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Muscles, Innervation and the Compartments of the Upper Limb Organized in an Unintentionally Difficult Manner
Fascia and compartments of the shoulder
PECTORALIS FASCIA - The only contents is Pectoralis Major; - Pectoralis fascia continue inferiorly as fascia of the anterior abdominal wall - It continues laterally-once it leaves the lateral edge of Pectoralis Major, it becomes AXILLARY FASCIA
AXILLARY FASCIA
- Continuous with the CLAVIPECTORAL FASCIA - Forms the floor of the axilla
CLAVIPECTORAL FASCIA
- Deep to the Pectoralis major muscle, the CLAVIPECTORAL FASCIA invests the subclavius muscle and pectoralis minor. - It forms the costocoracoid membrane above pectoralis minor, and the suspensory ligament of axilla below pectoralis
minor. The suspensory ligament drags the axillary fascia upwards when the arm is raised, forming the actual “pit” of the armpit -
Supraspinous, Infraspinous and Subscapular fascia - The supraspinatus, infraspinatus and subscapularis muscles are contained in their own little fascial compartments
Deltoid Fascia
- The deltoid has its own fascia, continous with the pectoral fascia and infraspinatus fascia - It has numerous fascial septa which separate the fascicles of the deltoid
Clavicle
Subclavius
Axillary fascia
Costocoracoid membrane
Axillary fascia
Pectoralis minor
Suspensory ligament of axilla
Lateral pectoral nerve
Pectoralis major, wrapped
up in pectoralis fascia
Supraspinatus
fascia
Subscapularis
fascia
Infraspinatus fascia
Spine of scapula
Clavicle
Pectoralis fascia
Deltoid fascia
Infraspinatus fascia
Fascial septa
Pectoralis fascia, infraspinatus fascia and deltoid fascia all continue down the arm to form the brachial fascia
and Thoracoacromial artery
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Anterior Axioappendicular Muscles of the Shoulder There are 3 distinct groups of shoulder muscles: ANTERIOR AXIOAPPENDICULAR MUSCLES – 4 muscles which move the pectoral girdle POSTERIOR AXIOAPPENDICULAR MUSCLES – 4 muscles which attach the upper lumb to the skeleton of the trunk
SCAPULOHUMERAL MUSCLES – 6 muscles which act on the glenohumeral joint
Anterior Axioappendicular muscles All supplied by stupidly different nerves. No pattern whatsoever.
Pectoralis Major Two heads:
- CLAVICULAR HEAD: lateral pectoral nerve
o Originates from the medial half of the anterior clavicle
- STERNOCOSTAL HEAD: medial pectoral nerve
o Originates from the anterior surface of the sternum, and the first 6 costoclavicular cartilages
o Also originates from the aponeurosis of the external oblique muscle of the abdomen
- INSERTS INTO THE LATERAL LIP OF THE INTERTUBERCULAR GROOVE OF THE HUMERUS
- Its inferior border forms the anterior axillary fold
o Abducts and medially rotates the humerus
o Draws scapula anteriorly and inferiorly by pulling on the humerus
- The heads can act independently:
o Clavicular head alone acts to flex the humerus
o When flexed, the sternocostal head extends it from its flexed position.
Pectoralis Minor medial pectoral nerve
- Originates at the 3rd, 4th and 5th ribs near the costal cartilages
- Inserts into the medial border and superior surface of the coracoid process of scapula
- Its job is to stabilize the scapula by pulling it anteriorly and inferiorly against the chest wall
- It also assists in elevating the ribs when breathing
- All the vessels and nerves to the arm travel under the pectoralis minor.
Subclavius nerve to subclavius
- Originates at the junction of the 1st rib and its costal cartilage - Inserts into the “groove for subclavius” on the inferior surface
of the middle third of the clavicle - Depresses and anchors the clavicle - Protects the subclavian vessels when the clavicle is fractured
Serratus anterior long thoracic nerve - Originates from the lateral surfaces of the first 8 ribs - Inserts into the medial border of scapula - Protracts the scapula, holds it against the chest wall, and
rotates it superiorly (eg when reaching for something up high). THE MAIN PROTRACTOR OF THE SCAPULA
- One of the most powerful muscles in the pectoral girdle. - Its paralysis causes a winged scapula. Also, the arm cannot be
abducted past the horizontal position (the scapula doesn’t rotate upwards anymore)
- If you insert your chest drain BELOW the mid-axillary line, you will cause this sort of paralysis, which is embarrassing.
.
Innervation
Pectoralis Major :
clavicular head
Pectoralis major:
sternocostal head
Intertubercular groove
of the humerus
Pectoralis Minor Subclavius
Serratus Anterior
Long Thoracic Nerve:
Off the roots of C5, 6 and 7
Serratus Anterior
Nerve to Subclavius:
Off the superior trunk
Subclavius
Medial Pectoral nerve:
Branch of the medial cord
Pectoralis Minor; sternocostal head of Pectoralis Major
Lateral Pectoral nerve:
Branch of the lateral cord
clavicular head of Pectoralis Major
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Posterior Axioappendicular Muscles of the Shoulder: the Extrinsic Group There are 2 layers, the superficial and the deep. The superficial group is trapezius and latissimus dorsi The deep group is the levator scapulae and the rhomboids
Posterior Axioappendicular Extrinsic Muscles Also supplied by confusingly different nerves.
Trapezius spinal accessory nerve - Originates from
o The external occipital protuberance
o Nuchal ligament o Medial third of superior nuchal line
o Spinous processes of C spine and T-spine
o he medial half of the anterior clavicle
- Inserts into : o Lateral third of the clavicle
o Acromion of scapula
o Spine of scapula
- Has 3 distinct parts: SUPERIOR (descending)part which elevates
the scapula
MIDDLE part which retracts the scapula
INFERIOR (ascending) part which depresses the scapula
All the parts together act to rotate the scapula superiorly, so the glenoid fossa faces up.
