Forearm Anatomy
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1
What anatomical extent defines the forearm?
From the elbow to the wrist
2
Which structure joins the radius and ulna along the forearm?
Interosseous membrane
3
What are three functions of the forearm interosseous membrane?
Ties forearm bones together, permits pronation/supination, and provides proximal attachment for deep muscles
4
Where are the head of the ulna and head of the radius located in the forearm?
Head of the ulna is distal; head of the radius is proximal
5
What defines the proximal boundary of the forearm?
The joint plane of the elbow
6
What is the functional role of forearm movement?
Assists the shoulder in applying force and controlling hand placement in space
7
Why do the wrist and finger flexors and extensors attach to the humeral epicondyles and ridges?
Elbow flexors and extensors occupy the central space
8
Why does the anterior compartment of the forearm communicate with the palm?
It passes through the carpal tunnel into the central palm compartment
9
How do the anterior flexor muscles compare in bulk and strength to the posterior extensor muscles?
Flexor muscles have approximately 2 times the bulk and strength of extensors
10
What separates the anterior flexor-pronator compartment from the posterior extensor compartment?
The radius, ulna, and the distal two-thirds of the interosseous membrane
11
Which structures hold the anterior wrist flexor tendons in place?
Palmar carpal ligament and flexor retinaculum (transverse carpal ligament)
12
Into how many functional layers are the anterior compartment forearm muscles arranged?
Three layers (superficial, intermediate, and deep)
13
Which four muscles comprise the superficial layer of the anterior forearm?
Pronator teres, flexor carpi radialis (FCR), palmaris longus, and flexor carpi ulnaris (FCU)
14
What forms the medial boundary of the cubital fossa?
Lateral border of the pronator teres
15
What are the proximal attachments (origins) of the pronator teres?
Ulnar head from coronoid process; humeral head from medial epicondyle (common flexor origin)
16
What is the distal attachment (insertion) of the pronator teres?
Middle of the convexity of the lateral surface of the radius
17
Which nerve innervates the pronator teres?
Median nerve (\$C_6, C_7\$)
18
What is the primary action of the pronator teres?
Pronates and flexes the forearm
19
What are the proximal and distal attachments of the flexor carpi radialis (FCR)?
Proximal: medial epicondyle; Distal: base of 2nd metacarpal
20
Which nerve innervates the flexor carpi radialis?
Median nerve (\$C_7, C_8\$)
21
What are the primary actions of the flexor carpi radialis?
Flexes and abducts (radially deviates) the hand at the wrist
22
In approximately what percentage of people is the palmaris longus absent?
Approximately 14% (on one or both sides)
23
Where does the palmaris longus tendon insert distally?
Distal half of flexor retinaculum and apex of palmar aponeurosis
24
Which nerve innervates the palmaris longus?
Median nerve (\$C_7, C_8\$)
25
What is the primary action of the palmaris longus?
Flexes the hand at the wrist and tenses the palmar aponeurosis
26
How does the ulnar nerve enter the forearm relative to the flexor carpi ulnaris?
Passes between the humeral and ulnar heads of its proximal attachment
27
Which superficial anterior forearm muscle is innervated by the ulnar nerve instead of the median nerve?
Flexor carpi ulnaris (FCU)
28
What are the distal attachments of the flexor carpi ulnaris?
Pisiform, hook of hamate, and 5th metacarpal
29
Which nerve innervates the flexor carpi ulnaris?
Ulnar nerve (\$C_7, C_8\$)
30
What are the primary actions of the flexor carpi ulnaris?
Flexes and adducts (ulnarly deviates) the hand at the wrist
31
Which muscle comprises the intermediate (second) layer of the anterior forearm?
Flexor digitorum superficialis (FDS)
32
Which nerve and artery enter the forearm by passing between the heads of the flexor digitorum superficialis?
Median nerve and ulnar artery
33
Where do the four tendons of the flexor digitorum superficialis insert distally?
Base and shaft of the middle phalanges of the medial four digits
34
Which nerve innervates the flexor digitorum superficialis?
Median nerve (\$C_7\text{--}T_1\$)
35
What is the primary action of the flexor digitorum superficialis?
Flexes middle phalanges at PIP joints, and assists with MCP and wrist flexion
36
Which three muscles comprise the deep (third) layer of the anterior forearm?
Flexor digitorum profundus (FDP), flexor pollicis longus (FPL), and pronator quadratus
37
What is the proximal attachment of the flexor digitorum profundus?
Proximal \$\frac{3}{4}\$ of medial and anterior surfaces of ulna and interosseous membrane
38
Where do the lateral and medial parts of the flexor digitorum profundus insert distally?
