POSTERIOR ASPECT OF THE
FORERARM
28. 12. 2012
Kaan Yücel
M.D., Ph.D.
http://yeditepeanatomy1.org
A TOTAL OF 4 FIGURES IN THE TEXT
Dr. Kaan Yücel
http://yeditepeanatomy1.org
Posterior aspect of the forearm
Muscles in the posterior compartment of the forearm occur in two layers: a superficial and a deep layer. The
muscles are associated with:
-movement of the wrist joint;
-extension of the fingers and thumb; and
-supination.
All muscles in the posterior compartment of the forearm are innervated by the radial nerve.
The seven muscles in the superficial layer are the brachioradialis, extensor carpi radialis longus, extensor carpi
radialis brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, and anconeus.
The deep layer of the posterior compartment of the forearm consists of five muscles: supinator, abductor
pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis.
Except for the supinator muscle, all these deep layer muscles originate from the posterior surfaces of the
radius, ulna, and interosseous membrane and pass into the thumb and fingers.
The blood supply to the posterior compartment of the forearm occurs predominantly through branches of the
radial, posterior interosseous, and anterior interosseous arteries.
The nerve of the posterior compartment of the forearm is the radial nerve. Most of the muscles are innervated
by the deep branch, which originates from the radial nerve in the lateral wall of the cubital fossa deep to the
brachioradialis muscle and becomes the posterior interosseous nerve after emerging from between the two heads of
the supinator muscle in the posterior compartment of the forearm.
The deep branch innervates the extensor carpi radialis brevis, then supplies the supinator muscle and then
emerges, as the posterior interosseous nerve. The posterior interosseous nerve supplies the remaining muscles in the
posterior compartment.
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Dr. Kaan Yücel
http://yeditepeanatomy1.org
Posterior aspect of the forearm
1. MUSSLES
Muscles in the posterior compartment of the forearm occur in two layers: a superficial and a deep layer.
The muscles are associated with:
movement of the wrist joint;
extension of the fingers and thumb; and
supination.
All muscles in the posterior compartment of the forearm are innervated by the radial nerve.
Figure 1. Muscles of the forearm-posterior aspect
http://www.bisonstrength.com/blog/wp-content/uploads/2010/04/posterior-forearm-muscles.jpg
SUPERFICIAL LAYER
The seven muscles in the superficial layer are the brachioradialis, extensor carpi radialis longus,
extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, and
anconeus.
In the anatomical position, the brachioradialis is part of the muscle mass overlying the anterolateral
surface of the forearm and forms the lateral boundary of the cubital fossa.
Because the brachioradialis is anterior to the elbow joint, it acts as an accessory flexor of this joint even though
it is in the posterior compartment of the forearm. Its action is most efficient when the forearm is midpronated
and it forms a prominent bulge as it acts against resistance.
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Dr. Kaan Yücel
http://yeditepeanatomy1.org
Posterior aspect of the forearm
The radial nerve emerges from the posterior compartment of the arm just deep to the brachioradialis in the
distal arm and innervates the brachioradialis.
The extensor carpi radialis longus muscle, in proximal regions, is deep to the brachioradialis muscle. The
extensor carpi radialis longus muscle extends and abducts the wrist.
Along much of its course, the extensor carpi radialis brevis lies deep to the extensor carpi radialis longus. The
extensor carpi radialis brevis muscle extends and abducts the wrist.
The extensor digitorum muscle is the major extensor of the four fingers (index, middle, ring, and little
fingers). It originates from the lateral epicondyle of the humerus and forms four tendons, each of which passes
into a finger. On the dorsal surface of the hand, adjacent tendons of the extensor digitorum are interconnected.
In the fingers, each tendon inserts, via a triangular-shaped connective tissue aponeurosis (the extensor hood),
into the base of the dorsal surfaces of the middle and distal phalanges of the all the fingers except those of the
thumb.
The extensor digiti minimi muscle is an accessory extensor of the little finger and is medial to the
extensor digitorum in the forearm. It inserts, together with the tendon of the extensor digitorum, into the
extensor hood of the little finger.
The extensor carpi ulnaris muscle is medial to the extensor digiti minimi. The extensor carpi ulnaris
extends and adducts the wrist, and is innervated by the posterior interosseous nerve.
The anconeus muscle is the most medial of the superficial extensors and has a triangular shape.. The
anconeus abducts the ulna during pronation to maintain the center of the palm over the same point when the
hand is flipped. It is also considered to be an accessory extensor of the elbow joint.
