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ANATOMY OF THE UPPER LIMB

High-Grade Notes | Source: Gray's Anatomy for Students & Thieme Atlas

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SECTION 1: OVERVIEW & BONES

Regions of the Upper Limb

• Pectoral (shoulder) girdle - clavicle + scapula
• Arm (brachium) - humerus
• Forearm (antebrachium) - radius + ulna
• Wrist (carpus) - 8 carpal bones
• Hand - 5 metacarpals + 14 phalanges

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1.1 Clavicle

• S-shaped bone; acts as an osseous strut bracing the shoulder against the sternum, forcing the upper limb away from the trunk
• Medial 2/3: convex anteriorly (rounded)
• Lateral 1/3: concave anteriorly (flattened)
• Fracture site: Middle 1/3 = 80% of cases; lateral 1/3 = 15%; medial 1/3 = 5%
• Mechanism: Fall on outstretched hand (FOOSH) or direct blow
• Ligaments:
  • Sternoclavicular ligament (medial end - sternum)
  • Costoclavicular ligament (medial end - rib I)
  • Acromioclavicular ligament (lateral end - acromion)
  • Coracoclavicular ligament (lateral end - coracoid process): trapezoid + conoid parts; most important in preventing acromioclavicular separation

1.2 Scapula

• Triangular flat bone; posterior thorax ribs 2-7
• Key features: spine, acromion, coracoid process, glenoid cavity (articulates with humeral head)
• Glenoid labrum: fibrocartilaginous ring deepening the glenoid cavity by ~50%
• Infraspinous fossa (posterior), supraspinous fossa (posterior), subscapular fossa (anterior/costal)
• Muscle attachment: 17 muscles attach to the scapula

1.3 Humerus

• Head: articulates with glenoid (glenohumeral joint)
• Anatomical neck: narrow groove just below articular head
• Surgical neck: common fracture site - axillary nerve at risk
• Greater tubercle: attachment of supraspinatus, infraspinatus, teres minor
• Lesser tubercle: attachment of subscapularis
• Intertubercular (bicipital) groove: contains tendon of long head of biceps brachii; bounded by crests of greater and lesser tubercles
• Deltoid tuberosity: deltoid insertion (midshaft lateral)
• Radial groove (spiral groove): radial nerve + profunda brachii artery; at risk in midshaft humerus fractures
• Medial epicondyle: common flexor origin; ulnar nerve passes posterior to it
• Lateral epicondyle: common extensor origin
• Capitulum: articulates with radial head
• Trochlea: articulates with ulnar trochlear notch

1.4 Radius & Ulna

• Olecranon: tip of elbow; olecranon bursa overlies it; site of triceps insertion
• Coronoid process: prevents posterior dislocation of elbow; fractured in "terrible triad" injury

1.5 Carpal Bones (proximal to distal, lateral to medial)

• Scaphoid: Most commonly fractured carpal; tenderness in anatomical snuffbox; blood supply enters distally (risk of avascular necrosis of proximal pole)
• Lunate: Most commonly dislocated carpal; can compress median nerve
• Hamate: hook of hamate fracture - ulnar nerve deep branch at risk
• Pisiform: sesamoid bone in flexor carpi ulnaris tendon

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SECTION 2: JOINTS

2.1 Glenohumeral (Shoulder) Joint

• Type: Ball-and-socket synovial joint
• Stability: Sacrificed for mobility - most mobile joint in body
• Articular surfaces: Head of humerus (1/3 sphere) on glenoid (1/4 sphere) - deepened by glenoid labrum
• Joint capsule: Arises from glenoid margins, attaches to anatomical neck of humerus
  • Loose inferiorly (axillary recess) - allows abduction
  • Reinforced anteriorly by glenohumeral ligaments

• Coracohumeral ligament: coracoid process → greater and lesser tubercles; stabilizes long head of biceps in intertubercular groove
• Coracoacromial ligament: coracoid → acromion; forms roof preventing superior dislocation

• Subacromial bursa (subdeltoid): lies between deltoid/acromion and rotator cuff; most clinically important; communicates with joint in full-thickness rotator cuff tears
• Subscapular bursa: beneath subscapularis tendon; communicates with joint cavity

Clinically: Rotator cuff tears most commonly involve supraspinatus tendon. "Painful arc" of 60-120° abduction = supromial impingement.

