67 UPPER LIMB

# UPPER LIMB

The upper limb is one of the highest-yield topics in MRCS Part A. A single fracture, dislocation or stab wound can be linked to a specific nerve, muscle group and predictable clinical picture. Master the brachial plexus and the course of the five major peripheral nerves and most upper limb SBAs can be answered by reasoning rather than memorisation.

Brachial plexus

The brachial plexus is formed from the anterior (ventral) rami of C5–T1. It supplies all motor and almost all sensory innervation to the upper limb. Five roots become three trunks, six divisions, three cords and five terminal branches.

Mnemonic: Real Texans Drink Cold Beer

Roots → Trunks → Divisions → Cords → Branches.

Level	Components
Roots	C5, C6, C7, C8, T1 (anterior rami)
Trunks	Upper (C5–C6), Middle (C7), Lower (C8–T1)
Divisions	Each trunk splits into anterior + posterior (3 + 3)
Cords	Lateral, Medial, Posterior (named relative to axillary artery)
Branches	Musculocutaneous, Axillary, Median, Radial, Ulnar (the "M")

The roots and trunks lie in the posterior triangle of the neck (supraclavicular). The divisions sit behind the clavicle. The cords and branches lie in the axilla (infraclavicular), wrapped around the axillary artery.

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A clear schematic of the brachial plexus showing roots, trunks, divisions, cords and the five terminal branches, with C5–T1 labelled and key branches (long thoracic, suprascapular, thoracodorsal) shown.

Purpose:

The plexus is impossible to learn from text alone. A single diagram saves hours of revision.

Suggested source: TeachMeAnatomy / Gray's Anatomy

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Cord-to-branch shortcuts

- Lateral cord → musculocutaneous + lateral root of median

- Medial cord → ulnar + medial root of median + medial cutaneous nerves

- Posterior cord → axillary + radial (+ thoracodorsal, subscapular)

The median nerve is the only terminal branch with contributions from two cords — it forms the "M" of the cords by joining the lateral and medial roots in front of the axillary artery.

Brachial plexus injuries

Erb's palsy — upper trunk (C5, C6)

Mechanism: forceful widening of the angle between neck and shoulder — shoulder dystocia at birth or motorbike fall in adults.

Clinical picture: "waiter's tip" — arm adducted (loss of deltoid/supraspinatus), internally rotated (loss of infraspinatus/teres minor), forearm pronated (loss of biceps supination), wrist flexed.

Klumpke's palsy — lower trunk (C8, T1)

Mechanism: forceful abduction of the arm above the head — breech delivery or an adult catching a branch while falling.

Clinical picture: claw hand (paralysis of all intrinsic hand muscles → extended MCPs, flexed IPs). May have Horner's syndrome if T1 is avulsed near the sympathetic chain.

A Pancoast (superior sulcus) tumour of the lung apex produces the same picture: intrinsic hand weakness, medial arm sensory loss ± Horner's.

> Pearl: Erb's = "waiter's tip" (upper plexus); Klumpke's = "claw hand" (lower plexus, ± Horner's).

Major peripheral nerves — the master table

Nerve	Roots	Cord	Motor	Sensory	Classic injury
Musculocutaneous	C5–C7	Lateral	Coracobrachialis, biceps, brachialis (elbow flexion + supination)	Lateral forearm (via lateral cutaneous n. of forearm)	Axillary stab; loss of elbow flexion
Axillary	C5–C6	Posterior	Deltoid (abduction 15–90°), teres minor (ER)	Regimental badge area (lateral shoulder)	Anterior shoulder dislocation; surgical neck of humerus #
Radial	C5–T1	Posterior	All extensors (triceps, wrist, fingers, thumb), brachioradialis, supinator	Posterior arm/forearm; dorsolateral hand, dorsum of thumb, 1st dorsal web space	Mid-shaft humeral # (spiral groove) → wrist drop
Median	C5–T1	Lateral + medial	Most forearm flexors (except FCU + medial ½ FDP), thenar muscles, lateral 2 lumbricals	Palmar lateral 3½ digits + their dorsal nail beds; central palm (via palmar cutaneous, spared in CTS)	Supracondylar # (AIN); carpal tunnel; wrist laceration
Ulnar	C8–T1	Medial	FCU, medial ½ FDP, all intrinsic hand muscles except thenars + 1st/2nd lumbricals	Medial 1½ digits (palmar + dorsal) + hypothenar skin	Medial epicondyle # (cubital tunnel); Guyon's canal at wrist

A trick that works for almost every hand question: the ulnar nerve runs the hand. Almost every small muscle in the hand is ulnar, with three median exceptions remembered as "LOAF": Lateral two Lumbricals, Opponens pollicis, Abductor pollicis brevis, Flexor pollicis brevis (superficial head).

