forearm bones and muscles

head of radius

articulates with capitulum of distal end of humerus

strong annular ligament hodls head of radius in contact with radial notch of ulna

interosseous border

thin layer of tissue that holds radius and ulna together and separates forearm in anter/posterior compartments

sharp edge spanning distal ½ of radius

attachment site for interosseous membrane

ulnar notch

a shallow notch located on the medial surface of the distal end of the radius

articulates with the head of the ulna

lister’s tubercle

aka distal tubercle of the radius

“bump” located on the distal and dorsal end of radius

acts as a pulley for the tendon of extensor pollicis longus

articular facets of radius

distal end of radius has two facets:

• scaphoid

• lunate

forearm joints

superior and inferior radioulnar → both are pivot synovial

radiocarpal → condyloid synovial

forearm nerve muscle innervations/where they run

ulnar - innervates 4th/5th digits

radial - innervates posterior

median - innervates 1-3 digits

forearm nerve - sensory innervations

ulnar - innervates 4th/5th digits

radial - innervates posterior

median - innervates 1-3 digits

forearm blood supply

brachial artery

radial artery and vein

ulnar artery and vein

compartments of forearm & how

interosseous membrane divides forearm into posterior and anterior compartments

interosseous membrane

hold ulnar and radial bones together

has a free upper margin, distal to radial tuberosity and a small, circular opening located distally

• allows for passage of vessels between anterior and posterior compartments

anterior compartment

flexor compartment

common features:

• assist in movements of the wrist

• flexion of digits

• pronation

• innervated by median or ulnar nerve

divided into three layers:

• superficial (4)

• intermediate (1)

• deep (3)

anterior compartment: superficial layer muscles

pronator teres

flexor carpi radialis

palmaris longus

flexor carpi ulnaris

share common origin from medial epicondyle

extend distally into wrist/hand (expect pronator teres)

innervated by median nerve → expect flexor carpi ulnaris = ulnar nerve

pronator teres

O:

• humeral head - medial epicondyle of humerus

• ulnar head - coronoid process of ulna

I:

• middle of convexity of lateral shaft of radius

N:

• median nerve

A:

• flexes and pronates the forearm at elbow

Flexor carpi radialis

O:

• medial epicondyle

I:

• base of 2nd metacarpal

N:

• median nerve

A:

• wrist flexion

• radial deviation/abduction

palmaris longus

O:

• medial epicondyle

I:

• apex of palmar aponeurosis

• distal ½ of flexor retinaculum

N:

• median nerve

A:

• assists in wrist flexion

• helps tighten tissue of palmar paoneurosis

• sometimes absent in one or both forearms

flexor carpi ulnaris

O:

• humeral head - medial epicondyle

• ulnar head - olecranon and posterior border of ulna

I:

• pisiform

• hook of hamate

• 5th metacarpal

N:

• ulnar nerve

A:

• wrist flexoin

  • ulnar deviation/adduction

flexor digitorum superficialis

only muscle in the intermediate layer

O:

• humeroulnar head - medial epicondyle

• radial head - superior ½ anterior border of radius

I:

• shaft of middle phalanx of digits 2-5

N:

• median nerve

A:

• MCP and PIP flexion

splits into the 4 tendons in distal forearm

4 tendons pass through the carpal tunnel under the flexor retinaculum to the medial 4 fingers

• at level of carpal tunnel the tendons to digits 3/4 are superficial to the tendons digits 2/5

flexor retinaculum

aka transverse carpal ligament

strong fibrous band crossing the volar/palmar surface of the wrist

roof of carpal tunnel

theoretically prevents bowstringing of flexor tendons (maintains correct alignment of tendons passing across carpals

anterior compartment: deep layer muscles

flexor digitorum profundus

flexor pollicis longus

pronator quadratus

innervated by median nerve → except FDP to digits 4-5

flexor digitorum profundus

O:

• proximal ¾ of medial and anterior ulna

• interosseous membrane

I:

• base of distal phalanges of medial four fingers

N:

• digits 2-3 = median nerve

• digits 4-5 = ulnar nerve

A:

• flex DIP

splits into 4 tendons in distal forearm

passes through carpal tunnel deep to FDS

FDS/FDP distal relationship

insertion: FDS tendon splits and travels around FDP tendon to insert onto the base of the shaft of the middle phalanges of medial 4 fingers

Camper’s Chiasm

aka tendinous chiasm

the area where FDS splits and FDP travels through

FDP lies deep to FDS

FDP travels beyond FDS insertion onto the base of the distal phalanx where it flexes DIP joint

Flexor Pollicis Longus

O:

• anterior surface of radius

• interosseous membrane

I:

• base of distal phalanx of thumb

N:

• median (anterior interosseous)

A:

• flexes all joints of thumb

one tendon in the distal forearm that passes through carpal tunnel, lateral to tendons of FDS/FDP