Latissimus dorsi Thoracodorsal nerve
- Originates from
o Inferior 6 thoracic vertebrae o Thoracolumbar fascia o Iliac crest o Inferior 3 or 4 ribs
- Inserts into the ANTERIOR surface of the humerus, at the floor of the intertubrercular groove
- Extends, adducts, medially rotates the humerus
- Lifts the body up too the arms when climbing
Levator scapulae dorsal scapular and cervical nerves
- Originates at the posterior tubercles of the spinous processes of the C1, 2, 3 and 4 vertebrae
- Inserts into the medial border of scapula, superior to the spine - Elevates that corner of the scapula, rotating it so the glenoid
cavity faces down - Extends the neck (when acting bilaterally) or flexes it laterally
(when acting unilaterally)
Rhomboid Minor dorsal scapular nerve - Originates from the nuchal ligament and the spinous processes
of C7 and T1 - Inserts into the medial border of the scapula, at the root of the
scapular spine - Retracts the scapula - Rotates the scapula so the glenoid cavity faces down - Fixes the scapula to the thoracic wall
Rhomboid Major dorsal scapular nerve
- Originates from the spinous processes of T2,3 4and 5 - Inserts into the medial border of the scapula, from the root of
spine down. - Retracts the scapula - Rotates the scapula so the glenoid cavity faces down - Fixes the scapula to the thoracic wall
.
Viewed from above
Floor of the intertubercular
groove, anteriorly on the
humerus
Superior part of
Trapesius
Middle part of
Trapesius
Middle part of
Trapesius
T7
Latissimus dorsi
Innervation
Levator scapulae
Rhomboid Minor
Rhomboid Major
Dorsal scapular nerve:
Off the roots of C5
Rhomboid major and minor Levator scapulae
Thoracodorsal Nerve:
Off the posterior cord
Latissimus dorsi
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Posterior Axioappendicular Muscles of the Shoulder: the Intrinsic Group with Rotator Cuff muscles These are the deltoid and teres major; and the 4 rotator cuff muscles (teres minor, supraspinatus, infraspinatus and subscapularis)
Posterior Axioappendicular Intrinsic muscles Again, supplied by totally different nerves.
Deltoid axillary nerve
- Originates from the lateral third of the clavicle, the acromion, and the lateral spine of scapula.
- Inserts into the deltoid tuberosity of humerus - THREE PARTS:
o Anterior part flexes and medially rotates the humerus
o Middle part abducts the humerus o Posterior part extends and laterally rotates the
arm o The middle part is multipennate; the others are
unipennate - It cannot initiate abduction on its own when the arm is fully
adducted- thus it needs supraspinatus to initiate the movement. It becomes effective after about 15 degrees of abduction.
- The deltoid’s anterior and posterior parts swing your arms while walking.it also helps to keep the humeral head in the glenoid fossa.
Teres major lower subscapular nerve
- Originates from the posterior surface of the inferior angle of scapula
- Inserts into the medial lip of the intertubercular groove of humerus
- Adducts and medially rotates the arm - Also keeps the head of humerus in the socket
Rotator Cuff Muscles Whatever other actions they may have, they all help hold the humeral head in the glenoid fossa
Supraspinatus suprascapular nerve - Originates in the supraspinous fossa of the scapula - Inserts into the superior facet of the greater tubercle of
humerus - Initiates abduction, and assists the deltoid with abduction of
the arm; its the only one that doesn't rotate the arm.
Infraspinatus suprascapular nerve - Originates in the infraspinous fossa of the scapula - Inserts into the middle facet of the greater tubercle of
humerus - Laterally rotates the arm
Teres Minor axillary nerve
- Originates from the middle of the lateral border of scapula - Inserts into the inferior facet of the greater tubercle of
humerus - Laterally rotates the arm
Subscapularis upper and lower subscapular nerves - Originates in the subscapular fossa - Inserts into the lesser tubercle of humerus - Medially rotates and abducts the arm
.
Innervation
Deltoid
Supraspinatus
Subscapularis
Teres Major
Iinsertion of deltoid, at the
Deltoid Tuberosity
Infraspinatus
Teres Minor
Deltoid
Supraspinatus
Subscapularis
Deltoid
Infraspinatus
Teres Major Teres Minor
Teres Major
Axillary nerve:
Off the posterior cord
Teres Minor Deltoid
Upper Subscapular nerve
Subscapularis Lower Subscapular nerve
Subscapularis Teres major
Suprascapular nerve
Supraspinatus Infraspinatus
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Muscles and Nerves involved in the movements of the shoulder joint
flexion: pectoralis major (clavicular head) – medial and lateral pectoral nerve deltoid (anterior part) – axillary nerve coracobrachialis – musculocutaneous nerve biceps femoris– musculocutaneous nerve
extension: deltoid (posterior part) – axillary nerve teres major– lower subscapular nerve
abduction: deltoid (central part) – axillary nerve supraspinatus– suprascapular nerve
adduction: pectoralis major – medial and lateral pectoral nerve
latissimus dorsi – thoracodorsal nerve
subscapularis - upper and lower subscapular nerve
infraspinatus – suprascapular nerve
teres minor– axillary nerve
medial rotation: subscapularis
pectoralis major –medial and lateral pectoral nerve
deltoid (anterior part) – axillary nerve
latissimus dorsi – thoracodorsal nerve
lateral rotation: infraspinatus – suprascapular nerve long head of triceps – radial nerve coracobrachialis – musculocutaneous nerve short head of biceps – musculocutaneous nerve
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Fascia and compartments of the proximal arm
Posterior Compartment: EXTENSORS
- Triceps Brachii - Anconeus
- Radial nerve - Deep artery of the arm (profunda brachii)
(A branch of the brachial artery)
- Superior ulnar collateral artery
- Ulnar nerve as depicted here is in the posterior
compartment; it travels anteriorly to the medial intermuscular septum, until it pierces it about half-way down the humerus, together with the superior ulnar collateral artery
Anterior Compartment: FLEXORS
- Biceps Brachii - Brachialis - Coracobrachialis - Median nerve - Musculocutaneous nerve
The medial cutaneous nerve of forearm is not inside
the fascial sheath, but is still important enough to warrant a brief mention.
- The Basilic vein and the Cephalic vein are usually superficial to the fascial planes
.
Brachial Fascia - Encloses the upper arm like a sleeve - Superiorly, it is continuous with the deltoid fascia,
infraspinatus fascia and pectoralis fascia - Inferiorly, it is attached to the epicondyles of the
humerus and the olecranon of ulna - It is continuous with the antebrachial fascia – the
fascia of the forearm o It contains two SEPTA: the MEDIAL and
LATERAL INTERMUSCULAR SEPTA. o The septa are attached to the supracondylar
ridges and to the shaft of humerus o They separate the arm into the
ANTERIOR COMPARTMENT and the POSTERIOR COMPARTMENT
Section at a level just short of half-way along the humeris
Anterior compartment
Posterior compartment
Medial intermuscular septum
Lateral intermuscular septum
Deltoid:
Not actually a part of the anterior
compartment, as it has its own
fascial compartment.
