ANATOMY: FOREARM
ANATOMY:FOREARM
ANATOMY:
FOREARM
•Extension: elbow
(functionally, distal humerus) to wrist
•Bones:
ulnar connected by interosseus membrane to the radius
•Movements:
flexor-pronation and extension-supination
•Compartments: anterior and posterior muscles with bulk
proximal while their tendons are distal (operative site)
•Attachments: muscles
attached to medial epicondylar ridge act are
flexors; muscles attached to lateral epicondylar ridge are extensors
FOREARM
Spiraling
gradually over the length of the forearm, the compartments become truly
anterior and posterior in position in the distal forearm and wrist
Because
neither boundary is crossed by motor nerves, they also provide sites for
surgical incision
Innervation:
Flexor-pronator muscles (median nerve and ulna nerve except brachioradialis supplied by the
radial nerve); extensor-supinator muscles (radial nerve)
FOREARM
Fascia:
ends at the joints; therefore, containing fluids and infections and cannot
readily spread to other compartments
The
anterior compartment is an exception because it communicates with the central
compartment of the palm through the carpal tunnel
Muscle:
The flexor muscles of the anterior compartment have approximately twice the
bulk and strength of the extensor muscles of the posterior compartment
FLEXOR-PRONATOR MUSCLES
The
tendons of most flexor muscles are located on the anterior surface of the wrist
and are held in place by the palmar carpal ligament and the flexor retinaculum
(transverse carpal ligament), thickenings of the antebrachial fascia
Layers:
3- superficial (pronator teres,
flexor carpi radialis, palmaris longus, and flexor carpi ulnaris), intermediate
(flexor digitorum superficialis) and deep
(flexor digitorum
profundus, flexor pollicis longus, and pronator quadratus)
FLEXOR-PRONATOR MUSCLES
The
five superficial and intermediate muscles cross the elbow joint; the three deep
muscles do not. With the exception of the pronator quadratus
The
more distally placed a muscle's distal attachment lies, the more distally and
deeply placed is its proximal attachment
The
long flexors of the digits (flexor digitorum superficialis and flexor digitorum profundus) also flex the metacarpophalangeal and wrist joint
FLEXOR-PRONATOR MUSCLES
The
flexor digitorum profundus flexes the fingers in slow action; this action is
reinforced by the flexor digitorum superficialis when speed and flexion against
resistance are required.
Tendons
of the long flexors of the digits pass through the distal part of the forearm,
wrist, and palm and continue to the medial four fingers. The flexor digitorum
superficialis flexes the middle phalanges, and the flexor digitorum profundus
flexes the distal phalanges.
PRONATOR TERES
It
is a fusiform muscle which is the most lateral of the superficial forearm
flexors. Its lateral border forms the medial boundary of the cubital fossa.
Test:
the person's forearm is flexed at the elbow and pronated from the supine
position against resistance provided by the examiner. If acting normally, the
muscle is prominent and can be palpated at the medial margin of the cubital
fossa.
FLEXOR CARPI RADIALIS
•FCR is a long
fusiform muscle located medial to the pronator teres
•Movement: flexion
(with the flexor carpi ulnaris), abduction of the
wrist (with the extensors carpi radialis longus and brevis), alone,FCR produces a
combination of flexion and abduction simultaneously at the wrist so that the
hand moves anterolaterally
•The FCR tendon is a
good guide to the radial artery, which lies just lateral to it
•Test: the person is
asked to flex the wrist against resistance. If acting normally, its tendon can
be easily seen and palpated
PALMARIS LONGUS
•Fusiform muscle with
a short belly and a long, cord-like tendon that passes superficial to the
flexor retinaculum and attaches to it and the apex of the palmar aponeurosis
•It is a useful guide
to the median nerve at the wrist; the tendon lies deep and slightly medial to
this nerve before it passes deep to the flexor retinaculum.
•Test: the wrist is
flexed and the pads of the little finger and thumb are tightly pinched
together. If present and acting normally, the tendon can be easily seen and
palpated.
•
FLEXOR CARPI ULNARIS
•FCU is the most
medial of the superficial flexor muscles
•Movement: flexes and
adducts the hand at the wrist if acting alone, wrist flexion with FCR and
adducts it extensor carpi ulnaris
•The ulnar nerve
enters the forearm by passing between the humeral and the ulnar heads of its
proximal attachment. It is fully innervated by the ulnar nerve; the tendon of
the FCU is a guide to the ulnar nerve and artery, which are on its lateral side
at the wrist.
•Test: the person puts
the posterior aspect of the forearm and hand on a flat table and is then asked
to flex the wrist against resistance while the examiner palpates the muscle and
its tendon.
•
FLEXOR DIGITORUM SUPERFICIALIS
•FDS is often included
with the superficial muscles of the forearm. When considered this way, it is
the largest superficial muscle in the forearm. However, it is intermediate. The
median nerve and ulnar artery enter the forearm by passing between its humeroulnar and radial heads
•Movement: flexes the
middle phalanges of the medial four fingers at the proximal interphalangeal joints, flexes the
proximal phalanges at the metacarpophalangeal joints and the wrist joint, it is capable of flexing
each finger it serves independently.
