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Anatomy of The Forearm
Dr. Fadel Naim
Orthopedic Surgeon
Cubital Fossa
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The cubital fossa is the
triangular hollow area on the
anterior aspect of the elbow
The boundaries of the
cubital fossa are:
Superiorly
1.
An imaginary line connecting
the medial and lateral
epicondyles
Medially
2.
The pronator teres
Laterally
3.
The brachioradialis
• The floor of the cubital fossa formed by:
– The brachialis muscle
– Supinator muscles of the arm and forearm
• The roof of the cubital fossa is formed by:
– Deep fascia and reinforced by the:
» Bicipital aponeurosis
» Subcutaneous tissue
» Skin
The contents of the cubital fossa
1.
2.
Median nerve
Terminal part of the brachial artery and
bifurcation into
– The radial artery
– The ulnar artery
3. (Deep) accompanying veins of the arteries
4. Biceps brachii tendon
5. The deep and superficial branches of the
radial nerve are within the floor of the fossa.
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Median cubital vein, lying anterior to the
brachial artery
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Superficially, in the subcutaneous tissue overlying
the fossa
Medial and lateral antebrachial cutaneous
nerves related to the basilic and cephalic
veins.
Cubital Fossa
Venous layer
1 cephalic vein
2 basilic vein
3 median cubital vein
Aponeurotic layer
1 bicipital aponeurosis
2 biceps tendon
Artery-nerve layer
1 brachial artery
2 median nerve
Muscular floor
1 supinator
2 brachialis
3 biceps tendon
Cubital Fossa
venous layer
1 cephalic vein
2 basilic vein
3 median cubital vein
Aponeurotic layer
1 bicipital aponeurosis
2 biceps tendon
artery-nerve layer
1 brachial artery
2 median nerve
muscular floor
1 supinator
2 brachialis
3 biceps tendon
Cubital Fossa
venous layer
1 cephalic vein
2 basilic vein
3 median cubital vein
aponeurotic layer
1 bicipital aponeurosis
2 biceps tendon
Artery-nerve layer
1 brachial artery
2 median nerve
muscular floor
1 supinator
2 brachialis
3 biceps tendon
Cubital Fossa
venous layer
1 cephalic vein
2 basilic vein
3 median cubital vein
aponeurotic layer
1 bicipital aponeurosis
2 biceps tendon
artery-nerve layer
1 brachial artery
2 median nerve
Muscular floor
1 supinator
2 brachialis
3 biceps tendon
Cubital Fossa
•Bony floor
1 humerus
2 radius
3 ulna
Distal Humerus
• Medial epicondyle:
– The pronator and flexor muscles of the
forearm originate here
• Lateral epicondyle:
– The extensor and supinator muscles of
the forearm originate here
• Medial supracondylar ridge
• Lateral supracondylar ridge
• Trochlea (medial condyle):
– Articulates with the trochlear notch of
the ulna
• Capitulum (lateral condyle):
– Articulates with the radial head
Distal Humerus
• Coronoid fossa:
– Accommodates the coronoid process
of the ulna during flexion.
– A fat pad is situated here
• Radial fossa:
– Accommodates the head of the radius
during flexion.
– A fat pad is situated here
• Olecranon fossa:
– Accommodates the olecranon.
– A fat pad is situated here
• Groove for ulnar nerve
Radius
• The radius is the lateral and shorter of the two forearm
bones.
• Its proximal end consists of:
1. A short cylindrical (or thick disc like) head
» The smooth superior aspect of the head of the radius is concave for
articnlation with the capitulum of the hnmerus during flexion and extension
of the elbow joint.
» The head also articulates peripherally with the radial notch of the ulna
» The head is covered with articular cartilage.
2. A neck
» Relatively constricted between the head and the tuberosity.
3. A medially directed tuberosity
» The oval radial tuberosity separates the proximal end of the radius from the
body.
Radius
• The body of the radius has a lateral convexity and gradually and
progressively enlarges in girth as it passes distally
Radius
• The distal end of the radius is
essentially rectangular when
sectioned transversely.
• Its medial aspect forms a
concavity, the ulnar notch, which
accommodates the head of the
ulna.
• Extending from its lateral aspect
is the radial styloid process.
• The dorsal tubercle, (Lister’s)
projecting dorsally lies between
grooves for the passage of the
tendons of forearm muscles
• The radial styloid process is much
larger than the ulnar styloid process
and extends approximately a finger's
breadth further distally
• This relationship is of clinical
importance when the ulna and/or the
radius are fractured
Radius
radial tuberosity
head
styloid process
Ulna
• The stabilizing bone of the
forearm is the medial and longer
of the two forearm bones
• Its proximal end has two
prominent projections:
– The olecranon:
» projects proximally from its posterior
aspect
– The coronoid process
» Projects anteriorly.