Lateral
intermuscular
septum
Cephalic vein Biceps brachii
Triceps brachii
Musculocutaneous nerve
Median nerve
Basilic vein
Brachial artery
Coracobrachialis
Brachialis
Medial
intermuscular
septum
Supplied by the MUSCULOCUTANEOUS NERVE
Ulnar nerve
Radial nerve
Superior ulnar collateral artery
Deep artery of the arm Lateral intermuscular septum
Supplied by the RADIAL NERVE
Medial intermuscular septum
Medial cutaneous
nerve of forearm
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The innervation and mechanics of the flexor and extensor muscle compartments of the arm
Anterior Compartment: FLEXORS All supplied by the MUSCULOCUTANEOUS NERVE
Biceps Brachii Two heads:
- SHORT HEAD: o The medial head. o Originates from the tip of the coracoid process
- LONG HEAD: o The lateral head. o Originates from the supraglenoid tubercle of the
glenoid fossa
- The biceps inserts into the tuberosity of radius; and it also inserts into the antebrachial fascia by virtue of the bicipital aponeurosis.
- It does very different things depending on what position the arm is in:
o It supinates the forearm by pulling on the aponeurosis, when the arm is pronated; it is the MOST POWERFUL SUPINATOR of the forearm
o when the forearm is supine if FLEXES the elbow joint by pulling on the attachment to the radial tuberosity.
o It is useless as a flexor when the forearm is pronated. - The short head resists dislocation of the shoulder
Coracobrachialis
- Originates at the tip of the coracoid process of scapula
- Inserts into the middle third of the medial humerus
- Helps flex and adduct the arm
- Resists dislocation of the shoulder: it’s a SHUNT muscle, it resists the downward dislocation of the humeral head
- Stabilizes the glenohumeral goint - A landmark – it is pierced by the musculocutaneous nerve
Brachialis - Originates from the distal half of the anterior humerus
- Inserts into the tuberosity of the ulna, and the coronoid process
- Flexes the forearm in all positions – it’s the PRIMARY FLEXOR
-
- .
Posterior Compartment: EXTENSORS
All supplied by the RADIAL NERVE Triceps Brachii
- LONG HEAD: o Originates from the infraglenoid tubercle
- LATERAL HEAD: o Originates from the proximal humerus, more
proximal than the radial groove
- MEDIAL HEAD: o Originates from the posterior surface of the humerus,
distal to the radial groove
The united triceps inserts into the olecranon of ulna It is the chief extensor of the arm. The long head resists dislocation of the head of humerus, especially during abduction
Anconeus - Originates from the posterior lateral epicondyle of humerus
- Inserts into the lateral surface of olecranon
- Assists the triceps in flexing the forearm, and stabilizes the elbow joint. It also pulls the joint capsule out of the way of the olecranon upon extension; otherwise it would get pinched in the olecranon fossa . Many anatomists believe it to be a vestigial and forgotten 4th head of the triceps.
Coracobrachialis
Tip of the coracoid
process
Transverse
humeral
ligament
Supraglenoid tubercle
ligament
Biceps Brachii
Brachialis
Short head
Long head
Bicipital aponeurosis
Coronoid process and
the tuberosity of ulna
Tuberosity of radius
Long head of triceps
Medial head of triceps
Lateral head
of triceps
Anconeus
Infraglenoid tubercle
Some of the brachialis is
innervated by the radial nerve-
the half that is posterior to the
insertion of deltoid
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Fascia and compartments of the distal arm
Section at the junction of distal third and proximal two thirds of the humerus
Section at the level of the humeral epicondyles
Superior ulnar collateral artery
Ulnar nerve
Deep artery of the arm
Radial nerve
Triceps brachii
Long
head
Medial
head Lateral
head
Cephalic vein
Biceps brachii
Musculocutaneous nerve
Median nerve
Basilic vein
Brachial artery
Coracobrachialis
Medial cutaneous nerve
of forearm which arises
from the MEDIAL CORD of the
brachial plexus
Posterior cutaneous nerve of
forearm which has just branched off
from the RADIAL nerve
Lateral cutaneous nerve of
forearm which has just branched off
from the MUSCULOCUTANEOUS nerve
Brachialis
Brachialis
Biceps brachii
Basilic vein
Cephalic vein
Radial nerve which has pierced the
lateral intermuscular septum a little while
ago, and now travels between brachialis
and brachioradialis
Brachial artery
Median nerve
Ulnar nerve
Triceps Brachii tendon Anconeus Which is unimportant, and arguably useless. In fact some anatomists believe it to a rudimentary 4th
triceps head. If it were missing, you would likely not notice.
Brachioradialis which is important for
a number of reasons: - Forms the lateral border
of the cubital fossa
- Innervated by the RADIAL NERVE
- Flexes the forearm, unlike
the rest of the forearm extensor
compartment
- Together with the Supinator, they
are the only extensor compartment
muscles which do not cross the wrist
and cause no movement there
PRONATOR TERES
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Fascia and compartments around the cubital fossa and distal forearm
Antebrachial Fascia - Extension of the brachial fascia - Also envelops the forearm like a sleeve - There are no “intermuscular” septa per se; the
muscles are all invested in their own fascia; however there are still two recogniseable compartments: the FLEXOR compartment and the EXTENSOR compartment.
Section at the level of the neck of radius Basilic vein
Cephalic vein
In 20% of people, the basilic vein branches off into a
“median basilic” vein, and when it joins the median
cephalic vein they form a clear “M”.
Median cubital vein
Cephalic vein Median antebrachial vein
Basilic vein
Highly variable tributaries
Neck of
Radius
ULNA
COMPARTMENTS IN THIS SECTION are not clear-cut or sensible.
- This is an intersection of several compartments. The EXTENSOR compartment of the forearm is anterolateral, represented by brachioradialis, extensor carpi radialis longus and brevis, and extensor digitorum. The FLEXOR compartment is posteromedial and represented by pronator teres, palmaris longus, flexor carpi ulnaris, and flexor digitorum profundus and superficialis. The ANTERIOR compartment of the arm is represented by the biceps tendon, and by brachialis.
- Anconeus is a lonely representative of the POSTERIOR compartment.
