial cord of the brachial plexus in the axilla (C8, T1). The ventral ramus of C7 also contributes (supplies flexor carpi ulnaris).

No branches are given in the axilla or the arm.

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Course in the Forearm

Enters the forearm by passing between the two heads of flexor carpi ulnaris (cubital tunnel).

Branches in the Forearm

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Course in the Hand

• Enters the hand superficial to the flexor retinaculum, lateral to the pisiform bone, through the ulnar tunnel (covered by the volar carpal ligament / palmar carpal ligament)
• Just distal to the pisiform, at the distal border of the retinaculum, divides into superficial and deep terminal branches

Terminal Branches

1. Superficial Terminal Branch (Sensory + Small Motor)

Superficial terminal branch
        │
        ├── Motor: Palmaris brevis
        │
        └── Sensory: Proper and common palmar digital branches
                     → Palmar skin of medial 1½ digits

2. Deep Terminal Branch (Purely Motor)

• Passes between abductor digiti minimi and flexor digiti minimi, pierces opponens digiti minimi
• Enters Guyon’s canal (pisohamate tunnel) — deep to pisohamate ligament
• Turns laterally within the concavity of the deep palmar arch
• Ends within the substance of adductor pollicis (terminal supply)

Muscles Supplied by Deep Branch

Articular Branches of Deep Branch

• Intercarpal joints
• Carpometacarpal joints
• Intermetacarpal joints

The ulnar nerve supplies all intrinsic muscles of the hand except the LOAF muscles (which are median nerve): Lumbricals 1 & 2, Opponens pollicis, Abductor pollicis brevis, Flexor pollicis brevis (superficial head).

The ulnar nerve is called the “musician’s nerve” because it supplies most of the intrinsic muscles responsible for fine hand movements.

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Applied Anatomy

A. Injury at the Elbow

Causes:

• Fracture-dislocation of the medial epicondyle
• Cubital tunnel syndrome (thickened fibrous roof)
• Compression between two heads of FCU
• Cubitus valgus → tardy (late) ulnar nerve palsy

Features:

• Wasting and flattening of hypothenar eminence
• Ulnar claw hand (partial claw) — ring and little fingers: hyperextension at MCP joints + flexion at IP joints; index and middle fingers less affected (1st + 2nd lumbricals intact via median nerve)
• Loss of abduction and adduction of fingers (interossei paralysed)
• Loss of adduction of thumb (adductor pollicis paralysed) → Froment’s sign positive
• Sensory loss over medial 1/3 of palm and dorsum; medial 1½ fingers
• Clawing is less pronounced at elbow (medial ½ FDP also paralysed → less DIP flexion)

B. Injury at the Wrist (Guyon’s Canal Syndrome)

Causes:

• Superficial position makes it vulnerable to cuts and lacerations
• Compression in Guyon’s canal (pisohamate tunnel) — ganglion, lipoma, hook of hamate fracture

Features:

• Ulnar claw hand — more pronounced than elbow injury (FDP intact → marked DIP flexion)
• Weakness of all intrinsic hand muscles (hypothenar, interossei, medial 2 lumbricals, adductor pollicis)
• Hypoaesthesia over palmar surface of medial 1½ digits
• Dorsum of hand sensation SPARED (dorsal cutaneous branch arises 5 cm above wrist, proximal to Guyon’s canal)
• Hypothenar eminence sensation SPARED (palmar cutaneous branch also arises proximal to canal)

Ulnar Paradox

When the ulnar nerve is injured at the wrist, clawing of ring and little fingers is more severe than when injured at the elbow. This is because at elbow-level injury, the medial ½ FDP is also paralysed (less IP flexion), reducing the deformity. At wrist level, FDP is intact, maximising IP flexion → worse claw. This apparent paradox — proximal lesion less deformity, distal lesion more deformity — is called the ulnar paradox.

Froment’s Sign

Patient asked to grasp a card between the thumb and index finger. Due to paralysis of adductor pollicis (ulnar nerve), the patient compensates by flexing the distal phalanx of the thumb using flexor pollicis longus (median nerve). Positive Froment’s sign = adductor pollicis paralysis.

Complete (True) Claw Hand

Combined injury of median + ulnar nerves (usually at elbow) produces complete claw hand affecting all four fingers:

• All lumbricals paralysed → hyperextension at all MCP joints
• Long flexors intact → flexion at all IP joints

Previous Year Questions

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