#mrcs

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HUMERUS 

Upper end

Head articulates with glenoid cavity

2 necks: anatomical & surgical neck

Anatomical 

separates head from greater & lesser tubercles 

Surgical 

 separates upper end & shaft 

has the axillary nerve & circumflex humeral vessels 

2 tuberosities (Mnemonic for insertions: SIT-S)

Greater tuberosity - insertion of

Supraspinatus muscle 

Infraspinatus muscle 

Teres minor muscle

Lesser tuberosity - insertion of:

Subscapularis muscle 

Bicipital groove 

Contains tendon of long head of biceps 

has 3 lips: (Mnemonic: lady between 2 majors)

Medial lip: Teres major insertion 

Floor: Latissmus dorsi insertion 

Lateral lip: Pectoralis major insertion 

Spiral groove 

Lies posteriorly on the shaft 

Related to radial nerve (winds around it between medial & lateral head of triceps) 

Lower end 

Trochlea -- articulates with ulna 

Capitulum -- articulates with radius 

Medial epicondyle more prominent than lateral epicondyle 

3 fossa: olecranon (posteriorly), radial & coronoid (anteriorly) 

FRACTURES OF HUMERUS - NERVES AFFECTED:

Surgical neck -- injury to axillary nerve --effect: flattened shoulder (deltoid muscle) 

Middle of shaft (spiral groove) -- injury to radial nerve -- effect: wrist drop 

Posterior to medial epicondyle -- injury to ulnar nerve -- effect: claw hand 

Supracondylar fracture -- injury to median nerve 

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[clumsy-medic]

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BRACHIAL PLEXUS 

Branches

Lateral cord 

Lateral pectoral nerve (C5, 6, 7) 

Lateral root of median nerve (C5, 6, 7)

Musculocutaneous nerve (C5, 6, 7) 

Medial cord 

Medial pectoral nerve (C8, T1) 

Medial root of median nerve (C8, T1)

Medial cutaneous nerve of forearm (C8, T1) 

Ulnar nerve (C7, 8, T1) 

Posterior cord 

Upper subscapular nerve (C5, 6)

Lower subscapular nerve (C5, 6)

Nerve to latissimus dorsi (C6, 7, 8)

Axillary (circumflex) nerve (C5, 6) 

Radial nerve (C5, 6, 7, 8, T1) 

Roots are posterior to scalenus anterior 

Cord is medial to axillary artery 

LINK: Drawing the brachial plexus 

https://www.youtube.com/watch?v=GLJuSRYamus

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RADIAL NERVE 

Terminal branch of posterior cord 

C5, 6, 7, 8, T1 

Arises posterior to 3rd part of axillary artery 

In spiral groove of humerus it is accompanies by profunda brachii artery 

Fracture of shaft of humerus injures radial nerve & profunda brachii artery 

Anterior to lateral epicondyle it gives posterior interroseous branch & continues downwards as superficial radial nerve 

Passes deep to brachioradialis 

LINK: Radial nerve - 3D anatomy *** 

https://www.youtube.com/watch?v=3M6dzH1i-GI

RADIAL NERVE INJURY 

In axilla (Saturday night paralysis) 

Motor 

Loss of elbow extension 

Loss of forearm pronation 

Wrist drop & finger drop 

Sensory 

Loss at base of thumb 

In spiral groove 

Same as above + CAN extend arm 

POSTERIOR INTEROSSEOUS NERVE 

Branch of radial 

Pierces supinator muscle 

Branches 

Supplies 2 muscles BEFORE piercing supinator 

extensor carpi radialis 

supinator 

Supplies 7 muscles AFTER piercing supinator 

Extensor carpi ulnaris 

Extensor digitorum 

Extensor digiti minimi 

Extensor indices 

ABDuctor pollicis longus 

Extensor pollicis brevis 

Extensor pollicis longus 

INJURY 

Only finger drop (No extension of IP joints) 

In fracture of shaft of humerus:

If patient cannot extend wrist but there is no sensory effect - injury to posterior interosseous nerve. 

If patient cannot extend wrist & sensation is affected - injury to radial nerve 

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DERMATOMAL DISTRIBUTION UPPER LIMB 

C4 

Supraclavicular nerve (C2, 3, 4)

Cholecystitis or subphrenic abscess --> shoulder tip pain (same root as phrenic nerve) 

C6

Lateral border of forearm 

Thumb 

C7

Middle finger 

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ANATOMICAL SNUFFBOX

Boundaries

Medially - Extensor pollicis longus (3rd compartment)

Laterally - Abductor pollicis longus & extensor pollicis brevis (1st compartment)

CONTENTS

Radial artery

Cephalic vein

Trapezium

Scaphoid

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MUSCULOCUTANEOUS NERVE 

Origin

continuation of lateral cord of brachial plexus

formed from anterior divisions of superior and middle trunks

Course

it leaves the axilla by piercing coracobrachialis muscle

it then passes down the arm beneath biceps muscle

it ends as the lateral cutaneous nerve of forearm

Sensory supply

skin of lateral forearm

Motor supply

anterior compartment of arm (BBC)

biceps – flexes elbow, supinates forearm

brachialis – flexes elbow

coracobrachialis – flexes and adducts the arm at the glenohumeral joint

CLINICAL FEATURES OF MUSCULOCUTANEOUS NERVE PALSY

SENSORY LOSS

numbness over lateral forearm

MOTOR DEFICIT

paralysis of anterior compartment of arm – very weak elbow flexion and weak forearm supination

absent biceps reflex

DEFORMITY

wasting of anterior compartment of arm

elbow usually held in extension with forearm pronated

A stab wound in the axilla with loss of sensation in lateral forearm indicates injury to musculoskeletal nerve (BBC muscles)