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functional groups of extensor muscles of forearm

1. muscles that extend and abduct or adduct the hand of the wrist joint: extensor carpi radialis longus (ECRL), extensor carpi radialis brevis (ECRB) and extensor carpi ulnaris (ECU)
2. muscles that extend the medial four digits: extensory digitorum, extensor indicis and extensor digiti minimi (EDM)
3. muscles that extend or abduct the thumb: abductor policis longus, extensory policis brevis and extensory policis longus

1

extensor tendons

held in place in the wrist region by the extensor retinaculum which prevents bowstringing of the tendons when the hand is extended at the wrist joint.
as the tendons pass over the dorsum of the wrist, they are covered with synovial tendon sheaths, which reduce friction for the extensor tendons as they traverse the osseofibrous tunnels, formed by the attachment of the extensor retinaculum to the distal radius and ulna

2

superficial layer of posterior compartment of forearm

extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, and extensor carpi ulnaris, brachioradialis, extensor carpi radialis longus

3

deep layer of posterior compartment of forearm

supinator

4

outcropping muscles of deep layer of posterior compartment of forearm

abductor policis longus
extensor policis longus
extensor policis brevis
extensor indicis

5

brachioradialis origin

proximal two thirds of lateral supraepicondylar ridge of humerus

6

brachioradialis insertion

lateral surface of dustal end of radius, proximal to styloid process

7

brachioradialis innervation

radial nerve (c5, c6, c7)

8

brachioradialis action

relatively weak flexion of elbow joint, maximal when forearm is in midpronated position

9

extensor carpi radialis longus origin

lateral supra-epicondylar ridge of humerus

10

extensor carpi radialis longus insertion

dorsal aspect of base of 2nd metacarpal

11

extensor carpi radialis longus innervation

radial nerve
C6, C7

12

extensor carpi radialis longus action

extends and abduct wrist joint
extensor carpi radialis brevis active during fist clenching

13

extensor carpi radialis brevis origin

lateral epicondyle of humerus (common extensor origin)

14

extensor carpi radialis brevis insertion

dorsal aspect of base of 3rd metacarpal

15

extensor carpi radialis brevis innervation

deep branch of radial nerve C7, C8

16

extensor carpi radialis brevis action

extend and abduct wrist joint
extensor carpi radialis brevis active during fist clenchin

17

extensor digitorum origin

lateral epicondyle of humerus (common extensor origin)

18

extensor digitorum insertion

extensor expansions of medial four fingers

19

extensor digitorum innervation

posterior interosseus nerve (C7, C8), continuation of deep branch of radial nerve

20

extensor digitorum action

extend wrist joint
extend medial four fingers primarily at metacarpophalangeal joints, secondarily at interphalangeal joints

21

extensor digiti minimi origin

lateral epicondyle of humerus (common extensor origin)

22

extensor digiti minimi insertion

extensor expansion of 5th finger

23

extensor digiti minimi innervation

posterior interosseus nerve (C7, C8), continuation of deep branch of radial nerve

24

extensor digiti minimi action

extends wrist joint
extends 5th finger primarily at metacarpophalngeal joint, secondarily at interphalangeal joint

25

extensor carpi ulnaris origin

lateral epicondyle of humerus
posterior border of ulna via a shared aponeurosis

26

extensor carpi ulnaris insertion

dorsal aspect of base of 5th metacarpal

27

extensor carpi ulnaris innervation

posterior interosseus nerve (c7, c8), continuation of deep branch of radial nerve

28

extensor carpi ulnaris action

extends and adducts wrist joint (also active during fist clenching)

29

supinator origin

lateral epicondyle of humerus, radial collateral and anular ligaments, supinator fossa, crest of ulna

30

supinator insertion

lateral, posterior and anterior surfaces of proximal third of radius

31

supinator innervation

deep branch of radial nerve (c7, C8)

32

supinator action

supinates forearm; rotates radius to turn palm anteriorly or superiorly (if elbow is flexed)

33

abductor policis longus origin

posterior surface of proximal halves of ulna, radius, and interosseus membrane

34

abductor policis longus insertion

base of 1st metacarpal

35

abductor policis longus innervation

posterior interosseus nerve (c7, c8), continuation of deep branch of radial nerve

36

abductor policis longus action

extends wrist joint
abducts thumb and extends it at carpometacarpal joint

37

extensor policis longus origin

posterior surface of middle third of ulna and interosseus membrane

38

extensor policis longus insertion

dorsal aspect of base of distal phalanx of thumb

39

extensor policis longus innervation

posterior interosseus nerve (c7, c8), continuation of deep branch of radial nerve

40

extensor policis longus action

extends wrist joint
extends distal phalanx of thumb at interphalangeal joint: extends metacarpophalangeal and carpometacarpal joints

41

extensor policis brevis origin

posterior surface of distal third of radius and interosseus membrane

42

extensor policis brevis distal attachment

dorsal aspect of base of proximal phalanx of thumb

43

extensor policis brevis innervation

posterior interosseus nerve (c7, c8), continuation of deep branch of radial nerve

44

extensor policis brevis action

extends wrist joint
extends proximal phalanx of thumb at metacarpophalangeal joint; extends carpometacarpal joint

45

extensor indicis origin

posterior surface of distal third of ulna and interosseus membrane

46

extensor indicis insertion

extensor expansion of 2nd finger

47

extensor indicis innervation

posterior interosseus nerve (c7, c8), continuation of deep branch of radial nerve

48

extensor indicis action

extends wrist joint
extends 2nd finger (enabling its independent extension)
helps extend hand at wrist

49

extensor retinaculum

holds extensor tendons in place in the wrist regions
prevents bowstringing of the tendons when the hand is extended at the wrist joint

50

synovial tendon sheaths

covers tendons as they pass over the dorsum of the wrist
reduce friction for the extensor tendons as they traverse the osseo-fibroys tunnels formed by the attachment of the extensor retinaculum to the distal radius and ulna

51

tendinous sheath of extensor digitorum and extensor indicis

common extensor synovial shearg

52

three oblique intertendinous connections

restrict independent extension of the fingersadjacent tends linked proximal to the metacarpophalangeal joints by tendons

53

extensor expansions

distal ends of metacarpals and along phalanges, four tendons of extensor digitorum flatter
each one is a triangular tendinous aponeurosis that wraps around the dorsum and sides of a head of the metacarpal and base of the proximal phalanx
hood over head of metacarpal is anchored on each side to the palmar ligament (a thickened portion of the fibrous layer of the joint capsule of the metacarpophalangeal joints)

54

median and lateral bands

extensor digitorum tendon divides into a median band which passes t the base of the middle phalanx and two lateral bands which pass to the base of the distal phlanx

55

retinacular ligament

delicate fibrous band that runs from proximal phalanx and fibrous digital sheath obliquely across middle phalanx and two interphalangeal joints
becomes taut during flexion of distal interphalangeal joint. taut ligament pulls proximal interphalangeal joint into flexion. on extending proximal joint, the distal joint is pulled by the retinacular ligment into nearly complete extension

56

snuff box

laterally: tendons of the APL and EPB
medially: tendon of EPL
visible as a hollow on the lateral aspect of the wrist when the thumb is extended fully
radial artery lies on the floor
radial styloid process can be palpated proximally and the base of the 1st metacarpal can be palpated distally in the snuff box
scaphoid and trapezium can be felt in the floor of the snuff box between the radial styloid process and the 1st metacarpal