The BICEPS TENDON: one part blends with the antebrachial fascia;
The other part dives deep to attach to the radial tuberosity Brachial artery which bifurcates at the level
of the radial head in the cubital fossa
Pronator teres which originates proximally to
the medial epicondyle, and forms the medial border
of the cubital fossa
The Flexors of the forearm which originate
at the Common Flexor origin, at the medial
epicondyle of the humerus
Brachioradialis Which forms the lateral
border of the cubital fossa
Brachialis
Brachialis
Biceps tendon
Extensor Carpi Radialis
Longus and Brevis
Extensor Digitorum
Anconeus
Brachioradialis
Radial artery
Ulnar artery Daughters of the recently
bifurcated Brachial Artery
BrR
ECRL, B
ED
Superficial branch of the
radial nerve which travels
under brachioradialis down the
arm, where it supplies sensation
to the dorsum of the hand
Deep branch of the Radial Nerve which
will pierce the Supinator, penetrate the
interosseous membrane and become the
Posterior Interosseous Nerve
The branches of the Radial Nerve
Median nerve which travels between the heads of P. teres
Pronator Teres
Palmaris Longus
Annular Ligament
Flexor Carpi Ulnaris which is fully
innervated by the ulnar nerve, unlike the
rest of the flexors
Flexor Digitorum Superficialis
(humeral head)
Flexor Carpi Radialis
Flexor Digitorum Profundis Half of which is innervated by the ulnar nerve, unlike the rest
of the flexors (which are all supplied by the Median nerve)
Ulnar nerve, which runs between the two
heads of flexor carpii ulnaris
THERE ARE 17 MUSCLES CROSSING THE ELBOW JOINT.
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Fascia and compartments of the middle forearm
Boundaries of the compartments:
Section at the level of the mid-forearm
FLEXOR COMPARTMENT This is the beefier compartment; twice as fat as the extensor compartment
4 layers of muscles:
EXTENSOR COMPARTMENT
Medial border: subcutaneous ulna
Interosseous membrane
Lateral border: radial artery
Flexor carpi radialis
Flexor
digitorum
superficialis
Median nerve
Palmaris Longus
Flexor carpi ulnaris
(ulnar nerve)
Flexor Pollicis
Longus
Flexor
digitorum
profundus
Anterior
Interosseous
Artery
Anterior Interosseous Nerve
Ulnar Nerve
Ulnar Artery
Medial cutaneous nerve of forearm
LAYER 1: pronator teres(not
shown, too proximal)
Flexor carpi radialis
Palmaris longus
Flexor carpi ulnaris
LAYER 2: Flexor digitorum
superficialis
LAYER 3:Flexor pollicis longus
Flexor digitorum
profundis
LAYER 4:Pronator Quadratus
(not shown, too distal)
Brachioradialis
Radial artery
Superficial branch of the radial nerve
Extensor pollicis Brevis
Extensor carpi
radialis brevis
Lateral cutaneous
nerve of the forearm
Extensor carpi
radialis longus Supinator
Extensor digitorum
Abductor pollicis longus
Extensor pollicis Longus
Extensor carpi ulnaris
Extensor indices
Posterior interosseous nerve
Posterior interosseous artery
Half of the Flexor Digitorum Profundus which is
innervated by the ulnar nerve, unlike the rest of the
flexors (which are all supplied by the Median nerve
Muscles of a similar purpose are grouped together in compartments. The EXTENSORS are posteromedial, and the FLEXORS are anterolateral. They spiral round the arm and eventually the flexors become truly anterior and the extensors become truly posterior.
- Functionally, the forearm includes the distal humerus because the muscles that attach at the supracondylar ridges and the epicondyles stretch along the forearm to move the wrist and fingers.
BOUNDARIES OF THE COMPARTMENTS POSTERIORLY (proximal forearm) and MEDIALLY (distal forearm), the
subcutaneous border of the ulna ANTERIORLY (proximal forearm) and then LATERALLY (distal forearm),
the radial artery
Because neither of these boundaries
is crossed by motor nerves they are
used for surgical incisions
The border between layers 1-2 and layers 3-4 is the primary
neurovascular plane of the anterior compartment: the
neurovascular bundles exclusive to this compartment travel within it
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The Flexor Compartment of the Forearm
The flexor compartment has 4 discrete layers:
LAYER 1: All of these, except the ulnar head of pronator quadratus, attach to the medial humeral epicondyle at the COMMON FLEXOR ORIGIN
- PRONATOR TERES o Forms the medial border of the cubital fossa; it’s the most lateral of the first layer of muscles o Has an ulnar head and a humeral head o The humeral head originates from the COMMON FLEXOR ORIGIN o The ulnar head originates from the coronoid process o Pronates and flexes the elbow
- FLEXOR CARPI RADIALIS o Originates from the COMMON FLEXOR ORIGIN o Inserts into the base of the 2nd metacarpal o Flexes and abducts the wrist o About half-way down the forearm, its belly is replaced
by a flat tendon which becomes cord-like at the wrist o It travels in the lateral carpal tunnel inside its own
synovial sheath (it doesn’t share) o The radial artery is just lateral to this tendon
- PALMARIS LONGUS o Originates from the COMMON FLEXOR ORIGIN o Inserts into the distal flexor retinaculum, and palmar aponeurosis. o Flexes and abducts the wrist, tenses the palmar aponeurosis o Its actually absent in 14% of people (usually on the left side). Those people don’t miss it being gone. o The tendon of palmaris longus is a marker for where the median nerve is – the tendon passes medially
to it, and then deep to it in the flexor retinaculum
- FLEXOR CARPI ULNARIS o Has an ulnar and a humeral head o Humeral head originates from the COMMON FLEXOR ORIGIN; Ulnar head originates from the
olecranon, and posterior border of ulna o Inserts into the pisiform, hook of hamate and the 5th metacarpal. o Flexes and abducts the wrist; has its own synovial sheath o The tendon of flexor carpi ulnaris is a marker for the ulnar artery, which passes laterally to it at the wrist
LAYER 2
- FLEXOR DIGITORUM SUPERFICIALIS o The fast flexor of the fingers. Has two heads: humeroulnar head and radial head o The humeroulnar head originates from BOTH the COMMON FLEXOR ORIGIN and the coronoid process
of ulna; the radial head originates the proximal half of the radius o It inserts into shafts of the middle phalanges o It flexes the metacarpophalangeal joints and the proximal interphalangeal joints; it can flex each joint
independently of the others. o Its tendons are enclosed in the COMMON FLEXOR SHEATH together with the tendons of flexor
digitorum profundus
LAYER 3 - FLEXOR DIGITORUM PROFUNDUS
o The slow flexor of the fingers o Originates from the interosseous membrane, and from the proximal three quarters of the anterior surface
of the ulna. It has two parts: medial and lateral parts; o The medial part is innervated by the ulnar nerve o The medial part flexes the distal interphalangeal joints of the 4th and 5th digits o The lateral part flexes the distal interphalangeal joints of the 2nd and 3rd digits o All parts can flex the wrist joint as well as the fingers o The lateral part is innervated by the ANTERIOR INTEROSSEOUS NERVE (a branch of the median
nerve). o The tendon to the index finger tends to separate early; it’s the only one which can operate independently.