• Anteroinferior: most common (95-97%); humeral head lies anterior to glenoid; causes:
  • Hill-Sachs lesion: posterosuperior humeral head impression fracture
  • Bankart lesion: avulsion of anteroinferior glenoid labrum ± bone fragment
• Axillary nerve damage: loss of deltoid function + "regimental badge" sensory loss over lateral shoulder

2.2 Acromioclavicular Joint

• Plane synovial joint; fibrocartilaginous disc common
• Stabilized by: AC ligament (horizontal stability) + coracoclavicular ligament (vertical stability)
• AC separation: graded I-VI (Rockwood); coracoclavicular ligament rupture = grade III+

2.3 Sternoclavicular Joint

• Only bony articulation of upper limb girdle with axial skeleton
• Saddle joint with intraarticular fibrocartilaginous disc
• Very stable; posterior dislocation rare but can compress trachea/great vessels

2.4 Elbow Joint

• Type: Hinge (uniaxial) synovial joint - trochlehumeral + capitohumeral + proximal radioulnar joints share one capsule
• Movements: Flexion/Extension (trochlehumeral) + Pronation/Supination (radioulnar)
• Normal carrying angle: ~15° valgus (greater in females)
• Joint capsule: attached to medial epicondyle + margins of olecranon, coronoid and radial fossae
• Fat pads: lie between fibrous capsule and synovial membrane over olecranon, coronoid, and radial fossae; displaced by hemarthrosis = "fat pad sign" on X-ray

• Medial (ulnar) collateral ligament (UCL): anterior band (strongest - resists valgus), posterior band, oblique band; medial epicondyle → coronoid/olecranon
• Lateral (radial) collateral ligament (RCL): lateral epicondyle → annular ligament
• Annular ligament of radius: encircles radial head against radial notch of ulna; allows rotation; Nursemaid's elbow = head pulled out of annular ligament in children

• Boundaries: Base = line between epicondyles; Lateral = brachioradialis; Medial = pronator teres
• Contents (lateral to medial): Tendon of biceps brachii, Brachial artery (divides into radial + ulnar), Median nerve
• Mnemonic: TBM or "The Big Monkey"
• Roof: bicipital aponeurosis (lacertus fibrosus), then skin/fascia

2.5 Wrist (Radiocarpal) Joint

• Type: Condyloid (ellipsoid) synovial joint
• Proximal surface: distal radius + articular disc of DRUJ (triangular fibrocartilage)
• Distal surface: Scaphoid, lunate, triquetrum
• Movements: Flexion, Extension, Abduction (radial deviation), Adduction (ulnar deviation), Circumduction
• Stability: Radial and ulnar collateral ligaments; palmar radiocarpal ligaments (strongest)

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SECTION 3: THE AXILLA

Boundaries

• Apex (inlet): continuous with neck; bounded by posterior surface of clavicle, superior border of rib I, lateral border of rib I - all bone
• Floor (base): dome of axillary skin between anterior and posterior folds
• Anterior wall: pectoralis major, pectoralis minor, subclavius, clavipectoral fascia
• Posterior wall: subscapularis (upper), teres major + latissimus dorsi (lower)
• Medial wall: serratus anterior over ribs 1-4
• Lateral wall: intertubercular sulcus of humerus (narrowest wall)

Axillary Muscle Spaces/Gaps (posterior wall openings):

Axillary Contents

1. Axillary artery (continuation of subclavian)
2. Axillary vein
3. Brachial plexus (cords and branches)
4. Axillary lymph nodes (5 groups)
5. Long thoracic nerve (on medial wall)
6. Intercostobrachial nerve (T2 lateral cutaneous branch - passes through medial wall)

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SECTION 4: BRACHIAL PLEXUS

Formation

• Roots: Anterior rami C5, C6, C7, C8, T1 (+ occasional contributions from C4 and T2)
• Trunks: formed from roots in posterior triangle of neck, posterior to subclavian artery
• Divisions: each trunk → anterior + posterior
• Cords: named relative to axillary artery

