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Upper Limb Anatomy - Complete Exam Guide

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1. BONES OF THE UPPER LIMB

Pectoral Girdle

• Clavicle - only bony connection between upper limb and axial skeleton; S-shaped; medial 2/3 convex anteriorly, lateral 1/3 concave anteriorly
• Scapula - triangular flat bone; key landmarks: acromion, coracoid process, glenoid cavity, spine of scapula, suprascapular notch (suprascapular nerve passes through it; suprascapular artery passes over it - "Army over the bridge")

Arm

• Humerus - head (articular), greater & lesser tubercles, bicipital groove (contains long head of biceps), surgical neck (vulnerable to fractures - axillary nerve injury), anatomical neck, deltoid tuberosity, medial & lateral epicondyles, lateral supraepicondylar ridge, capitulum (articulates with radius), trochlea (articulates with ulna), olecranon fossa, coronoid fossa, radial fossa

Forearm

• Radius - head (articulates with capitulum), radial tuberosity (insertion of biceps), styloid process, dorsal tubercle of Lister
• Ulna - olecranon process, coronoid process, trochlear notch, radial notch, head, styloid process

Hand (27 bones)

• 8 carpal bones (proximal row: Scaphoid, Lunate, Triquetrum, Pisiform; distal row: Trapezium, Trapezoid, Capitate, Hamate)
  • Mnemonic: "Some Lovers Try Positions That They Can't Handle"
• 5 metacarpals
• 14 phalanges (thumb has 2; fingers have 3 each)

Exam tip: Scaphoid fracture - tenderness in anatomical snuffbox; avascular necrosis risk because blood supply enters distally. Colles' fracture - distal radius, dinner fork deformity.

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2. BRACHIAL PLEXUS (Most Important Topic)

Structure: Roots → Trunks → Divisions → Cords → Branches

Trunks

Cords (named by relation to axillary artery 2nd part)

Key Branches (Exam Favorites)

• From roots: Dorsal scapular nerve (C5 - rhomboids), Long thoracic nerve (C5,6,7 - serratus anterior)
• From superior trunk: Suprascapular nerve (C5,6 - supraspinatus + infraspinatus), Nerve to subclavius (C5,6)
• From lateral cord: Lateral pectoral nerve, Musculocutaneous nerve, Lateral root of median nerve
• From medial cord: Medial pectoral nerve, Medial cutaneous nerve of arm, Medial cutaneous nerve of forearm, Ulnar nerve, Medial root of median nerve
• From posterior cord: Upper subscapular nerve, Thoracodorsal nerve, Lower subscapular nerve, Axillary nerve, Radial nerve

Brachial Plexus Injuries (High-Yield Clinical)

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3. AXILLA

1. Axillary artery (3 parts, divided by pectoralis minor)
2. Axillary vein
3. Brachial plexus (cords)
4. Axillary lymph nodes (5 groups: anterior/pectoral, posterior/subscapular, lateral, central, apical)
5. Long thoracic nerve (on serratus anterior)
6. Intercostobrachial nerve

• 1st part (1 branch): Superior thoracic artery
• 2nd part (2 branches): Thoraco-acromial + Lateral thoracic artery
• 3rd part (3 branches): Subscapular, Anterior circumflex humeral, Posterior circumflex humeral

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4. MUSCLES - BY COMPARTMENT

Shoulder (Rotator Cuff) - "SITS"

Arm - Anterior Compartment (Flexors)

Arm - Posterior Compartment

Forearm - Anterior Compartment (Flexors - Median & Ulnar nerves)

• Pronator teres, Flexor carpi radialis, Palmaris longus, Flexor carpi ulnaris, Flexor digitorum superficialis

• Flexor digitorum profundus (FDP) - lateral half (index + middle fingers) = median nerve; medial half (ring + little fingers) = ulnar nerve
• Flexor pollicis longus - anterior interosseous nerve (branch of median)
• Pronator quadratus - anterior interosseous nerve

Forearm - Posterior Compartment (Extensors - all radial nerve)

Exam tip: All forearm extensors = radial nerve. Radial nerve injury at spiral groove causes "wrist drop."

