TBL6 - Muscles, Nerves, and Arteries of the Forearm

Question 1

What do most muscles in the anteromedial forearm contribute to?

Answer 1

Most muscles in the anteromedial forearm contribute to flexion of the wrist, MCP, and IP joints

Question 2

Where is the brachioradialis located and where does it attach? What function does it have?

Answer 2

1) The brachioradialis muscle crosses the elbow joint and attaches to the distal radius
2) Thus, the brachioradialis assists in forearm flexion mainly in the pronated or semi-prone position

Question 3

What is the main proximal attachment for the superficial and intermediate muscles of the anteromedial forearm?

Answer 3

The medial epicondyle of the humerus is the main proximal attachment for the superficial and intermediate muscles of the anteromedial forearm

Question 4

What are the muscles that mainly flex the hand at the wrist? What are the muscles that mainly flex the middle phalanges of digits 2 to 5?

Answer 4

1) Flexor carpi radialis (FCR) - Flexes and abducts hand (at wrist)
2) Palmaris longus - Flexes hand (at wrist) and tenses palmar aponeurosis
3) Humeral head & Ulnar head of the Flexor carpi ulnaris (FCU) - Flexes and adducts hand (at wrist)
4) Humero-ulnar head & Radial head of the Flexor digitorum superficialis (FDS) - Flexes middle phalanges at proximal interphalangeal joints of middle four digits; acting more strongly, it also flexes proximal phalanges at metacarpophalangeal joints

Question 5

What do metacarpal attachments of the flexor carpi radialis (FCR) and flexor carpi ulnaris (FCU) muscles do individually? What do these muscles do when working together?

Answer 5

1) Metacarpal attachments of the flexor carpi radialis (FCR) and flexor carpi ulnaris (FCU) muscles abduct and adduct the hand, respectively
2) When working together, the muscles flex the hand at the wrist joint

Question 6

What flexes the distal phalanges of digits 2 to 5? What flexes both phalanges of digit 1?

Answer 6

1) The flexor digitorum profundus (FDP) of the deep muscle layer has distal tendinous attachments for flexion of the distal phalanges of digits 2 to 5
2) The flexor pollicis longus muscle (FPL) has distal tendinous attachment for flexion of both phalanges of digit 1

Question 7

Compare the pronator quadratus of the deep muscle layer to the pronator teres muscle in the superficial layer. What do both function to do?

Answer 7

1) Pronator quadratus - Pronates forearm; deep fibers bind radius and ulna together
2) Pronator teres - Pronates and flexes forearm (at elbow)
3) Both muscles function to pronate the forearm and hand (teres - more at the elbow; quadratus - more at the wrist)

Question 8

Which activities cause pronator syndrome and where does pain occur?

Answer 8

1) Pronator syndrome, a nerve entrapment syndrome, is caused by compression of the median nerve near the elbow
2) The nerve may be compressed between the heads of the pronator teres as a result of trauma, muscular hypertrophy, or fibrous bands
3) Individuals with this syndrome are first seen clinically with pain and tenderness in the proximal aspect of the anterior forearm, and hypesthesia (decreased sensation) of palmar aspects of the radial three and half digits and adjacent palm
4) Symptoms often follow activities that involve repeated pronation

Question 9

Where does the ulnar nerve derive from and what is a medial branch of this derivation?

Answer 9

The ulnar nerve is the direct continuation of the medial cord and the medial pectoral nerve is a branch of the medial cord

Question 10

Where does the ulnar nerve travel to?

Answer 10

The ulnar nerve descends in the medial aspect of the arm and passes posterior to the medial epicondyle of the humerus into the forearm

Question 11

What is the anatomical basis for avulsion of the medial epicondyle in children and which nerve is often injured?

Answer 11

1) Avulsion (forced separation) of the medial epicondyle in children can result from a fall that causes severe abduction of the extended elbow, an abnormal movement of this articulation
2) The anatomical basis of the avulsion is that the epiphysis for the medial epicondyle may not fuse with the distal end of the humerus until up to age 20
3) Traction injury of the ulnar nerve is a frequent complication of the abduction type of avulsion of the medial epicondyle of the humerus

Question 12

Where does the ulnar nerve pass through?

What does the ulnar nerve innervate?

