[Anatomy] Forearm And Hand

Front 1

anterior compartment of forearm

Back 1

- consists of superficial group (cross elbow) and deep group (does not cross elbow)
- mostly innervated by median nerve
- Exceptions: 1½ muscles are innervated by the ulnar nerve (flexor carpi ulnaris and the ulnar half (to digits 4 and 5) of flexor digitorum profundus)

Front 2

functions of anterior compartment of forearm

Back 2

o Flex wrist joint
o Flex fingers (e.g., at MCP and IP joints)
o Pronate forearm (palm down)
o Abduct (radial deviation)/adduct (ulnar deviation) wrist joint

Front 3

superficial group of anteror compartment of forearm

Back 3

o Common site of origin: Medial Epicondyle of Humerus
o Medial epicondylitis (“Golfer’s elbow”): inflammation of the common flexor origin and periosteum of the medial epicondyle
o Since the superficial group of muscles cross the elbow, they can assist in flexing this joint; however, this is not their primary action
o contains pronator teres, flexor carpi radialis, flexor carpi ulnaris, palmaris longus, flexor digitorum superficialis

Front 4

pronator teres

Back 4

• Insertion: midshaft of radius
• Action: pronate forearm
• Innervation: median nerve

Front 5

flexor carpi radialis

Back 5

o part of superficial group of anterior compartment of forearm
• Insertion: radial (lateral) side of hand
o Action: flex and abduct wrist joint
o Innervation: median nerve

Front 6

flexor carpi ulnaris

Back 6

• part of superficial group of anterior compartment of forearm
• Insertion: ulnar (medial) side of hand
• Action: flex and adduct wrist joint
• Innervation: ulnar nerve

Front 7

palmaris longus

Back 7

o part of superficial group of anterior forearm
o (absent in ~15% of people)
o Insertion: palmar aponeurosis
o Action: flex wrist joint
o Innervation: median nerve

Front 8

flexor digitorum superficialis

Back 8

• Insertion: middle phalanges of digits 2-5
• Action: flex digits 2-5 (MCP and PIP joints)
• Innervation: median nerve

Front 9

deep group of anterior compartment of forearm

Back 9

o Origins off: ulna, radius, interosseous membrane
o flexor digitorum profundus, flexor pollicis longus, pronator quadratus

Front 10

flexor digitorum profundus

Back 10

o part of deep group of anterior forearm
o Insertion: distal phalanges of digits 2-5
o Action: flex digits 2-5 (MCP, PIP, and DIP joints)
o Innervation: Lateral (radial) ½ = median nerve; Medial (ulnar) ½ = ulnar nerve

Front 11

flexor pollicis longus

Back 11

• part of deep group of anterior forearm
o (pollex=thumb)
• Action: flex thumb (at MCP and IP joints)
• Innervation: median nerve

Front 12

pronator quadratus

Back 12

• Insertion: distal radius
• Action: pronate forearm
• Innervation: median nerve

Front 13

flexor retinaculum

Back 13

o Band of deep fascia holding long flexor tendons in place as they cross the wrist
o Tendons are surrounded by synovial sheaths (allow tendons to move freely)
o The flexor retinaculum forms the roof of the carpal tunnel

Front 14

carpal tunnel

Back 14

- Contents of the carpal tunnel (deep to flexor retinaculum):
o median nerve
o tendons of flexor digitorum superficialis
o tendons of flexor digitorum profundus
o tendon of flexor pollicis longus

Front 15

carpal tunnel syndrome

Back 15

results from any significant reduction in the size of the carpal tunnel (e.g., inflammation of the synovial sheaths of the flexor tendons). Patients with this condition experience a progressive weakening of the thenar muscles (moving the thumb), which weakens the grip. Loss of sensation (usually not full anesthesia) on lateral 3 digits also affects grip. Surgery (partial to full opening of the flexor retinaculum) may be required, but often more conservative treatments can alleviate symptoms.

