Forearm: compartments, vessels, innervation, and movement

anterior compartment (forearm)

flexor compartment

interosseous membrane

division via radius and ulna; membrane between radius and ulna

posterior compartment

extensor compartment

muscles of posterior compartment

extensors, abductor pollicis longus, supinator

antebrachial fascia

arises from brachial fascia, and separates forearm into anterior and posterior compartments alongside interosseous membrane

anterior compartment vessels

1. radial artery, radial vein

2. anterior interosseous artery, anterior interosseous vein

3. ulnar artery, ulnar vein

anterior compartment nerves

1. medial

2. ulnar

3. superficial radial

4. anterior interosseous

anterior compartment muscles

flexor muscles + pronator muscles

posterior compartment vessels and nerve

1. posterior interosseous artery and veins

2. posterior interosseous nerve (continuation of deep radial nerve

posterior compartment muscles

extensor muscles + supinator

branching of arteries in forearm, in order

brachial artery → radial and ulnar arteries → ulnar artery → anterior interosseous artery and posterior interosseous artery → radial and ulnar arteries → palmar arches (superficial and deep)

when does the brachial artery branch into the radial and ulnar arteries?

after the elbow joint

radial artery

major contributor to deep palmar arch

ulnar artery

major contributor to superficial palmar arch

anastomosis

a connection between vessels that prevents a lack fo blood flow to a specific region if one blood vessel is compromised

• ie: palmar arches

forearm veins

• radial, ulnar, anterior interosseous, posterior interosseous, palmar venous system

• median antebrachial vein

• basilic and cephalic veins

musculocutaneous nerve

arises from lateral cord of brachial plexus; C5-C7 fibers

• innervates coracobrachialis, biceps brachii, brachialis

• continues as lateral antebrachial cutaneous nerve

lateral antebrachial cutaneous nerve

continuation of musculocutaneous nerve superficially in the forearm

• provides sensory innervation to lateral forearm

median nerve

arises from both lateral and medial cords of the brachial plexus: C5-T1 fibers

• courses along midline within anterior compartment

• branches into anterior interosseous nerve

anterior interosseous nerve

proximal branch of median nerve that innervates deep muscles the forearms

• innervates flexors and pronators + lateral intrinsic hand muscles (thenar muscles and 1st and 2nd lumbrical)

median nerve sensory innervation in forearm

1. palmar cutaneous branch

2. digital cutaneous branch

palmar cutaneous branch

branch of median nerve that provides sensory innervation to lateral palmar surface

• does NOT pass through carpal tunnel

digital cutaneous branch

branch of median nerve that provides sensory innervation to digits 1-3.5

• does NOT pass through carpal tunnel

radial nerve

arises from posterior cord of brachial plexus: C5-T1 fibers

• branches into deep radial nerve (motor) and superficial radial nerve (sensory)

deep radial nerve

innervates all muscles of posterior compartment of the forearm (extensors, abductor pollicis longus, supinator)

• motor branch of radial nerve in forearm

• branches into posterior interosseous nerve after innervating supinator

superficial radial nerve

innervates dorsum of hand (digits 1-3.5) in anterior forearm compartment

• sensory branch of radial nerve

posterior cutaneous nerve of forearm

branches off of radial nerve in posterior arm compartment

• innervates posterior forearm

ulnar nerve

arises from medial cord of brachial plexus (C8-T1 fibers)

• runs along medial surface then on anterior surface of ulna into the hand

ulnar nerve innervation

1. flexor carpi ulnaris and ulnar half of flexor digitorum profundus in forearm

2. deep intrinsic hand muscles and hypothenar muscles

ulnar nerve sensory innervation

1. palmar branch (medial palmar surface)

2. superficial branch (palmar surface of digits 4.5-5)

3. dorsal branch (dorsum of medial hand)

during pronation and supination…

radial head rotates within annular ligament

during pronation

radius rotates medially

• radial shaft crosses ulnar shaft anteriorly so the distal radius is positioned medially

• only instance of bones crossing

during supination

radius rotates laterally, returning to anatomical position