Answer 12

1) The ulnar nerve passes between the humeral and ulnar heads of the Flexor Carpi Ulnaris (FCU) to enter the forearm where it courses distally on the medial aspect of the Flexor Digitorum Profundus (FDU)
2) Thus, the ulnar nerve innervates the FCU and portion of the FDP that acts on the 4th and 5th digits

Question 13

What forms the muscular floor of the cubital fossa? From the fossa, where does the median nerve travel? What does the median nerve innervate?

Answer 13

1) The brachialis and supinator muscles form the muscular floor of the cubital fossa
2) From the fossa, the median nerve descends in the midline of the forearm
3) Thus, except the FCU, the median nerve innervates the superficial and intermediate muscles of the anteromedial forearm

Question 14

Where does the anterior interosseous nerve originate from? What does the anterior interosseous nerve innervate?

Answer 14

1) The median nerve generates the anterior interosseous nerve
2) The anterior interosseous nerve supplies the lateral portion of flexor digitorum profundus (FDP) acting on the distal phalanges of the 2nd and 3rd digits, the pronator quadratus and the flexor pollicis longus (FPL)

Question 15

What is the palmar carpal ligament derived from?

Answer 15

The palmar carpal ligament is a thickening of the ante-brachial fascia at the wrist

Question 16

What is the carpal tunnel? What nerve passes through it?

Answer 16

1) The carpal tunnel or carpal canal is the passageway on the palmar side of the wrist that connects the forearm to the middle compartment of the deep plane of the palm
2) The tunnel consists of bones and connective tissue
3) Several tendons and the median nerve pass through it

Question 17

Name the nine tendons that traverse the underlying carpal tunnel into the palm

Answer 17

A total of nine flexor tendons (not the muscles themselves) pass through the carpal tunnel:

1) Flexor digitorum profundus (four tendons)
2) Flexor digitorum superficialis (four tendons)
3) Flexor pollicis longus (one tendon)

Question 18

What do the tendons of the flexor digitorum superficialis (FDS) and the flexor digitorum profundis (FDP) pass through in the wrist?

Answer 18

Tendons of the FDS and FDP enter the common flexor sheath that originates at the wrist and extends through the carpal tunnel into the central palm

Question 19

Only the sheath of which digit is continuous with the common flexor sheath? What do these sheaths allow for?

Answer 19

1) Of the digital synovial sheaths, only the sheath of the 5th digit is continuous with the common flexor sheath
2) The sheaths enable the tendons to slide freely over each other during movements of the fingers

Question 20

How does dislocation of the lunate typically occur and what are the resulting symptoms?

Answer 20

1) Anterior dislocation of the lunate is an uncommon but serious injury that usually results from a fall on the dorsiflexed wrist
2) The lunate is pushed out of its place in the floor of the carpal tunnel toward the palmar surface of the wrist
3) The displaced lunate may compress the median nerve and lead to carpal tunnel syndrome
4) Because of its poor blood supply, avascular necrosis of the lunate may occur. In some cases, excision of the lunate may be required
5) In degenerative joint disease of the wrist, surgical fusion of carpals (arthrodesis) may be necessary to relieve the severe pain

Question 21

How are the 4th and 5th digits affected by Dupuytren contracture and how is it treated?

Answer 21

1) Dupuytren contracture is a disease of the palmar fascia resulting in progressive shortening, thickening, and fibrosis of the palmar fascia and aponeurosis
2) The fibrous degeneration of the longitudinal bands of the palmar aponeurosis on the medial side of the hand pulls the 4th and 5th fingers into partial flexion at the metacarpophalangeal and proximal interphalangeal joints
3) Treatment of Dupuytren contracture usually involves surgical excision of all fibrotic parts of the palmar fascia to free the fingers

Question 22

How do the common flexor sheath and the digital synovial sheathes determine the spread of infection from tenosynovitis?

Answer 22

1) Because the synovial sheath of the little finger is usually continuous with the common flexor sheath, tenosynovitis in this finger may spread to the common flexor sheath and thus through the palm and carpal tunnel to the anterior forearm, draining into the space between the pronator quadratus and the overlying flexor tendons (Parona space)
2) Likewise, tenosynovitis in the thumb may spread via the continuous synovial sheath of the FPL (radial bursa)

Question 23

What is the function of the brachioradialis? Where does it reside?