Axillary nerve

Wraps around the surgical neck of the humerus with the posterior circumflex humeral artery. Damaged in:

- Anterior glenohumeral dislocation

- Surgical neck of humerus fracture

- Poorly-applied crutches (rare)

Clinical: loss of shoulder abduction 15–90° (deltoid), loss of external rotation power (teres minor), numb regimental badge area.

Musculocutaneous nerve

Pierces coracobrachialis and supplies BBC: Biceps, Brachialis, Coracobrachialis. Continues as the lateral cutaneous nerve of the forearm. Injury → weak elbow flexion + lateral forearm numbness.

Median nerve

Travels with the brachial artery; at the cubital fossa lies medial to it. Passes between the two heads of pronator teres, then gives off the purely motor anterior interosseous nerve (AIN) supplying FPL + lateral half of FDP + pronator quadratus.

Enters the hand through the carpal tunnel. The palmar cutaneous branch leaves before the tunnel — which is why CTS spares the central palm. After the tunnel, the recurrent (motor) branch loops back to the thenar muscles (APB, OP, FPB superficial head) + 1st/2nd lumbricals.

Ulnar nerve

Starts medial to the brachial artery, then pierces the medial intermuscular septum to pass behind the medial epicondyle through the cubital tunnel — its most vulnerable point. Enters the forearm under FCU, then the hand via Guyon's canal (lateral to pisiform, medial to hook of hamate). Supplies almost all intrinsic hand muscles.

Ulnar paradox: a lesion at the wrist produces a worse claw than one at the elbow. High lesion → FDP also paralysed, so DIPs cannot flex. Low lesion → FDP intact, lumbricals gone → severe unopposed clawing. Lower lesion, worse-looking hand.

Radial nerve

Runs in the spiral groove on the posterior humerus with the profunda brachii artery — vulnerable in mid-shaft humeral #. At the lateral epicondyle it divides into:

- Superficial branch — sensory, dorsolateral hand + 1st dorsal web space

- Posterior interosseous nerve (PIN) — pure motor, supplies all extensors after passing through supinator

Mid-shaft humeral # → wrist drop but triceps spared (branches leave proximal to the groove). "Saturday night palsy" (compression in the axilla) does paralyse triceps.

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Diagram of the radial nerve in the spiral groove, with the mid-shaft of the humerus highlighted and triceps branching above the groove.

Purpose:

Explains why wrist drop occurs without elbow extension loss in mid-shaft #.

Suggested source: TeachMeAnatomy / Gray's Anatomy

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Shoulder

Rotator cuff — SItS

Four muscles that dynamically stabilise the shallow glenohumeral joint.

Muscle	Action	Nerve
Supraspinatus	Abduction 0–15°	Suprascapular n. (C5, C6)
Infraspinatus	External rotation	Suprascapular n.
teres minor	External rotation	Axillary n.
Subscapularis	Internal rotation	Upper + lower subscapular n.

Supraspinatus is the first to tear because its tendon passes under the acromion and is vulnerable to impingement.

Abduction in stages

- 0–15°: supraspinatus

- 15–90°: deltoid (axillary n.)

- > 90°: trapezius rotates the scapula (accessory n. CN XI, with C3/C4 proprioception)

- > 120°: serratus anterior protracts/rotates the scapula (long thoracic n., C5–C7)

Subacromial impingement & painful arc

The supraspinatus tendon and subacromial bursa sit between the humeral head and the acromion. Between 60–120° of abduction this space narrows — pinching produces the painful arc. A complete supraspinatus tear loses active abduction and gives a positive drop arm test.

Glenohumeral dislocation

Anterior dislocation is > 95%. Humeral head lies inferior and medial to the glenoid on AP X-ray. Axillary nerve at risk — document regimental badge sensation and deltoid pre- and post-reduction.

Posterior dislocation is rare, classically caused by electrocution or seizure (internal rotators overpower external) and shows a light bulb sign on X-ray.

Elbow

Cubital fossa

Triangular space at the front of the elbow.

