Anatomy of the upper limb

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Anatomy of the Upper Limb

Source: Gray's Anatomy for Students; Rosen's Emergency Medicine

1. Overview and Regions

The upper limb is divided into:

Shoulder / pectoral girdle (clavicle + scapula connecting the limb to the axial skeleton)
Arm (shoulder to elbow)
Forearm (elbow to wrist)
Hand (carpals, metacarpals, phalanges)
Axilla (armpit - a pyramid-shaped space that serves as the neurovascular highway)

2. Bones

Region	Bones
Pectoral girdle	Clavicle, Scapula
Arm	Humerus
Forearm	Radius (lateral), Ulna (medial)
Wrist	8 Carpal bones (proximal row: Scaphoid, Lunate, Triquetrum, Pisiform; distal row: Trapezium, Trapezoid, Capitate, Hamate)
Hand	5 Metacarpals, 14 Phalanges (proximal, middle, distal - except thumb which has 2)

Key landmarks:

Humerus: greater and lesser tubercles, intertubercular sulcus (biceps tendon), surgical neck (axillary nerve), radial groove (radial nerve), medial and lateral epicondyles
Ulna: olecranon, coronoid process, trochlear notch
Radius: head, radial tuberosity (biceps insertion), styloid process

3. Joints

Joint	Type	Key Features
Sternoclavicular	Synovial, saddle	Only bony articulation of upper limb with axial skeleton
Acromioclavicular	Synovial, plane	Site of AC joint dislocation
Glenohumeral (shoulder)	Synovial, ball-and-socket	Most mobile but least stable joint; reinforced by rotator cuff
Elbow (humeroulnar + humeroradial)	Synovial, hinge	Flexion/extension; carrying angle ~170°
Proximal + Distal Radioulnar	Synovial, pivot	Pronation/supination
Wrist (radiocarpal)	Synovial, condyloid	Flexion, extension, abduction, adduction
Carpometacarpal of thumb	Saddle	Enables thumb opposition

Rotator Cuff - four muscles that stabilize the glenohumeral joint (mnemonic SITS):

Supraspinatus (abduction, first 15°)
Infraspinatus (lateral rotation)
Teres minor (lateral rotation)
Subscapularis (medial rotation)

4. Brachial Plexus

The brachial plexus is the network of nerves supplying virtually all of the upper limb. It is formed by the anterior rami of C5-T1.

Structure: Roots → Trunks → Divisions → Cords → Branches

(Mnemonic: Real Texans Drink Cold Beer)

Brachial Plexus - components in the neck and axilla (Gray's Anatomy for Students)

Trunks

Trunk	Roots
Superior	C5 + C6
Middle	C7
Inferior	C8 + T1

Cords (named by relation to axillary artery)

Cord	Origin	Terminal nerves
Lateral (C5-C7)	Anterior div. of Superior + Middle	Musculocutaneous, lateral root of Median
Medial (C8-T1)	Anterior div. of Inferior	Ulnar, medial root of Median
Posterior (C5-T1)	All three posterior divs.	Radial, Axillary

Major Terminal Nerves

Nerve	Root	Motor	Sensory	Injury
Musculocutaneous	C5-C7	Biceps, brachialis, coracobrachialis	Lateral forearm (as lateral cutaneous n.)	Weak elbow flexion/supination
Median	C5-T1	Forearm flexors (except FCU + medial FDP), thenar muscles, lumbricals 1&2	Lateral 3.5 digits (palm)	Carpal tunnel; "ape hand", loss of thumb opposition
Ulnar	C8-T1	FCU, medial FDP, hypothenar, interossei, lumbricals 3&4, adductor pollicis	Medial 1.5 digits	"Claw hand" (ring/little fingers); at medial epicondyle
Radial	C5-T1	All extensors (triceps, wrist/finger extensors), supinator	Posterior arm/forearm, dorsal lateral 3.5 digits	"Wrist drop" (posterior cord/spiral groove injury)
Axillary	C5-C6	Deltoid, teres minor	Lateral shoulder (regimental badge area)	Loss of shoulder abduction; surgical neck fracture

5. Muscles

Arm

Coracobrachialis, Biceps brachii, and Brachialis muscles of the anterior compartment (Gray's Anatomy for Students)

Anterior compartment (innervated by musculocutaneous nerve, C5-C7):