Answer 23

1) The brachioradialis flexes the forearm

2) The brachioradialis resides in the superficial muscle layer of the posterolateral forearm

Question 24

In which layer in the supinator muscle found in the forearm? Where does it attach proximally and distally?

Answer 24

1) The deep layer of the forearm includes the supinator muscle
2) The supinator muscle attaches proximally to the lateral epicondyle of the humerus and proximal ulna
3) The supinator muscle attaches distally to the proximal radius

Question 25

When does the supinator muscle supinate the forearm and when does the biceps contribute to the supination?

Answer 25

1) The supinator is the prime mover for slow, unopposed supination, especially when the forearm is extended 2) The biceps brachii also supinates the forearm and is the prime mover during rapid and forceful supination against resistance when the forearm is flexed (e.g., when a right-handed person drives a screw)

Question 26

What is the main proximal attachment for the superficial extensor muscle layer?

Answer 26

The lateral epicondyle of the humerus is the main proximal attachment for the superficial muscle layer

Question 27

Where does the extensor digitorum mainly induce extension?

Answer 27

The extensor digitorum induces extension mainly at the MCP joints and secondarily at the IP joints

Question 28

What do the four tendons of the extensor digitorum do? What do the extensor expansions do?

Answer 28

1) The four tendons of the extensor digitorum flatten to form extensor expansions that wrap around the MCP joints and proximal phalanges before attaching to the middle and distal phalanges of the fingers 2) The extensor expansions hold the extensor tendons in the midline of the digits

Question 29

What causes elbow tendinitis, what are its symptoms, and when does it lead to lateral epicondylitis?

Answer 29

1) Elbow tendinitis (“tennis elbow”) is a painful musculoskeletal condition that may follow repetitive use of the superficial extensor muscles of the forearm 2) Pain is felt over the lateral epicondyle and radiates down the posterior surface of the forearm. People with elbow tendinitis often feel pain when they open a door or lift a glass 3) Repeated forceful flexion and extension of the wrist strain the attachment of the common extensor tendon, producing inflammation of the periosteum of the lateral epicondyle (lateral epicondylitis)

Question 30

How is a long extensor tendon commonly avulsed from its distal attachment and what is the resultant deformity?

Answer 30

1) Sudden severe tension on a long extensor tendon may avulse part of its distal attachment to the phalanx. The most common result of the injury is a mallet or baseball finger 2) This deformity results from the distal interphalangeal joint suddenly being forced into extreme flexion (hyperflexion) when, for example, a baseball is miscaught or a finger is jammed into the base pad 3) As a result, the person cannot extend the distal interphalangeal joint 4) The resultant deformity bears some resemblance to a mallet

Question 31

What digit does the extensor digiti minimi act on?

Answer 31

The extensor digiti minimi is partially detached from the extensor digitorum to act mainly on digit 5

Question 32

What digit does the extensor indicis act on?

Answer 32

The extensor indicis of the deep muscle layer independently extends digit 2

Question 33

What do the extensor carpi radialis longus (ECRL), extensor carpi radialis brevis (ECRB), and the extensor carpi ulnaris (ECU) brevis do? What enables these muscles to do so?

Answer 33

1) The extensor carpi radialis longus & brevis (ECRL & ECRB) abduct the hand 2) The extensor carpi ulnaris (ECU) adducts the hand 3) The base metacarpal attachments of these muscles enables them to abduct and adduct the hand, respectively

Question 34

What works synergistically with the ECRL & ECRB to abduct the hand? What muscles work together to extend the hand? What muscles work together to flex the hand?

Answer 34

1) The flexor carpi radialis (FCR) works synergistically with the ECRL and ECRB to abduct the hand 2) When acting with the ECU, the ECRL and ECRB extend the hand 3) The flexor carpi radialis (FCR) and flexor carpi ulnaris (FCU) synergistically flex the hand

Question 35

Where do outcropping muscles of the deep layer of the forearm attach to proximally? What is the anatomical snuff box?

Answer 35

1) The outcropping muscles of the deep layer attach proximally to the distal ulna 2) The anatomical snuff box is a triangular deepening on the radial, dorsal aspect of the hand—at the level of the carpal bones, specifically, the scaphoid and trapezium bones forming the floor 3) Tendons of the outcropping muscles define the anatomical snuff box at the lateral side of the wrist

Question 36

What tendons define the anterior and posterior regions of the anatomical snuff box?