Lateral part: bases of distal phalanges of digits 2 and 3; Medial part: bases of distal phalanges of digits 4 and 5
39
Which nerve innervates the lateral part of the flexor digitorum profundus (digits 2 and 3)?
Anterior interosseous nerve (\$C_8, T_1\$)
40
Which nerve innervates the medial part of the flexor digitorum profundus (digits 4 and 5)?
Ulnar nerve (\$C_8, T_1\$)
41
What is the primary action of the flexor digitorum profundus?
Flexes distal phalanges of digits 2–5 at the DIP joints
42
Which muscle is the sole flexor of the interphalangeal (IP) joint of the thumb?
Flexor pollicis longus (FPL)
43
What are the proximal and distal attachments of the flexor pollicis longus?
Proximal: anterior surface of radius and interosseous membrane; Distal: base of distal phalanx of thumb
44
Which nerve innervates the flexor pollicis longus?
Anterior interosseous nerve (\$C_8\text{--}T_1\$)
45
What are the proximal and distal attachments of the pronator quadratus?
Proximal: distal \$\frac{1}{4}\$ of anterior surface of ulna; Distal: distal \$\frac{1}{4}\$ of anterior surface of radius
46
Which nerve innervates the pronator quadratus?
Anterior interosseous nerve (\$C_8\text{--}T_1\$)
47
What are the primary actions of the pronator quadratus?
Pronates the forearm and binds the radius and ulna together
48
What structure forms the superficial roof of the carpal tunnel?
Flexor retinaculum (transverse carpal ligament)
49
What are the four bony attachment points of the flexor retinaculum?
Pisiform, hook of hamate, scaphoid tubercle, and tubercle of trapezium
50
How many total tendons and nerves pass through the carpal tunnel?
9 tendons and 1 nerve
51
Which nerve passes through the carpal tunnel?
Median nerve
52
Which nine tendons pass through the carpal tunnel?
4 tendons of FDS, 4 tendons of FDP, and 1 tendon of FPL
53
What resting hand deformity results from distal median nerve damage in carpal tunnel syndrome?
Ape hand
54
What clinical hand presentation occurs when a patient with a median nerve injury attempts to close their hand into a fist?
Hand of benediction
55
What nerve injury is associated with wrist drop according to the DR. CUMA mnemonic?
Radial nerve injury (DR = Drop Radial)
56
What nerve injury is associated with claw hand according to the DR. CUMA mnemonic?
Ulnar nerve injury (CU = Claw Ulnar)
57
What are the superficial and deep boundaries of Guyon's canal (tunnel)?
Superficial: palmar (volar) carpal ligament; Deep: flexor retinaculum
58
What neurovascular structures travel inside Guyon's canal?
Ulnar nerve and ulnar artery
59
Where does the ulnar artery originate?
As the larger terminal branch of the brachial artery in the cubital fossa
60
Which artery branches from the ulnar artery to quickly divide into anterior and posterior interosseous arteries?
Common interosseous artery
61
Which artery runs distally on the anterior aspect of the interosseous membrane to the pronator quadratus?
Anterior interosseous artery
62
Which artery branches from the posterior interosseous artery to anastomose with the middle collateral artery?
Recurrent interosseous artery
63
What arterial arch is formed by the anastomosis of the palmar carpal branches of the radial and ulnar arteries?
Palmar carpal arch
64
Where does the radial artery run in the distal forearm relative to the FCR tendon?
Lies lateral to the flexor carpi radialis tendon
65
Which anatomical space does the radial artery cross on the lateral wrist before piercing the first dorsal interosseous muscle?
Floor of the anatomical snuffbox
66
Which artery ascends between brachioradialis and brachialis to anastomose with the radial collateral artery?
Radial recurrent artery
67
In which forearm compartment do the extensor muscles reside?
Posterior (extensor-supinator) compartment
68
Which nerve innervates all muscles of the extensor compartment of the forearm?
Radial nerve (and its branches)
69
What are the three physiological functional groups of forearm extensor muscles?
Muscles that extend/abduct/adduct the wrist, muscles that extend the medial four fingers, and muscles that extend or abduct the thumb
70
Which three muscles extend and abduct/adduct the hand at the wrist?
Extensor carpi radialis longus (ECRL), extensor carpi radialis brevis (ECRB), and extensor carpi ulnaris (ECU)
71
Which three muscles extend the medial four fingers?
Extensor digitorum, extensor indicis, and extensor digiti minimi
72
Which three muscles extend or abduct the thumb?
Abductor pollicis longus (APL), extensor pollicis brevis (EPB), and extensor pollicis longus (EPL)
73
What are the three structural anatomical layers of the posterior forearm muscles?
Superficial layer, deep layer, and outcropping muscles of the deep layer
74
Which six muscles make up the superficial layer of the extensor compartment?