- Lateral border: brachioradialis

- Medial border: pronator teres

- Floor: brachialis + supinator

- Roof: bicipital aponeurosis (separates superficial veins from deep structures)

Contents (lateral to medial): Radial nerve, Biceps tendon, Brachial artery, Median nerve — "Really Need Beer To Be At My Nicest" (or simply: median is most medial). The brachial artery bifurcates into radial and ulnar arteries at the apex of the fossa.

Epicondylitis

- Lateral epicondylitis = tennis elbow → common extensor origin (ECRB worst affected)

- Medial epicondylitis = golfer's elbow → common flexor origin

Both are overuse tendinopathies, not true inflammation.

Supracondylar fracture — paediatric classic

Child falls on outstretched hand; distal fragment displaces posteriorly and threatens:

- Brachial artery → absent radial pulse, risk of Volkmann's ischaemic contracture

- AIN of median → most commonly injured nerve; child cannot make the "OK" sign (FPL + lateral FDP paralysed)

> Exam classics:

> - Supracondylar # + can't make OK sign → AIN palsy

> - Supracondylar # + absent radial pulse → brachial artery injury

> - Pain out of proportion, pale pulseless fingers → compartment syndrome / Volkmann's

Wrist and hand

Anatomical snuffbox

A triangular depression on the radial dorsum of the wrist visible when the thumb is extended.

Border	Structure
Lateral (radial)	APL + EPB tendons
Medial (ulnar)	EPL tendon
Floor	Scaphoid + trapezium
Roof	Skin, superficial fascia, cephalic vein
Contents	Radial artery, branches of superficial radial nerve

Snuffbox tenderness after FOOSH = scaphoid fracture until proven otherwise. The scaphoid receives blood retrogradely from the dorsal carpal branch of the radial artery, entering at the distal pole — so a waist fracture cuts off blood to the proximal pole → AVN.

Initial X-rays miss ~20% of scaphoid #. Cast, repeat X-ray at 10–14 days; if still uncertain → MRI.

Carpal tunnel

Floor: arched carpal bones. Roof: flexor retinaculum. Contents: 9 tendons (4 FDS + 4 FDP + FPL) + median nerve. The palmaris longus tendon is the surface landmark; the median nerve lies just deep and slightly radial to it (PL absent in ~15%).

Carpal tunnel syndrome: nocturnal paraesthesia in lateral 3½ digits, central palm spared, positive Tinel's and Phalen's, late APB wasting with loss of thumb opposition. Treatment ladder: splints → steroid injection → flexor retinaculum release (definitive).

Extensor compartments

Six compartments under the extensor retinaculum, numbered radial to ulnar:

#	Tendons	Clinical
1	APL, EPB	de Quervain's tenosynovitis (Finkelstein's test)
2	ECRL, ECRB	—
3	EPL	Ruptures after Colles' # (rubs over Lister's tubercle)
4	ED, EI	—
5	EDM	—
6	ECU	—

EPL hooks around Lister's tubercle — dorsal callus or malunion from a Colles' # frays the tendon, presenting weeks later as inability to extend the thumb IP joint.

Dupuytren's contracture

Progressive fibrosis of the palmar fascia (not the tendons). Fixed flexion of the MCP and PIP joints, most often of the ring and little fingers. Familial; Northern European. Definitive treatment is fasciectomy.

Hand muscle quick wins

- Adductor pollicis → ulnar nerve → Froment's test (flex thumb IP to compensate when pinching paper)

- APB → median (recurrent branch) → "lift thumb off the table" with palm up

- Dorsal interossei abduct (DAB), palmar adduct (PAD)

- Lumbricals flex MCPs, extend IPs (median for 1st/2nd, ulnar for 3rd/4th)

Common upper limb fractures

Fracture	Mechanism	Classic complication
Clavicle (mid-shaft)	FOOSH, contact sport	Usually heals well; rare brachial plexus / subclavian vessel injury
Surgical neck of humerus	Fall in elderly	Axillary nerve + posterior circumflex humeral artery
Mid-shaft humerus	Direct blow	Radial nerve (spiral groove) → wrist drop
Supracondylar humerus	Paediatric FOOSH	AIN (median) + brachial artery → Volkmann's
Olecranon	Fall on flexed elbow	Triceps avulsion; needs tension-band wiring
Radial head	FOOSH	Limited supination/pronation; "fat pad" / sail sign on X-ray
Colles' (distal radius)	FOOSH in postmenopausal women	Dorsal displacement = dinner-fork deformity; late EPL rupture, median nerve symptoms, malunion
Smith's	Fall on dorsiflexed wrist (rarer)	Volar displacement (reverse Colles')
Scaphoid	FOOSH, young adult	AVN of proximal pole; non-union

[Image: MCQs banner]

Test yourself

Which roots form the upper trunk of the brachial plexus?