•Test: one finger is
flexed at the proximal interphalangeal joint against
resistance and the other three fingers are held in an extended position to
inactivate the flexor digitorum profundus.
•
FLEXOR DIGITORUM PROFUNDUS
•FDP is the only
muscle that can flex the distal interphalangeal joints of the fingers
•Movement: flexes the
distal phalanges of the medial four fingers after the FDS has flexed their
middle phalanges (i.e., it curls the fingers and assists with flexion of the
hand, making a fist), it can flex only the index finger independently; thus the
fingers can be independently flexed at the proximal but not the distal interphalangeal joints.
•Test: the proximal interphalangeal joint is held in the
extended position while the person attempts to flex the distal interphalangeal joint. The integrity
of the median nerve in the proximal forearm can be tested by performing this
test using the index finger, and that of the ulnar nerve can be assessed by
using the little finger.
FLEXOR POLLICIS LONGUS
•FPL is lateral to the
FDP, where it clothes the anterior aspect of the radius distal to the
attachment of the supinator.
•Movement: primarily
flexes the distal phalanx of the thumb at the interphalangeal joint and, secondarily, the proximal phalanx and 1st
metacarpal at the metacarpophalangeal and carpometacarpal
joints, respectively, it is the only muscle that flexes the interphalangeal joint of the thumb.
It also may assist in flexion of the wrist joint.
•To test the flexor pollicis longus, the proximal
phalanx of the thumb is held and the distal phalanx is flexed against
resistance.
PRONATOR QUADRATUS
It
is quadrangular and pronates the forearm. It cannot be palpated or observed,
except in dissections, because it is the deepest muscle in the anterior aspect
of the forearm.
Movement:
it is the prime mover for pronation. The muscle initiates pronation; it is
assisted by the pronator teres when more speed and power are needed. The
pronator quadratus also helps the interosseous membrane hold the radius and
ulna together, particularly when upward thrusts are transmitted through the
wrist (e.g., during a fall on the hand).
EXTENSOR MUSCLES
•Groups: 3- Muscles
that extend and abduct or adduct the hand at the wrist joint (extensor carpi radialis longus, extensor carpi radialis brevis, and extensor carpi ulnaris), Muscles
that extend the medial four fingers (extensor digitorum, extensor indicis, and extensor digiti minimi), Muscles
that extend or abduct the thumb (abductor pollicis longus, extensor pollicis brevis, and extensor pollicis longus).
•The extensor tendons
are 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 provided with synovial
tendon sheaths that 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
EXTENSOR MUSCLES
•Anatomical layers: superficial
and deep. Four of the
superficial extensors (extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, and extensor carpi ulnaris) are attached
proximally by a common extensor tendon to the lateral epicondyle
•The proximal
attachment of the other two muscles in the superficial group (brachioradialis and extensor carpi radialis longus) is to the lateral supraepicondylar ridge of the humerus and adjacent lateral
intermuscular septum. The four
flat tendons of the extensor digitorum pass deep to the extensor retinaculum to the medial
four fingers. The common tendons of the index and little fingers are joined on
their medial sides near the knuckles by the respective tendons of the extensor indicis and extensor digiti minimi (extensors of the
index and little fingers, respectively).
•
BRACHIORADIALIS
Fusiform
muscle, lying superficially on the anterolateral surface of the forearm; forms
the lateral border of the cubital fossa. It flexes the forearm at the elbow. It
is especially active during quick movements or in the presence of resistance
during flexion of the forearm.
The brachioradialis and the supinator are the
only muscles of the compartment that do not cross and therefore are incapable
of acting at the wrist. As it descends, the brachioradialis overlies the radial
nerve and artery where they lie together on the supinator, pronator teres
tendon, FDS, and FPL. The distal part of the tendon is covered by the abductors
pollicis longus and brevis as they pass to the thumb.
Test:
the elbow joint is flexed against resistance with the forearm in the midprone
position. If the brachioradialis is acting normally, the muscle can be seen and
palpated.
EXTENSOR CARPI RADIALIS LONGUS
ECRL
is a fusiform muscle overlapped by the brachioradialis, with which it often
blends. As it passes distally, posterior to the brachioradialis, its tendon is
crossed by the abductor pollicis brevis and extensor pollicis brevis. The ECRL
is indispensable when clenching the fist
Test
the wrist is extended and abducted with the forearm pronated. If acting
normally, the muscle can be palpated inferoposterior to the lateral side of the
elbow. Its tendon can be palpated proximal to the wrist
EXTENSOR CARPI RADIALIS BREVIS
ECRB
and ECRL pass under the extensor retinaculum together within the tendinous
sheath of the extensor carpi radiales
When
the two muscles act by themselves, they abduct the hand as they extend it.
Acting with the extensor carpi ulnaris, they extend the; acting with the FCR
they produce pure abduction. Their synergistic action with the extensor carpi
ulnaris is important in steadying the wrist during tight flexion of the medial
four fingers (clenching a fist), a function in which the longus is more active
EXTENSOR DIGITORUM
It
is the principal extensor of the medial four fingers occupying much of the
posterior surface of the forearm. Normally no finger can remain fully flexed as
the other ones are fully extended. Commonly, the fourth tendon is fused
initially with the tendon to the ring finger and reaches the little finger by a
tendinous band.
