💪 NRE Step-1 — Anatomy Notes
Upper Limb Anatomy
High-Yield NRE Notes
Brachial plexus, nerve injury correlations, rotator cuff, compartments, and applied anatomy of the upper limb — with 10 free NRE-style MCQs focused on clinical vignettes.
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Brachial plexus roots
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Rotator cuff muscles
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Main terminal nerves
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Free MCQs below
Overview
How Upper Limb Anatomy Is Tested in NRE
Upper limb anatomy is the most heavily tested anatomy region in NRE Step-1. Questions never ask you to recite anatomy — they always present a clinical scenario and ask you to identify which nerve is injured, which muscle is affected, or which anatomical relationship explains the clinical finding.
The three most consistently tested areas are brachial plexus injuries and their clinical deficits, fracture-nerve injury correlations, and the applied anatomy of the hand and wrist. Master these three areas and you will answer the majority of upper limb anatomy questions correctly.
NRE exam pattern: Upper limb questions follow a strict formula — mechanism of injury or clinical finding → which nerve/structure is injured → what deficit results. “A patient falls on an outstretched hand — which nerve is injured?” “A child is pulled up by the arm — what is the deficit?” Always reason from mechanism to anatomy to clinical deficit.
Brachial Plexus — Most Tested
Brachial Plexus — Roots to Branches
The brachial plexus arises from ventral rami of C5–T1 and supplies the entire upper limb. It is organised into roots → trunks → divisions → cords → branches. The cords are named by their relationship to the axillary artery.
| Level | Components | Key Clinical Point |
|---|---|---|
| Roots | C5, C6, C7, C8, T1 | C5–C6 = upper trunk (Erb’s). C8–T1 = lower trunk (Klumpke’s) NRE |
| Trunks | Upper (C5–C6), Middle (C7), Lower (C8–T1) | Upper trunk injury = Erb’s palsy (waiter’s tip) |
| Divisions | Each trunk splits into anterior + posterior division | Anterior = flexors. Posterior = extensors |
| Cords | Lateral (C5–C7), Medial (C8–T1), Posterior (C5–T1) | Named by position relative to axillary artery NRE |
| Terminal branches | Musculocutaneous, Median, Ulnar, Radial, Axillary | Most tested terminal nerves in NRE |
⚠️ Erb’s vs Klumpke’s — most tested brachial plexus injuries:
Erb’s palsy (C5–C6) — birth injury from lateral neck traction, shoulder dystocia. Arm hangs in adduction + internal rotation + pronation = “waiter’s tip” or “porter’s tip” posture. Deltoid, biceps, and supraspinatus most affected.
Klumpke’s palsy (C8–T1) — birth injury from upward arm traction, or Pancoast tumour. Intrinsic hand muscles paralysed → claw hand. Horner’s syndrome (ptosis, miosis, anhidrosis) if T1 sympathetic fibres involved.
Erb’s palsy (C5–C6) — birth injury from lateral neck traction, shoulder dystocia. Arm hangs in adduction + internal rotation + pronation = “waiter’s tip” or “porter’s tip” posture. Deltoid, biceps, and supraspinatus most affected.
Klumpke’s palsy (C8–T1) — birth injury from upward arm traction, or Pancoast tumour. Intrinsic hand muscles paralysed → claw hand. Horner’s syndrome (ptosis, miosis, anhidrosis) if T1 sympathetic fibres involved.
Nerve Injuries — NRE Favourite
Upper Limb Nerve Injuries — Mechanism to Deficit
Every nerve injury question in NRE gives you the mechanism first. Learn the three most common injury sites for each nerve and the exact deficit that results.