Front 16

compartments of palm

Back 16

The palm is organized into thenar, hypothenar, adductor, and central compartments

Front 17

thenar compartment

Back 17

o Contains the 3 thenar muscles acting on the thumb (pollex)

Front 18

adductor compartment

Back 18

o Contains the adductor pollicis muscle

Front 19

hypothenar compartment

Back 19

o Contains the 3 hypothenar muscles acting on digit 5

Front 20

central compartment

Back 20

o Deep to palmar aponeurosis, in center of palm
o Contains the long flexor tendons (flexor digitorum superficialis, flexor digitorum profundus, flexor pollicis longus), lumbricals, and most of the major vessels and nerves of the hand
o Untreated infections of the central compartment can spread through the carpal tunnel and into the anterior compartment of the forearm

Front 21

movements of digits 2-5

Back 21

o Flexion/Extension at MCP and IP joints
o Abduction/Adduction at MCP joints (relative to digit 3)

Front 22

thumb movements

Back 22

o Flexion: bending thumb across palm
o Extension: opposite of flexion
o Abduction: movement of thumb away from palm anteriorly
o Adduction: movement of thumb back towards palm
o Opposition: bringing thumb into contact with another digit
o Reposition: returning thumb and opposing finger to resting positions

Front 23

carpometacarpal joint of thumb

Back 23

• synovial joint between the trapezium and the 1st metacarpal
• very mobile compared to the other CMC joints (digits 2-5)
• Flexion/Extension
• Abduction/Adduction (abduction/adduction is very limited in the MCP joint of the thumb, instead takes place here at CMC joint)
• Opposition/Reposition

Front 24

intrinsic muscles of the hand

Back 24

thenar muscles, adductor pollicis, hypothenar muscles, central compartment muscles, interossei

Front 25

thenar muscles

Back 25

Innervated by the recurrent branch of the median nerve

Abductor pollicis brevis
Action: abduct thumb (CMC joint)

Flexor pollicis brevis
Action: flex thumb (CMC and MCP joints)

Opponens pollicis
Action: opposition of thumb (CMC joint)

Front 26

adductor pollicis

Back 26

o (oblique and transverse heads)
o NOT part of the thenar eminence, it occupies the adductor compartment
o Innervated by the ulnar nerve
o Action: adduct thumb (CMC joint)

Front 27

hypothenar muscles

Back 27

o Innervated by the ulnar nerve

Abductor digiti minimi
Action: abduct digit 5 (MCP joint)

Flexor digiti minimi brevis
Action: flex digit 5 (CMC and MCP joints)

Opponens digiti minimi
Action: opposition of digit 5 (CMC joint)

Front 28

central compartment muscles

Back 28

o Lumbricals (4)
o Origin: tendons of flexor digitorum profundus
o Insertion: extensor expansions of digits 2-5
o Action: flex MCP joints and extend PIP & DIP joints of digits 2-5
o Innervation: median nerve (lateral ½), ulnar nerve (medial ½)

Front 29

interossei

Back 29

o Innervated by the ulnar nerve

o Palmar interossei (n=3)
Action: adduct (“PAD”) MCP joints of digits 2, 4, & 5

o Dorsal interossei (n=4)
Action: abduct (“DAB”) MCP joints of digits 2-4

Front 30

median nerve

Back 30

o Does NOT innervate structures in the arm
o Courses through the cubital fossa
o “Mostly median” Innervates most of the muscles of the anterior forearm
o Proximal to flexor retinaculum, gives off branch (sensory to central palm)
o Travels deep to flexor retinaculum, within the carpal tunnel
o Recurrent branch: motor to the 3 thenar muscles

Front 31

proximal lesion of median nerve

Back 31

1) Pronation lost
2) Flexion and abduction of wrist weakened dramatically
3) Flexion of PIPs of digits 2-5 and DIPs of digits 2-3 lost
4) Affects opposition of the thumb (3 thenar muscles)
5) Lumbricals to digits 2 and 3 paralyzed
6) Skin of the lateral palm and digits anesthetized
7) Test: pad-to-pad opposition of thumb, cutaneous sensation tip of digit 2

Front 32

ulnar nerve

Back 32

o Does NOT innervate structures in the arm
o Passes posterior to the medial epicondyle of the humerus, within cubital tunnel (area of the “funny bone”)
- Can be compressed here (cubital tunnel syndrome)
- Also at risk with a fracture of the medial epicondyle
- Innervates flexor carpi ulnaris, medial (ulnar) ½ of flexor digitorum profundus

