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Transcript
FOREARM
The region of the upper limb
between the elbow and the wrist.
BAAB 18/04/2016
Introduction:
• The forearm is a portion/segment occupying the
central part on the distal aspect of the upper limb
between the arm and the hand.
• It is homologous to the region of the lower limb
(leg) that lies between the knee and the ankle joint.
• Discussion will involve the following:
–
–
–
–
–
Osteology
Joints of
Muscles
Blood supply
Nerves supply
OSTEOLOGY
•
The forearm contains two long bones, the radius and the
ulna, forming the radioulnar joints. The interosseous
membrane connects these bones to form the fibrous
intermediate radioulnar joint. Ultimately, the forearm is
covered by skin, the anterior surface usually being less
hairy than the posterior surface.
•
The distal portion of the humerus is reviewed as it
contributes in the formation of the elbow joint which is
highly involving the radius and ulna.
Osteology cont…..
Osteology cont……
Osteology cont…..
JOINTS
• The elbow joint:
– Type; synovial ball and socket and hinge joints
– Articular bones; the capitulum and trochlea of
humerus in the upper arm with the round head of
radius and the head of ulna in the forearm
respectively.
– It is also involving the superior radioulnar joint
sharing the joint capsule with the elbow joint but
plays no functional role at the elbow.
– The elbow region includes prominent landmarks
such as the olecranon (the bony prominence at the
very tip of the elbow), the elbow pit, and the lateral
and medial epicondyles.
Elbow joint cont…..
Joints cont…….
Joint cont…..
• The radioulnar joints:
i.
Superior R/U joint a synovial type of pivot
(articular surfaces are head of radius and radial
notch of the ulna.
ii. Intermediate R/U joint a fibrous syndemosis.
( between the two shafts joined by the
interosseous membrane)
iii. Inferior R/U joint a synovial type of pivot
(articular surfaces are the head of the ulna and
the ulnar notch of the radius).
Joint cont……
MUSCLES
• Muscles of the forearm are mainly extrinsic muscles of
the Hand as they are principle flexors and extensors of the
hand as well as pronators and supinators of the forearm.
• Forearm is divided into two muscular compartments;
anterior or flexor/pronator and posterior or
extensor/supinator compartments.
• There are many muscles in the forearm.
• In the anterior compartment, muscles are split into three
categories – superficial, intemediate and deep levels.
• In general, muscles in the anterior compartment of the
forearm perform flexion at the wrist and fingers, and
pronation of the forearm.
Muscles cont……..
• A crross-section of the forearm to show the muscular
compartments
Muscles cont……
•
Superficial level
The superficial muscles in the anterior compartment are the flexor
carpi ulnaris, palmaris longus, flexor carpi radialis and pronator
teres. They all originate from a common tendon called the common
flexor origin. This arises from the medial epicondyle of the humerus.
•
Intermediate level
The flexor digitorum superficialis is the only muscle of the
intermediate compartment. It can sometimes be classed as a superficial
muscle, but in most cadavers it lies between the deep and superficial
muscle layers.
•
Deep level
There are three muscles in the deep anterior forearm; flexor digitorum
profundus, flexor pollicis longus, and pronator quadratus.
muscles cont……
• Superficial flexor group of muscles
Muscles cont……..
• This is a lone intermediate flexor muscle (FDS)
Muscles cont……
Muscles cont……
• Important notes:
i. Superficial muscles arise from the CFO and
some
from the ulna, intermediate muscle has two heads –
humeral and radial heads, the deep muscles arise from the
radial of the forearm and interosseous membrane.
ii. Palmaris longus is absent in about 15% of
the population.
iii. The FDS muscle is a good anatomical landmark in the
forearm – the median nerve and ulnar artery pass between
its two heads, and then they travel posteriorly.
Muscles cont…….
iv. FDS and FDP are spliting into four tendons of insertion into the digits.
v. The cubital fossa: This is also known as elbow pit which is a
triangular area on the anterior view of the elbow of a human or other
hominid animal. It is also called the antecubital fossa because it lies
anteriorly to the elbow (latin cubitus) when in standard anatomical
position.
• Boundaries
-superior (proximal) boundary — an imaginary horizontal line
connecting the medial epicondyle to the lateral epicondyle of the
humerus
-medial (ulnar) boundary — lateral border of Pronator Teres
muscle originating from the medial epicondyle of the humerus.
Muscles cont…….
