Median, Ulnar & Radial Nerve Injuries & Hand Deformities
Anatomy · Upper Limb · lean revision notes
Median, Ulnar & Radial Nerve Injuries & Hand Deformities
The three major nerves of the forearm and hand — median, ulnar and radial — produce classic, instantly recognisable deformities when injured. NEET PG repeatedly tests the deformity, the level of injury, the specific sensory loss area and the motor deficit for each. Master the intrinsic muscle innervation rule and you can reconstruct almost every answer from first principles.
Quick orientation: roots, cords & function
| Nerve | Root value | Cord origin | One-line function |
|---|---|---|---|
| Median | C5–T1 | Lateral + medial cords | "Labour nerve" — flexion, pronation, fine grip, thenar opposition |
| Ulnar | C8, T1 | Medial cord | "Musician's/nerve of fine movements" — intrinsics of hand |
| Radial | C5–T1 | Posterior cord | "Great extensor nerve" — all extensors of elbow, wrist, fingers |
High-yield: The median nerve has no branch in the arm (except occasionally to pronator teres). Both ulnar and radial nerves are predominantly motor in the hand, while the median is the great sensory nerve of the hand (lateral 3½ digits palmar).
The master rule of intrinsic hand muscles
Almost the entire deformity logic flows from one fact:
High-yield: ALL small (intrinsic) muscles of the hand are supplied by the ULNAR nerve (deep branch), EXCEPT the "LOAF" muscles supplied by the MEDIAN nerve.
LOAF = Lateral two Lumbricals (index, middle) + Opponens pollicis + Abductor pollicis brevis + Flexor pollicis brevis (superficial head).
So:
- Median (recurrent/thenar branch): thenar muscles (OP, APB, FPB superficial head) + lateral 2 lumbricals.
- Ulnar (deep branch): all interossei (4 dorsal, 3 palmar), medial 2 lumbricals, adductor pollicis, all hypothenar muscles, palmaris brevis, deep head of FPB.
Lumbrical flexes MCP and extends IP joints. Loss of lumbrical action → MCP hyperextension + IP flexion = claw. The claw is worse in ulnar palsy because the ulnar-supplied lumbricals (medial two, to ring & little fingers) act on the most powerful long flexor (FDP).
MEDIAN NERVE INJURY
Levels & deformities
Low (at wrist) → loss of thenar muscles + lateral 2 lumbricals. High (at elbow/above) → adds loss of long flexors and pronators.
Deformities (stepwise):
- Ape thumb (simian hand) — wasting of thenar eminence; thumb pulled back into the plane of the palm (loss of opposition + abduction). Seen in both high and low lesions.
- Pointing index / Hand of Benediction — when the patient tries to make a fist, the index (and partly middle) finger fails to flex because FDS (whole) and FDP (lateral half) are paralysed in a high lesion. The ulnar-supplied medial fingers flex normally.
- Pen test positive — cannot abduct thumb at right angle to the palm to touch an overlying pen (tests APB).
High-yield (very tested): Hand of Benediction appears on attempting to FLEX (make a fist) and is due to a high median lesion. The Pope's blessing / Papal hand at rest with claw is an ULNAR phenomenon. Do not confuse them — Benediction = active median deficit; ulnar claw = resting posture.
Sensory loss
Palmar: lateral 3½ fingers (thumb, index, middle, lateral half ring) + adjoining palm. Dorsal: dorsal tips of lateral 3½ fingers (nail beds).
High-yield: In a lesion at the wrist, the palm over the thenar eminence is SPARED because the palmar cutaneous branch arises proximal to the flexor retinaculum and runs superficial to it — this differentiates a wrist laceration from carpal tunnel compression.
Carpal tunnel syndrome (CTS) — commonest entrapment
- Compression of median nerve under flexor retinaculum.
- Features: nocturnal paraesthesia of lateral 3½ digits, thenar wasting, relieved by shaking the hand (flick sign).
- Provocative tests: Tinel's (percussion over carpal tunnel), Phalen's (wrist flexion 60 sec reproduces symptoms).
- Causes (mnemonic): pregnancy, hypothyroidism, acromegaly, rheumatoid arthritis, amyloidosis, diabetes.
- IOC: Nerve conduction study (NCS) — prolonged distal motor & sensory latency.
- Management: wrist splint + NSAIDs → local steroid injection → surgical decompression (flexor retinaculum release) if refractory or with thenar wasting.
High-yield: Pronator teres syndrome mimics CTS but spares the palmar cutaneous branch differently and is worsened by resisted forearm pronation; anterior interosseous nerve (AIN) syndrome = pure motor, loss of flexor pollicis longus + lateral FDP + pronator quadratus → inability to make the "OK" sign (cannot pinch tip-to-tip → makes a triangle instead).
ULNAR NERVE INJURY
Levels & the "ulnar paradox"
Low (at wrist / Guyon's canal) vs High (at elbow, behind medial epicondyle).