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Dr. Kaan Yücel
http://yeditepeanatomy1.org
Posterior aspect of the forearm
DEEP LAYER
The deep layer of the posterior compartment of the forearm consists of five muscles: supinator,
abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis.
Except for the supinator muscle, all these deep layer muscles originate from the posterior surfaces of the
radius, ulna, and interosseous membrane and pass into the thumb and fingers.
Three of these muscles-the abductor pollicis longus, extensor pollicis brevis, and extensor pollicis
longus-emerge from between the extensor digitorum and the extensor carpi radialis brevis tendons of the
superficial layer and pass into the thumb.Two of the three "outcropping" muscles (the abductor pollicis longus
and extensor pollicis brevis) form a distinct muscular bulge in the distal posterolateral surface of the forearm.
All muscles of the deep layer are innervated by the posterior interosseous nerve, the continuation of
the deep branch of the radial nerve.
The supinator muscle has two heads of origin, which insert together on the proximal aspect of the
radius:
 superficial (humeral) head originates mainly from the lateral epicondyle of the humerus and the related
anular ligament and the radial collateral ligament of the elbow joint;
 deep (ulnar) head originates mainly from the supinator crest on the posterolateral surface of the ulna.
The two heads wrap around the radius to insert on the lateral surface of the radius superior to the anterior
oblique line. The supinator muscle supinates the forearm and hand. The deep branch of the radial nerve
passes to the posterior compartment of the forearm by passing between the two heads of this muscle.
In the distal forearm,the abductor pollicis longus emerges between the extensor digitorum and extensor
carpi radialis brevis muscles to form a tendon that passes into the thumb. The tendon contributes to the lateral
border of the anatomical snuffbox at the wrist. The major function of the abductor pollicis longus is to abduct
the thumb at the joint between metacarpal I and trapezium bones.
The extensor pollicis brevis muscle arises distal to the origin of the abductor pollicis longus. Together
with the abductor pollicis longus, it emerges between the extensor digitorum and extensor carpi radialis brevis
muscles to form a bulge on the posterolateral surface of the distal forearm. The tendon of the extensor pollicis
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Dr. Kaan Yücel
http://yeditepeanatomy1.org
Posterior aspect of the forearm
brevis passes into the thumb. At the wrist, the tendon contributes to the lateral border of the anatomical
snuffbox. The extensor pollicis brevis extends the metacarpophalangeal and carpometacarpal joints of the
thumb.
Like the abductor pollicis longus and extensor pollicis brevis, the tendon of the extensor pollicis longus
emerges between the extensor digitorum and the extensor carpi radialis brevis muscles. The tendon forms the
medial margin of the anatomical snuffbox at the wrist. The extensor pollicis longus extends all joints of the
thumb.
The extensor indicis muscle is an accessory extensor of the index finger. The tendon passes into the
hand and inserts into the extensor hood of the index finger with the tendon of the extensor digitorum.
Figure 2. Muscles in the posterior compartment of the forearm
http://virtual.yosemite.cc.ca.us/rdroual/Lecture%20Notes/Unit%203/muscles%20with%20figures.htm
2. ARTERIES
The blood supply to the posterior compartment of the forearm occurs predominantly through branches of the
radial, posterior interosseous, and anterior interosseous arteries.
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Dr. Kaan Yücel
http://yeditepeanatomy1.org
Posterior aspect of the forearm
POSTERIOR INTEROSSEOUS ARTERY
The posterior interosseous artery originates in the anterior compartment from the common interosseous
branch of the ulnar artery and passes into the posterior compartment of the forearm. It contributes a branch,
the recurrent interosseous artery, to the vascular network around the elbow joint. The posterior interosseous
artery terminates by joining the dorsal carpal arch of the wrist.
ANTERIOR INTEROSSEOUS ARTERY
The anterior interosseous artery, also a branch of the common interosseous branch of the ulnar artery, is
situated in the anterior compartment of the forearm on the interosseous membrane. The terminal end of the
anterior interosseous artery joins the posterior interosseous artery.
RADIAL ARTERY
The radial artery has muscular branches, which contribute to the supply of the extensor muscles on the radial
side of the forearm.
Figure 3. Arteries in the posterior compartment of the forearm – view from the anterior surface of the elbow
http://classconnection.s3.amazonaws.com/677/flashcards/1672677/jpg/elbow_collateral_circulation1342935496865.jpg
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Dr. Kaan Yücel
http://yeditepeanatomy1.org
Posterior aspect of the forearm
3. VEINS
Deep veins of the posterior compartment generally accompany the arteries. They ultimately drain into brachial
veins associated with the brachial artery in the cubital fossa.