-lateral (radial) boundary — medial border of Brachioradialis muscle
originating from the lateral supraepicondylar ridge of the humerus.
-apex is directed inferiorly, and is formed by the meeting point of the
lateral and medial boundaries
-superficial boundary (roof)- skin, superficial fascia containing the
median cubital vein, the lateral cutaneous nerve of the forearm and
the medial cutaneous nerve of the forearm, deep fascia reinforced by
the bicipital aponeurosis (a sheet of tendon-like material that arises
from the tendon of the biceps brachii)
-deep boundary (floor)- brachialis and supinator muscles
Muscles cont….
•




Contents:
The contents of the cubital fossa include vessels, nerves and the
biceps tendon (lateral to medial) :
Radial nerve – This is not always strictly considered part of the
cubital fossa, but is in the vicinity, passing underneath the brachioradialis
muscle. As it does so, the radial nerve divides into its deep and superficial
branches.
Biceps tendon – It runs through the cubital fossa, attaching to the
radial tuberosity, just distal to the neck of the radius.
Brachial artery – The brachial artery supplies oxygenated blood the
forearm. It bifurcates into the radial and ulnar arteries at the apex
of the cubital fossa.
Muscles cont…..



Median nerve – Leaves the cubital between the two heads of the
pronator teres. It supplies the majority of the flexor muscles in
the forearm.
Median cubital vein – the median cubital vein (or median basilic
vein) is a superficial vein of the upper limb. It connects the basilic and
cephalic vein.
The bicipital aponeurosis – a tendon of biceps muscle which inserts
into the superficial fascia in the cubital fossa. The aponeurosis
reinforces the cubital fossa, and helps to protect the brachial artery and
the median nerve running under heath. This protection is important
during venipuncture (taking blood) from the median cubital vein.
Muscle cont…..
Muscles cont…..
• Clinical correlates
1. Brachial Pulse and Blood Pressure: The
brachial pulse palpation and measuring blood
pressure can be done immediately medial to the
biceps tendon in the cubital fossa. The
stethoscope must be placed there, to hear the
korotkoff sounds.
2. Venipuncture
The median cubital vein is located superficially
within the roof of the cubital fossa. It connects the
basilic and cephalic veins, and can be accessed
easily – this makes it a common site for
venipuncture.
Muscles cont…..
• Space of Parona.
This is a potential space between the pronator quadratus deep and
the overlying flexor tendons of the forearm that is continuous
through the carpal tunnel with the medial central palmar space.
It is also known as the sub-tendinous space of the wrist
- Pus in tendinous sheath in the hand can ascend in the radial bursa
and eventually rupture into this space;
- pus in little finger sheath can ascend in ulnar bursae and rupture
into this space of Parona;
- pus from thenar abscess or mid-palmar abscess may rupture into
space of Parona.
-if pus from either the radial or ulnar bursae ruptures into Parona’s
space, it can be drained by the same incision used for releasing pus
from the proximal end of the ulnar bursae.
Mucsle cont…..
3. Supracondylar Fractures
A supracondylar fracture of the humerus usually occurs by
falling on a flexed elbow. It is a transverse fracture, spanning
between the two epicondyles.
--The displaced fracture fragments may impinge and damage
the content of the cubital fossa.
--Direct damage, or post-fracture swelling can cause
interference to the blood supply of the forearm from
the brachial artery. The resulting ischaemia can
cause Volkmann’s ischaemic contracture – uncontrolled
flexion of the hand, as flexors muscles become fibrotic and
short.
--There also can be damage to the median or radial nerves.
Muscles cont…..
•
•
Muscles in the Posterior Compartment of the Forearm
The muscles in the posterior compartment of the forearm are
commonly known as the extensor supinator group of
muscles. The general function of these muscles is to produce
•
•
extension at the wrist and fingers and to supinate the forearm.
They are all innervated by the radial nerve.
Anatomically, the muscles in this compartment can be divided
into two layers; deep and superficial. These two layers are
separated by a layer of fascia.
Superficial layer: contains seven muscles. Four of these
muscles – extensor carpi radialis brevis, extensor digitorum,
extensor carpi ulnaris and extensor digiti minimi share a
common tendinous origin at the lateral epicondyle. This is a
common extensor origin
Muscle cont…..
•Deep Muscles --There are five muscles in the deep
compartment of the posterior forearm – the supinator,
abductor pollicis longus, extensor pollicis brevis, extensor
pollicis longus and extensor indicis.
--With the exception of the supinator, these muscles act on the
thumb and the index finger.
