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Lecture 27: Upper Extremities 4 – Muscles of the Forearm: Posterior compartment & Intrinsic Muscles of the Hand
Objectives
Bones of hand and wrist
Describe 9 muscles of posterior compartment of forearm (Table 11.13)
Describe general organization of intrinsic muscles of hand
Describe 4 intrinsic muscles of the hand that move the thumb
Review: Bony Features of the Hand & Wrist
“o e lo ers tr positio s that the a ’t ha dle :
o Trapezium comes before Trapezoid
(alphabetical order)
o The phrase goes from proximal-lateral (i.e.
upper thumb) to proximal-medial (i.e. upper
pinky), then the second/distal row goes from
lateral to medial again.
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From the carpal bones, they connect to the five
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metacarpals, which connect to the proximal phalanges
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via the metacarpophalangeal joint middle distal
phalange (except the thumb)
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Muscles of Posterior Compartment of Forearm
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Be aware that the muscles of forearm posterior compartment will extend the hand (giving high-five), while the
flexor muscles flex the hand (beckoning someone to come)
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Only 2 layers: Superficial & Deep
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1. Superficial: 2. Deep (Outcropping)
o Extensor carpi radialis brevis o Extensor indicis
o Extensor carpi radialis longus o Extensor policis brevis
o Extensor carpi ulnaris o Extensor pollicis longus
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o Extensor digitorum o Abductor pollicis longus
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o Brachioradialis o Supinator
Superficial Muscles
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Extensor Carpi Radialis Longus
o O: Lateral supracondyle
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ridge of humerus
o I: Base of 2nd metacarpal
(index)
o A: Extends and abducts
hand at wrist joint
(Crosses elbow & wrist)
o Inn: Radial nerve (C6, C7)
Extensor Carpi Radialis Brevis
o O: Lateral epicondyle of
humerus
o I: Base of 3rd metacarpal
(middle)
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o A: Extend and abduct hand at wrist joint (same as ECR Longus)
o Inn: Deep branch of radial nerve (C7,C8)
Extensor Digitorum
o O: Lateral Epicondyle
o I: Extensor expansion of medial 4 digits
o A: Extend 4 medial fingers (at metacarpophalangeal joints) & extend hand at wrist joint
o Inn: Posterior interosseous nerve (continuation of deep branch radial nerve)
Note: The anterior compartment has 2 muscles for carpi digit flexion: flexor digitorum superalis & profuundus
because flexion is a powerful movement. However, there is only 1 muscle for extending (extensor digitorum)
because extensor is more passive.
Extensor Carpi Ulnaris
o O: Lateral epicondyle + posterior border of ulna
o I: Base of 5th metacarpal (pinky)
o A: Extend & abduct hand at wrist joint (same as extensor carpi radialis longus & brevis)
o Inn: Same as extensor digitorum (posterior interosseous nerve)
Brachioradialis
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o O: Lateral supracondylar ridge (humerus) same as extensor carpi radialis longus
o I: Lateral surface – distal end of radius (near the protrusion of radial bone under the thumb)
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o A: Flexes forearm and synergizes with other forearm flexors (anterior compartment)
o Inn: Radial nerve (C5-C7)
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Note: Bra horadialis, tri eps, a o eus do ’t orr a out it , a d e te sor arpi radialis lo gus are the only
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muscles receiving direct innervation of the radial nerve.
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All the other muscles of posterior compartment receive innervation from the deep branch of radial nerve.
Extensor Expansions
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Also called: Dorsal expansion/Dorsal hood
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The flattened tendons (aponeurosis) of extensor muscles running into dorsum of the hand
Tendons of extensor muscles i.e. apo eurosis of the us les e pa d to for a hood o er the eta arpals,
the back and sides of the head of the metacarpal, and the proximal phalanx.
Expansions divide into 3 bands:
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o 1. 2 lateral bands pass on either side of proximal phalanx and reach all the way to the distal phalanx.
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Serve as insertion points for the: Lumbricals of the hand; dorsal interossei of the hand; and
palmar interossei.
o 2. A medial band passes down the middle and end at the base of the middle phalanx.
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o 3. Retinacular ligament runs obliquely along middle phalanx; connects fibrous digital sheath from the
anterior side of the phalanges to the extensor expansion.