Answer 36

1) The posterior border of the snuffbox is the tendon of the extensor pollicis longus 2) The anterior border (closest to the edge of the hand) is a pair of parallel and intimate tendons, of the extensor pollicis brevis and the abductor pollicis longus (Accordingly, the anatomical snuffbox is most visible, having a more pronounced concavity, during thumb extension)

Question 37

What artery courses along the floor of the snuff box?

Answer 37

Deep to the tendons which form the borders of the anatomical snuff box lies the radial artery, which passes through the anatomical snuffbox on its course from the normal radial pulse detecting area, to the proximal space in between the first and second metacarpals to contribute to the superficial and deep palmar arches

Question 38

Where do the extensor pollicis longus and brevis & the abductor pollicis longus attach distally?

Answer 38

1) Extensor pollicis longus (EPL) distal attachment: Dorsal aspect of base of distal phalanx of thumb 2) Extensor pollicis brevis (EPB) distal attachment: Dorsal aspect of base of proximal phalanx of thumb 3) Abductor pollicis longus distal attachment: Base of 1st metacarpal

Question 39

How do the distal attachments of the EPL, EPB, & APL enable extension and contribute to abduction of the thumb, respectively?

Answer 39

1) Extensor pollicis longus (EPL): Extends distal phalanx of thumb at interphalangeal joint; extends metacarpophalangeal and carpometacarpal joints 2) Extensor pollicis brevis (EPB): Extends proximal phalanx of thumb at metacarpophalangeal joint; extends carpometacarpal joint 3) Abductor pollicis longus (APL): Abducts thumb and extends it at carpometacarpal joint

Question 40

The radial nerve is a continuation of what? What is a muscle that the radial nerve innervates in the posterior arm? Where does the radial nerve travel in the posterior arm?

Answer 40

1) The radial nerve is the direct continuation of the posterior cord 2) The radial nerve innervates the triceps in the posterior arm 3) After coursing along the radial groove, the radial nerve passes anterior to the lateral epicondyle of the humerus into the cubital fossa

Question 41

What does the radial nerve innervate in the cubital fossa? Where does the sensory superficial branch course and terminate?

Answer 41

1) In the cubital fossa, the radial nerve innervates the brachioradialis and bifurcates into superficial and deep branches 2) The sensory superficial branch courses beneath the brachioradialis and envision it terminates on the dorsum of the hand

Question 42

What does the deep branch of the radial nerve innervate? What does the deep branch of the radial nerve become?

Answer 42

1) The deep branch of the radial nerve innervates the superficial extensor muscles and the supinator 2) After piercing the supinator, the deep branch becomes the posterior interosseous nerve that innervates the other muscles of the deep extensor layer

Question 43

What is the characteristic clinical sign after radial nerve injury in the radial groove of the humerus?

Answer 43

1) When the nerve is injured in the radial groove, the triceps is usually not completely paralyzed but only weakened because only the medial head is affected; however, the muscles in the posterior compartment of the forearm that are supplied by more distal branches of the nerve are paralyzed 2) The characteristic clinical sign of radial nerve injury is wrist-drop—inability to extend the wrist and the fingers at the metacarpophalangeal joints 3) Instead, the relaxed wrist assumes a partly flexed position owing to unopposed tonus of flexor muscles and gravity

Question 44

Where do the ulnar and radial arteries terminate? Where does the short, common interosseous artery branch from? What does the interosseous artery divide into?

Answer 44

1) The ulnar and radial arteries terminate in the palmar arches of the hand 2) The short common interosseous artery branches from the proximal ulnar artery 3) The interosseous artery divides into the anterior and posterior interosseous arteries

Question 45

What do the ulnar and anterior interosseous arteries supply? What does the poterior interosseous artery supply?

Answer 45

1) The ulnar and anterior interosseous arteries supply muscles of the anteromedial forearm 2) The posterior interosseous artery supplies muscles of the posterolateral forearm

Question 46

What does the radial artery supply?

Answer 46

The radial artery courses in the boundary between the antero-medial and posterolateral muscle groups; thus, it supplies both groups