Unlike the flexor digitorum superficialis, the profundus flexes all the DIPs together.
- FLEXOR POLLICIS LONGUS o Originates from the anterior surface of the radius and the nearby interosseous membrane o Inserts into the base of the distal phalanx of thumb. It has its own synovial sheal in the carpal tunnel o Also innervated by the ANTERIOR INTEROSSEOUS NERVE o It flexes the phalanges of the thumb; mainly the distal interphalangeal joint (it’s the only muscle that
flexes the DIP of the thumb)
LAYER 4 - PRONATOR QUADRATUS
o It originates from the distal quarter of the ulna, and inserts into the distal quarter of the radius o It is innervated by the ANTERIOR INTEROSSEOUS NERVE o It pronates the forearm (it’s the PRIMARY PRONATOR of the forearm) and its fibers hold the radius and
ulna together. When speed is needed, it is assisted by the Pronator Teres.
All supplied by the MEDIAN NERVE, …except:
Flexor Digitorum Profundis, ulnar half
Flexor Carpi Ulnaris, whole
Ulnar nerve
Ulnar nerve
Median nerve: mainly Layers 1 and 2 - Pronator teres - Flexor carpi radialis - Palmaris longus - Flexor digitorum superficialis
Anterior Interosseous nerve: mainly layer 3 - Flexor digitorum profundus, lateral half - Flexor pollicis longus - Pronator quadratus
Ulnar nerve: - flexor digitorum profundus, medial half - flexor carpi ulnaris
Pronator teres
Humeral head
Ulnar head is
hidden, but it
originates from
the coronoid
process
COMMON FLEXOR ORIGIN:
Pronator teres, humeral head
Flexor carpi radialis
Palmaris longus
Flexor carpi ulnaris, humeral head
Flexor digitorum superficialis, humeral head
Flexor carpi
radialis
The belly is
replaced by
a flat tendon
which
becomes
cord- like at
the wrist
Palmaris Longus
Flexor carpi Ulnaris
Two heads, one originating
from the humerus, the
other from the olecranon
Inserts into the Pisiform
Hook of hamate
Base of the 5th metacarpal
Median nerve
Lateral to the
palmaris
longus tendon
Radial
Artery
Lateral to the
flexor carpi
radialis
tendon
Flexor digitorum superficialis
Humeroulnar head
(common flexor origin and the
coronoid process)
Radial head
Flexor pollicis longus
Flexor digitorum
profundus:
Supplied by
MEDIAN NERVE
ULNAR NERVE
Pronator Quadratus
The flexors digitorum profundus and
superficialis are WEAKER when the
wrist is flexed, the tendons aren’t tense
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Extensor Compartment of the Forearm: Superficial layer
SUPERFICIAL LAYER OF EXTENSORS two originate from the supracondylar ridge as well as the adjacent
intermuscular septum:
Brachioradialis o radial nerve o Inserts at the lateral surface of the distal end of the radius o Flexes the forearm, in a feeble way, and mostly when the forearm
is pronated; it also acts as a shunt muscle to prevent subluxation of the head of radius. its most active in quick movements, and in movement against resistance.
o Forms the lateral border of the cubital fossa o under it run the radial nerve and the radial artery o Distally, its tendon is covered by the tendons of Abductor Pollicis
Longus and Extensor Pollicis Brevis.
Extensor Carpi Radialis Longus o radial nerve o Inserts at the dorsum of the 2nd metacarpal, at the base o extends and abducts the hand at the wrist o probably more involved in abduction than the ECRB o it is crucial in the clenching of the closed fist.
Four originate from the common extensor origin, at the lateral epicondyle of the humerus
Extensor Carpi Radialis Brevis o deep branch of radial nerve o Inserts into the dorsum of the 3rd metacarpal at the base o extends and abducts the hand at the wrist o it is covered by the Extensor Carpi Radialis Longus o They also share the same extensor tendon sheath at the wrist o the brevis is more involved in extension than the longus
Extensor Digitorum o posterior interosseous nerve which is really the continuation of
the deep branch of the radial nerve o inserts at the extensor expansions of the fingers o THE EXTENSOR EXPANSIONS are triangular aponeuroses
which wrap around the metacarpal head, and the proximal phalanx. They are united with the insertions of the lumbricals and the interosseous muscles.
o The tendons thus divide into a median band which passes to the base of the middle phalanx, and two lateral bands which insert at the base of the distal phalanx.
o Extends the fingers, primarily at the metacarpophalangeal joint; secondarily at the distal interphalangeal joint.
o Occupies a lot of space in the extensor compartment o Shares an extensor tendon sheath with the Extensor Indicis o Just proximally to the metacarpophalangeal joints, the
tendons are linked by intertendinous connections which prevent the fingers from being independently extended; thus you can never fully extend a finger while the others remain flexed. This is most true of the ring finger.
Extensor Digiti Minimi o posterior interosseous nerve o Divides into two tendons- the lateral one joins the pinky tendon of
the extensor digitorum, and then together with the medial one all three insert into the extensor expansion of the pinky finger.
o extends the pinky, primarily at the metacarpophalangeal joint; secondarily at the distal interphalangeal joint.
o this is really just a detached part of the extensor digitorum o However, it has its own tendon sheath
Extensor Carpi Ulnaris o posterior interosseous nerve o yes it does originate at the common extensor origin; thats the
humeral head. There is also an ulnar head, which originates at the ulnar border posteriorly, via an aponeurosis. This origin is also shared with the Flexor Digitorum profundis and the Flexor Carpi Ulnaris.
o inserts at the dorsum of the base of 5th metacarpal o extends the hand at the wrist joint, and abducts it o It has its own tendinous sheath at the wrist o It is also crucial to the formation of the closed fist
All extend the forearm, wrist or fingers – EXCEPT BRACHIORADIALIS Brachioradialis is the solitary exception: it is in the extensor compartment, but it flexes the forearm.