Deformity = Claw hand (main-en-griffe): hyperextension at MCP + flexion at IP joints of ring and little fingers (loss of medial 2 lumbricals + interossei).
High-yield — ULNAR PARADOX: A more proximal (high) ulnar lesion produces a LESS deformed claw, because FDP to the ring & little fingers is also paralysed, so the IP joints are not flexed. As the lesion heals/recovers and FDP returns, the claw worsens — paradoxically a recovering or distal lesion looks worse.
Motor signs (all ulnar intrinsics)
- Wasting of hypothenar eminence and dorsal interossei (guttering, esp. first dorsal interosseous web space).
- Card test (Froment's sign): to grip a card/paper between thumb and index, the patient flexes the thumb IP joint using FPL (median) because adductor pollicis (ulnar) is weak → positive Froment's sign.
- Egawa's sign: inability to abduct/adduct the middle finger (interossei).
- Book test (Froment) / loss of finger abduction-adduction.
Sensory loss
Palmar & dorsal: medial 1½ fingers (little + medial half ring) and the corresponding medial hand.
High-yield: In a lesion at Guyon's canal (wrist), the dorsal cutaneous branch is spared (it arises ~5 cm proximal to the wrist), so dorsum of medial 1½ fingers retains sensation — localises the lesion to the wrist rather than the elbow. The palmar cutaneous branch of ulnar is also spared at Guyon's.
Sites of injury
- Elbow: fracture of medial epicondyle, cubitus valgus → tardy (delayed) ulnar nerve palsy; most exposed at the postcondylar groove ("funny bone").
- Wrist: Guyon's canal compression (cyclist's palsy, hook of hamate fracture).
RADIAL NERVE INJURY
Levels & deformities
| Level of injury | Cause | Deficit | Wrist drop? |
|---|---|---|---|
| Axilla (high) | Crutch palsy, shoulder dislocation | Triceps + below | Yes + loss of elbow extension |
| Radial groove / mid-shaft humerus | Saturday night palsy, mid-shaft humerus #, Holstein-Lewis # | All extensors below; triceps spared | Yes (classic wrist drop) |
| Posterior interosseous nerve (PIN) at arcade of Frohse | Monteggia fracture, lipoma | Finger drop, NO sensory loss, wrist deviates radially (ECRL intact) | No true wrist drop |
| Superficial radial (wrist) | Handcuff / wristwatch | Pure sensory loss only | No |
Classic deformity = WRIST DROP — inability to extend wrist and fingers (MCP) due to paralysis of extensor compartment. The hand hangs flaccid at the wrist.
High-yield: PIN (posterior interosseous) syndrome causes finger drop WITHOUT sensory loss and WITHOUT true wrist drop (because ECRL, supplied above the bifurcation, still extends the wrist, though it deviates radially). PIN is purely motor.
Sensory loss
Smallest of all three nerves: a variable patch over the dorsal aspect of the first web space / anatomical snuff box (the only autonomous zone). Sensory loss is often minimal because of overlap.
High-yield: Saturday night palsy = compression of radial nerve in the radial groove from sleeping with the arm over a chair (alcohol-related); triceps is spared because its branches arise proximal to the groove. Crutch palsy is higher → triceps involved.
Grip myth
True grip strength appears reduced in wrist drop because finger flexors work best with the wrist extended (tenodesis). Passively extending the wrist restores grip — confirming the flexors (median/ulnar) are intact.
Deformity comparison table
| Feature | Median | Ulnar | Radial |
|---|---|---|---|
| Classic deformity | Ape thumb + Hand of Benediction (on flexion) | Claw hand (ring & little) | Wrist drop |
| Wasting | Thenar eminence | Hypothenar + interossei (guttering) | Forearm extensors (minimal hand) |
| Key sign | Pen test, OK-sign (AIN) | Froment's, Egawa's | Wrist/finger drop |
| Sensory autonomous zone | Tip of index finger (palmar) | Tip of little finger | First dorsal web space |
| Commonest entrapment | Carpal tunnel | Cubital tunnel / Guyon's | Radial groove (Saturday night) |
| Paradox | Benediction worse in HIGH lesion | Claw worse in LOW lesion | PIN = finger drop, no sensory loss |
Anatomical snuff box (frequently asked)
A triangular depression on the radial dorsum of the wrist, prominent on thumb extension.
Boundaries:
- Lateral (anterior): tendons of abductor pollicis longus + extensor pollicis brevis.
- Medial (posterior): tendon of extensor pollicis longus.
- Floor: scaphoid and trapezium (proximal to distal); also styloid process of radius, base of 1st metacarpal.
- Roof: skin + superficial radial nerve + cephalic vein commencement.
Contents (crossing the floor): radial artery (the key structure — pulse felt here), plus the superficial branch of radial nerve and cephalic vein in the roof.