The olecranon
• The olecranon is the most proximal
posterior eminence of the ulna
• It is on the dorsal subcutaneous border
and contains broad attachments for the
triceps posteriorly
• Anteriorly, the olecranon forms the
trochlear notch of the ulna, which
articulates with the trochlea
• The radial notch
– On the lateral side of the coronoid
process is a smooth, rounded
concavity, which articulates with the
head of the radius.
Ulna
• Inferior to the coronoid process is the
tuberosity of the ulna for
attachment of the tendon of the
Brachialis muscle.
• Inferior to the radial notch on the
lateral surface of the ulna is a
prominent ridge (the supinator
crest)
• Between it and the distal part of the
coronoid process is a concavity (the
supinator fossa)
• The deep part of the supinator
muscle attaches to the supinator
crest and fossa.
The body of the ulna is thick and cylindrical proximally, but it
tapers, diminishing in diameter as it continues distally
• At the narrow distal end of the ulna is a abrupt
enlargement forming a disclike head and a small,
conical styloid process.
• The articulation between the ulna and humerus allows
primarily only flexion and extension of the elbow
joint
• A small amount of abduction-adduction occurs during
pronation and supination of the forearm
styloid process
Ulna
trochlear notch
coronoid process
radial notch
olecranon process
head
styloid process
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A. Right radius
B. Right ulna
C. Left radius
D. Left ulna
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1. Proximal head
2. Neck
3. Radial tuberosity
4. Anterior oblique line
5. Interosseous border
6. Styloid process of radius
7. Ulnar notch
8. Olecranon process
9. Trochlear notch
10. Coronoid process
11. Ulnar tuberosity
12. Styloid process of ulna
13. Distal head
14. Distal neck
15. Radial notch
Colles’ fracture
• The ‘dinner fork’ deformity in this
fracture of the lower radius
• Caused by a fall on the outstretched
hand
Smith’s fracture
• A Smith’s fracture is a ‘reversed’ Colles’
fracture
• Often caused by a blow or fall on the
dorsum of the wrist.
• There may often be an associated fracture
of the ulnar styloid process.
Supracondylar fractures
• These fractures occur most commonly in
children between the ages of 6-9 years.
• These fractures may lead to vascular and
neurological complications
Olecranon Bursitis
"student's elbow"
• The subcutaneous olecranon bursa is exposed to
injury during:
– Falls on the elbow
– Infection from abrasions of the skin covering the
olecranon
– Repeated excessive pressure and friction
• Subtendinous olecranon bursitis is much less
common.
– Results from excessive friction between the triceps tendon
and olecranon resulting from repeated flexion-extension
of the forearm
• The pain is most severe during flexion of the
forearm because of pressure exerted on the
inflamed subtendinous olecranon bursa by the
triceps tendon.
Radial Head Fracture
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Radial head fractures
are generally caused by
longitudinal loading
from a fall on an
outstretched hand or
dislocation of the
elbow.
Olecranon Fractures
• Fracture of the olecranon commonly occur with a direct
blow or as an avulsion injury with triceps contracture
• The fractures generally are transverse or oblique in
orientation and enter the trochlear notch.
Fascial Compartment Of The Forearm
• Four interconnected
compartments of the forearm are
recognized
(1) the superficial volar compartment
(2) the deep volar compartment
(3) the dorsal compartment
(4) the lateral compartment
containing the mobile wad of
henry
» Brachioradialis
» Extensor carpi radialis longus
» Extensor carpi radialis brevis
Fascial
Compartment Of
The Forearm
• These fascial compartments are separated by an interosseous membrane
connecting the radius and ulna.
• The flexors and pronators of the forearm are in the anterior compartment and are
served mainly by the median nerve;
• The one and a half exceptions are innervated by the ulnar nerve.
• The extensors and supinators of the forearm are in the posterior compartment and are
all served by the radial nerve
• The proximal parts of the "anterior" (flexor-pronator)
compartment of the forearm lie anteromedially
• The posterior (extensor-supinator) compartment lies
posterolaterally
• The compartments become truly anterior and posterior in
position in the distal forearm and wrist.
• The anterior compartment of the forearm is exceptional
because it communicates with the central compartment
of the palm through the carpal tunnel
Compartment Syndrome
• TRUE ORTHOPEDIC EMERGENCY
• A condition characterised by raised pressure within a closed space
with a potential to cause irreversible damage to the contents of the
closed compartment
• Leads to muscle ischemia and necrosis.