Radial Nerve (C5–C8)
Wrist drop — most recognisable deficit
OriginPosterior cord of brachial plexus
Axilla injurySaturday night palsy / crutch palsy — loss of all extension (wrist, fingers, thumb) + loss of triceps reflex
Spiral grooveMidshaft humerus fracture — WRIST DROP (extensors paralysed). Triceps spared (branch already given off above). Thumb extension lost
ElbowPosterior interosseous nerve (deep branch) injury — no wrist drop (ECRL spared) but finger/thumb extension lost
Key testCannot extend wrist against gravity (wrist drop). Cannot extend fingers at MCPs
Median Nerve (C6–T1)
Ape hand — carpal tunnel syndrome
OriginLateral + medial cords of brachial plexus
Elbow injurySupracondylar fracture in children — “hand of benediction” on attempted grip (cannot flex index/middle fingers)
Wrist injuryCarpal tunnel syndrome — compression under flexor retinaculum. Pain + tingling in lateral 3½ fingers, thenar wasting, Tinel’s/Phalen’s positive
Ape handComplete median nerve lesion — thenar eminence wasted, thumb cannot oppose → ape/simian hand deformity
Key testCannot oppose thumb. Cannot make OK sign (AIN branch). Sensation lost over lateral 3½ fingers and thenar eminence
Ulnar Nerve (C8–T1)
Claw hand — medial epicondyle fracture
OriginMedial cord of brachial plexus
Elbow injuryMedial epicondyle fracture or cubital tunnel. Claw hand (ring + little fingers). Loss of intrinsics, hypothenar wasting
Wrist injuryGuyon’s canal compression — affects hypothenar muscles + intrinsics but spares FCU and FDP (branches given off above wrist)
Claw handRing + little fingers hyperextended at MCPs, flexed at IPs (lumbricals lost). Worse at wrist than elbow (ulnar paradox)
Key testFroment’s sign — adductor pollicis paralysed → uses FPL to hold paper (thumb IP joint flexes). Card test — cannot abduct fingers
Axillary Nerve (C5–C6)
Deltoid wasting — shoulder dislocation
OriginPosterior cord of brachial plexus
Injury siteSurgical neck of humerus fracture or anterior shoulder dislocation
DeficitDeltoid paralysis → cannot abduct shoulder beyond 15° (first 15° by supraspinatus). Deltoid wasting visible
SensationLoss over regimental badge area (lateral arm over deltoid)
Key testAsk patient to abduct arm — deltoid flattened. Sensation test over lateral shoulder
Musculocutaneous Nerve (C5–C7)
Weak flexion + lateral forearm sensory loss
OriginLateral cord of brachial plexus
Injury siteCoracobrachialis penetrating injury — rare. More common in upper trunk injuries
DeficitWeak elbow flexion (biceps + brachialis paralysed). Lateral forearm sensation lost (lateral cutaneous nerve of forearm)
Biceps reflexAbsent or reduced biceps jerk (C5–C6)
Key testWeak supination (biceps is powerful supinator). Weak elbow flexion in supination position
Long Thoracic Nerve (C5–C7)
Winged scapula — serratus anterior
OriginDirectly from roots C5–C7 (not brachial plexus proper)
InjuryMastectomy, axillary surgery, blow to lateral chest wall, heavy backpack
DeficitSerratus anterior paralysis → winged scapula (medial border of scapula protrudes posteriorly)
Key testAsk patient to push against wall — medial scapular border wings out prominently
Function lostCannot fully flex arm above 90° (serratus needed for scapular rotation). Shoulder abduction weakened
Fracture — Nerve Correlations
Fractures and Their Nerve Injury Associations
NRE loves pairing a specific fracture with its associated nerve injury. This table is one of the most direct recall areas in upper limb anatomy — learn every pair.
