Ulnar Nerve — Complete Overview

1. Origin & Root Value

• Roots: C8, T1
• Cord: Medial cord of the brachial plexus
• Associated with the medial brachial and medial antebrachial cutaneous nerves at its origin.

2. Course

Axilla / Arm

• Enters the arm with the median nerve and axillary artery, lying medial to the axillary artery.
• No branches in the arm.
• At the mid-arm, pierces the medial intermuscular septum and enters the posterior compartment, running anterior to the medial head of triceps brachii.

Elbow

• Passes posterior to the medial epicondyle of the humerus in the ulnar groove (bony sulcus between medial epicondyle and olecranon). This is where the nerve is superficial and palpable.
• Enters the forearm by passing between the two heads of flexor carpi ulnaris (the humeral-ulnar aponeurosis), forming the roof of the cubital tunnel.

Forearm

• Runs in the plane between flexor carpi ulnaris (medially) and flexor digitorum profundus (laterally/deep).
• Ulnar artery lies lateral to the nerve in the distal two-thirds of the forearm.
• About 5–8 cm proximal to the wrist, the dorsal cutaneous branch exits and passes posteriorly deep to the FCU tendon.

Wrist / Hand

• Enters the hand superficial to the flexor retinaculum, lateral to the pisiform — through Guyon's canal (ulnar tunnel), bounded by the pisiform and hook of hamate, roofed by the volar carpal ligament/palmaris brevis.
• Divides into a superficial (sensory) branch and a deep (motor) branch.

3. Branches

4. Motor Supply (Summary)

• Flexor carpi ulnaris (FCU)
• Flexor digitorum profundus — medial half (ring & little fingers)

• Hypothenar muscles: abductor digiti minimi, flexor digiti minimi brevis, opponens digiti minimi
• All 4 dorsal interossei
• All 3 palmar interossei
• 3rd and 4th lumbricals
• Adductor pollicis
• Deep head of flexor pollicis brevis

5. Sensory Supply

Key point: Because the palmar and dorsal cutaneous branches leave the nerve proximal to Guyon's canal, a wrist lesion spares dorsal hand sensation and medial palm sensation.

6. Ulnar Nerve Palsies

A. Elbow Palsy (Cubital Tunnel Syndrome / Ulnar Groove Syndrome)

• Compression of nerve by thickened humeral-ulnar aponeurosis (cubital tunnel syndrome)
• External pressure from resting a flexed elbow on a hard surface
• Nerve subluxation over medial epicondyle
• Fracture/dislocation of elbow
• Tardy ulnar palsy — delayed palsy from old elbow fracture causing cubitus valgus deformity
• Osteophytes from elbow arthritis
• Ganglion, lipoma, Charcot elbow
• Occupations with repeated elbow flexion

• Sensory: numbness/tingling of little finger and ring finger (ulnar 1½ digits); sensory loss includes dorsum of hand (dorsal branch intact)
• Weakness of FCU and FDP to ring/little (forearm muscles affected)
• Intrinsic hand muscle weakness + wasting (especially 1st dorsal interosseous)
• Ulnar claw hand (4th and 5th fingers) — but less pronounced than wrist lesion (ulnar paradox — see below)
• Froment's sign — when pinching paper between thumb and index finger, distal phalanx of thumb flexes involuntarily (flexor pollicis longus compensates for weak adductor pollicis)
• Wartenberg's sign — little finger abducted due to weakness of 3rd palmar interosseous
• Pain around elbow; Tinel's sign at elbow
• Sensory loss does NOT extend above the wrist

B. Wrist Palsy (Guyon's Canal Syndrome)

• Ganglion cyst (most common)
• Chronic pressure: hand tools, bicycle handlebars, canes, excessive push-ups
• Fracture of pisiform or hook of hamate
• Rheumatoid arthritis
• Distal vascular anomalies

• If superficial + deep branches compressed: motor + sensory loss confined to palmar surface of ulnar 1½ digits only (dorsal hand sensation SPARED)
• If only deep motor branch: purely motor — interossei and hypothenar weakness, NO sensory loss
• Distal compression at pisohamate hiatus: selective deep branch — hypothenar muscles relatively spared, interossei weak
• More pronounced claw (see ulnar paradox)

7. The Ulnar Paradox

Ulnar Paradox: A lesion of the ulnar nerve at the wrist produces a more severe claw deformity than a lesion at the elbow — even though the elbow lesion is at a higher level and causes more functional loss.

• Loss of lumbrical function → loss of MCP flexion
• Unopposed long flexors (FDP) → IP joint flexion
• Unopposed extensors → MCP hyperextension

8. Important Clinical Signs

9. Investigations

• Nerve conduction study (NCS):
  • Focal slowing of motor conduction velocity (>10–15 m/sec) across the elbow
  • Conduction block (reduction in CMAP amplitude/area >20–30%) across elbow
  • Elbow segment should be studied with elbow flexed 70–90° (reduces measurement error)
  • Additional recording from 1st dorsal interosseous (in addition to abductor digiti minimi) increases yield
  • Ulnar SNAP — abnormal in wrist lesions affecting sensory fibers; can be normal in purely motor wrist lesions
• EMG (needle):
  • Denervation in FCU, FDP (4th/5th) — indicates elbow or higher lesion
  • Denervation confined to hand muscles — indicates wrist lesion
  • Spare dorsal cutaneous territory on EMG = wrist lesion
• Neuromuscular ultrasound:
  • Identifies nerve thickening, subluxation, structural lesions (ganglion, lipoma)
  • Nerve cross-sectional area >10 mm² suggests entrapment
• MRI:
  • Identifies ganglia, soft tissue masses, post-traumatic changes
• Plain radiograph:
  • Assess for fractures (pisiform, hook of hamate, medial epicondyle), cubitus valgus, osteophytes

10. Treatment

Conservative

• Avoid provocative positions (prolonged elbow flexion, pressure on elbow/wrist)
• Elbow extension splint at night (cubital tunnel)
• NSAIDs for pain
• Occupational therapy / nerve gliding exercises
• Remove offending cause (bicycle handlebars, hand tools)

Surgical (when conservative fails or severe/progressive deficit)

• In situ decompression (ulnar neurolysis) — division of the humeral-ulnar aponeurosis; lower complication rate
• Medial epicondylectomy
• Anterior transposition (subcutaneous, intramuscular, or submuscular) — higher complication rate but preferred when subluxation is present
• Best outcomes if symptoms < 1 year; ~60% benefit from surgery
• Patients with significant conduction block (>50%) have more favourable prognosis

• Surgical decompression and exploration
• Ganglion excision if present
• Fracture fixation if applicable
• Prognosis generally good after surgical decompression

• Gray's Anatomy for Students, pp. 881, 905, 936–937
• Bradley and Daroff's Neurology in Clinical Practice, pp. 2638–2641
• General Anatomy and Musculoskeletal System (THIEME Atlas), p. 392