It is the only flexor innervated by the radial nerve.
All supplied by the RADIAL NERVE, or some branch thereof
two layers: the SUPERFICIAL and DEEP
Brachioradialis
Extensor Carpi
Radialis Longus
Extensor Carpi
Radialis Brevis which
lies under the Extensor
Carpi Radialis Longus
Brachioradialis tendon
which lies under
the tendons of
Abductor Pollicis Longus
and
Extensor Pollicis Brevis
Common extensor origin
The Insertions of the Extensors
Carpi Radialis tendons:
Bases of the metacarpals
Longus inserts into the 2nd
Brevis inserts into the 3rd
The common tendon
sheath of th extensors
carpi radialis: both travel
within the same sheath
Extensor Carpi Ulnaris
Extensor Digiti Minimi
The Tendon of Extensor
Digit Minimi divides into
two tendons; the lateral
one joins the extensor
digitorum tendon to the
little finger
Extensor Digitorum
The fattest muscle here
Tendon sheaths:
Extensor carpi ulnaris
has its own; and so
does extensor digiti
minimi. The extensor
digitorum shares a
sheath with the tendon
of Extensor Indicis
Intertendinous connections which
unite the extensor digitorum
tendons and prevent the digits from
extending independently
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Extensor Compartment of the Forearm: Deep layer
DEEP LAYER OF EXTENSORS "true" deep layer
Supinator o deep branch of radial nerve which pierces it on its way
to transforming into the posterior interosseous nerve o originates from everywhere... the lateral humeral
epicondyle, the radial collateral ligament, the annular ligament, the supinator fossa and the crest of ulna
o inserts into the lateral posterior and anterior surfaces of the proximal third of radius
o it supinates the forearm, turning the arm to face anteriorly and superiorly when the forearm is flexed. It is the PRIME MOVER for slow unopposed suination
o The supinator forms the floor of the cubital fossa together with brachialis. It is a sheet-like muscle, and it envelops the radius.
Extensor Indicis o Posterior interosseous nerve o originates from the posterior surface of the distal third of
the ulna, and the interosseous membrane o inserts into the extensor expansion of the index finger o extends the index finger, enabling independent extension o helps extend the hand at the wrist
"outcropping" deep layer these originate from the proximal, middle and distal thirds of the ulna (as a generalization). They emerge in the surface in the furrow that forms in the extensor compartment
Abductor Pollicis Longus o Posterior interosseous nerve o originates from the posterior surface of the proximal
radius and ulna, as well as the interosseous membrane o inserts into the base of the 1st metacarpal, and
occasionally also the trapezium. o abducts and extends the thumb at the carpometacarpal
joint o shares a common tendon sheath with the extensor
pollicis brevis at the wrist
Extensor Pollicis Brevis o Posterior interosseous nerve o originates from the posterior surface of the distal third of
the ulna, and the interosseous membrane o inserts into the dorsum of the base of the proximal
phalanx of the thumb o extends the proximal phalanx of the thumb at the
metacarpophalangeal joint; also extends the carpometacarpal joints of the thumb.
o partly covered by the abductor pollicis longus o its tendon is immediately medial to the APL o these two tendons form the anterior boundary of the
anatomical snuffbox.
Extensor Pollicis Longus o Posterior interosseous nerve o originates from the posterior surface of the middle third
of the ulna, and the interosseous membrane o inserts into the dorsum of the base of the distal phalanx
of the thumb o extends the distal phalanx of the thumb; also extends
the metacarpophalangeal and the carpometacarpal joints of the thumb. It also rotates the thumb laterally.
o It enjoys its own tendon sheath at the wrist; it passes medially over the dorsal tubercle of radius, using it as a pulley.
o the EPL forms the posterior border of the anatomical snuffbox
Supinator
Attachments of the Supinator to the
Epicondyle of humerus
Radial collateral ligament
Annular ligament of radius
Ulnar Supinator crest and fossa
Ulnar posterior surface
Abductor pollicis longus
Extensor Pollicis Longus
Extensor Pollicis Brevis
Interosseous membrane
Extensor Indices
Which shares an extensor
tendon sheath with the
Extensor Digitorum tendon
Common sheath for the
tendons of the extensor
pollicis brevis and abductor
pollicis longus
APL inserts into the base of 1st metacarpal
EPB inserts into the base of proximal phalanx
EPL inserts into the base of distal phalanx
the Supinator wraps around the
radius to insert into the anterior
surface of it. Together with the
brachialis it forms the floor of
the cubital fossa
Extensor digitorum tendon
Extensor expansion
Medial band attaches to the base of
the middle phalanx
Lateral bands attach to the
base of the distal phalanx
The hood which attaches to the palmar tendon
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Flexor and Extensor Tendons at the Wrist: level of the Distal Radioulnar Joint
- attaches
Palmaris Longus
Ready to merge with the
palmar aponeurosis
Median Nerve
Ulnar Artery
Ulnar nerve
Flexor Carpi Ulnaris can cover the ulnar
artery and obscure its pulsation
Flexor Carpi Radialis
Flexor Pollicis Longus
Radial Artery
Abductor Pollicis Longus
Extensor Pollicis Brevis
Extensor Carpi Radialis Longus
Extensor Carpi Radialis Brevis
Extensor Pollicis Longus
Extensor Indices
Extensor Digitorum
Extensor Digiti Minimi
Extensor Carpi Ulnaris
Flexor Digitorum Superficialis
Flexor Digitorum Profundus
RRAADDIIUUSS
UULLNNAA
The Extensor Retinaculum - Attaches to the lateral border of the radius - Does NOT attach to the border of the ulna, because the ulna moves too much. - Instead, attaches to the pisiform and the triquetrum - Also attaches to the ridges of the radius, thus forming osseofibrous tunnels for the above tendons to run
through - There are 6 tunnels in total:
1. One for abductor pollicis longus and extensor pollicis brevis 2. One for extensor carpi radialis longus and extensor carpi radialis brevis 3. One for extensor pollicis longus 4. One for extensor digitorum and extensor indices 5. One for extensor digiti minimi 6. One for extensor carpi ulnaris
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The Flexor retinaculum is stretched between four
bony posts:
1) Hook of hamate
2) Pisiform bone
3) Tuberosity of scaphoid
4) Tuberosity of trapezium
The Carpal Tunnel and its Contents
Radial Artery
Crossing over to the
dorsum of the hand
Abductor Pollicis Longus
Extensor Pollicis Brevis
Extensor Carpi Radialis Longus
Extensor Carpi Radialis Brevis
Extensor Pollicis Longus
Extensor Digiti minimi
Palmaris Longus
Thenar muscles
Hypothenar muscles
Extensor Digitorum Extensor Indices
Extensor Carpi Ulnaris
TRAPEZIUM
TRAPEZOID
CAPITATE
HAMATE
Ulnar Artery
Ulnar Nerve
Flexor retinaculum Median Nerve
Flexor Digitorum Profundus
Flexor Digitorum
Superficialis
Flexor Carpi Radialis
Flexor Pollicis Longus
Hook of Hamate Tuberosity of
Trapezium
Tuberosity
of Scaphoid
Pisiform
This is a narrow enclosed space. Needless to say, if anything in here swells, the median nerve will get compressed. It is the most sensitive structure in the carpal tunnel.
