Transcript Dissection of the Anterior Compartment of the Forearm

Dissection of the
Anterior Compartment
of the Forearm
Place the cadaver in the supine position. Make
a vertical skin incision down the center of the
anterior surface of the forearm from the
cubital fossa to the distal transverse crease of
the wrist. Incise the skin transversely across
the front of the wrist. Reflect the skin flaps
medially and laterally. Identify the cephalic
and basilic veins and the lateral and medial
cutaneous nerves of the forearm. Remove the
superficial fascia along the lines of the skin
incision.
Cut the bicipital aponeurosis and
remove the deep fascia of the
anterior compartment of the
forearm along the lines of the
skin incisions. Do not damage the
underlying structures.
Identify again the brachiordialis
muscle and confirm that it arises
from the upper two-thirds of the
lateral supracondylar ridge of the
humerus. This muscle is situated
in the lateral fascial compartment
of the forearm and will be
considered later.
Superficial Flexor muscles
Identify the following superficial
group of muscles in the anterior
fascial compartment and note that
they possess a common tendon
of origin which is attached to the
medial epicondyle of the
humerus. The muscles are named
as follows, from lateral to medial:
1. Pronator teres, with its humeral
and ulnar heads. 2. Flexor carpi
radialis. 3. Palmaris longus (not
always present). 4. Flexor carpi
ulnaris.
Now transect the humeral head of
the pronator teres as it crosses the
underlying median nerve. At the
same level, transect the bellies of
the flexor carpi radialis and the
palmaris longus muscles. The
flexor digitorum superficialis
muscle is now exposed.
Note that the pronator teres is supplied
by a branch of the median nerve that
arises in the cubital fossa. The flexor
carpi radialis and the palmaris longus are
supplied by branches of the median
nerve deep to the pronator teres. The
flexor carpi ulnaris is supplied by
branches of the ulnar nerve as it enters
the forearm by passing behind the medial
epicondyly of the humerus.
Intermediate Flexor Muscle. Study now the
flexor digitorum superficialis muscle. Note
that the humeroulnar head arises from the
common tendon attached to the medial
epicondyle of the humerus and the medial
margin of the coronoid process of the ulna; it
is also attached to the medial ligament of the
elbow joint. A radial head arises from the
oblique line on the anterior surface of the
shaft of the radius. Observe that the two heads
are connected by a fibrous arch beneath which
pass the median nerve and the ulnar artery.
Deep Flexor Muscles. Transect the distal
portion of the belly of the flexor
digitorum superficialis just proximal to
the tendons. Avoid cutting the median
nerve, which is bound to the deep
surface of the muscle with fascia. Reflect
the muscle and thus expose the deep
muscles in this compartment, namely, the
flexor pollicis longus, flexor digitorum
profundus, and pronator quadratus
muscles.
Now expose and clean the main
arteries
in
the
anterior
compartment.
The radial artery, one of the terminal branches of
the brachial artery, arises in the cubial fossa and
passes downward and laterally overlapped by
the brachioradialis muscle. Observe that in the
lower half of the forearm the radial artery
emerges
on
the
medial
side
of
the
brachioradialis tendon and then lies on the
lateral side of the tendon of the flexor carpi
radialis.
Here, the radial artery is covered only by skin
and fascia, and it rests posteriorly on the
anterior surface of the distal part of the radius.
Note that in the middle third of its course the
superficial branch of the radial nerve lies
lateral to it. The radial artery leaves the
forearm by winding around the lateral aspect
of the wrist to reach the posterior surface of
the hand.
Identify
the
following
branches of the radial artery:
1.Muscular branches to
neighnoring muscles.
2. Recurrent branch, which joins
the arterial anastomosis around the
elbow joint.
3. Superficial palmar branch,
which arises above the wrist and
enters the palm of the hand.
The ulnar artery, one of the terminal
branches of the brachial artery, arises
in the cubital fossa and passes
downward, deep to the superficial
flexor
muscles
and
digitorum superficialis.
the
flexor
At the wrist it emerges between the
tendon of the flexor carpi ulnaris and the
tendon of the flexor digitorum
superficialis muscle. Note that in the
lower two-thirds of its course the ulnar
nerve lies on the medial side of the
flexor digitorum superficialis muscle.