• ((C5–C6::☑️ Upper trunk = C5 + C6; injury gives Erb's palsy, the "waiter's tip".))
• ((C5–C7::Wrong; C7 forms the middle trunk on its own.))
• ((C7 alone::This is the middle trunk.))
• ((C8–T1::This is the lower trunk; injury gives Klumpke's claw hand.))

A newborn has a limp arm held adducted, internally rotated and pronated after shoulder dystocia. Diagnosis?

• ((Erb's palsy::☑️ C5–C6 upper trunk injury; classic "waiter's tip" from shoulder dystocia.))
• ((Klumpke's palsy::C8–T1 lower trunk; gives claw hand and sometimes Horner's.))
• ((Radial nerve palsy::Would give wrist drop, not the waiter's tip posture.))
• ((Cerebral palsy::Central lesion; pattern would be spastic, not flaccid at birth.))

👩‍⚕️ The opposite mechanism — arm pulled overhead — gives Klumpke's.

A patient has weakness of the intrinsic hand muscles and numbness of the medial arm. Which lesion?

• ((Pancoast (superior sulcus) tumour::☑️ Apical lung tumour compresses lower trunk (C8/T1) ± Horner's.))
• ((Carpal tunnel syndrome::Only median nerve at the wrist; spares the medial arm.))
• ((Cervical rib::Possible thoracic outlet picture, but tumour is the textbook answer here.))
• ((Erb's palsy::Upper trunk; wouldn't affect intrinsic hand muscles.))

After anterior shoulder dislocation a patient cannot abduct the shoulder and has numbness over the lateral upper arm. Which nerve?

• ((Axillary::☑️ Wraps the surgical neck; deltoid + regimental badge sensation.))
• ((Suprascapular::Supplies supraspinatus/infraspinatus; no skin innervation.))
• ((Musculocutaneous::Elbow flexion + lateral forearm sensation, not shoulder.))
• ((Radial::Triceps and wrist extension; sensation is posterior, not regimental.))

A young man is stabbed in the axilla and has lateral forearm numbness with weak elbow flexion. Which nerve?

• ((Musculocutaneous::☑️ Pierces coracobrachialis; supplies BBC + lateral forearm skin.))
• ((Median::Lateral forearm is not median territory; flexion of fingers, not elbow.))
• ((Radial::Extends, not flexes, the elbow.))
• ((Axillary::Shoulder abductor; no forearm sensation.))

A patient with a mid-shaft humeral fracture cannot extend the wrist. Which nerve and where?

• ((Radial nerve in the spiral groove::☑️ Mid-shaft humeral # = classic wrist drop, triceps spared.))
• ((Posterior interosseous nerve::A radial branch in the forearm; spares brachioradialis.))
• ((Axillary at the surgical neck::Causes deltoid weakness, not wrist drop.))
• ((Median at the elbow::Affects flexion + thenar, not extension.))

👩‍⚕️ Triceps is spared in spiral-groove injuries because its branches leave above the groove.

A child with a supracondylar fracture cannot make the "OK" sign. Which nerve?

• ((Anterior interosseous nerve (AIN)::☑️ Pure motor branch of median; supplies FPL + lateral FDP + PQ.))
• ((Ulnar at the elbow::More typical in flexion-type supracondylar #; would cause clawing.))
• ((Radial::Wrist drop, not weak thumb/index pinch.))
• ((Posterior interosseous::Causes finger drop, not loss of pinch.))

A child with a supracondylar fracture has an absent radial pulse. The most urgent concern is:

• ((Brachial artery injury::☑️ Risk of Volkmann's ischaemic contracture; needs urgent reduction.))
• ((Median nerve compression::Important but not limb-threatening as fast as ischaemia.))
• ((Compartment syndrome::Develops later; rising pain out of proportion is the warning.))
• ((Radial nerve injury::Less commonly threatened in supracondylar #.))

A patient has clawing of the ring and little fingers after a long-standing elbow problem. Where is the lesion and why is the claw less severe than expected?

• ((Ulnar nerve at the cubital tunnel — FDP also paralysed::☑️ Ulnar paradox: high lesion paralyses FDP too, so DIPs don't flex.))
• ((Ulnar at Guyon's canal::Would cause a worse claw (FDP spared).))
• ((Median at carpal tunnel::Affects thenar + lateral 3½ digits, not ring/little flexion.))
• ((Radial nerve::Causes wrist drop, not clawing.))