Branches of the Cords

• Lateral pectoral nerve (pectoralis major)
• Lateral root of median nerve
• Musculocutaneous nerve (C5,C6,C7)

• Medial pectoral nerve (pec major + minor)
• Medial cutaneous nerve of arm (medial brachial cutaneous)
• Medial cutaneous nerve of forearm (medial antebrachial cutaneous)
• Medial root of median nerve
• Ulnar nerve (C7,C8,T1)

• Upper subscapular nerve (C5,C6) - subscapularis
• Thoracodorsal nerve (C6,C7,C8) - latissimus dorsi
• Lower subscapular nerve (C5,C6) - subscapularis + teres major
• Axillary nerve (C5,C6)
• Radial nerve (C5,C6,C7,C8,T1) - largest branch

Clinically Important Plexus Injuries

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SECTION 5: MUSCLES OF THE UPPER LIMB

5.1 Muscles Acting on Shoulder Girdle

Winging of scapula: Damage to long thoracic nerve → serratus anterior paralysis → medial border + inferior angle of scapula lift away from thorax. Cannot elevate arm above 90°.

5.2 Deltoid Muscle

• Origin: Lateral 1/3 clavicle, acromion, spine of scapula (entire lower border)
• Insertion: Deltoid tuberosity of humerus
• Nerve: Axillary nerve (C5, C6)
• Actions: Anterior fibers - flexion + medial rotation; Middle fibers - abduction (main abductor 15-90°); Posterior fibers - extension + lateral rotation
• Damage → loss of shoulder contour ("flat shoulder")

5.3 Arm Muscles

5.4 Anterior Forearm Muscles (median + ulnar nerves)

5.5 Posterior Forearm Muscles (radial nerve + posterior interosseous nerve)

PIN (Posterior Interosseous Nerve) = deep branch of radial nerve after passing between the two heads of the supinator through the Arcade of Frohse. Injury → "wrist drop" (cannot extend wrist/fingers); radial deviation of wrist on extension (ECRL preserved, ECU lost).

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SECTION 6: MAJOR NERVES OF THE UPPER LIMB

6.1 Musculocutaneous Nerve (C5,C6,C7)

• From lateral cord; pierces coracobrachialis
• Motor: coracobrachialis, biceps brachii, brachialis
• Becomes lateral cutaneous nerve of forearm (sensation to lateral forearm)
• Injury: weak elbow flexion (brachialis partially survives via radial nerve), lost supination

6.2 Median Nerve (C6,C7,C8,T1) - "Labourer's nerve"

• Forms from lateral + medial roots anterior to 3rd part of axillary artery
• No branches in arm (runs medial to brachial artery)
• In cubital fossa: passes deep to bicipital aponeurosis (lacertus fibrosus)
• Forearm branches:
  • Pronator teres, FCR, palmaris longus, FDS (all via main trunk)
  • Anterior interosseous nerve: FPL, lateral FDP, pronator quadratus
  • Palmar cutaneous branch (before carpal tunnel): sensory to lateral palm
• In hand (via carpal tunnel):
  • Recurrent branch (thenar branch): opponens pollicis, abductor pollicis brevis, superficial head flexor pollicis brevis - this is the motor branch; does NOT pass through carpal tunnel
  • Digital branches: lateral 2 lumbricals (index + middle), and sensation to palm + palmar surface of thumb, index, middle, lateral half of ring finger
• Injury patterns:
  • High lesion: "hand of benediction" (cannot flex index/middle fingers when trying to make fist; FDP of these spared, but FDS lost)
  • Low lesion (carpal tunnel): "ape hand" (thenar wasting, thumb cannot oppose, median sensory loss)
  • Carpal tunnel syndrome: most common compression neuropathy; nocturnal pain/tingling in median nerve distribution; positive Tinel's/Phalen's tests; treat with splinting → steroid injection → surgical decompression