High-yield: Tenderness in the anatomical snuff box = scaphoid fracture until proven otherwise. Scaphoid blood supply is retrograde (distal to proximal) → proximal pole at risk of avascular necrosis and non-union.
Stepwise clinical approach to a hand deformity
Look at the resting posture → Claw? (ulnar/median) vs Wrist drop? (radial) → Ask patient to make a fist → Benediction appears on flexion = high median → Card/Froment test positive = ulnar → Check sensory autonomous zones (index tip = median, little finger tip = ulnar, 1st web dorsum = radial) → Localise level using spared cutaneous branches (palmar cutaneous spared = wrist median; dorsal cutaneous spared = wrist ulnar; triceps spared = radial groove).
Diagnosis & investigation of choice
- IOC for entrapment/peripheral neuropathy: Nerve conduction studies (NCS) + EMG — localises level (conduction block, latency, denervation potentials).
- Imaging: High-resolution ultrasound and MR neurography for structural causes (ganglion, lipoma, nerve thickening).
- Tinel's sign to track regeneration (advancing point of paraesthesia = axonal regrowth at ~1 mm/day).
Management / principles
- Neuropraxia (compression): conservative — remove cause, splint, physiotherapy; most recover.
- Axonotmesis/neurotmesis (laceration): primary microsurgical repair / nerve grafting; tendon transfers for late presentation.
- Drug-adjuncts: neuropathic pain → gabapentin/pregabalin, amitriptyline; nutritional support (vitamin B12).
- Specific: CTS → splint + steroid → carpal tunnel release; cubital tunnel → ulnar nerve transposition; wrist drop → cock-up splint + tendon transfers (e.g., PT→ECRB, FCU→EDC, PL→EPL).
Complications
- Trophic changes, dryness (loss of sudomotor function), ulceration over anaesthetic skin.
- Joint contractures (especially fixed claw if intrinsics are not splinted).
- Complex regional pain syndrome (CRPS).
- Volkmann's ischaemic contracture (after supracondylar fracture compromising brachial artery — median + AIN most affected).
Key differentials
- Claw hand: ulnar palsy vs C8/T1 root lesion (Klumpke's palsy, also a true claw of all fingers) vs leprosy (commonest cause of bilateral ulnar/median claw in India) vs Pancoast tumour.
- Wrist drop: radial palsy vs lead poisoning (bilateral, painless) vs C7 radiculopathy.
- Thenar wasting: median (CTS) vs T1 root vs syringomyelia (dissociated sensory loss).
High-yield: Leprosy is the commonest cause of peripheral neuropathy/claw hand in India — thickened ulnar nerve at elbow and lateral popliteal nerve are classically palpable; produces a combined median–ulnar claw ("total claw").
Recently asked / exam angle
- "Hand of Benediction is seen on attempting to flex — which nerve?" → High median. Distinguish from resting ulnar claw (Pope's blessing).
- "Froment's sign tests which muscle?" → Adductor pollicis (ulnar).
- "Saturday night palsy spares which muscle?" → Triceps (branches arise above radial groove).
- "Finger drop without sensory loss and without wrist drop" → PIN syndrome.
- "OK sign cannot be made / pinch failure" → Anterior interosseous nerve syndrome (FPL + lateral FDP + pronator quadratus).
- "Snuff box floor / tenderness" → Scaphoid → fracture & AVN risk.
- "All intrinsic muscles of hand supplied by ulnar except…" → LOAF (median).
- "Sensation over dorsum of medial 1½ fingers retained in ulnar lesion at wrist — why?" → Dorsal cutaneous branch spared (arises 5 cm proximal).
- "Ulnar paradox" — high lesion = lesser claw — recurring conceptual MCQ.
- "Most common nerve injured in mid-shaft humerus fracture" → Radial.
Rapid revision
- Median = labour nerve; radial = great extensor; ulnar = nerve of fine hand movements.
- All hand intrinsics = ulnar, EXCEPT LOAF = median.
- Ape thumb + Benediction (on flexion) = median; claw = ulnar; wrist drop = radial.
- Hand of Benediction (active flexion) = HIGH median; Pope's blessing at rest = ulnar claw.
- Ulnar paradox: higher lesion → less obvious claw (FDP also out).
- Froment's sign +ve = weak adductor pollicis = ulnar palsy.
- CTS: thenar wasting, Tinel/Phalen +ve, IOC = NCS, treat → splint/steroid/release; palmar cutaneous branch spared.
- AIN syndrome = pure motor, cannot make OK sign; PIN syndrome = finger drop, NO sensory loss, NO true wrist drop.
- Saturday night palsy = radial groove, triceps spared; crutch palsy = axilla, triceps lost.
- Snuff box floor = scaphoid + trapezium; contains radial artery; tenderness = scaphoid # → AVN (retrograde supply).
- Autonomous sensory zones: index tip (median), little finger tip (ulnar), 1st dorsal web space (radial).
- Leprosy = commonest cause of claw hand in India; thickened ulnar nerve at elbow.