Front 33

Common and proper digital nerves of median nerve

Back 33

motor to lumbricals to digits 2 & 3; sensory to skin on lateral palm and lateral 3 ½ digits

Front 34

path of ulnar nerve

Back 34

o Travels superficial to the flexor retinaculum with the ulnar artery
- Due to its location superficial to the flexor retinaculum, suicide attempts by wrist slashing can sever the ulnar nerve, resulting in full paralysis and anesthesia of the innervated structures

Front 35

deep branch of ulnar nerve

Back 35

motor to hypothenar muscles, interossei, lumbricals to digits 4 & 5, and adductor pollicis

Front 36

common and proper digital nerves of ulnar nerve

Back 36

sensory to skin on medial aspect of the palm, medial 1 ½ digits (also medial aspect of dorsal hand)

Front 37

proximal lesion of ulnar nerve

Back 37

1) Flexion and adduction of the wrist weakened
2) Flexion of DIPs of digits 4-5 lost
3) Affects grasp (hypothenar & adductor pollicis muscles paralyzed)
4) Intricate hand movements affected. Interossei muscles paralyzed (adduction/abduction of digits 2-5 lost), lumbricals to digits 4 & 5 paralyzed (MCP flexion, PIP & DIP extension affected).
5) Skin of medial hand anesthetized
6) Test: adduct/abduct digits 2-5, cutaneous sensation tip of digit 5

Front 38

posterior compartment of the forearm

Back 38

- Superficial group (crosses elbow) and deep group (do not cross elbow)
- Innervated by the radial nerve
- Functions:
o Extend wrist joint and fingers (e.g., at MCP and IP joints)
o Supinate forearm (palm up)
o Abduct (radial deviation)/Adduct (ulnar deviation) wrist joint
o Extend, abduct, reposition the thumb

Front 39

extensor retinaculum

Back 39

o Band of deep fascia holding long extensor tendons in place as they cross the wrist
o Tendons are surrounded by synovial sheaths (allow tendons to move freely)

Front 40

synovial (ganglionic) cysts

Back 40

(fluid-filled swellings) can develop within the synovial sheaths; the cause is unknown, but movement enlarges the cysts. Common site of occurrence: synovial sheath of the extensor carpi radialis brevis tendon.

Front 41

superficial group of posterior compartment of forearm

Back 41

o Common site of origin: Lateral Epicondyle of Humerus
o Lateral epicondylitis (tennis elbow): inflammation of the common extensor origin and periosteum of the lateral epicondyle
o brachioradilais, extensor carpi radialis longus, extensor carpi radialis brevis, extensor carpi ulnaris, extensor digitorum, extensor digiti minimi

Front 42

brachioradialis

Back 42

o Insertion: distal radius
o Action: flex elbow joint (exception to posterior compartment action rule)
o Note: a brachioradialis reflex test can be used to assess the C6 spinal level

Front 43

extensor carpi radialis longus

Back 43

o part of posterior compartment of arm; innervated by radial nerve
o Insertion: radial (lateral) side of hand
o Action: extend and abduct wrist joint

Front 44

infection of palm

Back 44

Infections in the hypothenar, thenar, and adductor compartments usually cause swelling on the dorsal aspect of the hand because the palmar fascia (& aponeurosis) is so taut that expansion in a palmar direction is limited

o Untreated infections of the central compartment can spread through the carpal tunnel and into the anterior compartment of the forearm

Front 45

extensor carpi radialis brevis

Back 45

o Insertion: radial (lateral) side of hand
o Action: extend and abduct wrist joint

Front 46

extensor carpi ulnaris

Back 46

o Insertion: ulnar (medial) side of hand
o Action: extend and adduct wrist joint

Front 47

extensor digitorum

Back 47

o Insertion: forms extensor expansions of digits 2-5
o Action: extend digits 2-5 (MCP, PIP, and DIP joints), extend wrist joint

Front 48

extensor digit minimi

Back 48

o Insertion: helps form extensor expansion of digit 5
o Action: extend digit 5 (MCP, PIP, and DIP joints)