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5. MAJOR NERVES AND INJURIES

Median Nerve (C6-T1)

• Course: Lateral cord (C6,7) + medial cord (C8,T1) → down medial arm → cubital fossa (medial to brachial artery) → between heads of pronator teres → anterior interosseous nerve branch → carpal tunnel → palm
• In forearm: Innervates all flexors EXCEPT flexor carpi ulnaris and medial half of FDP
• In hand: Thenar muscles (LOAF = Lumbricals 1&2, Opponens pollicis, Abductor pollicis brevis, Flexor pollicis brevis), palmar and digital sensation of lateral 3.5 fingers
• Lesion at wrist (carpal tunnel): Ape hand (loss of opposition), sensory loss lateral 3.5 fingers, no wrist drop
• Lesion at elbow: "Pointing index" with loss of hand grasp + loss of pronation
• Clinical test: "OK sign" (inability = AIN injury)

Ulnar Nerve (C8-T1)

• Course: Medial cord → behind medial epicondyle (very vulnerable!) → between heads of FCU → Guyon's canal (lateral to pisiform) → deep and superficial branches in hand
• In forearm: FCU + medial half FDP
• In hand: Hypothenar muscles, all interossei, medial 2 lumbricals, adductor pollicis + half flexor pollicis brevis; sensation of medial 1.5 fingers
• Lesion: Claw hand (ring + little fingers mostly), froment's sign (uses FPL to compensate), loss of finger abduction/adduction (interossei)
• "Claw worse with wrist lesion" - paradox of ulnar nerve - more claw with distal lesion because intrinsics are non-functional but FDP still pulling

Radial Nerve (C5-T1)

• Course: Posterior cord → spiral groove of humerus (behind lateral intermuscular septum) → lateral epicondyle → divides into superficial (sensory) and deep (posterior interosseous nerve, PIN)
• Muscles: All posterior arm + forearm extensors
• Lesion at axilla: Saturday night palsy - wrist drop + finger drop + loss of triceps (triceps reflex lost), sensory loss dorsal forearm/hand
• Lesion at spiral groove: Wrist drop (triceps spared - supplied above lesion)
• PIN injury (at radial tunnel): Finger drop without wrist drop (ECRL spared because innervated above PIN)

Musculocutaneous Nerve (C5-C7)

• From lateral cord; pierces coracobrachialis; supplies all 3 anterior arm muscles; continues as lateral cutaneous nerve of forearm

Axillary Nerve (C5-C6)

• From posterior cord; exits through quadrangular space with posterior circumflex humeral artery
• Supplies: Deltoid + teres minor; skin over deltoid (regimental badge area)
• Injury: Surgical neck of humerus fracture or shoulder dislocation → loss of shoulder abduction

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6. JOINTS

Sternoclavicular Joint

• Only true joint between upper limb and axial skeleton
• Saddle joint (functionally), fibrocartilage articular disc present
• Ligaments: anterior + posterior sternoclavicular, costoclavicular, interclavicular

Acromioclavicular Joint

• Plane joint; fibrocartilage articular disc (may be absent)
• Key stabilizer: coracoclavicular ligament (conoid + trapezoid ligaments) - prevents superior displacement of clavicle
• Injury: AC separation (falls on shoulder tip)

Glenohumeral (Shoulder) Joint

• Ball-and-socket synovial joint
• Most mobile but least stable joint of the body
• Stability provided by: Rotator cuff muscles (primary dynamic stabilizers), glenoid labrum (deepens socket), glenohumeral ligaments, long head of biceps
• Weak point: Inferior wall - dislocation almost always anterior and inferior
• Bursae: Subacromial/subdeltoid bursa (most important - supraspinatus tendon lies below it)
• Movements: Flexion, extension, abduction, adduction, medial/lateral rotation, circumduction
• Abduction: 0-15° = supraspinatus; 15-90° = deltoid; 90-180° = trapezius + serratus anterior (scapular rotation)

Elbow Joint

• Hinge joint (flexion/extension); includes proximal radioulnar joint (pronation/supination)
• Medial collateral ligament (anterior bundle most important) resists valgus stress
• Lateral collateral ligament (radial collateral + lateral ulnar collateral) resists varus
• Carrying angle: Normal 5-15° valgus; increased = cubitus valgus (delayed ulnar nerve palsy)
• Pulled elbow (nursemaid's elbow) - radial head subluxation in children
• Fat pad sign on X-ray = joint effusion (intracapsular fracture)

Wrist (Radiocarpal) Joint

• Condyloid joint; between radius + articular disc proximally, and scaphoid + lunate distally
• Movements: Flexion, extension, abduction (radial deviation), adduction (ulnar deviation)
• Carpal tunnel syndrome: Compression of median nerve - pain/tingling lateral 3.5 fingers, worse at night, thenar wasting; Tinel's + Phalen's test positive

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7. CARPAL TUNNEL

• Boundaries: Floor = carpal bones (arch); Roof = flexor retinaculum
  • Lateral attachment: Scaphoid tubercle + trapezium tubercle
  • Medial attachment: Pisiform + hook of hamate
• Contents: 9 tendons + 1 nerve
  • 4 tendons FDS + 4 tendons FDP + 1 tendon FPL + Median nerve
  • Ulnar nerve and artery pass ANTERIOR to the retinaculum (in Guyon's canal) - NOT through carpal tunnel

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8. HAND MUSCLES AND SPACES

Thenar Eminence (Median nerve - C8, T1)