- The lateral three and a half digits will get diminished sensation - Sensation on the thenar eminence will be spared because the palmar cutaneous branch splits
from the median nerve long before the flexor retinaculum - The movement of the thenar muscles is controlled by a terminal motor branch of the median nerve,
and so the thenar muscles will atrophy in carpal tunnel syndrome
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A Summary of the Innervation of the Extensors and Flexors of the Forearm
Extensors All innervated by branches of the RADIAL NERVE Radial nerve itself: innervates muscles with attachments proximal to
the cubital fossa - Brachioradialis - Extensor Carpi Radialis Longus - Both of these originate at the supracondylar ridge
Deep branch of the radial nerve: a branch which splits off from
the radial nerve at the level of the humeral condyle in the cubital fossa; it pierces the supinator muscle, and becomes the posterior interosseous nerve
- Extensor Carpi Radialis Brevis - Supinator
Posterior interosseous nerve: travels along the posterior aspect
of the interosseous membrane; innervates most of the extensor muscles
- Extensor digitorum - Extensor Indicis - Extensor Digiti minimi - Extensor Carpi Ulnaris - Extensor Pollicis Longus - Extensor Pollicis Brevis - Abductor Pollicis Longus
Flexors Innervated by either the ULNAR or the MEDIAN nerves
Median nerve itself: - Pronator Teres - Palmaris Longus - Flexor carpi Radialis - Flexor Digitorum Superficialis
Anterior interosseous nerve, a branch of the median nerve:
- Flexor Digitorum Profundus - lateral half - Flexor Pollicis Longus - Pronator Quadratus
Ulnar nerve: - Flexor Digitorum profundus, only the medial half - Flexor Carpi Ulnaris
Deep branch of
the radial nerve
is in pink
Radial nerve is in red
Posterior interosseous nerve is in green
Ulnar nerve :
Innervates the muscles
directly adjacent to it along
its course down the arm
Median nerve:
Innervates mainly the 1st
and 2nd layer of flexors
Anterior Inerosseous
nerve: innervates the 3
deepest muscles
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Fascia, Septa, Tendon Sheaths and the Potential Spaces of the Hand
These fascial layers are continuous with the fascial sleeve of the forearm. Centrally the fascia of the palm thickens in the centre, where the palmaris longs tendon attaches to it, which is also where it merges with the flexor retinaculum. This whole thickened area is called the palmar aponeurosis. Distally, the palmar aponeurosis divides into four bands which attach to the bases of the proximal phalanges, and there it becomes a part of the digital sheaths
Palmaris Longus tendon
Antebrachial Fascia
Flexor retinaculum
All merge into the
Palmar Aponeurosis
Palmar Aponeurosis so thick and tough that any infections
in the palmar spaces will actually
cause the weaker DORSAL fascia to
bulge out.
In Dupuytren’s contracture, the
palmar aponeurosis becomes nodular,
fibrosed, and thickened
Thenar fascia
Hypothenar fascia
Palmar Aponeurosis
Lateral fibrous septum of the palm which stretches from the palmar
aponeurosis to the 3rd metacarpal
Medial fibrous septum of
the palm which stretches from the palmar
aponeurosis to the 5th metacarpal
The Thenar Space
Of the two septa, the LATERAL is the strongest
The Midpalmar Space Unlike the thenar
space, this one is
continuous with the
anterior compartment
of the forearm- it
communicates with it
via the carpal tunnel.
Common flexor sheath: FDS and FDP
The common flexor sheath continues to the
5th digit. The other digits have their own
Digital Synovial Sheaths
Digital Synovial Sheaths
Synovial sheath for Flexor
Pollicis Longus
Synovial sheath for Flexor
Carpi Radialis
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Compartments of the palm and their contents
Thenar compartment Contains the thenar muscles
Central compartment Contains the flexor tendons and their sheaths, the lumbricals, the superficial arterial palmar arch, and the digital vessels and nerves Hypothenar compartment Contains the hypothenar muscles
Adductor compartment Contains only Adductor Pollicis
Interosseous compartments Contains the interossei muscles
Flexor Pollicis Brevis: Superficial head
which is innervated by the MEDIAN NERVE
Deep Head which is innervated by the
DEEP BRANCH OF THE ULNAR NERVE
Abductor Pollicis Brevis
Opponens Pollicis
1st Dorsal Interoissei
2nd Dorsal Interoissei
3rd Dorsal Interoissei
4th Dorsal Interoissei
1st Palmar Interoissei 2nd Palmar Interoissei
3rd Palmar Interoissei
Abductor Digiti Minimi
Flexor Digiti Minimi Brevis
Opponens Digiti Minimi
1st and 2nd Lumbricals which are unipennate and which are
innervated by the MEDIAN NERVE 3rd and 4th Lumbricals which are bipennate and which are
innervated by the DEEP BRANCH OF THE ULNAR NERVE
Adductor Pollicis
Thenar Compartment
Adductor compartment
Interosseous compartment
Hypothenar
Compartment
Central
Compartment
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Thenar and Hypothenar muscles There are 3 Thenar muscles, 3 Hypothenar muscles, 1 Adductor muscle, 4 Lumbricals, 4 dorsal interossei and 3 palmar interossei
Hypothenar Muscles In the HYPOTHENAR compartment
Opponens Digiti Minimi o deep branch of ULNAR NERVE o originates from hook of hamate and the flexor retinaculum o inserts into the medial border of the 5th metacarpal o pulls the 5th metacarpal anteriorly, and rotates the 5th digit so
it can participate in opposition with the thumb o acts exclusively at the MCP joint
Flexor Digiti Minimi Brevis o deep branch of ULNAR NERVE o originates from hook of hamate and the flexor retinaculum o inserts into the medial side of the base of the 5th proximal
phalanx o flexes the proximal phalanx of the 5th digit
Abductor digiti Minimi o deep branch of ULNAR NERVE o originates from the pisiform o inserts into the medial surface of the bae of the 5th proximal
phalanx o Abducts the 5th digit and assists in its flexion o It is the most superficial of the three hypothenar muscles
Thenar Muscles In the ADDUCTOR compartment
Adductor Pollicis o deep branch of the Ulnar nerve
- TRANSVERSE HEAD originates from the anterior surface of the 3rd metacarpal
- OBLIQUE HEAD originates from the bases of the 2nd and 3rd metacarpals, from the capitate bone, and from any carpals around the capitate.