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Deep Layer
Supinator
o O: Lateral epicondyle of humerus; radial collateral & annular ligaments; supinator fossa &
crest of ulna
o I: Wraps around proximal-lateral 1/3 of radius
o A: Supinates forearm (flips it upwards) b/c muscle wraps/inserts on the lateral side of
radius, it pulls the radius towards the other side so that supination occurs
o Inn: Deep branch of radial nerve
Abductor Pollicis Longus
o O: Posterior surface of ulna, radius, and interosseous membrane
o I: Base of 1st metacarpal (thumb)
o A: Abducts thumb & extends it at metacarpal joint / it’s lo ated at the ase, he it
pulls, the thumb will flick outwards
o Inn: Deep branch of radial nerve (posterior interosseous nerve)
Extensor Indicis
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o O: Posterior surface of ulna & interosseous membrane
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o I: Extensor expansion of 2nd digit
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o A: Extends index finger & helps with hand extension.
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o Inn: Posterior interosseous nerve (deep branch of radial nerve)
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Extensor Pollicis Longus
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o O: Posterior surface of ulna (above extensor indicis) & interosseous membrane
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o I: Base of distal phalanx of thumb TIP of thumb
o A: Extends distal phalanx of thumb at carpometacarpal and interphalangeal joints
o Inn: Posterior interosseous nerve
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Extensor pollicis brevis
aC s
o O: Posterior surface of radius & interosseous membrane
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o I: Base of proximal phalanx of thumb
o A: Extends proximal phalanx at carpometacarpal joint
o Inn: Posterior interosseous nerve (deep branch of radial nerve)
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Anatomical Snuffbox
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Formed by tendons of extensor pollicis longus & brevis
Note: The abductor pollicus longus always stops at the very base of the
thumb, while the extensor pollicis brevis continues to the distal
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phalanx.
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Clinical Note: De Quervan’s Tenosynovitis & Finkelstein Test
De Quervan’s Tenosynovitis – Chronic inflammation and pain in
tendons of abductor pollicis longus & extensor pollicis brevis.
Finkelstein Test – Pain felt during this test indicates De Quer a ’s
Syndrome
Opposable Thumb
Opposa le = Ca oppose/tur a k agai st other four fi gers
Enables hand to refine its grip in holding objects – a power grip & a precision grip
Allowed development of fine motor skills & development of tools – allows dexterity
Muscles Acting on the Thumb
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Extrinsic Muscles: Muscle bellies are located outside of the hand:
o Flexor pollicis longus
o Abductor pollicis longus
o Extensor pollicis longus
o Extensor pollicis brevis
Intrinsic Muscles of the Hand (Thenar Muscles) – Divided into thenar eminence & hypothenar eminence
(pinky)
o Abductor pollicis brevis
o Flexor pollicis brevis
o Opponens pollicis
o Adductor pollicis
2 heads:
-Oblique head (base of 2nd – 3rd metacarpal,
capitate, and adjacent carpals)
- Transverse head: Anterior surface of 3rd
metacarpal
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Intrinsic Muscles of the Hand
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Responsible for fine movements of hand: Pinky & Thumb – Abduction, adduction, flexion
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& opposition
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3 Groups of muscles:
o Thenar muscles (4) rs e
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o Hypothenar muscles (3) – Act on the pinky
Abductor digiti minimi
Opponens digiti minimi
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Flexor digiti minimi
aC s
Palmaris brevis (ignore)
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**All are innervated by ulnar nerve
o Palmar muscles:
1. Interosseus (between bones)
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4 DAB (dorsal interossei)
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3 PAD (palmar interossei)
2. Lumbricals (worm-like) (4)
Palmar Muscles
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4 Dorsal Interossei
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o Abduct fingers away
from middle finger
o Bi-pennate msucles
3 Palmar Interossei
o Adduct fingers
towards middle
finger
o Assist lumbricals
o Uni-pennate
muscles (i.e. single
muscle belly)
Lumbricals
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o Allow flexion at metacarpophalangeal joints & maintaining extension
at interphalangeal joints (i.e. proximo-middle-distal joints) I.e.
aki g the L shape ith our ha d
o Do NOT directly attach to bones – attach:
Proximally to tendons of the flexor digitorum profundus
(recall: FDP extends to distal fingers) &
Distally to extensor expansions on dorsal surface of hand
Innervation of Intrinsic Muscles of the Hand
Median Nerve
o 3 Lateral Thenar muscles
o 2 Lateral Lumbricals
Ulnar Nerve
o 2 Medial Lumbricals
o All other intrinsic muscles of the hand (PAD, DAB)
Radial Nerve
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o No motor functions
o Sensory functions only
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aC s
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