Test:
the forearm is pronated and the fingers are extended. The person attempts to
keep the fingers extended at the metacarpophalangeal joints as the examiner
exerts pressure on the proximal phalanges by attempting to flex them. If acting
normally, the extensor digitorum can be palpated in the forearm, and its
tendons can be seen and palpated on the dorsum of the hand.
EXTENSOR DIGITI MINIMI
EDM,
a fusiform slip of muscle, is a partially detached part of the extensor
digitorum. The tendon of this extensor of the little finger runs through a
separate compartment of the extensor retinaculum, posterior to the distal
radioulnar joint, within the tendinous sheath of the extensor digiti minimi.
The tendon then divides into two slips; the lateral one is joined to the tendon
of the extensor digitorum, with all three tendons attaching to the dorsal
digital expansion of the little finger. After exerting its traction primarily
on the 5th finger, it contributes to extension of the hand.
EXTENSOR CARPI ULNARIS
ECU,
a long fusiform muscle medially located, has 2 heads: a humeral head and an
ulnar head
Acting
with the ECRL and ECRB, it extends the hand; acting with the FCU, it adducts
the hand. Like the ECRL, it is indispensable when clenching the fist.
Test:
the forearm is pronated and the fingers are extended. The extended wrist is
then adducted against resistance. If acting normally, the muscle can be seen
and palpated in the proximal part of the forearm and its tendon can be felt
proximal to the head of the ulna.
SUPINATOR
It
lies deep in the cubital fossa and, along with the brachialis, forms its floor
The
deep branch of the radial nerve passes between the humeral and ulnar heads as
it leaves the cubital fossa to enter the posterior part of the arm thereby
forming the posterior interosseus nerve. The supinator rotates the radius
The
deep extensors of the forearm act on the thumb and the index finger (extensor
indicis). The three muscles acting on the thumb are referred to as outcropping
muscles
ABDUCTOR POLLICIS LONGUS
APL
is fusiform and lies just distal to the supinator and is closely related to the
EPB
It
acts with the APB during abduction of the thumb and with the extensor pollicis
muscles during extension of this digit
Test:
the thumb is abducted against resistance at the metacarpophalangeal joint. If
acting normally, the tendon of the muscle can be seen and palpated at the
lateral side of the anatomical snuff box and on the lateral side of the
adjacent extensor pollicis brevis tendon.
EXTENSOR POLLICIS BREVIS
In
continued action after acting to flex the proximal phalanx of the thumb, or
acting when that joint is fixed by its antagonists, it helps extend the 1st
metacarpal and extend and abduct the hand. When the thumb is fully extended, a
hollow called the anatomical snuff box, can be seen on the radial aspect of the
wrist
Test:
the thumb is extended against resistance at the metacarpophalangeal joint. If
the EPB is acting normally, the tendon of the muscle can be seen and palpated
at the lateral side of the anatomical snuff box and on the medial side of the
adjacent APL tendon
EXTENSOR POLLICIS LONGUS
The
tendon passes under the extensor retinaculum in its own tunnel, within the
tendinous sheath of the extensor pollicis longus, medial to the dorsal tubercle
of the radius. It uses the tubercle as a trochlea (pulley) to change its line
of pull as it proceeds to the base of the distal phalanx of the thumb. The gap
thus created between the long extensor tendons of the thumb is the anatomical
snuff box. The EPL also adducts the extended thumb and rotates it laterally.
EXTENSOR POLLICIS LONGUS
To
test the extensor pollicis longus, the thumb is
extended against resistance at the interphalangeal joint. If the EPL is acting normally, the tendon of the
muscle can be seen and palpated on the medial side of the anatomical snuff box.
The
tendons of the APL and EPB bound the anatomical snuff box anteriorly, and the tendon of
the EPL bounds it posteriorly. The snuff box is
visible when the thumb is fully extended; this draws the tendons up and
produces a triangular hollow between them. Observe that the:
Radial
artery lies in the floor of the snuff box.
Radial
styloid process can be
palpated proximally and the base of the 1st metacarpal can be palpated distally
in the snuff box.
EXTENSOR INDICIS
The
extensor indicis has a narrow,
elongated belly that lies medial to and alongside that of the EPL. This muscle
confers independence to the index finger in that the extensor indicis may act alone or
together with the extensor digitorum to extend the index finger at the proximal interphalangeal joint, as in
pointing. It also helps extend the hand.
ARTERIES OF THE FOREARM
VEINS OF THE FOREARM
NERVES OF THE FOREARM
NEUROVASCULAR STRUCTURES OF THE FOREARM
CLINICAL ANATOMY
Elbow
Tendinitis or Lateral Epicondylitis
Mallet
or Baseball Finger
Fracture
of the Olecranon
Synovial
Cyst of the Wrist
Median
Nerve Injury
Pronator syndrome
Ulnar and radial Nerve
Injury
SURFACE ANATOMY
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