Front 49

deep group of posterior compartment of forearm

Back 49

Origins off: ulna, radius, interosseous membrane

Abductor pollicis longus
Action: abduct and extend thumb (CMC joint)

Extensor pollicis brevis
Action: extend thumb (CMC and MCP joints)

Extensor pollicis longus
Action: extend thumb at (CMC, MCP and IP joints)

Extensor indicis
Insertion: extensor expansion of digit 2
Action: extend digit 2 (MCP, PIP and DIP joints)

Supinator
Insertion: proximal radius
Action: supinate forearm (when elbow is flexed or extended)
Note: Biceps brachii also supinates the forearm, but it requires a flexed elbow

Front 50

dorsal hand

Back 50

o Long extensor tendons only (no muscle)
o Dorsal interossei are not part of this compartment
o Anatomical Snuff Box

Front 51

anatomical snuff box

Back 51

o Depression proximal to the thumb, on the dorsal hand
o Most prominent when thumb is fully extended
o Anterior border: tendons of abductor pollicis longus and extensor pollicis brevis
o Posterior border: tendon of extensor pollicis longus
o Floor: scaphoid and trapezium bones
o Contents: radial artery
o The scaphoid bone can fracture as a result of landing on an outstretched hand. This type of fracture presents as tenderness/pain upon palpation of the anatomical snuff box.

Front 52

radial nerve

Back 52

o Travels in radial groove of the humerus with the deep artery of the arm
 Susceptible to injury with midshaft humeral fractures
o Innervates all the muscles in the posterior compartment of the arm
o Innervates the skin of the posterior arm
o Posterior cutaneous nerve of the forearm branches off in the arm, and innervates the skin on the posterior forearm
o Divides into deep and superficial branches near the elbow

Front 53

deep branch / posterior interosseus nerve of radial nerve

Back 53

(posterior interosseous nerve) innervates the muscles of the posterior compartment of forearm

Front 54

superficial branch of radial nerve

Back 54

provides sensory innervation for skin of lateral wrist (including skin over the anatomical snuff box) and the lateral aspect of the dorsal hand

Front 55

proximal lesion of radial nerve

Back 55

1) Loss of elbow extension
2) Loss of extension at the wrist and MCP joints (“wrist drop”)
3) Supination maintained by biceps brachii
4) Skin anesthetized along posterior arm, forearm, and dorsolateral wrist and hand

Front 56

brachial artery

Back 56

gives rise to the ulnar and radial arteries in the cubital fossa

Front 57

ulnar artery

Back 57

• Gives rise to common interosseous artery, which divides into:
- Anterior interosseous artery supplies muscles deep in the anterior and posterior forearm compartments
- Posterior interosseous artery is the main supply of blood to the posterior forearm
• Gives rise to ulnar recurrent arteries (anastomoses around elbow)
• Travels with ulnar nerve along medial aspect of forearm
• Courses superficial to flexor retinaculum with ulnar nerve (can palpate ulnar pulse here)
• Gives rise to superficial palmar arch which provides primary blood supply to the common and proper digital arteries
• Anastomoses with the radial artery via the superficial and deep palmar arches

Front 58

radial artery

Back 58

• Gives rise to radial recurrent artery (anastomoses around elbow)
• The pulse rate is usually measured on the radial artery at the wrist, where it lies lateral to the tendon of flexor carpi radialis
• Courses through the anatomical snuff box
• Gives rise to deep palmar arch which provides modest blood supply to the digital arteries (exception: main blood supply to the thumb)
• Anastomoses with the ulnar artery via the superficial and deep palmar arches

Front 59

dorsal carpal arch

Back 59

o Ulnar, radial, and anterior interosseous arteries form the dorsal carpal arch
o Dorsal carpal arch provides blood to digits, but the palmar arches (superficial and deep) provide the majority of the blood to the hand

Front 60

deep veins of forearm and hand

Back 60

o Accompany arteries and have the same names (e.g., ulnar, radial)
o Typically paired
o Communicate with superficial veins
o Note: most of the hand is drained by the superficial veins on the dorsal hand which eventually drain into the cephalic and basilic veins