| Fracture / Injury | Nerve at Risk | Clinical Deficit |
|---|---|---|
| Surgical neck of humerus | Axillary nerve NRE | Deltoid paralysis, loss of shoulder abduction >15°, regimental badge anaesthesia |
| Midshaft humerus (spiral groove) | Radial nerve NRE | Wrist drop, loss of finger extension, loss of thumb extension. Triceps usually spared |
| Supracondylar humerus (children) | Anterior interosseous (median branch) NRE | Cannot make OK sign (FPL + FDP to index affected). No sensory loss (pure motor) |
| Medial epicondyle | Ulnar nerve NRE | Claw hand (ring + little), intrinsic wasting, hypothenar wasting, Froment’s sign |
| Anterior shoulder dislocation | Axillary nerve | Deltoid wasting, cannot abduct beyond 15°, lateral shoulder sensory loss |
| Clavicle fracture (middle ⅓) | Brachial plexus (lower trunk) | Klumpke-type deficit — intrinsic hand weakness |
| Scaphoid fracture | Avascular necrosis (not nerve) | Anatomical snuffbox tenderness. Risk of AVN of proximal pole |
| Colles’ fracture (distal radius) | Median nerve (acute carpal tunnel) | Thenar tingling, carpal tunnel symptoms acutely |
| Lunate dislocation | Median nerve compression NRE | Acute median nerve compression → thenar pain + lateral finger paraesthesia |
Rotator Cuff
Rotator Cuff — SITS Muscles
The rotator cuff stabilises the glenohumeral joint and provides precise rotational movements of the shoulder. It is tested both as anatomy and as clinical examination in NRE Step-2 OSCE stations.
| Muscle | Nerve | Action | Clinical Test |
|---|---|---|---|
| Supraspinatus | Suprascapular (C5–C6) | Initiates abduction (0–15°). Most commonly torn NRE | Empty can test (Jobe’s test). Painful arc 60–120° |
| Infraspinatus | Suprascapular (C5–C6) | External rotation of shoulder | Resisted external rotation with elbow at side |
| Teres Minor | Axillary (C5–C6) | External rotation + weak adduction | External rotation test (combined with infraspinatus) |
| Subscapularis | Upper + lower subscapular (C5–C6) | Internal rotation + adduction. Only anterior muscle NRE | Lift-off test (Gerber’s test). Bear hug test |
SITS mnemonic: Supraspinatus + Infraspinatus + Teres minor + Subscapularis. Supraspinatus is the most commonly torn rotator cuff muscle — impingement under the coracoacromial arch. Painful arc (60–120°) is the classic clinical sign of supraspinatus pathology.
Wrist and Hand Anatomy
Carpal Tunnel, Anatomical Snuffbox, and Hand Spaces
| Structure | Contents / Key Facts | Clinical Relevance |
|---|---|---|
| Carpal tunnel | Roof = flexor retinaculum. Contents: median nerve + 4 FDS tendons + 4 FDP tendons + FPL tendon (9 tendons + 1 nerve) | Carpal tunnel syndrome — median nerve compression → thenar wasting + lateral 3½ finger paraesthesia + positive Tinel’s/Phalen’s NRE |
| Guyon’s canal | Ulnar nerve + ulnar artery at wrist. Between pisiform and hook of hamate | Hypothenar wasting + intrinsic weakness — spares FCU + FDP (given off before canal) |
| Anatomical snuffbox | Radial border: APL + EPB. Ulnar border: EPL. Floor: scaphoid + trapezium. Contents: radial artery + cephalic vein origin | Tenderness = scaphoid fracture. Scaphoid AVN risk from disrupted blood supply (retrograde from distal pole) NRE |
| Thenar eminence muscles | APB, FPB, OP (all median nerve C8–T1) + AdP (ulnar nerve) | Thenar wasting = median nerve lesion (carpal tunnel or higher) |
| Hypothenar eminence | ADM, FDM, ODM — all ulnar nerve (C8–T1) | Hypothenar wasting = ulnar nerve lesion |
| Lumbricals | Lateral 2 = median nerve. Medial 2 = ulnar nerve | Loss → claw hand (MCP hyperextension, IP flexion) in ulnar lesion NRE |
Ulnar paradox — must know for NRE: A wrist-level ulnar nerve injury produces a WORSE claw hand than an elbow-level injury. This seems counterintuitive. Reason: at elbow level, FDP (to ring + little) is also paralysed → fingers cannot flex at IPs → less claw. At wrist level, FDP is intact (branch given off above wrist) → active IP flexion pulls fingers into tight claw. The higher the lesion, the less the claw.