4. NERVES
RADIAL NERVE
The nerve of the posterior compartment of the forearm is the radial nerve. Most of the muscles are
innervated by the deep branch, which originates from the radial nerve in the lateral wall of the cubital fossa
deep to the brachioradialis muscle and becomes the posterior interosseous nerve after emerging from
between the two heads of the supinator muscle in the posterior compartment of the forearm.
The deep branch innervates the extensor carpi radialis brevis, then supplies the supinator muscle and then
emerges, as the posterior interosseous nerve. The posterior interosseous nerve supplies the remaining muscles
in the posterior compartment.
Figure 4. Radial nerve in the posterior compartment of the forearm
Revised from http://www.eorthopod.com/content/radial-tunnel-syndrome
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Dr. Kaan Yücel
http://yeditepeanatomy1.org
Posterior aspect of the forearm
Table 1. Muscles of the superficial layer of the posterior compartment of the forearm
Muscle
Brachioradialis
Extensor carpi
radialis longus
(ECRL)
Extensor carpi
radialis brevis
(ECRB)
Extensor
digitorum
Extensor digiti
minimi (EDM)
Proximal Attachment
Proximal part of
supraepicondylar
ridge of humerus
Distal Attachment
Lateral surface of
distal end of
radius proximal to
styloid process
Distal part of
supraepicondylar
ridge of humerus
Base of 2nd
metacarpal
Base of 2nd and
3rd metacarpals
Lateral epicondyle of
humerus (common
extensor origin)
Four tendons, via
extensor hoods
into the into the
dorsal aspects of
the bases of the
middle and distal
phalanges of the
medial four digits
Extensor
expansion (hood)
of the 5th digit
Innervation
Radial nerve
before division into
superficial and deep
branches
Deep branch of
radial nerve
Posterior
interosseous
nerve
continuation of deep
branch of radial nerve
Main Action
Relatively weak
flexion of forearm;
maximal when
forearm is in
midpronated
position; an
accessory of flexor of
the elbow joint
Extend and abduct
hand at the wrist
joint; ECRL active
during fist clenching
Extends medial four
digits primarily at
metacarpophalangeal
joints, secondarily at
interphalangeal joints
; can also extend
the wrist
Extends the little
finger
Extensor carpi
ulnaris (ECU)
Base of the 5th
metacarpal
Extends and adducts
hand at wrist joint
(also active during
fist clenching)
Anconeus
Olecranon and
Radial nerve
proximal posterior
surface of ulna
Abduction of the ulna
in pronation;
accessory extensor of
the elbow joint;
assists triceps ine
extending forearm
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Dr. Kaan Yücel
http://yeditepeanatomy1.org
Posterior aspect of the forearm
Table 2. Muscles of the deep layer of the posterior compartment of the forearm
Muscle
Supinator
Proximal Attachment Distal Attachment Innervation
Superficial
Lateral surface of Deep branch of
(humeroulnar) head: radius superior to radial nerve
the anterior
 lateral epicondyle oblique line
of humerus
 radial collateral
and anular
ligaments
Muscle Action
Supinates forearm;
rotates radius to turn
palm anteriorly or
superiorly (if elbow is
flexed)
Deep (ulnar) head
Extensor indicis
Abductor pollicis
longus (APL)
Extensor pollicis
longus (EPL)
Extensor pollicis
brevis (EPB)
Supinator crest of the
ulna
Posterior surface of
distal 1/3 of ulna and
interosseous
membrane
Extensor
expansion (hood)
of 2nd digit
Posterior surface of
proximal halves of
ulna, radius, and
interosseous
membrane
Posterior surface of
middle third of ulna
and interosseous
membrane
Base of 1st
metacarpal
Posterior surface of
distal third of radius
and interosseous
membrane
Dorsal surface of
base of proximal
phalanx of the
thumb
Dorsal surface of
base of distal
phalanx of thumb
Posterior
interosseous
nerve
continuation of deep
branch of radial nerve
Extends 2nd digit
(enabling its
independent
extension); helps
extend hand at wrist
Abducts
carpometacarpal
joint of thumb;
accessory extensor of
the thumb
Extends distal
phalanx of thumb at
interphalangeal joint;
extends
metacarpophalangeal
and carpometacarpal
joints
Extends proximal
phalanx of thumb at
metacarpophalangeal
joint; extends
carpometacarpal
joint
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