Brachioradialis, ECRL, ECRB, extensor digitorum, extensor digiti minimi, and ECU
75
Which two muscles comprise the deep layer of the extensor compartment?
Supinator and extensor indicis
76
Which three muscles are the outcropping muscles of the deep layer?
Abductor pollicis longus, extensor pollicis brevis, and extensor pollicis longus
77
What forms the lateral border of the cubital fossa?
Brachioradialis
78
Why is the brachioradialis unique among extensor compartment muscles?
It acts as a flexor of the forearm at the elbow
79
Does the brachioradialis cross the wrist joint?
No, it inserts proximal to the wrist
80
What is the proximal attachment of the brachioradialis?
Proximal \$\frac{2}{3}\$ of the lateral supra-epicondylar ridge of the humerus
81
What is the distal attachment of the brachioradialis?
Lateral surface of the distal end of the radius proximal to the styloid process
82
Which nerve innervates the brachioradialis?
Radial nerve (\$C_5\text{--}C_7\$)
83
In which forearm position is flexion force of the brachioradialis maximal?
Mid-pronated ("handshake") position
84
Which two tendons cross the tendon of the extensor carpi radialis longus?
Abductor pollicis longus (APL) and extensor pollicis brevis (EPB)
85
Why is the extensor carpi radialis longus indispensable during fist clenching?
It prevents wrist flexion caused by the finger flexors, maintaining optimal grip force
86
What is the proximal attachment of the extensor carpi radialis longus?
Lateral supra-epicondylar ridge of the humerus
87
What is the distal attachment of the extensor carpi radialis longus?
Dorsal aspect of the base of the 2nd metacarpal
88
Which nerve innervates the extensor carpi radialis longus?
Radial nerve (\$C_6, C_7\$)
89
What are the primary actions of the extensor carpi radialis longus?
Extends and abducts (radially deviates) the hand at the wrist
90
How does the length and origin of the ECRB compare to the ECRL?
ECRB is shorter and arises more distally from the lateral epicondyle
91
What is the proximal attachment of the extensor carpi radialis brevis?
Lateral epicondyle of the humerus (common extensor origin)
92
What is the distal attachment of the extensor carpi radialis brevis?
Dorsal aspect of the base of the 3rd metacarpal
93
Which nerve branch innervates the extensor carpi radialis brevis?
Deep branch of the radial nerve (\$C_7, C_8\$)
94
What are the primary actions of the extensor carpi radialis brevis?
Extends and abducts the hand at the wrist
95
What is the principal extensor of the medial four digits?
Extensor digitorum
96
Which muscle tendon shares a synovial sheath with the extensor digitorum under the extensor retinaculum?
Extensor indicis
97
What structures link the extensor digitorum tendons proximal to the MCP joints?
Three oblique intertendinous connections
98
Which finger's independent extension is most restricted by intertendinous connections?
The ring finger (4th digit)
99
What is the proximal attachment of the extensor digitorum?
Lateral epicondyle of the humerus (common extensor origin)
100
What is the distal attachment of the extensor digitorum?
Extensor expansions of the medial four digits
101
Which nerve innervates the extensor digitorum?
Posterior interosseous nerve (\$C_7, C_8\$)
102
At which joints does the extensor digitorum primarily act?
Metacarpophalangeal (MCP) joints
103
From which muscle is the extensor digiti minimi a partially detached slip?
Extensor digitorum
104
What is the distal attachment of the extensor digiti minimi?
Extensor expansion of the 5th digit
105
Which nerve innervates the extensor digiti minimi?
Posterior interosseous nerve (\$C_7, C_8\$)
106
What is the primary action of the extensor digiti minimi?
Extends the 5th digit primarily at the MCP joint
107
What are the two heads of origin for the extensor carpi ulnaris (ECU)?
Humeral head (common extensor tendon) and ulnar head (posterior border of ulna via shared aponeurosis)
108
Where does the distal tendon of the ECU run at the wrist?
In a groove between the ulnar head and ulnar styloid process
109
What is the distal attachment of the extensor carpi ulnaris?
Dorsal aspect of the base of the 5th metacarpal
110
Which nerve innervates the extensor carpi ulnaris?
Posterior interosseous nerve (\$C_7, C_8\$)
111
What are the primary actions of the extensor carpi ulnaris?
Extends and adducts (ulnarly deviates) the hand at the wrist
112
Which two muscles form the floor of the cubital fossa?
Brachialis and supinator
113
Which nerve passes between the fibers of the supinator muscle?
Deep branch of the radial nerve
114
What does the deep branch of the radial nerve become after emerging from the supinator?