Rapid Revision
High-Yield Key Points — NRE Checklist
💪 Upper Limb Anatomy — Must Know for NRE
- Brachial plexus — C5 to T1 — roots → trunks → divisions → cords → branches. Cords named by position relative to axillary artery
- Erb’s palsy (C5–C6) — waiter’s tip posture — adduction + internal rotation + pronation — from birth trauma or shoulder dystocia
- Klumpke’s palsy (C8–T1) — claw hand + Horner’s syndrome — from upward arm traction or Pancoast tumour
- Radial nerve in spiral groove — midshaft humerus fracture → WRIST DROP. Triceps usually spared. Thumb extension lost
- Axillary nerve — surgical neck of humerus or anterior dislocation → deltoid wasting, cannot abduct >15°, regimental badge anaesthesia
- Median nerve at wrist — carpal tunnel syndrome → thenar wasting + lateral 3½ finger paraesthesia + Tinel’s/Phalen’s positive
- Median nerve at elbow — supracondylar fracture → AIN injury → cannot make OK sign (FPL + FDP index affected) — no sensory loss
- Ulnar nerve — medial epicondyle fracture → claw hand (ring + little) + intrinsic wasting + Froment’s sign
- Long thoracic nerve (C5–C7) — serratus anterior → winged scapula on wall push test
- Rotator cuff — SITS: Supraspinatus (most torn, initiates abduction 0–15°, painful arc 60–120°), Infraspinatus (ER), Teres minor (ER), Subscapularis (IR — only anterior muscle)
- Carpal tunnel contents — 9 tendons + median nerve. Roof = flexor retinaculum. Ulnar nerve passes in Guyon’s canal (NOT carpal tunnel)
- Anatomical snuffbox floor = scaphoid. Tenderness = scaphoid fracture. Risk of AVN of proximal pole
- Lumbricals — lateral 2 = median, medial 2 = ulnar. Loss of ulnar lumbricals → claw of ring + little fingers
- Froment’s sign — adductor pollicis paralysed (ulnar) → compensates with FPL (median) → thumb IP flexes when holding paper
- Ulnar paradox — wrist ulnar lesion causes WORSE claw than elbow lesion (FDP intact at wrist → active IP flexion)
Free Practice MCQs
Test Yourself — 10 NRE-Style Questions
These questions follow the NRE clinical vignette format — mechanism → anatomy → deficit. Use the notes above to work through each scenario.
Question 1
A 45-year-old man falls off a bicycle and lands directly on his shoulder. X-ray shows a fracture of the surgical neck of the humerus. On examination he cannot abduct his shoulder beyond 15°. There is numbness over the lateral aspect of his shoulder. Which nerve is most likely injured?
A. Radial nerve
B. Axillary nerve ✓
C. Musculocutaneous nerve
D. Suprascapular nerve
Explanation: Axillary nerve injury at the surgical neck of the humerus — the nerve winds around the surgical neck in the quadrilateral space. Deficit: deltoid paralysis (cannot abduct beyond 15° — supraspinatus handles first 15°) + sensory loss over regimental badge area (lateral shoulder over deltoid). Radial nerve is at risk at the midshaft (spiral groove). Musculocutaneous nerve injury causes weak elbow flexion. Suprascapular nerve injury causes weakness of supraspinatus and infraspinatus.
Question 2
A 30-year-old man is found sleeping with his arm draped over a chair back for several hours (Saturday night palsy). On waking he has a wrist drop and cannot extend his fingers. His triceps is intact. Sensation is reduced over the dorsum of the hand. Which nerve is injured and where?
A. Radial nerve at the axilla
B. Radial nerve at the spiral groove of the humerus ✓
C. Posterior interosseous nerve at the elbow
D. Ulnar nerve at the elbow
Explanation: Radial nerve at the spiral groove (midshaft humerus) — compressed by prolonged pressure. Wrist drop + loss of finger extension + dorsal hand sensory loss. Triceps is SPARED because its branch arises above the spiral groove. If the nerve were injured at the axilla, triceps would also be paralysed. If the posterior interosseous nerve were injured at the elbow, there would be no wrist drop (ECRL, which extends the wrist, is supplied above this level) but finger extension would still be lost.