6.3 Ulnar Nerve (C7,C8,T1) - "Musician's nerve"

• From medial cord
• Arm: no branches; passes posterior to medial epicondyle in cubital tunnel
• Forearm: FCU, medial half of FDP
• Wrist: passes lateral to pisiform through Guyon's canal (between pisiform and hook of hamate)
• Hand:
  • Deep branch: hypothenar muscles (ADM, FDM, ODM), all palmar + dorsal interossei, medial 2 lumbricals, adductor pollicis, deep head of FPB
  • Superficial branch: palmaris brevis; sensation to little finger + medial half of ring finger
• Injury patterns:
  • High lesion: wrist level signs less severe (FDP still cuts, so less claw of ring/little finger) - "ulnar paradox"
  • Low lesion (Guyon's canal): "ulnar claw" (ring + little fingers - hyperextended MCP, flexed IP); positive Froment's sign (compensatory IP flexion of thumb when pinching due to adductor pollicis paralysis); "wasted hand" (interosseous wasting)
  • Mechanism: prolonged leaning on elbow, medial epicondyle fracture, hook of hamate fracture

6.4 Radial Nerve (C5,C6,C7,C8,T1) - "Anatomist's nerve"

• From posterior cord
• Arm: passes through triangular interval with profunda brachii; winds around humerus in radial groove
• Branches in arm: posterior cutaneous nerve of arm/forearm, triceps branches (before groove - safe)
• At lateral epicondyle: divides into superficial (sensory) and deep (PIN - motor) branches
• Superficial branch: dorsal skin of lateral 3.5 fingers, dorsum of hand (excluding fingertips)
• PIN: passes between heads of supinator (Arcade of Frohse) → all posterior forearm extensors
• Injury:
  • Midshaft humerus fracture (radial groove): "wrist drop" - loss of wrist/finger extension; brachioradialis and ECRL spared if lesion distal to their origin; triceps usually spared (branches above groove)
  • Saturday night palsy / crutch palsy: compression at axilla - triceps also affected
  • PIN palsy: loss of finger extension, finger drop but NO wrist drop (ECRL preserved)

6.5 Axillary Nerve (C5,C6)

• From posterior cord; exits axilla through quadrangular space with posterior circumflex humeral artery
• Motor: deltoid, teres minor
• Sensory: "regimental badge area" - lateral aspect of arm over deltoid insertion
• Injury: surgical neck of humerus fracture, anterior shoulder dislocation
• Signs: inability to abduct arm beyond 15°, loss of shoulder contour, sensory loss over lateral shoulder

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SECTION 7: VESSELS OF THE UPPER LIMB

7.1 Arterial Supply

• Brachial artery lies on medial side of arm between biceps and triceps
• Median nerve crosses it anteriorly (medial → anterior in cubital fossa)
• Profunda brachii (deep brachial): accompanies radial nerve in radial groove; gives nutrient branch to humerus
• Divides in cubital fossa into:
  • Radial artery: passes lateral forearm → anatomical snuffbox → dorsum of hand → pierces 1st dorsal interosseous → palm → deep palmar arch
  • Ulnar artery: passes medial forearm → Guyon's canal → superficial palmar arch

The arches interconnect: allows perfusion of hand even if one major vessel injured (test with Allen's test).

7.2 Venous Drainage

• Cephalic vein: originates from lateral side of dorsal venous network of hand → lateral forearm → lateral arm → deltopectoral groove → pierces clavipectoral fascia in deltopectoral triangle → empties into axillary vein
• Basilic vein: medial side of dorsal venous network → medial forearm → perforates deep fascia at midarm → joins brachial veins → axillary vein
• Median cubital vein: crosses anterior cubital fossa connecting cephalic to basilic; separated from brachial artery only by bicipital aponeurosis; preferred site for venepuncture

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SECTION 8: THE HAND

8.1 Carpal Tunnel

• Boundaries: floor = carpal bones (arch); roof = flexor retinaculum (transverse carpal ligament)
• Contents (9 tendons + 1 nerve):
  • FPL (1 tendon)
  • FDS tendons x4
  • FDP tendons x4
  • Median nerve (most superficial and radial)
  • Radial and ulnar bursae (synovial sheaths)
• NOT inside carpal tunnel: ulnar nerve + artery (pass through Guyon's canal), FCR (own tunnel lateral), palmaris longus (superficial to retinaculum), recurrent branch of median nerve (exits distal to tunnel)

8.2 Muscles of the Hand

• Abductor pollicis brevis
• Opponens pollicis (rotates thumb into opposition)
• Flexor pollicis brevis (superficial head - median; deep head - ulnar)