• Compartment syndrome may result from
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A fracture
A soft-tissue injury
An arterial injury causing ischemia, necrosis, and edema
A burn
By external compression from immobilization
Compartment Syndrome
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Sings and symptoms the 6 “P’s”:
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Treatment
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Pain?
Paresthesias?
Paralysis?
Pallor?
Pulselessness?
poikilothermia (cool limb)?
Emergency fasciotomy
Decreases pressure by opening “closed space”
Often, will leave skin open because of severe swelling of
muscles
Delayed primary closure or secondary clousre
Volkmann's ischemic contracture
• If compartment syndrome is untreated or
inadequately treated, compartmental pressures
continue to rise until irreversible tissue
ischemia occurs.
• Volkmann ischemic contracture is the result of
several different degrees of tissue injury
• The earliest changes usually involve the flexor
digitorum profundus muscles in the middle
third of the forearm
• The typical clinical picture of established
volkmann contracture includes:
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Elbow flexion
Forearm pronation
Wrist flexion
Thumb adduction
Metacarpophalangeal joint extension
finger flexion
Flexor-Pronator Muscles of the Forearm
• In the anterior compartment of the forearm
• Separated from the extensor muscles by:
– The radius
– The ulna
– The interosseous membrane
• 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
– The flexor retinaculum
• The flexor muscles are arranged in four layers and are divided into three groups
– Superficial
– Intermediate
– Deep
• A superficial group of five muscles
1.
2.
3.
4.
5.
Pronator teres
Flexor carpi radialis
Palmaris longus
Flexor carpi ulnaris
Flexor digitorum superficialis [FDS] ( intermediate)
• These muscles all attach, at least in part, by a
common flexor tendon from the medial
epicondyle of the humerus the common flexor
attachment
• A deep group of three muscles:
1. Flexor digitorum profundus [FDP]
2. Flexor pollicis longus
3. Pronator quadratus
• All muscles in the anterior compartment of the forearm
are supplied by the median and/or ulnar nerves
• Functionally, the brachioradialis is a flexor of the forearm
• It is located in the posterior (posterolateral) or extensor
compartment
• It is supplied by the radial nerve
• A major exception to the rule that:
– The radial nerve supplies only extensor muscles
– All flexors lie in the anterior (flexor) compartment.
1. Pronator Teres
• Origin:
– Humeral head:
» Medial epicondyle
» Medial supracondylar ridge
» Medial intermuscular septum
– Ulnar head:
» Medial border of coronoid process
• Insertion:
– Middle of lateral surface of radius
– Just posterior to most prominent part of
lateral convexity of radius
• Innervatlon:
– Median nerve (C6 and C7)
• Action:
– Pronator of the forearm and a flexor of
the elbow joint.
Pronator Teres
• The pronator teres is prominent
when the forearm is strongly flexed
and pronated
• Its lateral border forms the medial
boundary of the cubital fossa.
• To test the pronator teres:
– The person's forearm is pronated from
the supine position against resistance
provided by the examiner.
– If acting normally, the muscle can be
seen and palpated at the medial margin
of the cubital fossa.
2. Flexor Carpi Radialis
• Origin:
– Medial epicondyle of humerus
• Insertion:
– Base of 2nd and 3rd metacarpal bone
• Innervation:
– Median nerve (C6 and C7)
• Action:
– Flexion (when acting with the flexor carpi
ulnaris)
– Abduction of the wrist (when acting with
the extensors carpi radialis longus and
brevis)
– A combination of flexion and abduction at
the wrist ( when acting alone )
Flexor Carpi Radialis
• Located medial to the pronator
teres.
• In the middle of the forearm, its
fleshy belly
• The tendon of the flexor carpi
radialis is a good guide to the
radial artery, which lies just lateral
to it
• To test the flexor carpi radialis:
– The person is asked to flex the wrist
against resistance.
– If acting normally, the tendon can be
easily seen and palpated.
3. Palmaris Longus
•Origin:
– Medial epicondyle of humerus
•Insertion:
– Distal half of flexor retinaculum
and palmar aponeurosis
•Innervation:
– Median nerve (C7 and C8)
•Action:
– Flexes hand (at wrist)
– Tightens palmar aponeurosis
Palmaris Longus
• This small fusiform muscle is absent on one or
both sides (usually the left) in approximately
10% of people, but its actions are not missed.
• The palmaris longus tendon 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.
• To test the palmaris longus:
– The wrist is flexed and the pads of the little finger
and thumb are pinched together.
– If present and acting normally, the tendon can be
easily seen and palpated.