Pronator Quadratus

flat square muscle in distal forearm

O:

• distal ¼ of anterior ulna

I:

• distal ¼ of anterior radius

N:

• median (anterior interosseous)

A:

• pronation

• holds radius and ulna together

posterior compartment of the forearm - both layers

aka extensor compartment

common features for muscles:

• assist in movements of wrist

• extend digits

• supination

• innervated by radial nerve

• all pass through tunnels created by extensor retinaculum which help guide, position, and align tendons as they pass from f/a into hand

divided into 2 layers - superficial (5) and deep (6)

posterior compartment: superficial layer

muscles:

• brachioradialis

• extensor carpi radialis longus

• extensor carpi radialis brevis

• extensor digitorum communis

• extensor digiti minimi

• extensor carpi ulnaris

commonalities:

• originate from supracondylar ridge and lateral epicondyle of humerus

• innervated by radial nerve

• all have tendons extending into the hand other than brachioradialis

brachioradialis

O:

• proximal ⅔ of supracondylar ridge of humerus

I:

• lateral distal end of radius proximal to styloid

N:

• radial nerve

A:

• flex elbow when forearm is in neutral

extensor carpi radialis longus

O:

• lateral supraepicondylar ridge of humerus

I:

• dorsal aspect of base of 2nd metacarpal

N:

• radial nerve

A:

• strong wrist extensor

• abducts at wrist

extensor capri radialis brevis

O:

• lateral epicondyle (common extensor tendon)

I:

• dorsal aspect of base of 3rd metacarpal

N:

• radial nerve

A:

• strong wrist extensor

• abducts at wrist

lies deep to ECRL

extensor digitorum communis

O:

• lateral epicondyle (common extensor tendon)

I:

• into extensor hood (triangular shaped CT)

• into base of dorsal surface of middle and distal phalanges of medial 4 fingers

N:

• radial (posterior interosseous) nerve

A:

• MCP extension

forms 4 tendons in distal forearm

tendons pass under extensor retinaculum

extensor retinaculum

a strong fibrous band stretching obliquely across the back of the wrist and holds down the extensor tendons of the fingers and thumb

helps guide, position, and align tendons as they travel from the forearm into the hand (synovial sheaths for lubrication and protection)

extensor digiti minimi

O:

• lateral epicondyle

I:

• extensor expansion of 5th digit

N:

• radial (posterior interosseous) nerve

A:

• 5th digit MCP and IP extension

extensor carpi ulnaris

O:

• lateral epicondyle

• posterior border of ulna

I:

• dorsal aspect of base of 5th metacarpal

N:

• radial (posterior interosseous) nerve

A:

• wrist extension

• ulnar deviation

posterior compartment: deep layer

muscles:

• abductor pollicis longus

• extensor pollicis brevis

• extensor indicis

• extensor pollicis longus

• supinator

commonalities:

• originate from posterior surface of radius and ulna, and interosseous membrane - expect supinator

• innervated by radial nerve

• under extensor retinaculum - except supinator

abductor pollicis longus

O:

• posterior proximal ½of radius

• ulna

• interosseous membrane

I:

• base of 1st metacarpal

N:

• radial (posterior interosseous) nerve

A:

• thumb abduction

• MCP extension

extensor pollicis brevis

O:

• posterior distal ⅓ of radius

• interosseous membrane

I:

• dorsal aspect of base of proximal phalanx of thumb

N:

• radial (posterior interosseous) nerve

A:

• extension of MCP and CMC thumb

extensor pollicis longus

O:

• posterior middle ⅓ ulna

• interosseous membrane

I:

• dorsal aspect of base of distal phalanx of thumb

N:

• radial (posterior interosseous) nerve

A:

• extension of all joints of the thumb

• CMC joint

Extensor Indicis

O:

• posterior distal ⅓ of ulna

• interosseous membrane

I:

• extensor expansion of index (2nd) finger

N:

• radial (posterior interosseous) nerve

A:

• extension of 2nd digit

• extend hand at wrist

supinaotr

O:

• lateral epicondyle

• annular and radial collateral ligaments

• proximal ulna at supinator crest

I:

• lateral posterior and anterior surface of proximal ⅔ of radius

N:

• radial nerve

A:

• supination

Dorsal extensor compartments

6 tunnels:

1: APL and EPB

2: ECRL and ECRM

3: EPL

4: EDC and EI

5: EDM

6: ECU

pronation muscles

pronator teres

pronator quadratus

wrist extension muscles

ECRL and ECRB = strongest

ECU

Long finger extensors assist slightly

wrist flexion muscles

FCR and FCU - strongest

long finger flexors assist (FDP, FDS)

radial deviation of wrist muscles

FCR

ECRL, ECRB

APL

ulnar deviation of wrist muscles

FCU

ECU

finger flexion muscles

FDS - PIP joint

FDP - DIP joint

digit extension muscles

EDC

EI

EDM