• Abductor digiti minimi
• Flexor digiti minimi
• Opponens digiti minimi

• Lateral 2 (index, middle): median nerve (C8,T1)
• Medial 2 (ring, little): ulnar nerve (C8,T1)
• Origin: FDP tendons; Insertion: extensor hood (lateral band)
• Action: MCP flexion + IP extension (writing position)

• 4 Dorsal interossei (DAB): Abduct fingers (away from middle finger axis)
• 3 Palmar interossei (PAD): Adduct fingers (toward middle finger axis)
• Action (like lumbricals): MCP flexion + IP extension

8.3 Anatomical Snuffbox

• Borders:
  • Lateral: APL + EPB tendons
  • Medial: EPL tendon (hooks around Lister's tubercle)
  • Floor: scaphoid + trapezium + distal ends of ECRL/ECRB tendons
• Contents: radial artery (deep), superficial branch of radial nerve + origin of cephalic vein (roof)
• Clinical: tenderness = scaphoid fracture until proven otherwise; radial pulse palpable here

8.4 Extensor Hoods (Dorsal Digital Expansion)

• Extensor tendons expand over dorsum of each finger into triangular hood
• Lumbricals + interossei insert into lateral bands of extensor hood
• Middle slip → middle phalanx (P2)
• Lateral bands reunite distally → distal phalanx (P3)
• Boutonniere deformity: rupture of central slip → MCP hyperextension + PIP flexion + DIP hyperextension
• Mallet finger: rupture of terminal extensor tendon → DIP flexion deformity

8.5 Flexor Tendon Sheaths

• FDS + FDP tendons enclosed in fibrous digital sheaths (from MCP level to distal phalanx)
• Pulley system (A1-A5 annular pulleys + C1-C3 cruciate pulleys) - prevents bowstringing
• A2 (over proximal phalanx) + A4 (over middle phalanx): most important pulleys - must preserve in surgery
• Synovial sheaths of thumb + little finger are continuous with radial and ulnar bursae in carpal tunnel → spread of infection (horseshoe abscess)

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SECTION 9: CLINICAL CORRELATIONS (HIGH-YIELD)

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SECTION 10: DERMATOMES & SURFACE ANATOMY

Key Dermatomes

• C5: Lateral arm (badge area)
• C6: Lateral forearm + thumb + index finger
• C7: Middle finger
• C8: Ring + little finger + medial forearm
• T1: Medial arm
• T2: Axilla region (intercostobrachial nerve)

Key Surface Landmarks

• Cephalic vein - lateral arm in deltopectoral groove (IV access)
• Median cubital vein - anterior cubital fossa (venepuncture)
• Brachial artery - medial groove between biceps and triceps (blood pressure cuff site)
• Radial pulse - anterior wrist lateral to FCR; also in anatomical snuffbox
• Ulnar pulse - medial to FCR tendon, lateral to pisiform
• Cubital fossa - contents lateral to medial: biceps tendon, brachial artery, median nerve
• Ulnar nerve - palpable at medial epicondyle (cubital tunnel); "funny bone"

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1. Bones - Clavicle, scapula, humerus, radius/ulna, carpals (with mnemonics and fracture patterns)
2. Joints - Glenohumeral (ligaments, rotator cuff, dislocations), elbow (cubital fossa contents, ligaments), wrist - all with clinical correlations
3. Axilla - All boundaries, the three muscular spaces/gaps (quadrangular/triangular), axillary artery parts and branches
4. Brachial Plexus - Complete roots-trunks-divisions-cords-branches table, with Erb's and Klumpke's palsy
5. Muscles - All compartments with origin/insertion/nerve/action in tables
6. Nerves - Median, ulnar, radial, axillary, musculocutaneous - course, branches, injury patterns, and clinical signs
7. Vessels - Arterial supply, palmar arches, superficial veins (cephalic/basilic/median cubital)
8. Hand - Carpal tunnel contents, thenar/hypothenar/intrinsic muscles, anatomical snuffbox, extensor hoods, flexor pulleys
9. Clinical table - 16 high-yield injury patterns mapped to nerve/structure and key sign
10. Dermatomes - C5-T2 mapped to upper limb regions