Posterior compartment

plan

Muscles

· 2 proximal

· supinator, anconeus

· 3 of mobile wad laterally

· BR, ECRL, ECRU

· 3 posterior

· EDC, EDM, ECU

· 3 between these

· APL, EPB, EPL

· 1 separate

· EIP

· 6 long muscles attach to humerus

· BR, ECRL to lateral humerus

· ECRB, EDC, EDM, ECU to common extensor origin

· special points

· mobile wad of 3 - ECRB = lateral humerus and radial n

· posterior 3 + ECRB- common ext. origin and post int n

Neurovascular

· post int n (and radial n)

· passes between 2 heads of supinator

mobile wad

Brachioradialis

Origin

· upper 2/3 of lateral supracondylar ridge of humerus

Path

· along radial border of forearm

· runs over supinator, PT, FDS, FPL

· lower part covered by APL and EPB

Relations

· overlies radial a and n

Insertion

· base of radial styloid

Extensor carpi radialis longus

Origin

· lower 1/3 of lateral supracondylar ridge

Path

· runs under BR

Insertion

· base of MC II

Extensor carpi radialis brevis

Origin

· common extensor origin (lateral epicondyle of humerus)

Path

· runs under ECRL

Insertion

· base of MC III

Posterior muscles

Extensor digitorum communis

Origin

· common extensor origin

Path

· diverges from mobile wad

· separated from them by emerging thumb muscles

· 4 tendons develop under extensor retinaculum

· overlie tendon of EIM

Insertion

· extensor expansion

Extensor digiti minimi

Origin

· common extensor origin

Path

· separates from EDC

· splits into 2

Insertion

· extensor expansion of V

Extensor carpi ulnaris

Origin

· extensor expansion

· aponeurosis from subcutaneous ulna

· in common with FCU

Path

· passes down ulnar border

· tendon lies in groove on ulnar styloid

Insertion

· base of MC V

thumb muscles

Abductor pollicis longus

Origin

· both bones proximally and intervening IOM

Path

· emerges from between EDC and ECRL

· spirals round mobile wad

· splits into 3 or 4 bands

Insertion

· base of MC I

Extensor pollicis brevis

Origin

· radius and IOM

· distal to APL

Path

· muscle on ulnar side of APL

· tendon lies with APL

Insertion

· base of P1 of thumb

Extensor pollicis longus

Origin

· ulna and IOM

· distal to APL

Path

· muscle on ulnar side of EPB

· hooks around Lister’s tubercle

Insertion

· base of P2 of thumb

· stabilised by expansions from AbPB and AdP

other muscles

Anconeus

Origin

· lateral epicondyle of humerus

Path

· fans out towards ulna

Insertion

· lateral side of olecranon

Supinator

Origin

· superficial (humeral) head

· lateral epicondyle of humerus

· lateral collateral ligament of elbow

· deep (ulnar) head

· supinator crest and fossa of ulna

Path

· superficial head

· slope downwards towards radius

· over deep fibres

· deep head

· pass horizontally around radius

Relations

· posterior interosseous nerve passes between heads

Insertion

· superficial head

· radius just above anterior oblique line

· deep head

· radius between anterior and posterior oblique lines

Extensor indicis

Origin

· ulna

· distal to EPL

Path

· tendon remains deep to EDC

· then passes on ulnar side of EDC II

Insertion

· extensor expansion of II

anatomical snuffbox

· formed by

· EPL (ulnar)

· APL and EPB (radial)

· crossed by

· radial artery (floor)

· branches of superficial radial nerve (surface)

· cephalic vein (forms in)

· in base

· radial styloid

· tubercle of scaphoid

· base of MC I

nerves

Radial nerve

· supplies

· anconeus

· BR

· ECRL

· divides into two

Posterior interosseous nerve

· passes between 2 heads of supinator

· passes over origin of APL

· dips down to reach IOM

· ends at wrist joint

· supplies

· supinator

· ECRB

· EDC

· EDM

· ECU

· periosteum and IOM

vessels

Posterior interosseous artery

· passes

· between radius and ulna

· above IOM

· below oblique cord

· accompanies posterior interosseous nerve

· supplies proximal deep extensor muscles only (failure)

· replaced distally by anterior interosseous nerve

· pierces IOM above PQ