A patient is asked to grip paper between thumb and index finger and flexes the thumb IP joint to do so. What does this demonstrate?

• ((Positive Froment's sign — adductor pollicis (ulnar) weakness::☑️ Patient compensates with FPL (AIN/median) to hold the paper.))
• ((Carpal tunnel syndrome::Tested with Tinel's and Phalen's, not Froment's.))
• ((Median nerve palsy::Would weaken thumb abduction, not adduction.))
• ((Trigger thumb::Mechanical catching, not weakness.))

A 50-year-old woman falls on the outstretched hand. The wrist has a "dinner-fork" deformity. Diagnosis?

• ((Colles' fracture::☑️ Dorsally displaced distal radius #; classic postmenopausal injury.))
• ((Smith's fracture::Volar displacement — fall on dorsiflexed wrist, the "reverse Colles'".))
• ((Scaphoid fracture::Snuffbox tenderness, no dinner-fork deformity.))
• ((Galeazzi fracture::Radial shaft # with distal radio-ulnar dislocation.))

Three months after a Colles' fracture treated in a cast, a patient cannot extend the thumb. Most likely cause?

• ((EPL tendon rupture::☑️ EPL passes over Lister's tubercle; frayed by dorsal callus/malunion.))
• ((Posterior interosseous nerve palsy::Would cause multiple finger drops, not isolated thumb.))
• ((AVN of the radius::Distal radius has rich blood supply; AVN is essentially unheard of.))
• ((Median nerve injury::Median doesn't extend the thumb.))

A 22-year-old falls on the outstretched hand and has snuffbox tenderness; X-rays are normal. Next step?

• ((Immobilise in cast and repeat imaging at 10–14 days::☑️ Initial X-rays miss ~20% of scaphoid #; MRI if still uncertain.))
• ((Discharge with analgesia::Misses scaphoid #; risk of AVN and non-union.))
• ((Immediate ORIF::Not indicated without a visible fracture or displacement.))
• ((CT scan today::MRI is preferred for occult scaphoid #, after repeat X-ray.))

👩‍⚕️ Proximal pole scaphoid # is the classic cause of AVN because blood enters at the distal pole.

Which muscle initiates shoulder abduction (first 15°)?

• ((Supraspinatus::☑️ First 15°; the rotator cuff muscle most commonly torn.))
• ((Deltoid::Takes over from 15° to 90°.))
• ((Trapezius::Rotates scapula above 90°.))
• ((Serratus anterior::Scapular rotation above 120°; long thoracic n.))

A painter develops sudden shoulder pain and cannot maintain the arm at 90° after passive abduction (positive drop arm test). Diagnosis?

• ((Supraspinatus tear::☑️ Loss of active abduction; tendon is the first cuff structure to fail.))
• ((Subacromial impingement::Causes painful arc 60–120° but power preserved.))
• ((Frozen shoulder::Global stiffness, both active and passive.))
• ((Axillary nerve injury::Loss of deltoid + regimental badge sensation, usually post-trauma.))

A typist has nocturnal hand tingling, drops objects, and has wasting of the thenar eminence. Definitive treatment?

• ((Flexor retinaculum release::☑️ Decompresses the carpal tunnel; gold standard once conservative measures fail.))
• ((Steroid injection::Useful conservatively but not definitive.))
• ((Wrist splinting::First-line conservative; not definitive once wasting present.))
• ((Fasciectomy::Treatment for Dupuytren's, not carpal tunnel.))

A man cannot extend the ring and little finger IP joints; the fingers cannot be passively straightened either. Which condition?

• ((Dupuytren's contracture — treat with fasciectomy::☑️ Palmar fascia fibrosis; familial, ring/little fingers commonest.))
• ((Trigger finger::Catches during flexion, not fixed extension loss.))
• ((Ulnar claw::Affects MCP/IP posture but fingers passively straighten.))
• ((Mallet finger::Loss of DIP extension only, after extensor avulsion.))

Which structure is most medial in the cubital fossa?

• ((Median nerve::☑️ Order lateral→medial: Radial n., Biceps tendon, Brachial artery, Median n.))
• ((Brachial artery::Just lateral to the median nerve.))
• ((Biceps tendon::Centre of the fossa.))
• ((Radial nerve::Most lateral, under brachioradialis.))