Posterior interosseous nerve
115
Which muscle is the prime mover for slow, unopposed supination with an extended forearm?
Supinator
116
Which muscle is the prime mover for rapid, resisted supination when the elbow is flexed?
Biceps brachii
117
What are the proximal attachments of the supinator?
Lateral epicondyle of humerus, radial collateral and anular ligaments, supinator fossa, and supinator crest of ulna
118
What is the distal attachment of the supinator?
Lateral, posterior, and anterior surfaces of the proximal \$\frac{1}{3}\$ of the radius
119
Which nerve innervates the supinator?
Deep branch of the radial nerve (\$C_7, C_8\$)
120
What functional advantage does the extensor indicis provide to the hand?
Confers independence to the index finger
121
What is the proximal attachment of the extensor indicis?
Posterior surface of the distal \$\frac{1}{3}\$ of the ulna and interosseous membrane
122
What is the distal attachment of the extensor indicis?
Extensor expansion of the 2nd digit
123
Which nerve innervates the extensor indicis?
Posterior interosseous nerve (\$C_7, C_8\$)
124
What are the proximal attachments of the abductor pollicis longus (APL)?
Posterior surface of proximal halves of ulna, radius, and interosseous membrane
125
What are the distal attachments of the abductor pollicis longus?
Lateral base of the 1st metacarpal (and sometimes trapezium)
126
Which nerve innervates the abductor pollicis longus?
Posterior interosseous nerve (\$C_7, C_8\$)
127
What are the primary actions of the abductor pollicis longus?
Abducts the thumb and extends it at the carpometacarpal (CMC) joint
128
What is the proximal attachment of the extensor pollicis brevis (EPB)?
Posterior surface of the distal \$\frac{1}{3}\$ of the radius and interosseous membrane
129
What is the distal attachment of the extensor pollicis brevis?
Dorsal aspect of the base of the proximal phalanx of the thumb
130
Which nerve innervates the extensor pollicis brevis?
Posterior interosseous nerve (\$C_7, C_8\$)
131
What is the primary action of the extensor pollicis brevis?
Extends the proximal phalanx of the thumb at the MCP joint
132
Which tendon forms the dorsal (ulnar) boundary of the anatomical snuffbox?
Extensor pollicis longus (EPL) tendon
133
Which tendons form the palmar (radial) boundary of the anatomical snuffbox?
Abductor pollicis longus (APL) and extensor pollicis brevis (EPB) tendons
134
Which major artery lies in the floor of the anatomical snuffbox?
Radial artery
135
Which carpal bones can be palpated in the floor of the anatomical snuffbox?
Scaphoid and trapezium
136
Which bony landmark serves as an anatomical pulley for the extensor pollicis longus tendon?
Dorsal tubercle of the radius (Lister's tubercle)
137
What is the proximal attachment of the extensor pollicis longus?
Posterior surface of the middle \$\frac{1}{3}\$ of the ulna and interosseous membrane
138
What is the distal attachment of the extensor pollicis longus?
Dorsal aspect of the base of the distal phalanx of the thumb
139
Which nerve innervates the extensor pollicis longus?
Posterior interosseous nerve (\$C_7, C_8\$)
140
What is the primary action of the extensor pollicis longus?
Extends the distal phalanx of the thumb at the IP joint
141
What is the primary function of the extensor retinaculum at the wrist?
Holds extensor tendons in place and prevents bowstringing
142
How many osseofibrous compartments exist under the extensor retinaculum?
6 compartments
143
Which tendons pass through Compartment 1 of the extensor retinaculum?
Abductor pollicis longus (APL) and extensor pollicis brevis (EPB)
144
Which tendons pass through Compartment 2 of the extensor retinaculum?
Extensor carpi radialis longus (ECRL) and extensor carpi radialis brevis (ECRB)
145
Which tendon passes through Compartment 3 of the extensor retinaculum?
Extensor pollicis longus (EPL)
146
Which tendons pass through Compartment 4 of the extensor retinaculum?
Extensor digitorum and extensor indicis
147
Which tendon passes through Compartment 5 of the extensor retinaculum?
Extensor digiti minimi (EDM)
148
Which tendon passes through Compartment 6 of the extensor retinaculum?
Extensor carpi ulnaris (ECU)
149
Which cutaneous nerve provides sensory innervation to the lateral surface of the forearm?
Lateral cutaneous nerve of the forearm
150
Which cutaneous nerve provides sensory innervation to the posterior midline of the forearm?
Posterior cutaneous nerve of the forearm
151
Which cutaneous nerve provides sensory innervation to the medial side of the forearm?
Medial cutaneous nerve of the forearm
152
Which branch of the radial nerve supplies sensory innervation to the dorsum of the hand?
Superficial branch of the radial nerve
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