The ulnar artery enters the palm on the
lateral side of the pisiform bone.
Identify
the
following
branches of the ulnar artery:
1.Muscilar branches to neighboring
muscles.
2. Recurrent branches that join the
arterial anastomosis around the
elbow joint.
3. Anastomotic branches that take
part in the arterial anastomosis
around the wrist joint.
4. The common interosseous artery, which arises
from the upper part of the ulnar artery and
quickly divides into the anterior and posterior
interosseous arteries. The anterior interosseous
artery is small in size and should be followed
down the anterior surface of the interosseous
membrane between the flexor pollicis longus
and the flexor digitorum profundus.
Nerves of the Anterior
Compartment
Median nerve.
Now trace the course of the median nerve in the forearm.
The median nerve leaves the cubital fossa by passing
between the two heads of pronator teres. It continues
downward adherent to the posterior surface of the flexor
digitorum superficialis. At the wrist it emerges between the
lateral margin of the tendons of flexor digitorum
superficialis and the tendon of flexor carpi radialis. Here it
lies posterior to the palmaris longus tendon. The median
nerve enters the palm by passing posterior to the flexor
retinaculum.
Identify the following
branches of the median nerve.
1. Muscular branches in the cubital
fossa to the pronator teres, the flexor
carpi radialis, the palmaris longus,
and the flexor digitorum superficialis.
2. Articular branches to the
elbow joint.
3. Anterior interosseous nerve, which arises
from the median nerve as it emerges from
between the two heads of the pronator teres
muscle. It runs down on the anterior
surface of the interosseous membrane.
Trace branches from it to the flexor pollicis
longus, the lateral half of flexor digitorum
profundus, and the pronator quadratus.
4. Palmar cutaneous branch,
Which passes to the skin over the
lateral part of the palm.
Ulnar nerve.
The ulnar nerve enters the forearm from behin the medial
epicondyle of the humerus. Note that it crosses the medial
ligament of the elbow joint and passes between the two
heads of the flexor carpi ulnaris. Trace the nerve downward
between the flexor carpi ulnaris and the flexor digitorum
profundus muscles. At the wrist observe that the nerve lies
between the tendons of the flexor carpi ulnar and the flexor
digitorum superficialis muscles. The ulnar nerve enters the
palm lateral to the pisiform bone, anterior to the flexor
retinaculum.
Identify the following
branches of the ulnar nerve:
1. Muscular branches to the
flexor carpi ulnaris and to the
medial half of the flexor
digitorum profundus.
2. Articular branches to the
elbow joint.
3. Palmar cutaneous branch,
which arises in the middle of
the forearm and supplies the
skin over the hypothenar
eminence.
4. Dorsal branch, or posterior
cutaneous branch, which is large
and passes medially between the
tendon of flexor carpi ulnaris and
the ulna and is distributed on the
posterior surface of the hand and
fingers.
Dissection of the Posterior
Compartment of the Forearm
Clean the brachioradialis muscle and
verify that it arises from the upper twothirds of the lateral supracondylar ridge
of the humerus and from the adjoining
lateral intermuscular septum. Note that
its tendon is inserted into the base of the
styloid process of the radius.
Identify and clean the extensor
carpi radialis longus muscle and
note that it arises from the lower
third of the lateral supracondylar
ridge of the humerus and from
the adjoining laterl intermuscular
septum. Its tendon of insertion
will be examined later.
Radial Nerve. Review the course of
the radial nerve from the point where
it pierces the lateral intermuscular
septum and passes forward into the
cubital fossa. Note that at the level
of the lateral epicondyle the radial
nerve divides into superficial and
deep branches.
Identify and clean the
following branches of the
radial nerve:
1. Muscular branches to the
brachioradialis, to the extensor
carpi radialis longus, and to the
lateral part of the brachialis
muscle.
2. Articular branches to the elbow
joint.
3. Deep branches of the radial nerve.
The deep branch passes between the
superficial and deep layers of the
supinator muscle and enters the
forearm by winding round the neck
of the radius.
4. Superficial branch of the radial nerve,
which runs down the forearm beneath the
brachioradialis muscle. In the lower part of
the forearm, trace the nerve backward under
the tendon of the brachioradialis. It supplies
the skin on the dorsum of the hand and
dorsum of the lateral two and one-half
fingers.