Following a thoracotomy a patient has weak APB, weak first dorsal interosseous and numbness of the medial 1½ digits. Where is the lesion?

• ((Lower trunk of brachial plexus::☑️ Lower trunk supplies ulnar + medial root of median; near 1st rib/apex.))
• ((Median nerve at the wrist::Wouldn't cause ulnar territory loss.))
• ((Ulnar nerve at the elbow::Spares APB (median territory).))
• ((Posterior cord::Radial/axillary nerves; doesn't fit the picture.))

After axillary lymph node dissection a patient cannot extend the wrist. Which structure was injured?

• ((Posterior cord::☑️ Gives rise to the radial nerve; at risk during axillary dissection.))
• ((Lateral cord::Loss would affect musculocutaneous (elbow flexion).))
• ((Medial cord::Would affect ulnar/medial median territory.))
• ((Long thoracic nerve::Causes winging of scapula, not wrist drop.))

A patient post-thoracic surgery cannot push themselves up from a chair and has winging of the scapula. Which nerve?

• ((Long thoracic nerve (C5–C7)::☑️ Supplies serratus anterior; injury → winging and weak abduction > 120°.))
• ((Accessory nerve::Trapezius winging, mostly on shoulder shrugging.))
• ((Dorsal scapular::Rhomboids; rare cause of winging.))
• ((Thoracodorsal::Latissimus dorsi; arm adduction/internal rotation, no winging.))

Which carpal bone is most commonly fractured, and which part is at risk of AVN?

• ((Scaphoid — proximal pole at risk of AVN::☑️ Blood enters at the distal pole and flows retrogradely.))
• ((Lunate — proximal pole::Lunate AVN is Kienböck's, but scaphoid is the commoner fracture.))
• ((Trapezium — middle::Not the classic AVN site.))
• ((Hamate — hook::Hook of hamate # occurs in golfers; not the AVN classic.))

The third extensor compartment of the wrist contains which tendon?

• ((Extensor pollicis longus (EPL)::☑️ Hooks around Lister's tubercle; ruptures after Colles' #.))
• ((Extensor pollicis brevis::In the 1st compartment with APL.))
• ((Extensor digitorum::4th compartment with EI.))
• ((Extensor carpi ulnaris::6th compartment.))

Revision summary

- Brachial plexus = anterior rami C5–T1. RTDCB: Roots → Trunks (upper C5–6, middle C7, lower C8–T1) → Divisions → Cords (Lateral, Medial, Posterior) → Branches (M-shape: musculocutaneous, axillary, median, radial, ulnar).

- Erb's = upper trunk (C5–6) = "waiter's tip"; shoulder dystocia. Klumpke's = lower trunk (C8–T1) = claw hand ± Horner's; arm yanked overhead. Pancoast tumour mimics Klumpke's.

- Axillary (C5–6, posterior cord) → deltoid + teres minor + regimental badge; risk in anterior shoulder dislocation and surgical neck of humerus #.

- Musculocutaneous (C5–7, lateral cord) → BBC + lateral forearm sensation.

- Median (C5–T1) → forearm flexors (except FCU + medial ½ FDP) + thenar + LOAF. AIN injured in supracondylar #; CTS at the wrist (spares central palm).

- Ulnar (C8–T1, medial cord) → FCU + medial ½ FDP + all intrinsic muscles except LOAF. Cubital tunnel at elbow, Guyon's at wrist. Ulnar paradox: lower lesion → worse claw.

- Radial (C5–T1, posterior cord) → all extensors + posterior sensation + 1st dorsal web space. Spiral groove (mid-shaft humeral #) → wrist drop, triceps spared.

- Rotator cuff (SItS) stabilises GHJ. Supraspinatus tears first; abducts 0–15°; painful arc 60–120° is impingement.

- Anterior dislocation > 95%; axillary nerve at risk.

- Cubital fossa contents lateral→medial: Radial, Biceps tendon, Brachial artery, Median.

- Supracondylar # (kids): brachial artery → Volkmann's; AIN → can't make "OK sign".

- Snuffbox: APL/EPB lateral, EPL medial, scaphoid floor, radial artery inside. Scaphoid # → AVN of proximal pole.

- Carpal tunnel: 9 tendons + median; spares central palm; Tinel's, Phalen's, APB wasting. Definitive Rx = flexor retinaculum release.

- EPL ruptures weeks after a Colles' # at Lister's tubercle.

- Dupuytren's = palmar fascia → fasciectomy.

- Colles' = dorsal (dinner-fork); Smith's = volar.