Biceps brachii - flexes elbow, supinates forearm (long head from supraglenoid tubercle; short head from coracoid; inserts on radial tuberosity)
Brachialis - prime mover of elbow flexion (inserts on ulnar tuberosity)
Coracobrachialis - flexes arm (from coracoid to medial humerus)

Posterior compartment (innervated by radial nerve, C6-C8):

Triceps brachii - extends elbow; long head originates from infraglenoid tubercle; inserts on olecranon

Forearm

Anterior compartment (flexors, generally median and ulnar nerves):

Superficial layer: Pronator teres, Flexor carpi radialis (FCR), Palmaris longus, Flexor carpi ulnaris (FCU - ulnar n.), Flexor digitorum superficialis (FDS)

Deep layer: Flexor digitorum profundus (FDP - lateral half median, medial half ulnar), Flexor pollicis longus (FPL - AIN/median), Pronator quadratus (AIN/median)

Posterior compartment (extensors, radial nerve):

Superficial: Brachioradialis, ECRL, ECRB, Extensor digitorum, Extensor digiti minimi, Extensor carpi ulnaris, Anconeus

Deep: Supinator, APL, EPL, EPB, Extensor indicis

Hand

Thenar muscles (median nerve): Abductor pollicis brevis, Flexor pollicis brevis (superficial head), Opponens pollicis
Hypothenar muscles (ulnar nerve): Abductor digiti minimi, Flexor digiti minimi, Opponens digiti minimi
Lumbricals: flex MCP, extend IP joints (L1&2 = median; L3&4 = ulnar)
Interossei: Dorsal = abduct fingers (DAB); Palmar = adduct fingers (PAD) - all ulnar nerve
Adductor pollicis (ulnar nerve)

6. Blood Supply

Vessel	Origin	Territory
Subclavian artery	Brachiocephalic trunk (R) / Aortic arch (L)	Becomes axillary artery at lateral border of 1st rib
Axillary artery (3 parts, divided by pectoralis minor)	From subclavian	Branches: thoracoacromial, lateral thoracic, subscapular, anterior/posterior circumflex humeral
Brachial artery	Continues from axillary at lower border of teres major	Entire arm; divides at cubital fossa
Radial artery	Terminal branch of brachial	Lateral forearm, anatomical snuffbox, deep palmar arch
Ulnar artery	Terminal branch of brachial	Medial forearm, superficial palmar arch

Palmar arches:

Superficial palmar arch = primarily ulnar artery + small contribution from radial
Deep palmar arch = primarily radial artery + deep branch of ulnar

7. Venous Drainage

Superficial veins (clinically important):

Cephalic vein - lateral; runs in deltopectoral groove; drains to axillary vein
Basilic vein - medial; pierces deep fascia in arm; drains to axillary vein
Median cubital vein - connects cephalic and basilic in the cubital fossa; preferred site for venipuncture

Deep veins accompany the arteries (venae comitantes).

8. Lymphatics

Axillary lymph nodes (drain the upper limb and breast) are arranged in 5 groups:

Pectoral (anterior) - drain anterior chest wall and breast
Humeral (lateral) - drain most of the upper limb
Subscapular (posterior) - drain posterior wall, shoulder, neck
Central - receive from the above three groups
Apical - drain all other groups; efferent vessels form the subclavian trunk

Axillary node clearance (e.g., in breast cancer surgery) or axillary radiotherapy can damage lymphatic drainage, causing lymphoedema of the upper limb.

9. Key Clinical Correlates

Injury	Mechanism	Deficit
Erb's palsy (upper brachial plexus, C5-C6)	Forced neck-shoulder separation	"Waiter's tip" - arm adducted, medially rotated, elbow extended
Klumpke's palsy (lower, C8-T1)	Forced arm abduction	Intrinsic hand weakness; "claw hand" ± Horner syndrome
Axillary nerve injury	Shoulder dislocation / surgical neck fracture	Loss of deltoid contraction; loss of regimental badge sensation
Radial nerve in spiral groove	Mid-shaft humeral fracture	Wrist drop; loss of finger extension
Median nerve at carpal tunnel	CTS	Thenar wasting; loss of thumb opposition; first 3.5 digit numbness
Ulnar nerve at medial epicondyle	Cubitus valgus fracture	Ring/little finger claw; loss of interossei; Froment's sign
Anterior interosseous nerve	Compressive injury	Loss of FDP (index/middle) + FPL; "pinch" defect; no sensory loss

Sources: Gray's Anatomy for Students (9780323934237), Rosen's Emergency Medicine (9780323757898)

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