Muscle cont……
• Muscles of the
Posterior/extensor
Compartment of the
forearm
Muscle cont…..
• Important notes:
1. The brachioradialis is a paradoxical muscle. Its origin
and innervation are characteristic of a extensor muscle,
but it is actually a flexor at the elbow. The muscle is
most visible when the forearm is half pronated, and
flexing at the elbow against resistance.
2. Retinacular. These are fibrous bands found on both
anterior and posterior sides of the forearm. They are
special structures which hold down and in place the long
flexor and extensor muscles.
Extensor retinaculum
Extensor retinaculum
Muscle cont…..
3. Clinical correlates
-- Lateral epicondylitis (or tennis elbow) refers to inflammation of the
periosteum of the lateral epicondyle. The peak age of onset is 40-50
years old. It is caused by repeated use of the superficial extensor
muscles, which strains their common tendinous attachment to the
lateral epicondyle.
drop is a sign of radial nerve injury that has occurred proximal
• Wrist
to the elbow. There are two common characteristic sites of damage:
Axilla – injured via humeral dislocations or fractures of the proximal
humerus.
Radial groove of the humerus – injured via a humeral shaft fracture.
radial nerve innervates all muscles in the extensor compartment of
• The
the forearm. In the event of a radial nerve lesion, these muscles are
paralysed. The muscles that flex the wrist are innervated by the
median nerve, and thus are unaffected. The tone of the flexor muscles
produces unopposed flexion at the wrist joint – wrist drop.
BLOOD SUPPLY IN THE FOREARM
Arteries
•
•
•
•
Arteries run from the shoulder down to the wrist with just a
few branches given off near the elbow. Superficial and deep
veins return blood toward the heart. Following is a brief
overview:
Brachial artery: This artery stems from the axillary artery. It
runs along the anterior part of the arm, enters the cubital fossa,
and divides into the radial and ulnar arteries
Ulnar artery: This artery runs from the cubital fossa down the
anterior and medial portion of the forearm until it enters the
wrist.
Radial artery: This artery runs from the cubital fossa down
the anterior and lateral portion of the forearm until it enters the
wrist.
Blood supply………
Veins
• Cephalic and basilic veins: These veins provide
•
superficial venous return.
Brachial, radial, and ulnar veins: These veins are
deeper. They accompany the arteries of the same
names.
Blood supply
•
. It also has the following branches that form arterial anastomoses
(joined arteries) that supply the elbow:
– Deep artery of the arm (profunda brachii artery)
– Superior ulnar collateral artery
– Inferior ulnar collateral artery
Anastomosis around the elbow
There are 9 branches;
-- 4 descending branches
-- 4 ascending branches
-- communicating artery
Blood supply cont…..
• It is constituted by the following branches:
1. Superior ulnar collateral branch of brachial artery
2. Anterior branch of inferior ulnar collateral aa. of
brachial artery
3. Anterior and posterior branches of profunda brachii
artery.
4. Interosseous recurrent a branch of post. interosseous
aa. of ulnar artery
5. Radial recurrent branch of radial artery
6. Superior and inferior ulnar recurrent branches of ulnar
artery
7. A communicating aa. between post branch of inf. Ulnar
collateral and post radial collateral branch of brachial
artery.
NERVE SUPPLY OF THE FOREARM
nerves branch from the brachial plexus and travel through the
The
arm to supply the elbow and the forearm. Some of these nerves
continue through the forearm to supply the wrist and hand.
•
Median nerve: This nerve starts from the brachial plexus and runs
down alongside the brachial artery. It descends into the cubital fossa.
It gives off branches that serve the elbow joint and continues down
the anterior part of the forearm and into the hand through the carpal
tunnel.
•
Ulnar nerve: This nerve starts from the brachial plexus, passes
through the arm medial to the brachial artery, continues posterior to
the medial epicondyle of the humerus, and enters the forearm. It
travels along the medial part of the forearm until it enters the hand at
the wrist.
Nerves cont…..
•
Radial nerve: This nerve starts from the brachial plexus and
runs posterior to the brachial artery and anterior to the long
head of the triceps. It curves around the shaft of the humerus
and continues toward the cubital fossa. From there it branches
into the deep and superficial branches and continues down the
lateral part of the forearm to enter the hand.
•
Musculocutaneous nerve: This nerve runs from the brachial
plexus through the anterior part of the arm and becomes the
lateral cutaneous nerve of the forearm.