Question 3
A 7-year-old child falls onto an outstretched hand. X-ray confirms a supracondylar fracture of the humerus. The next day, the mother notices the child cannot form an “OK” sign with the thumb and index finger. There is no sensory loss. Which nerve branch is injured?
A. Main trunk of median nerve
B. Anterior interosseous nerve (branch of median) ✓
C. Ulnar nerve
D. Radial nerve
Explanation: Anterior interosseous nerve (AIN) is a pure motor branch of the median nerve — no sensory fibres. It supplies FPL (flexes thumb IP), FDP to index and middle fingers, and pronator quadratus. AIN injury = cannot make OK sign (tip-to-tip pinch) — thumb and index both extend when trying. No sensory loss. This is the classic supracondylar fracture nerve injury in children. The main median trunk injury would also produce thenar wasting and sensory loss over the lateral 3½ fingers.
Question 4
A 25-year-old motorcyclist is involved in an accident. His arm is forcefully pulled downward and laterally. He presents with the arm in adduction, internal rotation, and pronation — the “waiter’s tip” posture. Which nerve roots are most likely injured?
A. C5 and C6 (upper trunk of brachial plexus) ✓
B. C8 and T1 (lower trunk of brachial plexus)
C. C7 only (middle trunk)
D. The entire brachial plexus C5–T1
Explanation: Erb’s palsy — upper trunk injury (C5–C6) from excessive lateral neck-to-shoulder angle. The muscles supplied by C5–C6 lose their function: deltoid, biceps, supraspinatus, infraspinatus → arm falls into the “waiter’s tip” posture (gravity + unopposed C7–T1 muscles: adduction by pectorals, internal rotation by subscapularis, pronation by pronators). Klumpke’s palsy (C8–T1) = intrinsic hand muscles affected + claw hand. Adult brachial plexus injuries (motorbike) typically affect upper trunk (Erb’s) from shoulder being forced down while head goes opposite way.
Question 5
A 55-year-old woman presents with pain and tingling in her thumb, index, middle, and the radial half of her ring finger, worse at night. She notices weakness when unscrewing jar lids. Tinel’s test at the wrist is positive. What is the most likely diagnosis?
A. Cubital tunnel syndrome
B. Cervical radiculopathy C6
C. Carpal tunnel syndrome ✓
D. Thoracic outlet syndrome
Explanation: Carpal tunnel syndrome — median nerve compression under the flexor retinaculum. Classic features: pain and paraesthesia in lateral 3½ fingers (thumb + index + middle + lateral half of ring — median nerve sensory distribution), worse at night and with wrist flexion, Tinel’s test positive (tingling on percussion over carpal tunnel), Phalen’s test positive (symptoms with wrist flexion for 60 seconds). Weakness of thenar muscles (APB) causes difficulty with screwing/unscrewing. Cubital tunnel = ulnar nerve = ring + little finger + medial forearm.
Question 6
A 40-year-old woman presents with inability to abduct her right arm above 90°. She had a right mastectomy 2 months ago. On examination, when she pushes against a wall, her right medial scapular border protrudes prominently. Which nerve was damaged during surgery?
A. Axillary nerve
B. Thoracodorsal nerve
C. Long thoracic nerve ✓
D. Suprascapular nerve
Explanation: Long thoracic nerve (C5–C7) supplies serratus anterior — the muscle that holds the scapula flat against the chest wall and rotates it for arm elevation above 90°. Injury during axillary lymph node dissection (mastectomy) → serratus anterior paralysis → winged scapula (medial border protrudes, especially on wall push test). Axillary nerve injury causes deltoid wasting. Thoracodorsal nerve supplies latissimus dorsi (arm extension and adduction). Suprascapular nerve supplies supraspinatus and infraspinatus.