- Inserts into the medial side of the base of proximal phalanx of thumb. There tends to be a sesamoid bone at the site of insertion.
- Adducts the thumb towards the lateral border of the palm (presses it against the palm)
In the THENAR compartment
Flexor Pollicis Brevis o DEEP HEAD: deep branch of ULNAR NERVE o SUPERFICIAL HEAD: Recurrent branch of MEDIAN NERVE o originates from the flexor retinaculum and the tubercles of the
scaphoid and trapezium. o Inserts into the lateral aspect of the base of the proximal phalanx
of the thumb o Flexes the thumb: brings its tip towards the base of pinky
Abductor Pollicis Brevis: Recurrent branch of MEDIAN NERVE o originates from the flexor retinaculum and the tubercles of the
scaphoid and trapezium. o Inserts into the lateral aspect of the base of the proximal phalanx
of the thumb o Abducts and helps oppose the thumb
Opponens Pollicis Brevis: Recurrent b. of MEDIAN NERVE o originates from the flexor retinaculum and the tubercles of the
scaphoid and trapezium; Inserts into the lateral side of the 1st metacarpal.
o Opposes the thumb: medially rotates and the pulls medially the 1st metacarpal. Acts exclusively at the MCP joint
ADDUCTOR POLLICIS, which has
2 heads, between the origins of which the
RADIAL ARTERY emerges to form the
deep palmar arch
Transverse head of Adductor Pollicics,
which originates from the 3rd metacarpal
Oblique head of Adductor Pollicics,
which originates from the 3rd metacarpal
as well as from the 2nd metacarpal, the
capitate bone, and all adjacent carpal
bones
Adductor pollicis inserts into the lateral
part of the 1st proximal phalanx
Flexor pollicis brevis with two heads: the
superficial and the deep. The deep head is
innervated by the deep branch of the ulnar
nerve
Opponens Pollicis
Abductor Pollicis Brevis
Both of these muscles originate from the
flexor retinaculum and the tubercles of
scaphoid and trapezium; they both insert
into the lateral aspect of the base of the
proximal phalanx of the thumb.
Also originates from the flexor
retinaculum and the tubercles of scaphoid and trapezium;
however it inserts into the lateral border of the 1st metacarpal.
Both of these muscles originate from the flexor retinaculum
and the tubercles of scaphoid and trapezium; they both insert
into the lateral aspect of the base of the proximal phalanx of the
thumb.
Flexor retinaculum
Abductor Digiti Minimi
Which originates at the
pisiform and inserts into the
medial side of the base of
base of 5th proximal phalanx
Flexor Digiti Minimi Brevis
Which originates from the flexor
retinaculum and the hook of
hamate, and inserts into the
medial side of the base of the 5th
proximal phalanx
Opponens Digiti Minimi
Which originates from the
flexor retinaculum and the
hook of hamate, and inserts
into the medial border of
the 5th metacarpal
There is also Palmaris Brevis; a useless little muscle which wrinkles
the skin of the palm; it originates at the flexor retinaculum and inserts
into the skin. The ulnar nerve innervates it.
IT IS NOT PART OF THE HYPOTHENAR COMPARTMENT
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Short muscles of the Hand
o there are 4 lumbricals, 4 dorsal interossei, and 3 palmar interossei; you count them starting at the THUMB
The LUMBRICALS - Originate from the tendons of the FLEXOR DIGITORUM PROFUNDIS
- Sit in the central compartment of the palm - From the palm, cross over to the dorsum of the hand
- Insert into the extensor expansions on the dorsum of the proximal phalanges
- The FIRST and SECOND lumbricals are innervated by the median nerve. All other short muscles are innervated by the deep branch of the ulnar nerve
- The THIRD and FOURTH lumbricals are bipennate; the other two are unipennate
- FLEX the metacarpophalangeal joints
- EXTEND the proximal interphalangeal joints
The DORSAL INTEROSSEI - Originate from the sides of two metacarpals (ALL of them are bipennate) - Sit in their own INTEROSSEOUS compartment of the hand - Insert into the bases of the proximal phalanges and into the extensor
expansions
- ABDUCT the hand away from the axis of the middle finger (the axis as shown)- hence “DAB” (“ Dorsal Interosei ABduct”)
- Also help the lumbricals flex the MCPs and extend the PIPs
- When the thumb is flexed, the first dorsal interossei can be seen as the lump that appears on the dorsum of the hand.
The PALMAR INTEROSSEI - Originate from the palmar surfaces of the metacarpals
- Sit in the anterior part of the INTEROSSEOUS compartment of the hand - Inset into the bases of the proximal phalanxes and into the extensor
expansions - ADDUCT the fingers towards the middle finger,
hence “PAD”- Palmar Interossei Adduct - There are only 3 palmar interossei; the deep part of the Flexor Pollicis
Brevis can be described as the 4th, because it does much the same thing as the rest, and is innervated by the same nerve
The Interossei all live inside the INTEROSSEOUS compartment. The Palmar
interossei occupy the anterior (palmar )part of it, and the dorsal interossei are
more properly between the metacarpals.
Together the short muscles all produce the “Z” movement of the fingers; the MCPs are
flexed, and the PIPs extended. This is the opposite of what happens in ulnar nerve palsy
(“claw hand”) when the MCPs are extended and the PIPs are flexed.
References: Moore’s Clinically Oriented Anatomy 5th
edition