• Abductor pollicis brevis (most superficial)
• Flexor pollicis brevis (superficial head median, deep head ulnar)
• Opponens pollicis
• (Adductor pollicis = ulnar nerve)

Hypothenar Eminence (Ulnar nerve)

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

Lumbricals

• 4 lumbricals; arise from FDP tendons
• Action: Flex MCP joints, extend IP joints ("intrinsic plus" position)
• Lateral 2 (index + middle) = median nerve; Medial 2 (ring + little) = ulnar nerve

Interossei

• 4 dorsal (abduct fingers = "DAB"); 3 palmar (adduct = "PAD")
• All = ulnar nerve
• Reference finger for abduction/adduction = middle finger

Palmar Arches

• Superficial palmar arch = mainly ulnar artery; lies superficial to long flexor tendons; gives common palmar digital arteries
• Deep palmar arch = mainly radial artery; lies on metacarpal bases; gives palmar metacarpal arteries; 1 cm proximal to superficial arch

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9. BLOOD SUPPLY

Axillary Artery (continuation of subclavian at lateral border of 1st rib)

• 3 parts (by pectoralis minor)
• Becomes brachial artery at lower border of teres major

Brachial Artery

• Main artery of arm; medial to humerus → cubital fossa (medial to biceps tendon, lateral to median nerve)
• Gives: Profunda brachii (deep brachial artery) → accompanies radial nerve in spiral groove
• Bifurcates at neck of radius into radial + ulnar arteries

Radial Artery

• Travels under brachioradialis → anatomical snuffbox → dorsum of hand → between heads of 1st dorsal interosseous → deep palmar arch

Ulnar Artery

• Larger branch; gives anterior + posterior interosseous arteries via common interosseous → Guyon's canal → superficial palmar arch

Clinical: Allen's Test

• Compress both radial and ulnar arteries; release one; assess filling of hand. Tests adequacy of palmar arch anastomosis.

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10. VEINS

Superficial Veins (Exam Favorite for IV access)

• Cephalic vein: Begins from dorsal venous arch (lateral) → lateral forearm → lateral to biceps → deltopectoral groove → pierces clavipectoral fascia → drains into axillary vein
• Basilic vein: Begins from dorsal venous arch (medial) → medial forearm → pierces deep fascia at mid-arm → becomes axillary vein at lower border of teres major
• Median cubital vein: In cubital fossa - connects cephalic and basilic; most common IV access site; brachial artery is deep to bicipital aponeurosis here

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11. ANATOMICAL SPACES (Clinical High-Yield)

Quadrangular Space

• Boundaries: Teres minor (superior), Teres major (inferior), Long head of triceps (medial), Surgical neck of humerus (lateral)
• Contents: Axillary nerve + posterior circumflex humeral artery

Triangular Space

• Boundaries: Teres minor (superior), Teres major (inferior), Long head of triceps (lateral)
• Contents: Circumflex scapular artery

Triangular Interval (Lower triangular space)

• Boundaries: Teres major (superior), Long head of triceps (medial), Lateral head of triceps/humerus (lateral)
• Contents: Radial nerve + Profunda brachii artery

Cubital Fossa

• Triangle: Brachioradialis (lateral), Pronator teres (medial), imaginary line between epicondyles (base)
• Contents (lateral to medial): Radial nerve, Brachial artery, Median nerve, Biceps tendon, Brachialis (floor)
• Mnemonic: "Really Nice Beverage Makes Me Happy" (Radial N, Biceps tendon (via Median n), Brachial artery, Median nerve)

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12. SURFACE ANATOMY AND CLINICAL LANDMARKS

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13. KEY CLINICAL CORRELATIONS FOR EXAMS

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14. LYMPHATICS

• Superficial lymphatics follow superficial veins
• Deep lymphatics follow deep arteries
• All lymph from upper limb drains ultimately to apical axillary nodes → subclavian lymph trunk
• Lateral group of axillary nodes: receive most limb lymph
• Apical group: receives all other axillary nodes

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Summary: Highest-Yield Topics for Exams

1. Brachial plexus - roots, trunks, divisions, cords, branches
2. Nerve injuries - median (ape hand/CTS), ulnar (claw/Froment's), radial (wrist drop), axillary
3. Rotator cuff - SITS muscles, supraspinatus most commonly injured
4. Carpal tunnel - contents, boundaries, CTS
5. Axilla - walls, contents, lymph nodes, axillary artery branches
6. Hand muscles - thenar (median), hypothenar (ulnar), lumbricals, interossei
7. Superficial veins - cephalic and basilic courses
8. Anatomical snuffbox - contents, scaphoid fracture
9. Cubital fossa - contents from lateral to medial
10. Glenohumeral joint - stability, dislocation pattern