4. Flexor Carpi Ulnaris
• Origin:
– Humeral head:
» medial epicondyle of humerus
– Ulnar head:
» olecranon and posterior border of ulna
• Insertion:
– Pisiform bone
– Hook of hamate bone
– 5th metacarpal bone
• Innervation:
– Ulnar nerve (C7 and C8)
• Action:
– Flexes and adducts the hand at the wrist simultaneously if acting alone.
– Flexes the wrist when it acts with the flexor carpi radialis
– Adducts it when acting with the extensor carpi ulnaris.
Flexor Carpi Ulnaris
• The most medial of the superficial flexor muscles.
• This muscle is exceptional among muscles of the anterior
compartment, being fully innervated by the ulnar nerve.
• The tendon of the flexor carpi ulnaris is a guide to the
ulnar nerve and artery, which are on its lateral side at the
wrist
• To test the flexor carpi ulnaris:
– The person is asked to put the posterior aspect of the
forearm and hand on a flat table.
– The person is then asked to flex the wrist against
resistance while the examiner palpates the muscle and
its tendon.
1. Flexor Digitorum Superficialis
• Origin:
– Humeroulnar head:
» Medial epicondyle of humerus
» Ulnar collateral ligament,
» Coronoid process of ulna
– Radial head:
» Superior half of anterior border of radius
• Insertion:
– Bodies of middle phalanges of medial four digits
• Innervation:
– Median nerve (C7, C8, and T1 )
• Action:
– Flexes middle phalanges at proximal interphalangeal joints
of medial four digits
– Acting more strongly, it also flexes proximal phalanges at
metacarpophalangeal joints and hand
Flexor Digitorum Superficialis
• The largest superficial muscle in the forearm.
• The FDS actually forms an intermediate
layer between the superficial and deep
groups of forearm muscles.
• The tendon to the middle and ring fingers
lays anterior to those of the index and little
fingers
• To test the FDS:
– 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 FDP.
Flexor Digitorum Profundus
• Origin:
– Proximal three-fourths of medial and anterior surfaces
of ulna
– Interosseous membrane
• Insertion:
– Bases of distal phalanges of medial four digits
• Innervation:
– Medial part ( the muscle serving digits 4 and 5 )
» Ulnar nerve (C8 and T1)
– Lateral part: ( the muscle serving digits 2 and 3 )
» Median nerve (C8 and T1 )
• Action:
– Flexes distal phalanges at distal interphalangeal
joints of medial four digits
– Assists with flexion of hand
Flexor Digitorum Profundus
• The FDP flexes the distal phalanges of the medial four digits after
the FDS has flexed their middle phalanges
• Each tendon is capable of flexing:
– Two interphalangeal joints
– Metacarpophalangeal joint
– The wrist joint
• The tendons of FDP pass posterior to the tendons of the FDS and the
flexor retinaculum.
• To test the FDP:
– 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
• Origin
– Anterior surface of radius and adjacent
interosseous membrane
• Insertion
– Base of distal phalanx of thumb
• Action
– Flexes phalanges of 1st digit (thumb
• Innervation
– Anterior interosseous nerve from median nerve (C8
and T1)
• The flexor pollicis longus is the only muscle
that flexes the interphalangeal joint of the
thumb.
• It also flexes:
– The metacarpophalangeal
– Carpometacarpal joints of the thumb
– May assist in flexion of the wrist joint.
• To test flexor pollicis longus
– The proximal phalanx of the thumb is held and the
distal phalanx is flexed against resistance.
Pronator Quadratus
• Origin
– Distal 1/4 of anterior surface of ulna
• Insertion
– Distal 1/4 of anterior surface of radius
• Action
– Pronates forearm; deep fibers bind radius
and ulna together
• Innervation
– Anterior interosseous nerve from median
nerve (C8 and T1)
Pronator Quadratus
• Cannot be palpated or observed because it is
the deepest muscle in the anterior aspect of the
forearm.
• The only muscle that attaches only to the ulna
at one end and only to the radius at the other
end.
• The prime mover in pronation.
• Initiates pronation
• Assisted by the pronator teres when more
speed and power are needed.
Radius and ulnar shaft fracture
Diagnosis
• It is important always to X-ray the whole shaft of both radius
and ulna and to include both the wrist and the elbow.
• Avoid missing:
 Monteggia fracture:
A dislocated head of radius with an isolated fracture of
the ulna
 Galeazzi fracture:
A dislocated distal radio-ulnar joint with an isolated
fracture of the radius
Radial Fracture
• Radius fracture proximal to
the insertion of pronator
teres muscle
– The supinator and biceps
brachii muscles supinate the
proximal fragment and draw
it laterally.
– The pronator teres and
pronator quadratus muscles
pronate the distal fragment
and draw it medially.