Question 7
A 28-year-old man sustains a medial epicondyle fracture in a rugby tackle. He presents with a claw deformity affecting the ring and little fingers. He cannot hold a piece of paper between his thumb and index finger without bending his thumb IP joint. What is this sign called and what does it indicate?
A. Tinel’s sign — median nerve compression
B. Phalen’s sign — carpal tunnel syndrome
C. Froment’s sign — ulnar nerve injury with adductor pollicis paralysis ✓
D. Finkelstein’s sign — de Quervain’s tenosynovitis
Explanation: Froment’s sign tests adductor pollicis (ulnar nerve). Ask the patient to hold a piece of paper between the thumb and index finger — normally adductor pollicis keeps the thumb straight. With ulnar nerve injury, adductor pollicis is paralysed → patient compensates using FPL (median nerve) → thumb IP joint flexes. This is Froment’s sign — positive = ulnar nerve lesion. The claw of ring + little fingers (from intrinsic paralysis) also confirms ulnar nerve injury at the elbow (medial epicondyle).
Question 8
A 22-year-old falls on an outstretched hand. X-ray of the wrist is initially reported as normal. Three months later she returns with persistent anatomical snuffbox tenderness and X-ray now shows sclerosis of the proximal carpal bone. What is the most likely diagnosis and its complication?
A. Colles’ fracture — acute carpal tunnel syndrome
B. Scaphoid fracture — avascular necrosis of the proximal pole ✓
C. Lunate dislocation — median nerve compression
D. Triquetral fracture — ulnar nerve injury
Explanation: Scaphoid fracture — most common carpal bone fracture, often missed on initial X-ray. Anatomical snuffbox tenderness is the key clinical sign. The blood supply enters the scaphoid distally — a fracture through the waist or proximal pole disrupts blood supply to the proximal pole → avascular necrosis (sclerosis on X-ray, appearing weeks to months later). Treatment: if suspected clinically (snuffbox tenderness) even with normal X-ray → immobilise + MRI to confirm → surgical fixation to prevent AVN.
Question 9
During a shoulder examination, a patient is asked to hold their arm at 90° abduction with the thumb pointing down (empty can position). They experience pain and weakness in this position. Which rotator cuff muscle is most likely affected?
A. Supraspinatus ✓
B. Infraspinatus
C. Subscapularis
D. Teres minor
Explanation: The empty can test (Jobe’s test) specifically tests supraspinatus. The arm is abducted to 90° in the scapular plane (30° forward) with internal rotation (thumb pointing down — like emptying a can). Resistance applied downward — pain and/or weakness indicates supraspinatus pathology (impingement or tear). Supraspinatus is the most commonly torn rotator cuff muscle. The painful arc (60–120° of abduction) is another classic supraspinatus sign. Infraspinatus: external rotation test. Subscapularis: lift-off test. All four are tested in NRE Step-2 OSCE stations.
Question 10
A newborn is delivered following a prolonged labour with shoulder dystocia. Examination reveals the right arm hangs limply at the side in adduction, internal rotation, and pronation. The Moro reflex is absent on the right. The hand grip is intact. Which nerve roots are injured?
A. C5 and C6 — upper trunk (Erb’s palsy) ✓
B. C8 and T1 — lower trunk (Klumpke’s palsy)
C. C7 — middle trunk
D. C5 to T1 — entire plexus
Explanation: Neonatal Erb’s palsy (C5–C6) from shoulder dystocia — excessive lateral traction stretches the upper trunk. Waiter’s tip posture: adduction (deltoid C5 lost), internal rotation (infraspinatus C5–C6 lost → subscapularis unopposed), pronation (biceps C5–C6 lost → pronators unopposed). Absent Moro reflex on affected side. Hand grip is INTACT (C8–T1 spared) — this distinguishes Erb’s from complete plexus injury. Klumpke’s (C8–T1) = hand intrinsics lost, claw hand, Horner’s syndrome — from upward arm traction during delivery (arm above head).
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